Dislocation is a serious complication to be avoided in total hip arthroplasty (THA) and its incidence risk increases in revision surgery. Combined anteversion (CA) of the cup and stem is a concept for appropriate implant positioning; however, the effect of functional changes in femoral rotation has not been well investigated. The aim of this study was to investigate whether functional CA, considering femoral rotation, is associated with dislocation in patients undergoing revision THA. Seventy-three patients who underwent revision THA and had at least one year of follow-up with pre- and postoperative supine CT imaging were included. Cup and stem were placed with a target combined angle of 37.3° using Widmer's formula. Anatomical and functional CA was calculated postoperatively using the following formula: Anatomical CA: cup anteversion + 0.7 × anatomical stem anteversion; Functional CA: cup anteversion + 0.7 × (anatomical stem anteversion + femoral rotation). Patient demographics, cup and stem angles, CA and their relationship to dislocation were statistically evaluated. Dislocation was observed in 12 patients. In these dislocated cases, there were no significant differences in cup angle, stem angle and anatomical CA compared to non-dislocated cases. However, dislocated cases showed significantly higher values of functional CA [52.7 ± 17.5° (range, 5.9–69.3) vs. 36.0 ± 12.5° (range, 8.6–68.8), p=0.009] and significant deviation from identical CA [17.3 ± 9.6° (range, 2.8–32) vs. 7.5 ± 7.1° (range, 0.1–28.7), p=0.010]. Functional CA considering femoral rotation was associated with dislocation in revision THA patients. This finding suggests that consideration of femoral rotation may be necessary for implant positioning in revision THA

Introduction. Malrotation following total knee replacement is directly related to poor outcome. The knowledge of proximal and distal rotational axes and angles of the femur is therefore of high importance. The aim of the study was to determine whether the most used proximal and distal femoral angles; femoral anteversion angle (FAA) and posterior condylar angle (PCA) were different within individuals, between right, left and gender. As well, we studied whether the “inferior condylar angle” is correlated to the PCA and therefore useful in determining the rotation of the distal femur. Material and Methods. From 36 cadavers the femora were obtained and after removing the soft tissue a Computed Tomography (CT) scan was made. Three angles were measured: (i) the FAA between femoral columnar line (FHNL) and posterior condylar line (PCL), (ii) the PCA between anatomical transepicondylar line (TEL) and PCL, (iii) the inferior condylar angle (ICA) between the TEL and inferior condylar line (ICL). Statistical analysis of comparative relationships between the different angles was examined by calculating correlation coefficients and a paired t-test. Results. The mean FAA, PCA and ICA for the whole group were respectively 12.0 degrees (range 0.2–31.6, SD 8.3, 95% CI 9.6–14.4), 4.8 degrees (range 0.9–9.6, SD 2.3, 95% CI 4.1–5.4) and 4.5 degrees (range 0.1–9.8, SD 2.1, 95% CI 3.9–5.1). A strong correlation of the FAA was found within the total group and left versus right (r = 0.82; p = 0.00). A weaker relationship was found for the total group of the PCA measurements (r = 0.59; p = 0.00). When FAA compared to the PCA subdivided in only sexes, there is a weak correlation for the female group (r = 0.54; p = 0.00) Despite the small mean difference of the mean ICA and PCA, there was no correlation between these two angles. Conclusion. Considering the weak correlation of the FAA and PCA within the group but also individuals, the importance of development of more individual approaches for determining the optimal rotation of the components in total knee surgery is essential. As a result, one should be aware that the widely used, current guidelines for knee rotation of 3 degrees of external rotation in placing total knee arthroplasties shows variation between individuals. A more individual approach in total knee arthroplasty seems essential for future knee prosthesis implantations

