Hip Capsulolabral Complex: Anatomy, Disease, MRI Features, and Postoperative Appearance.

The hip is a uniquely constrained joint with critical static stability provided by the labrum, capsule and capsular ligaments, and ligamentum teres. The labrum is a fibrocartilaginous structure along the acetabular rim that encircles most of the femoral head. Labral tears are localized based on the clock-face method, which determines the extent of the tear while providing consistent terminology for reporting. Normal labral variants can mimic labral disease and can be differentiated by assessment of thickness or width, shape, borders, location, and associated abnormalities. The Lage and Czerny classification systems are currently the most well-known arthroscopic and imaging systems, respectively. Femoroacetabular impingement is a risk factor for development of labral tears and is classified according to bone dysmorphisms of the femur ("cam") or acetabulum ("pincer") or combinations of both (mixed). The capsule consists of longitudinal fibers reinforced by ligaments (iliofemoral, pubofemoral, ischiofemoral) and circular fibers. Capsular injuries occur secondary to hip dislocation or iatrogenically after capsulotomy. Capsular repair improves hip stability at the expense of capsular overtightening and inadvertent chondral injury. The ligamentum teres is situated between the acetabular notch and the fovea of the femoral head. Initially considered to be inconsequential, recent studies have recognized its role in hip rotational stability. Existing classification systems of ligamentum teres tears account for injury mechanism, arthroscopic findings, and treatment options. Injuries to the labrum, capsule, and ligamentum teres are implicated in symptoms of hip instability. The authors discuss the labrum, capsule, and ligamentum teres, highlighting their anatomy, pathologic conditions, MRI features, and postoperative appearance. ©RSNA, 2024 Test Your Knowledge questions for this article are available in the supplemental material.

Precise single column resection and reconstruction with femoral head plus total hip replacement for primary malignant peri-acetabulum tumors.

To evaluate whether single acetabular column can be reserved and the effect of reconstruction with femoral head plus total hip replacement (THR) for primary malignant peri-acetabulum tumors. From 2007 to 2015, nineteen patients with primary malignant peri-acetabulum tumors were enrolled. All cases underwent single column resection with clear surgical margins. Ten of the 19 tumor's resections were assisted by computer navigation. Femoral heads were applied to reconstruct anterior or posterior column defects; THR was used for joint reconstruction. The surgical safety, oncologic outcome and prosthesis survivorship and function were evaluated by regular follow-up. The average follow-up period was 65.9 months. Surgical margins contained wide resection in 12 cases and marginal resection in 7 cases. One patient with Ewing's sarcoma died 14 months postoperative due to lung metastasis. One case with chondrosarcoma had recurrence. One prosthesis was removed due to infection. The average MusculoSkeletal Tumor Society (MSTS) function score was 83.7%. Due to the relative small number of cases, there was no significant difference in the recurrence rate and prosthesis failure rate between the navigation group and non-navigation group. Single column resection and reconstruction with femoral head autograft plus THR is an effective, safe method with less complication rate and better functional outcome for patients with peri-acetabular tumors.

Editorial Commentary: Concomitant Hip Arthroscopy and Periacetabular Osteotomy Treat Both the Cause and the Effects of Hip Dysplasia: The Best of Both Worlds.

In the management of true hip dysplasia, the bony deformity is nearly always accompanied by, and often causal of, intra-articular pathology. It is strongly recommended to conduct a comprehensive preoperative evaluation as well as arthroscopic evaluation and treatment of coexisting hip joint conditions prior to performing an open Bernese periacetabular osteotomy. The osteotomy improves coverage of the femoral head and corrects the abnormal joint mechanics and loading patterns, which result in cartilage damage and subsequent osteoarthritis. Arthroscopy allows treatment of the intra-articular pathology. Combining the hip arthroscopy and periacetabular osteotomy procedures into a single surgical intervention, performed by either a single surgeon or a collaborative surgical team, allows us to address both the cause and the effects of dysplasia. This once-controversial combined technique has become a standard practice in the field with widespread adoption.

