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

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

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

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

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

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

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

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

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

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

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