There are a variety of sizes currently available for reverse total shoulder arthroplasty (RTSA) implant systems. Common sizing options include a smaller 36 to 38 mm or a larger 40 to 42 mm glenosphere, and are typically selected based on surgeon preference or patient size. Previous studies have only evaluated the abduction and adduction range of motion within a single plane of elevation, providing a limited view of the joint's possible range of motion. The purpose of this study was to use computer modeling to evaluate the abduction and adduction range of motion across multiple planes of elevation for a range of glenosphere sizes. Computed tomography images of four cadaveric specimens (age: 54 ± 24 years) were used to obtain the osseous anatomy to be utilised in the model. Solid-body motion studies of the RTSA models were constructed with varying glenosphere diameters of 33, 36, 39, 42, and 45 mm in Solidworks (Dassault Systems, US). The implant components were scaled, while maintaining a consistent centre of rotation. Simulations encompassing the full range of abduction and adduction were conducted for the planes of elevation between −15˚ and 135˚ at 15˚ intervals, with the motion of the humerus being constrained in neutral internal-external rotation throughout all planes. Angles of elevation were obtained utilising the humeral long axis and the RTSA centre of rotation. Statistical analysis was performed using repeated measures ANOVA. Glenosphere diameter was found to significantly affect the adduction range of motion (p=0.043), in which the largest size provided approximately 17˚ more adduction range of motion than the smallest. However, abduction range of motion was not found to be significantly affected through the alteration of glenosphere size (p=0.449). The plane of elevation was not found to significantly affect abduction or abduction (p=0.585 & p=0.225, respectively). Increasing glenosphere diameter resulted in an increased adduction range of motion when averaged across the tested planes of elevation; however the observed influence on abduction was not significant. These are similar to the trends observed in the previous single plane of elevation studies. These findings illustrate the importance of implant sizing related to range of motion. Further studies are required to determine the influence of glenosphere size on internal and external range of motion

Posterior dislocation of replacement hips may occur during hip flexion and adduction. Whilst hip braces can restrict hip movement, they are cumbersome and have a low patient compliance. Knee braces are more comfortable to wear and also restrict hip movement by tightening the hamstrings. This study investigated the effect of a knee brace on hip flexion and adduction. The movement of 20 normal hips in 20 healthy volunteers aged 25–62, were assessed using a magnetic tracking system (Polhemus Fastrak). Tracking sensors were attached over the iliac crest and lateral thigh. Subjects were asked to lie on a couch and flex and adduct their hip three times with their knee bent. A knee brace was then applied and the hip movements were repeated with the knee extended. During each movement the tracker recorded hip flexion and adduction angles with an accuracy of 0.15 degrees. When the knee was flexed, the mean hip flexion angle was 66.00 (CI95 = 61.1, 70.8). When the knee was braced, the mean hip flexion angle was 35.30 (CI95 = 28.5, 42.1). Hence the knee brace reduced hip flexion by 46 % (30.70). A paired t-test found this highly significant (P < 0.001). When the knee was flexed, the mean hip adduction angle was 23.70 (CI95 = 20.6, 26.9). When the knee was braced, the mean hip adduction angle was 21.60 (CI95 = 19.2, 24.1). Hence the knee brace reduced hip adduction by 9 % (2.10). A paired t-test found this was not significant (P = 0.3). These results indicate that a knee brace can restrict hip flexion by almost 50%. This information may be useful for patients in whom restriction of hip flexion provides hip stability. As the knee brace is more comfortable than the hip brace, a better patient compliance can be expected

