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.

Pincer femoroacetabular impingement (FAI) is cited as being the result of a socket that is either too deep or retroverted, or both. Using 3D-CT analysis, we set out to quantify the acetabular rim shape and orientation to determine the roles of these two factors in FAI. Twenty pincer acetabulae were selected from patients undergoing image based navigated surgery, where the lateral centre edge angle was greater than 40° on plain radiographs. The normal group of disease free sockets were obtained from a CT colonography database. Using 3D reconstruction of their CT scans, a novel method of mapping the acetabular rim profile was created. The pelvis was aligned to the anterior pelvic plane. Starting at the most anterior rim point, successive markers were placed along the rim. A best fit plane (ARP) through the acetabulum was derived, and the subtended angle (SA) between each rim marker and a normal vector from the acetabular centre was calculated. Values above 90° indicated a peak, with less than 90° representing a trough. Inclination and version were measured from a horizontal plane and the ARP, in the coronal and axial view respectively. The results showed that asymmetric acetabular rim profiles in normal and pincer hips were very similar. However, pincer hips are significantly deeper overall (Mean SA 96±5° vs. 87±4° p< 0.00001) and at each anatomical point of the three eminences (pubic [SA: Normal 84±4° vs. Pincer 94±7° p< 0.00001], iliac [SA: 93±4° vs. 100±6° p=0.00021] and ischial [SA: 92±3° vs. 102±8° p=0.00005]) and two troughs (ilio-pubic [SA: Normal 83±4° vs. Pincer 94±8° p=0.00001] and ilio-ischial [SA: 92±3° vs. 102±8° p=0.00002]). The orientation of normal and pincer were almost identical (Inclination: 51±3° vs. 51±6° p=0.54 and Version: 24±6° vs. 25°±7° p=0.67). We conclude that the rim shape of pincer hips follows the same contour as normal hips. In agreement with current radiographic diagnosis, pincer-type hips are characterised by a deeper acetabulum. This ‘overcoverage’ of the femoral head confirms the biomechanical model of pincer-type impingement. Both inclination and version in these two groups were almost identical, with no truly retroverted acetabulum seen. Pincer impingement resulting from ‘acetabular retroversion’ is a concept currently based upon radiographic signs that we have been unable to confirm in this small 3D study using the subtended angle as the key descriptor of acetabular morphology

Purpose: Femoroacetabular impingement (FAI) results from abnormal abutment between the proximal femur and acetabulum (Ganz et al., 2003). FAI occurs in three forms; cam, pincer and mixed (cam and pincer combined). The cam type has been quantified radiographically (Beall et al., 2005), but pincer FAI is poorly defined. Radiographic measures, including the center-edge angle (Wiberg, 1953), and Sharp’s angle (Sharp, 1961) have been used to define hip dysplasia, but these measures have not been used to define FAI. The purpose was to test these measurements to compare pincer patients with controls. Method: This study is a retrospective, observational analysis of anterior-posterior pelvic radiographs for control (N=76 hips; 40 patients) and pincer (N=20 hips; 19 patients) groups. Control radiographs were obtained from injury-free pelvic x-rays from the emergency department. Lateral center-edge (CE) angle Sharp’s angle and a proposed measurement of Femoral Head Containment (FHC) were measured using PACS. FHC was defined as the percentage of the 2D area of the femoral head circle covered by the acetabulum, using chord length, height and diameter of the femur head. Non-parametric statistics with post-hoc analyses were used. Pearson’s correlations were calculated for within- and between-observer reproducibility. Results: Mean (± SD) CE angle was significantly larger in the FAI group [37.4° (±5.2)] compared to controls [31.0° (±3.9)]. Mean Sharp’s angle was significantly less in the FAI group [37.6° (±3.9)] compared to the controls [41.2° (±3.5)]. Mean FHC was significantly larger in the FAI group [26.4% (±5.3)] compared to control group [21.5% (±5.3)]. Intra-observer r-values ranged from 0.86–0.97 and inter-observer correlations ranged from 0.93–0.96. There was significantly greater acetabular overcoverage in the pincer group based on these three measures, suggesting these may be used diagnostically. Conclusion: Pincer FAI is a debilitating condition that has not been quantified. This study found that CE angle, Sharp’s angle and FHC measures may be useful in diagnosing pincer FAI. A new method of quantifying FHC was proposed, evaluated and appears to be a promising new measure for evaluating pincer FAI. The CE and Sharp’s angles are simple, reproducible measures that can easily be used in a clinic setting to assist with diagnosing pincer FAI

