The lateral view head-neck index (LVHNI): a diagnostic tool for the sequelae of slipped capital femoral epiphysis

Femoral Head-Neck Translation Ratio Is a Measurement of the True Deformity of Slipped Capital Femoral Epiphysis

A new method to quantify proximal femoral head-neck deformity in slipped capital femoral epiphysis (SCFE) is presented. In SCFE the femoral head slips posteriorly and inferiorly relative to the femoral neck. The distance of the femoral head center from the femoral neck axis (center-axis distance, CAD) represents the severity of the post-slip deformity. CAD is calculated on the anteroposterior and the frog-lateral pelvis views. It is shown that CAD is only a function of the femoral head-neck offset difference on both sides of the femoral neck. The percentage of CAD relative to the diameter of femoral neck is the femoral head-neck translation ratio (FHNTR) on the respective x-ray projection. Measurements on radiographs of 37 patients with history of unilateral SCFE were performed. The asymptomatic contralateral hips were used as controls. On the anteroposterior pelvis view, mean FHNTR was -12.2% and -4.3% for the affected and asymptomatic contralateral hips, respectively (paired t-test, p < .01), indicating inferior translation of the femoral head relative to the femoral neck. On the frog-lateral view, mean FHNTR was -21.1% and -6.5% for the affected and the contralateral hips, respectively (paired t-test, p < .01), indicating posterior translation of the femoral head relative to the femoral neck. There is a moderate inverse correlation between FHNTR on the frog-lateral pelvis view and Southwick's slip angle (Pearson correlation coefficient r = -0.679, p < .001). FHNTR on two radiological planes (anteroposterior and frog-lateral) is a simple measurement of the posteroinferior translation of the femoral head relative to the femoral neck in SCFE. It is a measurement of the true deformity of the proximal femur in SCFE. Calculation of FHNTR may be applicable to classify SCFE, to monitor femoral head-neck remodeling after slip stabilization, to describe the femoral head-neck relation in healthy individuals, and to monitor femoral head-neck changes secondary to other hip pathology, such as Perthes disease or developmental dysplasia of the hip.

Twelve percent of hips with a primary cam deformity exhibit a slip-like morphology resembling sequelae of slipped capital femoral epiphysis

BACKGROUND

In some hips with cam-type femoroacetabular impingement (FAI), we observed a morphology resembling a more subtle form of slipped capital femoral epiphysis (SCFE). Theoretically, the morphology in these hips should differ from hips with a primary cam-type deformity.

QUESTIONS/PURPOSES

We asked if (1) head-neck offset; (2) epiphyseal angle; and (3) tilt angle differ among hips with a slip-like morphology, idiopathic cam, hips after in situ pinning of SCFE, and normal hips; and (4) what is the prevalence of a slip-like morphology among cam-type hips?

METHODS

We retrospectively compared the three-dimensional anatomy of hips with a slip-like morphology (29 hips), in situ pinning for SCFE (eight hips), idiopathic cam deformity (171 hips), and 30 normal hips using radial MRI arthrography. Normal hips were derived from 17 asymptomatic volunteers. All other hips were recruited from a series of 277 hips (243 patients) seen at a specialized academic hip center between 2006 and 2010. Forty-one hips with isolated pincer deformity were excluded. Thirty-six of 236 hips had a known cause of cam impingement (secondary cam), including eight hips after in situ pinning of SCFE (postslip group). The 200 hips with a primary cam were separated in hips with a slip-like morphology (combination of positive fovea sign [if the neck axis did not intersect with the fovea capitis] and a tilt angle [between the neck axis and perpendicular to the basis of the epiphysis] exceeding 4°) and hips with an idiopathic cam. We evaluated offset ratio, epiphyseal angle (angle between the neck axis and line connecting the center of the femoral head and the point where the physis meets the articular surface), and tilt angle circumferentially around the femoral head-neck axis. Prevalence of slip-like morphology was determined based on the total of 236 hips with cam deformities.

