Increasing femoral offset in total hip replacement (THR) has several benefits including improved hip abductor strength and enhanced range of motion. Biomechanical studies have suggested that this may negatively impact on stem stability. However, it is unclear whether this has a clinical impact. Using data from the Australian Orthopaedic Association National Joint Replacement Registry (AOANJRR), the aim of this study was to determine the impact of stem offset and stem size for the three most common cementless THR prostheses revised for aseptic loosening. The study period was September 1999 to December 2020. The study population included all primary procedures for osteoarthritis with a cementless THR using the Corail, Quadra-H and Polarstem. Procedures were divided into small and large stem sizes and by standard and high stem offset for each stem system. Hazard ratios (HR) from Cox proportional hazards models, adjusting for age and gender, were performed to compare revision for aseptic loosening for offset and stem size for each of the three femoral stems. There were 55,194 Corail stems, 13,642 Quadra-H stem, and 13,736 Polarstem prostheses included in this study. For the Corail stem, offset had an impact only when small stems were used (sizes 8-11). Revision for aseptic loosening was increased for the high offset stem (HR=1.90;95% CI 1.53–2.37;p<0.001). There was also a higher revision risk for aseptic loosening for high offset small size Quadra-H stems (sizes 0-3). Similar to the Corail stem, offset did not impact on the revision risk for larger stems (Corail sizes 12-20, Quadra-H sizes 4-7). The Polarstem did not show any difference in aseptic loosening revision risk when high and standard offset stems were compared, and this was irrespective of stem size. High offset may be associated with increased revision for aseptic loosening, but this is both stem size and prosthesis specific

Introduction and Objective. A proper restoration of hip biomechanics is fundamental to achieve satisfactory outcomes after total hip arthroplasty (THA). A global hip offset (GO) postoperatively reduction of more than 5 mm was known to impair hip functionality after THA. This study aimed to verify the restoration of the GO radiographic parameter after primary THA by the use of a cementless femoral stem available in three different offset options without length changing. Materials and Methods. From a consecutive series of 201 patients (201 hips) underwent primary cementless THA in our centre with a minimum 3-year follow up, 80 patients (80 hips) were available for complete radiographic evaluation for GO and limb length (LL) and clinical evaluation with Harris hip score (HHS). All patients received the same femoral stem with three different offset options (option A with – 5 mm offset, option B and option C with + 5 mm offset, constant for each sizes) without changing stem length. Results. Mean GO significantly increased by + 3 mm (P < 0.05) and mean LL significantly decreased by + 5 mm (P < 0.05) after surgery, meaning that postoperatively the limb length of the operated side increased by + 5 mm. HHS significantly improved from 56.3 points preoperatively to 95.8 postoperatively (P < 0.001). Offset option A was used in 1 hip (1%), B in 59 hips (74%) and C in 20 hips (25%). Conclusions. The femur is lateralized with a mean of + 5mm after surgery than, the native anatomy, whatever type of stem was used. Thus, the use of this 3-offset options femoral stem is effective in restoring the native biomechanical hip parameters as GO, even if 2 offset options were considered sufficient to restore GO

Purpose. The ultimate goal in total hip arthroplasty is not only to relieve the pain but also to restore original hip joint biomechanics. The average femoral neck-shaft angle(FNSA) in Korean tend to have more varus pattern. Since most of conventional femoral stems have relatively high, single, fixed neck shaft angle, it's not easy to restore vertical and horizontal offset exactly especially in Korean people. This study demonstrates the advantages of dual offset(especially high-offset) stem for restoring original biomechanics of hip joint during the total hip arthroplasty in Korean. Materials and Methods. 180 hips of 155 patients who underwent total hip arthroplasty using one of the standard(132°) or extended(127°) offset Accolade cementless stems were evaluated retrospectively. Offset of stem was chosen according to the patient's own FNSA in preoperative templating. In a morphometric study, neck-shaft angle of proximal femur, vertical offset and horizontal offset, abductor moment arm were measured on preoperative and postoperative both hip AP radiographs and the differences and correlation of each parameters, between operated hip and original non-operated hip which had no deformity (preoperative ipsilateral or postoperative contralateral hip), were analyzed. Results. The standard stems were used in 34 hips and extended offset stems were used in 146 hips. The FNSA of non-operated hip was an average of 129.8°(127.2°□135.8°) in standard group and mean 125.4°(122.7°□129.9°) in extended offset group. The FNSA of operated hip was an average of 131.6° and 127.1° in each group. In the statistical analysis, there was no significant difference of mean horizontal and abductor moment arm between operated hip and non-operated hip in both groups and the restoration of horizontal offset and abductor moment arm showed(p=0.217, p=0.093) significant positive correlation(R=0.870, R=0.851) to the original value. However, vertical offset was increased an average of 1.4mm in operated hip and there was statistical significance. Restoration of vertical offset showed positive correlation to original value (R=0.845). Conclusion. Dual- or multi-offset stem, especially extended offset stem can provide easy restoration of hip biomechanics and soft tissue tension without significant alteration of leg length especially in Korean with more varus femoral neck compared to Caucacian. Precise radiographic measurements of original hip and application of proper-offset stem should be taken in order to restore ideal hip biomechanics successfully and easily. A use of a proper offset stem can afford to enhance joint stability and implant longevity by improving soft-tissue tension and reducing resultant force, and it will guarantee a successful results after total hip arthroplasty in the aspect of function and longevity

Aims. Hip arthroplasty does not always restore normal anatomy. This is due to inaccurate surgery or lack of stem sizes. We evaluated the aptitude of four total hip arthroplasty systems to restore an anatomical and medialized hip rotation centre. Methods. Using 3D templating software in 49 CT scans of non-deformed femora, we virtually implanted: 1) small uncemented calcar-guided stems with two offset options (Optimys, Mathys), 2) uncemented straight stems with two offset options (Summit, DePuy Synthes), 3) cemented undersized stems (Exeter philosophy) with three offset options (CPT, ZimmerBiomet), and 4) cemented line-to-line stems (Kerboul philosophy) with proportional offsets (Centris, Mathys). We measured the distance between the templated and the anatomical and 5 mm medialized hip rotation centre. Results. Both rotation centres could be restored within 5 mm in 94% and 92% of cases, respectively. The cemented undersized stem performed best, combining freedom of stem positioning and a large offset range. The uncemented straight stem performed well because of its large and well-chosen offset range, and despite the need for cortical bone contact limiting stem positioning. The cemented line-to-line stem performed less well due to a small range of sizes and offsets. The uncemented calcar-guided stem performed worst, despite 24 sizes and a large and well-chosen offset range. This was attributed to the calcar curvature restricting the stem insertion depth along the femoral axis. Conclusion. In the majority of non-deformed femora, leg length, offset, and anteversion can be restored accurately with non-modular stems during 3D templating. Failure to restore hip biomechanics is mostly due to surgical inaccuracy. Small calcar guided stems offer no advantage to restore hip biomechanics compared to more traditional designs. Cite this article: Bone Jt Open 2021;2(7):476–485

Aims. Achieving accurate implant positioning and restoring native hip biomechanics are key surgeon-controlled technical objectives in total hip arthroplasty (THA). The primary objective of this study was to compare the reproducibility of the planned preoperative centre of hip rotation (COR) in patients undergoing robotic arm-assisted THA versus conventional THA. Methods. This prospective randomized controlled trial (RCT) included 60 patients with symptomatic hip osteoarthritis undergoing conventional THA (CO THA) versus robotic arm-assisted THA (RO THA). Patients in both arms underwent pre- and postoperative CT scans, and a patient-specific plan was created using the robotic software. The COR, combined offset, acetabular orientation, and leg length discrepancy were measured on the pre- and postoperative CT scanogram at six weeks following surgery. Results. There were no significant differences for any of the baseline characteristics including spinopelvic mobility. The absolute error for achieving the planned horizontal COR was median 1.4 mm (interquartile range (IQR) 0.87 to 3.42) in RO THA versus 4.3 mm (IQR 3 to 6.8; p < 0.001); vertical COR mean 0.91 mm (SD 0.73) in RO THA versus 2.3 mm (SD 1.3; p < 0.001); and combined offset median 2 mm (IQR 0.97 to 5.45) in RO THA versus 3.9 mm (IQR 2 to 7.9; p = 0.019). Improved accuracy was observed with RO THA in achieving the desired acetabular component positioning (root mean square error for anteversion and inclination was 2.6 and 1.3 vs 8.9 and 5.3, repectively) and leg length (mean 0.6 mm vs 1.4 mm; p < 0.001). Patient-reported outcome measures were comparable between the two groups at baseline and one year. Participants in the RO THA group needed fewer physiotherapy sessions postoperatively (median six (IQR 4.5 to 8) vs eight (IQR 6 to 11; p = 0.005). Conclusion. This RCT suggested that robotic-arm assistance in THA was associated with improved accuracy in restoring the native COR, better preservation of the combined offset, leg length correction, and superior accuracy in achieving the desired acetabular component positioning. Further evaluation through long-term and registry data is necessary to assess whether these findings translate into improved implant survival and functional outcomes. Cite this article: Bone Joint J 2024;106-B(4):324–335

The purpose of this study was to describe the radiological characteristics of a previously unreported finding: posterior iliac offset at the sacroiliac joint and to assess its association with pelvic instability as measured by initial displacement and early implant loosening or failure. Radiographs from 42 consecutive patients with a mean age of 42 years (18 to 77; 38 men, four women) and mean follow-up of 38 months (3 to 96) with Anteroposterior Compression II injuries, were retrospectively reviewed. Standardised measurements were recorded for the extent of any diastasis of the pubic symphysis, widening of the sacroiliac joint, static vertical ramus offset and a novel measurement (posterior offset of the ilium at the sacroiliac joint identified on axial CT scan). Pelvic fractures with posterior iliac offset exhibited greater levels of initial displacement of the anterior pelvis (anterior sacroiliac widening, pubic symphysis diastasis and static vertical ramus offset, p < 0.001,0.034 and 0.028, respectively). Pelvic fractures with posterior ilium offset also demonstrated higher rates of implant loosening regardless of fixation method (p = 0.05). Posterior offset of the ilium was found to be a reliable and reproducible measurement with substantial inter-observer agreement (kappa = 0.70). Posterior offset of the ilium on axial CT scan is associated with greater levels of initial pelvic displacement and early implant loosening. Cite this article: Bone Joint J 2014;96-B:1535–9

Abstract. Introduction. There is growing interest in the use of robotic Total Knee Arthroplasty (TKA) to improve accuracy of component positioning. This is the first study to investigate the radiological accuracy of implant component position using the ROSA® knee system with specific reference to Joint Line Height, Tibial Slope, Patella Height and Posterior Condylar Offset. As secondary aims we compared accuracy between image-based and imageless navigation, and between implant designs (Persona versus Vanguard TKA). Methodology. This was a retrospective review of a prospectively-maintained database of the initial 100 consecutive TKAs performed by a high volume surgeon using the ROSA® knee system. To determine the accuracy of component positioning, the immediate post-operative radiograph was reviewed and compared with the immediate pre-operative radiograph with regards to Joint Line Height, Tibial Slope, Patella Height (using the Insall-Salvati ratio) and Posterior Condylar Offset. Results. Mean age of patients undergoing ROSA TKA was 70 years (range, 55 to 95 years). Mean difference in joint line height between pre and post-operative radiographs was 0.2mm (range −1.5 to +1.8mm, p<0.05), posterior condylar offset mean change 0.16mm (range −1.4 to +1.3mm, p<0.05), tibial slope mean change 0.1 degrees (p<0.05) and patella height mean change 0.02 (range −0.1 to +0.1 p<0.05). No significant differences were found between imageless and image-based groups, or between implant designs (Persona versus Vanguard). Conclusion. This study validates the use of the ROSA® knee system in accurately restoring Joint Line Height, Patella Height and Posterior Condylar Offset

