Finite element prediction of contact pressures in cam-type femoroacetabular impingement with varied alpha angles

Bibliometric analysis of the acetabular labrum

The acetabular labrum (AL) plays a crucial role in the normal physiological functioning of the hip joint. This study aims to present an overview of the current status and research hotspots concerning the AL and to explore the field from a bibliometric perspective. A total of 1918 AL-related records published between January 1, 2000 and November 8, 2023 were gathered from the Web of Science Core Collection database. By utilizing tools such as HisCite, CiteSpace, VOSviewer, and the R package "bibliometrix," the regions, institutions, journals, authors, and keywords were analyzed to predict the latest trends in AL research. Global research interest and publication output related to this topic continues to escalate. The United States leads in international collaborations, number of publications, and citation frequency, underscoring its preeminent position in this field. The American Hip Institute emerged as the most prolific institution, making the greatest contribution to publications. Notably, Arthroscopy and the American Journal of Sports Medicine are the 2 most popular journals in this domain, accounting for 13.29% and 10.1% of publications, respectively, and were also found to be the most co-cited journals. Amongst authors, Benjamin G. Domb leads with 160 articles (8.35%), while Marc J. Philippon is the most frequently cited author. The keyword co-occurrence network showed 3 hot clusters, including "AL," "femoral acetabular impingement (FAI)," and "osteoarthritis." In addition, "survivorship," "FAI," and "patient-reported outcomes" were identified as trending topics for future exploration. This study represents the first comprehensive bibliometric analysis, summarizing the present state and future trends in AL research. The findings serve as a valuable resource for scholars, offering practical insights into key information within the field and identifying potential research frontiers and emerging directions in the near future.

Preoperative Paralabral Cysts Predict More Significant Chondral Damage but Not 2-Year Functional Outcomes Following Arthroscopic Labral Repair

PURPOSE

To investigate whether paralabral cysts identified incidentally on preoperative magnetic resonance imaging/arthrography predict 2-year functional outcomes after arthroscopic acetabular labral repair.

METHODS

Prospectively collected data for patients undergoing primary hip arthroscopy by a single surgeon from 2014 to 2020 were retrospectively reviewed. Included patients were ≥18 years and completed baseline patient-reported outcome measures (PROMs) with additional follow-up at 3, 6, 12, and 24 months. Exclusion criteria were labral debridement, hip dysplasia, advanced hip osteoarthritis (Tönnis > 1), or previous ipsilateral hip surgery. Patients were stratified based on the presence of paralabral cysts identified on magnetic resonance imaging/arthrography. Primary outcomes were International Hip Outcome Tool and modified Harris Hip Score. Secondary outcomes included other PROMs and the visual analog pain scale. Outcomes were compared between cohorts using linear mixed-effects models and Fisher's exact tests. Sensitivity analyses accounted for preoperative PROMs, nonlinear improvement trajectories, and relevant baseline characteristics.

RESULTS

Of the 182 included hips (47.8% female; mean ± standard deviation age, 36.9 ± 11.4), 30 (16.4%) had paralabral cysts. During the 2-year study period, there were no significant differences between patients with and without paralabral cysts in terms of International Hip Outcome Tool scores (weighted difference = 1.60; 95% confidence interval [CI], -5.09, 8.28; P = .64), modified Harris Hip Scores (weighted difference = 0.56; 95% CI, -4.16, 5.28; P = .82), or any secondary outcomes (except for HOS-Sports Subscale at 3 months [mean difference = -11.85; 95% CI, -22.85, -0.84; P = .035]). Furthermore, there were no significant differences in clinically meaningful outcomes (P > .05 for all), revision rates (P > .99), or conversion to total hip arthroplasty between cohorts (P > .99). These results held across all sensitivity analyses.

CONCLUSIONS

Although preoperative paralabral cysts were associated with worse cam impingement and more severe chondral damage observed intraoperatively, they did not predict 2-year functional outcomes or clinically meaningful improvements, suggesting that incidentally discovered paralabral cysts are not a contraindication for arthroscopic labral repair.

