Birmingham Royal Orthopedic Hospital (BROH) CAM Offset: A Simplified Metric for Detection of CAM Morphology of the Hip

Abstract

Background

CAM morphology of the hip is a disorder of abnormal morphology of the femoral head–neck junction associated with loss of the osseous sphericity of the femoral head. Several radiological measurements exist to detect CAM morphology of the hip.

Objectives

The aim of the study was to evaluate the precision and efficacy of a new BROH CAM offset distance as a novel magnetic resonance imaging (MRI) parameter designed to detect CAM morphology of the hip.

Materials and Methods

Oblique axial MR images of 100 patients who underwent hip MRI scans were analyzed. Two readers measured the alpha angle and BROH CAM offset to detect CAM morphology. Diagnostic cutoff values for cam offset measurements were determined, and their diagnostic accuracies were evaluated.

Results

The mean “alpha angle” measured on an oblique projection was 34.31 degrees (standard deviation [SD] = 14.63), and when measured on an axial projection, it was 41.98 degrees (SD = 7.44). The BROH CAM offset distance was 3.49 mm (SD = 0.90 mm). There was an excellent correlation between the new BROH CAM offset and the alpha angle with a p-value of 0.006 (Pearson's linear correlation coefficient). Based on the results, a 57-degree alpha angle correlates to a BROH CAM offset of 4.11 mm, a 60-degree alpha angle correlates to a BROH CAM offset of 4.23 mm, and a 55-degree alpha angle correlates to a BROH CAM offset of 4.03 mm.

Conclusion

Our new BROH CAM offset shows an excellent correlation with the alpha angle and is the easiest metric that can be used for the detection of CAM morphology of the hip.

Keywords

CAM morphology - alpha angle - femoroacetabular impingement - magnetic resonance imaging

Data Availability Statement

Data can be shared on request.

Ethical Approval

All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards. Local ethical committee approval was obtained.

Patients' Consent

Patient consent was taken for this study.

Publication History

Article published online:
27 March 2025

• References

• 1 Albers CE, Wambeek N, Hanke MS, Schmaranzer F, Prosser GH, Yates PJ. Imaging of femoroacetabular impingement-current concepts. J Hip Preserv Surg 2016; 3 (04) 245-261
• 2 Dijkstra HP, Ardern CL, Serner A. et al. Primary cam morphology; bump, burden or bog-standard? A concept analysis. Br J Sports Med 2021; 55 (21) 1212-1221
• 3 Wyss TF, Clark JM, Weishaupt D, Nötzli HP. Correlation between internal rotation and bony anatomy in the hip. Clin Orthop Relat Res 2007; 460 (460) 152-158
• 4 Gosvig KK, Jacobsen S, Palm H, Sonne-Holm S, Magnusson E. A new radiological index for assessing asphericity of the femoral head in cam impingement. J Bone Joint Surg Br 2007; 89 (10) 1309-1316
• 5 Nötzli HP, Wyss TF, Stoecklin CH, Schmid MR, Treiber K, Hodler J. The contour of the femoral head-neck junction as a predictor for the risk of anterior impingement. J Bone Joint Surg Br 2002; 84 (04) 556-560
• 6 Nouh MR, Schweitzer ME, Rybak L, Cohen J. Femoroacetabular impingement: can the alpha angle be estimated?. AJR Am J Roentgenol 2008; 190 (05) 1260-1262
• 7 van Klij P, Reiman MP, Waarsing JH. et al. Classifying cam morphology by the alpha angle: a systematic review on threshold values. Orthop J Sports Med 2020; 8 (08) 2325967120938312
• 8 Ng KC, Lamontagne M, Adamczyk AP, Rakhra KS, Beaulé PE. Patient-specific anatomical and functional parameters provide new insights into the pathomechanism of cam FAI. Clin Orthop Relat Res 2015; 473 (04) 1289-1296
• 9 Amanatullah DF, Antkowiak T, Pillay K. et al. Femoroacetabular impingement: current concepts in diagnosis and treatment. Orthopedics 2015; 38 (03) 185-199
• 10 Mimura T, Mori K, Okumura N. et al. β-Angles of hips with femoroacetabular impingement versus asymptomatic normal hips in a Japanese population: a CT-based observational clinical study. J Orthop Sci 2020; 25 (02) 261-266
• 11 Agricola R, Waarsing JH, Arden NK. et al. Cam impingement of the hip: a risk factor for hip osteoarthritis. Nat Rev Rheumatol 2013; 9 (10) 630-634
• 12 Tang J, van Buuren MMA, Riedstra NS. et al. Cam morphology is strongly and consistently associated with development of radiographic hip osteoarthritis throughout 4 follow-up visits within 10 years. Osteoarthritis Cartilage 2023; 31 (12) 1650-1656
• 13 Dijkstra HP, Mc Auliffe S, Ardern CL. et al; Young Athlete's Hip Research (YAHiR) Collaborative. Oxford consensus on primary cam morphology and femoroacetabular impingement syndrome: part 1-definitions, terminology, taxonomy and imaging outcomes. Br J Sports Med 2022; 57 (06) 325-341
• 14 Tannast M, Siebenrock KA, Anderson SE. Femoroacetabular impingement: radiographic diagnosis: what the radiologist should know. AJR Am J Roentgenol 2007; 188 (06) 1540-1552
• 15 Fiorentino G, Fontanarosa A, Cepparulo R. et al. Treatment of cam-type femoroacetabular impingement. Joints 2015; 3 (02) 67-71
• 16 Royston E, Bush L. Femoroacetabular impingement: a classic case of cam-type impingement in a 21-year-old soldier. Radiol Case Rep 2015; 9 (03) 781
• 17 Saito M, Tsukada S, Yoshida K, Okada Y, Tasaki A. Correlation of alpha angle between various radiographic projections and radial magnetic resonance imaging for cam deformity in femoral head-neck junction. Knee Surg Sports Traumatol Arthrosc 2017; 25 (01) 77-83