We report on gender-specific reference intervals of the alpha angle and its association with other qualitative cam-type findings in femoroacetabular impingement at the hip, according to a population-based cohort of 2038 19-year-olds, 1186 of which were women (58%). The alpha angle was measured on standardised frog-leg lateral and anteroposterior (AP) views using digital measurement software, and qualitative cam-type findings were assessed subjectively on both views by independent observers. In all, 2005 participants (837 men, 1168 women, mean age 18.6 years (17.2 to 20.1) were included in the analysis. For the frog-leg view, the mean alpha angle (right hip) was 47° (26 to 79) in men and 42° (29 to 76) in women, with 97.5 percentiles of 68° and 56°, respectively. For the AP view, the mean values were 62° (40 to 105) and 52° (36 to 103) for men and women, respectively, with 97.5 percentiles of 93° and 94°. Associations between higher alpha angles and all qualitative cam-type findings were seen for both genders on both views. The reference intervals presented for the alpha angle in this cross-sectional study are wide, especially for the AP view, with higher mean values for men than women on both views. Cite this article: Bone Joint J 2014;96-B:449–54

Aims. Asphericity of the femoral head-neck junction is common in cam-type femoroacetabular impingement (FAI) and usually quantified using the alpha angle on radiographs or MRI. The aim of this study was to determine the natural alpha angle in a large cohort of patients by continuous circumferential analysis with CT. Methods. CT scans of 1312 femurs of 656 patients were analyzed in this cross-sectional study. There were 362 men and 294 women. Their mean age was 61.2 years (18 to 93). All scans had been performed for reasons other than hip disease. Digital circumferential analysis allowed continuous determination of the alpha angle around the entire head-neck junction. All statistical tests were conducted two-sided; a p-value < 0.05 was considered statistically significant. Results. The mean maximum alpha angle for the cohort was 59.0° (. sd. 9.4). The maximum was located anterosuperiorly at 01:36 on the clock face, with two additional maxima of asphericity at the posterior and inferior head-neck junction. The mean alpha angle was significantly larger in men (59.4°, . sd. 8.0) compared with women (53.5°, . sd. 7.4°; p = 0.0005), and in Caucasians (60.7°, . sd. 9.0°) compared with Africans (56.3°, . sd. 8.0; p = 0.007) and Asians (50.8°, . sd. 7.2; p = 0.0005). The alpha angle showed a weak positive correlation with age (p < 0.05). If measured at commonly used planes of the radially reconstructed CT or MRI, the alpha angle was largely underestimated; measurement at the 01:30 and 02:00 positions showed a mean underestimation of 4° and 6°, respectively. Conclusion. This study provides important data on the normal alpha angle dependent on age, gender, and ethnic origin. The normal alpha angle in men is > 55°, and this should be borne in mind when making a diagnosis of cam-type morphology. Cite this article: Bone Joint J 2018;100-B:570–8

The radiological evaluation of the anterolateral femoral head is an essential tool for the assessment of the cam type of femoroacetabular impingement. CT, MRI and frog lateral plain radiographs have all been suggested as imaging options for this type of lesion. The alpha angle is accepted as a reliable indicator of the cam type of impingement and may also be used as an assessment for the successful operative correction of the cam lesion. We studied the alpha angles of 32 consecutive patients with femoroacetabular impingement. The angle measured on frog lateral radiographs using templating tools was compared with that measured on CT scans in order to assess the reliability of the frog lateral view in analysing the alpha angle in cam impingement. A high interobserver reliability was noted for the assessment of the alpha angle on the frog lateral view with an intraclass correlation coefficient of 0.83. The mean alpha angle measured on the frog lateral view was 58.71° (32° to 83.3°) and that by CT was 65.11° (30° to 102°). A poor intraclass correlation coefficient (0.08) was noted between the measurements using the two systems. The frog lateral plain radiograph is not reliable for measuring the alpha angle. Various factors may be responsible for this such as the projection of the radiograph, the positioning of the patient and the quality of the image. CT may be necessary for accurate measurement of the alpha angle

