Aims. Femoroacetabular impingement (FAI) patients report exacerbation of hip pain in deep flexion. However, the exact impingement location in deep flexion is unknown. The aim was to investigate impingement-free maximal flexion, impingement location, and if cam deformity causes hip impingement in flexion in FAI patients. Methods. A retrospective study involving 24 patients (37 hips) with FAI and femoral retroversion (femoral version (FV) < 5° per Murphy method) was performed. All patients were symptomatic (mean age 28 years (SD 9)) and had anterior hip/groin pain and a positive anterior impingement test. Cam- and pincer-type subgroups were analyzed. Patients were compared to an asymptomatic control group (26 hips). All patients underwent pelvic CT scans to generate personalized CT-based 3D models and validated software for patient-specific impingement simulation (equidistant method). Results. Mean impingement-free flexion of patients with mixed-type FAI (110° (SD 8°)) and patients with pincer-type FAI (112° (SD 8°)) was significantly (p < 0.001) lower compared to the control group (125° (SD 13°)). The frequency of extra-articular subspine impingement was significantly (p < 0.001) increased in patients with pincer-type FAI (57%) compared to cam-type FAI (22%) in 125° flexion. Bony impingement in maximal flexion was located anterior-inferior at femoral four and five o’clock position in patients with cam-type FAI (63% (10 of 16 hips) and 37% (6 of 10 hips)), and did not involve the cam deformity. The cam deformity did not cause impingement in maximal flexion. Conclusion. Femoral impingement in maximal flexion was located anterior-inferior distal to the cam deformity. This differs to previous studies, a finding which could be important for FAI patients in order to avoid exacerbation of hip pain in deep flexion (e.g. during squats) and for hip arthroscopy (hip-preservation surgery) for planning of bone resection. Hip impingement in flexion has implications for daily activities (e.g. putting on shoes), sports, and sex. Cite this article: Bone Joint Res 2023;12(1):22–32

Femoroacetabular cam impingement is thought to be a cause of premature osteoarthritis of the hip. The presence of cam malformation was determined in 2803 standardised anteroposterior (AP) pelvic radiographs from the Copenhagen Osteoarthritis Study by measuring the alpha (α) angle and the triangular index, a new measure of asphericity of the femoral head. In addition, the α-angle and the triangular index were assessed on the AP and lateral hip radiographs of 82 men and 82 women randomly selected from patients scheduled for total hip replacement (THR). The influence of varying femoral rotation on the α angle and the triangular index was also determined in femoral specimens under experimental conditions. From the 2803 radiographs the mean AP α-angle was 55° (30° to 100°) in men and 45° (34° to 108°) in women. Approximately 6% of men and 2% of women had cam malformation. The α-angle and triangular index were highly inter-related. Of those patients scheduled for THR, 36 men (44%) and 28 women (35%) had cam malformation identifiable on the AP radiographs. The triangular index proved to be more reliable in detecting cam malformation when the hip was held in varying degrees of rotation. The combination of the α-angle and the triangular index will allow examination of historical radiographs for epidemiological purposes in following the natural history of the cam deformity

Aims. Hip arthroscopy has gained prominence as a primary surgical intervention for symptomatic femoroacetabular impingement (FAI). This study aimed to identify radiological features, and their combinations, that predict the outcome of hip arthroscopy for FAI. Methods. A prognostic cross-sectional cohort study was conducted involving patients from a single centre who underwent hip arthroscopy between January 2013 and April 2021. Radiological metrics measured on conventional radiographs and magnetic resonance arthrography were systematically assessed. The study analyzed the relationship between these metrics and complication rates, revision rates, and patient-reported outcomes. Results. Out of 810 identified hip arthroscopies, 359 hips were included in the study. Radiological risk factors associated with unsatisfactory outcomes after cam resection included a dysplastic posterior wall, Tönnis grade 2 or higher, and over-correction of the α angle. The presence of acetabular retroversion and dysplasia were also significant predictors for worse surgical outcomes. Notably, over-correction of both cam and pincer deformities resulted in poorer outcomes than under-correction. Conclusion. We recommend caution in performing hip arthroscopy in patients who have three positive acetabular retroversion signs. Acetabular dysplasia with a lateral centre-edge angle of less than 20° should not be treated with isolated hip arthroscopy. Acetabular rim-trimming should be avoided in patients with borderline dysplasia, and care should be taken to avoid over-correction of a cam deformity and/or pincer deformity. Cite this article: Bone Joint J 2024;106-B(8):775–782

Summary Statement. This study quantifies compositional differences in cartilage between CAM deformities of symptomatic FAI patients and normal cadaver controls. It shows a resemblance of CAM-FAI cartilage with those of osteoarthritic hips, objectively supporting previous hypothesis of abnormal contact stresses in CAM-FAI. Introduction. Degeneration of cartilage within articular joints is a pathological feature of osteoarthritis (OA). Femoroacetabular impingement (FAI), a condition of abnormal contact between the articular surfaces of the femur and acetabulum, has been widely associated with early onset OA of the hip. The purpose of this study was to quantitatively compare the proteoglycan (PG) content of the weight-bearing cartilage in surgical FAI patients versus those of cadavers without FAI. Patients and Methods. Osteochondral bone plugs were taken from the antero-superior weight-bearing surface of cam-deformities on the femoral heads of 11 surgical cam-FAI patients. These were compared to control specimens taken from 11 cadaveric hips (7 donors) at approximately the same location. The PG content of the specimens were then histologically compared using the model presented by Martin et al. In this method, Safranin-O binds to chondroitin sulfate, a PG abundant in cartilage, allowing it to be visualised and quantitatively compared. Specifically, the specimens were fixed in formalin, decalcified in EDTA and then sectioned to 7um thick. They were then stained with Safranin-O, which binds specifically and stoichiometrically with proteoglycan. This model allows for quantitative comparison of PG content whereby the red content (R. c. ) of the sample is linearly correlated with the amount of PG present in the sample when viewed under 4x microscopic magnification. Here, the red content was sampled by depth coordinate with superficial and deep zones analyzed. Results. In general, the R. C. in the cartilage of surgical patients was lower than that of the cadaveric controls in both the superficial and deep layers tested. This correlates to a decrease in the PG of the test subjects. In the surgical specimens, R. C. ranged from 0 – 31.9 in the superficial layer and 0 – 139.6 in the deep. When compared by layers, the R. C. of the superficial 30% specimens averaged an R. C. of 17.5 compared to 88.6 in the cadaveric controls. This represents an 80.2% depletion in the PG content. In the deep 70% layer, the average R. C. of the test subjects was 52.4, compared with 129.2 in the cadaveric controls. This represents a 59% depletion in the PG content of the deep layer. These results show large compositional change in the cartilage of surgical FAI versus control specimens that were statistically significant in all levels (superficial, deep, total yielding p<0.001, p=0.001, p<0.001, respectively). Discussion. The idea of abnormal cartilage at the cam deformity has been previously demonstrated through similar resection and staining techniques. Wagner et al showed cellular activity and qualitatively noted PG depletion in the cartilage on the Cam deformity, consistent with OA. However a quantitative assessment of PG content provides a better estimate of impingement severity and disease state. Results from this current study objectively corroborate previously obtained qualitative data, supporting existing hypothesis of abnormal contact stresses in cam-FAI while giving a more robust, objective quantification of cartilage breakdown at CAM sites

Introduction: Femoroacetabular impingement (FAI) is an important cause of hip pain in young adults and a precursor to osteoarthritis. Morphological abnormality of either the acetabulum, proximal femur, or both, may result in FAI. The majority of patients however, have a cam deformity of the proximal femur. From a research perspective, FAI is an example of how subtle morphological abnormality results in a predictable pattern of cartilage damage, and thereby offers great potential as a model to study early degenerative disease and for clinical trials of joint preserving treatments. Accurate classification of the morphology of the hip is essential for this further study. The aim of this study was to define normal, borderline, and abnormal parameters for the morphology of the proximal femur, in the context of the cam deformity, by studying asymptomatic individuals with normal clinical examination and no osteoarthritis from the general population. Methods: 157 individuals (79 male, 78 female, mean age 46 years) with no previous history of hip problems were recruited. The participants were the spouses/partners of patients involved in a cohort study of osteoarthritis and FAI. All participants underwent clinical (interview, examination, and hip scores) and radiological assessment (standardised AP Pelvic and cross-table lateral radiographs of each hip). Radiographs were scored for the presence of osteoarthritis, and the morphology of the proximal femur was analysed. The alpha angle, anterior offset ratio, presence of a cam ‘bump’, synovial herniation pit were recorded in each hip. Results: 21 subjects were excluded because they either had positive clinical features or radiological evidence of osteoarthritis (equivalent to a Kellgren and Lawrence grade of 2). From the remaining 136 subjects, with essentially ‘normal hips from the general population’, mean values for the alpha angle and anterior offset ratio were generated. Borderline and Abnormal values are suggested. Gender differences were noted with higher mean alpha angles and lower offset ratios occurring in men. Discussion: Although it has limitations, standardised plain radiography remains the cheapest and most convenient way to screen an individual for the presence of a cam deformity. Despite the recent interest in FAI, our knowledge of what is normal in the general population, as assessed using appropriate radiographic techniques, is modest. The ranges provided by this study will facilitate the accurate classification of subjects with FAI, thereby providing guidance for surgeons treating such patients, and also enable the generation of refined cohorts for the study of the natural history of subtle morphological abnormalities of the hip, and for enrolment in clinical trials

The cam-type deformity in femoroacetabular impingement is a 3D deformity. Single measurements using radiographs, CT or MRI may not provide a true estimate of the magnitude of the deformity. We performed an analysis of the size and location of measurements of the alpha angle (α°) using a CT technique which could be applied to the 3D reconstructions of the hip. Analysis was undertaken in 42 patients (57 hips; 24 men and 18 women; mean age 38 years (16 to 58)) who had symptoms of femoroacetabular impingement related to a cam-type abnormality. An α° of > 50° was considered a significant indicator of cam-type impingement. Measurements of the α° were made at different points around the femoral head/neck junction at intervals of 30°: starting at the nine o’clock (posterior), ten, eleven and twelve o’clock (superior), one, two and ending at three o’clock (anterior) position.

The mean maximum increased α° was 64.6° (50.8° to 86°). The two o’clock position was the most common point to find an increased α° (53 hips; 93%), followed by one o’clock (48 hips; 84%). The largest α° for each hip was found most frequently at the two o’clock position (46%), followed by the one o’clock position (39%). Generally, raised α angles extend over three segments of the clock face.

Single measurements of the α°, whether pre- or post-operative, should be viewed with caution as they may not be representative of the true size of the deformity and not define whether adequate correction has been achieved following surgery.

Cite this article: Bone Joint J 2014;96-B:1167–71.

