High prevalence of cam deformity in dysplastic hips: A three-dimensional CT study

A Computer Modeling-Based Target Zone for Transposition Osteotomy of the Acetabulum in Patients with Hip Dysplasia

BACKGROUND

This study aimed to determine the acetabular position to optimize hip biomechanics after transposition osteotomy of the acetabulum (TOA), a specific form of periacetabular osteotomy, in patients with hip dysplasia.

METHODS

We created patient-specific finite-element models of 46 patients with hip dysplasia to simulate 12 virtual TOA scenarios: lateral rotation to achieve a lateral center-edge angle (LCEA) of 30°, 35°, and 40° combined with anterior rotation of 0°, 5°, 10°, and 15°. Joint contact pressure (CP) on the acetabular cartilage during a single-leg stance and simulated hip range of motion without osseous impingement were calculated. The optimal acetabular position was defined as satisfying both normal joint CP and the required range of motion for activities of daily living. Multivariable logistic regression analysis was used to identify preoperative morphological predictors of osseous impingement after virtual TOA with adequate acetabular correction.

RESULTS

The prevalence of hips in the optimal position was highest (65.2%) at an LCEA of 30°, regardless of the amount of anterior rotation. While the acetabular position minimizing peak CP varied among patients, approximately 80% exhibited normalized peak CP at an LCEA of 30° and 35° with 15° of anterior rotation, which were the 2 most favorable configurations among the 12 simulated scenarios. In this context, the preoperative head-neck offset ratio (HNOR) at the 1:30 clock position (p = 0.018) was an independent predictor of postoperative osseous impingement within the required range of motion. Specifically, an HNOR of <0.14 at the 1:30 clock position predicted limitation of required range of motion after virtual TOA (sensitivity, 57%; specificity, 81%; and area under the receiver operating characteristic curve, 0.70).

CONCLUSIONS

Acetabular reorientation to an LCEA of between 30° and 35° with an additional 15° of anterior rotation may serve as a biomechanics-based target zone for surgeons performing TOA in most patients with hip dysplasia. However, patients with a reduced HNOR at the 1:30 clock position may experience limited range of motion in activities of daily living postoperatively.

CLINICAL RELEVANCE

This study provides a biomechanics-based target for refining acetabular reorientation strategies during TOA while considering morphological factors that may limit the required range of motion.

Improved Functional Outcomes of Combined Hip Arthroscopy and Periacetabular Osteotomy at Minimum 2-Year Follow-Up

PURPOSE

To evaluate patient-reported outcomes (PROs) and survivorship at minimum 2-year follow-up after combined hip arthroscopy and periacetabular osteotomy (PAO) performed in the setting of a single anesthetic event.

METHODS

Patients who underwent combined hip arthroscopy (M.J.P.) and PAO (J.M.M.) between January 2017 and June 2020 were identified. Preoperative and minimum 2-year postoperative PROs including Hip Outcome Score-Activities of Daily Living (HOS-ADL), HOS-Sport, modified Harris Hip Score (mHHS), Western Ontario and McMaster Universities Osteoarthritis Index, 12-Item Short Form Survey Mental Component Scores (SF-12 MCS), and 12-Item Short Form Survey Physical Component Score were collected and compared in addition to revision rate, conversion to total hip arthroplasty (THA), and patient satisfaction.

RESULTS

Twenty-four of 29 patients (83%) eligible for the study were available for 2-year minimum follow-up with a median follow-up time of 2.5 years (range, 2.0-5.0). There were 19 females and 5 males with mean age of 31 ± 12 years. Mean preoperative lateral center edge angle was 20° ± 5° and alpha angle was 71° ± 11°. One patient underwent reoperation for removal of a symptomatic iliac crest screw at 11.7 months after operation. Two patients, a 33-year-old woman and a 37-year-old man, were converted to THA at 2.6 and 1.3 years, respectively, following the combined procedure. Both patients had a Tönnis grade of 1 on radiographs, as well as bipolar Outerbridge grade III/IV defects requiring microfracture of the acetabulum. For patients who did not convert to THA (n = 22), there was significant improvement from before to after surgery for all scores (P < .05) except SF-12 MCS. The minimal clinically significant difference and patient-acceptable symptom state rates for HOS-ADL, HOS-Sport, and mHHS were 72%, 82%, 86%, and 95%, 91%, and 95%, respectively. Median patient satisfaction was 10 (range, 4 to 10).