Purpose. The purpose of this retrospective study was to investigate the acetabular morphology of pincer impingement hips in order to better understand damage pattern in these patients. We compared MRI measurements made at different postions from anterior to posterior on the acetbulum in patients with pure pincer type FAI to those made in patients with pure cam-type to collect parameters that may be useful in the diagnosis and classification of pincer impingement. Material and Methods. From an initial consecutive retrospective population of 1022 patients that underwent MRI with clinical impingement signs 78 hips which were selected with as clear cam (n=57) or pincer (n=21) impingement on plain radiographics. On these MR Imaging was performed with a 1.5-Tesla system. For analysis, a lateral angle of overcoverage on coronal MRI (MR_LCE), the MR extrusion index and the alpha angle (after Nötzli) were used. In addition to these the gamma angle, the acetabular depth and the angle of lateral acetabular overcoverage were described clock-wise on 7 radial slides from anterior to posterior. These were compared between the cam and pincer population using students-t-test. Measurements were obtained by two observers and inter-observer variability was assessed. Results. The acetabular depth showed in all 7 positions significant smaller values for pincer-type in comparison to cam-type impingement. Highest difference was found is superior-posterior position. The acetabular angle is also significant smaller for pincer than for cam in all radial positions. Highest difference of the acetabular angle is located in superior (pincer −102.93°/cam 109.62°) and anterior-superior position (pincer 102.48°/cam 108.77 °). The gamma angle showed significant differences in all radial positions except anterior position. The highest difference is located in superior-posterior position (pincer 86.18 °/cam 08.77°). The mean MR extrusion index was significant lower for pincer type (12.73%) compared to cam-type patients (17.76%) (p=0.004). LCE angle and extrusion index on MRI displayed a Person correlation coefficient of 0.920. The correlation of the acetabular depth and angle was 0.638. Conclusion. There are several morphological differences between pincer and cam acetabuli: They are significantly deeper in all radial positions than cam hips. They tend to have greater retroversion and have smaller gamma angles. Our results suggest that the superior-posterior quadrant displays greater coverage in pincer hips than cam hips, and therefore damage to the labrum and cartilage surface may extend further into the posterior portion of the acetabulum in pincer hips than in cam hips