LEVEL OF EVIDENCE

Level III, retrospective cohort study.

Cam morphology is strongly and consistently associated with development of radiographic hip osteoarthritis throughout 4 follow-up visits within 10 years

OBJECTIVE

To determine the association between cam morphology and the development of radiographic hip osteoarthritis (RHOA) at four time points within 10-year follow-up.

DESIGN

The nationwide prospective Cohort Hip and Cohort Knee study includes 1002 participants aged 45-65 years with 2-, 5-, 8-, and 10-year follow-ups. The associations of cam morphology (alpha angle >60°) and large cam morphology (alpha angle >78°) in hips free of osteoarthritis at baseline (Kellgren & Lawrence (KL) grade <2) with the development of both incident RHOA (KL grade≥2) and end-stage RHOA (KL grade≥3) were estimated using logistic regression with generalized estimating equation at each follow-up and using Cox regression over 10 years, adjusted for age, sex, and body mass index.

RESULTS

Both cam morphology and large cam morphology were associated with the development of incident RHOA at all follow-ups with adjusted Odd Ratios (aORs) ranging from 2.7 (95% Confidence interval 1.8-4.1) to 2.9 (95% CI 2.0-4.4) for cam morphology and ranging from 2.5 (95% CI 1.5-4.3) to 4.2 (95% CI 2.2-8.3) for large cam morphology. For end-stage RHOA, cam morphology resulted in aORs ranging from 4.9 (95% CI 1.8-13.2) to 8.5 (95% CI 1.1-64.4), and aORs for large cam morphology ranged from 6.7 (95% CI 3.1-14.7) to 12.7 (95% CI 1.9-84.4).

CONCLUSIONS

Cam morphology poses the hip at 2-13 times increased odds for developing RHOA within a 10-year follow-up. The association was particularly strong for large cam morphology and end-stage RHOA, while the strength of association was consistent over time.

Intraoperative Automated Radiographic Visualization Tool Allows for Higher Accuracy of Cam Lesion Resection When Used by Novice Surgeons for Arthroscopic Femoroplasty: Lowering the Learning Curve

PURPOSE

To compare the accuracy of conventional fluoroscopy versus an intraoperative radiographic visualization tool in assisting a novice and experienced hip arthroscopist in comprehensive cam correction to a desired alpha angle (AA).

METHODS

A cadaveric study was performed using 28 hemi-pelvises with cam-type deformity (AA > 55˚) measured on anteroposterior, lateral, and Dunn-view radiographs. Two fellowship-trained hip arthroscopists each performed 14 arthroscopic femoroplasties. The specimens were randomly assigned: 14 of the procedures were performed by the experienced surgeon, with 7 using the automated radiographic visualization tool (Guided Femoroplasty) and 7 using routine fluoroscopy (Control). The same number of hips was assigned to the novice surgeon, completing 7 femoroplasties with and without the visualization tool. Each hip was imaged before and after femoroplasty in 6 different positions using intraoperative fluoroscopy to evaluate head-neck offset. Femoroplasty AAs were compared between groups with and without visualization tool use, as well as between surgeons. One-way analysis of variance analysis was performed to evaluate the consistency of cam resection.

RESULTS

For the experienced hip arthroscopist, comparison of Guide Femoroplasty and Control groups resulted in similar accuracy when compared to the controls, with post-femoroplasty AA averages ranging from 41.4° ± 3.8˚ to 44.8° ± 2.8˚ (P = .511) and 40.2° ± 5.3˚ to 45.6° ± 2.2˚ (P = .225), respectively. For the novice hip arthroscopist, the Guided Femoroplasty group had higher accuracy, with post-femoroplasty AA averages ranging from 42.8° ± 2.6˚ to 46.1° ± 7.2˚(P = .689) with and 39.8° ± 3.1˚ to 51.9° ± 8.1˚ (P = .001) without the visualization tool. Comparison of procedure time did not show any statistically significant difference between the use of the radiographic visualization tool and controls for either surgeon (P > .05 for all).