Introduction. The posterior condylar axis of the knee is the most common reference for femoral anteversion. However, the posterior condyles, nor the transepicondylar axis, provide a functional description of femoral anteversion, and their appropriateness as the ideal reference has been questioned. In a natural standing positon, the femur can be internally or externally rotated, altering the functional anteversion of the native femoral neck or prosthetic stem. Uemura et al. found that the femur internally rotates by 0.4° as femoral anteversion increases every 1°. The aim of this study was to assess the relationship between femoral anteversion and the axial rotation of the femur before and after total hip replacement (THR). Method. Fifty-nine patients had a pre-operative CT scan as part of their routine planning for THR. The patients were asked to lie in a comfortable position in the CT scanner. The internal/external rotation of the femur, described as the angle between the posterior condyles and the CT coronal plane, was measured. The native femoral neck anteversion, relative to the posterior condyles, was also determined. Identical measurements were performed at one-week post-op using the same CT methodology. The relationship between femoral IR/ER and femoral anteversion was studied pre- and post-op. Additionally, the effect of changing anteversion on the axial rotation of the femur was investigated. Results. There was a strong correlation between axial rotation of the femur and femoral anteversion, both pre-and post-operatively. Pearson correlation coefficients of 0.64 and 0.66 respectively. This supported Uemura et al.'s findings that internal rotation of the femur increases with increasing anteversion. Additionally, there was a moderate correlation, r = 0.56, between the change in axial rotation of the femur and change in anteversion. This trend suggested that external rotation of the leg would increase, if stem anteversion was decreased from the native. Conclusions. Patients with high femoral anteversion may have a natural mechanism of “correction” with femoral internal rotation. Equally, patients with femoral retroversion tend to naturally externally rotate their leg. Decreasing stem anteversion from native, trended toward an increase in external rotation of the femur. This finding is supported by the clinical observation of patients with high anteversion and compensatory in-toe, who have normal foot progression angle post-operatively after having their anteversion decreased. These findings have implications when planning implant alignment in THR

Introduction: It is commonly believed that markedly increased femoral anteversion is a primary abnormality and a consistent feature of hip dysplasia. It is also considered to be one of the main factors leading to redislocation. Apart from limited cadaveric studies, the true normal range of anteversion in infants is largely unknown. We measured femoral anteversion in infants using ultrasound. We are presenting our results measuring the femoral anteversion in both normal and DDH hips. Methods and materials: Anteversion measurements are taken at the time of routine ultrasound screening for Developmental Dysplacia of Hip. This method was previously validated. We measured femoral anteversion in 76 infants with normal hips. We measured femoral ante-version in 27 hips with DDH. The mean femoral ante-version in normal babies is compared to the value in the babies with hip dysplasia using unpaired t-test. Results: The mean value of femoral anteversion in normal babies in our series was 46.75° with 95% reference interval of 36.34° to 57.17°. The mean femoral anteversion in dysplastic hips was 50.39° with a 95% reference interval of 34.88° to 65.89°. The difference between normal and dysplastic hips was statistically significant (p value −0.0095 and 95% CI of 6.36° to 0.90°). This showed a small increase of femoral anteversion in the dysplastic hips. Conclusion: We established reference ranges of femoral anteversion in normal and dysplastic hips. Our series showed only a small increase of femoral anteversion in the dysplastic hips. We showed that the markedly increased femoral anteversion was not a primary abnormality in hip dysplasia

Introduction: Patella maltracking is dependent on multifactorial reasons. We have been able to identify one of major and important factor being the rotational alignment of the femoral component. The other subtle variable factors that have a cumulative effect on the tracking of the patella is recognized, which is not the major thrust this study. Methods and Materials: This is a prospective study on a total of 200 TKR. The first subset of 100 done by the same surgeon and same type of prosthesis and the same sequence of all femoral cuts followed by the tibial cut. Thus, the rotation of the femoral component was referenced from the posterior condyles. The second subset of 100 cases, the distal femoral cut was followed by the tibial resection. The susequent femoral resection was referenced from the tibial cut. Thus the rotation of the femoral component was dependent on the tibial axis, and not on the posterior femoral condyles, which in deficient condyles can lead to a significant rotational error. Conclusion: In the first subset the incidence of lateral release were 3% and 10% asymptomatic patellar tilt. In the second subset, where the femoral rotation was referenced from the tibial axis, excluding the severe valgus knees, the incidence of lateral release was 0% with asymptomatic patellar tilt of 6%. since all other factors were unchanged i.e. patella replacement, rotation of the tibial prosthesis, same prosthesis, the single variable factor being the femoral rotation leads us to conclude that femoral rotation is a major in appropriate patellar tracking. As a corollary ‘Patellar tracking is the index of orientation, sizing of all components of the prosthesis and soft tissue balance’