CONCLUSIONS

Single-stage combined hip arthroscopy with periacetabular osteotomy for patients with symptomatic hip dysplasia results in improvement in PROs and arthroplasty free survivorship of 92% at median 2.5 year follow-up.

LEVEL OF EVIDENCE

Level IV, case series.

Combined Hip Arthroscopy and Periacetabular Osteotomy (PAO): Technical Focus on Arthroscopically Elevating the Iliocapsularis and Performing the Open PAO

In this Technical Note, we discuss the combined hip arthroscopy and periacetabular osteotomy (PAO) for the treatment of symptomatic hip dysplasia, with a focus on the technique we use for the PAO. We identify modifications that can be made during the arthroscopic portion of the procedure to assist in the PAO dissection, including arthroscopic capsular closure and arthroscopic elevation of the iliocapsularis muscle off the capsule, which allows for expedited open exposure during the PAO.

Primary cam morphology; bump, burden or bog-standard? A concept analysis

BACKGROUND

Cam morphology, a distinct bony morphology of the hip, is prevalent in many athletes, and a risk factor for hip-related pain and osteoarthritis. Secondary cam morphology, due to existing or previous hip disease (eg, Legg-Calve-Perthes disease), is well-described. Cam morphology not clearly associated with a disease is a challenging concept for clinicians, scientists and patients. We propose this morphology, which likely develops during skeletal maturation as a physiological response to load, should be referred to as primary cam morphology. The aim of this study was to introduce and clarify the concept of primary cam morphology.

DESIGN

We conducted a concept analysis of primary cam morphology using articles that reported risk factors associated with primary cam morphology; we excluded articles on secondary cam morphology. The concept analysis method is a rigorous eight-step process designed to clarify complex 'concepts'; the end product is a precise definition that supports the theoretical basis of the chosen concept.

RESULTS

We propose five defining attributes of primary cam morphology-tissue type, size, site, shape and ownership-in a new conceptual and operational definition. Primary cam morphology is a cartilage or bony prominence (bump) of varying size at the femoral head-neck junction, which changes the shape of the femoral head from spherical to aspherical. It often occurs in asymptomatic male athletes in both hips. The cartilage or bone alpha angle (calculated from radiographs, CT or MRI) is the most common method to measure cam morphology. We found inconsistent reporting of primary cam morphology taxonomy, terminology, and how the morphology is operationalised.

CONCLUSION

We introduce and clarify primary cam morphology, and propose a new conceptual and operational definition. Several elements of the concept of primary cam morphology remain unclear and contested. Experts need to agree on the new taxonomy, terminology and definition that better reflect the primary cam morphology landscape-a bog-standard bump in most athletic hips, and a possible hip disease burden in a selected few.

Characterization of version in the dysplastic hip and the need for subsequent femoral derotational osteotomy after periacetabular osteotomy

Hip dysplasia is a three-dimensional pathomechanical condition that is often more complex than the standard method of measuring lateral center edge angle (CEA) can quantify. Yet there is a paucity of literature examining the differences in version seen between dysplastic and non-dysplastic femoroacetabular impingement (FAI) hips, the relationship of acetabular and femoral version (FV) within dysplastic hips and the contribution of each of these factors to symptoms and outcomes of dysplasia treatment. We sought to describe the acetabular version (AcetV) and FV in dysplastic hips and quantify how these measurements compared with non-dysplastic FAI hips. We also sought to analyze the association of these factors with patient-reported outcomes (PROs) after periacetabular osteotomy (PAO) and determine the need for subsequent femoral derotational osteotomy after PAO. A total of 113 dysplastic patients who underwent PAO (92% female, mean age 24) were compared with 1332 (45% female, mean age 25) non-dysplastic FAI (CEA > 25°) patients. We found that dysplastic hips had a statistically higher AcetV and FV than non-dysplastic FAI hips. There was a very weak correlation between AcetV and FV in dysplastic hips, suggesting that patients with higher AcetV did not necessarily have higher FV. There was no association with AcetV or FV and patient outcomes in our very limited analysis of PROs after PAO, and only 5% of patients with excessive FV (>20°) required subsequent femoral derotational osteotomy, suggesting that in a majority of patients with hip dysplasia, FV may not impact the post-operative clinical course.

