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. 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

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. Excellent outcomes have been reported following CT-based robotic arm-assisted total hip arthroplasty (rTHA) compared with manual THA; however, its superiority over CT-based navigation THA (nTHA) remains unclear. This study aimed to determine whether a CT-based robotic arm-assisted system helps surgeons perform accurate cup placement, minimizes leg length, and offsets discrepancies more than a CT-based navigation system. Methods. We studied 60 hips from 54 patients who underwent rTHA between April 2021 and August 2023, and 45 hips from 44 patients who underwent nTHA between January 2020 and March 2021 with the same target cup orientation at the Department of Orthopedic Surgery at Ozu Memorial Hospital, Japan. After propensity score matching, each group had 37 hips. Postoperative acetabular component position and orientation were measured using the planning module of the CT-based navigation system. Postoperative leg length and offset discrepancies were evaluated using postoperative CT in patients who have unilateral hip osteoarthritis. Results. The absolute differences in radiological inclination (RI) and radiological anteversion (RA) from the target were significantly smaller in rTHA (RI 1.2° (SD 1.2°), RA 1.4° (SD 1.2°)) than in nTHA (RI 2.7° (SD 1.9°), RA 3.0° (SD 2.6°)) (p = 0.005 for RI, p = 0.002 for RA). The absolute distance of the target’s postoperative centre of rotation was significantly smaller in the mediolateral (ML) and superoinferior (SI) directions in rTHA (ML 1.1 mm (SD 0.8), SI 1.3 mm (SD 0.5)) than in nTHA (ML 1.9 mm (SD 0.9), SI 1.6 mm (SD 0.9)) (p = 0.002 for ML, p = 0.042 for SI). Absolute leg length and absolute discrepancies in the acetabular, femoral, and global offsets were significantly lower in the rTHA group than in the nTHA group (p = 0.042, p = 0.004, p = 0.003, and p = 0.010, respectively). In addition, the percentage of hips significantly differed with an absolute global offset discrepancy of ≤ 5 mm (p < 0.001). Conclusion. rTHA is more accurate in cup orientation and position than nTHA, effectively reducing postoperative leg length and offset discrepancy. Cite this article: Bone Jt Open 2024;6(1):3–11

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

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

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

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

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

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

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

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

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

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