Capsular ligaments provide a passive stabilizing force to protect the hip against edge loading

Correlating Movement Impairments As Potential Risk Factors for Musculoskeletal Dysfunction: A Retrospective Cross-Sectional Analysis in a Rehabilitation Setting

BACKGROUND

Mechanical musculoskeletal disorders diminish quality of life and increase healthcare costs but lack prevention strategies. The lack of validated risk factors may be a reason. This study supports the previously hypothesized motion impairments as one potential risk factor in causing mechanical musculoskeletal disorders.

METHODS

A retrospective chart review of individuals in a rehabilitation setting with mechanical musculoskeletal disorders was done to identify the presence of co-existing motion impairments. A correlational analysis of their co-existing presence with a description of how they may directly contribute to those disorders followed.

RESULTS

All individuals with mechanical musculoskeletal disorders whose charts were reviewed, presented with co-existing motion impairments. Pearson's correlation coefficient (R) was 1 indicating a strong positive correlation between variables. Linear regression revealed a coefficient of determination (R2) of 1 suggesting that variation in the dependent variable was explained by the independent variable.

CONCLUSION

The results of this study may be of value as a hypothesis generator highlighting the need for the investigation of motion impairments as a potential risk factor for musculoskeletal dysfunction.

Specimen-specific finite element representations of implanted hip capsules

The hip capsule is a ligamentous structure that contributes to hip stability. This article developed specimen-specific finite element models that replicated internal-external (I-E) laxity for ten implanted hip capsules. Capsule properties were calibrated to minimize root mean square error (RMSE) between model and experimental torques. RMSE across specimens was 1.02 ± 0.21 Nm for I-E laxity and 0.78 ± 0.33 Nm and 1.10 ± 0.48 Nm during anterior and posterior dislocation, respectively. RMSE for the same models with average capsule properties was 2.39 ± 0.68 Nm. Specimen-specific models demonstrated the importance of capsule tensioning in hip stability and have relevance for surgical planning and evaluation of implant designs.

Optimal hip capsular release for joint exposure in hip resurfacing via the direct anterior approach

Aims

Surgical approaches that claim to be minimally invasive, such as the direct anterior approach (DAA), are reported to have a clinical advantage, but are technically challenging and may create more injury to the soft-tissues during joint exposure. Our aim was to quantify the effect of soft-tissue releases on the joint torque and femoral mobility during joint exposure for hip resurfacing performed via the DAA.

Methods

Nine fresh-frozen hip joints from five pelvis to mid-tibia cadaveric specimens were approached using the DAA. A custom fixture consisting of a six-axis force/torque sensor and motion sensor was attached to tibial diaphysis to measure manually applied torques and joint angles by the surgeon. Following dislocation, the torques generated to visualize the acetabulum and proximal femur were assessed after sequential release of the joint capsule and short external rotators.

Results

Following initial exposure, the ischiofemoral ligament (7 to 8 o'clock) was the largest restrictor of exposure of the acetabulum, contributing to a mean 25% of overall external rotational restraint. The ischiofemoral ligament (10 to 12 o'clock) was the largest restrictor of exposure of the proximal femur, contributing to 25% of overall extension restraint. Releasing the short external rotators had minimal contribution in torque generated during joint exposure (≤ 5%).

Conclusion

Adequate exposure of both proximal femur and acetabulum may be achieved with minimal torque by performing a full proximal circumferential capsulotomy while preserving short external rotators. The joint torque generated and exposure achieved is dependent on patient factors; therefore, some cases may necessitate further releases.

Instantaneous Generation of Subject-Specific Finite Element Models of the Hip Capsule

Subject-specific hip capsule models could offer insights into impingement and dislocation risk when coupled with computer-aided surgery, but model calibration is time-consuming using traditional techniques. This study developed a framework for instantaneously generating subject-specific finite element (FE) capsule representations from regression models trained with a probabilistic approach. A validated FE model of the implanted hip capsule was evaluated probabilistically to generate a training dataset relating capsule geometry and material properties to hip laxity. Multivariate regression models were trained using 90% of trials to predict capsule properties based on hip laxity and attachment site information. The regression models were validated using the remaining 10% of the training set by comparing differences in hip laxity between the original trials and the regression-derived capsules. Root mean square errors (RMSEs) in laxity predictions ranged from 1.8° to 2.3°, depending on the type of laxity used in the training set. The RMSE, when predicting the laxity measured from five cadaveric specimens with total hip arthroplasty, was 4.5°. Model generation time was reduced from days to milliseconds. The results demonstrated the potential of regression-based training to instantaneously generate subject-specific FE models and have implications for integrating subject-specific capsule models into surgical planning software.