Aims. It has been well documented in the arthroplasty literature that lumbar degenerative disc disease (DDD) contributes to abnormal spinopelvic motion. However, the relationship between the severity or pattern of hip osteoarthritis (OA) as measured on an anteroposterior (AP) pelvic view and spinopelvic biomechanics has not been well investigated. Therefore, the aim of the study is to examine the association between the severity and pattern of hip OA and spinopelvic motion. Methods. A retrospective chart review was conducted to identify patients undergoing primary total hip arthroplasty (THA). Plain AP pelvic radiographs were reviewed to document the morphological characteristic of osteoarthritic hips. Lateral spine-pelvis-hip sitting and standing plain radiographs were used to measure sacral slope (SS) and pelvic femoral angle (PFA) in each position. Lumbar disc spaces were measured to determine the presence of DDD. The difference between sitting and standing SS and PFA were calculated to quantify spinopelvic motion (ΔSS) and hip motion (ΔPFA), respectively. Univariate analysis and Pearson correlation were used to identify morphological hip characteristics associated with changes in spinopelvic motion. Results. In total, 139 patients were included. Increased spinopelvic motion was observed in patients with loss of femoral head contour, cam deformity, and acetabular bone loss (all p < 0.05). Loss of hip motion was observed in patients with loss of femoral head contour, cam deformity, and acetabular bone loss (all p < 0.001). A decreased joint space was associated with a decreased ΔPFA (p = 0.040). The presence of disc space narrowing, disc space narrowing > two levels, and disc narrowing involving the L5–S1 segment were associated with decreased spinopelvic motion (all p < 0.05). Conclusion. Preoperative hip OA as assessed on an AP pelvic radiograph predicts spinopelvic motion. These data suggest that specific hip osteoarthritic morphological characteristics listed above alter spinopelvic motion to a greater extent than others. Cite this article: Bone Joint J 2023;105-B(5):496–503

Femoroacetabular impingement (FAI) results from a morphological deformity of the hip and is associated with osteoarthritis (OA). Increased bone mineral density (BMD) is observed in the antero-superior acetabulum rim where impingement occurs. It is hypothesized that the repeated abnormal contact leads to damage of the cartilage layer, but could also cause a bone remodelling response according to Wolff's Law. Thus the goal of this study was to assess the relationship between bone metabolic activity measured by PET and BMD measured in CT scans. Five participants with asymptomatic cam deformity, three patients with uni-lateral symptomatic cam FAI and three healthy controls were scanned in a 3T PET-MRI scanner following injection with [18F]NaF. Bone remodelling activity was quantified with Standard Uptake Values (SUVs). SUVmax was analyzed in the antero-superior acetabular rim, femoral head and head-neck junction. In these same regions, BMD was calculated from CT scans using the calibration phantom included in the scan. The relationship between SUVmax and BMD from corresponding regions was assessed using the coefficient of determination (R. 2. ) from linear regression. High bone activity was seen in the cam deformity and acetabular rim. SUVmax was negatively correlated with BMD in the antero-superior region of the acetabulum (R. 2. =0.30, p=0.08). SUVmax was positively correlated with BMD in the antero-superior head-neck junction of the femur (R. 2. =0.359, p=0.067). Correlations were weak in other regions. Elevated bone turnover was seen in patients with a cam deformity but the relationship to BMD was moderate. This study demonstrates a pathomechanism of hip degeneration associated with FAI deformities, consistent with Wolff's law and the proposed mechanical cause of hip degeneration in FAI. [18F]-NaF PET SUV may be a biomarker of degeneration, especially in early stages of degeneration, when joint preservation surgery is likely to be the most successful

Purpose. To determine the differences of biomechanical properties in three conditions including 1) native cam deformity 2) cam deformity with incomplete resection and 3) cam deformity with complete resection. Methods. A cadaveric study was performed using 8 frozen, hemi-pelvises with cam-type deformity (alpha angle >55°) measured on CT scan and an intact labrum. Intraarticular pressure maps were produced for each specimen under the following conditions: 1) native cam deformity, 2) cam deformity with incomplete resection and 3) cam deformity with complete resection. A 5.5-mm burr was used to resect the lateral portion of the cam deformity to a depth of 3–4 mm. The specimen was placed in a custom designed jig in the MTS electromechanical test system to create pressure and area map measurements. In each condition, three biomechanical parameters were obtained including contact pressure, contact area and peak force within a region-of-interest (ROI). Repeated measurements were performed for three times in each condition and the average value of each parameter was used for statistical analysis. ANOVA was used to compare biomechanical parameters between three conditions. Results. Repeated measures ANOVA analysis demonstrated that the pressures averages of hips with complete resection of cam lesions were significantly lower when compared to averages of hips with incomplete femoral cam lesion and intact cam deformity (2.48. +. 0.56 kg/cm. 3. vs 2.32. +. 0.50 kg/cm. 3. vs 2.02. +. 0.54 kg/cm. 3. , respectively; p-value=0.01). Percentage reduction of contact pressure in the complete resection and incomplete resection groups compared to the native CAM deformity groups were 18.49% and 1.58% respectively. There was no statistically significant difference in contact pressures between the incomplete resection and unoperated groups. Contact area and peak force showed no statistically significant differences across three conditions. Conclusion. There are lower intraarticular hip contract pressures in complete resection of the cam lesions when compared to an incomplete resection and intact hip without resection. These observations underscore the importance of ensuring complete resection of femoral cam lesions in patients undergoing hip arthroscopy for femoroacetabular impingement syndrome. For any tables or figures, please contact the authors directly

Aims. The aim of this study was to examine the real time in vivo kinematics of the hip in patients with cam-type femoroacetabular impingement (FAI). Patients and Methods. A total of 50 patients (83 hips) underwent 4D dynamic CT scanning of the hip, producing real time osseous models of the pelvis and femur being moved through flexion, adduction, and internal rotation. The location and size of the cam deformity and its relationship to the angle of flexion of the hip and pelvic tilt, and the position of impingement were recorded. Results. In these patients with cam-type FAI, there was significant correlation between the alpha angle and flexion to the point of impingement (mean 41.36°; 14.32° to 57.95°) (R = -0.5815 and p = < 0.001). Patients with a large cam deformity (alpha angle > 78°) had significantly less flexion to the point of impingement (mean 36.30°; 14.32° to 55.18°) than patients with a small cam deformity (alpha angle 60° to 78°) (mean 45.34°; 27.25° to 57.95°) (p = < 0.001). Conclusion. This study has shown that cam-type impingement can occur early in flexion (40°), particularly in patients with large anterior deformities. These patients risk chondrolabral damage during routine activities such as walking, and going up stairs. These findings offer important insights into the cause of the symptoms, the mechanisms of screening and the forms of treatment available for these patients. Cite this article: Bone Joint J 2017;99-B(4 Supple B):41–8

Arthroscopic hip procedures have increased dramatically over the last decade as equipment and techniques have improved. Patients who require hip arthroscopy for femoroacetabular impingement on occasion require surgery on the contralateral hip. Previous studies have found that younger age of presentation and lower Charlson comorbidity index have higher risk for requiring surgery on the contralateral hip but have not found correlation to anatomic variables. The purpose of this study is to evaluate the factors that predispose a patient to requiring subsequent hip arthroscopy on the contralateral hip. This is an IRB-approved, single surgeon retrospective cohort study from an academic, tertiary referral centre. A chart review was conducted on 310 primary hip arthroscopy procedures from 2009-2020. We identified 62 cases that went on to have a hip arthroscopy on the contralateral side. The bilateral hip arthroscopy cohort was compared to unilateral cohort for sex, age, BMI, pre-op alpha angle and centre edge angle measured on AP pelvis XRay, femoral torsion, traction time, skin to skin time, Tonnis grade, intra-op labral or chondral defect. A p-value <0.05 was deemed significant. Of the 62 patients that required contralateral hip arthroscopy, the average age was 32.7 compared with 37.8 in the unilateral cohort (p = 0.01) and BMI was lower in the bilateral cohort (26.2) compared to the unilateral cohort (27.6) (p=0.04). The average alpha angle was 76.3. 0. in the bilateral compared to 66. 0. in the unilateral cohort (p = 0.01). Skin to skin time was longer in cases in which a contralateral surgery was performed (106.3 mins vs 86.4 mins) (p=0.01). Interestingly, 50 male patients required contralateral hip arthroscopy compared to 12 female patients (p=0.01). No other variables were statistically significant. In conclusion, this study does re-enforce existing literature by stating that younger patients are more likely to require contralateral hip arthroscopy. This may be due to the fact that these patients require increased range of motion from the hip joint to perform activities such as sports where as older patients may not need the same amount of range of motion to perform their activities. Significantly higher alpha angles were noted in patients requiring contralateral hip arthroscopy, which has not been shown in previous literature. This helps to explain that larger CAM deformities will likely require contralateral hip arthroscopy because these patients likely impinge more during simple activities of daily living. Contralateral hip arthroscopy is also more common in male patients who typically have a larger CAM deformity. In summary, this study will help to risk stratify patients who will likely require contralateral hip arthroscopy and should be a discussion point during pre-operative counseling. That offering early subsequent or simultaneous hip arthroscopy in young male patients with large CAMs should be offered when symptoms are mild

Outcomes following different types of surgical intervention for femoroacetabular impingement (FAI) are well reported individually but comparative data are deficient. The purpose of this study was to conduct a systematic review (SR) and meta-analysis to analyze the outcomes following surgical management of FAI by hip arthroscopy (HA), anterior mini open approach (AMO), and surgical hip dislocation (SHD). This SR was registered with PROSPERO. An electronic database search of PubMed, Medline, and EMBASE for English and German language articles over the last 20 years was carried out according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. We specifically analyzed and compared changes in patient-reported outcome measures (PROMs), α-angle, rate of complications, rate of revision, and conversion to total hip arthroplasty (THA). A total of 48 articles were included for final analysis with a total of 4,384 hips in 4,094 patients. All subgroups showed a significant correction in mean α angle postoperatively with a mean change of 28.8° (95% confidence interval (CI) 21 to 36.5; p < 0.01) after AMO, 21.1° (95% CI 15.1 to 27; p < 0.01) after SHD, and 20.5° (95% CI 16.1 to 24.8; p < 0.01) after HA. The AMO group showed a significantly higher increase in PROMs (3.7; 95% CI 3.2 to 4.2; p < 0.01) versus arthroscopy (2.5; 95% CI 2.3 to 2.8; p < 0.01) and SHD (2.4; 95% CI 1.5 to 3.3; p < 0.01). However, the rate of complications following AMO was significantly higher than HA and SHD. All three surgical approaches offered significant improvements in PROMs and radiological correction of cam deformities. All three groups showed similar rates of revision procedures but SHD had the highest rate of conversion to a THA. Revision rates were similar for all three revision procedures

Cam-type femoroacetabular impingement is caused by bone excess on the femoral neck abutting the acetabular rim. This can cause cartilage and labral damage due to increased contact pressure as the cam moves into the acetabulum. However, the damage mechanism and the influence of individual mechanical factors (such as sliding distance) are poorly understood. The aim of this study was to identify the cam sliding distance during impingement for different activities in the hip joint. Motion data for 12 different motion activities from 18 subjects, were applied to a hip shape model (selected as most likely to cause damage, anteriorly positioned with a maximum alpha angle of 80°). The model comprised of a pointwise representation of the acetabular rim and points on the femoral head and neck where the shape deviated from a sphere (software:Matlab). The movement of each femoral point was tracked in 3D while an activity motion was applied, and impingement recorded when overlap between a cam point and the acetabular rim occurred. Sliding distance was recorded during impingement for each relevant femoral point. Angular sliding distances varied for different activities. The highest mean (±SD) sliding distance was for leg-crossing (42.62±17.96mm) and lowest the trailing hip in golf swing (2.17±1.11mm). The high standard deviation in the leg crossing sliding distances, indicates subjects may perform this activity in a different manner. This study quantified sliding distance during cam impingement for different activities. This is an important parameter for determining how much the hip moves during activities that may cause damage and will provide information for future experimental studies