Hip Morphology on Post-Reduction MRI Predicts Residual Dysplasia 10 Years After Open or Closed Reduction.

BACKGROUND: There is limited evidence supporting the value of morphological parameters on post-reduction magnetic resonance imaging (MRI) to predict long-term residual acetabular dysplasia (RAD) after closed or open reduction for the treatment of developmental dysplasia of the hip (DDH). METHODS: We performed a retrospective study of 42 patients (47 hips) undergoing open or closed reduction with a minimum 10 years of follow-up; 39 (83%) of the hips were in female patients, and the median age at reduction was 6.3 months (interquartile range [IQR], 3.3 to 8.9 months). RAD was defined as additional surgery with an acetabular index >2 standard deviations above the age- and sex-specific population-based mean value or Severin classification grade of >2 at last follow-up. Acetabular version and depth-width ratio, coronal and axial femoroacetabular distance, cartilaginous and osseous acetabular indices, transverse ligament thickness, and the thickness of the medial and lateral (limbus) acetabular cartilage were measured on post-reduction MRI. RESULTS: At the time of final follow-up, 24 (51%) of the hips had no RAD; 23 (49%) reached a failure end point at a median of 11.4 years (IQR, 7.6 to 15.4 years). Most post-reduction MRI measurements, with the exception of the cartilaginous acetabular index, revealed a significant distinction between the group with RAD and the group with no RAD when mean values were compared. The coronal femoroacetabular distance (area under the receiver operating characteristic curve [AUC], 0.95; 95% confidence interval [CI], 0.90 to 1.00), with a 5-mm cutoff, and limbus thickness (AUC, 0.91; 95% CI, 0.83 to 0.99), with a 4-mm cutoff, had the highest discriminatory ability. A 5-mm cutoff for the coronal femoroacetabular distance produced 96% sensitivity (95% CI, 78% to 100%), 83% specificity (95% CI, 63% to 95%), 85% positive predictive value (95% CI, 65% to 96%), and 95% negative predictive value (95% CI, 76% to 100%). A 4-mm cutoff for limbus thickness had 96% sensitivity (95% CI, 78% to 100%), 63% specificity (95% CI, 41% to 81%), 71% positive predictive value (95% CI, 52% to 86%), and 94% negative predictive value (95% CI, 70% to 100%). CONCLUSIONS: Coronal femoroacetabular distance, a quantitative metric assessing a reduction's concentricity, and limbus thickness, a quantitative metric assessing the acetabulum's cartilaginous component, help to predict hips that will have RAD in the long term after closed or open reduction. LEVEL OF EVIDENCE: Diagnostic Level IV . See Instructions for Authors for a complete description of levels of evidence.

Management of chondral and osteochondral lesions of the hip : A comprehensive review.

Chondral and osteochondral lesions encompass several acute or chronic defects of the articular cartilage and/or subchondral bone. These lesions can result from several different diseases and injuries, including osteochondritis dissecans, osteochondral defects, osteochondral fractures, subchondral bone osteonecrosis, and insufficiency fractures. As the cartilage has a low capacity for regeneration and self-repair, these lesions can progress to osteoarthritis. This study provides a comprehensive overview of the subject matter that it covers. PubMed, Scopus and Google Scholar were accessed using the following keywords: "chondral lesions/defects of the femoral head", "chondral/cartilage lesions/defects of the acetabulum", "chondral/cartilage lesions/defects of the hip", "osteochondral lesions of the femoral head", "osteochondral lesions of the acetabulum", "osteochondral lesions of the hip", "osteochondritis dissecans," "early osteoarthritis of the hip," and "early stage avascular necrosis". Hip osteochondral injuries can cause significant damage to the articular surface and diminish the quality of life. It can be difficult to treat such injuries, especially in patients who are young and active. Several methods are used to treat chondral and osteochondral injuries of the hip, such as mesenchymal stem cells and cell-based treatment, surgical repair, and microfractures. Realignment of bony anatomy may also be necessary for optimal outcomes. Despite several treatments being successful, there is a lack of head-to-head comparisons and large sample size studies in the current literature. Additional research will be required to provide appropriate clinical recommendations for treating chondral/osteochondral injuries of the hip joint.