Standard evaluation and diagnosis of pincer-type femoroacetabular impingment (FAI) relies on anteroposterior (AP) radiographs, clinical evaluation, and/or magnetic resonance imaging (MRI). However, the current evaluation techniques do not offer a method for accurately defining the amount of acetabular rim overcoverage in pincer-type FAI. Several studies have remarked on the particular problems with radiographic evaluation, including beam divergence, difficulty with defining the acetabular rim, and pelvic tilt. Some studies have proposed methods to mitigate these issues; however, radiographic analysis still relies on projected and distorted images, making it difficult to acquire an accurate quantitative estimate of the amount of crossover. We propose a technique that utilises computed tomography (CT) data to accurately quantify the amount of acetabular crossover while accounting for known diagnostic problems, specifically pelvic tilt. This work describes a novel method that utilises CT data of a patient's afflicted hip joint region to assess the amount of acetabular overcoverage due to pincer deformity. The amount of overcoverage was assessed using a spline curve defined through the segmentation of the acetabular rim from CT data. To mitigate pelvic tilt, the user selected points to define both the pubic symphysis and the promontory in a lateral digitally reconstructed radiograph. The algorithm corrected the pelvic tilt by adjusting to a defined neutral position (in our case, a 60°), and the user adjusted for slight rotation differences ensuring there was a vertical line connecting the symphysis and the sacrococcygeal joint. After successfully repositioning the pelvis, the algorithm computed the amount of acetabular overcoverage. The algorithm identified the superolateral point of the acetabulum and the most inferior points of the anterior and posterior rim. A line, the mid-acetabular axis, was constructed between the superolateral point and the midpoint of the most inferior points on the anterior and posterior rims; the mid-acetabular axis was extended anterior and posterior to create a plane. Crossover occurred when the anterior rim of the acetabulum intersected this plane. If an intersection occurred, the algorithm measured the length of the mid-acetabular axis, and the length and width of the section representing overcoverage. These points were then projected onto anteroposterior DRRs and again measured to generate a basis of comparison. We tested our method on four cadaveric specimens to analyze the relationship between radiographic assessment and our technique. We simulated varying degrees of impingement in the cadavers by increasing the amount of pelvic tilt and defining that as the neutral position for a given trial. Moreover, we assessed interobserver variability in repositioning the pelvis as to the effect this would have on the final measurement of crossover length and width. The software achieved consistent, quantitative measurements of the amount of acetabular overcoverage due to pincer deformity. When compared with conventional radiographic measurements for crossover, there was a significant different between the two modalities. Specifically, both the ratios of crossover length to acetabular length and crossover width to crossover length were less using the CT-based approach (p < 0.001). Moreover, there were no significant differences between observers using our approach. The proposed technique can form the basis for a new way to diagnosis and measure acetabular overcoverage resulting in pincer impingement. This computational method can help clinicians to accurately correct for tilt and rotation, and subsequently provide consistent, quantitative measurement of acetabular overcoverage

Introduction. Ectopic ossification (EO) at the acetabular rim has been suggested to be associated with pincer impingement and to lead to ossification of the labrum. However, this has never been substantiated with histological, radiographic and MRI findings in large cohorts of patients. We hypothesized that it is more a bone apposition of the acetabular rim and that it occurs more frequently in coxa profunda (CP) hips. Materials and Methods. In the first part, a cohort of 20 hips with this suspected ectopic rim ossification (EO) pattern were identified. The radiographic features that could be associated with this ossification pattern were described and evaluated by a histologic examination of intra-operative samples taken from the rim trimming. In the second part, we assessed the prevalence of this ectopic ossification process in a cohort of 203 patients treated for FAI. Results. Histologic examination revealed that new acetabular bone formation was either overgrowing the non-ossified labrum or moving it away from the native rim. Radiologically, this was associated with an “indentation sign” and/or a “double line sign”. There were no specimens that had shown any evidence of labral ossification. EO was found in 26 hips (18%) of the second cohort. Twenty of 26 hips (77%) with EO had CP morphology and 29% of CP hips had EO signs. In contrast, only 6 non-profunda hips (8%) were associated with EO. There was a high correlation between XR and MRI findings as >80% of XR findings were confirmed on MRI. Sixty-nine hips had CP morphology. The double line sign (N = 13), the indentation sign (N = 12) and a prominent lateral rim (N = 11) were found. Hips with an EO pattern were found in patients that were significantly older than those without EO (p = 0.01). The acetabular characteristics of the EO groups were not significantly different from the CP hips without EO. The femoral characteristics were significantly different between groups with lower neck shaft angles (128° vs 134°;p = 0,0002) and shorter femoral necks lengths (62mm vs 65mm; p = 0,04)) in the EO group. The mean Tonnis classification was not significantly different (p = 0,18). In addition, the mean acetabular cartilage degeneration status was not different between both groups (p = 0,9). Rim trimming down to the native acetabular bone was done in all cases either by arthroscopy (N = 40) or open surgical dislocation (N = 17). Discussion. Ectopic ossification of the acetabular rim predominantly occurs in CP and is associated with specific anatomic features of the proximal femur. This type of impingement seems to be different and less aggressive than other described impingement processes. The double line sign and indentation sign are highly indicative for this EO process and are indicative for a longstanding impingement problem. Trimming of the acetabular rim should be conducted