Aims. This paper aims to review the evidence for patient-related factors associated with less favourable outcomes following hip arthroscopy. Methods. Literature reporting on preoperative patient-related risk factors and outcomes following hip arthroscopy were systematically identified from a computer-assisted literature search of Pubmed (Medline), Embase, and Cochrane Library using Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) guidelines and a scoping review. Results. Assessment of these texts yielded 101 final articles involving 90,315 hips for qualitative analysis. The most frequently reported risk factor related to a less favourable outcome after hip arthroscopy was older age and preoperative osteoarthritis of the hip. This was followed by female sex and patients who have low preoperative clinical scores, severe hip dysplasia, altered hip morphology (excess acetabular retroversion or excess femoral anteversion or retroversion), or a large cam deformity. Patients receiving workers’ compensation or with rheumatoid arthritis were also more likely to have a less favourable outcome after hip arthroscopy. There is evidence that obesity, smoking, drinking alcohol, and a history of mental illness may be associated with marginally less favourable outcomes after hip arthroscopy. Athletes (except for ice hockey players) enjoy a more rapid recovery after hip arthroscopy than non-athletes. Finally, patients who have a favourable response to local anaesthetic are more likely to have a favourable outcome after hip arthroscopy. Conclusion. Certain patient-related risk factors are associated with less favourable outcomes following hip arthroscopy. Understanding these risk factors will allow the appropriate surgical indications for hip arthroscopy to be further refined and help patients to comprehend their individual risk profile. Cite this article: Bone Joint J 2020;102-B(7):822–831

Femoro-acetabular impingement involves a deformity of the hip joint and is associated with hip osteoarthritis. Although 15% of the asymptomatic population exhibits a deformity, it is not clear who will develop symptoms. Current diagnostic imaging measures have either low specificity or low sensitivity and do not consider the dynamic nature of impingement during daily activities. The goal of this study is to determine stresses in the cartilage, subchondral bone and labrum of normal and impinging hips during activities such as walking and sitting down. Quantitative CT scans were obtained of a healthy Control and a participant with a symptomatic femoral cam deformity (‘Bump’). 3D models of the hip were created from automatic segmentation of CT scans. Cartilage layers were added so the articular surface was the mid-line of the joint. Finite element meshes were generated in each region. Bone elastic modulus was assigned element-by-element, calculated from CT intensity converted to bone mineral density using a calibration phantom. Cartilage was modelled as poroelastic, E=0.467 MPa, v=0.167, and permeability 3×10. -16. m. 4. /N s. The pelvis was fixed while rotations and contact forces from Bergmann et al. (2001) were applied to the femur over one load cycle for walking and sitting in a chair. All analyses were performed in FEBio. High shear stresses were seen near the acetabular cartilage-labrum junction in the Bump model, up to 0.12 MPa for walking and were much higher than in the Control. Patient-specific modelling can be used to assess contact and tissue stresses during different activities to better understand the risk of degeneration in individuals, especially for activities that involve high hip flexion. The high stresses at the cartilage labrum interface could explain so-called bucket-handle tears of the labrum

Hip Osteoarthritis (HOA) is the most common joint disorder and a major cause of disability in the adult population, leading to total hip replacement (THR). Recently, evidence has mounted for a prominent etiologic role of femoroacetabular impingement (FAI) in the development of early OA in the non-dysplastic hip. FAI is a pathological mechanical process, caused by abnormalities of the acetabulum and/or femur leading to damage the soft tissue structures. FAI can determine chondro-labral damage and groin pain in young adults and can accelerate HOA progression in middle-aged adults. The aim of the study was to determine if the presence of calcium crystal in synovial fluid (SF) at the time of FAI surgery affects the clinical outcomes to be used as diagnostic and predictive biomarker. 49 patients with FAI undergoing arthroscopy were enrolled after providing informed consent; 37 SFs were collected by arthrocentesis at the time of surgery and 35 analyzed (66% males), median age 35 years with standard deviation (SD) 9.7 and body mass index (BMI) 23.4 kg/m. 2. ; e SD 3. At the time of surgery, chondral pathology using the Outerbridge score, labral pathology and macroscopic synovial pathology based on direct arthroscopic visualization were evaluated. Physical examination and clinical assessment using the Hip disability & Osteoarthritis Outcome Score (HOOS) were performed at the time of surgery and at 6 months of follow up. As positive controls of OA signs, SF samples were also collected from cohort of 15 patients with HOA undergoing THR and 12 were analysed. 45% FAI patients showed CAM deformity; 88% presented labral lesion or instability and 68% radiographic labral calcification. 4 patients out of 35 showed moderate radiographic signs of OA (Kellegren-Lawrence score = 3). Pre-operative HOOS median value was 61.3% (68.10-40.03) with interquartile range (IQR) of 75-25% and post-operative HOOS median value 90% with IQR 93.8-80.60. In both FAI and OA patients the calcium crystal level in SFs negatively correlated with glycosaminoglycan (component of the extracellular matrix) released, which is a marker of cartilage damage (Spearman rho=-0.601, p<0.001). In FAI patients a worst articular function after surgery, measured with the HOOS questionnaire, was associated with both acetabular and femoral chondropathy and degenerative labral lesion. Moreover, radiographic labral calcification was also significantly associated with pain, worst articular function and labral lesion. Calcium crystal level in SFs was associated with labral lesions and OA signs. We concluded that the levels of calcium crystals in FAI patients are correlated with joint damage, OA signs and worst post-operative outcome. The presence of calcium crystals in SF of FAI patients might be a potential new biomarker that might help clinicians to make an early diagnosis, evaluate disease progression and monitor treatment response

Recently, femoroacetabular impingement has been recognised as a cause of early osteoarthritis. There are two mechanisms of impingement: 1) cam impingement caused by a non-spherical head and 2) pincer impingement caused by excessive acetabular cover. We hypothesised that both mechanisms result in different patterns of articular damage. Of 302 analysed hips only 26 had an isolated cam and 16 an isolated pincer impingement. Cam impingement caused damage to the anterosuperior acetabular cartilage with separation between the labrum and cartilage. During flexion, the cartilage was sheared off the bone by the non-spherical femoral head while the labrum remained untouched. In pincer impingement, the cartilage damage was located circumferentially and included only a narrow strip. During movement the labrum is crushed between the acetabular rim and the femoral neck causing degeneration and ossification. Both cam and pincer impingement lead to osteoarthritis of the hip. Labral damage indicates ongoing impingement and rarely occurs alone

Osteochondroplasty procedure for cam deformity provides excellent outcomes on alleviating pain, improving quality of life and clinical function in femoroacetabular impingement syndrome (FAIS) patients. Although medium-term outcomes on gait biomechanics have been reported, it is unclear how it would translate to better hip muscle forces and joint loading in high range of motion tasks. The purpose of this study was to compare the muscle forces and hip joint contact forces (HCF) during a squat task in individuals before and after cam-FAIS surgical correction. Ten cam-FAIS patients prior and 2-years after osteochondroplasty, and 10 BMI- age- and sex-matched healthy control participants (CTRL) underwent 3D motion and ground reaction forces capture while performing a deep squatting task. Muscle and HCF were estimated using musculoskeletal modeling and comparisons were done using statistical parametric mapping (SPM). Postoperatives squatted down with a higher anterior pelvic tilt and higher hip flexion compared with the preoperatives. Preoperative semimembranosus generated lower forces than the two other groups on the squat ascending, with no differences detected between post-ops and CTRLs. Preoperatives also showed reduced forces for the distal, ischial and medial portions of the adductor magnus relative to the CTRLs, which although reduced, still presented differences postoperatively. Preoperative anterior and medial contact forces were significantly lower than the CTRL group during both phases of the squat. Postoperative vertical and medial forces were also lower compared to the CTRLs. However, with higher vertical forces during the ascent phase of the squat compared to the preoperative, the postoperative group, significantly increased its HCF magnitude. A higher anterior pelvic tilt was associated with an innate restoration of the pelvis position, once the cam deformity no longer existed. The increased force of the semimembranosus muscle while ascending the squat generated higher vertical HCF, which also influenced the increased HCF total magnitude. For any tables or figures, please contact the authors directly

The literature indicates that femoroacetabular impingement (FAI) patients do not return to the level of controls (CTRL) following surgery. The purpose of this study was to compare hip biomechanics during stair climbing tasks in FAI patients before and two years after undergoing corrective surgery against healthy controls (CTRL). A total of 27 participants were included in this study. All participants underwent CT imaging at the local hospital, followed by three-dimensional motion analysis done at the human motion biomechanics laboratory at the local university. Participants who presented a cam deformity >50.5° in the oblique-axial or >60° in the radial planes, respectively, and who had a positive impingement test were placed in the FAI group (n=11, age=34.1±7.4 years, BMI=25.4±2.7 kg/m2). The remaining participants had no cam deformity and negative impingement test and were placed in the CTRL group (n=16, age=33.2±6.4 years, BMI=26.3±3.2 kg/m2). The CTRL group completed the biomechanics protocol once, whereas the FAI group completed the protocol twice, once prior to undergoing corrective surgery for the cam FAI, and the second time at approximately two years following surgery. At the human motion biomechanics laboratory, participants were outfitted with 45 retroreflective markers placed according to the UOMAM marker set. Participants completed five trials of stairs task on a three step instrumented stair case to measure ground reaction forces while 10 Vicon MX-13 cameras recorded the marker trajectories. Data was processed using Nexus software and divided into stair ascent and stair descent tasks. The trials were imported into custom written MatLab software to extract peak pelvis and hip kinematics and hip kinetic variables. Non-parametric Kruskal-Wallis tests were used to determine significant (p < 0.05) differences between the groups. No significant differences occurred during the stair descent task between any of the groups. During the stair ascent task, the CTRL group had significantly greater peak hip flexion angle (Pre-Op=58±7.1°, Post-Op=58.1±6.6°, CTRL=64.1±5.1°) and sagittal hip range of motion (ROM) (Pre-Op=56.7±6.7°, Post-Op=56.3±5.5°, CTRL=61.7±4.2°) than both the pre- and post-operative groups. Pre-operatively, the FAI group had significantly less peak hip adduction angle (Pre-Op=2±4.5°, Post-Op=3.4±4.4°, CTRL=5.5±3.7°) and hip frontal ROM (Pre-Op=9.9±3.4°, Post-Op=11.9±5.4°, CTRL=13.4±2.5°) compared to the CTRL group. No significant differences occurred in the kinetic variables. Our findings are in line with the Rylander and colleagues (2013) who also found that hip sagittal ROM did not improve following corrective surgery. Their study included a mix of cam and pincer-type FAI, and had a mean follow-up of approximately one year. Our cohort included only cam FAI and they had a mean follow-up of approximately two years, indicating with the extra year, the patients still did not show sagittal hip kinematics improvement. In the frontal plane, there was no significant difference between the post-op and the CTRL, indicating that the postoperative FAI reached the level of the CTRLs. This is in line with recent work that indicates a more medialized hip contact force vector following surgery, suggesting better hip stabilization