[Femoroacetabular impingement in adolescents]. / Femoroazetabuläres Impingement beim Jugendlichen und Adoleszenten.

Femoroacetabular impingement syndrome (FAIS) is caused by a repetitive mechanical conflict between the acetabulum and the proximal femur, occurring in flexion and internal rotation. In cam impingement, bony prominences of the femoral head-neck junction induce chondrolabral damage. The acetabular type of FAIS, termed pincer FAIS, may be either due to focal or global retroversion and/or acetabular overcoverage. Combinations of cam and pincer morphology are common. Pathological femoral torsion may aggravate or decrease the mechanical conflict in FAI but can also occur in isolation. Of note, a high percentage of adolescents with FAI-like shape changes remain asymptomatic. The diagnosis of FAIS is therefore made clinically, whereas imaging reveals the underlying morphology. X­rays in two planes remain the primary imaging modality, the exact evaluation of the osseous deformities of the femur and chondrolabral damage is assessed by magnetic resonance imaging (MRI). Acetabular coverage and version are primarily assessed on radiographs. Evaluation of the entire circumference of the proximal femur warrants MRI which is further used in the assessment of chondrolabral lesions, and also bone marrow and adjacent soft tissue abnormalities. The MRI protocol should routinely include measurements of femoral torsion. Fluid-sensitive sequences should be acquired to rule out degenerative or inflammatory extra-articular changes.

[Hip dysplasia]. / Hüftdysplasie.

BACKGROUND: Hip dysplasia is one of the most common malformations in childhood and has a significant impact on the further life of those affected. A distinction must be made between congenital and the much rarer acquired dysplasia. Early diagnosis and therapy are pivotal for further development of patients. OBJECTIVES: The paper gives an overview of current radiological possibilities of diagnosis with focus on congenital hip dysplasia supplemented by insights into therapeutic options. MATERIALS AND METHODS: Basic and review papers were analyzed. RESULTS: Clinical examination of the newborn has low sensitivity and specificity in the diagnosis of hip dysplasia. The introduction of Graf ultrasound screening has significantly improved the early detection of dysplastic hips. With the help of sonography, but also magnetic resonance imaging (MRI), the shape of the acetabulum and the position of the femoral head in the socket can be precisely and quickly determined, while X­ray examinations have their place especially in the context of follow-up examinations after treatment from the age of 1 year and in the diagnosis of secondary dysplasia. Therapeutic options range from spreading treatment to open reduction with fixation in the newborn as well as conversion osteotomy in older children. CONCLUSION: Early detection of hip dysplasia is critical to the course of treatment. The right choice of examination method and correct performance are essential for further treatment.

Editorial Commentary: Cam Femoroacetabular Impingement Requires Dynamic Assessment of Beta-Angle (Femoroacetabular Excursion Angle) and Consideration of Femoral and Acetabular Version: Cam Impingement in Patients With Acetabular or Femoral Retroversion May Warrant Greater Osteoplasty.

Radiographs, magnetic resonance imaging, and computed tomography scans have been commonly used to evaluate femoroacetabular impingement (FAI) and are well accepted forms of surgical planning. Assessing and addressing both the femoral and acetabular sides result in a combination of "one-sided" treatments that, in sum, net a successful treatment of FAI. However, combining one-sided approaches may not consider the dynamic interaction of the femoral head with the acetabulum. Elevated alpha angles alone can be indicative of a cam-type lesion without necessitating the presence of functional FAI. The presence of a cam-type lesion on lateral radiographs, as suggested by a positive alpha angle, does not necessitate a decrease in clearance between the femoral head and acetabular rim as measured by the beta angle. Assessment of the beta angle, or femoroacetabular excursion angle, has the potential to address dynamic nature of FAI more accurately by directly measuring the degree of clearance between the femoral head and acetabulum. In addition, a comprehensive assessment of physical examination findings, particularly range of motion, as well as a summation of acetabular and femoral version (as measured by the McKibbin Index), are required. Cam-type of FAI poses a larger challenge in the patient with acetabular or femoral retroversion, which may warrant greater and more localized osteoplasty, distally, during hip arthroscopy.