Acetabular retroversion in dysplastic hips is associated with decreased 3D femoral head coverage independently from lateral center-edge angle

INTRODUCTION

The clinical significance of acetabular retroversion in non-dysplastic hips can be explained as pincer-type femoroacetabular impingement (FAI), whereas that in dysplastic hips is not clarified because FAI normally poses little problems for dysplastic hips. We aimed to evaluate three-dimensional (3D) femoral head coverage in dysplastic hips with and without acetabular retroversion and to elucidate the role of acetabular retroversion on the 3D femoral head coverage.

MATERIALS AND METHODS

We retrospectively investigated 93 hips in 93 patients (9 males and 84 females) that underwent periacetabular osteotomy for hip dysplasia. Dysplastic hips were divided into anteversion and retroversion groups according to their cranial anteversion, which was measured on the axial section 5 mm caudal to the acetabular roof. The 3D femoral head coverage was provided as a percentage of the acetabulum-covered surface area of the upper femoral hemisphere using a 3D preoperative planning software for total hip arthroplasty.

RESULTS

Of the 93 dysplastic hips, 15 hips (16%) were assigned to the retroversion group, which had significantly younger age at surgery (31.9 years versus 39.2 years; p = 0.033). The lateral center-edge angles were comparable between the groups (13.8° versus 12.9°; p = 0.68); however, the hips in the retroversion group had a trend of smaller 3D femoral head coverage than those in the anteversion group (59% versus 63%; p = 0.058). Multivariate analysis using two-way analysis of covariance showed that lateral center-edge angle (partial regression coefficient = 0.83; t value = 17.3; p < 0.001) and acetabular retroversion (partial regression coefficient = - 2.3; t value = - 4.9; p < 0.001) were independent factors that contributed to the 3D femoral head coverage.

CONCLUSIONS

Acetabular retroversion in dysplastic hips was associated with decreased 3D femoral head coverage independently from lateral center-edge angle. The age at surgery in the retroversion group was significantly younger, suggesting a relationship between decreased 3D coverage and potentially earlier symptom onset.

Surgical Outcomes in the Treatment of Concomitant Mild Acetabular Dysplasia and Femoroacetabular Impingement: A Systematic Review

PURPOSE

To analyze the current approaches and clinical outcomes in the surgical management of concomitant mild acetabular dysplasia and femoroacetabular impingement (FAI).

METHODS

Following the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-analyses) method, the PubMed and Medline databases were searched in March 2019 for studies that reported on surgical outcomes in hips with concomitant mid acetabular dysplasia and FAI. Studies published in English that focused on the surgical outcomes after hip arthroscopy, open surgery, or periacetabular osteotomy of concomitant acetabular dysplasia and FAI, in which the lateral center-edge angle of all subjects was between 15° and 25°, were included. Articles that included subjects with lateral center-edge angle <15°, with a minimum follow-up duration <1 year, had <5 subjects, or were not original articles were excluded.

RESULTS

The initial search yielded 748 studies, and 5 studies met the inclusion criteria. All these 5 studies focused on hip arthroscopic treatment for patients with concomitant mild acetabular dysplasia and FAI. Three studies had level III evidence, whereas 2 studies had level IV evidence. The mean patient age range across the studies was 29.8 to 49.6 years, and the female-to-male ratio was 1.14. Improved patient-reported outcomes (Hip Outcome Score-Activities of Daily Living, Hip Outcome Score-Sport, modified Harris Hip Score, Short Form-12 Physical Component Summary, Western Ontario and McMaster Universities Osteoarthritis Index) at a minimum 2-year follow-up were obtained in 4 of the 5 studies. Two of these 4 studies had a comparative cohort of patients with FAI with normal acetabular coverage, and there was no significant difference in the postoperative outcomes and secondary procedure rate between patients with mild acetabular dysplasia and those with normal acetabular coverage.

