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There have been considerable recent advances in the understanding and management of femoroacetabular impingement and associated labral and chondral pathology. We have developed a classification system for acetabular chondral lesions. In our system, we use the six acetabular zones previously described by Ilizaliturri et al. The cartilage is then graded on a scale of 0 to 4 as follows: grade 0, normal articular cartilage lesions; grade 1, softening or wave sign; grade 2, cleavage lesion; grade 3, delamination; and grade 4, exposed bone. The site of the lesion is further classed as A, B or C based on whether the lesion is less than one-third of the distance from the acetabular rim to the cotyloid fossa, one-third to two-thirds of the same distance and greater than two-thirds of the distance, respectively. In order to validate the classification system, six surgeons graded ten video recordings of hip arthroscopy. Our findings showed a high intra-observer reliability of the classification system with an intraclass correlation coefficient of 0.81 and a high interobserver reliability with an intraclass correlation coefficient of 0.88. We have developed a simple reproducible classification system for lesions of the acetabular cartilage, which it is hoped will allow standardised documentation to be made of damage to the articular cartilage, particularly that associated with femoroacetabular impingement.

This prospective study on symptomatic adult patients with femoroacetabular impingement (FAI) who underwent open surgical intervention for management was designed to identify any obvious histological differences in the damaged acetabular cartilage within different subgroups of FAI. 20 patients underwent surgical intervention following safe surgical dislocation of the hip. There were 6 cases of cam impingement, 5 cases of pincer impingement and 9 of the mixed type. Pincer impingement cases demonstrated a characteristic focal, well-circumscribed and localized area of severe damage. On the other hand, cases with cam impingement showed a diffuse area of involvement affecting a larger surface of the acetabular cartilage, with degenerative changes, superficial erosions and some discontinuities. A small biopsy specimen of the acetabular rim including bone, cartilage and labrum from the affected zone was obtained in all cases. Histological evaluation was performed under normal and polarized light microscopy. Histological findings helped corroborate the pre-operative diagnosis and also define the unique nature of impingement and specific damage according to the type of impingement.

Athletic injuries in or around the hip in the adolescent athlete encompass possible causes such as a single, traumatic event to those of repetitive microtrauma. The injuries may involve the bone or the soft tissues, with former involving the epiphysis, apophysis, metaphysis, or diaphysis, whereas the latter includes muscles and tendons. With the improvements in surgical technique and instrumentation for hip arthroscopy and the development of magnetic resonance arthrography, clinicians have been able to diagnose and treat labral tears, hip instability, snapping hip, loose bodies, chondral injuries, and femoroacetabular impingement. The clinician needs to consider acquired conditions that may have coincidentally become apparent as a result of the adolescent's participation in an organized sports program. These include slipped capital femoral epiphysis, Legg-Calvé-Perthes disease, and pathologic lesions and fractures. This study reviews the more common acute and chronic overuse injuries in or around the hip in the adolescent athlete and discusses hip injury prevention in this active patient population.

Minimally invasive hip surgery is an innovative surgical technique mainly used in femoroacetabular impingement (FAI). The purpose of the surgical correction in FAI deformity is to eliminate the etiologic factor in the development of the so-called idiopathic hip osteoarthritis. Decisive for the success of joint preservation is the preoperative assessment of the deformity and the possible damage to the cartilage. The optimal intervention in the presence of substantial cartilage damage is joint replacement. The patient's history and the findings of physical examination with detailed radiographs and magnetic resonance imaging based on a sagittal oblique localizer optionally using intra-articular contrast prevent underestimation of the stage of the disease. Knowledge about the options and techniques of minimally invasive hip surgery helps to identify patients appropriate for other interventions like surgical dislocation of the hip and the periacetabular osteotomy.