Outcomes of arthroscopy of the hip for femoroacetabular impingement based on intraoperative assessment using the Outerbridge classification.

Aims: Hip arthroscopy (HA) has become the treatment of choice for femoroacetabular impingement (FAI). However, less favourable outcomes following arthroscopic surgery are expected in patients with severe chondral lesions. The aim of this study was to assess the outcomes of HA in patients with FAI and associated chondral lesions, classified according to the Outerbridge system. Methods: A systematic search was performed on four databases. Studies which involved HA as the primary management of FAI and reported on chondral lesions as classified according to the Outerbridge classification were included. The study was registered on PROSPERO. Demographic data, patient-reported outcome measures (PROMs), complications, and rates of conversion to total hip arthroplasty (THA) were collected. Results: A total of 24 studies were included with a total of 3,198 patients (3,233 hips). Patients had significantly less improvement in PROMs if they had Outerbridge grade III and IV lesions (p = 0.012). Compared with microfracture, autologous matrix-induced chondrogenesis (AMIC) resulted in significantly reduced rates of conversion to THA (p = 0.042) and of revision arthroscopy (p = 0.038). Chondral repair procedures in these patients also did not significantly reduce the rates of conversion to THA (p = 0.931), or of revision arthroscopy (p = 0.218). However, compared with microfracture, AMIC significantly reduced the rates of conversion to THA (p = 0.001) and of revision arthroscopy (p = 0.011) in these patients. Those with Outerbridge grade III and IV lesions also had significantly increased rates of conversion to THA (p = 0.029) and of revision arthroscopy (p = 0.023) if they had associated lesions of the acetabulum and femoral head. Those who underwent labral debridement had a significantly increased rate of conversion to THA compared with those who underwent labral repair (p = 0.015). Conclusion: There is universal improvement in PROMs following HA in patients with FAI and associated chondral lesions. However, those with Outerbridge grade III and IV lesions had significantly less improvement in PROMs and a significantly increased rate of conversion to THA than those with Outerbridge grade I and II. This suggests that the outcome of HA in patients with FAI and severe articular cartilage damage may not be favourable.

Complete Ossification of Transverse Acetabular Ligament - Embryological and Clinical Perspective.

Abstract: Transverse acetabular ligament (TAL) is one of the important ligaments, which provide stability to the hip joint. On rare occasions, it can get ossified leading to limited mobility of the hip joint. Ossified TAL also converts acetabular notch to a foramen and neurovascular structures passing through the notch can get compressed leading to ischaemic symptoms. During routine demonstration of hip bone to undergraduate students, complete ossification of TAL was found in a right sided hip bone. Present case report with this rare finding also includes a short review of literature impressing on embryological and clinical perspectives of ossified TAL. Ossification of this ligament can be caused by defective ossification of hip bone as three secondary ossification centres develop around the acetabulum in triradiate carti-lage. Also, this can be caused due to heterotopic ossification of TAL after an inflammatory or traumatic injury. This ligament is extremely important in total hip replacement surgery being utilised in determining the position of the acetabular component. Anatomical knowledge of abnormal ossification of TAL is imperative in diagnosis and treatment of various pathologies of the hip joint.

Surgical treatment for pelvic bone metastatic disease from renal cell carcinoma.