With the growing number of individuals with asymptomatic cam-type deformities, elevated alpha angles alone do not always explain clinical signs of femoroacetabular impingement (FAI). Differences in additional anatomical parameters may affect hip joint mechanics, altering the pathomechanical process resulting in symptomatic FAI. The purpose was to examine the association between anatomical hip joint parameters and kinematics and kinetics variables, during level walking. Fifty participants (m = 46, f = 4; age = 34 ± 7 years; BMI = 26 ± 4 kg/m²) underwent CT imaging and were diagnosed as either: symptomatic (15), if they showed a cam deformity and clinical signs; asymptomatic (19), if they showed a cam deformity, but no clinical signs; or control (16), if they showed no cam deformity and no clinical signs. Each participant's CT data was measured for: axial and radial alpha angles, femoral head-neck offset, femoral neck-shaft angle, medial proximal femoral angle, femoral torsion, acetabular version, and centre-edge angle. Participants performed level walking trials, which were recorded using a ten-camera motion capture system (Vicon MX-13, Oxford, UK) and two force plates (Bertec FP4060–08, Columbus, OH, USA). Peak sagittal and frontal hip joint angles, range of motion, and moments were calculated using a custom programming script (MATLAB R2015b, Natick, MA, USA). A one-way, between groups ANOVA examined differences among kinematics and kinetics variables (α = 0.05), using statistics software (IBM SPSS v.23, Armonk, NY, USA); while a stepwise multiple regression analysis examined associations between anatomical parameters and kinematics and kinetics variables. No significant differences in kinematics were observed between groups. The symptomatic group demonstrated lower peak hip abduction moments (0.12 ± 0.08 Nm/kg) than the control group (0.22 ± 0.10 Nm/kg, p = 0.01). Sagittal hip range of motion showed a moderate, negative correlation with radial alpha angle (r = −0.33, p = 0.02), while peak hip abduction moment correlated with femoral neck-shaft angle (r = 0.36, p = 0.009) and negatively with femoral torsion (r = −0.36, p = 0.009). With peak hip abduction moment in the stepwise regression analysis, femoral torsion accounted for a variance of 13.3% (F(1, 48) = 7.38; p = 0.009), while together with femoral neck-shaft angle accounted for a total variance of 20.4% (R² change = 0.07, F(2, 47) = 6.01; p = 0.047). Although elevated radial alpha angles may have limited sagittal range of motion, the cam deformity parameters did not affect joint moments. Femoral neck-shaft angle and femoral torsion were significantly associated with peak hip abduction moment, suggesting that the insertion location of the abductor affects muscle's length and its resultant force vector. A varus neck angle, combined with severe femoral torsion, may ultimately influence muscle moment arms and hip mechanics in individuals with cam FAI

Abstract. Objectives. Outcomes following different types of surgical intervention for FAI are well reported individually but comparative data is deficient. The purpose of this study was to conduct a systematic review (SR) and meta-analysis to analyse the outcomes following surgical management of FAI by hip arthroscopy (HA), anterior mini open approach (AMO) and surgical hip dislocation (SHD). Methods. This SR was registered with PROSPERO. An electronic database search of Pubmed, Medline and EMBASE for English and German language articles over the last 20 years was carried out according to the PRISMA guidelines. We specifically analysed and compared changes in patient reported outcome measures PROMs, α-angle, rate of complications, rate of revision and conversion to total hip arthroplasty (THA). Results. A total of 48 articles included for final analysis with a total of 4384 hips in 4094 patients. All subgroups showed a significant correction in mean alpha angle post-operatively with a mean change of 28.8° (95% CI, 21°-36.5°; p <0.01) after AMO, 21.1° (95% CI, 15.1°-27°; p <0.01) after SHD and 20.39° (95% CI, 15.66°-25.12°; p <0.01) after HA. AMO group showed a significantly higher increase in PROMs (3.7; 95% CI, 3.2–4.2; p <0.01) versus arthroscopy (2.47; 95% CI, 2.22–2.73; p <0.01) and SHD (2.4; 95% CI, 1.5–3.3; p <0.01). However, the rate of complications following AMO was significantly higher than HA and SHD. Conclusion. All three surgical approaches offered significant improvements in outcomes and radiological correction of cam deformities. All three groups showed similar rates of revision procedures and SHD had the highest rate of conversion to a THA. Revision rates was similar for all three revision procedures

Abstract. Introduction. Recent reports show that spinopelvic mobility influences outcome following total hip arthroplasty. This scoping review investigates the relationship between spinopelvic parameters (SPPs) and symptomatic femoroacetabular impingement (FAI). Methods. A systematic search of EMBASE, PubMed and Cochrane for literature related to SPPs and FAI was undertaken as per PRISMA guidelines. Clinical outcome studies and prospective/retrospective studies investigating the role of SPPs in symptomatic FAI were included. Review articles, case reports and book chapters were excluded. Information extracted pertained to symptomatic cam deformities, pelvic tilt, acetabular version, biomechanics of dynamic movements and radiological FAI signs. Results. The search identified 42 papers for final analysis out of 1168 articles investigating the link between SPPs and pathological processes characteristic of FAI. Only one (2.4%) study was of level 1 evidence, five (11.9%) studies) were level 2, 17 (40.5%) were level 3 and 19 (45.2%) were level 4. Three studies associated FAI pathology with a greater pelvic incidence (PI), while four associated it with a smaller PI. Anterior pelvic tilt was associated with radiographic overcoverage parameters of FAI. In dynamic movements, decreased posterior pelvic tilt was a common feature in symptomatic FAI patients at increased hip flexion angles. FAI patients additionally demonstrated reduced sagittal pelvic ROM during dynamic hip flexion. Six studies found kinematic links between sagittal spinopelvic movement and sagittal and transverse plane hip movements. Conclusions. Our study shows that spinopelvic parameters can influence radiological and clinical manifestations of FAI, with pelvic incidence, acetabular version and muscular imbalances being aetiologically implicated. These factors may be amenable to non-surgical therapy. Individual spinopelvic mechanics may predispose to the development of FAI. If FAI pathoanatomy already exists, sagittal pelvic parameters can influence whether FAI symptoms develop and is an area of further research interest

Introduction and Objective. Slipped Capital Femoral Epiphysis (SCFE) is one of the most common hip disorders in children and is characterized by a proximal femoral deformity, resulting in early osteoarthritis. Several studies have suggested that SCFE patients after in situ fixation show an altered gait pattern. Early identification of gait alterations might lead to earlier intervention programs to prevent osteoarthritis. The aim of this study is to analyse gait alterations in SCFE patients after in situ fixation compared to typically developed children, using the Computer Assisted Rehabilitation Environment (CAREN) system. Materials and Methods. This is a cross-sectional, multi-center case-control study in the Netherlands. Eight SCFE patients and eight age- and sex-matched typically developed were included from two hospitals. Primary outcomes were kinematic parameters (absolute joint angles), studied with gait analysis using statistical parametric mapping (SPM). Secondary outcomes were spatiotemporal parameters, the Notzli alpha angle, muscle activation patterns (EMG), and clinical questionnaires (VAS, Borg CR10, SF-36, and HOOS), analyzed using non-parametric statistical methods. Results. Patients (mean BMI=28±9 kg/m. 2. ) showed altered gait patterns, with significantly increased external hip rotation and decreased downward pelvic obliquity during the pre-swing phase of the gait cycle compared to typically developed (mean BMI=22±3 kg/m. 2. ). Walking speed, cadence, % stance time, and step length were reduced in SCFE patients. Coefficient of variances of cadence, stance time, and step length were increased. Patients had a mean alpha angle of 64, SD=7.9. Clinical questionnaires showed that general health (SF-36) was 80±25, energy/fatigue (SF-36) was 67±15, pain (VAS) was 0±1.5, and total HOOS score was 85±18. Conclusions. SCFE patients after in situ fixation appear to have developed a compensation mechanism, showing slight alterations in gait parameters, good general health, little functional limitations of the hip, and no self-reported pain. Cam deformities, altered joint loading, and this compensation mechanism might influence long-term early osteoarthritis. BMI reduction should be implemented in care plans, as obesity might also play a role in unfavorable long-term outcomes

Summary. The cartilage layer from cam-type femoroacetabular impingement deformities had lower stiffness and increased permeability compared to normal cartilage. This is consistent with osteoarthritis and supports the hypothesis of abnormal contact stresses. Introduction. Femoroacetabular impingement (FAI) has recently been associated with osteoarthritic (OA) degeneration of the hip and may be responsible for up to 90% of adult idiopathic OA cases. FAI results from deformities in the hip joint which may lead to abnormal contact stresses and degeneration. The more common cam-type deformity consists of a convex anterior femoral head-neck junction which impinges the anterosuperior acetabular rim during flexion and internal rotation of the hip. Increased subchondral bone density has been reported in this region which may be a bone remodelling response to increased contact stress. The abnormal contact is expected to cause degeneration of the cartilage layer. The goal of this study was to assess the mechanical properties of cartilage retrieved from the cam deformity and to compare this with normal articular cartilage from the femoral head. It is hypothesised that the cartilage will have a lower elastic modulus and higher permeability than normal cartilage. Patients & Methods. Osteochondral biopsies were retrieved from nine patients undergoing surgical correction of a symptomatic cam deformity as well as 10 fresh cadaveric specimens (10 hips, 6 donors). An indentation stress relaxation test was performed on each specimen to 10% of the estimated cartilage thickness. A needle penetration test was performed to accurately measure the thickness. The equilibrium modulus was calculated per Hayes et al. A specimen-specific axisymmetric finite element model was used in a non-linear optimization to obtain the fibril-reinforced poroelastic properties of the cartilage that best fit the experimental data. The material properties were non-fibrillar modulus (E. s. ), Poisson's ratio (ν. s. ) and permeability (k) and strain-independent and –dependent moduli (E. 0. , E. ε. )[4]. Results. The equilibrium modulus was 0.14 MPa and 0.63 from surgical and cadaver specimens, respectively (p=0.002). Compared to cadaver specimens, E. s. in surgical specimens was 73% lower (p=0.01), ν. s. was 43% lower (p=0.01) and k was an order of magnitude higher (p=0.02). Fibril moduli were not significantly different (p>0.35). Discussion/Conclusions. This study showed decreased elastic modulus and increased permeability in cartilage from cam deformities compared to cadaver controls. These differences are consistent with changes expected in osteoarthritic cartilage degeneration. Fibril moduli were 14% to 57% lower in surgical specimens consistent with fibrillation, however results were not significant due to high variability. Altered cellular activity and proteoglycan depletion has been reported in cartilage of cam deformities, which are similar to changes expected in osteoarthritis. The altered mechanical and biochemical properties of this cartilage therefore support the hypothesis that osteoarthritis is secondary to cam FAI deformities and is a result of abnormal contact stresses between the deformity and acetabular rim