Introduction & aims. Correct prosthetic alignment is important to the longevity and function of a total hip replacement (THR). With the growth of 3-dimensional imaging for planning and assessment of THR, the importance of restoring, not just leg length and medial offset, but anterior offset has been raised. The change in anterior offset will be influenced by femoral anteversion, but there are also other factors that will affect the overall change after THR. Consequently, the aim of this study was to investigate the relationship between anterior offset and stem anteversion to determine the extent to which changing anteversion influences anterior offset. Method. Sixty patients received a preoperative CT scan as part of their routine planning for THR (Optimized Ortho, Sydney). All patients received a Trinity cementless shell and a cemented TaperFit stem (Corin, UK) by the senior author through an anterolateral approach. Stem anteversion was positioned intraoperatively to align with cup anteversion via a modified Ranawat test. Postoperatively, patients received a CT scan which was superimposed onto the pre-op CT scan. The difference between native and achieved stem anteversion was measured, along with the 3-dimensional change in head centre from pre-to post-op. Finally, the relationship between change in stem anteversion and change in anterior offset was investigated. Results. Mean change in anterior offset was −2.3mm (−14.0 to 7.0mm). Mean change in anteversion from native was −3.0° (−18.8° to 10.5°). There was a strong correlation between change in anterior offset and change in anteversion, with a Pearson correlation coefficient of 0.89. A 1° increase in anteversion equated to a 0.7mm increase in anterior offset. Conclusions. A change in the anteroposterior position of the femoral head is primarily affected by a change in stem anteversion, with a 1° increase in anteversion equating to a 0.7mm increase in anterior offset. The AP position of the stem in the canal, along with the flexion of the stem will also contribute. Given the well-recognised influence of leg length, medial offset and combined anteversion on restoring hip function, it seems reasonable to assume that anterior offset will also have a significant effect on the biomechanics of the replaced hip

Background. Total hip arthroplasty requires proper sizing and placing of implants to ensure excellent outcomes and reduce complications. Calculation of femoral offset is an important consideration for optimal reconstruction of the hip biomechanics. Femoral offset can be measured on plain films or with flouroscopy if the x-ray beam is perpendicular to the plane determined by the angle between the neck axis and femoral shaft axis. This distance is evident only with the femur in the correct degree of rotation. Though pre-operative templating for femoral component size and offset is a regular accepted practice, a consistent method for assessing correct femoral rotation on the AP x-ray view has not been established. Purpose/Hypthesis. The purpose of the current study was to establish and validate a method for identifying radiographic landmarks on the proximal femur that would reliably indicate that the femur was in the proper degree of rotation to represent the true offset from the head center to shaft center. Methods. Lead markers were placed on areas of the greater trochanter followed by xrays. Markers placed on locations on the anterior and posterior greater trochanter duplicated reliable radiographic lines. Proximal femurs were dissected to the bone and rotated about their long axis from neutral rotation, defined at the point when the anterior and posterior aspects of the greater trochanter were aligned radiographically. Radiographs were taken at 2 degree increments in both internal and external rotation until 10 degrees, then again at 30 degrees. A custom script was used to calculate the femoral offset at these rotations at these locations. Descriptive analysis was performed to assess the relationship between rotation angle and femoral offset. Results. The mean femoral offset was observed to be 38.21 mm (SD 4.93, median 37.82, range 30.52–46.27). The mean rotation of max offset was −3.6° (SD 5.6, median −6, range −10 to +8). The average underestimation error (the difference between calculated offset at neutral rotation and observed maximum femoral offset) was 0.92 mm (median 0.74, range 0 to 2.07 mm). Conclusion. Alignment of the radiographic lines created by the anterior and posterior aspects of the greater trochanter is a reliable and accurate rotational positioning method for measuring femoral offset when using plain films or fluoroscopy. It is a feasible method that can be applied preoperatively and/or intraoperatively to optimize accuracy of femoral offset for THA procedures. For any tables or figures, please contact the authors directly

Aims. Traditionally, total hip arthroplasty (THA) templating has been performed on anteroposterior (AP) pelvis radiographs. Recently, additional AP hip radiographs have been recommended for accurate measurement of the femoral offset (FO). To verify this claim, this study aimed to establish quantitative data of the measurement error of the FO in relation to leg position and X-ray source position using a newly developed geometric model and clinical data. Methods. We analyzed the FOs measured on AP hip and pelvis radiographs in a prospective consecutive series of 55 patients undergoing unilateral primary THA for hip osteoarthritis. To determine sample size, a power analysis was performed. Patients’ position and X-ray beam setting followed a standardized protocol to achieve reproducible projections. All images were calibrated with the KingMark calibration system. In addition, a geometric model was created to evaluate both the effects of leg position (rotation and abduction/adduction) and the effects of X-ray source position on FO measurement. Results. The mean FOs measured on AP hip and pelvis radiographs were 38.0 mm (SD 6.4) and 36.6 mm (SD 6.3) (p < 0.001), respectively. Radiological view had a smaller effect on FO measurement than inaccurate leg positioning. The model showed a non-linear relationship between projected FO and femoral neck orientation; at 30° external neck rotation (with reference to the detector plane), a true FO of 40 mm was underestimated by up to 20% (7.8 mm). With a neutral to mild external neck rotation (≤ 15°), the underestimation was less than 7% (2.7 mm). The effect of abduction and adduction was negligible. Conclusion. For routine THA templating, an AP pelvis radiograph remains the gold standard. Only patients with femoral neck malrotation > 15° on the AP pelvis view, e.g. due to external rotation contracture, should receive further imaging. Options include an additional AP hip view with elevation of the entire affected hip to align the femoral neck more parallel to the detector, or a CT scan in more severe cases. Cite this article: Bone Jt Open 2022;3(10):795–803

Because the femoral head/neck junction is preserved in hip resurfacing, patients may be at greater risk of impingement, leading to abnormal wear patterns and pain. We assessed femoral head/neck offset in 63 hips undergoing metal-on-metal hip resurfacing and in 56 hips presenting with non-arthritic pain secondary to femoroacetabular impingement. Most hips undergoing resurfacing (57%; 36) had an offset ratio ≤ 0.15 pre-operatively and required greater correction of offset at operation than the rest of the group. In the non-arthritic hips the mean offset ratio was 0.137 (0.04 to 0.23), with the offset ratio correlating negatively to an increasing α angle. An offset ratio ≤ 0.15 had a 9.5-fold increased relative risk of having an α angle ≥ 50.5°. Most hips undergoing resurfacing have an abnormal femoral head/neck offset, which is best assessed in the sagittal plane

Introduction. Offset femoral broach handles have become more common as the anterior approach in total hip arthroplasty has increased in popularity. The difference in access to the femur compared to a posterior approach necessitates anterior and, in some cases, lateral offsets incorporated into the design of the broach handle to avoid interference with the patient's body and to ensure accessibility of the strike plate. Using a straight broach handle with a primary stem, impaction force is typically directed along the axis of the femoral broach. However, the addition of one or more offsets to facilitate an anterior approach results in force transmission in the transverse plane, which is unnecessary for eating the femoral broach. The direction of forces transmitted to the broach via strike plate impaction can introduce a large moment. A negative consequence of this moment is the amplification of stresses/strains at the bone/broach interface, which increases the likelihood of femoral fracture during impaction. It was proposed that optimizing the angle of the strike plate could minimize the moment to reduce the unintended stresses/strains at the bone/broach interface. Objectives. The objective was to minimize the stresses/strains imparted to the proximal aspect of the bone femur when broaching with a given dual offset broach handle design. Methods. Trigonometric calculations were used to optimize the strike plate angle for a given dual offset broach handle design. The point of intersection of the stem axis and transverse plane that intersects the medial calcar of the smallest size broach was assumed to be the ideal location of zero moment, given that intraoperative fractures related to this issue tend to occur in the proximal region of the femur. The strike plate was angled anteriorly and laterally such that the impaction force vector is directed at this point of intersection, thus negating the moment at this point. A prototype broach handle body was fabricated to accept different strike plates. Of the two strike plates tested, one strike plate was made such that the impaction surface followed the optimized angle, while the other simulated the strike plate angle of a previous, non-optimized design. Each broach handle configuration was connected to an identical broach and implanted into one of two identical Sawbones® femoral models. Equal loads were placed on the strike plates of each handle perpendicular to the strike plate angles. Digital image correlation was used to compare the resultant strains in both samples. Results. Testing demonstrated a 30% reduction in maximum strain on the proximal aspect of the bone using the broach handle with the optimized strike plate. Conclusions. While the optimal strike plate angle is dependent on the individual broach handle design, this method of optimization can be applied to the design of any offset broach handle. Optimization of offset broach handle strike plate angles could reduce the incidence of intraoperative femoral fractures when broaching by reducing the stresses/strains on the proximal aspect of the femur

Introduction. Highly crosslinked, ultra-high molecular weight polyethylene (HXLPE) acetabular liners inherently have a risk of fatigue failure associated with femoral neck impingement. One of the potential reasons for liner failure was reported as crosslinking formulations of polyethylene, increasing the brittleness and structural rigidity. In addition, the acetabular component designs greatly affect the mechanical loading scenario, such as the offset (lateralized) liners with protruded rim above the metal shells, which commonly induce a weak resistance to rim impingement. The purpose of the present study was to compare the influence of the liner offset length on the impingement resistance in the annealed (first generation) and vitamin E-blended (second-generation) HXLPE liners with a commercial design. Materials and Methods. The materials tested were the 95-kGy irradiated annealed GUR1020, and the 300-kGy irradiated vitamin E-blended GUR1050 HXLPE offset liners, which were referred to as “20_95” and “50E_300”, respectively. These liners had 2, 3, 4-mm rim offset, 2.45-mm rim thickness, and 36-mm internal diameter. Their rims were protruded above the metal rim at 2, 3, 4mm. Rim impingement testing was performed using an electrodynamic axial-torsional machine. The cyclic impingement load of 25–250N was applied on the rims through the necks of the femoral stems at 1Hz. The rotational torque was simultaneously generated by swinging the stem necks on the rims at 1Hz and its rotational angle was set at the range of 0–10˚. The percent crystallinity was analyzed on the as-received (intact) and impinged HXLPE acetabular rims by confocal Raman microspectroscopy. Results. The number of cycles to failure was dependent on the offset length (2, 3, 4-mm) in 20_95 and 50E_300 liners. Our results showed that the shorter the rim offset, the shorter the number of cycles to failure. In both HXLPEs, accumulation of impingement damages significantly decreased crystallinity in their near-surfaces, indicating the occurrence of crystallographic breakdown. In each offset length tested, the fracture always occurred much earlier in 50E_300 than 20_95. However, the magnitudes of the microstructural changes at the time of failure were much less in 50E_300 than 20_95. Conclusions. Although it is known that vitamin E blend into HXLPE can improve the fatigue resistance of HXLPE, the impingement resistance of 50E_300 was lower than vitamin-E free 20_95, indicating a larger negative contribution of high-dose radiation (300kGy) over a positive contribution of the vitamin E blend in 50E_300. Our results implied that the reduction of the protruded rim length in the offset liners may increase the neck-rim contact stresses at the time of impingement, causing a decrease in the fatigue durability. Therefore, if HXLPE offset liner is used, surgeons should take special care in maximizing the volume of the protruded lip section