INTRODUCTION: Pelvic bone metastases from renal cell carcinoma (RCC) are challenging due to their destructive pattern, poor response to radiotherapy and hypervascularity. The purpose of our study was to review a series of patients undergoing surgical treatment with the aim to investigate: 1) survival; 2) local disease control; and 3) complications. METHODS: A series of 16 patients was reviewed. A curettage procedure was performed on 12 patients. In eight the lesion involved the acetabulum; a cemented hip arthroplasty with cage was performed in seven; a flail hip in one. Four patients received a resection; in two cases with acetabular involvement, reconstruction was performed with a custom-made prosthesis and with an allograft and prosthesis. RESULTS: Disease-specific survival accounted for 70% at 3 years and 41% at 5 years. Only one local tumor progression after curettage occurred. Revision surgery (flail hip) was necessary for deep infection of the custom-made prosthesis. CONCLUSION: A prolonged survival in patients affected by bone metastatic disease from RCC can justify also major surgical procedures. Due to a low local progression rate after intralesional procedures, curettage, cement and a total hip arthroplasty with cage, when feasible, should be considered as an alternative to more demanding surgeries like resections and reconstructions. LEVEL OF EVIDENCE (OXFORD): Level 4.

Editorial Commentary: In Patients With Hip-Spine Syndrome, a Single Simple Solution May Not Apply: Occam's Razor Becomes Blunt.

The importance of hip-spine syndrome in a nonarthritic population, in which patients present with coexisting symptoms in both the hip and lumbar spine, is becoming more clear. Several studies have shown inferior outcomes in patients undergoing treatment for femoral acetabular impingement syndrome with coexisting spinal symptoms. The most important factor when treating HSS patients is understanding each patient's pathology. A history and physical examination with provocative tests for spinal and hip pathology often provide the answer. Routine standing and seated lateral radiographs are required to assess spinopelvic mobility. If the cause of pain is unclear, diagnostic intra-articular hip injections with local anesthetic and further imaging of the lumbar spine are recommended. In patients with degenerative spine disease with neural impingement, these symptoms may persist after hip arthroscopy, particularly if not improved by intra-articular injections. Patients should be appropriately counseled. If hip symptoms predominate, treatment of femoroacetabular impingement syndrome results in improved outcomes, even with coexisting neural impingement. If spine symptoms predominate, referral to an appropriate specialist may be required. In patients with HSS, Occam's razor becomes blunt; thus, a single simple solution may not apply, and we may need to consider treating each pathology separately.

[Modified Harrington Procedure in the Treatment of Extensive Tumor Defects of the Acetabulum]. / Modifikovaná Harringtonova operace v terapii rozsáhlých nádorových defektu acetabula.

PURPOSE OF THE STUDY The increasing prevalance of patients with metastatic bone cancer and their improved survival puts more emphasis on the quality of treatment of bone metastases. Although most pelvic lesions are treated non-operatively, extensive destruction of the acetabular segment poses a therapeutic challenge. A potential treatment option may be the modified Harrington procedure. MATERIAL AND METHODS At our department, this surgical procedure has been opted for in 14 patients (5 men and 9 women) since 2018. The mean age at the time of surgery was 59 years (range 42 to 73). Twelve patients suffered from metastatic cancer, one patient had a fibrosarcoma metastasis and one female patient presented with aggressive pseudotumor. Radiological and clinical followup of the patients was performed. Pain was assessed using the Visual Analogue Scale, and the Harris Hip Score and the MSTS score were used to evaluate the functional outcome. The paired samples Wilcoxon test was used to analyze the statistical significance of the difference. RESULTS The mean follow-up period was 25 months. At the time of assessment, ten patients were alive with the mean follow-up of 29 months (range 2 to 54 months) and four patients had died of cancer progression, with the mean follow-up being 16 months. No perioperative death or mechanical failure were reported. One female patient developed a hematogenous infection during febrile neutropenia, which was successfully managed with early revision and implant preservation. Statistically, a significant improvement in the MSTS (median 23) and HHS (median 86) functional scores compared to the preoperative values (MSTS median 2, p<0.01, r-effect size = 0.6; HHS preop median 0, p<0.005, r-effect size = -0.7) was observed. There was also a statistically significant reduction in pain (VAS postoperative median 1, VAS preoperative median 8, p<0.01, r-effect size = -0.6). All patients were capable of independent ambulation after the surgery, nine patients walked without support. DISCUSSION There are not many alternatives to this surgical procedure. Apart from non-operative palliative treatment, the options include ice cream cone prostheses or customized 3D implants which are, impractical in terms of time and cost. Our results are comparable to other studies, confirming the reproducibility and reliability of the method. CONCLUSIONS The Harrington procedure is an efective method for management of large acetabular tumor defects with good functional outcomes, an acceptable perioperative risk and a low risk of failure in the medium term, thus suitable also for patients with good cancer prognosis. Key words: umor, metastasis, acetabulum, pelvis, Harrington, reconstruction.