Introduction: Posterior dislocation of replacement hip joints may occur during hip flexion and adduction. A hip brace is commonly used for recurrent dislocations in patients awaiting revision surgery or when unfit for it. However, these hip braces are cumbersome and have a low patient compliance. Knee braces are more comfortable to wear, and they also restrict hip movement by tightening the hamstrings. With this background we investigated the effect of a knee brace, applied in full extension, on hip flexion and adduction. Methods: The movement of 20 normal hips in 20 healthy volunteers aged 25–62, were assessed using a magnetic tracking system (Polhemus Fastrak). One tracking sensor was attached near the anterior superior iliac spine and another one on the lateral aspect of the thigh at a fixed distance from the knee joint. Subjects were then asked to lie on a couch and flex and adduct their hip three times each with the knee bent and then with their knee braced in extension. Two sets of three readings were recorded. During each movement the tracker recorded hip flexion and adduction angles, with a measurement accuracy of 0.15 degrees. Results: With a flexed knee, the mean hip flexion angle was 66.0 degrees (CI95 = 61.1, 70.8). With the knee braced, the mean hip flexion angle was 35.3 (CI95 = 28.5, 42.1). Hence the knee brace reduced hip flexion by 46% (30.7 deg). A paired t-test found this highly significant, with P < < 0.001. With a flexed knee, the mean hip adduction angle was 23.7 degrees (CI95 = 20.6, 26.9). With the knee braced, the mean hip adduction angle was 21.6 (CI95 = 19.2, 24.1). Hence the knee brace reduced hip adduction by 9% (2.1 deg). A paired t-test found this was not significant with P = 0.3. Conclusion: The results indicate that a knee brace can restrict hip flexion by almost 50%. This information may be useful for patients in whom restriction of hip flexion provides hip stability. As the knee brace is more comfortable than the hip brace, a better patient compliance is expected

Introduction: Posterior dislocation of replacement hips may occur during extreme hip flexion and adduction. Hip braces restrict movement, but they are uncomfortable and have a low patient compliance. Knee braces are more comfortable, and also restrict hip movement, by tightening the hamstrings. This study investigated the effect of a knee brace on hip movement. Methods: A magnetic tracker was used to measure the movement of 20 normal hips in 20 volunteers, aged 25–62. Sensors were attached over the iliac spine and lateral thigh. Subjects were asked to lie on a couch and flex and adduct their hip three times with their knee bent and three times with their knee braced in extension. During each movement the tracker recorded hip flexion and adduction angles, with an accuracy of 0.15 degrees. Results: With the knee flexed, the mean hip flexion angle was 66.00 (SD 11.0). With the knee braced, the mean hip flexion angle was 35.30 (SD 15.4). Hence the knee brace reduced hip flexion by 46 % (30.70) (paired t-test, P < < 0.001). With the knee flexed, the mean hip adduction angle was 23.70 (SD 7.1). With the knee braced, the mean hip adduction angle was 21.60 (SD 5.6). Hence the knee brace reduced hip adduction by 9 % (2.10). This was not significant (paired t-test, P = 0.3). Discussion: These results indicate that a knee brace can restrict hip flexion by almost 50%. This information may be useful for patients in whom restriction of hip flexion provides hip stability. As the knee brace is more comfortable than the hip brace, a better patient compliance is expected

1. Seventy-three congenital club feet in fifty-one children have been reviewed between the ages of four and fourteen years to determine the incidence of residual adduction ofthe forefoot. 2. A radiological method of measuring metatarsus varus, based on the naviculo-metatarsal angle, is described. 3. On clinical examination 52 per cent of the feet had residual adduction of the forefoot, and metatarsus varus was present in 74 per cent of these. 4. There was no residual adduction in 48 per cent but only 45 per cent of these showed normal radiographic features. In the remainder various forms of spurious correction were seen. 5. For early treatment, detachment of the origin of the abductor hallucis muscle is recommended at the time of extended posterior release, with tenotomy of the tendon of insertion as an additional measure

Aims. This study aimed to analyze kinematics and kinetics of the tibiofemoral joint in healthy subjects with valgus, neutral, and varus limb alignment throughout multiple gait activities using dynamic videofluoroscopy. Methods. Five subjects with valgus, 12 with neutral, and ten with varus limb alignment were assessed during multiple complete cycles of level walking, downhill walking, and stair descent using a combination of dynamic videofluoroscopy, ground reaction force plates, and optical motion capture. Following 2D/3D registration, tibiofemoral kinematics and kinetics were compared between the three limb alignment groups. Results. No significant differences for the rotational or translational patterns between the different limb alignment groups were found for level walking, downhill walking, or stair descent. Neutral and varus aligned subjects showed a mean centre of rotation located on the medial condyle for the loaded stance phase of all three gait activities. Valgus alignment, however, resulted in a centrally located centre of rotation for level and downhill walking, but a more medial centre of rotation during stair descent. Knee adduction/abduction moments were significantly influenced by limb alignment, with an increasing knee adduction moment from valgus through neutral to varus. Conclusion. Limb alignment was not reflected in the condylar kinematics, but did significantly affect the knee adduction moment. Variations in frontal plane limb alignment seem not to be a main modulator of condylar kinematics. The presented data provide insights into the influence of anatomical parameters on tibiofemoral kinematics and kinetics towards enhancing clinical decision-making and surgical restoration of natural knee joint motion and loading. Cite this article: Bone Joint Res 2024;13(9):485–496