Hip resurfacing is being performed more frequently in the United Kingdom. The possible benefits include more accurate restoration of leg length, femoral offset and femoral anteversion than occurs after total hip arthroplasty (THA). We compared anteroposterior radiographs from 26 patients who had undergone hybrid THA (uncemented cup/cemented stem), with 28 who had undergone Birmingham Hip Resurfacing arthroplasty (BHR). We measured the femoral offset, femoral length, acetabular offset and acetabular height with reference to the normal contralateral hip. The data were analysed by paired t-tests. There was a significant reduction in femoral offset (p = 0.0004) and increase in length (p = 0.001) in the BHR group. In the THA group, there was a significant reduction in acetabular offset (p = 0.0003), but femoral offset and overall hip length were restored accurately. We conclude that hip resurfacing does not restore hip mechanics as accurately as THA

Several factors have been implicated in unsatisfactory results after total hip replacement (THR). We examined whether femoral offset, as measured on digitised post-operative radiographs, was associated with pain after THR. The routine post-operative radiographs of 362 patients (230 women and 132 men, mean age 70.0 years (35.2 to 90.5)) who received primary unilateral THRs of varying designs were measured after calibration. The femoral offset was calculated using the known dimensions of the implants to control for femoral rotation. Femoral offset was categorised into three groups: normal offset (within 5 mm of the height-adjusted femoral offset), low offset and high offset. We determined the associations to the absolute final score and the improvement in the mean Western Ontario and McMaster Universities osteoarthritis index (WOMAC) pain subscale scores at three, six, 12 and 24 months, adjusting for confounding variables. The amount of femoral offset was associated with the mean WOMAC pain subscale score at all points of follow-up, with the low-offset group reporting less WOMAC pain than the normal or high-offset groups (six months: 7.01 (. sd. 11.69) vs 12.26 (. sd. 15.10) vs 13.10 (. sd. 16.20), p = 0.006; 12 months: 6.55 (. sd. 11.09) vs 9.73 (. sd. 13.76) vs 13.46 (. sd. 18.39), p = 0.010; 24 months: 5.84 (. sd. 10.23) vs 9.60 (. sd. 14.43) vs 13.12 (. sd. 17.43), p = 0.004). When adjusting for confounding variables, including age and gender, the greatest improvement was seen in the low-offset group, with the normal-offset group demonstrating more improvement than the high-offset group. . Cite this article: Bone Joint J 2014;96-B:36–42

Instability following total hip arthroplasty (THA) is an unfortunately frequent and serious problem that requires thorough evaluation and preoperative planning before surgical intervention. Prevention through optimal index surgery is of great importance, as the management of an unstable THA is challenging even for an experienced joints surgeon. However, even after well-planned surgery, a significant incidence of recurrent instability still exists. Moreover leg-length discrepancy (LLD) after THA can pose a substantial problem for the orthopaedic surgeon. Such discrepancy has been associated with complications including nerve palsy, low back pain, and abnormal gait. Consequently we may use a big femoral head or increase femoral offset (FO) in unstable THA for avoiding LLD. However we do not know the relationship between FO and STT. The objective of this study is to assess hip instability of three different FOs in same patient undergoing THA during an operation. We performed 70 patients who had undergone unilateral THA using CT based navigation system at a single institution for advanced osteoarthoritis from May 2013 to May 2014. We used postero-lateral approach in all patients. After cup and stem implantation, we assessed soft tissue tensioning in THA during operation. Trial necks were categorized into one of three groups: standard femoral offset (sFO), high femoral offset (hFO, +4mm compared to sFO) and extensive high femoral offset (ehFO, +8 mm compared to sFO). We measured distance of lift-off about each of three femoral necks using CT based navigation system and a force gauge with hip flexed at 0 degrees and 30 degrees under a traction of lower extremity. Traction force was 40% of body weight. Forty patients had leg length restored to within +/− 3mm of the contralateral side by post-operative CT analysis. We examined these patients. Traction force was 214±41.1Nm. The distances of lift-off were 8.8±4.5mm (sFO), 7.4±4.1mm (eFO), 5.1±3.9mm (ehFO) with 0 degrees hip flexion and neutral abduction(Abd) / adduction(Add) and neutral internal rotation(IR)/ external rotation(ER). The distance of lift-off were 11.5±5.9mm (sFO),10.5±5.5mm (eFO),9.1±5.9mm (ehFO) with 30 degrees hip flexion and neutral Abd / Add and neutral IR/ER. Significant difference was observed between 0 degrees hip flexion and 30 degrees hip flexion on each FO (p<0.05). On changing the distance of lift-off, hFO to ehFO (2.2±1.6mm)was more stable than sFO to hFO (1.4±1.7mm)with 0degrees hip flexion.(p<0.05). On the other hands, hFO to ehFO (1.4±1.6mm) was more stable than sFO to hFO (1.0±1.3mm) with 30 degrees hip flexion. However, we did not find significant difference (p=0.18). Hip instability was found at 30 degrees hip flexion more than at 0 degrees hip flexion. We found that changing ehFO to sFO can lead to more stability improvement of soft tissue tensioning than sFO to eFO, especially at 0 degrees hip flexion. Whereas In a few cases, the distance of lift-off did not change with increasing femoral offset by 4mm. When you need more stability in THA without LLD, We recommend increasing FO by 8mm

Purpose of the study: The extramedullary anatomy of the femur must be reproduced during total hip arthroplasty in order to ensure correct tension on the gluteus muscles. This requires:. correct offset of the femur, measured as the distance between the center of the head and the anatomic axis of the shaft;. offset of the center of rotation, measured as the distance between the center of the head and the pubic symphesis. Addition of these two offsets gives the overall offset. The purpose of this work was to analyze postoperative offset after standard total hip arthroplasty as a function of the preoperative head-shaft angle. Material and methods: Prospective study of 150 files of patients who underwent first-intention total hip arthroplasty. A prosthesis with matched increasing head size was implanted. The head-shaft angle was 135°. Mean offset was 41.7 mm (range 33–47 mm) for the 0 head-neck. The preoperative neck-shaft angle was measured on the upright ap view (comparable rotation of the two hemipelvi). Pre- and postoperative femur and center of rotation offset were noted. Results: The preoperative neck-shaft angle varied from 118° to 1400. Mean preoperative femur offset was 40.2 mm (range 29–52 mm). Mean postoperative femur offset was 42.2 mm. This gave a 2 mm lateralization of the femur, which was apparently negligible, favorable, and therefore satisfactory. Mean offset was 90.5 mm preoperatively and 84.5 mm postoperatively, medializing the center of rotation 6°. Mean overall offset was thus displaced medially (6 mm minus 2 mm = 4 mm). This was considered acceptable. Among these 150 files, 24 were coxa vara hips with a neck-shaft angle 125°. For these 25 coxavara hips, the mean preoperative femur offset was 44.5 mm. The mean postoperative femur offset was 42.2 mm. This produced, inversely, a medial displacement of the postoperative femur offset of 2.3 mm. The center of rotation was displace medially 6 mm. Thus globally the medial displacement was 6 mm plus 2.3 mm = 8.3 mm. This appeared to be excessive. Discussion: The postoperative offset of the femur is prosthesis-dependent. The majority of implants currently marketed have a mean offset in the 40–45mm range. The offset of the center of rotation is operator-dependent: as the acetabular reaming is accentuated, the center of rotation is displaced medially. Acetabular reaming is necessary to reach the subchondral bone. The medial offset can be limited but at least some displacement is inevitable. Thus in the event of a coxavara hip, it is very difficult to limit excessive overall medial offset when using a standard prosthesis. If the goal is to mimic the anatomic femur offset, it would appear justified to use prostheses with a smaller neck-shaft angle for patients with coxavara. A 10° reduction, from 135° to 125° would increase the femur offset 5 mm and thus enable reproduction of the preoperative anatomy

Background. Posterior referencing (PR) total knee arthroplasty (TKA) aims to restore posterior condylar offset. When a symmetric femoral implant is externally rotated (ER) to the posterior condylar axis, it is impossible to anatomically restore the offset of both condyles. PR jigs variously reference medially, laterally, or centrally. The distal femoral cutting jigs typically reference off the more distal medial condyle, causing distal and posterior resection discrepancies. We used sawbones to elucidate differences between commonly used PR cutting jigs with regards to posterior offset restoration. Materials/Methods. Using 32 identical sawbones, we performed distal and posterior femoral resections using cutting guides from 8 widely available TKA systems. 6 systems used a central-referencing strategy, 1 system used a lateral-referencing strategy, and 1 system used a medial-referencing strategy with implants of asymmetric thickness. Distal femoral valgus resection was set at 5 degrees for all specimens. Rotation was set at 3 degrees for 2 sawbones and 5 degrees for 2 sawbones with each system. We measured the thickness of all bone resections, and compared those values to known implant thickness. Results. Central- and lateral-referenced systems with symmetric implants showed distal lateral under-resection. The medial-referenced system with asymmetric implants restored the anatomic joint line medially and laterally. Central-referenced systems showed close to 1mm (SD ±0.2) postero-lateral offset over-restoration and postero-medial offset under-restoration at 3 degrees of ER, and a 1.6mm change in each offset at 5 degrees of ER. The lateral-referenced system demonstrated a 1.7mm mismatch between the distal-medial and the postero-medial resections at 3 degrees of rotation. There was a 3.9mm mismatch at 5 degrees of ER. Medial-referenced systems demonstrated a mismatch between the distal-lateral and postero-lateral resections, present only with 5 degrees of ER. Conclusion. Our data offers insight for arthroplasty surgeons into the bony resections taken by widely used TKA instrumentation systems. The lateral-referenced jigs reduced the postero-medial offset by 4 degrees at 5 degrees, a difference on the order of 1 to 2 femoral sizes depending on the implant system. The medial-referenced system, with the use of asymmetric condylar thicknesses, restored condylar anatomy within 1mm in the majority of circumstances. When set at 5 degrees of external rotation, over-restoration of the postero-lateral femoral offset occurred. Center-referenced systems resulted in minor changes in offset at 3 degrees of rotation, but a decrease in the postero-medial offset by 2mm at 5 degrees of external rotation. The distal femoral cutting jig typically restores the medial joint line in extension when there is minimal medial wear. Referencing laterally in flexion may introduce a discrepancy between the extension and flexion gaps. Available medial- and lateral-referenced jigs provide the option of shifting the bony resections anteriorly or posteriorly and adjusting the sizing as needed

Introduction. The inferior/medial shift in the center of rotation (CoR) associated with reverse shoulder arthroplasty (rTSA) shortens the anterior and posterior shoulder muscles; shortening of these muscles is one explanation for why rTSA often fails to restore active internal/external rotation. This study quantifies changes in muscle length from offsetting the humerus in the posterior/superior directions using an offset humeral tray/liner with rTSA during two motions: abduction and internal/external rotation. The offset and non-offset humeral tray/liner designs are compared to evaluate the null hypothesis that offsetting the humerus in the posterior/superior direction will not impact muscle length with rTSA. Methods. A 3-D computer model was developed to simulate abduction and internal/external rotation for the normal shoulder, the non-offset reverse shoulder, and the posterior/superior offset reverse shoulder. Seven muscles were modeled as 3 lines from origin to insertion. Both offset and non-offset reverse shoulders were implanted at the same location along the inferior glenoid rim of the scapula in 20° of humeral retroversion. Muscle lengths were measured as the average of the 3 lines simulating each muscle and are presented as an average length over each arc of motion (0 to 65° abduction with a fixed scapula and 0 to 40° of internal/external rotation with the humerus in 0° abduction) relative to the normal shoulder. Results. Both the offset and non-offset reverse shoulders shifted the CoR medially by 27.1 mm and inferiorly by 4.5 mm relative to the normal shoulder. The offset humeral tray/liner shifted the humerus posteriorly and superiorly relative to the non-offset reverse shoulder. As depicted in Figures 1–3, the inferior shift in the CoR elongated the anterior, middle, and posterior heads of the deltoid for both the offset and non-offset reverse shoulders during both types of motions. The more superior position of the humerus with the offset tray elongating the deltoid less than did the non-offset tray. As depicted in Figures 2 and 3, the medial shift in the CoR shortened the subscapularis, infraspinatus, teres major, and teres minor for both the offset and non-offset reverse shoulders during both types of motions. However, the more posterior position of the humerus with the offset tray better restored the anatomic muscle length of all 7 muscles during both types of motion. Discussion and Conclusions. Offsetting the humerus in the posterior/superior direction using the offset humeral tray/liner altered muscle lengths and resulted in more anatomic muscle tensioning (e.g. each muscle length approached 0%) relative to the non-offset reverse shoulder. These observations related to muscle shortening may describe the mechanism for instability and poor internal/external rotation with rTSA; and if so, more anatomic muscle tensioning with the offset humeral tray offers the potential for improved internal/external rotation capability. Based upon these results, we reject the null hypothesis and conclude that offsetting the position of the humerus in the posterior/superior direction does impact muscle length with rTSA. Future work should evaluate the clinical significance of these observed changes in muscle length

