Corrections in alpha angle following two different operative approaches for CAM-type femoral acetabular impingement - Ganz surgical hip dislocation vs anterior mini-open

When are patients with osteoarthritis referred for surgery?

Current treatment strategies in hip and knee osteoarthritis (OA) involve a combined approach that includes not only modification of risk factors and conservative treatment but also joint-preserving surgical therapy in the early stages, or joint replacement in late OA. With the recent development of new etiological concepts (i.e. hip dysplasia and femoroacetabular impingement as major risk factors for hip OA), treatment alternatives for joint preservation could be extended significantly. Satisfactory results of osteotomies and other reconstructive procedures around hip and knee joints can only be expected in early OA (Kellgren/Lawrence grade 0-II). If patients with advanced radiographic OA grades III-IV do not respond to conservative treatment over at least 3 months and express a relevant burden of disease, joint replacement might be considered. Prior to surgery, potential contraindications must be excluded, patient expectations need to be discussed, and modifiable risk factors, which may negatively influence the outcome, should be optimized.

Do patients with femoroacetabular impingement syndrome who undergo hip arthroscopy display improved alpha angle (magnetic resonance imaging) and radiographic hip morphology?

AIMS

To compare (a) the change in radiological bony morphology between participants with femoroacetabular impingement (FAI) syndrome who underwent arthroscopic hip surgery compared to physiotherapist-led non-surgical care and (b) the change in radiological bony morphology between participants with FAI syndrome who underwent arthroscopic hip surgery involving cam resection or acetabular rim trimming or combined cam resection and acetabular rim trimming.

METHODS

Maximum alpha angle measurements on magnetic resonance imaging and Hip2 Norm standardized hip measurements on radiographs were recorded at baseline and at 12 months postoperatively. One-way analysis of covariance and independent T tests were conducted between participants who underwent arthroscopic hip surgery and physiotherapist-led non-surgical care. Independent T tests and analysis of variance were conducted between participants who underwent the 3 different arthroscopic hip procedures.

RESULTS

Arthroscopic hip surgery resulted in significant improvements to mean alpha angle measurements (decreased from 70.8° to 62.1°) (P value < .001, 95% CI -11.776, -4.772), lateral center edge angle (LCEA) (P value = .030, 95% CI -3.403, -0.180) and extrusion index (P value = 0.002, 95% CI 0.882, 3.968) compared to physiotherapist-led management. Mean maximum 1-year postoperative alpha angle was 59.0° (P value = .003, 95% CI 4.845, 18.768) for participants who underwent isolated cam resection. Measurements comparing the 3 different arthroscopic hip procedures only differed in total femoral head coverage (F[2,37] = 3.470, P = .042).

CONCLUSION

Arthroscopic hip surgery resulted in statistically significant improvements to LCEA, extrusion index and alpha angle as compared to physiotherapist-led management. Measured outcomes between participants who underwent cam resection and/or acetabular rim trimming only differed in total femoral head coverage.

Normative values of the alpha angle and triangular index measured from the hip radiographs of an African population

INTRODUCTION

Undetected femoroacetabular impingement (FAI), caused by asphericity of the femoral head, has been implicated as a leading cause of hip osteoarthritis in later stages. Two known types of impingement of the femur head with the acetabulum include the cam-type and pincer type, and the alpha angle and triangular index are indices applied in determining the presence of FAI in a hip radiograph.

OBJECTIVE

To determine the normal range and upper limit of normal of the alpha angle and triangular index of an African population using non-pathological hip radiographs.

MATERIALS AND METHODS

Hip radiographs of 104 subjects reported to be normal were retrospectively studied. The images were reassessed jointly by three radiographers and afterwards by three consultant radiologists. The alpha angle and triangular index of selected radiographs were measured with appropriate electronic callipers. Values obtained were correlated with the age and gender of the patients.

RESULTS

The mean ± SD of the alpha angle for the population studied was 46.70 ± 12.34⁰ with a range of 33.30⁰-96.82⁰ (males: 45.09 ± 12.03⁰, females: 47.32 ± 12.37⁰), and the upper limit of normal obtained was 79.16⁰. The mean triangular index was 1.71±1.38 with a range of 0.03-5.98 (males: 1.77 ± 1.39, females: 1.65 ± 1.36), 4.12 being the upper limit of normal. There was no statistically significant difference between measurements of both indices with age and gender. However, there was excellent agreement between and within raters for both measurements (alpha angle: 0.992; triangular index: 0.924).

CONCLUSION

The upper limits of normal for the alpha angle and triangular index of the studied population are 79.16⁰ and 4.12. Age and gender were independent of the values measured, and the measurements demonstrated excellent inter-rater and intra-rater agreement. A normal range is thus provided, with upper limits beyond which a possible femoroacetabular impingement may be diagnosed.