Related methods of total hip replacement for acetabular dysplasia
There were acetabular medial wall displacement osteotomy, Scanchez-Sotelo et al[11] acetabular insertion method, Dorr[12] method, Luo et al[13] acetabular forming displacement method, and Stamos et al acetabular forming method. These methods are controversial at home and abroad. A previous study[14] has confirmed no loose occurred in 101 cases (106 hips) using non-bone cement acetabular prosthesis installation and fixation in patients with averagely 49 years when surgery. Follow up was performed for averagely 7.8 years. These results have demonstrated that follow-up outcomes were good in short and middle phases postsurgery. Bone union was detected within half a year at the acetabular medial wall bone cut and bone graft sites, without severe postoperative complications. It has advantages that cannot be replaced by other methods. Lateral displacement of acetabular cup liner not only shortened gravity arm to reduce gravity moment, but also increased prosthesis length of femoral neck to obtain a prosthesis handle with big off-center moment. Simultaneously, it could maintain normal dissection of femoral neck shaft angle, but had small effects on limb length. Thus, it maybe a consummate method, and is beneficial to keep dynamic balance of hip joint abductor[15]. Simultaneously, this method avoids massive bone transplantation, ensures good installation angle and good inclusiveness of femoral head. Its biomechanics advantages: ① bone cut position is within Soucil line; small force of acetabular medial wall; ② rotation center displacement of the femora head shortens gravity moment, lessens pressure of femoral head and reduces prosthetic abrasion. Simultaneously, there are potential complications. For example: displacement of medial wall results in obstruction of adjacent vessels in the pelvic cavity and damage to adjacent organs. The displacement of rotation center of the femoral head leads to changes in lower limb force line, excessive eversion of the knee joint, thigh pain surrounding the tip of the femoral handle, finally affects hip joint activities.
Case analysis of acetabular medial wall displacement osteotomy
There were few reports concerning above-mentioned method, but authors believed many physicians from Department of Joint Surgery have used this method. Thus, there may be some cases. In accordance with a previous study[16], there was no unified standard of the displacement distance of acetabular medial wall osteotomy. This study has quantized and standardized the reference scale of the displacement distance. In severe acetabular dysplasia patients, especially when the contact area was less than 75% between acetabular prosthesis and host bone, total hip replacement for acetabular medial wall displacement osteotomy can ensure acetabular bone mass, which makes provision for future revision[17]. With regard to mechanics changes in soft tissue surrounding the hip joint, this study did not involve the loading of elasticity in muscle tissue that provides stability for the hip joint[18], which deserves further investigations. Experimental statistical analysis has shown that the range between 1 mm away from the pelvic cavity and 1 mm in the pelvic cavity as well as 4.0-5.0 mm in the pelvic cavity has slight effects on the distribution of Mises stress and shear stress. However, the optima position was different. The position was less in shear stress then in compressive stress, and the solution of compressive stress problems was a major contradiction. Therefore, the reasonable range of acetabular medial wall displacement was from 1 mm outside the pelvic cavity to 1 mm in the pelvic cavity. The optimal position was 1 mm in the pelvic cavity. The stress distribution of artificial prosthesis has great effects on bearing capacity, abrasion and loose of the artificial hip joint; advanced finite element analysis software with a powerful function was utilized to deeply study the force condition and biomechanics function of the artificial hip joint[19]. This application has important theoretical and practical significance for improving the design of artificial hip joint, preparing artificial hip joint that is consistent with anatomical characteristics of Chinese people, reducing occurrence rate of postoperative sterile loose and patients’ pain, elevating bearing capacity and abradability of the prosthesis as well as replacement level and useful life of artificial hip joint.