In a prospective study between 2000 and 2005, 22 patients with primary osteoarthritis of the shoulder had a total shoulder arthroplasty with a standard five-pegged glenoid component, 12 with non-offset humeral head and ten with offset humeral head components. Over a period of 24 months the relative movement of the glenoid component with respect to the scapula was measured using radiostereometric analysis. Nine glenoids needed reaming for erosion. There was a significant increase in rotation about all three axes with time (p < 0.001), the largest occurring about the longitudinal axis (anteversion-retroversion), with mean values of 3.8° and 1.9° for the non-offset and offset humeral head eroded subgroups, respectively. There was also a significant difference in rotation about the anteversion-retroversion axis (p = 0.01) and the varus-valgus (p < 0.001) z-axis between the two groups. The offset humeral head group reached a plateau at early follow-up with rotation about the z-axis, whereas the mean of the non-offset humeral head group at 24 months was three times greater than that of the offset group accounting for the highly significant difference between them

Introduction:. Implant dislocations are often caused by implant or bone impingement, and less impingement is critical to prevent dislocations. Several reports demonstrated that greater femoral offset delayed bony impingement and led to an improved range of motion (ROM) after THA. Therefore, an increase in the femoral offset may improve ROM and decrease implant dislocation. The aim of this study was to clarify the effect of the femoral offset in avoiding component or bony impingement after total hip arthroplasty (THA). Methods:. Seventy-eight patients underwent THA with a Pinnacle cup and Summit stem (DePuy). Intraoperative kinematic analysis was performed with a navigation system, which was used to obtain intraoperative range of motion (ROM) measurements during trial insertion of stems of 2 different offset lengths with the same head size. Further, ROM was also measured after actual component insertion. Results:. Maximal ROM was independent of the femoral offset of the stem in each patient (Figure 1). Further, we measured the intraoperative maximal ROM corresponding to high offset stems of 2 different lengths (stem sizes 1–3; + 6 mm, stem sizes 4–9; +8 mm), and compared the maximal ROMs between the standard- and high-offset stems. There were no statistically significant differences (Figure 2). These results indicate that an excessive offset length of the stem may not affect ROM. We also analyzed the correlation between femoral offset length and ROM, and found that the range of external rotation was significantly greater in patients with greater femoral offset (RR = 0.36, P = 0.02) (Figure 3). However, we could not show any correlation for the ROM values in the other planes of motion. Discussions:. Summit stem is available in 9 different sizes with standard offset lengths ranging from 36.0 mm to 44.0 mm. The average offset of Summit stem was larger than other stems. These differences in offset length could be the reason why the high offset stem did not change maximal ROM in our study. Further, the summit stem employs 2 different types of high offset lengths (+6 mm and +8 mm). We did not find any difference in maximal ROM even after using the +8 mm high offset stem. Our results indicated that even the Summit standard offset stem might have enough femoral offset to avoid implant/bone impingement. However, several reports showed that increasing stem offset increased the bending moment on the prosthesis and increased the strain in the medial cortex, and may lead to early failure of the femoral component. Nevertheless, selection of the offset stem should be performed carefully to prevent offset complications

Objectives. Preservation of posterior condylar offset (PCO) has been shown to correlate with improved functional results after primary total knee arthroplasty (TKA). Whether this is also the case for revision TKA, remains unknown. The aim of this study was to assess the independent effect of PCO on early functional outcome after revision TKA. Methods. A total of 107 consecutive aseptic revision TKAs were performed by a single surgeon during an eight-year period. The mean age was 69.4 years (39 to 85) and there were 59 female patients and 48 male patients. The Oxford Knee Score (OKS) and Short-form (SF)-12 score were assessed pre-operatively and one year post-operatively. Patient satisfaction was also assessed at one year. Joint line and PCO were assessed radiographically at one year. Results. There was a significant improvement in the OKS (10.6 points, 95% confidence interval (CI) 8.8 to 12.3) and the SF-12 physical component score (5.9, 95% CI 4.1 to 7.8). PCO directly correlated with change in OKS (p < 0.001). Linear regression analysis confirmed the independent effect of PCO on the OKS (p < 0.001) and the SF-12 physical score (p = 0.02). The overall rate of satisfaction was 85% and on logistic regression analysis improvement in the OKS (p = 0.002) was a significant predictor of patient satisfaction, which is related to PCO; although this was not independently associated with satisfaction. Conclusion. Preservation of PCO should be a major consideration when undertaking revision TKA. The option of increasing PCO to balance the flexion gap while maintaining the joint line should be assessed intra-operatively. Cite this article: N. D. Clement, D. J. MacDonald, D. F. Hamilton, R. Burnett. Posterior condylar offset is an independent predictor of functional outcome after revision total knee arthroplasty. Bone Joint Res 2017;6:172–178. DOI: 10.1302/2046-3758.63.BJR-2015-0021.R1

Aims: Femoral offset is routinely measured prior to total hip arthroplasty in order to recreate the position of optimum abductor function. We aim to determine how radiologically measured offset changes with hip rotation and to evaluate the clinical relevance of any changes. Methods: We took standardised radiographs of a proximal femur at ten degree increments of rotation and measured the offset derived in each position. We then measured the apparent offset obtained in full internal and external rotation in a series of twenty consecutive patients attending for hip arthroplasty. Results: The model demonstrated that femoral offset is maximal between ten and twenty degrees of internal rotation and that small changes in rotation can cause large changes in apparent offset. From the clinical series of elderly, arthritic patients we show that there is a signiþcant change (mean of 11.4mm or 29%) in measured offset between internal and external rotation. In our series this discrepancy would have led to a change in selected femoral prosthesis in almost half the cases. Conclusion: Femoral offset measurements are only accurate, and therefore useful, if taken with the hip in or close to þfteen degrees of internal rotation

Reverse total shoulder arthroplasty (RTSA) is an increasingly common treatment for osteoarthritic shoulders with irreparable rotator cuff tears. Although very successful in alleviating pain and restoring some function, there is little objective information relating geometric changes imposed by the reverse shoulder and arm function, particularly the moment generating capacity of the shoulder muscles. Recent modeling studies of reverse shoulders have shown significant variation in deltoid muscle moment arms over a typical range of humeral offset locations in shoulders with RTSA. The goal of this study was to investigate the sensitivity of muscle moment arms as a function of varying the joint center and humeral offset in three representative RTSA subjects that spanned the anatomical range from our previous study cohort. We hypothesized there may exist a more beneficial joint implant placement, measured by muscle moment arms, compared to the actual surgical implant configuration. A 12 degree of freedom, subject-specific model was used to represent the shoulders of three patients with RTSA for whom fluoroscopic measurements of scapular and humeral kinematics during abduction had been obtained. The computer model used subject-specific in vivo abduction kinematics and systematically varied humeral offset locations over 1521 different perturbations from the surgical placement to determine moment arms for the anterior, lateral and posterior aspects of the deltoid muscle. The humeral offset was varied from its surgical position ±4 mm in the anterior/posterior direction, ±12mm in the medial/lateral direction, and −10 mm to 14 mm in the superior/inferior direction. The anterior deltoid moment arm varied up to 20 mm with humeral offset and center of rotation variations, primarily in the medial/lateral and superior/inferior directions. Similarly, the lateral deltoid moment arm demonstrated variations up to 20 mm, primarily with humeral offset changes in the medial/lateral and anterior/posterior directions. The posterior deltoid moment arm varied up to 15mm, primarily in early abduction, and was most sensitive to changes of the humeral offset in the superior/inferior direction. The goal of this study was to assess the sensitivity of the deltoid muscle moment arms as a function of joint configuration for existing RTSA subjects. High variations were found for all three deltoid components. Variation over the entire abduction arc was greatest in the anterior and lateral deltoid, while the posterior deltoid moment arm was mostly sensitive to humeral offset changes early in the abduction arc. Moment arm changes of 15–20 mm represent a significant amount of the total deltoid moment arm. This means there is an opportunity to dramatically change the deltoid moment arms through surgical placement of the joint center of rotation and humeral stem. Computational models of the shoulder may help surgeons optimize subject-specific placement of RTSA implants to provide the best possible muscle function, and assist implant designers to configure devices for the best overall performance

Purpose of the study: Theoretically, in first-intention total hip arthroplasty (THA), restoration of femoral offset (distance between the femoral axis and the joint centre) enables optimal function. The purpose of this study was to determine acceptable limits for variation in femoral offset without loss of function. Material and method: We studied 122 hips (108 patients) who had THA with a straight cemented stem and a modular cone which could be adapted to enable three dimensional adjustment of the offset (more than 100 configurations). Mean patient age was 64 years. Most had primary or secondary degenerative disease (n=80) of the hip joint or osteonecrosis of the femoral head (n=21). The preoperative PMA score was 11.9 and the Harris score 49. Clinical and radiographic assessment was noted at mean 4.5 years follow-up. The radiographic femoral offset was measured semiautomatically in comparison with the healthy hip using the method described by Steinberg and Harris. Results: At last follow-up, the mean PMA score was 16.4 and the mean Harris score 89. These clinically scores were statistically different depending on the degree of variation of the femoral offset. Outcome was better for offset increased 0 to 5 mm (PMA 17 and Harris 93). They were less satisfactory for decreased offset (PMA 15.9 and Harris 83) (p=0.01). They were also less satisfactory for an offset increased more than 8 mm, but non significantly. Discussion: It has been established that increasing the femoral offset decreases the rate of dislocation, reduces the incidence of limping, the use of crutches, and increases the force of the gluteus medius, as well as range of motion and abduction. However, there is no known limit value. Conclusion: It is advisable to increase the femoral offset during total hip arthroplasty; the increase should be to the order of 0 to 5 mm, and never be too great