Aims. Cam and pincer morphologies are potential precursors to hip osteoarthritis and important contributors to non-arthritic hip pain. However, only some hips with these pathomorphologies develop symptoms and joint degeneration, and it is not clear why. Anterior impingement between the femoral head-neck contour and acetabular rim in positions of hip flexion combined with rotation is a proposed pathomechanism in these hips, but this has not been studied in active postures. Our aim was to assess the anterior impingement pathomechanism in both active and passive postures with high hip flexion that are thought to provoke impingement. Methods. We recruited nine participants with cam and/or pincer morphologies and with pain, 13 participants with cam and/or pincer morphologies and without pain, and 11 controls from a population-based cohort. We scanned hips in active squatting and passive sitting flexion, adduction, and internal rotation using open MRI and quantified anterior femoroacetabular clearance using the β angle. Results. In squatting, we found significantly decreased anterior femoroacetabular clearance in painful hips with cam and/or pincer morphologies (mean -11.3° (SD 19.2°)) compared to pain-free hips with cam and/or pincer morphologies (mean 8.5° (SD 14.6°); p = 0.022) and controls (mean 18.6° (SD 8.5°); p < 0.001). In sitting flexion, adduction, and internal rotation, we found significantly decreased anterior clearance in both painful (mean -15.2° (SD 15.3°); p = 0.002) and painfree hips (mean -4.7° (SD 13°); p = 0.010) with cam and/pincer morphologies compared to the controls (mean 7.1° (SD 5.9°)). Conclusion. Our results support the anterior femoroacetabular impingement pathomechanism in hips with cam and/or pincer morphologies and highlight the effect of posture on this pathomechanism. Cite this article: Bone Jt Open 2021;2(11):988–996

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

This study used a national registry to assess the outcomes of hip arthroscopy (HA) for the treatment femoroacetabular impingement (FAI). All HAs for FAI recorded in the UK Non-Arthroplasty Hip Registry (NAHR) between January 2012 and September 2023 were identified. Cases were grouped according to the index procedure performed for FAI (cam, pincer, or mixed). Patient outcomes captured included the International Hip Outcome Tool (iHOT)-12. 7,511 HAs were identified; 4,583 cam (61%), 675 pincer (9%), 2,253 mixed (30%). Mean age (34.8) was similar between groups. There was a greater proportion of females in the pincer group (75%) compared to cam (52%) and mixed (50%). A higher proportion of patients had a recorded cartilage injury in association with a cam lesion compared to pincer. The pincer group had poorer mean pre-op iHOT-12 scores (31.6 \[95%CI 29.9 to 33.3\]; n=364) compared to cam (33.7 \[95%CI 32.1 to 34.4\]; n=3,941) and achieved significantly lower scores at 12 months (pincer = 52.6 (50.2 to 55); n=249, cam = 58.3 (57.1 to 59.5); n=1,679). Overall, significant (p < 0.0001) iHOT-12 and EQ-5D improvement vs baseline pre-operative scores were achieved for all FAI subtypes at 6 months (overall mean iHOT-12 improvement +26.0 \[95%CI 25.0 to 26.9\]; n=2,983) and maintained out to 12 months (+26.2 \[25.1 to 27.2\]; n=2,760) at which point 67% and 48% of patients continued to demonstrate a score improvement greater than or equal to the minimum clinically important difference (>/=13 points) and substantial clinical benefit (>/=28 points) for iHOT-12 respectively. This study demonstrates excellent early functional outcomes following HA undertaken for FAI in a large national registry