CONCLUSIONS

Femoroplasty with and without the use of automated radiographic visualization tool results in accurate cam resection when used by both the experienced and novice surgeon. However, higher accuracy was observed when resecting to a desired AA performed by a novice surgeon using the visualization tool. Additionally, use of the visualization tool did not result in longer procedure times for either surgeon.

CLINICAL RELEVANCE

The impact of incomplete cam resections and over-resection on patient outcomes in the literature has led to the recent development of automated intraoperative radiographic visualization tools that allow for assistance of cam resection accuracy for the treatment of femoroacetabular impingement syndrome. This cadaveric study demonstrates that femoroplasty with the use of an intraoperative automated radiographic visualization tool may result in more accurate cam resections.

Preoperative Alpha Angles Can Predict Severity of Acetabular Rim Chondral Damage in Symptomatic Cam-Type Femoroacetabular Impingement: A Prospective Observatory Study

PURPOSE

To identify the relationship between the alpha angle and the severity of chondrolabral separation as well as acetabular rim chondral damage in symptomatic cam-type femoroacetabular impingement (FAI) with or without focal pincer-type FAI.

METHODS

Patients who received hip arthroscopy under the diagnosis of symptomatic cam-type FAI between January 2018 and August 2018 were identified in a prospectively collected database. Patients were excluded if preoperative lateral center-edge angle <25°, lateral center-edge angle ≥40°, Tönnis grade >1, with previous surgery on the affected hip, or with concomitant synovial disease. The chondrolabral junction was classified into intact chondrolabral junction, stable chondrolabral separation and unstable chondrolabral separation. The classification of acetabular rim chondral damage was modified from the MAHORN (Multicenter Arthroscopy of the Hip Outcomes Research Network) classification: normal/softening, bubble, pocket, flap, and exposed bone. The relationship between the hip morphology and severity of chondrolabral junction and acetabular rim chondral damage was assessed.

RESULTS

A total of 71 patients with the mean age of 33.2 ± 11.0 years were included. Preoperative alpha angles on anteroposterior (AP) or Lauenstein view positively correlated with the severity of acetabular rim chondral damage (P = .028 and P = .016, respectively). A significant increment of the alpha angle between 2 consecutive grades of acetabular rim chondral damage was 7.1° (P = .001) on AP view and 5.2° on Lauenstein view (P = .001). The cut-off values for predicting advanced acetabular rim chondral damage (pocket, flap or bony exposure) were an AP alpha angle of 70° (P = .025) and a Lauenstein alpha angle of 57° (P = .003). There was no significant association between the alpha angle and the severity of chondrolabral separation.

CONCLUSIONS

In patients with symptomatic cam-type FAI with or without focal pincer-type FAI, greater preoperative alpha angles on AP and Lauenstein views can predict more severe acetabular chondral damage.

LEVEL OF EVIDENCE

Level III.

How Does Chondrolabral Damage and Labral Repair Influence the Mechanics of the Hip in the Setting of Cam Morphology? A Finite-Element Modeling Study

BACKGROUND

Individuals with cam morphology are prone to chondrolabral injuries that may progress to osteoarthritis. The mechanical factors responsible for the initiation and progression of chondrolabral injuries in these individuals are not well understood. Additionally, although labral repair is commonly performed during surgical correction of cam morphology, the isolated mechanical effect of labral repair on the labrum and surrounding cartilage is unknown.

QUESTION/PURPOSES

Using a volunteer-specific finite-element analysis, we asked: (1) How does cam morphology create a deleterious mechanical environment for articular cartilage (as evaluated by shear stress, tensile strain, contact pressure, and fluid pressure) that could increase the risk of cartilage damage compared with a radiographically normal hip? (2) How does chondrolabral damage, specifically delamination, delamination with rupture of the chondrolabral junction, and the presence of a chondral defect, alter the mechanical environment around the damage? (3) How does labral repair affect the mechanical environment in the context of the aforementioned chondrolabral damage scenarios?

