The Finite Element Analysis And Clinical Application Of Subtrochanteric Oblique Or Transverse Shortening Osteotomy In Total Hip Arthroplasty For Crowe IV Developmental Dislocation Of The Hip

It is accepted that the rotational center should be at the level of the true acetabulum in total hip arthroplasty(THA) for Crowe IV developmental dislocation of the hip(DDH), so the femur usually should be shortened to return the dislocated femur head. Many studies on different osteotomies have been published, but which technique should be chosen is still controversial and there are few studies about its biomechanical feature. Looking up all studies related to this topic, we find that the subtrochanteric oblique osteotomy(SOO) or subtrochanteric transverse osteotomy(STO) is the primary choice at present. In the present study, we developed a 3-dimensional(3D) FE model to evaluate the initial stability of SOO and STO, based on the analysis of von Mises stress in the femur-stem complex and displacement under different oblique angles. On the other hand, the lesser trochanter osteotomy(LTO) group was used as the reference, and we reported our experience combining subtrochanteric shortening osteotomy and S-ROM stem to treat those patients with severe dislocated hip and tried to deep our insight into the effect of subtrochanteric osteotomy geometries on rotational stability and clinical outcomes. The present research consists of two major parts, finite element analysis and clinical contrastive study, aiming to provide biomechanical basic theories and data for clinical application.Section one: the finite element contrastive analysis between subtrochanteric oblique osteotomy and subtrochanteric transverse osteotomy. The objective of the section is to explore the biomechanical pattern of femur-prosthesis complex after total hip arthroplasty with the subtrochanteric osteotomy technique. Besides, the different oblique angles impacts on stability of the osteotomy plane have been figured out. The numerical data of the femur were based on a middle-aged male volunteer without any hip disease. Five virtual total hip arthroplasty were performed according to the literature. They are one model without osteotomy and four models with osteotomy under angles at 30°, 45°, 60° and 90°, respectively. We selected the S-ROM stem as it is suitable for patients with DDH. The validity test was completed by comparing the data between the finite element model without osteotomy and the cadaver under same load. The results obtained from the model without osteotomy are in agreement with the cadaver upon stress. This validated femur-stem complex model could be applied to predict hip biomechanical mechanics and laid the foundation for further biomechanical study. Adopting single-leg stance loading and setting contact condition, the peak Von Mises stress and displacement of S-ROM stem or cortical bone were evaluated in all five models. The results showed that subtrochanteric osteotomy technique changed the stress distribution in the femur-stem complex, the distal fragment of the femur bore most of the stresses and the tight press-fit of S-ROM stem and the distal fragment of the femur played a key role in the initial stability of the femur-stem complex. For the osteotomy region, an oblique angle at 45o appears to be the optimal choice for initial stability by striking a balance between rotational stability and axial stability and yielding the minimum relative displacement value among those specific angles.Section two: the clinical contrastive study of subtrochanteric oblique osteotomy. Via registration follow-up system, 36 cases(43 hips) with mean age of 41.8 years who met inclusion criteria were operated between February 2005 and March 2015. Those patients were divided into three group based on different osteotomies: Group I is the patients who undergo SOO at 45°; the STO was completed in Group Ⅱ; the LTO was carried out in Group Ⅲ. Group I and Group Ⅱ can be classified as subtrochanteric osteotomy Group, while Group Ⅲ can be named lesser trochanteric osteotomy Group. Clinical and radiographic data were retrospectively reviewed. All the clinical data were collected to statistical analysis in order to report our experience in treatment for highly dislocated DDH. Compared with subtrochanteric osteotomy, the lesser trochanteric osteotomy showed the limitation of shortening the femoral and did not restore the hip joint function completely. The next step was to compare the two types of subtrochanteric osteotomy techniques. The results showed that Group I have advantages in less operation time, less internal fixation number and shorter osteotomy healing time than Group Ⅱ. Complications included five intraoperative crack of femur; five deep venous thrombosisand and two dislocations occurred while they were addressed properly afterward. There are two cases of nerve damage in the lesser trochanter osteotomy group. The motor function nearly recovered after half year and one year postoperatively, respectively, but sensory in calf skin did not.According to the two investigations, subtrochanteric oblique osteotomy at 45° combined with S-ROM stem is considered as a suitable osteotomy technique in THA for Crowe IV DDH. It could shorten the operation time, reduce the number of additional fixation and provide the initial stability of the osteotomy region from the perspective of biomechanics. Accordingly, the union time is shortened and the risk related to the technique is reduced as well. On the other hand, subtrochanteric oblique osteotomy combined with the freely-rotatable S-ROM stem provided favorable short-middle term outcomes by affording both morphological and functional advantages. Innovation points in this paper include: 1. The application of finite element model analysis showed the biomechanical effects of subtrochanteric osteotomy technique on the femur-prosthesis complex, figuring out that the fit and fill of the distal fragment of the femur and the stem is essential for the initial stability of the subtrochanteric osteotomy region. 2. From the perspective of biomechanics, the results provide theory basis for the choice of oblique angle in the subtrochanteric osteotomy, namely the optimal oblique angle for this technique appears to be 45°. 3. Adopted clinical comparative study, the related clinical indicators reveal the advantages of oblique osteotomy and provide clinical data support for the choice of the ways of femoral osteotomy in THA for Crowe IV DDH.