Hip joint contact pressure and force: a scoping review of in vivo and cadaver studies

Aims

Research on hip biomechanics has analyzed femoroacetabular contact pressures and forces in distinct hip conditions, with different procedures, and used diverse loading and testing conditions. The aim of this scoping review was to identify and summarize the available evidence in the literature for hip contact pressures and force in cadaver and in vivo studies, and how joint loading, labral status, and femoral and acetabular morphology can affect these biomechanical parameters.

Methods

We used the PRISMA extension for scoping reviews for this literature search in three databases. After screening, 16 studies were included for the final analysis.

Results

The studies assessed different hip conditions like labrum status, the biomechanical effect of the cam, femoral version, acetabular coverage, and the effect of rim trimming. The testing and loading conditions were also quite diverse, and this disparity limits direct comparisons between the different researches. With normal anatomy the mean contact pressures ranged from 1.54 to 4.4 MPa, and the average peak contact pressures ranged from 2 to 9.3 MPa. Labral tear or resection showed an increase in contact pressures that diminished after repair or reconstruction of the labrum. Complete cam resection also decreased the contact pressure, and acetabular rim resection of 6 mm increased the contact pressure at the acetabular base.

Conclusion

To date there is no standardized methodology to access hip contact biomechanics in hip arthroscopy, or with the preservation of the periarticular soft-tissues. A tendency towards improved biomechanics (lower contact pressures) was seen with labral repair and reconstruction techniques as well as with cam correction.

Dynamic finite element analysis of hip replacement edge loading: Balancing precision and run time in a challenging model

An important aspect in evaluating the resilience of hip replacement designs is testing their performance under adverse conditions that cause edge loading of the acetabular liner. The representation of edge loading conditions in finite element models is computationally challenging due to the changing contact locations, need for fine meshes, and dynamic nature of the system. In this study, a combined mesh and mass-scaling sensitivity study was performed to identify an appropriate compromise between convergence and solution time of explicit finite element analysis in investigating edge loading in hip replacement devices. The optimised model was then used to conduct a sensitivity test investigating the effect of different hip simulator features (the mass of the translating fixture and mediolateral spring damping) on the plastic strain in the acetabular liner. Finally, the effect of multiple loading cycles on the progressive accumulation of plastic strain was then also examined using the optimised model. A modelling approach was developed which provides an effective compromise between mass-scaling effects and mesh refinement for a solution time per cycle of less than 1 h. This 'Recommended Mesh' model underestimated the plastic strains by less than 10%, compared to a 'Best Estimate' model with a run time of ∼190 h. Starting with this model setup would therefore significantly reduce any new model development time while also allowing the flexibility to incorporate additional complexities as required. The polyethylene liner plastic strain was found to be sensitive to the simulator mass and damping (doubling the mass or damping had a similar magnitude effect to doubling the swing phase load) and these should ideally be described in future experimental studies. The majority of the plastic strain (99%) accumulated within the first three load cycles.

Femoral impingement in maximal hip flexion is anterior-inferior distal to the cam deformity in femoroacetabular impingement patients with femoral retroversion : implications for hip arthroscopy

AIMS

Femoroacetabular impingement (FAI) patients report exacerbation of hip pain in deep flexion. However, the exact impingement location in deep flexion is unknown. The aim was to investigate impingement-free maximal flexion, impingement location, and if cam deformity causes hip impingement in flexion in FAI patients.

METHODS

A retrospective study involving 24 patients (37 hips) with FAI and femoral retroversion (femoral version (FV) < 5° per Murphy method) was performed. All patients were symptomatic (mean age 28 years (SD 9)) and had anterior hip/groin pain and a positive anterior impingement test. Cam- and pincer-type subgroups were analyzed. Patients were compared to an asymptomatic control group (26 hips). All patients underwent pelvic CT scans to generate personalized CT-based 3D models and validated software for patient-specific impingement simulation (equidistant method).

RESULTS

Mean impingement-free flexion of patients with mixed-type FAI (110° (SD 8°)) and patients with pincer-type FAI (112° (SD 8°)) was significantly (p < 0.001) lower compared to the control group (125° (SD 13°)). The frequency of extra-articular subspine impingement was significantly (p < 0.001) increased in patients with pincer-type FAI (57%) compared to cam-type FAI (22%) in 125° flexion. Bony impingement in maximal flexion was located anterior-inferior at femoral four and five o'clock position in patients with cam-type FAI (63% (10 of 16 hips) and 37% (6 of 10 hips)), and did not involve the cam deformity. The cam deformity did not cause impingement in maximal flexion.

CONCLUSION

Femoral impingement in maximal flexion was located anterior-inferior distal to the cam deformity. This differs to previous studies, a finding which could be important for FAI patients in order to avoid exacerbation of hip pain in deep flexion (e.g. during squats) and for hip arthroscopy (hip-preservation surgery) for planning of bone resection. Hip impingement in flexion has implications for daily activities (e.g. putting on shoes), sports, and sex.Cite this article: Bone Joint Res 2023;12(1):22-32.