The knee adduction moment is indicative of the degree of medial compartmental loading at the knee joint and has been related to the presence and progression of knee osteoarthritis (OA). Studies have reported differences between OA and asymptomatic groups when measuring the adduction moment at the knee; however, there have been various biomechanical models used to describe this moment. In addition, non-invasive interventions have been shown to decrease the adduction moment but only at certain portions of the gait cycle. The objective of the study was to determine if changing the biomechanical model would affect the ability to detect differences between OA and asymptomatic gait and whether these differences depended on which portion of the gait cycle was analysed. The gait of forty-four asymptomatic and forty-four moderate OA subjects was measured. The adduction moment was calculated using three different biomechanical models commonly used in the literature:. a 2D representation of the lower limb,. a 3D coordinate system based in the tibia, and. a 3D coordinate system based in both the tibia and femur. The adduction moment waveforms were compared between groups for various portions of the gait cycle for all three models. The choice of biomechanical model changed the overall magnitude and shape of the adduction moment waveform. These changes affected the ability to detect group differences using commonly reported parameters of the adduction moment. However, group separation was achieved (regardless of model) when analyzing the overall magnitude of the adduction moment across stance phase and the mid-stance portion of the gait cycle. These results demonstrate that the OA subjects are not unloading the medial compartment of the knee at full weight acceptance as well as the healthy controls. Furthermore, the OA subjects are experiencing a higher medial compartment load that is being sustained for the duration of the stance phase of the gait cycle. Group differences that are not model dependent may be important in understanding the pathomechanics of OA and evaluating interventions. These findings support the need for a better understanding of the anatomical mechanisms associated with the adduction moment

Osteoarthritis is one of the major causes of immobility. Most commonly, osteoarthritis manifests at the knee joint. Prevalence of knee osteoarthritis (KNOA) increases with age. Another important risk factor for KNOA is obesity. Research has shown that obese subjects have almost four times the risk of developing KNOA, which may be explained by both an increased knee loading. In medial compartment KNOA, the knee adduction moment (KAM) during gait is considered a marker for disease severity. KAM is dependent of the magnitude of the ground reaction force and its moment arm relative to the knee joint centre. In addition, obesity has been reported to augment KAM during gait. However, after removal of the direct contributions of body weight, KAM parameters may be different due to obesity-related gait adaptations to limit knee loading. While KAM has been thoroughly investigated during gait, little is known about KAM during stair negotiation, during which knee loads are higher compared to gait. The aim of the current study is therefore to compare normalized KAM during the stance phase of stair negotiation between lean KNOA patients, obese KNOA patients, and healthy controls. This case control study included 20 lean controls, 14 lean KNOA patients, and 16 obese KNOA patients. All subjects ascended and descended a two-step staircase at a self-selected, comfortable speed. Radiographic imaging and MRI were used to evaluate knee cartilage and KNOA status. Motion analysis was performed with a three-dimensional motion capture system. Kinetic data were obtained by one force platform. The parameters of study included: stance phase duration, toe-out angle, KAM peaks and KAM impulse. During stair ascent obese KNOA patients showed a longer stance phase than healthy controls (P 0.050). Despite high between-subject variability, KAM impulse was found 45% higher in the obese KNOA group during stair descent, when compared to healthy controls (P =0.012). The absence of a significant effect of groups on the normalized KAM during stair negotiation may be explained by a lower ambulatory speed in the obese KNOA group, that effectively lowers GRFz. Decreasing ambulatory speed may be an effective strategy to lower KAM during stair negotiation