Purpose. Incidence of malrotation of femoral fractures after intramedullary nailing is as high as 28%. Prevention of malrotation is superior to late derotation osteotomy. The lesser trochanter (LT) profile has been in use for some time as a radiographic landmark of femoral rotation. One of the authors has previously described a linear regression model that describes the relationship of the LT to rotation. This paper aims to validate the use of this equation in predicting femoral rotation. Method. A survey was created and circulated online. Twenty images of cadaveric femurs of known rotation were chosen randomly from a large series. Thirty individuals with varying degrees of orthopaedic experience were invited to participate. Participants were asked to take measurements of the LT in a standardized fashion. Inter-observer variation for predicted rotation and the precision of predicted rotation was calculated. Results were grouped into those with the LT readily visible and those with the LT hidden by the femoral shaft. Results. A pilot study found the standard deviation for films with the LT hidden was 10.8 degrees, and only 6.0 degrees for films with the LT visible. The mean difference between the predicted and actual rotation was equally high in both groups (18.3 and 17.3 degrees respectively). Conclusion. Preliminary results found that the LT must be clearly visible to predict femoral rotation. This suggests that the surgeon should place the femur in a neutral or externally rotated position. In a favourable position most predictions were within a 6.0 degree spread, which would be sufficient to prevent a fifteen degree malrotation. Predicted rotation was however not precise enough to prevent a fifteen degree malrotation, regardless of LT visibility. The precision of predicted rotation may be improved by using a non-linear model. Such a model has recently been designed by a group of engineers at the University of Manitoba. The r squared value of the non-linear model was 0.88, in comparison to 0.78 for the linear equation. Precision may be further improved by using the contra-lateral LT for comparison

Introduction:: Various reference axes are used in total knee arthroplasty to determine the femoral rotation including transepicondylar axis, posterior condylar axis and Whiteside’s line. However, there are currently no golden standards as to the ideal axes to determine the true femoral rotation. Materials and Methods: A prospective observational study was performed to analyse the various axes used to determine femoral rotation during total knee replacement. All consecutive patients who underwent MRI of the knee between December 2006 and May 2007 were considered to be included in the study. Patients below the age of 20 years, above the age of 40 years and mass lesions obscuring the bony landmarks were excluded. The transepicondylar, posterior condylar, posterior femoral cortical, anterior femoral cortical and tibial anteroposterior axes were measured on the PACS system. Results: Of the 100 patients, there were 75 males and 25 females with a mean age of 31(20–39) years. The mean relation between the posterior condylar axes and transepicondylar axes was 3.9 (SD−1.71, 95% CI 3.58–4.26), posterior condylar axes and posterior femoral cortical axes was 5.85 (SD−2.76, CI 5.3–6.4), posterior condylar axis and anterior cortical axis was 6.21 (SD−3.09, CI 5.6–6.8) and posterior condylar axes and tibial anteroposterior axes was 89.6 (SD−5.18, CI 88.5–90.6). Conclusion: The transepicondylar axis appears to be the most consistent amongst the landmarks used to determine femoral rotation. However even the transepicondylar axis shows a significant variation. If transepicondylar axis is not available we suggest the use of femoral anterior cortical axes as a reference landmark