CONCLUSIONS

This systematic review indicates that improved patient-reported outcomes can be obtained with hip arthroscopy in the treatment of concomitant mild acetabular dysplasia and FAI at a minimum 2-year follow-up.

LEVEL OF EVIDENCE

Level IV, systematic review of Level III and Level IV studies.

Dynamic hip kinematics before and after periacetabular osteotomy in patients with dysplasia

BACKGROUND

We prospectively analyzed the hip kinematics in patients with developmental dysplasia of the hip (DDH) before and after periacetabular osteotomy (PAO) and in healthy subjects while squatting to determine the influence of coverage of the femoral head on hip kinematics.

METHODS

14 hips in 14 patients with DDH and 10 hips in 10 volunteers were included. Continuous radiographs while squatting and computed tomography images were obtained to assess the in vivo kinematics of the hip and the rim-neck distance using density-based 3D-to-2D model-to-image registration techniques.

RESULTS

The maximum hip flexion angles were 100.4° and 94.9° before and after PAO (p = 0.0863), respectively. The maximum hip flexion angles after PAO did not significantly differ from those of normal hips (102.2°; p = 0.2552). The hip abduction angles at maximum hip flexion were 31.7° and 26.2° before and after PAO (p = 0.1256), respectively. The rim-neck distance decreased from averaged 12.2 mm-8.9 mm (p = 0.0044) after PAO. The lateral center edge angle (LCEA) and anterior center edge angle (ACEA) significantly improved 14.7°-42.4° and 50.4°-54.0° after PAO (p < 0.0001, p = 0.0347), respectively; in particular, the ACEA after PAO did not significantly differ from that in the normal hips (p = 0.1917). The ACEA was not correlated with hip flexion, or the rim-neck distance (p = 0.9601, 0.8764). The LCEA was also not correlated with hip abduction (p = 0.1683).

CONCLUSION

Patients after PAO showed no significant difference in maximum hip flexion while squatting compared to before PAO and normal hips. Horizontalized weight-bearing acetabulum with normalized ACEA could be adequate correction of the acetabular fragment to restore hip RoM without coxalgia that induce the inability to perform squats after PAO.

What factors affect fluoroscopy use during Bernese periacetabular osteotomy for acetabular dysplasia?

Periacetabular osteotomy (PAO) is the treatment of choice for acetabular dysplasia in the skeletally mature. Little is known about factors affecting fluoroscopy use in PAO. Therefore, we strived to determine patient and surgery factors are associated with the amount of fluoroscopy time and radiation dose during PAO. We performed a retrospective review of 378 patients who underwent PAO between January 2012 and August 2017. The mean age was 21.7 years and 326 (86%) were females. A total of 85 patients underwent concomitant arthroscopy and 60 underwent open arthrotomy. We recorded fluoroscopy time in minutes and radiation dose area product (DAP) in mGy·m². Multivariate general linear modeling identified independent predictors of fluoroscopy time and radiation dose. Mean fluoroscopy time was 1.21 minutes and mean fluoroscopy DAP was 0.71 mGy·m². Multivariate predictors of increased fluoroscopy time were male gender (P = 0.001), surgeon (P < 0.001) and whether an arthroscopy was performed (P < 0.001). Multivariate predictors of increased fluoroscopy DAP were increased body mass index (BMI) (P = 0.001), surgeon (P < 0.001) and whether an arthroscopy was performed (P < 0.001). Patients undergoing hip arthroscopy concomitant to PAO are at higher risk of longer fluoroscopy time and higher radiation dose. Other factors affecting fluoroscopy time included male gender and surgeon, while radiation dose was further affected by surgeon and BMI. Our findings can facilitate discussion about the risk of radiation exposure during PAO.

