Radiologic And Three-dimensional Finite Element Biomechanical Analysis For Femoroacetabular Impingement

BACKGROUND: Femoroacetabular impingement(FAI) is thought to be a cause of premature osteoarthritis of the hip. Over the past decade, extensive research into the importance of femoroacetabular abnormalities has been conducted. The concept of femoroacetabular impingement has been recognised. Magnetic resonance imaging, arthroscopic studies have shown that cam, Pincer impingement between the femoral head or the head-neck junction and the acetabular labrum can result in hypertrophy, fraying and detachment of the labrum thereby exposing the junction of the cartilaginous and bony acetabulum. It is assumed that this precipitates the degenerative process.The underlying anatomical malformations are subclinical asphericity of the femoral head, which occurs mainly in men in cam impingement, coxa profunda and/or a retroverted acetabulum in Pincer impingement and acetabular dysplasia in sliding or subluxing impingement. While the clinical presentation of femoroacetabular impingement have been extensively elucidated in the literature, biomechanic of femoroacetabular impingement have not been studied and the epidemiology of FAI in china have not been described.OBJECTIVE: (1) To retrospectively analyze clinical epidemiology and their influence of FAI in X-ray"negative"patients with hip pain. (2) To construct a three-dimensional (3D) finite element normal and FAI hip models including acetabular bone,cartilage,labrum and bone, cartilage of femoral head by using Chinese Visible Human (CVH) dataset for biomechanics. (3) To analyze pressure distribution during activities of daily living in normal and FAI hip,and discuss biomechanical factor of joint degeneration and cartilage injure mechanism.METHODS: (1) The retrospectively investigation analysis about FAI in X-ray"negative"chinese patients with hip pain was performed at the Southwest hospital from December 2007 to August 2008. 1128 patients with hip pain whose X-ray were"negative"were investigated, and exclusion criteria were applied. To measureɑangles (°), ratio of perpendicular height to the cortex on the point of 1/2r or 1/1r and the radius of the femoral head ,and observe figure-8 configuration that describes acetabular retroversion. Epidemiological investigation was based on measure and observation。FAI diagnostic criteria : Cam impingement,αangles>55°; Pincer impingement, figure-8 configuration positive. Outcome measures:αngles (°), ratio of perpendicular height to the cortex on the point of 1/2 r or 1/1r and the radius of the femoral head, and figure-8 configuration were measured and observed. Epidemiological investigation was accomplished,and the relationships betweenɑangles and ratio of perpendicular height to the cortex on the point of 1/2 r or 1/1r and the radius of the femoral head were evaluated. (2)The images of hip dataset in CVH were obtained for construction of 3D hip biomechanical model. Normal hip and three kinds of FAI hip(Cam, Pincer and mixed)model including acetabular bone, cartilage, labrum and bone, cartilage of femoral head was constructed with AutoCAD and Solidworks software by using these images. These hip models were imported into ABAQUS analysis system and had Meshing of the hip joint contact surface, then Loading test (400 N) was performed in 5°hip flexion and 20°external rotation. The contact pressure distribution on the cartilage and labrum was observed. (3) When construction of a three-dimensional (3D) finite element normal and FAI hip models were completed, these 3D finite element hip models were imported into ABAQUS analysis system under different loading condition that mimic activities of daily living, including normal walking, standing on one or two legs, climbing up and going down stairs, standing up and sitting down. Joint contact area and pressure distribution were calculated.RESULTS: (1) there remained 269 radiographs of 121 men and 148 women on which further analysis could be performed applying these criteria to the gross material. Gender-related difference in distribution was found,while the prevalence of FAI was 22.3% in men and 10.1% in women.ɑangles: Cam impingement group was 86.3°±16. 7°, and the group that did not accord with FAI diagnostic criteria was 46.3°±4. 1°.There was significant difference between both group. 1/2Ra and1/1Ra: Cam impingement group respectively were 1.02±0.04 and 0.74±0.06, and the group that did not accord with FAI diagnostic criteria were 0.86±0.03 and 0.69±0.05. There was significant difference of 1/2Ra between both group,while 1/1Ra was not. (2) The constructed 3D hip model reflected the real hip anatomy. The constructed 3D finite element hip model reflected biomechanical behavior similar to previous research. (3) In standing up, sitting down and climbing up stairs, pressure distribution of FAI hip models were different from normal hip, and the peak pressures were located on the front of labrum.CONCLUSION: (1)The high prevalence of FAI in X-ray"negative"chinese patients with hip pain suggest FAI could be important cause of hip pain in these patients. The results also support that 1/2Ra could be thought to be a new special radiological index for diagnosis of FAI. (2) The hip dataset of CVH can be used for 3-D construction accurately. The construction of 3D finite element hip model avoids the disadvantages of other construction methods, such as imprecision of cartilage construction and absence of labrum, provides basic data which are critical for accurately modeling either normal loads, or the effects of abnormal condition of the hip. (3) Difference on pressure distribution between normal hip and FAI hip models while standing up, sitting down and climbing up stairs, indicate occurrence of impingement. Abnormal peak pressure on the front of labrum maybe is one of the main causes of labrum degeneration and osteoarthritis.