RESULTS

Offset ratio was decreased anterosuperiorly in idiopathic cam, slip-like, and postslip (eg, 1 o'clock position with a mean offset ranging from 0.00 to 0.14; p < 0.001 for all groups) compared with normal hips (0.25 ± 0.06 [95% confidence interval, 0.13-0.37]) and increased posteroinferiorly in slip-like (eg, 8 o'clock position, 0.5 ± 0.09 [0.32-0.68]; p < 0.001) and postslip groups (0.55 ± 0.12 [0.32-0.78]; p < 0.001) and did not differ in idiopathic cam (0.32 ± 0.09 [0.15-0.49]; p = 0.323) compared with normal (0.31 ± 0.07 [0.18-0.44]) groups. Epiphyseal angle was increased anterosuperiorly in the slip-like (eg, 1 o'clock position, 70° ± 9° [51°-88°]; p < 0.001) and postslip groups (75° ± 13° [49°-100°]; p = 0.008) and decreased in idiopathic cam (50° ± 8° [35°-65°]; p < 0.001) compared with normal hips (58° ± 8° [43°-74°]). Posteroinferiorly, epiphyseal angle was decreased in slip-like (eg, 8 o'clock position, 54° ± 10° [34°-74°]; p < 0.001) and postslip (44° ± 11° [23°-65°]; p < 0.001) groups and did not differ in idiopathic cam (76° ± 8° [61°-91°]; p = 0.099) compared with normal (73° ± 7° [59°-88°]) groups. Tilt angle increased in slip-like (eg, 2/8 o'clock position, 14° ± 8° [-1° to 30°]; p < 0.001) and postslip hips (29° ± 10° [9°-48°]; p < 0.001) and decreased in hips with idiopathic cam (-7° ± 5° [-17° to 4°]; p < 0.001) compared with normal (-1° ± 5° [-10° to 8°]) hips. The prevalence of a slip-like morphology was 12%.

CONCLUSIONS

The slip-like morphology is the second most frequent pathomorphology in hips with primary cam deformity. MRI arthrography of the hip allows identifying a slip-like morphology, which resembles hips after in situ pinning of SCFE and distinctly differs from hips with idiopathic cam. These results support previous studies reporting that SCFE might be a risk factor for cam-type FAI.

45°-45°-30°Frog-leg radiograph for diagnosing cam-type anterior femoroacetabular impingement: Reproducibility and thresholds

BACKGROUND

The many radiographic views suggested for evaluating anterior femoroacetabular impingement (FAI), due to a cam effect, are not specific for this condition and have not been proven of diagnostic value in studies, including control groups. Using a new and specific radiographic view, we evaluated the reproducibility of the main radiographic criteria for FAI, determined normal values for these criteria in a control group, and established diagnostic threshold values.

HYPOTHESIS

This specific view offers good reproducibility and effectively detects abnormal values of criteria for FAI.

MATERIALS AND METHODS

Inter-observer and intra-observer reproducibility of specific radiographic criteria (αangle and modified head-neck offset [HNO]) were computed from preoperative and postoperative radiographs of 96 hips (75 patients, 61 males and 14 females) using the specific 45°-45°-30° frog-leg view (F45 view). Values in the group with FAI were compared to those in a control group of asymptomatic volunteers (100 hips, 27 males and 23 females).

RESULTS

Inter-observer and intra-observer reproducibility was very good, with intra-class correlation coefficients of 0.955and 0.987, respectively, for the α angle and of 0.895 and 0.984, respectively, for the HNO. Mean values of both parameters differed significantly between the FAI and control groups: 73.9° (53° to 96°) vs. 49.3° (35° to 69°) for the αangle, respectively; and 2.5mm (-4.6 to 9.4) vs. 7.6mm (1.7 to 11.8) for HNO, respectively. The normal values defined as the boundary of the 95% reference interval in the control group were<60.2° for the α angle, and>4.6mm for the HNO.