Introduction:. Total hip arthroplasty (THA) is extremely effective in treating debilitating arthritic conditions of the hip. With the many modular prosthetic designs available, surgeons can now precisely construct mechanical parameters such as femoral offset (FO). Although several studies have investigated relationships between offset choice and hip abductor strength, hip range of motion, and prosthetic wear rate, there is scarce data on the effect of FO on pain and functional outcomes following THA. The objective of this study was to assess the effect of restoring FO (within varying degrees compared to the contralateral non-diseased hip [CL]) on physical function, mental well-being, pain, and stiffness outcomes as measured by the Short Form 12 Health Survey (SF-12) and Western Ontario and McMaster University Osteoarthritis Index (WOMAC) at post-operative follow-up. Methods:. We prospectively collected data on 249 patients that underwent unilateral THA with no or minimal disease of the contralateral hip. Baseline data collection included: age, gender, diagnosis, femoral head size, type of stem, and pre-operative SF-12 and WOMAC scores. Post-operative SF-12 and WOMAC scores were recorded during annual follow-up visits. Post-operative FO was retrospectively measured on standard anteroposterior (AP) pelvis radiographs and compared to FO of CL. FO was measured as the perpendicular distance from the femoral head center of rotation to the anatomic axis of the femur with appropriate adjustments made for image magnification. Patients were categorized into one of three groups: decreased femoral offset (dFO, less than −5 mm compared to CL), normal femoral offset (nFO, between −5 and +5 mm of CL), and increased femoral offset (iFO, greater than +5 mm compared to CL). Results:. In all, 31 patients were categorized into dFO, 163 categorized into nFO, and 55 categorized into iFO. At baseline, the groups differed in categorical diagnoses (p = 0.01). Further analysis revealed a higher percentage of posttraumatic arthritis in dFO as compared to nFO and iFO (12.9%, 1.2%, and 1.8%, respectively). Moreover, a higher percentage of hip dysplasia was present in iFO as compared to nFO and dFO (14.5%, 3.6%, and 6.5%, respectively). Pre-operatively, dFO had lower WOMAC Pain scores than nFO and iFO (29.68, 43.39, and 43.63, respectively; p < 0.005). (Please see Table 1 for comparison of baseline characteristics between groups.) All other pre-operative demographic and survey characteristics were similar. At most recent post-operative follow-up, dFO had lower WOMAC Physical Function scores than nFO and iFO (72.03, 83.23, and 79.51, respectively; p < 0.02) (see Table 2). Discussion:. Reduction of patients' native FOs by greater than 5 mm during THA can lead to inferior levels of physical function. Furthermore, increasing FO by greater than 5 mm did not lead to increased levels of pain nor decreased levels of function

Introduction. One of the important criteria of the success of TKR is achievement of the Flexion ROM. Various factors responsible to achieve flexion are technique, Implant and patient related. Creation of the Posterior condylar offset is one such important factor to achieve satisfactory flexion. Aim. To correlate post op femoral condylar offset to final flexion ROM at 1 yr. post op. Methods. This is a clinico-radiological study of the cases done prospectively between September 2011 and August 2012. Inclusion criteria:. All patients undergoing Bilateral TKRs and have agreed for the follow up at 1 yr. Exclusion criteria:. Patients who had previous bony surgery on lower end femur. Patients with previous fracture of lower end femur. All the patients had PS PFC Sigma (De Puy, Warsaw) components cemented. ROMs were measured at 6 weeks, 3 months, & 1 year post op. The last reading was taken as final flexion ROM as measured by a Physiotherapist with the help of a Goniometer. Results. We had 21 cases of Bilateral TKRs who satisfied our criteria. Pre and post op femoral condylar offset was measured in mm. on lateral x ray. Pre and post op flexion was measured. Results showed that variation in the posterior femoral offset by > 3mm in post op x ray was related to loss of flexion of an average 21 deg. (16 – 24 degrees). Greater the deflection from the normal offset, greater was the loss of flexion. These patients also showed lesser improvement in KSS functional score. Discussion. Flexion is one of the most important yardsticks for the measurement of success of TKR. This factor is more important more so in Asian population. Literature has shown that three important determinants for good flexion are…. Posterior Condylar Offset Restoration. Tibial slope restoration. Femoral Roll back in flexion. An increased offset permits greater flexion before impingement between the tibial insert and the femur. In our study we kept Tibial slope and Femoral Roll back constant by using the same prosthesis. The femoral condylar offset changed as per the size of the AP femoral cutting block. (Anterior referencing guide used). Overresection of the posterior condyles reduced the posterior femoral condylar offset and hence significant loss of post op flexion. The shorter posterior condyle of smaller femoral component can increase the potential for bone impingement proximal to the posterior condyles. In our study the opposite side replaced knee acted as a control. It is generally stated that after a TKR flexion can improve upto 1 year and hence was taken as final possible flexion. Conclusion. Keeping Tibial slope and Femoral roll back constant during the surgery, posterior condylar offset restoration within 3 mm of its original pre op offset was necessary to achieve satisfactory flexion at 1 year. Undersizing the femoral component to achieve more flexion is perhaps suboptimal. Appropriate AP femoral sizing is a must to restore the normal offset

Proper restoration of posterior condylar offset during TKA has been shown to be important to maximize range of motion and minimize flexion instability. However, there is little information as to the importance of restoration of mid-sagittal femoral geometry. There is controversy as to whether a TKA prosthesis should have a single radius or multiple radii of curvature. The purpose of this study is to evaluate the effectiveness of a multi-radius femoral component at restoring mid sagittal femoral offset. A consecutive series of 100 TKAs with digital preoperative and postoperative radiographs and standardized radiographic markers were analyzed. There were 71 female and 29 male knees with mean age of 59 years. All TKAs were performed by a single surgeon using a multi-radius femoral component design. The distal femoral resection was set to resect 10 mm from the distal femoral condyle and a posterior referencing system was used to size the femoral component. Using radiographic perfect lateral projections of the knees, a line was drawn along the posterior femoral shaft and another parallel line down the anterior femoral shaft. A 3rd line was then drawn parallel to the posterior shaft at the furthest point posterior on the condyle. A 4th line was drawn parallel to the anterior shaft at the furthest point anterior on the femur. 90 degree angles were constructed to create a grid in the anterior and posterior directions, similar to a previously reported technique. Finally, 45 degree angle lines were created in the grid to assess mid flexion dimensions [Fig-1 and 2]. The percent change in posterior condylar offset (PCO), anterior femoral offset (AFO), mid femoral anterior offset (MAFO) and mid femoral posterior offset (MFPO) were calculated. The mean reproduction of the mid-anterior femoral offset and mid-posterior femoral offset were 101.1% [range 56.5%–167.5%] and 96.8% [range 54.9%–149.0%] of preoperative measurements respectively. The average restoration of posterior offset and anterior offset were 92.8% [range 49.0%–129.8%] and 115.3% of preoperative measurements [range 35.7%–400.0%] respectively. When the posterior condylar offset was restored to within 10% of the native anatomy, the MPFO restoration more closely resembled normal anatomy (103.0% vs. 93.9%, p = 0.005). When the postoperative posterior condylar offset was decreased greater than 20%, both the MAFO (90.1% vs. 104.5%, p = 0.004) and MPFO (78.5% vs. 102.9%, p < 0.001) decreased compared to the native knee. There was no relationship between restoration of the PCO and the MAFO correction (104.6% vs. 99.4%, p = 0.213). Finally, there was no correlation between restoration of anterior femoral offset within 10% of normal and the restoration of mid sagittal femoral offset; 98.0% vs 102.0% for MAFO (p = 0.320) and 98.7% vs 96.3% for MPFO (p = 0.569). A modern multi-radius condylar knee design is capable of reproducing the mid-sagittal geometry of the preoperative knee. However, the restoration of mid sagittal offset is largely dependent on the restoration of the posterior condylar offset. Intraoperative adjustments in anterior and posterior femoral resections can have significant impact in the ability of the implant to reproduce mid-sagittal femoral anatomy

Background. Most of contemporary total knee systems address on improving of range of motion and bearing materials. Although new total knee designs in most systems accommodated the knee morphology according to gender differences, reestablishing of the same anterior offset of the distal femur during total knee arthroplasty (TKA) has not been well addressed. Furthermore, in most total knee systems, the anterior offset of the femoral component is constant regardless of the increment of the femoral size. We hypothesized that change of the anterior offset of the distal femur during TKA might affect the quadriceps strength and immediate clinical outcomes which may result in improved design of the future femoral component. Purpose. To evaluate the peak quadriceps strength and immediate clinical outcomes related to the change of anterior offset of the distal femur during TKA. Materials & Methods. We prospectively evaluated 75 patients (75 knees) who had primary osteoarthritis and underwent an uncomplicated TKA. A measured-resection technique of surgery using a single design of semi-constrained posterior-stabilized prosthesis with patellar resurfacing was used in all knees. In every TKA, the patellar resection was quantified in order to provide a similar thickness of the patellar composite to the original patellar thickness. A uniform perioperative protocol was applied. The mean thickness from the medial and lateral sides of the resected anterior femur were evaluated and compared with the mean thickness of the anterior part of the femoral component. The peak quadriceps strength and peak hip flexor strength was evaluated before surgery, and then at 2 weeks, 6 weeks and 3 months, postoperatively, using a digital dynamometer. The Difference of thickness between the resected anterior femoral bone and the anterior femoral component was defined as the change of the anterior offset of the distal femur. Clinical outcomes, including Knee Society Scores (KSS) and Western Ontario and McMaster University Arthritis Index (WOMAC) scores at 2 weeks, 6 weeks and 12 weeks were evaluated in relation of muscle strengths. Results. Patients were divided in 2 groups according to the change of the anterior offset of the distal femur during TKA. Thirty knees (group A) had similar or increased anterior offset of the distal femur and 45 knees (group B) had decreased anterior offset of the distal femur. The mean thickness of the resected anterior femoral bones in group A and B were 4.8 mm and 9.7 mm, respectively. The mean changes of anterior offset in group A and B were (+)0.7 mm and (−)4.2 mm with statistical difference (p, 0.01). There were no differences in patient's demographic data including age, sex, and body mass index (BMI). Preoperatively, both groups had similar mean peak quadriceps strength (108.04 N vs.115.52 N, p, 0.191) and mean peak hip flexor strength (105.98 N vs.108.05 N, p.0.745). At 2-week follow-up (FU), group A had significantly better peak quadriceps strength (111.53 N vs. 99.75 N, p, 0.03) and improve of total WOMAC score (32.4 points vs. 27.4 points, p, 0.03) than those of group B, The improved WOMAC score was statistical significant in subgroup of function (16.7 points vs. 12.7, p, 0.04) However, the peak hip flexor strength, KSS clinical scores and function scores were not different. At 6-week FU 12-week FU, there were no differences in all measuring parameters. Discussion and Conclusion. Biomechanical study has shown that the anterior offset of the distal femur provides role as a lever arm for a proper quadriceps function. Therefore, with maintaining of the patellar thickness during TKA in individual patient, a constant thickness of the anterior offset of the femoral component regardless of size may result in change of the anterior offset of the distal femur and may affect the function of quadriceps. The present study demonstrated that, at 2 weeks postoperatively, patients who had increased anterior offset of the distal femur could significantly gain better peak quadriceps strength and improved WOMAC function score than those who did not. In addition, change of anterior offset of the distal femur had no relation with the peak hip flexor strength. A mean 4.2-mm decreasing of anterior offset of the distal femur during TKA caused a shorter lever arm to the quadriceps and resulted in reducing the peak quadriceps strength with no gross effect on hip flexor strength. Although peak quadriceps strength in patients who had increased anterior offset of distal femur correlated with improved WOMAC function score, this marginal statistical significance provided a very short time for advantages. As there was a similar or slightly increased of anterior femoral offset in Group A, the anterior overstuff should be very minimal. At 6 weeks and 12 weeks after surgery, we found that investigated parameters, as well as clinical outcomes, were not different in both groups. We concluded that the change of femoral offset during TKA provided a short effect on quadriceps strength and clinical outcomes for few weeks which had no clinical impact on the drive to improve the prosthetic design of the femoral component which has a constant thickness of the anterior offset