Objectives. The purpose of this study was to investigate whether the femoral head–neck contour, characterised by the alpha angle, varies with the stage of physeal maturation using MRI evaluation of an asymptomatic paediatric population. . Methods. Paediatric volunteers with asymptomatic hips were recruited to undergo MRI of both hips. Femoral head physes were graded from 1 (completely open) to 6 (completely fused). The femoral head–neck contour was evaluated using the alpha angle, measured at the 3:00 (anterior) and 1:30 (anterosuperior) positions and correlated with physeal grade, with gender sub-analysis performed. Results. A total of 43 asymptomatic paediatric volunteers (26 male, 17 female) with mean age 13.0 years (eight to 18) were included with review of bilateral hip MRIs. Correlation between the physeal grade and alpha angle was moderate in males at both the 3:00 (r = 0.477, p < 0.001) and 1:30 (r = 0.509, p < 0.001) positions, whereas there was no significant correlation in females. A significant difference was found between the alpha angles of all the physeal grades (3:00, p = 0.030, 1:30, p = 0.005), but only in males, with the angle increasing with higher grades. For physeal grading, the inter-reader reliability was substantial (intraclass correlation coefficient (ICC) = 0.694), and the intra-reader reliability was also substantial (ICC = 0.788). . Conclusion . The femoral head–neck contour varies and correlates with the stage of physeal development, but only in males, with the alpha angle increasing with progressive physeal maturation. This suggests that gender differences exist in the natural physiological growth, development or remodelling of femoral head–neck junction. In males, pre-physeal fusion may be a critical period of vulnerability for development of morphologic abnormalities of the femoral head–neck junction. Cite this article: Bone Joint Res 2015;4:17–22

Objectives. The spinopelvic relationship (including pelvic incidence) has been shown to influence pelvic orientation, but its potential association with femoroacetabular impingement has not been thoroughly explored. The purpose of this study was to prove the hypothesis that decreasing pelvic incidence is associated with increased risk of cam morphology. Methods. Two matching cohorts were created from a collection of cadaveric specimens with known pelvic incidences: 50 subjects with the highest pelvic incidence (all subjects > 60°) and 50 subjects with the lowest pelvic incidence (all subjects < 35°). Femoral version, acetabular version, and alpha angles were directly measured from each specimen bilaterally. Cam morphology was defined as alpha angle > 55°. Differences between the two cohorts were analysed with a Student’s t-test and the difference in incidence of cam morphology was assessed using a chi-squared test. The significance level for all tests was set at p < 0.05. Results. Cam morphology was identified in 47/100 (47%) femurs in the cohort with pelvic incidence < 35° and in only 25/100 (25%) femurs in the cohort with pelvic incidence > 60° (p = 0.002). The mean alpha angle was also greater in the cohort with pelvic incidence < 35° (mean 53.7°, . sd. 10.7° versus mean 49.7°, . sd. 10.6°; p = 0.008). Conclusions. Decreased pelvic incidence is associated with development of cam morphology. We propose a novel theory wherein subjects with decreased pelvic incidence compensate during gait (to maintain optimal sagittal balance) through anterior pelvic tilt, creating artificial anterior acetabular overcoverage and recurrent impingement that increases risk for cam morphology. Cite this article: W. Z. Morris, C. A. Fowers, R. T. Yuh, J. J. Gebhart, M. J. Salata, R. W. Liu. Decreasing pelvic incidence is associated with greater risk of cam morphology. Bone Joint Res 2016;5:387–392. DOI: 10.1302/2046-3758.59.BJR-2016-0028.R1

Femoroacetabular impingement is a cause of hip pain in adults and is potentially a precursor of osteoarthritis. Our aim in this study was to determine the prevalence of bilateral deformity in patients with symptomatic cam-type femoroacetabular impingement as well as the presence of associated acetabular abnormalities and hip pain. We included all patients aged 55 years or less seen by the senior author for hip pain, with at least one anteroposterior and lateral pelvic radiograph available. All patients with dysplasia and/or arthritis were excluded. A total of 113 patients with a symptomatic cam-impingement deformity of at least one hip was evaluated. There were 82 men and 31 women with a mean age of 37.9 years (16 to 55). Bilateral cam-type deformity was present in 88 patients (77.8%) while only 23 of those (26.1%) had bilateral hip pain. Painful hips had a statistically significant higher mean alpha angle than asymptomatic hips (69.9° vs 63.1°, p < 0.001). Hips with an alpha angle of more than 60° had an odds ratio of being painful of 2.59 (95% confidence interval 1.32 to 5.08, p = 0.006) compared with those with an alpha angle of less than 60°. Of the 201 hips with a cam-impingement deformity 42% (84) also had a pincer deformity. Most patients with cam-type femoroacetabular impingement had bilateral deformities and there was an associated acetabular deformity in 84 of 201 patients (42%). This information is important in order to define the natural history of these deformities, and to determine treatment