Forty-four feet in 28 children previously treated by a one-stage posteromedial release operation (the Turco procedure) were reviewed clinically and radiologically to determine the cause of residual adduction of the forefoot. In 21 clinically adducted feet (48%) the main cause of residual deformity was metatarsus varus alone or metatarsus varus in spite of talonavicular overcorrection; in five feet the cause was talonavicular subluxation. There was no residual adduction in 23 feet (52%) but only 12 had normal radiographic measurements. In the remaining feet, various forms of spurious correction of metatarsus varus and talonavicular subluxation or both were seen, resulting in normal-looking feet. Recession of the origin of abductor hallucis and release of the short plantar muscles and fascia at the time of posteromedial release is recommended. The forefoot adduction was satisfactorily corrected in 91% of the feet subsequently operated on using this modified procedure

Aims. Optimal glenoid positioning in reverse shoulder arthroplasty (RSA) is crucial to provide impingement-free range of motion (ROM). Lateralization and inclination correction are not yet systematically used. Using planning software, we simulated the most used glenoid implant positions. The primary goal was to determine the configuration that delivers the best theoretical impingement-free ROM. Methods. With the use of a 3D planning software (Blueprint) for RSA, 41 shoulders in 41 consecutive patients (17 males and 24 females; means age 73 years (SD 7)) undergoing RSA were planned. For the same anteroposterior positioning and retroversion of the glenoid implant, four different glenoid baseplate configurations were used on each shoulder to compare ROM: 1) no correction of the RSA angle and no lateralization (C-L-); 2) correction of the RSA angle with medialization by inferior reaming (C+M+); 3) correction of the RSA angle without lateralization by superior compensation (C+L-); and 4) correction of the RSA angle and additional lateralization (C+L+). The same humeral inlay implant and positioning were used on the humeral side for the four different glenoid configurations with a 3 mm symmetric 135° inclined polyethylene liner. Results. The configuration with lateralization and correction of the RSA angle (C+L+) led to better ROM in flexion, extension, adduction, and external rotation (p ≤ 0.001). Only internal rotation was not significantly different between groups (p = 0.388). The configuration where correction of the inclination was done by medialization (C+M+) led to the worst ROM in adduction, extension, abduction, flexion, and external rotation of the shoulder. Conclusion. Our software study shows that, when using a 135° inlay reversed humeral implant, correcting glenoid inclination (RSA angle 0°) and lateralizing the glenoid component by using an angled bony or metallic augment of 8 to 10 mm provides optimal impingement-free ROM. Cite this article: Bone Jt Open 2024;5(10):851–857

Introduction. Lateralizing the center of rotation (COR) of reverse total shoulder arthroplasty (rTSA) has the potential to increase functional outcomes of the procedure, namely adduction range of motion (ROM). However, increased torque at the bone-implant interface as a result of lateralization may provoke early implant loosening, especially in situations where two, rather than four, fixation screws are used. The aim of this study was to utilize finite element (FE) models to investigate the effects of lateralization and the number of fixation screws on micromotion and adduction ROM. Methods. Four patient-specific scapular geometries were developed from CT data in 3D Slicer using a semi-automatic threshold technique. A generic glenoid component including the baseplate, a lateralization spacer, and four fixation screws was modelled as a monoblock. Screws were simplified as 4.5 mm diameter cylinders. The glenoid of each scapula was virtually reamed after which the glenoid component was placed. Models were meshed with quadratic tetrahedral elements with an edge length of 1.3 mm. The baseplate and lateralization spacer were assigned titanium material properties (E = 113.8 GPa and ν = 0.34). Screws were also assigned titanium material properties with a corrected elastic modulus (56.7 GPa) to account for omitted thread geometry. Cortical bone was assigned an elastic modulus of 17.5 GPa and Poisson's ratio of 0.3. Cancellous bone material properties in the region of the glenoid were assigned on an element-by-element basis using previously established equations to convert Hounsfield Units from the CT data to density and subsequently to elastic modulus [1]. Fixed displacement boundary conditions were applied to the medial border of each scapula. Contact was simulated as frictional (μ = 0.8) between bone and screws and frictionless between bone and baseplate/spacer. Compressive and superiorly-oriented shear loads of 686 N were applied to the baseplate/spacer. Lateralization of the COR up to 16 mm was simulated by applying the shear load further from the glenoid surface in 4 mm increments (Fig. 1A). All lateralization levels were simulated with four and two (superior and inferior) fixation screws. Absolute micromotion of the baseplate/spacer with respect to the glenoid surface was averaged across the back surface of the spacer and normalized to the baseline configuration considered to be 0 mm lateralization and four fixation screws. Adduction ROM was measured as the angle between the glenoid surface and the humeral stem when impingement of the humeral cup occurred (Fig. 1B). Results. Lateralization (p = 0.015) and reducing the number of fixation screws (p = 0.008) significantly increased micromotion (Fig. 2). Lateralization significantly increased adduction ROM (p = 0.001). Relationships between lateralization, the number of fixation screws, micromotion, and adduction ROM were shoulder-specific (Fig. 3). Conclusions. Lateralizing the COR of rTSA can improve functional outcomes of the procedure, however may compromise long-term survival of the implant by increasing micromotion. Our results indicate that the trade-offs of lateralizing should be considered on a patient-specific basis, taking into account factors such as quality and availability of bone stock