METHODS

The mechanical conditions of a representative hip with normal bony morphology (characterized by an alpha angle of 37°) and one with cam morphology (characterized by an alpha angle of 78°) were evaluated using finite-element models that included volunteer-specific anatomy and kinematics. The bone, cartilage, and labrum geometry for the hip models were collected from two volunteers matched by age (25 years with cam morphology and 23 years with normal morphology), BMI (both 24 kg/m2), and sex (both male). Volunteer-specific kinematics for gait were used to drive the finite-element models in combination with joint reaction forces. Constitutive material models were assigned to the cartilage and labrum, which simulate a physiologically realistic material response, including the time-dependent response from fluid flow through the cartilage, and spatially varied response from collagen fibril reinforcement. For the cam hip, three models were created to represent chondrolabral damage conditions: (1) "delamination," with the acetabular cartilage separated from the bone in one region; (2) "delamination with chondrolabral junction (CLJ) rupture," which includes separation of the cartilage from the labrum tissue; and (3) a full-thickness chondral defect, referred to throughout as "defect," where the acetabular cartilage has degraded so there is a void. Each of the three conditions was modeled with a labral tear and with the labrum repaired. The size and location of the damage conditions simulated in the cartilage and labrum were attained from reported clinical prevalence of the location of these injuries. For each damage condition, the contact area, contact pressure, tensile strain, shear stress, and fluid pressure were predicted during gait and compared.

RESULTS

The cartilage in the hip with cam morphology experienced higher stresses and strains than the normal hip. The peak level of tensile strain (25%) and shear stress (11 MPa) experienced by the cam hip may exceed stable conditions and initiate damage or degradation. The cam hip with simulated damage experienced more evenly distributed contact pressure than the intact cam hip, as well as decreased tensile strain, shear stress, and fluid pressure. The peak levels of tensile strain (15% to 16%) and shear stress (2.5 to 2.7 MPa) for cam hips with simulated damage may be at stable magnitudes. Labral repair only marginally affected the overall stress and strain within the cartilage, but it increased local tensile strain in the cartilage near the chondrolabral junction in the hip with delamination and increased the peak tensile strain and shear stress on the labrum.

CONCLUSION

This finite-element modeling pilot study suggests that cam morphology may predispose hip articular cartilage to injury because of high shear stress; however, the presence of simulated damage distributed the loading more evenly and the magnitude of stress and strain decreased throughout the cartilage. The locations of the peak values also shifted posteriorly. Additionally, in hips with cam morphology, isolated labral repair in the hip with a delamination injury increased localized strain in the cartilage near the chondrolabral junction.

CLINICAL RELEVANCE

In a hip with cam morphology, labral repair alone may not protect the cartilage from damage because of mechanical overload during the low-flexion, weightbearing positions experienced during gait. The predicted findings of redistribution of stress and strain from damage in the cam hip may, in some cases, relieve disposition to damage progression. Additional studies should include volunteers with varied acetabular morphology, such as borderline dysplasia with cam morphology or pincer deformity, to analyze the effect on the conclusions presented in the current study. Further, future studies should evaluate the combined effects of osteochondroplasty and chondrolabral treatment.

Femoroacetabular impingement syndrome and labral injuries: grading the evidence on diagnosis and non-operative treatment-a statement paper commissioned by the Danish Society of Sports Physical Therapy (DSSF)

This statement summarises and appraises the evidence on diagnostic tests and clinical information, and non-operative treatment of femoroacetabular impingement (FAI) syndrome and labral injuries. We included studies based on the highest available level of evidence as judged by study design. We evaluated the certainty of evidence using the Grading of Recommendations Assessment Development and Evaluation framework. We found 29 studies reporting 23 clinical tests and 14 different forms of clinical information, respectively. Restricted internal hip rotation in 0° hip flexion with or without pain was best to rule in FAI syndrome (low diagnostic effectiveness; low quality of evidence; interpretation of evidence: may increase post-test probability slightly), whereas no pain in Flexion Adduction Internal Rotation test or no restricted range of motion in Flexion Abduction External Rotation test compared with the unaffected side were best to rule out (very low to high diagnostic effectiveness; very low to moderate quality of evidence; interpretation of evidence: very uncertain, but may reduce post-test probability slightly). No forms of clinical information were found useful for diagnosis. For treatment of FAI syndrome, 14 randomised controlled trials were found. Prescribed physiotherapy, consisting of hip strengthening, hip joint manual therapy techniques, functional activity-specific retraining and education showed a small to medium effect size compared with a combination of passive modalities, stretching and advice (very low to low quality of evidence; interpretation of evidence: very uncertain, but may slightly improve outcomes). Prescribed physiotherapy was, however, inferior to hip arthroscopy (small effect size; moderate quality of evidence; interpretation of evidence: hip arthroscopy probably increases outcome slightly). For both domains, the overall quality of evidence ranged from very low to moderate indicating that future research on diagnosis and treatment may alter the conclusions from this review.