Purpose: The purpose of this study is to systematically review the content and clinimetric evidence (rigor of rating scales and indexes for the description of clinical phenomena) of published patient-reported outcome (PRO) instruments used to assess femoroacetabular impingement (FAI) and labral hip pathology., Methods: We used Medical Subject Heading terms related to FAI and labrum/labral tears to search the Medline, Embase, and Cochrane databases for studies of FAI and labral hip pathology. Studies with hip-related PRO instruments, with any operative intervention except total hip arthroplasty, were included. We excluded studies with a skeletally immature population, revision surgeries in more than 10% of cases, or a primary diagnosis of hip osteoarthritis. We conducted a second review using the same databases for studies reporting clinimetric properties of at least 1 of the PRO instruments identified previously. Articles were selected in an independent, stepwise manner by 2 reviewers. Selected articles were evaluated to determine the presence and quality of measurement properties of the outcome instruments., Results: We found 5 articles assessing 3 PRO instruments: the Hip Outcome Score (HOS), the Non-Arthritic Hip Score, and the 12-item modified Western Ontario and McMaster Universities Osteoarthritis Index. The HOS had the highest positive rating for internal consistency, construct validity, agreement, responsiveness, lack of floor/ceiling effect, and interpretability. The Non-Arthritic Hip Score showed evidence for validity and lack of floor/ceiling effect. The modified Western Ontario and McMaster Universities Osteoarthritis Index was only strong for internal consistency and was indeterminate for construct validity., Conclusions: Only 3 PRO instruments have shown clinimetric evidence to support their use to measure outcomes in FAI and labral pathology patients. The HOS has the greatest amount of clinimetric evidence and is the most proven instrument for use in this population. This review shows that further clinimetric evaluation of commonly used PRO instruments for nonarthritic hip pathology is warranted., (Copyright © 2011 Arthroscopy Association of North America. Published by Elsevier Inc. All rights reserved.)

Introduction: Arthroscopic femoral osteoplasties might be technically demanding, might cause prolonged operative times and restrict the intraoperative overview. An automated navigated matching process of preoperative CT-data and intraoperative fluoroscopy should allow for noninvasive registration for FAI-surgery., Method: Six hip joints were used with a conventional navigation system. Defined osseous lesion (2 × 2 mm) in the femoral neck, head neck junction, and head region were created followed by automated segmentation including CT-fluoro image fusion by the navigation system. Precision of registration process was tested trough a lateral arthroscopic portal. In vivo distances between pointer tip to bone were measured. Secondary in vivo distances between an inserted navigated shaver and the osseous lesions were measured., Results: Our results allow a CT-fluoroscopy matching procedure for noninvasive registration process for navigated FAI-surgery in multiplanar planes. Precision is more accurate at the femoral neck and head-neck junction than at the femoral head area., Conclusion: Future navigated applications might simplify and increase precision of FAI-surgery.

Background: The arthroscopic treatment of intra-articular hip disease and associated structural abnormalities continues to evolve. Nevertheless, contemporary diagnostic tools have significant limitations in predicting severity of disease preoperatively., Hypothesis: Clinical characteristics and radiographic parameters correlate with and predict intra-articular disease patterns in patients undergoing hip arthroscopy., Study Design: Cohort study; Level of evidence, 3., Methods: In sum, 355 hips in 338 patients undergoing hip arthroscopy by a single surgeon were retrospectively reviewed. Clinical characteristics and radiographic findings (on anteroposterior pelvis and frog lateral radiographs) of mild dysplasia, cam, and pincer-type femoroacetabular impingement were compared with intraoperative labral and chondral disease patterns., Results: Labral tears were present in 90.1% of hips, and acetabular cartilage lesions were present in 67.3%, including 41.7% with grade 3 or 4 chondromalacia. Multivariate logistic regression analysis found male sex, older age (<30, 30-50, >50 years old), Tönnis osteoarthritis grade, and alpha angle >50° on frog lateral radiograph to be independently associated with increased risk of grade 3 or 4 acetabular chondromalacia (all P < .001). Insidious onset of pain (in contrast to acute onset) was independently associated with the presence of acetabular chondromalacia (P = .002). Cam-type femoroacetabular impingement (alpha angle >50°) was strongly associated with more severe labral disease (P < .001). Findings of acetabular dysplasia and pincer femoroacetabular impingement did not remain significantly associated with acetabular chondral disease in the multivariate analysis., Conclusion: Several clinical and radiographic characteristics--most notably, male sex, older age, Tönnis grade, and elevated alpha angle--are associated with more severe intra-articular hip disease. The recognition of these associations between clinical and radiographic characteristics and hip disease patterns is important for patient selection, surgical planning, and patient counseling.