Objectives. The purpose of this study was to evaluate the existing literature from 2005 to 2016 reporting on the efficacy of surgical management of patients with femoroacetabular impingement (FAI) secondary to slipped capital femoral epiphysis (SCFE). Methods. The electronic databases MEDLINE, EMBASE, and PubMed were searched and screened in duplicate. Data such as patient demographics, surgical technique, surgical outcomes and complications were retrieved from eligible studies. Results. Fifteen eligible level IV studies were included in this review comprising 261 patients (266 hips). Treatment groups included arthroscopic osteochondroplasty, surgical hip dislocation, and traditional open osteotomy. The mean alpha angle corrections were 32.14° (standard deviation (. sd). 7.02°), 41.45° (. sd. 10.5°) and 6.0° (. sd. 5.21°), for arthroscopy, surgical hip dislocation, and open osteotomy groups, respectively (p < 0.05). Each group demonstrated satisfactory clinical outcomes across their respective scoring systems. Major complication rates were 1.6%, 10.7%, and 6.7%, for arthroscopy, surgical dislocation and osteotomy treatments, respectively. Conclusion. In the context of SCFE-related FAI, surgical hip dislocation demonstrated improved correction of the alpha angle, albeit at higher complication and revision rates than both arthroscopic and open osteotomy treatments. Further investigation, including high-quality trials with standardised radiological and clinical outcome measures for young patients, is warranted to clarify treatment approaches and safety. Cite this article: K. O. Oduwole, D. de Sa, J. Kay, F. Findakli, A. Duong, N. Simunovic, Y. Yi-Meng, O. R. Ayeni. Surgical treatment of femoroacetabular impingement following slipped capital femoral epiphysis: A systematic review. Bone Joint Res 2017;6:472–480. DOI: 10.1302/2046-3758.68.BJR-2017-0018.R1

Aims. Recently, there has been considerable interest in quantifying the associations between bony abnormalities around and in the hip joint and osteoarthritis (OA). Our aim was to investigate the relationships between acetabular undercoverage, acetabular overcoverage, and femoroacetabular impingement (FAI) with OA of the hip, which currently remain controversial. . Materials and Methods. A total of 545 cadaveric skeletons (1090 hips) from the Hamann-Todd osteological collection were obtained. Femoral head volume (FHV), acetabular volume (AV), the FHV/AV ratio, acetabular version, alpha angle and anterior femoral neck offset (AFNO) were measured. A validated grading system was used to quantify OA of the hip as minimal, moderate, or severe. Multiple linear and multinomial logistic regression were used to determine the factors that correlated independently with the FHV, AV, and the FHV/AV ratio. . Results. Female cadavers had smaller FHVs (standardised beta -0.382, p < 0.001), and AVs (standardised beta -0.351, p < 0.001), compared with male patients, although the FHV/AV ratio was unchanged. Every 1° increase in alpha angle increased the probability of having moderate OA of the hip compared with minimal OA by 7.1%. Every 1 mm decrease in AFNO increased the probability of having severe or moderate OA of the hip, compared with minimal OA, by 11% and 9%, respectively. The relative risk ratios of having severe OA of the hip compared with minimal OA were 7.2 and 3.3 times greater for acetabular undercoverage and overcoverage, respectively, relative to normal acetabular cover. . Conclusion . Acetabular undercoverage and overcoverage were independent predictors of increased OA of the hip. The alpha angle and AFNO had modest effects, supporting the hypothesis that bony abnormalities both in acetabular dysplasia and FAI are associated with severe OA. Cite this article: Bone Joint J 2017;99-B:432–9