Introduction. Inappropriate soft tissue tension around an artificial hip is regarded as one cause of dislocation or abductor muscle weakness. It has been considered that restoration of leg offset is important to optimise soft tissue tension in THA, while it is unclear what factors determine soft tissue tension around artificial hip joints. The purpose of the present study was to assess how postoperative leg offset influence the soft tissue tension around artificial hip joints. Materials and Methods. The subjects were 89 consecutive patients who underwent mini-incision THA using a navigation system through antero-lateral or postero-lateral approach. Soft tissue tension was measured by applying traction amounting to 40% of body weight with the joint positioned at 0°, 15°, 30°, and 45° of flexion. The distance of separation between the head and the cup was measured using the navigation system. Results. The distance of cup/head separation differed significantly for different angles of flexion, with the greatest distance at 15° of flexion which was 11±5 (SD) mm. Stepwise multiple regression analysis showed that postoperative leg offset discrepancy, antero-lateral approach, preoperative abduction ROM were correlated with the distance of cup/head separation at 15° of flexion. Postoperative leg offset discrepancy were also correlated negatively with the distance of cup/head separation at 0° and 30° of flexion. Conclusion. Postoperative leg offset discrepancy influenced significantly the soft tissue tension around THA at a wider range of flexion

The aim of this retrospective cohort study was to identify any difference in femoral offset as measured on pre-operative anteroposterior (AP) radiographs of the pelvis, AP radiographs of the hip and corresponding CT scans in a consecutive series of 100 patients with primary end-stage osteoarthritis of the hip (43 men and 57 women with a mean age of 61 years (45 to 74) and a mean body mass index of 28 kg/m. 2. (20 to 45)). Patients were positioned according to a standardised protocol to achieve reproducible projection and all images were calibrated. Inter- and intra-observer reliability was evaluated and agreement between methods was assessed using Bland-Altman plots. In the entire cohort, the mean femoral offset was 39.0 mm (95% confidence interval (CI) 37.4 to 40.6) on radiographs of the pelvis, 44.0 mm (95% CI 42.4 to 45.6) on radiographs of the hip and 44.7 mm (95% CI 43.5 to 45.9) on CT scans. AP radiographs of the pelvis underestimated femoral offset by 13% when compared with CT (p < 0.001). No difference in mean femoral offset was seen between AP radiographs of the hip and CT (p = 0.191). Our results suggest that femoral offset is significantly underestimated on AP radiographs of the pelvis but can be reliably and accurately assessed on AP radiographs of the hip in patients with primary end-stage hip osteoarthritis. We, therefore, recommend that additional AP radiographs of the hip are obtained routinely for the pre-operative assessment of femoral offset when templating before total hip replacement

Introduction. Subluxation and dislocation are frequently cited reasons for THA revision. For patients who cannot accommodate a larger femoral head, an offset liner may enhance stability. However, this change in biomechanics may impact the mechanical performance of the bearing surface. To our knowledge, no studies have compared wear rates of offset and neutral liners. Herein we radiographically compare the in-vivo wear performance of 0mm and 4mm offset acetabular liners. Methods. Two cohorts of 40 individuals (0mm, 4mm offset highly crosslinked acetabular liners, respectively) were selected from a single surgeon's consecutive caseload. All patients received the same THA system via the posterior approach. AP radiographs were taken at 6-week (‘pre’) and 5-year (‘post’) postoperative appointments. Patients with poor radiograph quality were excluded (n. 0mm. =5, n. 4mm. =4). Linear and volumetric wear were quantified according to Patent US5610966A. Briefly, images were processed in computer aided design (CAD) software. Differences in vector length between the center of the femoral head and the acetabular cup (pre- and post-vector, Figure 1) allow for calculation of linear wear and wear rate. The angle (β) between the linear wear vector and the cup inclination line was quantified (Figure 1). Patients with negative β were excluded from volumetric analyses (n. 0mm. =11, n. 4mm. =7). Volumetric wear was accordingly calculated accounting for wear vector direction. The results from three randomly selected patients were compared to results achieved using the “Hip Analysis Suite” software package (UChicagoTech). Results. Linear wear rate (Figure 2A) for 0mm offsets was significantly lower than the 4mm offsets (0.011±0.091 vs. 0.080±0.122mm/yr, p=0.008). Volumetric wear rate (Figure 2B) for 0mm offsets was significantly lower than the 4mm offsets (30.37±20.45 versus 61.58±42.14mm. 3. /year, p=0.001). Demographic differences existed between the two cohorts (age, gender, femoral head size, and acetabular cup size). However, there were no significant correlations found between linear/volumetric wear rate and any demographic including age, gender, BMI, femoral head size, or acetabular cup size. Validation showed no significant differences between the CAD method used herein and the gold standard method (0.083±0.014 versus 0.093±0.041mm/year, p=0.71). Discussion. This study is the first to show that 0mm offset liners have significantly lower linear and volumetric wear rates than do 4mm offset liners. Despite this difference, no revisions have been required in either cohort. The linear wear rates computed in this study are below literature-reported clinically relevant values for wear-induced-osteolysis (∼0.10mm/year). As such, the clinical impact of this wear rate difference is unknown. The higher wear rate in the offset group may owe to the altered biomechanics of the construct. By lateralizing the femoral head through an offset liner, the femur is lateralized with respect to the patient's center of mass (COM) (Figure 3). To maintain stability, the patient must pull the COM over the femoral head by increasing force from the hip abductors. This increased force is transmitted through the polyethylene acetabular liner. Thus, increased wear may result from the forces required to maintain balance in gait. Further work is needed to determine whether these higher wear rates will have clinical sequelae

Introduction. Accurate evaluation of femoral offset is difficult with conventional anteroposterior (AP) X-rays. Routine CT imaging is costly and exposes patients to a significant dose of radiation. The EOS® imaging system is an innovative slot-scanning radiography system that makes possible the acquisition of simultaneous and orthogonal AP and lateral images of the patient in standing position. These 2-dimensional (2D) images are equivalent to standard plane X-rays. Three-dimension (3D) reconstructions are obtained from these paired images according to a validated protocol. This prospective study explores for the first time the value of the EOS® imaging system for comparing measurements of femoral offset obtained from 2D images and 3D reconstructions. Materials and Methods. Following our standard protocol, we included a series of 100 patients with unilateral total hip arthroplasty (THA). The 2D offset was measured on the AP view with the same protocol as for standard X-rays. The 3D offset was calculated from the reconstructions based on the orthogonal AP and lateral views. Reproducibility and repeatability studies were conducted for each measurement. We compared the 2D and 3D offsets for both hips (with and without THA). Results. For the global series (100 hips with and 100 without THA), the 2D offset was 40 mm (SD: 7.3; range 7 to 57 mm). The standard deviation was 6.5 mm for repeatability and 7.5 mm for reproducibility. The 3D offset was 43 mm (SD: 6.6; range 22 to 62 mm), with a standard deviation of 4.6 mm for repeatability and 5.5 mm for reproducibility. The 2D offset for the hips without THA was 40 mm (SD: 7.0; range 26 to 56 mm), and the 3D offset was 43 mm (SD: 6.6; range 28 to 62 mm). For the THA side, the 2D offset was 41 mm (SD: 8.2; range 7 to 57 mm) and the 3D offset was 45 mm (SD: 4.8; range 22 to 61 mm). Comparison of the two protocols shows a significant difference between the 2D and 3D measurements, with the 3D offsets having higher values. Comparison of the sides with and without surgery for each case showed a 5-mm deficit for the offset in 35% of the patients according to the 2D measurement but in only 26% according to the 3D calculation. Conclusions. This study highlights the limitations of 2D measurements of femoral offset on plane X-rays. The reliability of the EOS® 3D models has been previously demonstrated with CT scan reconstructions as a reference. The EOS® imaging system could be an option for obtaining accurate and reliable offset measurements while significantly limiting the patient's exposure to radiation

During total hip arthroplasty various femoral stem offsets are available. Additionally, the femoral stem can be placed in either varus or valgus. The overall effect of this is to increase or decrease the functional offset at the hip joint. To our knowledge no studies have concentrated on the effects of these variations in offset, if any, upon the loading and function of the knee joint. The aim of this study was to investigate the effects, if any, of reducing functional offset at the knee. A computer model was constructed to study the effects of variations in functional offset in different anatomical settings

Background The magnitude of the medial offset and the limb length discrepancy after a total hip replacement (THR) significantly alters the biomechanics of the hip. If both these components are not properly restored, the rate of dislocation may increase. Further decreased offset may result in impingement at the extremes of movement, and also results in soft-tissue laxity, while increased offset increases stress within the stem that may lead to stem fracture or loosening. In addition to affecting the clinical outcome, limb length discrepancy may also cause legal problems. Aim To find out whether intraoperative assessment and restoration of desired offset, and correction of limb length discrepancy actually corrects these two components as assessed by postoperative radiographs. Material and Methods We evaluated 39 consecutive THRs in 37 patients who had the surgery performed via the posterior approach. Intraoperatively the medial offset was measured using a ruler from the tubercle in the trochanteric fossa to the centre of rotation of the head, and then check again after the seating of the femoral prosthesis. The size of the head was then accordingly altered. The limb length was measured using the ruler parallel from the lesser trochanter, and taking it upto the tip of the greater trochanter. The preoperative and the postoperative radiographs were evaluated for the medial offset and limb length discrepancy. The medial offset was calculated as a ratio in reference to the opposite side. Results The median medial offset was 93.9 (85–100) preoperatively and 94.2 (85–110) postoperatively. The median limb length discrepancy was improved from a preoperative −4.84mm (0 to −30mm) to a postoperative −0.06mm (−9 to +16mm). Discussion Preoperative templating may be a way of obtaining the correct medial offset and limb length in THRs. However, varus or valgus placement, and sinking or protrusion of the prosthesis may alter both these components significantly. Hence, intraoperative measurement and thus changing the components and the position of the stem accordingly may be the best method in addition to preoperative templating, in achieving the required offset and minimising limb length discrepancy in THRs

Introduction. The effect of the implant posterior condylar offset has recently generated much enthusiasm among researchers. Some reports were concerned about the relationship between the posterior condylar offset and an extension gap. However, the posterior condylar offset was measured in a flexed knee position or in reference to femoral anatomy alone. Posterior femoral condylar offset relative to the posterior wall of the tibia (posterior offset ratio; POR) is possibly the risk of knee flexion contracture associated with posterior femoral condylar offset after TKA. However, there are no reports concerning the relationship between POR and flexion contracture in vivo. The aim of this study is to evaluate the relationship between the measurement of POR and flexion contracture of the knee in vivo. Methods. Twenty-seven patients who underwent a primary total knee arthroplasty (PFC Sigma RP-F) were participated in the study. The lateral femoro-tibial angle (lateral FTA) was measured using lateral radiographs obtained by two procedures. Two procedures are applied to obtain true lateral radiographs of the lower extremities. (1) Full-length true lateral radiographs on standing, (2) True lateral radiographs in the prone position (Fig. 1A). ‘Posterior offset ratio’ was defined as Fig. 1B. Significant differences among groups were assessed using two-tailed Student's t-tests. Spearman's correlation analysis was performed to evaluate the relationship between lateral FTA and posterior offset ratio of patients. Results. The mean value of the POR on standing was 14.94 ± 7.53%. The mean value of flexion contracture of the knee on standing was 11.67 ± 9.21 degree and that in the prone position was 4.22 ± 6.17 degree (P = 0.001). The POR was negatively correlated with flexion contracture of the knee in all procedures with statistical significance (standing: r = 0.62, P = 0.0039; prone: r = 0.66, P = 0.0001) (Fig. 2). Discussion. We have evaluated flexion contracture by two procedures. The mean value of flexion contracture of the knee on standing was 11.67 ± 9.21 degree, whereas that in the prone position was 4.22 ± 6.17 degree. We surmised that this discrepancy occurred due to the flexor muscle tension on standing. In terms of the evaluation of posterior soft tissue tightness of the knee, muscle relaxation can be achieved in prone position is rather than standing position. Our study investigated the relationship between the posterior protrusions of the posterior condyle of the femur relative to the tibia (POR) and flexion contracture after TKA evaluated by two measurement procedures. POR is strongly correlated with flexion contracture evaluated by both measurement procedures. The value of POR of this implant in vitro was about 25% in previous study, whereas the mean value of POR in vivo was 14.94%, suggesting that POR in the flexion contracture knee relatively reduced because posterior soft tissue pushed femoral component anteriorly. Our result clearly showed that if posterior clearance is insufficient, flexion contracture occur due to posterior soft tissue tightness. In conclusion, POR after TKA in vivo negatively correlate with flexion contracture presumably because posterior soft tissue pushed femoral component anteriorly