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

Aims. Hip arthroplasty aims to accurately recreate joint biomechanics. Considerable attention has been paid to vertical and horizontal offset, but femoral head centre in the anteroposterior (AP) plane has received little attention. This study investigates the accuracy of restoration of joint centre of rotation in the AP plane. Methods. Postoperative CT scans of 40 patients who underwent unilateral uncemented total hip arthroplasty were analyzed. Anteroposterior offset (APO) and femoral anteversion were measured on both the operated and non-operated sides. Sagittal tilt of the femoral stem was also measured. APO measured on axial slices was defined as the perpendicular distance between a line drawn from the anterior most point of the proximal femur (anterior reference line) to the centre of the femoral head. The anterior reference line was made parallel to the posterior condylar axis of the knee to correct for rotation. Results. Overall, 26/40 hips had a centre of rotation displaced posteriorly compared to the contralateral hip, increasing to 33/40 once corrected for sagittal tilt, with a mean posterior displacement of 7 mm. Linear regression analysis indicated that stem anteversion needed to be increased by 10.8° to recreate the head centre in the AP plane. Merely matching the native version would result in a 12 mm posterior displacement. Conclusion. This study demonstrates the significant incidence of posterior displacement of the head centre in uncemented hip arthroplasty. Effects of such displacement include a reduction in impingement free range of motion, potential alterations in muscle force vectors and lever arms, and impaired proprioception due to muscle fibre reorientation. Cite this article: Bone Joint Res 2022;11(3):180–188

Total knee arthroplasty in last years has changing the field of applications: from old patients with low demand activities is shifting toward younger patients with higher level of activities demand. Details are promising to more reliable outcomes. Surgeons in conjunction with orthopaedic industries are studying a new instrumentation to better fit the anatomy in M.I.S. surgery and more precise design able to reproduce the correct tensioning of ligaments. In the years, two philosophies were developing to the assess femoral rotation in total knee arthroplasty: bone references and ligament references. The first one use the bone landmarks to assess the right femoral rotation while the second one use the ligament tensioning to assess the femoral rotation. Both technique and instruments are able to attend good outcomes, further anatomic and biomechanical studies seem to show that the difference between the two surgical approach can be avoided. Instead of developing a new class of instruments, we put together the two philosophies giving to the surgeon more challenge to assess the femoral rotation in total knee arthroplasty. This study shows the early results with FBI instrumentation (Zimmer ins, Warsaw). We operated 24 patients using FBI instrumentation. The case load included 16 men and 8 women. The age distribution was from 63 to 75 years with a median age of 68. The operation time has been the same one of the traditional instrumentation. So far the patients have been shown good and improved early recovery. There was not any complication during the early post-operative time. This is use a mini soft tissue tenser good to fit in MIS surgery and a IM rod for the free femoral rotation, at same time surgeon can check the femoral landmarks (Whiteside line and epi-line) to put the two ways in conjunction and fitting better outcomes

Aims. Periacetabular osteotomy (PAO) is an established treatment for acetabular dysplasia. It has also been proposed as a treatment for patients with acetabular retroversion. By reviewing a large cohort, we aimed to test whether outcome is equivalent for both types of morphology and identify factors that influenced outcome. Methods. A single-centre, retrospective cohort study was performed on patients with acetabular retroversion treated with PAO (n = 62 hips). Acetabular retroversion was diagnosed clinically and radiologically (presence of a crossover sign, posterior wall sign, lateral centre-edge angle (LCEA) between 20° and 35°). Outcomes were compared with a control group of patients undergoing PAO for dysplasia (LCEA < 20°; n = 86 hips). Femoral version was recorded. Patient-reported outcome measures (PROMs), complications, and reoperation rates were measured. Results. The mean Non-Arthritic Hip Score (NAHS) preoperatively was 58.6 (SD 16.1) for the dysplastic hips and 52.5 (SD 12.7) for the retroverted hips (p = 0.145). Postoperatively, mean NAHS was 83.0 (SD 16.9) and 76.7 (SD 17.9) for dysplastic and retroverted hips respectively (p = 0.041). Difference between pre- and postoperative NAHS was slightly lower in the retroverted hips (18.3 (SD 22.1)) compared to the dysplastic hips (25.2 (SD 15.2); p = 0.230). At mean 3.5 years’ follow-up (SD 1.9), one hip needed a revision PAO and no hips were converted to total hip arthroplasty (THA) in the retroversion group. In the control group, six hips (7.0%) were revised to THA. No differences in complications (p = 0.106) or in reoperation rate (p = 0.087) were seen. Negative predictors of outcome for patients undergoing surgery for retroversion were female sex, obesity, hypermobility, and severely decreased femoral anteversion. Conclusion. A PAO is an effective surgical intervention for acetabular retroversion and produces similar improvements when used to treat dysplasia. Femoral version should be routinely assessed in these patients and when extremely low (< 0°), as an additional procedure to address this abnormality may be necessary. Females with signs of hypermobility should also be consulted of the likely guarded improvement. Cite this article: Bone Jt Open 2021;2(9):757–764