Combined femoral and acetabular version and synovitis are associated with dGEMRIC scores in people with femoroacetabular impingement (FAI) syndrome.

This study sought to explore, in people with symptoms, signs and imaging findings of femoroacetabular impingement (FAI syndrome): (1) whether more severe labral damage, synovitis, bone marrow lesions, or subchondral cysts assessed on magnetic resonance imaging (MRI) were associated with poorer cartilage health, and (2) whether abnormal femoral, acetabular, and/or combined femoral and acetabular versions were associated with poorer cartilage health. This cross-sectional study used baseline data from the 50 participants with FAI syndrome in the Australian FASHIoN trial (ACTRN12615001177549) with available dGEMRIC scans. Cartilage health was measured using delayed gadolinium-enhanced MRI of cartilage (dGEMRIC) score sampled at the chondrolabral junction on three midsagittal slices, at one acetabular and one femoral head region of interest on each slice, and MRI features were assessed using the Hip Osteoarthritis MRI Score. Analyses were adjusted for alpha angle and body mass index, which are known to affect dGEMRIC score. Linear regression assessed the relationship with the dGEMRIC score of (i) selected MRI features, and (ii) femoral, acetabular, and combined femoral and acetabular versions. Hips with more severe synovitis had worse dGEMRIC scores (partial η2 = 0.167, p = 0.020), whereas other MRI features were not associated. A lower combined femoral and acetabular version was associated with a better dGEMRIC score (partial η2 = 0.164, p = 0.021), whereas isolated measures of femoral and acetabular version were not associated. In conclusion, worse synovitis was associated with poorer cartilage health, suggesting synovium and cartilage may be linked to the pathogenesis of FAI syndrome. A lower combined femoral and acetabular version appears to be protective of cartilage health at the chondrolabral junction.

[Definition of hip dysplasia in 2023 : Signs of macro and micro instability]. / Definition der Hüftdysplasie im Jahr 2023 : Zeichen der Makro- und Mikroinstabilität.

BACKGROUND: Hip dysplasia is a complex static-dynamic pathology leading to chronic joint instability and osteoarthritis. Because our understanding of the underlying pathomorphologies of hip dysplasia, both on the macro and micro levels, has evolved, an updated definition is needed. QUESTION: What is the definition of hip dysplasia in 2023? METHODS: By summarizing and reviewing relevant literature, we provide an up-to-date definition of hip dysplasia with a guide to appropriately making the diagnosis. RESULTS: In addition to the pathognomonic parameters, supportive and descriptive indicators, as well as secondary changes are used to fully characterize instability inherent in hip dysplasia. The primary diagnostic tool is always the plain anteroposterior pelvis radiograph, which can be supplemented by additional investigations (MRI of the hip with intraarticular contrast agent; CT) if necessary. CONCLUSION: The complexity, subtlety, and diversity of the pathomorphology of residual hip dysplasia requires careful, multilevel diagnosis and treatment planning in specialized centers.

Tissue Integration and Chondroprotective Potential of Acetabular Labral Augmentation with Autograft Tendon: Study of a Porcine Model.