Objective: To investigate the clinical diagnosis and arthroscopic treatment of acetabular labral tears., Methods: Twenty-one patients with unilateral acetabular labral tears hospitalized from November 2008 to December 2009 were included in this retrospective study. A definitive diagnosis was made preoperatively on the basis of physical examination, plain radiography and magnetic resonance arthrography (MRA). All cases were treated with arthroscopic surgeries: labral debridement (14 cases), labral debridement plus femoral osteoplasty (5 cases), and labral repair plus osteoplasty (2 cases). All patients were followed-up and the results evaluated using the visual analogue scale (VAS) and Harris hip score., Results: A positive flexion, abduction and internal rotation (FADIR) impingement sign was found in all 21 affected hips, a positive flexion, abduction and external rotation (FABER) impingement sign in 15, and a positive McCarthy test in 9. Plain radiography showed 11 cases had cam type impingement, in 6 of whom it was combined with pincer type impingement; and 2 cases had acetabular retroversion alone. Labral tears were observed on MRA in all cases and were all confirmed by arthroscopy. All patients were followed up for an average of 11.6 months (range, 6 to 19 months). The VAS decreased from (5.3 ± 1.3) preoperatively to (1.4 ± 0.9) 6 months postoperatively. The mean Harris hip score improved from (63 ± 9) preoperatively to (84 ± 10) 6 months postoperatively. All these differences were statistically significant., Conclusions: Acetabular labral injury is closely correlated with femoro-acetabular impingement. Impingement tests and MRA have high sensitivity and accuracy in clinical diagnosis of labral tears. Arthroscopic debridement, repair and osteoplasty for labral tears results in a good early outcome., (© 2011 Tianjin Hospital and Blackwell Publishing Asia Pty Ltd.)

Femoroacetabular impingement is a relatively recently described condition in which an abnormally shaped proximal part of the femur or acetabular overcoverage causes interference between the femoral head-neck junction and the acetabular rim. These disorders are now recognized as common causes of prearthritic hip pain and secondary osteoarthritis. Two mechanisms have been described. Cam-type impingement is caused by insufficient concavity of the femoral head-neck junction. Pincer-type impingement is caused by overcoverage of the femoral head by the acetabulum. Abnormal femoroacetabular abutment predisposes affected patients to labral tears, articular cartilage damage, and premature osteoarthritis. Early diagnosis of hip disease and referral for specialized care may optimize clinical outcomes and alter the natural history of these disorders. This review aims to describe this syndrome and to review the contemporary concepts of the etiology and surgical treatment of the disorder.

This review article describes the role of hip arthroscopy and the development of the technique over the past decade. The refinement of this technique has led to the discovery of ''new'' diseases of the hip joint. Recently, femoro-acetabular impingement (FAI) has been proposed as a source of soft tissue dysfunction, motion loss, and early osteoarthritis in the hip. Recognition of FAI is important, as failure to address this underlying pathology may lead to early onset osteoarthritis and subsequent hip replacement. The preliminary results after hip arthroscopy are described.