Objectives. The purpose of this study was to compare the thickness of the hip capsule in patients with surgical hip disease, either with cam-femoroacetabular impingement (FAI) or non-FAI hip pathology, with that of asymptomatic control hips. Methods. A total of 56 hips in 55 patients underwent a 3Tesla MRI of the hip. These included 40 patients with 41 hips with arthroscopically proven hip disease (16 with cam-FAI; nine men, seven women; mean age 39 years, 22 to 58) and 25 with non-FAI chondrolabral pathology (four men, 21 women; mean age 40 years, 18 to 63) as well as 15 asymptomatic volunteers, whose hips served as controls (ten men, five women; mean age 62 years, 33 to 77). The maximal capsule thickness was measured anteriorly and superiorly, and compared within and between the three groups with a gender subanalysis using student’s t-test. The correlation between alpha angle and capsule thickness was determined using Pearson’s correlation coefficient. Results. Superiorly, the hip capsule was significantly greater in cam- (p = 0.028) and non-FAI (p = 0.048) surgical groups compared with the asymptomatic group. Within groups, the superior capsule thickness was significantly greater than the anterior in cam- (p < 0.001) and non-FAI (p < 0.001) surgical groups, but not in the control group. There was no significant correlation between the alpha angle and capsule thickness. There were no gender differences identified in the thickness of the hip capsule. Conclusion. The thickness of the capsule does not differ between cam- and non-FAI diseased hips, and thus may not be specific for a particular aetiology of hip disease. The capsule is, however, thicker in diseased surgical hips compared with asymptomatic control hips. Cite this article: K. S. Rakhra, A. A. Bonura, R. Nairn, M. E. Schweitzer, N. M. Kolanko, P. E. Beaule. Is the hip capsule thicker in diseased hips? Bone Joint Res 2016;5:586–593. DOI: 10.1302/2046-3758.511.2000495

Aims. What represents clinically significant acetabular undercoverage in patients with symptomatic cam-type femoroacetabular impingement (FAI) remains controversial. The aim of this study was to examine the influence of the degree of acetabular coverage on the functional outcome of patients treated arthroscopically for cam-type FAI. Patients and Methods. Between October 2005 and June 2016, 88 patients (97 hips) underwent arthroscopic cam resection and concomitant labral debridement and/or refixation. There were 57 male and 31 female patients with a mean age of 31.0 years (17.0 to 48.5) and a mean body mass index (BMI) of 25.4 kg/m. 2. (18.9 to 34.9). We used the Hip2Norm, an object-oriented-platform program, to perform 3D analysis of hip joint morphology using 2D anteroposterior pelvic radiographs. The lateral centre-edge angle, anterior coverage, posterior coverage, total femoral coverage, and alpha angle were measured for each hip. The presence or absence of crossover sign, posterior wall sign, and the value of acetabular retroversion index were identified automatically by Hip2Norm. Patient-reported outcome scores were collected preoperatively and at final follow-up with the Hip Disability and Osteoarthritis Outcome Score (HOOS). Results. At a mean follow-up of 2.7 years (1 to 8, . sd. 1.6), all functional outcome scores significantly improved overall. Radiographically, only preoperative anterior coverage had a negative correlation with the improvement of the HOOS symptom subscale (r = -0.28, p = 0.005). No significant difference in relative change in HOOS subscale scores was found according to the presence or absence of radiographic signs of retroversion. Discussion. Our study demonstrated the anterior coverage as an important modifier influencing the functional outcome of arthroscopically treated cam-type FAI. Cite this article: Bone Joint J 2018;100-B:831–8

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

Aims. The purpose of this study was to evaluate spinopelvic mechanics from standing and sitting positions in subjects with and without femoroacetabular impingement (FAI). We hypothesize that FAI patients will experience less flexion at the lumbar spine and more flexion at the hip whilst changing from standing to sitting positions than subjects without FAI. This increase in hip flexion may contribute to symptomatology in FAI. Patients and Methods. Male subjects were prospectively enrolled to the study (n = 20). Mean age was 31 years old (22 to 41). All underwent clinical examination, plain radiographs, and dynamic imaging using EOS. Subjects were categorized into three groups: non-FAI (no radiographic or clinical FAI or pain), asymptomatic FAI (radiographic and clinical FAI but no pain), and symptomatic FAI (patients with both pain and radiographic FAI). FAI was defined as internal rotation less than 15° and alpha angle greater than 60°. Subjects underwent standing and sitting radiographs in order to measure spine and femoroacetabular flexion. Results. Compared with non-FAI controls, symptomatic patients with FAI had less flexion at the spine (mean 22°, . sd. 12°, vs mean 35°, . sd. 8°; p = 0.04) and more at the hip (mean 72°, . sd. 6°, vs mean 62°, . sd. 8°; p = 0.047). Subjects with asymptomatic FAI had more spine flexion and similar hip flexion when compared to symptomatic FAI patients. Both FAI groups also sat with more anterior pelvic tilt than control patients. There were no differences in standing alignment among groups. Conclusion. Symptomatic patients with FAI require more flexion at the hip to achieve sitting position due to their inability to compensate through the lumbar spine. With limited spine flexion, FAI patients sit with more anterior pelvic tilt, which may lead to impingement between the acetabulum and proximal femur. Differences in spinopelvic mechanics between FAI and non-FAI patients may contribute to the progression of FAI symptoms. Cite this article: Bone Joint J 2018;100-B:1275–9