Purpose: To test the null hypotheses that no significant differences in the net external knee adduction moment waveform captured during gait exist between neutral, toe in and toe out foot progression angle (FPA) modifications and between those with mild to moderate knee OA and asymptomatic control subjects. Method: Ten patients with mild to moderate knee OA (age 45±7 years) and 16 asymptomatic control subjects (age 54±8 years) participated. Informed consent was obtained for all participants. Three-dimensional (3D) motion and ground reaction force data were recorded during gait. Five trials of each condition,. Self-selected walking (Neutral),. Toe out walking (10o> self-selected, velocity +/− 0.1 m/s of self-selected) and. Toe in walking (10o. Results: There was a significant condition effect for FPA (Neutral=7o, Toe out=24o and Toe in=−9o) and a significant group effect for walking velocity (Asymptomatic=1.46m/s, Knee OA=1.27m/s). In both groups, a toe out FPA produced. a reduction in the overall knee adduction moment (captured by PC1),. a reduction in the late stance magnitude of the knee adduction moment magnitude (captured by PC2 and PC3) and. an increase in the early stance knee adduction moment magnitude (captured by PC2) (p< 0.05). Conclusion: The knee adduction moment is considered an indicator of medial tibio-femoral compressive loading. In this study, a toe out FPA modification during gait altered the characteristics of the knee adduction moment. A reduction in the overall magnitude, more specifically during late stance was found with the toe out gait modification. An increased initial stance peak magnitude was also found during toe out gait. This finding is novel, indicating that a greater peak medial compartment load is produced

Abstract. Objective. Explore whether high tibial osteotomy (HTO) changes knee contact forces and to explore the relationship between the external knee adduction moment (EKAM) pre and 12 months post HTO. Methods. Three-dimensional gait analysis was performed on 17 patients pre and 12-months post HTO using a modified Cleveland marker-set. Tibiofemoral contact forces were calculated in SIMM. The scaled musculoskeletal model integrated an extended knee model allowing for 6 degrees of freedom in the tibiofemoral and patellofemoral joint. Joint angles were calculated using inverse kinematics then muscle and contact forces and secondary knee kinematics were estimated using the COMAC algorithm. Paired samples t-test were performed using SPSS version 25 (SPSS Inc., USA). Testing for normality was undertaken with Shapiro-Wilk. Pearson correlations established the relationships between EKAM1 to medial KCF1, and EKAM2 to medial KCF2, pre and post HTO. Results. Total knee contact force peak 1 significantly reduced from 2.6 x body weight pre-HTO to 2.3 x body weight 12-months post-HTO. Medial contact force peak 1 significantly reduced from 1.7 x body weight pre-HTO to 1.5 x body weight 12-months post-HTO. Second peak lateral knee contact force significantly increased from 0.9 body weight pre-HTO to 1.1 x body weight 12-months post-HTO. Furthermore, this study found very strong correlations between EKAM1 and medial KCF1 pre-HTO (r=0.85) as well as post-HTO (r=0.91). There was a significantly moderate relationship between EKAM2 and medial KCF2 pre-HTO (r=0.625). Conclusion. HTO significantly reduced overall and medial KCF during the first half of stance whilst increasing second half of stance peak lateral knee contact force. This study demonstrated a strong relationship between EKAM peaks and respective medial KCF peaks, supporting the usefulness of EKAM as a surrogate measure of medial compartment tibiofemoral contact forces. This demonstrates HTO successfully offloads the tibiofemoral joint overall, as well as offloading the medial compartment

