Abstract
Objective
The description of femoral head sphericity and related risk for femoroacetabularimpingement is currently limited to an angular estimate—the alpha angle—whose relevance and accuracy have been challenged. We developed a three-dimensional approach for both automated digital measurement of the alpha angle and the detection of camdeformities. Accuracy and diagnostic relevance of the alpha angle estimated by means of the oblique axial and multiple radial plane protocol were compared with the computed results.
Materials and methods
Using subject-specific statistical information of the femur head and mid-neck region, a method was developed to accurately compute the maximum alpha angle and to define aspherical eccentric areas at the femoral head-neck junction. The method was evaluated on 102 dry cadaver femur specimens.
Results
Average detection limit for bony prominences at the head-neck transition was 0.98 mm. Pixel size of the investigated CT data was 0.79 mm. Mean maximum computed alpha angle of the femurs with cam-type morphology as identified by the morphological method was 67.72° (range 53.04–88.02°). Mean maximum computed alpha angle of the femurs without cam deformity was 47.65° (range 38.67–59.81°). Alpha angle estimates obtained by means of the multiple radial plane protocol correlated better (R = 0.88) and showed higher diagnostic agreement (phi = 0.77) with the 3D computational analysis compared to the oblique axial protocol (R = 0.60; phi = 0.67).
Conclusions
The alpha angle seems to be a relevant screening tool when obtained by 3D computed analysis or when estimated according to the multiple radial plane protocol. Estimates obtained by means of the oblique axial protocol have insufficient diagnostic and measurement accuracy.
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References
Myers SR, Eijer H, Ganz R. Anterior femoroacetabular impingement after periacetabular osteotomy. Clin Orthop Relat Res. 1999;363:93–9.
Ganz R, Leunig M, Leunig-Ganz K, Harris WH. The etiology of osteoarthritis of the hip: an integrated mechanical concept. Clin Orthop Relat Res. 2008;466(2):264–72.
Notzli 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(4):556–60.
Johnston TL, Schenker ML, Briggs KK, Philippon MJ. Relationship between offset angle alpha and hip chondral injury in femoroacetabular impingement. Arthroscopy. 2008;24(6):669–75.
Beall DP, Sweet CF, Martin HD, Lastine CL, Grayson DE, Ly JQ, et al. Imaging findings of femoroacetabular impingement syndrome. Skeletal Radiol. 2005;34(11):691–701.
Nouh MR, Schweitzer ME, Rybak L, Cohen J. Femoroacetabular impingement: can the alpha angle be estimated? AJR Am J Roentgenol. 2008;190(5):1260–2.
Rakhra KS, Sheikh AM, Allen D, Beaule PE. Comparison of MRI alpha angle measurement planes in femoroacetabular impingement. Clin Orthop Relat Res. 2009;467(3):660–5.
Pollard TC, Villar RN, Norton MR, Fern ED, Williams MR, Simpson DJ, et al. Femoroacetabular impingement and classification of the cam deformity: the reference interval in normal hips. Acta Orthop. 2010;81(1):134–41.
Zebaze RM, Jones A, Welsh F, Knackstedt M, Seeman E. Femoral neck shape and the spatial distribution of its mineral mass varies with its size: clinical and biomechanical implications. Bone. 2005;37(2):243–52.
Kordelle J, Millis M, Jolesz FA, Kikinis R, Richolt JA. Three-dimensional analysis of the proximal femur in patients with slipped capital femoral epiphysis based on computed tomography. J Pediatr Orthop. 2001;21(2):179–82.
Abel MF, Sutherland DH, Wenger DR, Mubarak SJ. Evaluation of CT scans and 3-D reformatted images for quantitative assessment of the hip. J Pediatr Orthop. 1994;14(1):48–53.
Beaule PE, Zaragoza E, Motamedi K, Copelan N, Dorey FJ. Three-dimensional computed tomography of the hip in the assessment of femoroacetabular impingement. J Orthop Res. 2005;23(6):1286–92.
Howe WG. Two-sided tolerance limits for normal populations—some improvements. J Am Stat Assoc. 1969;64:610–20.
Lohan DG, Seeger LL, Motamedi K, Hame S, Sayre J. Cam-type femoral-acetabular impingement: is the alpha angle the best MR arthrography has to offer? Skeletal Radiol. 2009;38(9):855–62.
Tanzer M, Noiseux N. Osseous abnormalities and early osteoarthritis: the role of hip impingement. Clin Orthop Relat Res. 2004;429:170–7.
Leunig M, Beaule PE, Ganz R. The concept of femoroacetabular impingement: current status and future perspectives. Clin Orthop Relat Res. 2009;467(3):616–22.
Brunner A, Horisberger M, Herzog RF. Evaluation of a computed tomography-based navigation system prototype for hip arthroscopy in the treatment of femoroacetabular cam impingement. Arthroscopy. 2009;25(4):382–91.
Musahl V, Plakseychuk A, Fu FH. Current opinion on computer-aided surgical navigation and robotics: role in the treatment of sports-related injuries. Sports Med. 2002;32(13):809–18.
Tannast M, Kubiak-Langer M, Langlotz F, Puls M, Murphy SB, Siebenrock KA. Noninvasive three-dimensional assessment of femoroacetabular impingement. J Orthop Res. 2007;25(1):122–31.
Acknowledgments
We would like to thank the Department of Experimental Anatomy of the Vrije Universiteit Brussels for granting us access to their osteological library. This work was supported by the Institute for the Promotion of Innovation through Science and Technology in Flanders (I.W.T.-Vlaanderen) and Materialise NV (Heverlee, Belgium).
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Audenaert, E.A., Baelde, N., Huysse, W. et al. Development of a three-dimensional detection method of cam deformities in femoroacetabular impingement. Skeletal Radiol 40, 921–927 (2011). https://doi.org/10.1007/s00256-010-1021-2
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DOI: https://doi.org/10.1007/s00256-010-1021-2