A Cadaveric Study of Cam-Type Femoroacetabular Impingement: Biomechanical Comparison of Contact Pressures Between Cam Morphology, Partial Femoral Osteoplasty, and Complete Femoral Osteoplasty

PURPOSE

To compare the biomechanical properties of the hip joint with an intact femoral cam lesion, partial cam resection, and complete cam resection.

METHODS

A cadaveric study was performed using 8 hemipelvises with cam-type morphology (alpha angle > 55°) and intact labra. Intra-articular pressure maps were produced for each specimen under the following conditions: (1) native cam morphology (intact), (2) cam morphology with incomplete resection (partial), and (3) cam morphology with complete resection (complete). By use of an open technique, resection of the superior portion of the cam morphology was performed with a 5.5-mm burr to create the partial resection, followed by the inferior portion to create the complete resection. In each condition, 3 biomechanical parameters were obtained: contact pressure, contact area, and peak force within a region of interest. Measurements were performed 3 times in each condition, and the average value was used for statistical analysis. Analysis of variance was used to compare biomechanical parameters between conditions.

RESULTS

A statistically significant difference was found between the pre- and post-resection alpha angles (62.2° ± 3.9° vs 40.9° ± 1.4°, P < .001). Repeated-measures analysis of variance showed that the normalized average pressure values of hips with complete resection of cam lesions were significantly lower than those of hips with incomplete femoral cam lesions and hips with intact cam morphology (100% vs 93.6% ± 8.3% and 82.6% ± 16.2%, respectively; P < .0001). The percentage reduction of contact pressure in the complete and partial groups was 17.4% and 6.4%, respectively, compared with the intact group. Contact area and peak force showed no statistically significant differences across the 3 conditions (P > .05).

CONCLUSIONS

Complete cam resection results in significantly lower intra-articular hip contact pressures than incomplete cam resection and native cam morphology in a cadaveric hip model. These observations underscore the importance of ensuring complete resection of femoral cam lesions in patients undergoing hip arthroscopy for femoroacetabular impingement syndrome.

CLINICAL RELEVANCE

Previous studies have shown that the most common reason for revision hip arthroscopy in patients with femoroacetabular impingement syndrome is incomplete femoral cam resection during the index operation. This study shows biomechanical differences associated with partial cam resection compared with the complete cam resection state that may translate to persistent symptoms.

Classifying Cam Morphology by the Alpha Angle: A Systematic Review on Threshold Values

Background

The alpha angle is the most often used measure to classify cam morphology. There is currently no agreement on which alpha angle threshold value to use.

Purpose

To systematically investigate the different alpha angle threshold values used for defining cam morphology in studies aiming to identify this threshold and to determine whether data are consistent enough to suggest an alpha angle threshold to classify cam morphology.

Study Design

Systematic review; Level of evidence, 3.

Methods

The Embase, Medline (Ovid), Web of Science, Cochrane Central, and Google Scholar databases were searched from database inception to February 28, 2019. Studies aiming at identifying an alpha angle threshold to classify cam morphology were eligible for inclusion.