Aims. Cam and pincer morphologies are potential precursors to hip osteoarthritis and important contributors to non-arthritic hip pain. However, only some hips with these pathomorphologies develop symptoms and joint degeneration, and it is not clear why. Anterior impingement between the femoral head-neck contour and acetabular rim in positions of hip flexion combined with rotation is a proposed pathomechanism in these hips, but this has not been studied in active postures. Our aim was to assess the anterior impingement pathomechanism in both active and passive postures with high hip flexion that are thought to provoke impingement. Methods. We recruited nine participants with cam and/or pincer morphologies and with pain, 13 participants with cam and/or pincer morphologies and without pain, and 11 controls from a population-based cohort. We scanned hips in active squatting and passive sitting flexion, adduction, and internal rotation using open MRI and quantified anterior femoroacetabular clearance using the β angle. Results. In squatting, we found significantly decreased anterior femoroacetabular clearance in painful hips with cam and/or pincer morphologies (mean -11.3° (SD 19.2°)) compared to pain-free hips with cam and/or pincer morphologies (mean 8.5° (SD 14.6°); p = 0.022) and controls (mean 18.6° (SD 8.5°); p < 0.001). In sitting flexion, adduction, and internal rotation, we found significantly decreased anterior clearance in both painful (mean -15.2° (SD 15.3°); p = 0.002) and painfree hips (mean -4.7° (SD 13°); p = 0.010) with cam and/pincer morphologies compared to the controls (mean 7.1° (SD 5.9°)). Conclusion. Our results support the anterior femoroacetabular impingement pathomechanism in hips with cam and/or pincer morphologies and highlight the effect of posture on this pathomechanism. Cite this article: Bone Jt Open 2021;2(11):988–996

Create an optimization model of the internal structure of the knee joint to quantify the correlation between external knee adduction moment (M[add]) during gait with the medial-to-lateral ratio of compartment loading (MLR). Patients were examined the week before, and six months after, surgical knee joint realigment with a high tibial osteotomy (HTO). Thirty patients (six females, twenty-four males; age = 50.0 ± 9.4 yrs.; BMI = 30.0±2.8) with clinically diagnosed OA primarily affecting the medial compartment of the knee underwent a medial opening wedge HTO. Walking gait analysis was performed immediately pre-surgery and at six months post-surgery using optical motion analysis (eight Eagle camera EvaRT system, Motion Analysis Corp, Santa Rosa, CA, USA) and floor-mounted force plate (OR6, AMTI, Watertown, MA, USA). External joint kinetics were calculated using inverse dynamics. Kinematic and force plate data served as input for the internal knee joint model. The anatomical geometry was generic but scaled to patient height and knee alignment. Included were four ligaments (ACL, PCL, LCL, MCL), two contact surfaces (medial and lateral) and eleven muscles (quadriceps, hamstrings, gracilis, sartorius, popliteus and gatrocnemius). A loading solution was found to satisfy mechanical equilibrium and minimise the sum of squares of all structural loads. Output was the ratio of medial-to-lateral compartment compression (MLR). Paired t-tests compared M[add] pre-op versus post-op and MLR pre-op versus post-op. A Pearson R2 coefficient of determination was calculated correlating M[add] to MLR for the pre-operative condition. Peak M[add] decreased from 2.53 ± 1.32 to 1.63 ± 0.81 [%body weight*ht] (p< 0.001). The peak MLR decreased from 2.63 ± 1.08 to 1.52 ± 0.56 [unit-less] (p< 0.001). There was a moderate correlation between M[add] and MLR with the Pearson R2=0.457 (p=0.014). These results suggest that adduction moment is an acceptable proxy for quantifying the internal compressive loading in the knee. Even without considering muscle loading and possible co-contraction of antagonists, adduction moment explains nearly half of the variance in the internal loading of the knee joint compartments. However, further research is required with a larger sample size to increase confidence in this proxy measure in a clinical setting