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

FAI may cause pain or functional impairment for an individual, as well as potentially resulting in arthritis and degeneration of the hip joint. Results from recent randomised control trials demonstrate the superiority of surgery over physiotherapy in patients with FAI. However, there is paucity of evidence regarding which factors influence outcomes for FAI surgery, most notably on patient reported outcomes measures (PROMs). Our study looks to explore factors influencing the outcomes for patients undergoing surgery for FAI utilising data from the Non-Arthroplasty Hip Registry. This study is a retrospective analysis of data collected prospectively via the NAHR database. Patients meeting the inclusion criteria, who underwent surgery between January 2011 and September 2019 were identified and included in the study. Follow-up data was captured in September 2020 to allow a minimum of 12 months follow-up. Patients consenting to data collection received questionnaires to determine EQ-5D Index and iHOT-12 scores preoperatively and at 6 months, 1, 2- and 5-year follow-up. Changes in outcome scores were analysed for all patients and sub-analysis was performed looking at the influence of; FAI morphological subtype, age, and sex, on outcome scores. Our cohort included 4,963 patients who underwent arthroscopic treatment for FAI. There was significant improvement from pre-operative PROMs when compared with those at 6 and 12 months. Pre-operatively, and at 12-month follow-up, iHOT-12 scores were significantly better for the cam / mixed groups compared to the pincer group (p<0.01). In multivariable regression analysis, pincer pathology and a high-grade chondral lesion were associated significantly poorer iHOT-12 improvement at 6 and 12 months (p<0.05). Age (<40 vs >40) demonstrated no statistical significance when considering 12 months outcome scores. This study demonstrates that hip arthroscopy is an effective treatment for patients with symptomatic FAI and shows statistically significant improvements at 12 months. The findings of this study are relevant to orthopaedic surgeons who manage young adults with hip pathology. This will help them to; predict which patients may benefit from operative intervention, and better inform patients, when undertaking shared decision making

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

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

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

Introduction. Magnetic resonance arthrogram (MRA) is the investigation of choice in young adults with symptoms of femero acetabular impingement. The aim of the study is to assess the accuracy of MRA when correlated with surgical findings on hip arthroscopy. Materials and Method. Between June 2007 and January 2014, 136 patients had MRA followed by subsequent arthroscopy at our institution. The radiology information system was used to gather MRA data. All scans were reported by a consultant radiologist with a specialist interest in musculoskeletal radiology. Patient records were reviewed to gather surgical data. Assessment was made of labral injury, Camshaft (CAM) or Pincer lesion and degeneration of the cartilage. Results. Mean age at MRA was 34.5 years with a 2.5:1 female to male ratio. For labral pathology sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) were 89, 100, 100 and 22% respectively. For CAM (62, 80, 79 and 64% respectively) and Pincer lesions (15, 84, 81 and 18% respectively). MRA was specific for picking up Grade 3/4 degenerate changes in the articular cartilage (92.2%) but was not as sensitive (60%), PPV 55 and NPV 94. Conclusion. These findings demonstrate that MRA is a sensitive and specific imaging modality for assessing the labrum and articular surface, but not as good for assessing CAM and Pincer lesions. This could be due to the static nature of the MRA or a lack of firm definition as to what constitutes a CAM or Pincer lesion leading to under reporting. This maybe better assessed with plane X ray or Computed tomography with 3 dimensional reconstruction. Further to this it would be interesting to combine the plane X ray and MRA finding and see if sensitivity and specificity was improved