Several theoretical models have shown that the range of motion of the hip joint is impaired in patients with femoroacetabular impingement, and that the acetabular cartilage is at risk of being damaged as a result of abnormal shear stresses, even during normal everyday activities. Computer aided technologies might add to the early diagnosis and adequate treatment of such lesions. This paper describes the technique, theories and algorithms we have developed for patient-specific detection, analysis and computer aided surgery of femoroacetabular impingement. Currently available models applicable to femoroacetabular impingement offer modeling based on collision analysis of a constrained hip joint. Such an approach implies that neither the femur nor the acetabulum can be analyzed completely separately for the presence of structural lesions responsible for the impingement problem. Moreover, a constrained model does not allow for comprehensive prediction of the possible locations and extent of secondary cartilage lesions (so-called contre-coup lesions) of the posterior acetabulum opposite the anterior impingement site. We report a new technique for the subject-specific morphological analysis of the proximal femur, acetabulum and hip joint. The technique offers a number of advantages compared to currently used techniques for the diagnosis and evaluation of hip impingement, and has direct orthopaedic applications as it allows computer aided planning and minimally invasive surgery for patients with femoroacetabular impingement.

Introduction: Surgical treatment of femoroacetabular impingement can be performed under arthroscopic control, to limit associated morbidity. Encouraged by recent good reports, arthroscopy is replacing alternative techniques for this indication., Hypothesis: Arthroscopy enables femoroacetabular impingement to be corrected with a low rate of associated morbidity., Aim of Study: To assess the indications for and quality of the technique and its impact on preliminary results and complications. To investigate preoperative prognostic factors., Patient and Methods: One hundred and eleven hips in 110 patients (78 male, 32 female; mean age, 31 years) were operated on under arthroscopic control for femoroacetabular impingement, by six senior surgeons. Sixty-five patients showed no radiographic sign of osteoarthritis, and 36 showed grade-1 early osteoarthritis on the Tönnis scale., Results: Mean WOMAC score rose from 60.3 preoperatively to 83 (p<0.001) at a mean 10 months' FU (range, 6-18 mo). Seventy-seven percent of patients were satisfied or very satisfied with their result. Patients with early osteoarthritis had significantly lower WOMAC and satisfaction scores than those free of osteoarthritis. Operative crossover to open surgery occurred in only one case. Five patients (4%) had revision: total hip replacement or resurfacing. There were seven complications (6%): three cases of heterotopic ossification, one of crural palsy, one of pudendal palsy, one of labium majus necrosis, and one non-displacement stress fracture of the femoral head/neck junction (managed by non-weight-bearing). There was no palsy of the territory of the lateral cutaneous nerve of the thigh., Discussion: Results confirmed the efficacy and low associated morbidity of arthroscopy in the management of femoroacetabular impingement. Short-term functional results matched those of the literature. Planning and assessment seem not yet to be fully standardized. Preoperative osteoarthritis on X-ray was associated with poorer functional results. This attitude does not seem to be indicated for hips showing evolved osteoarthritis (>grade 1)., (Copyright © 2010 Elsevier Masson SAS. All rights reserved.)

Two hundred and ninety-two patients under the age of 50 years, presenting with mechanical hip pain, were included in a prospective multicenter study. In 241 cases, imaging assessment included AP standing pelvic X-ray and Lequesne's false profile (LFP) and/or lateral neck (Ducroquet, Dunn or variant) hip X-ray. Cross-sectional arthroscan and/or arthro-MRI images were available in 81 cases. Exploration looked for acetabular and femoral head/neck dysplasia liable to induce cam or pincer anterior femoroacetabular impingement (AFAI), respectively. Labral and chondral lesions arise secondarily to hip osteoarthritis (HOA) and/or AFAI. Two-thirds of patients showed HOA. Only 6% showed a strictly normal aspect on imaging. More than half (52%) of cases had cam AFAI, half of these involving an osteophytic neck, associated in more than 90% of cases with large multifocal bone spurs of the head, neck and acetabula. These cases were considered ambiguous, due to the uncertainty as to the congenital nature of the cervico-cephalic dysmorphy; if they are excluded, only 23% of the series involved cam AFAI. Crossover sign on AP standing pelvic X-ray is the best assessment criterion for acetabular retroversion, the most frequent form of acetabular dysplasia underlying pincer AFAI, and should be explored for. Secondary neck lesions were visible only on lateral neck view in 42% of cases: this view should be included in standard radiologic work-up in under-50 year-olds. The alpha angle can be measured on this type of lateral view and on axial arthroscan and arthro-MR images; more than half of the cases in which it was pathological involved an osteophytic neck and thus a pseudo-cam effect., (Copyright © 2010 Elsevier Masson SAS. All rights reserved.)