BACKGROUND: The aim of this study was to explore the tissue healing process and changes in articular cartilage following acetabular labral augmentation in a porcine model. METHODS: The labrum was resected unilaterally from 10 o'clock to 1 o'clock on the capsular side in 36 pigs. Eighteen pigs underwent labral augmentation (AUG group) using autologous Achilles tendon. No additional procedures were performed in the remaining pigs (control group). The pigs were killed at 6, 12, or 24 weeks postoperatively for histological assessment and measurement of the inflammatory cytokines interleukin (IL)-6, IL-1ß, and tumor necrosis factor (TNF)-α in synovial fluid. RESULTS: All autografts were well placed in the labral defect in the AUG group, and good integration of the autograft with the remnant chondrolabral junction was observed at 24 weeks; only scar tissue was observed in the control group at 6, 12, and 24 weeks. Fibrochondrocytes were concentrated at the transition between the autograft and native labrum at early time points, and the cells within the autograft labrum were predominantly fibrochondrocytes at 24 weeks. Rough and irregular articular cartilage surfaces were observed in 3 of the 6 samples in the AUG group at 24 weeks; the others appeared smooth. Focal cartilage erosion (predominantly in the acetabulum) occurred in all samples in the control group at 12 and 24 weeks. The Mankin score at 24 weeks was significantly lower in the AUG group than in the control group (mean [95% confidence interval]: 2.33 [1.06 to 3.6] versus 9 [8.06 to 9.94], p < 0.001). Likewise, the concentrations of all cytokines (in pg/mL) were significantly lower in the AUG group than in the control group at 24 weeks (IL-6: 166.6 [155.22 to 177.94] versus 245.9 [242.66 to 249.14], p < 0.001; IL-1ß: 122.1 [116.4 to 127.83] versus 282.9 [280.29 to 285.51], p < 0.001; and TNF-α: 56.22 [53.15 to 59.29] versus 135 [131.66 to 138.24], p < 0.001). CONCLUSIONS: Autograft tendon used for labral augmentation was able to integrate well with the native labrum, which may help to preserve the articular cartilage. CLINICAL RELEVANCE: Labral augmentation with autograft tendon may be a feasible option in cases of viable labral remnants.

Can a Computational Model Predict the Effect of Lesion Location on Cam-type Hip Impingement?

BACKGROUND: The Warwick consensus defined femoroacetabular impingement syndrome as a motion-related clinical disorder of the hip with a triad of symptoms, clinical signs, and imaging findings representing symptomatic premature contact between the proximal femur and acetabulum. Several factors appear to cause labral and cartilage damage, including joint shape and orientation and patient activities. There is a lack of tools to predict impingement patterns in a patient across activities. Current computational modeling tools either measure pure ROM of the joint or include complexity that reduces reliability and increases time to achieve a solution. QUESTIONS/PURPOSES: The purpose of this study was to examine the efficacy of a low computational cost approach to combining cam-type hip shape and multiple hip motions for predicting impingement. Specifically, we sought to determine (1) the potential to distinguish impingement in individual hip shapes by analyzing the difference between a cam lesion at the anterior femoral neck and one located at the superior femoral neck; (2) sensitivity to three aspects of hip alignment, namely femoral neck-shaft angle, femoral version angle, and pelvic tilt; and (3) the difference in impingement measures between the individual activities in our hip motion dataset. METHODS: A model of the shape and alignment of a cam-type impinging hip was created and used to describe two locations of a cam lesion on the femoral head-neck junction (superior and anterior) based on joint shape information available in prior studies. Sensitivity to hip alignment was assessed by varying three aspects from a baseline (typical alignment described in prior studies), namely, femoral neck-shaft angle, femoral version, and pelvic tilt. Hip movements were selected from an existing database of 18 volunteers performing 13 activities (10 male, eight female; mean age 44 ± 19 years). A subset was selected to maximize variation in the range of joint angles and maintain a consistent number of people performing each activity, which resulted in nine people per activity, including at least three of each sex. Activities included pivoting during walking, squatting, and golf swing. All selected hip motion cases were applied to each hip shape model. For the first part of the study, the number of motion cases in which impingement was predicted was recorded. Quantitative analyses of the depth of penetration of the cam lesion into the acetabular socket and qualitative observations of impingement location were made for each lesion location (anterior and superior). In the second part of the study, in which we aimed to test the sensitivity of the findings to hip joint orientation, full analysis of both cam lesion locations was repeated for three modified joint orientations. Finally, the results from the first part of the analysis were divided by activity to understand how the composition of the activity dataset affected the results. RESULTS: The two locations of cam lesion generated impingement in a different percentage of motion cases (anterior cam: 56% of motion cases; superior cam: 13% of motion cases) and different areas of impingement in the acetabulum, but there were qualitatively similar penetration depths (anterior cam: 6.8° ± 5.4°; superior cam: 7.9° ± 5.8°). The most substantial effects of changing the joint orientation were a lower femoral version angle for the anterior cam, which increased the percentage of motion cases generating impingement to 67%, and lower neck-shaft angle for the superior cam, which increased the percentage of motion cases generating impingement to 37%. Flexion-dominated activities (for example, squatting) only generated impingement with the anterior cam. The superior cam generated impingement during activities with high internal-external rotation of the joint (for example, the golf swing). CONCLUSION: This work demonstrated the capability of a simple, rapid computational tool to assess impingement of a specific cam-type hip shape (under 5 minutes for more than 100 motion cases). To our knowledge, this study is the first to do so for a large set of motion cases representing a range of activities affecting the hip, and could be used in planning surgical bone removal. CLINICAL RELEVANCE: The results of this study imply that patients with femoroacetabular impingement syndrome with cam lesions on the superior femoral head-neck junction may experience impinging during motions that are not strongly represented by current physical diagnostic tests. The use of this tool for surgical planning will require streamlined patient-specific hip shape extraction from imaging, model sensitivity testing, evaluation of the hip activity database, and validation of impingement predictions at an individual patient level.