Hip joint preservation remains a preferred treatment option for hips with mechanically correctable pathologies prior to the development of significant secondary arthrosis. The pathologies most amenable to joint preservation are hip dysplasia and femoroacetabular impingement. These pathologies sometimes overlap. Untreated acetabular dysplasia of modest severity always leads to arthrosis if uncorrected. Acetabular dysplasia is best treated by periacetabular osteotomy, usually combined with arthrotomy for management of labral pathology and associated cam-impingement if present. Pre-operative variables associated with the best long-term outcomes include less secondary arthrosis, younger age, and concentric articular surfaces. The earlier PAO series show 20 year survivorship of 81% and 65% in Tonnis Grade 0 and 1 hips. Femoroacetabular impingement has become progressively recognised as perhaps the most common cause of secondary arthrosis. The etiology of impingement is multifactorial and includes both genetic factors and stresses experienced by the hip prior to cessation of growth. Cam impingement can be quantified by the alpha angle as measured on plain radiographs and radial MR sequences. Cam impingement can be treated by arthroscopic or open femoral head-neck osteochondroplasty. As with hip dysplasia, prognosis following treatment is correlated with the severity of pre-operative secondary arthrosis but unfortunately impinging hips more commonly have some degree of arthrosis pre-operatively whereas dysplastic hips can become symptomatic with instability in the absence of arthrosis. The scientific basis for the treatment of pincer impingement is less strong. Unlike cam impingement and hip dysplasia, pincer impingement pathology in the absence of coxa profunda has not been correlated with arthrosis and so rim trimming with labral refixation is probably performed more often than is clinically indicated. Overall, joint preserving surgery remains the preferred treatment for hips with mechanically correctable problems prior to the development of significant secondary arthrosis

Chondral hip injuries are common secondary to femoroacetabular impingement (FAI). Treatment with arthroscopic procedures including chondroplasty and microfracture is becoming increasingly common but literature is limited to case series at specialist centres. The aim of this study is to compare outcomes of arthroscopic acetabular chondral procedures using the NAHR dataset (UK) which represents the largest series to date. All adult Arthroscopies recorded in the NAHR from Jan 2012 were available for inclusion. Exclusions included significant arthritis and femoral, complex or revision chondral procedures. Patients completed iHOT-12 & EQ-5D Index pre-operatively, 6 and 12 months. Data was analysed using T-test/ANOVA for between group/within group for continuous variables, chi square test for categorical variables and linear regression model for multivariable analysis. 5,752 patients, 60% female. 27% Chondroplasty, 5% Microfracture, 68% no Chondral Procedure. Maximum acetabular Outerbridge classification 14% Grade 1, 15% Grade 2, 17% Grade 3, 8% Grade 4, 9% no damage, not recorded in 37%. Higher proportion of Cam impingement in association with chondral treatments and a larger proportion of patients with no impingement recorded in group with no chondral procedures. There was a significant improvement versus baseline for all groups in iHOT-12 and EQ-5D Index (p<0.0001) including Grade four Outerbridge. There was significantly greater improvement in pre-operative scores in the chondroplasty group compared to the microfracture group at 6 and 12 months (p<0.05). Following hip arthroscopy, patients with chondral procedures experienced improved outcome scores despite Outerbridge 4 chondral damage. Presence of cam lesions are more commonly associated with chondral treatments. Good outcomes were maintained up to 12 months for chondral procedures, regardless of age or impingement pathology however pincers improved less and patients over 40 years took longer to see improvement

Hip joint preservation remains a preferred treatment option for hips with mechanically correctable pathologies prior to the development of significant secondary arthrosis. The pathologies most amenable to joint preservation are hip dysplasia and femoroacetabular impingement. These pathologies sometimes overlap. Untreated acetabular dysplasia of modest severity always leads to arthrosis if uncorrected. Acetabular dysplasia is best treated by periacetabular osteotomy, usually combined with arthrotomy for management of labral pathology and associated cam-impingement if present. Preoperative variables associated with the best long-term outcomes include less secondary arthrosis, younger age, and concentric articular surfaces. Femoroacetabular impingement has become progressively recognised as perhaps the most common cause of secondary arthrosis. The etiology of impingement is multifactorial and includes both genetic factors and stresses experienced by the hip prior to cessation of growth. Cam impingement can be quantified by the alpha angle as measured on plain radiographs and radial MR sequences. Cam impingement can be treated by arthroscopic or open femoral head-neck osteochondroplasty. As with hip dysplasia, prognosis following treatment is correlated with the severity of preoperative secondary arthrosis but unfortunately impinging hips more commonly have some degree of arthrosis preop whereas dysplastic hips can become symptomic with instability in the absence of arthrosis. The scientific basis for the treatment of pincer impingement is less strong. Unlike cam impingement and hip dysplasia, pincer impingement pathology in the absence of coxa profunda has not been correlated with arthrosis and so rim trimming with labral refixation is probably performed more often than is clinically indicated. Overall, joint preserving surgery remains the preferred treatment for hips with mechanically correctible problems prior to the development of significant secondary arthrosis

Introduction. Acetabular and spino-pelvic (SP) morphological parameters are important determinants of hip joint dynamics. This study aims to determine whether acetabular and SP morphological differences exist between hips with and without cam morphology and between symptomatic and asymptomatic hips with cam morphology. Patients/Materials & Methods. A prospective cohort of 67 patients/hips was studied. Hips were either asymptomatic with no cam (Controls, n=18), symptomatic with cam (n=26) or asymptomatic with cam (n=23). CT-based quantitative assessments of femoral, acetabular, pelvic and spino-pelvic parameters were performed. Measurements were compared between controls and those with a cam deformity, as well as between the 3 groups. Morphological parameters that were independent predictors of a symptomatic Cam were determined using a regression analysis. Results. Hips with cam deformity had slightly smaller subtended angles superior-anteriorly (87° Vs 84°, p=0.04) and greater pelvic incidence (53° Vs 48°, p=0.003) compared to controls. Symptomatic Cams had greater acetabular version (p<0.01), greater subtended angles superiorly and superior-posteriorly (p=0.01), higher pelvic incidence (p=0.02), greater alpha angles and lower femoral neck-shaft angles compared to asymptomatic cams (p<0.01) and controls (p<0.01). The four predictors of symptomatic cam included antero-superior alpha angle, femoral neck-shaft angle, acetabular depth and pelvic incidence. Discussion. Symptomatic hips had a greater amount of supero-posterior coverage; which would be the contact area between a radial cam and the acetabulum, when the hip is flexed to 90°. Furthermore, individuals with symptomatic cam morphology had greater PI. Acetabular- and SP parameters should be part of the radiological assessment of femoro-acetabular impingement. Conclusion. Because of the association between a high PI and an increased risk of hip OA (also shown to be increased with c-FAI), the relationship between the PI and FAI should be taken into consideration in prospective longitudinal studies looking at factors influencing the formation of cam morphology as well as those at risk of developing symptoms and degenerative changes

Hip joint preservation remains a preferred treatment option for hips with mechanically correctable pathologies prior to the development of significant secondary arthrosis. The pathologies most amenable to joint preservation are hip dysplasia and femoroacetabular impingement. These pathologies sometimes overlap. Untreated acetabular dysplasia of modest severity, if left uncorrected, always leads to arthrosis. Acetabular dysplasia is best treated by periacetabular osteotomy, usually combined with arthrotomy for management of labral pathology and associated cam-impingement if present. Pre-operative variables associated with the best long-term outcomes include less secondary arthrosis, younger age, and concentric articular surfaces. Femoroacetabular impingement has become progressively recognised as perhaps the most common cause of secondary arthrosis. The etiology of impingement is multifactorial and includes both genetic factors and stresses experienced by the hip prior to cessation of growth. Cam impingement can be quantified by the alpha angle as measured on plain radiographs and radial MR sequences. Further, significant cam impingement is clearly associated with the development of osteoarthrosis. Treatment can be performed either by arthroscopic or open femoral head-neck osteochondroplasty. As with hip dysplasia, prognosis following treatment is correlated with the severity of preoperative secondary arthrosis but unfortunately impinging hips more commonly have some degree of arthrosis preop whereas dysplastic hips can become symptomatic with instability in the absence of arthrosis. The scientific basis for the treatment of pincer impingement is less strong. Unlike cam impingement and hip dysplasia, pincer impingement pathology in the absence of coxa profunda has not been correlated with arthrosis and so rim trimming with labral refixation is probably performed more often than is clinically indicated. Similarly, caution should be exercised when considering rim-trimming for protrusion since high central contact pressures due to an enlarged acetabular notch are not corrected by rim trimming. Overall, joint preserving surgery remains the preferred treatment for hips with mechanically correctable problems prior to the development of significant secondary arthrosis

Surgical invention to preserve the native hip joint remains a preferred treatment option for hips in young patients with mechanically correctable pathologies prior to the development of significant secondary arthrosis. The two most common pathologies most amenable to joint preservation are hip dysplasia and femoroacetabular impingement. These pathologies sometimes overlap. Untreated acetabular dysplasia of modest severity, if left uncorrected, always leads to arthrosis. Acetabular dysplasia is best treated by periacetabular osteotomy, usually combined with arthrotomy for management of labral pathology and associated cam-impingement, if present. Correction of deformities on the femoral side is now less common and reserved for only the more severe combined femoral and acetabular dysplasias or the rare isolated femoral dysplasia. Pre-operative variables associated with the best long-term outcomes include less secondary arthrosis, younger age, and concentric articular surfaces. Femoroacetabular impingement has become progressively recognised as perhaps the most common cause of secondary arthrosis. The etiology of impingement is multifactorial and includes both genetic factors and stresses experienced by the hip prior to cessation of growth. Cam impingement can be quantified by the alpha angle as measured on plain radiographs and radial MR sequences. Further, significant cam impingement is clearly associated with the development of osteoarthrosis. Treatment can be performed either by arthroscopic or open femoral head-neck osteochondroplasty. As with hip dysplasia, prognosis following treatment is correlated with the severity of pre-operative secondary arthrosis but unfortunately impinging hips more commonly have some degree of arthrosis pre-op whereas dysplastic hips can become symptomatic with the onset of instability in the absence of significant secondary arthrosis. The scientific basis for the treatment of pincer impingement is less strong. Unlike cam impingement and hip dysplasia, pincer impingement pathology in the absence of coxa profunda has not been correlated with arthrosis and so rim trimming with labral refixation is probably performed more often than is clinically indicated. Similarly, caution should be exercised when considering rim-trimming for protrusion since high central contact pressures due to an enlarged acetabular notch are not corrected by rim trimming. Overall, joint preserving surgery remains the preferred treatment for hips with mechanically correctable problems prior to the development of significant secondary arthrosis