Introduction. Positioning of a femoral sizing guide has been cited as being a critical intraoperative step during measured-resection based TKA as it determines femoral component rotation. Consequently, modern femoral sizing guides permit surgeons to ‘dial in’ external rotation when placing the guide. Although this feature facilitates guide placement, its effect on posterior femoral condylar resection and flexion gap stability is unknown. This study examines the effect of rotation on posterior femoral condylar resection among different posterior-referencing TKA designs. Methods. Left-sided posterior-referencing femoral sizing guides and cutting blocks from nine posterior-referencing femoral sizing guides belonging to six TKA manufacturers were collected. Each guide underwent high-resolution photography at a setting of zero, three and greater than three degrees of external rotation. The axis of rotation for each guide was then identified and its location from the posterior condylar axis was recorded (figure). Cutting blocks from each system were then photographed and the amount of posterior condylar resection from the medial and lateral condyles was calculated for each setting of external rotation (figure). The posterior resection was then compared to the standard distal resections for each system. Results. Two sizing guides had axes of rotation that were eccentrically located and in proximity to the posterior condylar axis, six were centrally based and one was slightly eccentric. Axis of rotation location had substantial effects on posterior condylar resection. Guides with centrally-based axes tended to resect more medial posterior condyle and less lateral condyle as rotation increased. Guides with eccentric axes tended to resect either less lateral or more medial condyle only. Discussion. This study is the first to investigate femoral rotation and posterior condylar resection, and the first to compare different sizing guide designs. Our results indicate that guides with centrally-based axes of rotation increase medial condylar resection as external rotation increases. This increased resection may unintentionally create a larger flexion gap in the case of a valgus knee

Background. When positioning and rotating the femoral cutting block (AP) on the femur it can either be done according to bony landmarks (measured resection) or by tensioning the flexion gap and positioning it parallel to the tibia (gap balanced technique.) Accurate rotation of the femoral component is essential to ensure a symmetric flexion gap to ensure optimal tibio-femoral kinematics and patello-femoral tracking. Methods. 74 consecutive total knee replacements were assessed intra-operatively for symmetry of the flexion gap by applying a varus and a valgus stress and digitally recording the opening with a computer assisted navigation system. External rotation of the femoral component according to the bony landmarks was measured radiologically. This was compared to the external rotation suggested by the navigation intra-operatively using a gap balanced workflow. Results. The gap balanced technique gave a symmetric flexion gap with less than 3 mm side to side difference in 95% of cases. In 84% of cases (62 of 74) the gap balanced technique was more accurate than the measured resection technique in determining femoral rotation. In 16 % of cases (12 of 74) the same rotation was measured with the two techniques. In no case was the measurement more accurate with the measured resection technique. This result was highly statistically significant. Conclusion. The gap balanced technique is more accurate than measured resection for determining axial rotation of the femoral component in total knee arthroplasty. NO DISCLOSURES

Introduction

The achieved anteversion of uncemented stems is to a large extent limited by the internal anatomy of the bone. A better understanding of this has recently become an unmet need because of the increased use of uncemented stems.

We aimed to assess plan compliance in six degrees of freedom to evaluate the accuracy of PSI and guides for stem positioning in primary THAs.