Tissue Regrowth and Its Vascularization Through Bone Marrow Stimulation: Microfracture at the Acetabular Rim for Irreparable Labral Tear in a Porcine Model.

BACKGROUND: The treatment of irreparable acetabular labral tear remains a great challenge. Whether fibrocartilage-like tissue can regrow with sufficient volume to fill the labral defect area through bone marrow stimulation remains unknown. PURPOSE: To characterize the healing process and vascularization course of the regrown tissue after microfracture at the acetabular rim for irreparable labral tears in a porcine model. STUDY DESIGN: Descriptive laboratory study. METHODS: Twelve pigs randomly underwent unilateral microfracture at the acetabular rim after the resection of a 10 mm-long section of labrum from 10 to 1 o'clock. Pigs were randomly sacrificed at 6 and 12 weeks postoperatively. The regrown tissues were harvested for macroscopic evaluation and histologic assessment. The regrown tissue was zoned into 2 halves to observe the vascular distribution: the capsular half (zone I) and the articular half (zone II). Each zone was divided into 2 parts: the peripheral part (IA and IIA) and the part attached to the acetabulum (IB and IIB). RESULTS: At 6 weeks, all regrown tissue was hypotrophic with <50% filling of the labral defect. Fibrochondrocytes were concentrated at the interface between the acetabulum and the regrown tissue. The vascularization was equal among each part within the regrown tissue. As compared with regrown tissue at 12 weeks, proteoglycan and collagen type 1 and 2 were more evident within the regrown tissue at 6 weeks. At 12 weeks, tissue disintegration occurred in all regrown tissue with <25% filling of the labral defect area. The vascular structure could barely be observed, with few fibrochondrocytes found at the area adjacent to the acetabulum. CONCLUSION: Fibrocartilage-like tissue did regrow with well-distributed vascular ingrowth of each part of the regrown tissue through bone marrow stimulation at the early stage. However, insufficient volume of the regrown tissue led to loss of the hip suction seal and subsequent tissue disintegration. CLINICAL RELEVANCE: Microfracture at the rim of the acetabulum alone could not restore the morphology and function of the acetabular labrum. Nonetheless, microfracture at the acetabular rim might be a viable adjunct to labral reconstruction, as the well-distributed vascularization through bone marrow stimulation might overcome the obstacle of poor vascular ingrowth of the articular half of the autograft.