Introduction. Reverse shoulder arthroplasty (rTSA) increases the deltoid abductor moment arm length to facilitate the restoration of arm elevation; however, rTSA is less effective at restoring external rotation. This analysis compares the muscle moment arms associated with two designs of rTSA humeral trays during two motions: abduction and internal/external rotation to evaluate the null hypothesis that offsetting the humerus in the posterior/superior direction will not impact muscle moment arms. Methods. A 3-D computer model simulated abduction and internal/external rotation for the normal shoulder, the non-offset reverse shoulder, and the posterior/superior offset reverse shoulder. Four muscles were modeled as 3 lines from origin to insertion. Both offset and non-offset reverse shoulders were implanted at the same location along the inferior glenoid rim of the scapula in 20° of humeral retroversion. Abductor moment arms were calculated for each muscle from 0° to 140° humeral abduction in the scapular plan using a 1.8: 1 scapular rhythm. Rotation moment arms were calculated for each muscle from 30° internal to 60° external rotation with the arm in 30° abduction. Results. During abduction with the normal shoulder, the subscapularis and infraspinatus act as abductors throughout the range of motion and the teres minor converts from an adductor to abductor at 60°. In the non-offset reverse shoulder, the subscapularis converts from an adductor to abductor at 82°, the infraspinatus converts at 68°, and the teres minor converts at 135°. Because the offset humeral tray shifts the humerus superiorly relative to the non-offset tray, each muscle converts from an adductor to abductor earlier in abduction, where the subscapularis converts at 62°, the infraspinatus converts at 43°, and the teres minor converts at 110°. During rotation (Figures 1–3), both the offset and non-offset reverse shoulders decrease the internal rotation capability of the subscapularis and teres major but increase the external rotation capability of the infraspinatus and teres minor relative to the normal shoulder. Because the offset tray shifts the humerus posteriorly, the internal rotation capability of the subscapularis and teres major is decreased by 7.1 and 9.5 mm while the external rotation capability of the infraspinatus and teres minor is increased by 8.6 and 7.8 mm, respectively. Discussion and Conclusions. Changing humeral position using an offset humeral tray modified the function of each muscle. In abduction, the offset tray caused each muscle to convert from adductors to abductors earlier. Improved abduction capability limits each muscle's antagonistic behavior with the deltoid, potentially reducing the deltoid force required to elevate the arm. In rotation, the offset tray caused the posterior shoulder muscles to be more effective external rotators. Improved external rotation capability is important for patients with external rotation deficiency; as external rotation is required for many activities of daily living, increasing the rotator moment arm lengths of the only two external rotators is advantageous to restore function. Therefore, we reject the null hypothesis and conclude the offset humeral tray does impact muscle moment arms with rTSA. Future work should evaluate the clinical significance of these observed changes in muscle moment arms

Introduction. Total hip replacement (THR) is a very common procedure performed for the treatment of osteoarthritis of the hip. The aim of THR is to restore function and quality of life of the patients, by restoring femoral offset, leg length, centre of rotation, and achieving stability, to avoid dislocation postoperatively. Method. We aimed to perform preoperative assessment of femoral offset on anteroposterior (AP) radiographs of the hip, and on corresponding CT scans, for patients undergoing primary THR. Patients were positioned according to a standardised protocol prior to obtaining radiographs of the hip and CT scan. Inter- and intra-observer reliability was evaluated between 3 observers of differing levels of seniority – an orthopaedic trainee, a fellow, and a consultant. CT scan measurements of offset were performed by one consultant radiologist. The researchers measuring radiographic offset were blinded to the results of the CT measurements. Results. In the entire cohort of 50 patients, the mean femoral offset was 44 mm on AP radiographs of the hip and 45 mm on CT scans. No significant difference in mean femoral offset was seen between AP radiographs of the hip and CT. There was good inter and intra-observer reliability in the measurement of femoral offset on AP radiographs of the hip. There was no difference in the radiographic measurements between observers of differing levels of seniority. Conclusions. Accurate restoration of femoral offset is very important in the good functioning of THR. AP radiographs of the hip are accurate, and should be routinely obtained preoperatively for templating, prior to THR

Introduction: During total hip arthroplasty various femoral stem offsets are available and the femoral stem can be placed in either varus or valgus. The overall effect of this is to increase or decrease the functional offset at the hip joint. Many authors have investigated the effects of the functional offset upon the reconstructed hip joint. To our knowledge no studies have concentrated on the effects, if any, upon the loading and function of the knee joint. The aim of this study was to investigate the effects, if any, of reducing functional offset at the knee. Materials and methods: To study the effects of alterations in functional offset during hip arthroplasty, a biomechanical computer model was constructed. Normal lower limb anthropometric measurements available in the literature were used within this program. The model thus constructed calculated the effect of different functional offsets upon moments about the knee in stationary standing on one leg. The model also allowed for different varus/valgus placement of the stem. Results: Reducing prosthetic neck length reduces the moment arm created by the ground reaction force about the knee axis. Placing the stem in valgus reduces the moment arm. This reduction depends upon the length of the neck. Discussion: In the one legged stance, the line of weight is offset in the coronal plane from the AP axis of the knee joint producing an adducting moment about the knee, balanced by tension in the lateral collateral ligament of the knee and the iliotibial tract. Any reduction in this moment arm would alter the loading of the knee, altering the value of the force on the lateral compartment of the knee. Indeed, it is possible to develop a situation where the knee moment arm creates an abducting moment about the knee, increasing the loading of the lateral compartment of the knee. This may lead to valgus malalignment of the knee

In recent years the majority of X-ray departments have moved to a digital format of recording and archiving radiographs. These digital images (as with previous ‘films’) have a built in magnification factor (variable with each patient), which, may cause errors in templating for joint replacement surgery. Placing a marker of known size at the same level as the joint in question allows calculation of the magnification. This may help to restore hip offset in total hip replacement. To establish the magnification factor for digital radiographs taken in our unit. To assess the usefulness of marker images in accurate preoperative templating. Preoperative marker radiographs were identified retrospectively. The apparent size of the marker was measured on digital image. This value was used to calculate the magnification of the image. The scaled X-ray was up loaded to a digital templating software programme. This software uses a ‘scaling tool’ to calculate the magnification of the image. The hip joint templating tool was the used to calculate the offset of the proximal femur, this was performed with the calculated magnification and also an assumed magnification of 120%. The recommended offset of Exeter V40 stem was noted for both values. Images were identified for 40 patients with markers. The average magnification was 122% for both PACS and Orthoview with a range 113% – 129% and a standard deviation of 4%. The median value for magnification was 120%. The average change in offset between calculated and estimated magnification was 1.275mm with a maximum change of 3mm. In two cases this difference resulted in a change in the recommended offset (5%). The use of marker radiographs is widely described. In this small series the magnification is the same as previously reported in other studies. The difference in offset between calculated and estimated magnification was relatively small and caused a change in the recommended offset in only two patients. Variation in the use of the templating tool in our software can produce a much greater change in offset. Marker radiographs will only be useful as part of a standardised method of pre-operative templating

After total hip replacement, force generating capacity of gluteal muscles is an impotant parameter on joint contact forces and primary fixation of total hip replacement. Femoral offset is an option to optimize muscle moment arms, especially main abductor Gluteus Medius and Minimus. To investigate relationship with weak gluteal muscles (Gluteus Medius and Minimus) and increased femoral offset, we build a musculoskeletal model. Creating of three-dimensional femur geometry and scaling of the musculoskeletal model according to the subject were performed with computed tomography data. Obtained gait kinematic and kinetic data were applied and to mimic gluteal muscle weakness, the force generating capacities of Gluteus Medius and Minimus reduced (%20-%80). Analysis were done for both anatomical and +10mm offset. Then, muscle and joint reaction forces obtained from musculoskeletal analysis transfered to CT based finite element model to evaluate changes in maximum principle stresses on femur. According to the results of the musculoskeletal analysis, the weakness of the gluteal muscles caused an increase in the activation of Gluteus Maximus, Rectus Femoris and Tensor Fasciae Latae. Effects of +10 mm femoral offset on total abductor muscle activity increased with reduced muscle strength. As a result of the finite element analysis, no significant difference was observed for maximum principle stresses on femur with varying muscle activites. The results of these analyses are important to understand weakness of gluteal muscles and for planning hip surgery

Introduction: Restoration of hip biomechanics is an important part of successful total hip replacement. Preoperative templating acts as a guide to selection of size and positioning of prostheses to enable this. We aimed to Establish how closely natural femoral offset could be reproduced using the manufacturers templates for 10 femoral stems in common use in the U.K. Method: The10 most frequently used femoral components from the U.K. national joint registry (cemented and un-cemented) were identified. Sets of templates for these designs were used to template a series of 47 consecutive pre-operative radiographs from patients who had undergone unilateral total hip replacement for unilateral osteoarthritis of the hip. The non-operated on side of the pelvic radiographs were templated using the 10 sets of templates according to the technique of Schmalzreid. This demonstrated how much the offset of the hip would be changed if that prosthesis were selected and implanted in the templated position. 3 different surgeons performed the complete process. The standard deviation of change in offset between the templated centre of rotation and the normal centre of rotation of the set of radiographs for each prosthesis was then calculated allowing us to rank the templates and hence implants according to their ability to reproduce the normal anatomical offset. Results: The most accurate template was the CPS with a Root Mean Square Error of 2.0mm followed in rank order by: C stem 2.16, CPT 2.40, Exeter 3.23, Stanmore 3.28, Charnley 3.65, Corail 3.72, ABG II 4.30, Furlong HAC 5.08, Furlong modular 7.14. Discussion: There is fairly wide variation in the ability of the femoral prosthesis templates to reproduce normal femoral offset in a series of standard pre-operative hip radiographs. The more modern polished tapered stems with high modularity were best able to reproduce femoral offset. There is however no correlation between the prostheses ability to restore offset and clinical results. Some of the older less modular stems, which were unable to get close to normal offset, have some of the best longterm clinical results. With the increasing digitalisation of radiographs a change in the method of templating is required. This may allow manufactures to re-examine their templates and improve the accuracy of this process