Purpose: Over recent years, several authors have estimated that the distal femur presents an epiphyseal torsion which can be measured intraoperatively or on the preoperative scan. This measurement does not however take into account the dynamic mechanical axis, particularly the mechanical axis at 90° flexion when walking. We used a computer-assisted navigation system (Ortho-pilot®) to attempt to measure femoral rotation by dynamic gonometry in extension and 90° flexion before and after implantation of a total knee arthroplasty. Material and methods: We recorded the preoperative (Rx) and intraoperative (Orthopilot) HKA in extension and in 90° flexion before and after implantation of 50 total knee prostheses (Search®, Aesculup, AG, Tuttlingen) and again postoperatively (Rx). The series included 19 knees with genu valgum (mean HKA 187.36±5.4°, range 181°–203°), 30 knees with genu varum (HKA 169.2±4.11, range 160°–176°), and one normal axis knee. Results: The radiographic values obtained preoperatively were confirmed by Orthopilot, respectively 186.68±5.25° and 169.76±3.84° in extension. At 90° flexion, HKA was 178.63±5.7° before implantation for genu valgum giving a significant varus due to lateral opening during flexion,and 171.6±4.15° for genu varum, showing persistence of varus. After implantation of the total knee prosthesis, the values were as follows. For the genu varum: HKA in extension 180.57±0.82° and HKA in 90° flexion 176.86±2.55° giving a mean residual varus of 3.16±2.86° (from 4–8° varus) without external rotation of the femoral implant. For genu valgum, HKA in extension was 179.60±0.92° and HKA in 90° flexion was 176.1±3.23°, giving a mean residual varus of 3.26±2.86° (0–10° varus), recalling that in the event of genu valgum we impose external rotation due to the frequent hypoplasia of the lateral condyle. Discussion: Orthopilot-assisted implantation of total knee prostheses provides new information concerning dynamic gonometry, particularly the varus or valgus in flexion, which corresponds to measuring natural external or internal rotation. Measuring epiphyseal torsion of the distal femur with classical methods does not take into account the global rotation of the femur which is often an external rotation (up to 8° for genu varum). Systematic implantation of the femoral component in external rotation raises the risk of increasing considerably the varus forced to the implant during flexion

Introduction: Patients with developmental dysplasia of the hip with secondary osteoarthritis are often found to have severe anatomical deformities of the hip. Total hip replacement in such patients is a complex undertaking associated with complication and failure rates. Subtrochanteric derotational osteotomy with customized uncemented total hip arthroplasty has been described to combat the problems of severe femoral anteversion. We present the medium term follow up of 12 patients where such a procedure was undertaken. Materials and Methods: 11 female and 3 male patients with an average age of 49 (range, 32–79 years) were reviewed by an independent observer. The mean follow up was 50 months (range, 24–93 months). Patients were classified on AP radiographs according to Crowe and Hartofilakidis. All have femoral neck anteversions of greater than 45° on CT scans. The patients were followed up radiographically and clinically using the WOMAC, Oxford and Harris hip scores. Results: 1 patient died due to unrelated causes. The average Harris hip score improved from 44 (range, 38–57) preoperatively to 88 (range, 67–94). The average WOMAC score improved from 83 (range, 45–112) pre-operatively to 36 (range, 25–72). The average Oxford score improved from 44 (range, 38–57) preoperatively to 19 (range, 14–34). Radiologically, the prosthesis appears to have osseointegrated with union of the osteotomy site in all cases and there is no evidence of implant migration or osteolysis. Conclusion: Custom total hip arthroplasty with subtrochanteric osteotomy provides a method whereby the hip centre can be restored to its normal level, proximal bone stock is preserved and a more normal proximal femoral morphology is created. We have undertaken this procedure routinely in patients with excessive femoral anter-version and report excellent medium term clinical and radiographic results

Unknown femur orientation during X-ray imaging may cause inaccurate radiographic measurements. The aim of this study was to assess the effect of 3D femur orientation during radiographic imaging on the measurement of greater trochanter to femoral head centre (GT-FHC) distance.

Three-dimensional femoral shapes (n=100) of unknown gender were generated using a statistical shape model based on a training data of 47 CT segmented femora. Rotations in the range of 0° internal to 50° external and 50° of flexion to 0° of extension (at 10 degree increments) were applied to each femur. A ray tracing algorithm was then used to create 2D images representing radiographs of the femora in known 3D orientations. The GT-FHC distance was then measured automatically by identifying the femoral head, shaft axis and tip of greater trochanter.

Uniaxial rotations had little impact on the measurement with mean absolute error of 0.6 mm and 3.1 mm for 50° for pure external rotation and 50° pure flexion, respectively. Combined flexion and external rotation yielded more significant errors with 10° around each axis introducing a mean error of 3.6 mm and 20° showing an average error of 8.8 mm (Figure 1.). In the cohort we studied, when the femur was in neutral orientation, the tip of greater trochanter was never below the femoral head centre.