Editorial Commentary: Revision Arthroscopy for Borderline Dysplastic Hips: A Borderline Surgical Indication

Patients with mild or borderline acetabular dysplasia who present with refractory hip pain are challenging patients. Recommending open versus arthroscopic surgery for these patients is a difficult decision, in part because there are conflicting data regarding the outcomes of these procedures. Equally challenging is deciding on a treatment course in a borderline dysplastic patient who has not responded to a previous arthroscopic surgery. Surgeons must give great consideration before recommending revision arthroscopy in this setting.

Surgical Treatment for FAI: Arthroscopic and Open Techniques for Osteoplasty

PURPOSE OF REVIEW

To review the relevant literature and techniques regarding arthroscopic and open treatment of femoroacetabular impingement (FAI). To discuss both the senior authors' preferred method of arthroscopic and open treatment of FAI.

RECENT FINDINGS

Routine treatment of FAI has moved away from open techniques and is more focused arthroscopic methods. Arthroscopic treatment of FAI has more recently focused on differing techniques of hip access and capsular management. Open techniques still have a role in FAI, but indications for open management are focused on cases with more severe pathology. While arthroscopic techniques have shown better outcomes in the short term and higher return to play, it is not without risk and is a procedure with a steep learning curve. In cases of complex joint pathology, such as FAI coupled with dysplasia or Legg-Calve-Perthes, arthroscopy may be not indicated and an open approach preferred. We outline various techniques for both arthroscopic and open treatment of FAI and their outcomes when possible.

Modifications to the Hip Arthroscopy Technique When Performing Combined Hip Arthroscopy and Periacetabular Osteotomy

In the realm of hip preservation, hip arthroscopy is often used to address intra-articular impingement pathology, whereas periacetabular osteotomy (PAO) is used to address dysplasia and instability. Indications to combine these 2 procedures include hip dysplasia and symptomatic instability with a concomitant symptomatic labral tear or the other symptomatic intra-articular pathology (i.e., loose body, chondral flap). The arthroscopic portion of the procedure allows repair of the injured labrum and close inspection of the hip joint, and the PAO addresses undercoverage and/or inappropriate version of the acetabulum. The open approach used in PAO also allows access to the peripheral compartment to debride a cam lesion, if present, and the subspine region is accessible to perform subspine decompression, if needed. In this technique, we highlight special considerations pertaining to hip arthroscopy that is performed in combination with a PAO. Hip arthroscopy is the first procedure that takes place in this combined case, and modifications to the standard hip arthroscopic technique can prevent unnecessary difficulty during the PAO that follows.

What Are the Results of Surgical Treatment of Hip Dysplasia With Concomitant Cam Deformity?

BACKGROUND

Periacetabular osteotomy (PAO) is a reliable procedure to correct the deficient acetabular coverage in hips with developmental dysplasia. It is unclear how the presence of additional femoral cam-type deformity might influence the clinical and radiographic treatment results of PAO.

QUESTIONS/PURPOSES

(1) Are there differences in clinical scores (WOMAC, EQ-5D) and examination findings (impingement sign) or radiographic measures of acetabular orientation and head sphericity after PAO for isolated acetabular dysplasia when compared with the combined pathology of dysplasia and additional femoral cam deformity? (2) Are these clinical and radiographic findings after combined surgical therapy for additional cam deformity influenced by different pathology-adjusted surgical techniques?

METHODS

From July 2005 to December 2010, 86 patients (106 hips) underwent PAO for hip dysplasia. Surgical and outcome data were prospectively collected and retrospectively reviewed in a comparative observational study. Indications for surgery were a lateral center-edge angle less than 25° and hip pain for at least 6 months. The contraindications for surgery were advanced radiographic osteoarthritis (Kellgren-Lawrence Grade 3), incongruency of joint space, and patient age > 50 years. Depending on preoperative hip ROM, impingement test, and presence of a radiographically visible cam deformity, treatment allocation was performed: Group I: isolated PAO in patients without symptomatic asphericity, Group IIa: PAO with subsequent osteochondroplasty through arthrotomy for patients with symptomatic cam deformity and no labrochondral pathology, and Group IIb: arthroscopically assisted osteochondroplasty and additional labrochondral repair with subsequent PAO when patients had labrochondral lesions in addition to a symptomatic cam deformity. Clinical outcome (impingement test, EQ-5D, WOMAC) as well as radiographic parameters (lateral center-edge angle, crossover sign, alpha angle, osteoarthritis grade) were obtained after a mean followup of 63 ± 18 months (range, 31-102 months) and compared with the baseline data. Eleven patients (13%) were lost to followup. With the numbers available, our study had 80% power to detect a difference between Groups I and II of 10 points on the WOMAC scores.