DISCUSSION

The45°-45°-30° frog-leg view is useful for diagnosing FAI due to a cam effect. This view is easy to perform, and the thresholds determined in our study assist in its interpretation: α angle values>58° in females and>63° in males indicate cam-type femoral geometry. In both genders, HNO values<5mm support a diagnosis of anterior FAI.

LEVEL OF EVIDENCE

Level III, case-control study.

The frequency of sequelae of slipped upper femoral epiphysis in cam-type femoroacetabular impingement

Slipped upper femoral epiphysis (SUFE) is one of the known causes of cam-type femoroacetabular impingement (FAI). The aim of this study was to determine the proportion of FAI cases considered to be secondary to SUFE-like deformities.

We performed a case–control study on 96 hips (75 patients: mean age 38 years (15.4 to 63.5)) that had been surgically treated for FAI between July 2005 and May 2011. Three independent observers measured the lateral view head–neck index (LVHNI) to detect any SUFE-like deformity on lateral hip radiographs taken in 45° flexion, 45° abduction and 30° external rotation. A control group of 108 healthy hips in 54 patients was included for comparison (mean age 36.5 years (24.3 to 53.9).

The impingement group had a mean LVHNI of 7.6% (16.7% to -2%) versus 3.2% in the control group (10.8% to -3%) (p < 0.001). A total of 42 hips (43.7%) had an index value > 9% in the impingement group versus only six hips (5.5%) in the control group (p < 0.001). The impingement group had a mean α angle of 73.9° (96.2° to 53.4°) versus 48.2° (65° to 37°) in the control group (p < 0.001).

Our results suggest that SUFE is one of the primary aetiological factors for cam-type FAI.

Cite this article: Bone Joint J 2014; 96-B:724–9.

Frequency of radiographic signs of slipped capital femoral epiphysiolysis sequelae in hip arthroplasty candidates for coxarthrosis

INTRODUCTION

The rate of osteoarthritis of the hip secondary to slipped capital femoral epiphysis (SCFE) is a subject of debate, and its frequency is underestimated in particular because of subclinical forms that may not be diagnosed during childhood.

HYPOTHESIS

The frequency of radiographic anomalies subsequent to SCFE in adults requiring hip arthroplasty is higher than that reported in recent studies (6% to 15%).

MATERIALS AND METHODS

A prospective single-center epidemiological radiography study was performed by one observer. Hip X-rays of patients who were being treated by arthroplasty for advanced hip osteoarthritis between January 2010 and May 2012 were analyzed. The etiology of osteoarthritis was classified in each patient according to the data obtained (primary, SCFE, dysplasia, protrusio acetabuli, other). The lateral view head-neck index (LVHNI) was used to quantify posterior translation of the femoral head, and identify SCFE sequelae.

RESULTS

One hundred and eighty-six hips were included. Osteoarthritis was considered primary in 51 patients (27.4%), secondary to dysplasia in 42 (22.5%), protrusio acetabuli in 38 (20.5%) or another disease in nine (4.9%) while 46 hips (24.7%) presented a radiographic image suggesting SCFE past history. SCFE type deformities were the primary etiology of osteoarthritis in patients less than 60years old (30/84 or 35.7%). The mean age of patients in the SCFE group was 56.2years old (26-80) compared to 66 (54-91) for the primary osteoarthritis group (P<0.0001). The mean LVHNI was 13% (9-24%) in the SFCE group, the mean body mass index was 27.1kg/m(2) (±3.5; 18.2-35.4) in the SFCE group and the male to female ratio was 7.3/1.

CONCLUSION

Our study identified a population with a morphological SCFE type anomaly of the coxofemoral joint (LVHNI>9%), which results in the development of earlier osteoarthritis than that found in the rest of the population. SCFE is more common than reported in the literature because it is the first etiology of osteoarthritis of the hip in subjects less than 60years old.

LEVEL OF EVIDENCE

Level III. Diagnostic prospective study with a control group.