Greater trochanter to femoral head centre measurement was insensitive to rotations around a single axis (i.e. flexion or external rotation). Modest combined rotations caused the tip of greater trochanter to appear more distal in 2D and led to deviation from the true value. This study suggests that a radiograph with the greater trochanter appearing below femoral head centre may have been acquired with 3D rotation of the femur.

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Summary

From a large 3D Caucasian bone data base, female population had significantly larger acetabular anatomical anteversion angle and combined acetabular-femoral anteversion angle than that of male population. There was no significant difference in femoral neck anteversion angles between the groups.

Patellofemoral complications are among the important reasons for revision knee arthroplasty. Femoral component malposition has been implicated in patellofemoral maltracking, which is associated with anterior knee pain, subluxation, fracture, wear, and aseptic loosening. Rotating-platform mobile bearings compensate for malrotation between the tibial and femoral components. It has been suggested that rotating bearings may also reduce the patellofemoral maltracking resulting from femoral component malposition.

We constructed a dynamic musculoskeletal model of weight-bearing knee flexion in a knee implanted with posterior cruciate-retaining arthroplasty components (LifeMOD/KneeSIM, LifeModeler Inc). The model was validated using tibiofemoral and patellofemoral kinematics and forces measured in cadaver knees on an Oxford knee rig. Knee kinematics and patellofemoral forces were measured after simulating axial malrotation of the femoral component (±3° of the transepicondylar reference line). Differences in patellofemoral kinematics and forces between the fixed- and rotating-bearing conditions were analysed.

Rotational malalignment of the femoral component affected tibial rotation near full extension and tibial adduction at higher flexion angles. In the fixed-bearing conditions, external rotation of the femoral component increased patellofemoral lateral tilt, patellofemoral lateral shift, and patellofemoral lateral shear forces. Up to 6° of bearing rotation relative to the tibia was noted in the rotating-bearing condition. However, the rotating bearing had minimal effect in reducing the patellofemoral maltracking or shear induced by femoral component rotation.

The rotating bearing does not appear to be forgiving of malalignment of the extensor mechanism resulting from femoral component malrotation. The rotating bearing may correct tibiofemoral axial malrotation near full extension but not at higher knee flexion angles. These results support the value of improving existing methodologies for accurate femoral component alignment in knee arthroplasty.

Adult hip dysplasia AHD is a complex 3D pathology of lateral coverage, version and/or volume and is often associated with increased femoral anteversion. The Mckibbin index MI is the combination of acetabular version AV and femoral version FV and is used as a measure of anterior hip Stability/ Impingement(1). The Bernese Periacetabular osteotomy PAO is a powerful tool in treating AHD, but it does not address FV. De-rotational femoral osteotomies FO increases risk of complications, operative time and might condemn the patient to Secondary osteotomies to balance the gait. We aim to investigate the effect of MI and FV on PROMs in patients undergoing PAO only. 593 PAOs identified on the Local Hip preservation registry between 01/2013 and 7/2023. PAOs for retroversion, residual Perthes and those combined with FO were excluded. Patients with no available PROMS at 2 years were excluded. Independent variables were collected from E-notes and imaging including MI and FV. A multiple linear regression analysis was performed against preoperative iHot12, and iHot12 change at 2years. The mean FV was 18.86± 12.4 SD. Mean MI was 36.07, SD 15.36. Mean preop iHot12 score was 29.83 ± 17.38 SD. Mean change in iHot12 at 2 years was+36.47 ± 28.44 SD. Females and a higher BMI were statistically correlated to a lower preoperative iHot12. A lower preop iHot12 score and a higher preop AI were correlated to a bigger change in iHot12 at 2years with statistical significance. MI and FV were not found to have a statistically significant correlation with Outcome measures,. An increased Mckibbin index and femoral anteversion were not correlated with worse outcomes at two years. PAO alone in the presence of increased femoral anteversion avoids risks associated with FO which can be performed later if required