Aims. Acetabular dysplasia is frequently associated with intra-articular pathology such as labral tears, but whether labral tears should be treated at the time of periacetabular osteotomy (PAO) remains controversial. The purpose of this study was to compare the clinical outcomes and radiographic corrections of PAO for acetabular dysplasia between patients with and without labral tears pre-operatively. Patients and Methods. We retrospectively reviewed 70 hips in 67 patients with acetabular dysplasia who underwent PAO. Of 47 hips (45 patients) with labral tears pre-operatively, 27 (25 patients) underwent PAO alone, and were classified as the labral tear alone (LT) group, and 20 (20 patients) underwent combined PAO and osteochondroplasty, and were classified as the labral tear osteochondroplasty (LTO) group. The non-labral tear (NLT) group included 23 hips in 22 patients. Results. There were no significant differences between groups for post-operative Harris hip scores, degree of progression of osteoarthritis or rate of reoperation. The pre-operative alpha angle was significantly larger in the LTO group compared with the other groups (p < 0.0001). Conclusion. PAO provides equivalent short-term relief of pain and functional outcome in patients with or without labral tears. The rate of progression of osteoarthritis and reoperation was not significantly increased in patients with labral tears. Take home message: PAO provides equivalent short-term pain relief and functional outcomes in patients with acetabular dysplasia with and without labral tears. We did not find significantly increased risks of progression of osteoarthritis or re-operation in those with labral tears. Cite this article: Bone Joint J 2016;98-B:741–6

Aims. The aims of this study were to review the surgical technique for a combined femoral head reduction osteotomy (FHRO) and periacetabular osteotomy (PAO), and to report the short-term clinical and radiological results of a combined FHRO/PAO for the treatment of selected severe femoral head deformities. Patients and Methods. Between 2011 and 2016, six female patients were treated with a combined FHRO and PAO. The mean patient age was 13.6 years (12.6 to 15.7). Clinical data, including patient demographics and patient-reported outcome scores, were collected prospectively. Radiologicalally, hip morphology was assessed evaluating the Tönnis angle, the lateral centre to edge angle, the medial offset distance, the extrusion index, and the alpha angle. Results. The mean follow-up was 3.3 years (2 to 4.6). The modified Harris Hip Score improved by 33.0 points from 53.5 preoperatively to 83.4 postoperatively (p = 0.03). The Western Ontario McMasters University Osteoarthritic Index score improved by 30 points from 62 preoperatively to 90 postoperatively (p = 0.029). All radiological parameters showed significant improvement. There were no long-term disabilities and none of the hips required early conversion to total hip arthroplasty. Conclusion. FHRO combined with a PAO resulted in clinical and radiological improvement at short-term follow-up, suggesting it may serve as an appropriate salvage treatment option for selected young patients with severe symptomatic hip deformities

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

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

Aims

The effect of pelvic tilt (PT) and sagittal balance in hips with pincer-type femoroacetabular impingement (FAI) with acetabular retroversion (AR) is controversial. It is unclear if patients with AR have a rotational abnormality of the iliac wing. Therefore, we asked: are parameters for sagittal balance, and is rotation of the iliac wing, different in patients with AR compared to a control group?; and is there a correlation between iliac rotation and acetabular version?

Aims

The prevalence of combined abnormalities of femoral torsion (FT) and tibial torsion (TT) is unknown in patients with femoroacetabular impingement (FAI) and hip dysplasia. This study aimed to determine the prevalence of combined abnormalities of FT and TT, and which subgroups are associated with combined abnormalities of FT and TT.

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

This paper aims to review the evidence for patient-related factors associated with less favourable outcomes following hip arthroscopy.