The Influence Of Acetabular Reaming Depth On The Rotation Center Reconstruction In Primary Total Hip Arthroplasty

Objective: To study the impact of the acetabular reaming depth on the reconstruction of the rotation center of the hip joint during the primary total hip arthroplasty.Methods: We performed a retrospective study on 100 inpatients who had unilateral primary total hip arthroplasty due to osteonecrosis of femoral head from January, 2013 to April, 2015 in our hospital. Of the 100 inpatients, 59 were men and 41 were women. Their ages ranged from 24 to 79 years with an average of 55.9 years. Standard anteroposterior radiographs of bilateral hips were taken to all of the inpatients after total hip arthroplasty. The following parameters were measured on the anteropoterior radiographs: the distance between the rotation center of the healthy femoral head to the vertical line across the midpoint of pubic symphysis(a1), the diameter of the healthy femoral head(b1), the distance between the center of the prosthetic femoral head to the vertical line across the midpoint of pubic symphysis(a2), the diameter of the prosthetic femoral head(b2), the thickness of the healthy teardrop(c), the thickness of the acetabular cup together with the liner(d), and the distance between the medial edge of the acetabular cup and the medial border of teardrop(e), which is defined as the horizontal reaming depth, the distance between the rotation center of the healthy femoral head and the connection line of bilateral teardrops(f1), the distance between the rotation center of the prosthetic femoral head and the connection line of bilateral teardrops(f2), the distance from inferior border of acetabular cup to the connection line of inferior borders of bilateral teardrops(g), which is defined as the longitudinal reaming depth and the abduction angle of prosthetic acetabular cup(H). Parameters(a)(a = a2- a1) and(f)(f = f2- f1) were used to evaluate the rotation center reconstruction on the operated hip. IBM SPSS 21.0 was used for statistic analysis.Results: The value of c is 6.077±1.443 mm. Parameter a and parameter e were positively related and their Pearson’s correlation coefficient is 0.335 when p=0.05. Furthermore, the value of e is 8.121 mm when a2 equals a1. On the other hand, when p=0.05, parameter g and parameter f were inversely correlated and the correlation coefficient was-0.540. The value of g is 2.640 mm when f2 equals f1.Conclusion: The reaming depth of the acetabulum can influence the reconstruction of the rotation center during primary total hip arthroplasty. When the horizontal reaming depth is 8.121 mmm, or when the distance between the medial edge of the cup and the lateral border of the teardrop(the bottom of fovea) is 2.044±1.443 mm, the rotation center can be rebuilt most accurately. This optimal rebuilt could also be achieved when the longitudinal reaming depth is 2.640 mm.