Arthroscopic femoral osteochondroplasty improves clinical outcome in patients with unilateral cam-type femoroacetabular impingement. The goal of this study was to evaluate the clinical outcome and pathological similarities in patients who have had bilateral arthroscopic femoral osteochondroplasy for cam-type femoroacetabular impingement. The study group included 82 patients who had sequential bilateral hip arthroscopies for symptomatic cam-type femoroacetabular impingement with a minimum of 12 months follow-up. All patients had bilateral restricted hips at presentation. We differentiated between patients who had bilateral painful hips and those with unilateral pain at presentation. Scores and surgical findings were compared between the 2 study groups and between bilateral surgeries in each group. Pre- and postoperative Modified Harris Hip Scores and Non-Arthritic Hip Scores were undertaken prospectively by an independent observer. Mean patient age at the first surgery was 29 years (range, 14-63 years). The average time difference between arthroscopies was 5 months (range, 0.3-30 months). Postoperative scores improved significantly in both study groups in the first and second (contralateral) surgeries. Intra-articular pathologies between sides were linearly correlated for both groups. The time interval between surgeries had a linear correlation to age, reverse correlation to chondral damage, and reverse correlation to postoperative scores at the first surgery. Our results suggest that symptomatic patients with cam-type femoroacetabular impingement have similar accompanied pathologies on both sides and can benefit from sequential arthroscopic osteochondroplasty., (Copyright 2010, SLACK Incorporated.)

The paper presents modern concepts in the aetiology and development of osteoarthritis of the hip. Femoroacetabular impingement (FAI) is a condition characterized by a repetitive abnormal contact of the acetabular rim with the femoral head-neck region, which leads to the development of early osteoarthritis of the hip. There are three types of FAI: cam type, pincer type, and mixed type. FAI is diagnosed on the basis of history, clinical assessment and imaging evidence from radiographs, magnetic resonance imaging, ultrasound scans and computed tomography. Early diagnosis and appropriate treatment of FAI make it possible to halt the development of osteoarthritis of the hip.

Background: Femoroacetabular impingement (FAI) is a condition characterized by repetitive abnormal contact of the femoral acetabulum with the femoral head-neck region, which leads to the development of early-stage coxarthrosis. Early diagnosis and appropriate treatment of FAI can halt the development of coxarthrosis., Material and Methods: We present the early results of surgical treatment of 13 patients with FAI by osteochondroplasty of the head-neck region. An anterior approach to the hip joint was employed without surgical dislocation of the femoral head. The follow-up period ranged from 1.5 to 4 years. Clinical assessment was conducted according to the Harris classification. The FAI index was measured during radiographic evaluation., Results: Clinical assessment revealed an improvement in 12 patients. Radiographically, the value of FAI index was normal in all the patients who underwent the surgery., Conclusions: Osteochondroplasty of the head-neck region appears to be an effective treatment of FAI in early-stage coxarthrosis.

Acetabular labral tears have been the focus of much attention in recent years. With the increased use of hip arthroscopy and magnetic resonance arthrography, the infrequent labral tear has proved to be more prevalent than previously thought. The majority of labral tears occur due to an underlying anatomic abnormality. Anatomic abnormalities that can lead to labral tears include femoracetabular impingement, acetabular retroversion, abnormal femoral head, Legg Calvé Perthes, slipped capital epiphysis, capsular laxity, and dysplasia of the hip. Tears in the labrum may lead to the advancement of osteoarthritis. Optimal management of a labral tear may involve addressing underlying anatomic abnormalities in addition to the labral tear itself.