Results

We included 4 case-control studies, 10 cohort studies, and 1 finite-element study from 2437 identified publications. Studies (n = 3) using receiver operating characteristic (ROC) curve analysis to distinguish asymptomatic people from patients with femoroacetabular impingement syndrome consistently observed alpha angle thresholds between 57° and 60°. A 60° threshold was also found to best discriminate between hips with and without cam morphology in a large cohort study based on a bimodal distribution of the alpha angle. Studies (n = 8) using the upper limit of the 95% reference interval as threshold proposed a wide overall threshold range between 58° and 93°. When stratified by sex, thresholds between 63° and 93° in male patients and between 58° and 94° in female patients were reported.

Conclusion

Based on the available evidence, mostly based on studies using ROC curve analysis, an alpha angle threshold of ≥60° is currently the most appropriate to classify cam morphology. Further research is required to fully validate this threshold.

Demographic and Radiographic Factors Associated With Intra-articular Hip Cartilage Injury: A Cross-sectional Study of 1511 Hip Arthroscopy Procedures

BACKGROUND

Moderate to severe (grade 3-4) hip joint cartilage injury seems to impair function in patients with femoroacetabular impingement syndrome.

PURPOSE

To investigate whether demographic and radiographic factors were associated with moderate to severe hip joint cartilage injury.

STUDY DESIGN

Cross-sectional study; Level of evidence, 3.

METHODS

Patients were identified in the Danish Hip Arthroscopy Registry. The outcome variables were acetabular cartilage injury (modified Beck grade 0-2 vs 3-4) and femoral head cartilage injury (International Cartilage Repair Society grade 0-2 vs 3-4). Logistic regressions assessed the association with the following: age (<30 vs 30-50 years); sex; sport activity level (Hip Sports Activity Scale); alpha angle (AA) assessed as normal (AA <55°), cam (55°≤ AA <78°), or severe cam (AA ≥78°); lateral center-edge angle (LCEA) assessed as normal (25°≤ LCEA ≤ 39°), pincer (LCEA >39°), or borderline dysplasia (LCEA <25°); joint space width (JSW) assessed as normal (JSW >4.0 mm), mild reduction (3.1 mm ≤ JSW ≤ 4.0 mm), or severe reduction (2.1 mm ≤ JSW ≤ 3.0 mm).

RESULTS

A total of 1511 patients were included (mean ± SD age: 34.9 ± 9.8 years). Male sex (odds ratio [OR], 4.42), higher age (OR, 1.70), increased AA (cam: OR, 2.23; severe cam: OR, 4.82), and reduced JSW (mild: OR, 2.04; severe: OR, 3.19) were associated (P < .05) with Beck grade 3-4. Higher age (OR, 1.92), increased Hip Sports Activity Scale (OR, 1.13), borderline dysplasia (OR, 3.08), and reduced JSW (mild: OR, 2.63; severe: OR, 3.04) were associated (P < .05) with International Cartilage Repair Society grade 3-4.

CONCLUSION

Several demographic and radiographic factors were associated with moderate to severe hip joint cartilage injury. Most notably, increased cam severity and borderline dysplasia substantially increased the risk of grade 3-4 acetabular and femoral head cartilage injury, respectively, indicating that specific deformity may drive specific cartilage injury patterns in the hip joint.

The association between specific sports activities and sport performance following hip arthroscopy for femoroacetabular impingement syndrome: A secondary analysis of a cross-sectional cohort study including 184 athletes

The main purpose of this secondary analysis was to compare the proportion of athletes with moderate-to-extreme difficulties in eight specific sport activities in athletes with optimal versus impaired sport performance after a hip arthroscopy for femoroacetabular impingement syndrome. Subjects were identified in a nationwide registry and invited to answer a return to sport and performance questionnaire, and the Copenhagen Hip and Groin Outcome Score Sport subscale investigating difficulties in eight specific sports activities (HAGOS sport items) as; none, mild, moderate, severe or extreme. Subjects were divided into two groups based on sport performance (optimal or impaired). The proportion of athletes with none-to-mild versus moderate-to-extreme difficulties in the eight specific sport activities was compared between groups. The association between difficulties in sport activities and sport performance were investigated using logistic regression analysis. One hundred and eighty-four athletes (31 athletes with optimal and 153 athletes with impaired sport performance) were included at a mean follow-up of 33.1 ± 16.3 months. Up to six athletes (<20%) with optimal sport performance had moderate-to-extreme difficulties in sport activities. Contrary, 43–108 athletes (28.1–70.6%) with impaired performance had moderate-to-extreme difficulties in sport activities. Furthermore, moderate-to-extreme difficulties in HAGOS sport items: ‘running as fast as you can’ and ‘kicking, skating etc.’ increased the odds (14.7 and 6.1 times, respectively) of having impaired sport performance. Many athletes with impaired sport performance reported moderate-to-extreme difficulties in sport activities, specifically moderate-to-extreme difficulties in ‘running as fast as you can’ and ‘kicking, skating etc.’ were associated with patients having impaired sport performance.