Abstract. OBJECTIVES. Cam femoroacetabular impingement (FAI – femoral head-neck deformity) and developmental dysplasia of the hip (DDH – insufficient acetabular coverage) constitute a large portion of adverse hip loading and early degeneration. Spinopelvic anatomy may play a role in hip stability thus we examined which anatomical relationships can best predict range of motion (ROM). METHODS. Twenty-four cadaveric hips with cam FAI or DDH (12:12) were CT imaged and measured for multiple femoral (alpha angles, head-neck offset, neck angles, version), acetabular (centre-edge angle, inclination, version), and spinopelvic features (pelvic incidence). The hips were denuded to the capsule and mounted onto a robotic tester. The robot positioned each hip in multiple flexion angles (Extension, Neutral 0°, Flexion 30°, Flexion 60°, Flexion 90°); and performed internal-external rotations to 5 Nm in each position. Independent t-tests compared the anatomical parameters and ROM between FAI and DDH (CI = 95%). Multiple linear regressions determined which anatomical parameters could predict ROM. RESULTS. The FAI group demonstrated restricted ROM in deep hip flexion, with DDH showing higher ROM in Flexion 30° (+20%, p = 0.03), 60° (+31%, p = 0.001), and 90° (+36%, p = 0.001). In Neutral 0° and Flexion 30°, femoral neck and version angles together predicted ROM (R. 2. = 60%, 58% respectively); whereas in Flexion 60°, pelvic incidence and femoral neck angle predicted ROM (R. 2. = 77%). In Flexion 90°, pelvic incidence and radial alpha angle together predicted ROM (R. 2. = 81%), where pelvic incidence alone accounted for 63% of this variance. CONCLUSIONS. Pelvic incidence is essential to predict hip ROM. Although a cam deformity or acetabular undercoverage can elevate risks of labral tears and progressive joint degeneration, they may not be primary indicators of restrictive hip impingement or dysplastic instability. Better delineating additional spinopelvic characteristics can formulate early diagnostic tools and improve opportunities for nonsurgical management. Declaration of Interest. (b) declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research reported:I declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research project

In Japan, osteoarthritis (OA) of the hip secondary to acetabular dysplasia is very common, and there are few data concerning the pathogeneses and incidence of femoroacetabular impingement (FAI). We have attempted to clarify the radiological prevalence of painful FAI in a cohort of Japanese patients and to investigate the radiological findings. We identified 176 symptomatic patients (202 hips) with Tönnis grade 0 or 1 osteoarthritis, whom we prospectively studied between August 2011 and July 2012. There were 61 men (65 hips) and 115 women (137 hips) with a mean age of 51.8 years (11 to 83). Radiological analyses included the α-angle, centre–edge angle, cross-over sign, pistol grip deformity and femoral head neck ratio. Of the 202 hips, 79 (39.1%) had acetabular dysplasia, while 80 hips (39.6%) had no known aetiology. We found evidence of FAI in 60 hips (29.7%). Radiological FAI findings associated with cam deformity were the most common. There was a significant relationship between the pistol grip deformity and both the α-angle (p < 0.001) and femoral head–neck ratio (p = 0.024). Radiological evidence of symptomatic FAI was not uncommon in these Japanese patients. Cite this article: Bone Joint J 2013;96-B:172–6

Introduction. Bony deformities in the hip that cause femoroacetabular impingement (FAI) can be resected in order to delay the onset of osteoarthritis and improve hip range of motion. However, achieving accurate osteoplasty arthroscopically is challenging because the narrow hip joint capsule limits field of view. Recently, image-based navigation using a preoperative plan has been shown to improve the accuracy of femoral bone surfaces following arthroscopic osteoplasty for FAI. The current standard for intraoperative monitoring, 3D x-ray fluoroscopy, is accurate at the initial registration step to within 0.8±0.5mm but involves radiation. Intraoperative 3D ultrasound (US) is a promising radiation-free alternative for providing real-time visual feedback during FAI osteoplasty. The objective was to determine if intraoperative 3D US of the femoral head/neck region can be registered to a CT-based preoperative plan with comparable accuracy to fluoroscopic navigation in order to visualise progress during arthroscopic FAI osteoplasty. Methods. The experiment used a plastic femur model that had a cam deformity on the femoral head/neck. Thirty metal fiducial markers were placed on the US-accessible anterior and lateral surfaces of the femur. A CT image was acquired and reconstructed, then used to develop a preoperative plan for resection of the cam deformity. Twenty-two sets of 3D US data were then gathered from the phantom using a clinical ultrasound machine and 3D transducer while the phantom was submerged in water. US surfaces from the anterior/lateral regions of the femur were extracted using a recently proposed image processing algorithm. Fiducials in the US volume were manually registered to corresponding CT fiducials to provide a reference standard registration. The reference standard fiducial registration error (FRE) was measured as the average distance between corresponding fiducials. After fiducial-based registration, each US surface was randomly misaligned and re-registered using a coherent point-drift algorithm. The resulting surface registration error (SRE) was measured using average distance between US and CT surfaces. Finally, a plastic model of the preoperative cam deformity resection plan was 3D-printed to represent the postoperative femur. Five US scans were acquired of the postoperative model near the femoral head/neck. Each US scan was initialised for 20 trials using three reference points, and then registered using coherent point drift. Surgical outcome accuracy was reported using final surface registration error (fSRE). Results. The reference standard FRE was 0.41±0.19mm. The distance between surfaces following misalignment and re-registration for all 2200 automated registration trials was similarly small (SRE = 0.31±0.04mm) and well below the required clinical limit. Lastly, the postoperative model was accurately registered to corresponding US scans (fSRE = 0.58±0.07mm). Qualitative visualisation showed good surface matching following US to CT registration. Conclusion. Initial registration between intraoperative 3D US and preoperative CT is critical for accurate visualisation of surgical progress during FAI osteoplasty. Given spatial initialisation, the achievable registration accuracy of 3D US to CT is 0.31±0.04mm (SRE) which is well within the fluoroscopy standard, 0.8±0.5mm. The results suggest strong potential for ultrasound to guide computer-assisted arthroscopic FAI osteoplasty

Introduction: Subtle deformity of the hip joint may cause osteoarthritis. In femoroacetabular impingement (FAI), cam deformities damage acetabular cartilage. Whether surgical removal of cam lesions halts progression is unknown. Sensitive, non-invasive assays of chondral damage are required to evaluate early treatment efficacy. Delayed gadolinium-enhanced MRI of cartilage (dGEMRIC) permits inference of glycosaminoglycan (GAG) distribution. We aimed to determine whether hips with cam deformities have altered GAG content, using dGEMRIC. Methods: Subjects were recruited from a prospective cohort study. All were clinically and radiographically assessed. Hips with a normal joint space width (> 2.5mm) were eligible for dGEMRIC. 32 Hips (18 male, 14 female, mean age 51.7 years, none of whom had been investigated for hip pain) with (n=21) and without (n=11) cam deformities were scanned. 2 regions of interest (ROI) were studied:. acetabular cartilage from 12 to 3 O’Clock (T1-Index-acet). total cartilage (femoral and acetabular) for the joint from 9 to 3 O’Clock (T1-Indextotal). The average of all pixels within the given ROI defined the T1-index. For each hip, the ratio of the GAG content T1-Index-acet/T1-Indextotal was calculated. Mean T1-Indexto-tal and T1-Indexacet/T1-Indextotal were compared. Results: T1-Indextotal were similar (689ms v 700ms, p=0.79) but T1-Indexacet/T1-Indextotal was lower in cam hips (0.93 v 1.01, p=0.017), indicating localised depletion of GAG content. Cam hips with positive clinical signs had lower T1-Indextotal than cam hips without (629ms v 717ms, p=0.055), and non-cam hips (629ms v 722ms, p=0.049). Discussion: Cam hips have lower GAG content of their anterosuperior acetabular cartilage. dGEMRIC identified more generalised disease in cases with positive clinical findings. Ratios of GAG content for specific ROIs enable mapping of chondral damage. This may aid understanding of early disease mechanisms, track progression, and facilitate assessment of the efficacy of surgical procedures

Femoroacetabular impingement (FAI) has been identified as the cause of idiopathic osteoarthritis in young patients. FAI is the result of decreased femoral head/neck offset ratio due to bony deformities and causes hip pain and labral tears. Because the unique design and bone preserving nature of metal-onmetal hip resurfacing implants, it is extremely difficult to correct extensive bony deformities associated with FAI. Poor patient selection and lack of orrection/undercorrection of the underlying FAI deformity may lead to prosthetic impingement, extensive wear and metal ion release, component loosening, and subsequent implant failure. Hence, it is critical to define the patient population undergoing hip resurfacing. Because metal-on-metal hip resurfacing is performed more frequently in a younger population, we hypothesize that this patient population will have a larger proportion of femoroacetabular impingement than the general population and identification of this patient population is critical to the longevity of the implant. A retrospective review of 153 hips undergoing metal-on-metal hip resurfacing was performed. 52 hips were excluded based on the exclusion criteria of inadequate preoperative films (6 subjects), existing hardware/history of trauma (11 subjects), or if the resurfacing was performed due to avascular necrosis secondary to trauma, steroids, etc (35 subjects). The remaining 101 hips (76 male, 25 female) had an average age of 51.8 years. Preoperative x-rays were utilized to assess impingement according to previously published methods. An acetabular index (AI) of x ≤ 0°, center edge angle (CE angle) of x > 39°, a Sharp angle of x < 33°, and a present cross-over sign were considered pathologic findings for pincer impingement. Pathologic findings for cam impingement included the triangular index (TI; pathologic with R=r+2mm) and an α angle greater than 83° in men or 57° in women. Subjects were categorized as having impingement if they had one or more pathologic finding for either cam or pincer impingement and as having mixed impingement if they had one pathologic finding for both cam and pincer measurements. Prevalence rates were compared to published data for the general population. Fifty-five subjects had at least one pathologic finding for cam impingement (18, 7, and 30 subjects had pathologic measurements for α angle, TI, and both measurements, respectively); 24 subjects had at least one pathologic pincer measurement (4, 6, 14, and 4 pathologic measurements for AI, CE angle, cross-over sign, and Sharp angle, respectively; 3 subjects had multiple pincer findings) 13 subjects were classified as having mixed impingement (with α angle and cross-over sign as the most prevalent cam and pincer measurements). When compared to published data for the general population (M: 17%, F: 4%), we found a significantly larger proportion of cam impingement in both males (60.5%) and females (36%) in patients undergoing resurfacing at our institution (p< 0.001). There was also a significantly larger proportion of pincer impingement in our population (23.8%) than in the general population (10.7%) (p=0.01). There was no significant difference between our proportion of patients with mixed impingement (12.9%) and the general population (20.8%) (p=0.150). The patient population for metal-on-metal hip resurfacing shows a greater prevalance of FAI than the general population. Because the femoral head/neck junction is preserved with hip resurfacing, patients undergoing this type of procedure might be at increased risk of impingement. Hence, it is important to assess the degree of FAI preoperatively. This will allow proper patient selection and careful planning of surgical correction of the underlying FAI deformity to increase implant longevity