Objectives. Posterior condylar offset (PCO) and posterior tibial slope (PTS) are critical factors in total knee arthroplasty (TKA). A computational simulation was performed to evaluate the biomechanical effect of PCO and PTS on cruciate retaining TKA. Methods. We generated a subject-specific computational model followed by the development of ± 1 mm, ± 2 mm and ± 3 mm PCO models in the posterior direction, and -3°, 0°, 3° and 6° PTS models with each of the PCO models. Using a validated finite element (FE) model, we investigated the influence of the changes in PCO and PTS on the contact stress in the patellar button and the forces on the posterior cruciate ligament (PCL), patellar tendon and quadriceps muscles under the deep knee-bend loading conditions. Results. Contact stress on the patellar button increased and decreased as PCO translated to the anterior and posterior directions, respectively. In addition, contact stress on the patellar button decreased as PTS increased. These trends were consistent in the FE models with altered PCO. Higher quadriceps muscle and patellar tendon force are required as PCO translated in the anterior direction with an equivalent flexion angle. However, as PTS increased, quadriceps muscle and patellar tendon force reduced in each PCO condition. The forces exerted on the PCL increased as PCO translated to the posterior direction and decreased as PTS increased. Conclusion. The change in PCO alternatively provided positive and negative biomechanical effects, but it led to a reduction in a negative biomechanical effect as PTS increased. Cite this article: K-T. Kang, Y-G. Koh, J. Son, O-R. Kwon, J-S. Lee, S. K. Kwon. A computational simulation study to determine the biomechanical influence of posterior condylar offset and tibial slope in cruciate retaining total knee arthroplasty. Bone Joint Res 2018;7:69–78. DOI: 10.1302/2046-3758.71.BJR-2017-0143.R1

Surgeons are becoming increasingly aware of the importance of matching a patient’s native offset during hip arthroplasty. During the course of a previous study investigating proximal femoral geometry in New Zea-landers it was noted that accurately measuring the femoral offset of a hip arthroplasty patient by traditional methods is difficult and inaccurate. The relationship of various surface parameters were studied to find a simple and reliable method for the surgeon. Eighteen cadaver femora were skeletalised and the offset was measured using a standardised radiological technique. The femoral neck was then sectioned from a point 1–2 cm above the lesser trochanter to the base of the trochanteric fossa. The femoral head was sectioned in the coronal plane and the centre of the head located with concentric circles. The distance from the centre of the head to the most lateral spike of bone was measured. This measure was compared to the radiological offset. Offset correlated closely with the measurement from the centre of rotation to the most lateral spike of bone provided the neck cut extends to the base of the tro-chanteric fossa. Eleven of eighteen measurements were within 2mm of true offset and fifteen were within 3mm. A simple intra-operative technique taking no longer than one or two minutes and requiring no special equipment has been devised to allow the surgeon to accurately estimate the patients femoral offset

We have studied the concept of posterior condylar offset and the importance of its restoration on the maximum range of knee flexion after posterior-cruciate-ligament-retaining total knee replacement (TKR). We measured the difference in the posterior condylar offset before and one year after operation in 69 patients who had undergone a primary cruciate-sacrificing mobile bearing TKR by one surgeon using the same implant and a standardised operating technique. In all the patients true pre- and post-operative lateral radiographs had been taken. The mean pre- and post-operative posterior condylar offset was 25.9 mm (21 to 35) and 26.9 mm (21 to 34), respectively. The mean difference in posterior condylar offset was + 1 mm (−6 to +5). The mean pre-operative knee flexion was 111° (62° to 146°) and at one year postoperatively, it was 107° (51° to 137°). There was no statistical correlation between the change in knee flexion and the difference in the posterior condylar offset after TKR (Pearson correlation coefficient r = −0.06, p = 0.69)

Hip simulator studies have shown reduced hip offset can cause microseparation and increased wear in hard-on-hard hip bearings. However this has not been analysed yet in vivo. We studied the effect of reduced hip offset on serum metal ion levels in patients with metal-on-metal (MoM) hip arthroplasty. From all patients who underwent unilateral MoM bearing hip arthroplasty between 2005 and 2009, 63 patients had complete clinical evaluation, measurement of serum chromium and cobalt ion levels as well as biomechanical measurements on pre- and post operative radiographs (cup inclination, head inclination, change in hip offset and change in hip length.). Ten arthroplasties were revised due to adverse metal reaction and six patients awaiting revision. 55% of ASR hips showed higher metal ions (>7 ppb) whereas only 15% of non-ASR hips had higher ion levels. Patients with reduced postoperative hip offset by more than 5 mm had significantly higher mean metal ion levels compared to the the rest of the hips (31.8 ppb vs. 7.4 ppb, p=0.002). On subgroup analysis this effect was present in non-ASR hips (18.7 ppb vs. 4.7 ppb, p=0.025) but was not significant in ASR hips (29.6 ppb vs. 16.3 ppb, p=0.347). Our study demonstrated significantly higher serum metal ion levels in patients who lost more than 5 mm hip offset after arthroplasty. Reduced soft tissue tension leading to microseparation of the articulation and edge loading is a theoretical explanation for this effect. This may be relevant in other hard bearings such as ceramic-on-ceramic as well

Introduction:. One of the important criteria of the success of TKR is achievement of the Flexion ROM. Various factors responsible to achieve flexion are technique, Implant and patient related. Creation of the Posterior condylar offset is one of the important factors to achieve satisfactory flexion. Aim:. To correlate post op femoral condylar offset to final flexion ROM at 1 yr. post op. Methods:. This is a clinico-radiological study of the cases done prospectively between September 2011 and August 2012. Inclusion criteria:. All patients undergoing Bilateral TKRs and have agreed for the follow up at 1 yr. Exclusion criteria: . 1). Patients who had previous bony surgery on lower end femur. 2). Patients with previous fracture of lower end femur. All the patients had PS PFC Sigma (De Puy, Warsaw) components cemented. ROMs were measured at 6 weeks, 3 months, & 1 year post op. The last reading was taken as final flexion ROM as measured by an independent Physiotherapist with the help of a Goniometer. Results:. We had 21 cases of Bilateral TKRs who satisfied our criteria. Pre and post op femoral condylar offset was measured in mm. on lateral x ray. Pre and post op flexion was measured. Results showed that variation in the posterior femoral offset by > 3 mm in post op x ray was related to loss of flexion of an average 21 deg. (16–24 degrees). Greater the deflection from the normal offset, greater was the loss of flexion. These patients also showed lesser improvement in KSS functional sco. Discussion:. Flexion is one of the most important yardsticks for the measurement of success of TKR. This factor is more important more so in Asian population. Literature has shown that three important determinants for good flexion are…. . 1). Posterior Condylar Offset Restoration. 2). Tibial slope restoration. 3). Femoral Roll back in flexion. An increased offset permits greater flexion before impingement between the tibial insert and the femur. In our study we kept Tibial slope and Femoral Roll back constant by using the same prosthesis. The femoral condylar offset changed as per the size of the AP femoral cutting block. (Anterior referencing guide used). Overresection of the posterior condyles reduced the posterior femoral condylar offset and hence significant loss of post op flexion. The shorter posterior condyle of smaller-sized femoral component can increase the potential for bone impingement proximal to the posterior condyles. In our study the opposite side replaced knee acted as a control and hence eliminating patient bius. It is generally stated that after a TKR flexion can improve upto 1 year and hence that was taken as final possible flexion. Conclusion:. Keeping Tibial slope and Femoral roll back constant during the surgery, posterior condylar offset restoration within 3 mm of its original pre op offset was necessary to achieve satisfactory flexion at 1 year. Undersizing the femoral component to achieve more flexion is perhaps suboptimal. Appropriate AP femoral sizing is a must to restore the normal offset

Background:. We studied the effect of posterior condylar offset on maximum knee flexion after a posterior stabilised total knee arthroplasty. We also looked at gender difference and the post-operative change in posterior condylar offset. Methods:. Eighty consecutive computer navigated posterior stabilised total knee replacements were prospectively assessed intra-operatively for maximum knee flexion. The flexion angle was measured and recorded with an imageless computer navigation system (Brainlab) before and after implantation of the prosthesis. This was correlated with a radiological review of the posterior condylar offset pre- and post-operatively, as defined by posterior condylar offset ratio (PCOR) originally described by Soda (2007) and modified by the Bristol Knee Group (2010). Results:. No relationship could be found between change in posterior femoral offset ratio and the change in knee flexion before and after implantation of the prosthesis (p = 0.46.)This was especially true for female subjects (p = 0.87.)For male patients there was a trend towards an inverse relationship demonstrating decreasing flexion with an increase in PCOR (p = 0.16.) PCOR increased in 91 % of cases and overall increased from an average of 0.44 pre-operatively to 0.49 post-operatively. The increase in PCOR was smaller where a large pre-operative PCOR was present (p = 0.0006.)Pre-operative flexion correlated significantly with postoperative flexion (p = 0.00.)There was no difference in PCOR between male and female patients. Conclusion:. Knee flexion is not influenced by a change in posterior condylar offset in posterior stabilised knees. The increase in posterior condylar offset with a posterior stabilised TKA could by explained a larger increase in the flexion gap than in the extension gap, when sectioning the posterior cruciate ligament. The PCOR increases in cases with smaller pre-operative posterior condylar offset. Pre-operative flexion is a significant predictor of postoperative flexion

Introduction. Leg length and offset are important considerations in total hip arthroplasty (THA). Navigation systems are capable of providing intra-operative measurements of leg length and offset, and high accuracy has been shown in experimental studies. Objective. This in-vivo study assesses the accuracy of an imageless navigation system, with a pin-less femoral array, in measuring offset and leg length changes. Method. A prospective, consecutive series of 24 patients undergoing navigated total hip arthroplasty were included in the study. Intra-operative measurements of leg length and offset were recorded using the navigation system. For each patient pre- and post-operative digital radiographs were scaled and analysed to provide radiographic measurements of change in leg length and offset. Results. Measurements of leg length change made by the navigation system showed a statistically significant correlation with the size of change measured radiographically (R=.77, P < 0.0001). The mean difference between the radiographic and navigational measurement was 0.4 ± 2.8 mm. The navigation system was accurate to within 1 mm of the radiographic measurement in 50% of cases, within 2 mm in 67% of cases, and within 5 mm in 96% of cases. Measurements of offset change by the navigation system also showed a statistically significant correlation with radiographic measurements, however the correlation was less pronounced (R=.47, P=0.02). The mean difference between navigational and radiographic measurements was 1.4 ± 6.4 mm. The navigation system was accurate to within 1 mm of the radiographic measurement in 8% of cases, within 2 mm in 25% of cases, and within 5 mm in 75% of cases. Conclusion. This study demonstrates in-vivo that an imageless, non-invasive navigation system is a reliable tool for intra-operative leg length and offset measurement

Hip prostheses that do not reproduce the patients’ preoperative femoral offset have been correlated with increased wear rate, instability, abductor weakness and reduced range of motion. We have reviewed the results of 54 primary low friction arthroplasties with low offset stem commonly called “¾ neck Charnley” in 49 patients (47 females and 2 males). There has been no publication in literature on the results of this stem. Mean age was 68 years (range 30 to 83). The operations were performed by one of us, (VR) as an orthopaedic trainee, with a mean follow up of 8.7 ± 2 years. The preoperative diagnosis was 40 OA, 8 protrusio, 2 DDH, 2 post-traumatic, 1 SUFE and 1 RA. The preoperative offset was 41.9 ± 7.1 mm (mean ± STD), weight 65 ± 8.4 kg, height 156.4 ± 8 cm. At their latest review 3 cases had been revised for infection or recurrent instability with a survivorship of 93.5% using Kaplan Meyer’s analysis. None of the femoral or acetabular components were loose or at risk of loosening. 16 cups showed demarcation in 1 zone of ≤ 1mm, and 2 cups had a 2 mm demarcation in 2 zones that was not progressive. 7 stems had ≤ 1mm demarcation in 1 zone, and 5 stems at 2 zones. Condensation at the tip of the stem was noted in 2 hips. The linear wear rate was 0.2 ± 0.08mm/year. Using Pearson’s correlation coefficient with P< 0.05, no statistically significant correlation was found between the preoperative offset and the linear wear rate. We believe that the surgeon should try to reproduce the patient’s femoral offset aiming for the best intra-operative soft tissue balance. The linear wear rate in this series is higher than previously reported in cases that survived for over 20 years from this unit. However, at this stage of analysis low offset Charnley stems produce good medium term results