Recently the relevance of femoroacetabular impingement as a cause of hip and groin pain in sportsmen has been recognized. The entity often poses diagnostic and therapeutic problems to the sports physician. The patients go through an odyssey of different diagnostic and therapeutic modalities before the correct diagnosis is made and an adequate therapy is implemented. Not seldom, patients get even operated at another site which is thought to cause the problems. The present review analyzes the current literature concerning diagnostic standards and therapy of femoroacetabular impingement focussing on their relevance for sports medicine. It is aimed to help the sports physician to recognise this entity as a cause for groin and hip pain in the athlete and realise its importance for the short term performance of the athlete and its long term significance in terms of development of early hip osteoarthrosis., (© Georg Thieme Verlag KG Stuttgart · New York.)

Objective: The purpose of this study was to investigate whether T1-mapping of hip joint with intra-articular delayed gadolinium-enhanced magnetic resonance imaging (MRI) of cartilage (ia-dGEMRIC) is comparable to the already established intravenous (iv)-technique for assessing different grades of cartilage degeneration., Materials and Methods: The study cohort consisted of 53 patients with symptomatic femoroacetabular impingement (FAI) that were randomly recruited for either iv-dGEMRIC or ia-dGEMRIC studies. RI was performed in supine position at a 1.5 Tesla (T) system (Magnetom Avanto, Siemens, Erlangen, Germany) using a body matrix-phased array coil. Twenty-six patients (18 males, 8 females; mean age +/- standard deviation [SD]: 32.1 +/- 8.8 years, range: 17-49 years) underwent iv-dGEMRIC whereas 27 patients (17 males, 10 females; mean age 34.0 +/- 10.8 years, range: 13.0-57 years) underwent ia-dGEMRIC mapping. On average patients suffered from FAI for 23.9 +/- 20.9 months in the iv-dGEMRIC group (range: 5-108 months) whereas FAI was symptomatic for 20.9 +/- 25.2 months in the ia-dGEMRIC group (range: 3-120 months). Patient demographics and symptomatology in both groups were not statistically different., Results: Mapping with both techniques (iv and ia) demonstrated appropriately similar differences between various grades of cartilage degeneration. Overall, there was no significant difference between iv-dGEMRIC and ia-dGEMRIC T1 mean values in all grades of cartilage findings (P: 0.394, 0.400, and 0.173). Of note, the T1 values after iv-dGEMRIC were higher (544.3 +/- 104.2 milliseconds) in regions with cartilage damage extent <0.75 cm than in regions where no damage was noted (535.7 +/- 112.4 milliseconds). After ia-dGEMRIC the T1 values were similar (521.2 +/- 125.1 milliseconds vs. 521.1 +/- 94.3 milliseconds)., Conclusions: Intravenous contrast remains the standard method of contrast administration in the current scenario when dGEMRIC imaging is performed. Our results demonstrate that the information and mapping values obtained by the ia-technique are similar to those of the iv-technique. The intravenous route can have its own problems in certain patients with impaired renal function tests or when parenteral access is an issue in many patients. Intra-articular technique could be a good alternative in such cases whereas maintaining the quality of imaging and obtained information. Thus, in well-selected cases ia-dGEMRIC mapping may be a potential alternative to iv-dGEMRIC for hip joint cartilage analysis., Level of Evidence: Prospective case series, Diagnostic study comparing different modalities of assessing status of hip joint cartilage: Level II evidence.