RESULTS

There was no difference in the increase of WOMAC scores in patients with PAO alone (Group I; preoperative score 74 ± 17 versus postoperative 91 ± 15, p = 0.033) when compared with PAO and concurrent osteochondroplasty (Groups II A and B preoperative 73 ± 19 versus postoperative 90 ± 13 p < 0.001). The mean postoperative alpha angles in Group II (38° ± 6°) improved when compared with preoperative values (56° ± 15°; p < 0.001) and were even lower than native offset alpha angles in Group I (47° ± 11°). Clinical scores as well as postoperative radiographic parameters were not different between patients with conventional osteochondroplasty alone (Group IIA) and patients with arthroscopically assisted cam resection and intraarticular labrochondral repair (Group IIB).

CONCLUSIONS

With the numbers available, we detected no differences in outcome scores and radiographic results between patients who had been treated with PAO alone and patients who underwent combined PAO and offset correction for cam deformity. Although arthroscopically assisted treatment of advanced labrochondral lesions together with osteochondroplasty is possible during PAO and the results were not different in this small study when compared with patients with PAO and osteochondroplasty alone, the type and extent of damage that would indicate additional cartilage surgery over cam resection alone remain unclear.

LEVEL OF EVIDENCE

Level III, therapeutic study.

Femoral Morphology in the Dysplastic Hip: Three-dimensional Characterizations With CT

BACKGROUND

Hip dysplasia represents a spectrum of complex deformities on both sides of the joint. Although many studies have described the acetabular side of the deformity, to our knowledge, little is known about the three-dimensional (3-D) head and neck offset differences of the femora of dysplastic hips. A thorough knowledge of proximal femoral anatomy is important to prevent potential impingement and improve results after acetabular reorientation.

QUESTIONS/PURPOSES

(1) Are there common proximal femoral characteristics in patients with symptomatic hip dysplasia undergoing periacetabular osteotomy (PAO)? (2) Where is the location of maximal femoral head and neck offset deformity in hip dysplasia? (3) Do certain subgroups of dysplastic hips more commonly have cam-type femoral morphology? (4) Is there a relationship between hip ROM as well as impingement testing and 3-D head and neck offset deformity?

METHODS

Using our hip preservation database, 153 hips (148 patients) underwent PAO from October 2013 to July 2015. We identified 103 hips in 100 patients with acetabular dysplasia (lateral center-edge angle [LCEA] < 20°) and who had a Tönnis grade of 0 or 1. Eighty-six patients (86%) underwent preoperative low-dose pelvic CT scans at our institution as part of the preoperative planning for PAO. It is currently our standard to obtain preoperative low-dose pelvic CT scans (0.75-1.25 mSv, equivalent to three to five AP pelvis radiographs) on all patients before they undergo PAO unless a prior CT scan is performed at an outside institution. Hips with a history of a neuromuscular disorder, prior trauma, prior surgery, radiographic evidence of joint degeneration, ischemic necrosis, or Perthes-like deformities were excluded. Fifty hips in 50 patients met inclusion criteria and had CT scans available for review. Hips were analyzed with Dyonics Plan software and characterized with regard to version, neck-shaft angle, femoral head diameter, head and neck offset, femoral neck length, femoral offset, head center height, trochanteric height, and alpha angle. The maximum head and neck offset deformity was assessed using an entire clockface and an alpha angle ≥ 55° defined coexisting cam morphology. Subgroups included severity of lateral dysplasia: mild (LCEA 15°-20°) and moderate/severe (LCEA < 15°). Femoral version subgroups were defined as normal (5°-20°), decreased (≤ 5°), or increased (> 20°). The senior author (JCC) performed all physical examination testing.