Aims. In the native hip, the hip capsular ligaments tighten at the limits of range of hip motion and may provide a passive stabilizing force to protect the hip against edge loading. In this study we quantified the stabilizing force vectors generated by capsular ligaments at extreme range of motion (ROM), and examined their ability to prevent edge loading. Methods. Torque-rotation curves were obtained from nine cadaveric hips to define the rotational restraint contributions of the capsular ligaments in 36 positions. A ligament model was developed to determine the line-of-action and effective moment arms of the medial/lateral iliofemoral, ischiofemoral, and pubofemoral ligaments in all positions. The functioning ligament forces and stiffness were determined at 5 Nm rotational restraint. In each position, the contribution of engaged capsular ligaments to the joint reaction force was used to evaluate the net force vector generated by the capsule. Results. The medial and lateral arms of the iliofemoral ligament generated the highest inbound force vector in positions combining extension and adduction providing anterior stability. The ischiofemoral ligament generated the highest inbound force in flexion with adduction and internal rotation (FADIR), reducing the risk of posterior dislocation. In this position the hip joint reaction force moved 0.8° inbound per Nm of internal capsular restraint, preventing edge loading. Conclusion. The capsular ligaments contribute to keep the joint force vector inbound from the edge of the acetabulum at extreme ROM. Preservation and appropriate tensioning of these structures following any type of hip surgery may be crucial to minimizing complications related to joint instability. Cite this article: Bone Joint Res 2021;10(9):594–601

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

Determine the association between net external knee adduction moment (KAM) characteristics and foot progression angle (FPA) in asymptomatic individuals and those with moderate and severe osteoarthritis through discrete variable and principal component analysis (PCA). Fifty-nine asymptomatic (age 52 ± 10 years), fifty-five with moderate knee OA (age 60 ± 9 years) and sixty-one individuals with severe knee OA (age 67 ± 8 years, tested within one week of total knee replacement surgery) participated. Three-dimensional (3D) motion (Optotrak) and ground reaction force (AMTI) data were recorded during gait. Subjects walked at a self-selected velocity. The KAM, calculated using inverse dynamics was time normalised to one complete gait cycle. FPA was calculated using stance phase kinematic gait variables. The discrete variable, peak KAM, was extracted for the interval (30–60%) of the gait cycle. PCA was used to extract the predominant waveform features (Principal Components (PC)) of which PC-Scores were computed for each original waveform. Pearson Product Moment Correlations were calculated for the FPA and both the PC-scores and peak KAM. Alpha of 0.05 used to test significance. No significant correlations were noted for the groups between peak KAM and the FPA, or for the first PC-Scores (PC1) of which captured the original KAM waveforms overall magnitude and shape. The second PC (PC2) captured the shape and magnitude during the second interval of stance (30–60%) with respect to the first. Correlations of FPA to PC2 were significant for the asymptomatic group(r=−0.40, p=0.002) and the moderate OA group (r=−0.32, p=0.017) but not for the severe group(r=−0.13, p=0.316). No relationship between FPA and peak KAM was found across the groups using discrete variable analysis despite reports of associations in asymptomatic subjects. The PCA results suggest a toe out FPA was moderately correlated to a decreased KAM during 30–60% of the gait cycle for asymptomatic and moderate OA individuals only. These individuals respond to a toe out progression angle, altering the KAM which directly affects medial knee compartment loading, where those with severe OA do not

Aims

The objective of this study was to compare simulated range of motion (ROM) for reverse total shoulder arthroplasty (rTSA) with and without adjustment for scapulothoracic orientation in a global reference system. We hypothesized that values for simulated ROM in preoperative planning software with and without adjustment for scapulothoracic orientation would be significantly different.