Few epidemiological studies from Asian countries have addressed this issue and reported that FAI is less prevalent in Asian population. The purpose of this study was to determine the prevalence of radiographic hip abnormalities associated with FAI in asymptomatic Korean volunteers. The authors hypothesized that the prevalence of FAI in Korean population would not be less than that in western population. Two hundred asymptomatic volunteers with no prior hip surgery or childhood hip problems underwent three-view plain radiography (pelvis anteroposterior (AP) view, Sugioka view, and 45° Dunn view) of both hips. Cam lesions were defined as the presence of the following signs on each views: pistol-grip deformity, osseous bump at the femoral head-neck junction, flattening of the femoral head-neck offset, or alpha angle >50°. Pincer lesions were determined by radiographic signs, including crossover sign, posterior wall deficient sign, or lateral center-edge (CE) angle >40°. Only positive cases agreed by both observers were defined as true FAI-related deformities. There were 146 male and 254 female hips, with a mean age of 34.7 years. On pelvis AP view, the prevalence of pistol grip deformity, bump, flattening, and alpha angle >50° was 1.3% (male 3.4%, female 0%), 0.8% (male 2.1%, female 0%), 0.8% (male 2.1%, female 0%), and 1.0% (male 2.7%, female 0%), respectively. On Sugioka view, the prevalence of bump, flattening, and alpha angle >50° was 9.8% (male 14.4%, female 7.1%), 13.5% (male 20.5%, female 9.4%), and 14.0% (male 26.7%, female 6.7%), respectively. On 45° Dunn view, the prevalence of bump, flattening, and alpha angle >50° was 8.0% (male 14.4%, female 4.3%), 17.5% (male 27.4%, female 11.8%), and 27.5% (male 44.5%, female 17.7%), respectively. The prevalence of cam lesion which was identified on at least one radiograph was 42.5% (male 62.3%, female 31.1%). The prevalence of cam lesion which was identified on ≥2 radiographs was 19.3% (male 30.8%, female 12.6%). The prevalence of cam type FAI (at least one cam lesion) was 2.0% (male 5.5%, female 0%) on pelvis AP view, 25.8% (male 37.0%, female 19.3%) on Sugioka view, and 35.8% (male 55.5%, female 24.4%) on 45° Dunn view. On pelvis AP view, the prevalence of crossover sign, posterior wall sign, and CE angle >40° was 20.0% (male 23.3%, female 18.1%), 20.8% (male 22.6%, female 19.7%), and 2.0% (male 2.7%, female 1.6%), respectively. The prevalence of pincer type of FAI (at least one pincer lesion) was 23.0% (male 27.4%, female 20.5%). In asymptomatic Korean volunteers, the prevalence of cam type FAI was low on AP pelvis radiographs, whereas the prevalence of cam type FAI on Sugioka and 45° Dunn view was found to be comparable to that previously reported in Western populations. The prevalence of pincer type FAI in asymptomatic Korean volunteers was also comparable that in Western populations and was similar in both gender. Considering the high prevalence of FAI morphologic features on plain radiographs in asymptomatic Korean populations, it is also important to determine whether FAI is a cause of hip pain when considering surgery in Asian patients

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

Background. Hip arthroscopy is a rapidly growing, evolving area within arthroscopic Orthopaedic Surgery, with annual rates increasing as much as 25-fold each year. Despite improvements in equipment and training, it remains a challenging procedure. Rates of revision surgery have been reported as 6.3% to 16.9%. Objectives. The primary objective was to determine the success of joint preservation after hip arthroscopy. The secondary objective was to determine whether patient characteristics or PROM functional score trends could predict revision hip arthroscopy or Total Hip Arthroplasty (THA). Study Design & Methods. We reviewed 1363 hip arthroscopies performed from January 2010 to December 2016 by a single high-volume surgeon at a single institution. Data was prospectively collected and retrospectively reviewed with a minimum 2-year follow-up. Functional outcomes were assessed with the International Hip Outcome Tool (IHOT-33). Hip arthroscopy failures were defined as Total Hip Arthroplasty or revision hip arthroscopy after index hip arthroscopy. Results. There were751 females and 612 males with an average age of 34.63 years (19 – 58 years). There were 199 cases (14.6%) of labrum repairs only, 286 (20.9%) cam and labrum repairs, 319 (23.4%) cam and pincer surgeries and 193 (14.1%) cam only surgeries. All pre-operative IHOT-33 patient-reported outcomes scores (27.42 ± 6.2) improved significantly at the 6 week-, 3 month- and 6-month follow-up visits (p<0.05). The best improvements were seen in symptoms and functional improvements (IHOT-SFL) (p<0.05) while the poorest amelioration of job-related concerns (IHOT-JRC) existed at all time points (p<0.05). There were 223 failures, 131 patients (9.61%) underwent revision hip arthroscopy and 92 required THA (6.75%) at 18.45 months ± 7.34 months. The 2-year survival rate was 89.2%. The THA conversion rate was 8.4% for patients > 50 years old and 3.72% for patients < 50 years old. Age (>50 years) and female sex were associated with increased risk of conversion to THA (p<0.05) while young (<25 years old) and female patients were most likely to undergo hip revision arthroscopy. Surgery involving repair of the labrum only are more likely to result in revision arthroscopy surgery and THA (70.7% at 10.6 years). CAM & pincer surgery have best longevity (90.9% at 10.6 years). Conclusions. Joint preservation and no subsequent surgery at 10.6 years is 83.64%. This study showed that predictors of revision hip arthroscopy or THA included poor pre-morbid functional score, female gender, age > 45, sudden functional score decrease at 3 months follow-up and cases in which only the labrum is surgically repaired