Femoroacetabular impingement causes pain in the hip in young adults and may predispose to the development of osteoarthritis. Genetic factors are important in the aetiology of osteoarthritis of the hip and may have a role in that of femoroacetabular impingement. We compared 96 siblings of 64 patients treated for primary impingement with a spouse control group of 77 individuals. All the subjects were screened clinically and radiologically using a standardised protocol for the presence of cam and pincer deformities and osteoarthritis. The siblings of those patients with a cam deformity had a relative risk of 2.8 of having the same deformity (66 of 160 siblings hips versus 23 of 154 control hips, p < 0.00001). The siblings of those patients with a pincer deformity had a relative risk of 2.0 of having the same deformity (43 of 116 sibling hips versus 29 of 154 control hips, p = 0.001). Bilateral deformity occurred more often in the siblings (42 of 96 siblings versus 13 of 77 control subjects, relative risk 2.6, p = 0.0002). The prevalence of clinical features in those hips with abnormal morphology was also greater in the sibling group compared with the control group (41 of 109 sibling hips versus 7 of 46 control hips, relative risk 2.5, p = 0.007). In 11 sibling hips there was grade-2 osteoarthritis according to Kellgren and Lawrence versus none in the control group (p = 0.002). Genetic influences are important in the aetiology of primary femoroacetabular impingement. This risk appears to be manifested through not only abnormal joint morphology, but also through other factors which may modulate progression of the disease

This study evaluates the outcome of arthroscopic femoral osteochondroplasty for cam lesions of the hip in the absence of additional pathology other than acetabular chondral lesions. We retrospectively reviewed 166 patients (170 hips) who were categorised according to three different grades of chondral damage. The outcome was assessed in each grade using the modified Harris Hip Score (MHHS) and the Non-Arthritic Hip Score (NAHS). Overall, at the last follow-up (mean 22 months, 12 to 72), the mean MHHS had improved by 15.3 points (95% confidence interval (CI), 8.9 to 21.7) and the mean NAHS by 15 points (95% CI, 9.4 to 20.5). Significantly better results were observed in hips with less severe chondral damage. Microfracture in limited chondral lesions showed superior results. Arthroscopic femoral osteochondroplasty for cam impingement with microfracture in selected cases is beneficial. The outcome correlates with the severity of acetabular chondral damage

Surgical management of cam-type femoroacetabular impingement (FAI) aims to preserve the native hip, restore joint function, and delay the onset of osteoarthritis. However, it is unclear how surgery affects joint mechanics and hip joint stability. The aim was to examine the contributions of each surgical stage (i.e., intact cam hip, capsulotomy, cam resection, capsular repair) towards hip joint centre of rotation and microinstability. Twelve fresh, frozen cadaveric hips (n = 12 males, age = 44 ± 9 years, BMI = 23 ± 3 kg/m2) were skeletonized to the capsule and included in this study. All hips indicated cam morphology on CT data (axial α = 63 ± 6°, radial α = 74 ± 4°) and were mounted onto a six-DOF industrial robot (TX90, Stäubli). The robot positioned each hip in four sagittal angles: 1) Extension, 2) Neutral 0°, 3) Flexion 30°, and 4) Flexion 90°, and performed internal and external hip rotations until a 5-Nm torque was reached in each direction, while recording the hip joint centre's neutral path of translation. After the (i) intact hip was tested, each hip underwent a series of surgical stages and was retested after each stage: (ii) T-capsulotomy (incised lateral iliofemoral capsular ligament), (iii) cam resection (removed morphology), and (iv) capsular repair (sutured portal incisions). Eccentricity of the hip joint centre was quantified by the microinstability index (MI = difference in rotational foci / femoral head radius). Repeated measures ANOVA and post-hoc paired t-tests compared the within-subject differences in hip joint centre and microinstability index, between the testing stages (CI = 95%, SPSS v.24, IBM). At the Extension and Neutral positions, the hip joint centre rotated concentrically after each surgical stage. At Flexion 30°, the hip joint centre shifted inferolaterally during external rotation after capsulotomy (p = 0.009), while at Flexion 90°, the hip joint centre further shifted inferolaterally during external rotation (p = 0.005) and slightly medially during internal rotation after cam resection, compared to the intact stages. Consequently, microinstability increased after the capsulotomy at Flexion 30° (MI = +0.05, p = 0.003) and substantially after cam resection at Flexion 90° (MI = +0.07, p = 0.007). Capsular repair was able to slightly restrain the rotational centre and decrease microinstability at the Flexion 30° and 90° positions (MI = −0.03 and −0.04, respectively). Hip microinstability occurred at higher amplitudes of flexion, with the cam resection providing more intracapsular volume and further lateralizing the hip joint during external rotation. Removing the cam deformity and impingement with the chondrolabral junction also medialized the hip during internal rotation, which can restore more favourable joint loading mechanics and stability. These findings support the pathomechanics of cam FAI and suggest that iatrogenic microinstability may be due to excessive motions, prior to post-operative restoration of static (capsular) and dynamic (muscle) stability. In efforts to limit microinstability, proper nonsurgical management and rehabilitation are essential, while activities that involve larger amplitudes of hip flexion and external rotation should be avoided immediately after surgery

Although the association between femoroacetabular impingement and osteoarthritis is established, it is not yet clear which hips have the greatest likelihood to progress rapidly to end-stage disease. We investigated the effect of several radiological parameters, each indicative of a structural aspect of the hip joint, on the progression of osteoarthritis. Pairs of plain anteroposterior pelvic radiographs, taken at least ten years apart, of 43 patients (43 hips) with a pistol-grip deformity of the femur and mild (Tönnis grade 1) or moderate (Tönnis grade 2) osteoarthritis were reviewed. Of the 43 hips, 28 showed evidence of progression of osteoarthritis. There was no significant difference in the prevalence of progression between hips with initial Tönnis grade 1 or grade 2 osteoarthritis (p = 0.31). Comparison of the hips with and without progression of arthritis revealed a significant difference in the mean medial proximal femoral angle (81° vs 87°, p = 0.004) and the presence of the posterior wall sign (39% vs 7%, p = 0.02) only. A logistic regression model was constructed to predict the influence of these two variables in the development of osteoarthritis. Mild to moderate osteoarthritis in hips with a pistol-grip deformity will not progress rapidly in all patients. In one-third, progression will take more than ten years to manifest, if ever. The individual geometry of the proximal femur and acetabulum partly influences this phenomenon. A hip with cam impingement is not always destined for end-stage arthritic degeneration

Several previous pathoanatomical and biomechanical studies focused primarily on the cam morphology as the primary contributor to symptoms of femoroacetabular impingement (FAI) and limited range of motion. However, there is a growing population of individuals with asymptomatic cam morphologies who show no clinical signs; thus, the cam deformity, alone, may not fully delineate an individual's symptomatology or limited motion. These studies expanded beyond the cam morphology, to determine how additional anatomical characteristics could contribute to symptoms and influence functional mobility, using: 1) in vivo analyses, where we asked how specific anatomical parameters (in addition to the cam morphology) can predict individuals at risk of symptoms; 2) In silico simulations, where we examined how pathoanatomical features contributed to adverse loading conditions, resulting in higher risks of hip joint degeneration; 3) In vitro cadaveric experiments, where we examined the contributions of the cam morphology and encapsulating ligaments to joint mechanics and microinstability. This research further highlights that more emphasis should be placed on proper patient selection. There are implications of how structural anatomy can affect musculature, joint loading and stability, which should all be closely examined to improve the effectiveness of hip preservation surgery as well as the understanding of non-surgical management

Femoroacetabular impingement recently was recognized as cause for osteoarthritis of the hip. There are two mechanism of impingement: (1) cam impingement caused by a non-spherical head, and (2) pincer impingement due to acetabular overcover. We hypothesized that both mechanism result in different articular damage patterns. Of 302 analyzed hips only 26 had an isolated cam and 16 an isolated pincer impingement. Cam impingement caused anterosuperior acetabular cartilage damage with a separation between labrum and cartilage. During flexion the cartilage is sheared off the bone by the non-spherical part of the femoral head. In pincer impingement the cartilage damage was located circumferentially, invovolving only a narrow strip along the acetabular rim. During motion the labrum is crushed between the acetabular rim and the femoral neck causing degeneration and ossification of the labrum. Cam and pincer impingement are two basic mechanism that lead to osteoarthrosis of the hip. The articular damage pattern differs substantially. Isolated cam or pincer impingement is rare, in most hips a combination is present. Labral damage indicates ongoing impingement and rarely occurs alone

Introduction: Obligatory external rotation during flexion is well recognised as a cardinal feature of Slipped Upper Femoral Epiphyses (SUFE). We have evaluated the significance of acetabular version in contributing to the external rotational deformity that is seen in otherwise normal hips. We present a small case series focussing on the characteristics of this pathology, highlighting its significance and outlining a treatment strategy. Method: Five patients (eight hips) presented with disabling hip pain during non-sporting activities. All their hip radiographs had been reported as normal. The rotational profile of both acetabulum and femur in these patients was evaluated by MRI and CT scans. Results: Clinical examination revealed otherwise normal hips but for an external rotation deformity which got worse on hip flexion. The average external rotation deformity with the hip in extension was 60 degrees, which worsened to 90 degrees during hip flexion. Three of these hips had been previously treated with in situ pinning for SUFE. Other hips were in patients who were either skeletally mature or close to skeletal maturity. We found that all were “profunda hips” with severe acetabular retroversion. The abnormality in acetabular version was best defined on axial imaging. Conclusions: The femoral head is a spherical conchoid. The concept of version of the hip (both femoral and acetabular) as described by McKibbin, Tonnis and Ganz is reviewed. Femoral retroversion is common in patients with SUFE, but the addition of acetabular retroversion makes these hips disproportionately symptomatic. This deformity causes a combination of pincer and cam impingement, which is responsible for the marked disability. SUFE alone causes cam impingement, whilst a corresponding degree of slip without retroversion and profunda of the acetabulum is not that disabling

Over an eight-month period we prospectively enrolled 122 patients who underwent arthroscopic surgery of the hip for femoroacetabular impingement and met the inclusion criteria for this study. Patients with bilateral hip arthroscopy, avascular necrosis and previous hip surgery were excluded. Ten patients refused to participate leaving 112 in the study. There were 62 women and 50 men. The mean age of the patients was 40.6 yrs (95% confidence interval (CI) 37.7 to 43.5). At arthroscopy, 23 patients underwent osteoplasty only for cam impingement, three underwent rim trimming only for pincer impingement, and 86 underwent both procedures for mixed-type impingement. The mean follow-up was 2.3 years (2.0 to 2.9). The mean modified Harris hip score (HHS) improved from 58 to 84 (mean difference = 24 (95% CI 19 to 28)) and the median patient satisfaction was 9 (1 to 10). Ten patients underwent total hip replacement at a mean of 16 months (8 to 26) after arthroscopy. The predictors of a better outcome were the pre-operative modified HHS (p = 0.018), joint space narrowing ≥ 2 mm (p = 0.005), and repair of labral pathology instead of debridement (p = 0.032). Hip arthroscopy for femoroacetabular impingement, accompanied by suitable rehabilitation, gives a good short-term outcome and high patient satisfaction

Aims

To evaluate how abnormal proximal femoral anatomy affects different femoral version measurements in young patients with hip pain.