Background: The aims of this study were to evaluate the construct validity (known group), concurrent validity (criterion based) and test-retest (intra-rater) reliability of manual goniometers to measure passive hip range of motion (ROM) in femoroacetabular impingement patients and healthy controls., Methods: Passive hip flexion, abduction, adduction, internal and external rotation ROMs were simultaneously measured with a conventional goniometer and an electromagnetic tracking system (ETS) on two different testing sessions. A total of 15 patients and 15 sex- and age-matched healthy controls participated in the study., Results: The goniometer provided greater hip ROM values compared to the ETS (range 2.0-18.9 degrees; P < 0.001); good concurrent validity was only achieved for hip abduction and internal rotation, with intraclass correlation coefficients (ICC) of 0.94 and 0.88, respectively. Both devices detected lower hip abduction ROM in patients compared to controls (P < 0.01). Test-retest reliability was good with ICCs higher 0.90, except for hip adduction (0.82-0.84). Reliability estimates did not differ between the goniometer and the ETS., Conclusions: The present study suggests that goniometer-based assessments considerably overestimate hip joint ROM by measuring intersegmental angles (e.g., thigh flexion on trunk for hip flexion) rather than true hip ROM. It is likely that uncontrolled pelvic rotation and tilt due to difficulties in placing the goniometer properly and in performing the anatomically correct ROM contribute to the overrating of the arc of these motions. Nevertheless, conventional manual goniometers can be used with confidence for longitudinal assessments in the clinic.

We describe our modified anterior mini-invasive technique and results obtained in our first consecutive 117 cases in 105 patients. To assess the influence of preoperative Tönnis degenerative stage, cases were divided into group A (Tönnis 0, 32 hips), B (Tönnis 1, 61 hips), and C (Tönnis 2, 24 hips). The clinical score Dexeus combined score (DCS) was used preoperatively, 3 months, 6 months, and every year after operation. At 3-month follow-up, impingement test results improved significantly in 30 hips of group A (94%; p<0.001) and in 58 of group B (95%; p<0.001), whereas in group C, improvement was observed in only 14 cases (58%; p>0.05). No statistical difference was observed at 3-year visit in all groups. Merle d'Aubigné-Postel and WOMAC scores improved significantly in group A (p<0.001) and B (p<0.001) after 1 year and remained unchanged at subsequent yearly follow-ups. For group C, clinical outcomes scores did not show any significant improvement overall (p>0.05). We concluded that anterior mini-invasive technique is an effective method to treat femoroacetabular impingement, and results are highly influenced by preoperative degenerative state, especially in stage Tönnis 2. Therefore, it seems to be a reasonable early surgical treatment in symptomatic patients.

Introduction: A novel computerized algorithm for hip joint motion simulation and collision detection, called the Equidistant Method, has been developed. This was compared to three pre-existing methods having different properties regarding definition of the hip joint center and behavior after collision detection. It was proposed that the Equidistant Method would be most accurate in detecting the location and extent of femoroacetabular impingement., Materials and Methods: Five plastic pelves and ten plastic femora with modified acetabula and head-neck junctions, allowing for 50 different morphologic combinations, were examined, along with six cadaver hips. First, motions along anatomically relevant paths were performed. These motions were tracked by a navigation system and impingement locations were digitized with a pointer. Subsequently, previously generated 3D models of all the specimens, together with the recorded anatomic motion paths, were applied to all four simulation algorithms implemented in a diagnostic computer application. Collisions were detected within the motion paths, and the linear and angular differences regarding the location as well as the size of the detected impingement areas were compared and analyzed., Results: The Equidistant Method detected impingement with significantly higher linear and angular accuracy compared to the other methods (p < 0.05). The size of the detected impingement area was smaller than that detected with the other methods, but this difference was not statistically significant., Conclusions: The increased accuracy of the Equidistant Method is achieved by implementing a dynamic hip joint center, more closely resembling the natural characteristics of the hip joint. Clinical application of this algorithm might serve as a diagnostic adjunct and support in the planning of joint-preserving surgery in patients with femoroacetabular impingement.