Influence of evolution on cam deformity and its impact on biomechanics of the human hip joint

Anatomy and biomechanics of the human hip joint are a consequence of the evolution of permanent bipedal gait. Habitat and behaviour have an impact on hip morphology and significant differences are present even within the same biological family. The forces acting upon the hip joint are mainly a function of gravitation and strength of the muscles. Acetabular and femoral anatomy ensure an inherently stable hip with a wide range of motion. The femoral head in first human ancestors with upright gait was spherical (coxa rotunda). Coxa rotunda is also seen in close human relatives (great apes) and remains the predominant anatomy of present-day humans. High impact sport during adolescence with open physis however can activate an underlying genetic predisposition for reinforcement of the femoral neck, causing an epiphyseal extension and the formation of an osseous asphericity at the antero-superior femoral neck (cam deformity). The morphology of cam deformity is similar to the aspherical hips of quadrupeds (coxa recta), with the difference that in quadrupeds the asphericity is posterior. It has been postulated that this is due to the fact that humans bear weight on the extended leg, while quadrupeds bear weight at 90-100° flexion. The asphericity alters the biomechanical properties of the joint and as it is forced into the acetabulum leading to secondary cartilage damage. It is considered a risk factor for later development of osteoarthritis of the hip. Clinically this presents as reduced range of motion, which can be an indicator for the structural deformity of the hip. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 9999:XX-XX, 2018.

The Influence of Squat Kinematics and Cam Morphology on Acetabular Stress

PURPOSE

To evaluate the effect of varying degrees of simulated cam morphology on acetabular stress magnitude and location using a finite element model with 1 subject that incorporates population-specific hip/pelvis kinematics during a squat task.

METHODS

A reference model of the hip joint was created from magnetic resonance images obtained from 1 asymptomatic 28-year-old man without femoroacetabular impingement (FAI) morphology or hip dysplasia (alpha angle 41.9°, lateral center edge angle 34.0°, neck-shaft angle 137°, and no visible articular cartilage lesions or bone marrow edema on magnetic resonance). The femoral head/neck geometry was manipulated to mimic different cam morphology severities as reported in a previous study (minimum, moderate, and large). Peak hip and pelvis squat kinematics from healthy individuals (hip flexion 112.6°, abduction 10.5°, internal rotation 14.8°) and persons with FAI (hip flexion 106.3°, abduction 10.5°, internal rotation 8.9°) were applied to the control and cam models. Relative acetabular joint stress values and location of contact were the variables of interest.

RESULTS

Average von Mises stress values for control, minimum, moderate, and large cam models were 9.64, 9.27, 11.36, and 28.43 MPa, respectively. Contact in the control and minimum cam models occurred within the acetabular cup. In the moderate and large cam models, contact shifted anterosuperiorly within the acetabular cup and to anterosuperior acetabular rim, respectively.

CONCLUSIONS

Despite simulating lower degrees of hip flexion and internal rotation, increased stress and a shift in contact location were observed in the simulated models of FAI. This finding suggests that decreased hip internal rotation in this population during functional tasks may be the result of bony abutment.

CLINICAL RELEVANCE

Clinicians should be cautious about prescribing deep squats for persons with cam morphology. Performing squat exercises with neutral or external hip rotation may limit bony abutment at high hip flexion angles.