Summary Statement. Pincer deformities are involved in the genesis of femoro-acetabular impingement (FAI). Radiographic patterns suggestive of pincer deformities are common among general population. Prevalence of the pincer deformities among general population may be overestimated if only plain radiographs are considered. Background. Pincer deformities (coxa profunda, protrusio acetabuli, global retroversion, isolated cranial over-coverage) have been advocated as a cause of femoro-acetabular impingement (FAI) and early hip osteoarthritis (OA). Different radiographic patterns may advocate the presence of a pincer deformity. The prevalence of these radiographic patterns among general adult population, as their role in early hip OA, is poorly defined. Methods. From a database of 40.351 pelvic radiograms and CT collected at our institution between 2005 and 2010, we selected 118 caucasian individuals (56 females, 62 males), aged between 15 and 60 years, who underwent both plain radiographs and CT of the pelvis. A series of exclusion criteria were strictly applied to achieve a sample of adult general population as more representative as possible. In particular patients with presence of any disease involving hip joint, including: advanced hip OA (grade II or III of Tonnis scale), head necrosis, fractures, heterotopic ossifications, bone and soft tissue tumors, rheumatic pathologies, classic hip dysplasia with lateral center-edge angle (L-CEA) less than 20°, clinical diagnosis of FAI or hip pain, were excluded from the present study. We also excluded patients in which open growth plates, osteopenia, hardware or evidence of prior surgery were present. Radiographs were investigated for pelvic tilt, signs of retroversion, lateral center-edge angle (L-CEA), presence of coxa profunda or protrusio acetabuli. EAV was measured on CT scans at the equatorial plane of the acetabulum passing by the 3 o'clock position, while CAV was calculated at a more cranial level corresponding to the 1 o'clock position EAV and CAV were obtained in the axial plane by measuring the angle made by a line connecting the anterior and posterior rims of the acetabulum and a line perpendicular to the line connecting the ischial spines. A new parameter, Acetabular torsion (AT), has been introduced in order to discriminate between global retroversion and isolated cranial over-coverage. AT was defined as the difference between EAV and CAV. Cam deformity was assessed by calculating the alpha angle on the femoral side; an alpha angle > 55° was considered abnormal and suggestive of cam deformity. Radiological signs of chondrolabral degeneration were noticed. Results. Mean EAV and mean CAV were higher in females, mean AA was higher in males. L-CEA, EAV and CAV increased with age. Mean AT was 8.8±6.3. AT was inversely related to CAV (r=−0.799; p<0.0005) but independent from EAV (r=−0.076; p=0.244). EAV≤10.2° was defined as the marker of global retroversion, while AT≥21.2° was defined as the marker of isolated cranial over-coverage. Overall prevalence of pincer deformities was 21.6% (> females; p=0.02). Early OA changes were related to age (p<0.0005) and AA (p<0.0005), but not to pincer deformities (p=0.96). Radiological signs of retroversion showed good or excellent negative predictability but poor positive predictability. Conclusions. Radiographic patterns of pincer deformities are common among general population. Relationship with radiological signs of chondrolabral degeneration is poor. CT allows to discriminate between global retroversion and isolated cranial over-coverage. Prevalence of the pincer deformities among general population may be overestimated if only plain radiographs are considered

Purpose: Femoroacetabular impingement (FAI) has recently been described as a cause of adult hip pain and a precursor of hip osteoarthritis. Pincer type is secondary to acetabular retroversion or coxa profunda and Cam type is secondary to lack of concavity/offset of the antero-lateral femoral head-neck junction. Purpose of this study was to determine the prevalence of bilateral deformity in patients with cam type FAI as well as the presence of associated acetabular abnormalities. Method: One hundred and thirteen patients with symptomatic cam impingement (alpha (α) angle of Notzli > 55.5°) of at least one hip were evaluated. Eighty-two males, 31 females with an average age of 37.9 yrs (16–55). Standardized AP pelvis and bilateral Dunn views were reviewed. Alpha angle of Notzli was measured on Dunn views. Cam impingement was defined by α angle > 55.5 on the Dunn view and Pincer impingement was defined by the presence of either acetabular retroversion or coxa profunda. Statistical analysis was done using the two tailed paired t-test, chi-square test and intra-class correlation coefficient. Odds Ratios were calculated using conditional logistic regression. Results: Eighty-eight patients (77.8%) had bilateral deformity and 27% had symptoms in both hips. Mean α angles were higher for bilateral impingement deformity than for the impingement side only when unilateral deformity was present (72.10 versus 64.50, p< 0.001). Forty-four percent of hips with an impingement deformity also had a pincer deformity, either acetabular retroversion or coxa profunda. Painful hips had a statistically significant higher mean alpha angle than asymptomatic ones (69.70 versus 63.10, p< 0.001)). Comparing hips with α angles of 61–70 with those < 60 found an odds ratio of being painful of 2.59 (95% CI: 1.32–5.08, p=0.006). Hips with α angles > 71 had an odds ratio of being painful of 2.54 (95% CI: 1.3–4.96, p=0.007). Conclusion: The majority of patients with cam type FAI have bilateral deformities and an associated acetabular deformity less commonly. The severity of the deformity at the femoral head neck junction is a significant determining factor for the development of hip symptoms. This information is important as we better define the natural history of this deformity as well as devise effective treatment strategies

We examined the morphology of mammalian hips asking whether evolution can explain the morphology of impingement in human hips. We describe two stereotypical mammalian hips, coxa recta and coxa rotunda. Coxa recta is characterised by a straight or aspherical section on the femoral head or head-neck junction. It is a sturdy hip seen mostly in runners and jumpers. Coxa rotunda has a round femoral head with ample head-neck offset, and is seen mostly in climbers and swimmers. Hominid evolution offers an explanation for the variants in hip morphology associated with impingement. The evolutionary conflict between upright gait and the birth of a large-brained fetus is expressed in the female pelvis and hip, and can explain pincer impingement in a coxa profunda. In the male hip, evolution can explain cam impingement in coxa recta as an adaptation for running

Introduction: Femoro-acetabular impingement (FAI) is a common source of impaired motion of the hip, often attributed to the presence of an aspherical femoral head and reduced concavity of the anterior head/neck junction. However, other types of femoral deformity, including posterior slip, retroversion, and neck enlargement, can also limit hip motion. This study was performed to establish whether the “cam” impinging femur is a unique entity with a single deformity of the head/neck junction or is part of a multi-component continuum of femoral dysmorphia. Materials and Methods: Computer models of 71 femora (28 normal and 43 “cam” impinging) were prepared from CT scans. Morphologic parameters describing the shape and dimensions of the head, neck, and medullary canal were calculated for each specimen. The anteversion angle, alpha angle of Notzli, beta angle of Beaulé, and normalized anterior heads offset were also calculated. Average dimensions were compared between the normal and impinging femora. A dimensionless model of the femoral neck was also generated to determine whether there is an inherent difference in the shape of the femoral neck in cam impinging and normal femora, independent of any differences in specimen size. Results: Compared to the normal controls, the impinging femora had wider necks (AP: 15.2 vs 13.3 mm, p< 0.0001), larger heads (diameter: 48.3mm vs 46.0mm, p=0.032) and decreased head/neck ratios (1.60 vs 1.74, p=0.0002). However, there was no difference in neck/shaft angle (125.7° vs 126.5°, p=0.582) or anteversion angle (8.70 vs 8.44°, p=0.866). Most significantly, 53% of impinging femora also had a significant posterior slip (> 2mm), compared to only 14% of normal controls. Average head displacements for the two groups were: FAI: 1.93mm vs Normals: 0.78mm (p< 0.0001). Shape indices derived from individual dimensionless models showed slight AP widening of the abnormal femora (ap/ml ratio: 1.10 abnormal vs. 1.07 normal). Conclusions: The CAM impinging femur has many abnormalities apart from the morphology of the head/neck junction. These femora have increased neck width and head/neck ratio, a smaller spherical bearing surface, and reduced neck offset from the medullary canal. Moreover, the presence of posterior head displacement and reduced anteversion should be appreciated when assessing treatment options, as surgical treatment limited to localized re-contouring of the head–neck profile may fail to address significant components of the underlying abnormality

The current study aimed to determine the influence of acetabular coverage and intraarticular pathology on post-operative functional outcomes of arthroscopy for cam type FAI. Based on 762 hip scopes performed by a single surgeon between 2013 and 2016, we excluded patients with previous surgery on the hip, mixed FAI, surgical hip dislocation, and missing outcome scores. From this, 97 hips between the ages 17 and 48 that underwent arthroscopy for cam deformity were identified for analysis. Every patient received a partial capsulotomy, cam resection and either labral repair or resection. Measurements for acetabular coverage consisted of pre-operative lateral edge angle (LCEA) (mean 30°, range: 15.4°–40°) and three-dimensional anterior and posterior acetabular coverages. Intraoperative Beck scores were acquired from operative reports, and Hip Disability and Osteoarthritis Outcome Score (HOOS) was collected pre- and post-operatively. Significant post-operative improvement was found in scores of all categories of the HOOS (p < 0.05). However, improvement in HOOS was not correlated with the LCEA, anterior coverage, or posterior coverage. There was a trend toward lower Beck grades (1–3) resulting in better HOOS outcomes than higher Beck grades (4–5). Also, lower Beck grades showed significantly lower alpha angle (mean = 55.86) than higher grades (mean = 73.48). We showed that cam FAI arthroscopic resection improved patient outcome, and confirmed the relationship between the Beck score and functional outcome. However, functional improvement was not related to acetabular coverage suggesting that the so-called “borderline” dysplasia is not a useful radiographic indicator for surgical management

The intra-epiphyseal growth of the proximal femur has been focus of studies because of the potential relationship with the development of slipped capital femoral epiphysis and cam deformity in femoroacetabular impingement. We aimed to evaluate the developmental pattern of the epiphyseal tubercle and extension in normal boys and girls from eight to fifteen years, without hip conditions. We performed three-dimensional (3D) analysis of pelvic computed tomographic scans of 80 subjects with suspect of appendicitis, consisting of five boys and five girls for each age, from eight to 15 years old. Images were segmented slice by slice at the level of the growth plate using biplanar orientation. The 3D-segmented epiphyses were used to measure the location and height of the tubercle, the height of the epiphyseal extension, and the epiphyseal diameter. We found that the epiphyseal tubercle was eccentrically located at the posterolateral quadrant of the physeal surface. The absolute height of the epiphyseal tubercle did not vary between ages (R. 2. =0.04; p=0.101). The epiphyseal diameter increased with age (R. 2. =0.74; p<0.001), making the tubercle height proportionally smaller with the epiphyseal growth (9% reduction in tubercle height normalised by the epiphyseal diameter). The normalised epiphyseal extension height significantly increased by 160% from 8 to 15 years of age. Our observation validates the hypothesis of the cupping mechanism provided by the peripheral growth of the epiphyseal extension, while the epiphyseal tubercle relatively decreases in size during the skeletal growth. Further research will be important to determine the role of these structures in the epiphyseal stability