We investigated the development of CT-based bony radiological parameters associated with femoroacetabular impingement (FAI) in a paediatric and adolescent population with no known orthopaedic hip complaints. We retrospectively reformatted and reoriented 225 abdominal CTs into standardised CT pelvic images with neutral pelvic tilt and inclination (244 female and 206 male hips) in patients ranging from two to 19 years of age (mean 10.4 years). The Tönnis angle, acetabular depth ratio, lateral centre–edge angle, acetabular version and α-angle were assessed. Acetabular measurements demonstrated increased acetabular coverage with age and/or progressive ossification of the acetabulum. The α-angle decreased with age and/or progressive cortical bone development and resultant narrowing of the femoral neck. Cam and pincer morphology occurred as early as ten and 12 years of age, respectively, and their prevalence in the adolescent patient population is similar to that reported in the adult literature. Future aetiological studies of FAI will need to focus on the early adolescent population. Cite this article: Bone Joint J 2013;95-B:598–604

Abstract. Objective. To assess the prevalence of acetabular retroversion in patients presenting with Slipped Upper Femoral Epiphysis using both validated radiological signs and CT-angle measurements. Methods. A retrospective review of all cases involving surgical management for acute SUFE presenting to the Royal Children's Hospital, Melbourne were assessed from 2012–2018. Pre-operative plain radiographs were assessed for slip angle, validated radiological signs of retroversion (post wall/crossover/ischial spine sign) and standardised post-operative CT Scans were used to assess cranial and mid-acetabular version. Results. 116 SUFEs presented in 107 patients who underwent surgical intervention; 47 females and 60 boys, with an average age of 12.7 years (range 7.5–16.6 years). Complete radiological data was available for 91 patients (99 hips) with adequate axial CT imaging of both hips. 82% patients underwent pinning in situ (PIS) with subcapital realignment surgery (SRS) performed in 18% (slip angles >75°). Contralateral prophylactic hip PIS was performed in 72 patients (87%). On the slip side, 68% of patients had 1 or more radiological signs of retroversion in the slipped hip, with 60% on the contralateral side. The mean cranial and mid-acetabular version measurements were −8°(range −30 – 8°) and 10.5°(range −10 – 25°), respectively. Conclusions. Acetabular retroversion is rare in the normal population with studies reports ranging from 0–7%. This study showed an increased prevalence of 68% in SUFE patients, which is likely to be a primary anatomical abnormality, subsequently increasing the shear forces across the proximal femoral growth plate due to superior over-coverage. The resulting CAM lesion from SUFE in combination with the pincer lesion due to retroversion can lead to premature hip impingement and degeneration. Further larger studies are required to assess if acetabular retroversion is a true risk factor, and its role in helping guide management including prophylactic pinning. 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