RESULTS

The mean LCEA was 14° (±4°), whereas the mean femoral anteversion was 19° (±12°). Eight hips (16%) demonstrated relative femoral retroversion (≤ 5°), whereas 26 (52%) showed excessive femoral anteversion (> 20°). Four hips (8%) had ≥ 35° of femoral anteversion. The mean neck-shaft angle was 136° (±5°). The mean maximum alpha location was 2:00 o'clock (±45 minutes) and the mean maximum alpha angle was 52° (±6°). Minimum head-neck offset ratio was located at 1:30 with a mean of 0.14 (±0.03). An anterior head-neck offset ratio of ≤ 0.17 or an alpha angle ≥ 55° was found in 43 (86%) of hips. Twenty-one dysplastic hips (42%) had an alpha angle ≥ 55°. Mildly dysplastic hips had decreased femoral head and neck offset (9 ± 1) and head and neck offset ratio (0.20 ± 0.03) at 12 o'clock compared with moderate/severe dysplastic hips (10 ± 1 and 0.22 ± 0.03, respectively; p = 0.04 and p = 0.01). With the numbers available, we found that hips with excessive femoral anteversion (> 20°) had no difference in the alpha angle at 3 o'clock (42 ± 7) compared with hips with relative femoral retroversion (≤ 5°; 48 ± 4; p = 0.06). No other differences in femoral morphology were found between hips with mild or moderate/severe dysplasia or in the femoral version subgroups with the numbers available. Anterior impingement test was positive in 76% of hips with an alpha angle ≥ 55° and 83% of the hips with an alpha angle ≤ 55°. No correlation was found between proximal femoral morphology and preoperative ROM.

CONCLUSIONS

In this subset of dysplastic hips, cam deformity of the femoral head and neck was present in 42% of hips with maximal head-neck deformity at 2 o'clock, and 82% had reduced head-neck offset at the 1:30 point. We conclude that cam-type deformities and decreased head-neck offset in developmental dysplasia of the hip are common. Patients should be closely assessed for need of a head and neck osteochondroplasty, especially after acetabular correction. Future prospective studies should evaluate the influence of proximal femoral anatomy on surgical results of PAO for dysplastic hips.

LEVEL OF EVIDENCE

Level IV, prognostic study.

Prevalence of pincer, cam, and combined deformities in Japanese hip joints evaluated with the Japanese Hip Society diagnostic guideline for femoroacetabular impingement: A CT-based study

BACKGROUND

Femoroacetabular impingement (FAI) is thought to be associated with hip osteoarthritis. We investigated the prevalences of radiologic deformities of the pincer, cam, and their combinations in Japanese hip joints using computed tomography (CT) according to the Japanese Hip Society diagnostic guideline for FAI.

METHODS

Multi-slice CT images were evaluated. Pincer deformities were defined as: type 1: center-edge angle (CE) ≥40°; type 2: CE ≥ 30° and acetabular roof obliquity ≤0°; type 3: CE ≥ 25° and retroverted acetabulum. Cam deformities were defined as: type 1: CE ≥ 25°, α-angle ≥55°, and head-neck offset ratio <0.14; type 2: CE ≥ 25°, α-angle ≥55°, and herniation pit positive; type 3: CE ≥ 25°, α-angle ≥55°, and pistol grip deformity positive.

RESULTS

We studied 128 hips. Pincer was detected in 35.9% (type 1, 12.5%; type 2, 18.0%; type 3, 13.3%). Cam was detected in 24.2% (type 1, 23.4%; type 2, 7.8%; type 3, 10.9%). Combined deformities were detected in 10.2%. Type 3 pincer/type 1 cam was the most frequent combined deformity compared with all combined deformities. All of the cam deformities, total combined deformities, and all radiological FAIs appeared significantly more often in men.

CONCLUSIONS

When we used this guideline to diagnose FAI in a Japanese population, radiological FAI was common, and pincer deformities were more common than cam deformities. The most frequent seen pincer, cam, and combined deformities was type 2 pincer, type 1 cam, and the combination of type 3 pincer/type 1 cam, respectively.