Background

Surgical reconstruction of the anterior cruciate ligament is a common practice to treat the disability or chronic instability of the knee. Several factors associated with success or failure of the ACL reconstruction, including surgical technique and graft material and graft tension. We aimed to show how we can optimize the graft properties and achieve better post surgical outcomes during ACL reconstruction using 3-dimensional computational finite element simulation.

Hip resurfacing arthroplasty is emerging as an increasingly popular, conservative option for the treatment of end-stage osteoarthritis in the young and active patient. Despite the encouraging clinical results of hip resurfacing, aseptic loosening and femoral neck fracture remains concerns for the success of this procedure. This study used finite element analysis (FEA) to analyse the stresses within proximal femoral bone resulting from implantation with a conservative hip prosthesis. FEA is a computational method used to analyse the performance of real-world structures through the development of simplified computational models using essential features. The aim of this study was to examine the correlation between the orientation of the femoral component of a hip resurfacing prosthesis (using the Birmingham Hip Resurfacing as a model) and outcomes during both walking and stair climbing. The outcomes of interest were stresses in the femoral neck predisposing to fracture, and bone remodelling within the proximal femur. Multiple three-dimensional finite element models of a resurfaced femur were generated, with stem-shaft angles representing anatomic (135°), valgus (145°), and varus (125°) angulations. Applied loading conditions included normal walking and stair climbing. Bone remodelling was assessed in both the medial and lateral cortices. Analyses revealed that amongst all orientations, valgus positioning produced the most physiological stress patterns within these regions, thereby encouraging bone growth. Stress concentration was observed in cortical and cancellous bone regions adjacent to the rim of the prosthesis. As one would expect, stair climbing produced consistently higher stress than walking. The highest stress values occurred in the varus-orientated femur during both walking and stair climbing, whilst anatomic angulation resulted in the lowest stress values of all implanted femurs in comparison to the intact femur. This study has shown through the use of FEA that optimising the stem-shaft angle towards a valgus orientation is recommended when implanting a hip resurfacing arthroplasty. This positioning produces physiological stress patterns within the proximal femur that are conducive to bone growth, thus reducing the risk of femoral neck fracture associated with conservative hip arthroplasty

Purpose. The purpose of this study is to report the results of the first 1000 cases hip arthroplasty using the Bencox. ®. hip stem, the first hip prosthesis developed and manufactured in Korea. Material & Method. This study reviewed 1000 cases retrospectively who underwent arthroplasty using Bencox. ®. hip system. The Bencox. ®. hip stem is the first hip prosthesis developed and manufactured in Korea. This stem have a double-tapered, wedge shape figure with a rectangular-shaped cross-section and specially designed neck shape, which is design to achieve normal stress pattern of the proximal femur and to increase initial stability and to increase range of motion. Surface is treated with MAO (Micro Arc Oxidation) coating. From the first arthroplasty with this system in September 2006, sequentially 1000 arthroplasties were performed by single surgeon until the July 2014. This material included 439 men and 561 female. Average age of patients was 65 year old. Follow up period was average 72.1 month (minimum 34 months to maximum 120 months). 1000 cases consisted of 569 hips in patients with femoral neck or intertrochanteric fracture or subtrochanteric fracture (fracture group), 155 hips in osteoarthritis, 192 hips in patients with osteonecrosis of the femoral head (arthritis group), 84 hips in revision surgery (revision group). Revision cases consisted of 58 hips with aseptic loosening and 26 hips with loosening due to infection sequelae. They were underwent hip arthroplasty using a Bencox. ®. hip stem in combination with Bencox. ®. bipolar cup and Bencox. ®. acetabular cup. Patients in the fracture group usually underwent bipolar hip arthroplasty, and those in the arthritis group and revision group underwent total hip arthroplasty. They were reviewed by medical records, clinically and radiologically. Results. During the follow-up period, there were no cases of revision of the femoral stem. Radiographically, there were no cases of radiolucent line except very proximal part of the stem endosteal bone ongrowth was found in most cases. Postoperative complications such as stem loosening, infection, dislocation, and ceramic breakage were not noted. But periprosthetic fracture was encountered in 7 hips due to slip down. They were treated by open reduction and internal fixation with plate and cables. There were no cases of failure of these treatments. Conclusion. Clinical and radiographic evaluations of hip arthroplasty using the Bencox. ®. hip system showed excellent outcomes with average 72.1 month follow-up in 1000 case

Introduction. Although total hip arthroplasty (THA) has been one of the most successful, reliable and common prosthetic techniques since the introduction of cemented low-friction arthroplasty by Charnley in the early 1960s, aseptic loosening due to stem-cement and cement-bone interface failures as well as cement fractures have been known to occur. To overcome this loosening, the stem should be mechanically retentive and stable for long term repetitive loading. Migration studies have shown that all stems migrate within their cement mantle, sometimes leading to the stem being debonded from the cement [1]. If we adopt the hypothesis that the stems debond from the cement mantle, the stem surface should be polished. For the polished stem, the concept of a double taper design, which is tapered in the anteroposterior (AP) and mediolateral (ML) planes, and a triple-tapered design, which has trapezoidal cross-section with the double tapered, have been popularized. Both concepts performed equally well clinically [2]. In this study, we aimed to analyze stress patterns for both models in detail using the finite element (FE) method. Methods. An ideal cemented stem with bone was made using three dimensional FE analyses (ANSYS 13). The cortical bone was 105 mm long and 7 mm thick and the PMMA cement mantle was 5 mm in thickness surrounding the stem. Young's modulus was set at 200 GPa for the bone and 2.2 GPa for the cement. Poisson's ratio was 0.3 for both materials. The bone-cement interface was completely bonded and cement-stem interface was not bonded in cases where a polished stem surface was used. The two types of stems were compared. One being the double tapered (Fig 1 left) and the other the triple tapered (Fig 1 right). The coefficient of friction (μ) at the stem-cement interface was set at 0 for both models. The distal ends of the stems were not capsulated by the PMMA and therefore the stems were free to subside. All materials were assumed to be linearly isotropic and homogeneous. The distal ends of the bone were completely constrained against any movements and rotations. An axial load of 1200 N and a transverse load of 600 N were applied at the same time simulating the bending condition [3]. Results. Although the stress distribution differences between the designs were minor, the positions where higher stresses and absolute values in the cement were observed varied. For double tapered model, the highest maximum principal stress was 1.98 MPa observed around the corner of the stem at the proximal region. For the triple tapered model, the highest maximum principal stress was 1.67 MPa observed at more medial side than the double tapered model

Objective. To investigate the biomechanical basis and report preliminary clinical efficacy of eccentric rotational acetabular osteotomy (ERAO) when treating developmental dysplasia of the hip (DDH). Methods. Biomechanical model of the hip joint was established on cadaveric hips. After performed ERAO on the biomechanical model, we explored the impact of this surgery on biomechanics of the hip joint. Meanwhile, we reported postoperative follow-up cases who underwent ERAO in our hospital between November 2007 to July 2012. A total of 14 patients (15 hips) were reported, including 4 males and 10 females, mean age was 30 years old. Harris hip score was defined as clinical evaluation standard and radiographic assessment was based on the measurement and further comparison of pre- and post-operative AHI (Acetabular-head index), CE angle (Center-edge angle) and Sharp angle. Results. The established biomechanical model was accord with the physiological state of normal hip joint. Postoperative stress was not statistically significant compared with the preoperative stress. Meanwhile, by the end of follow-up, 13 patients (14 hips) were followed for an average time of 26 months, thus, the follow-up rate was 92.9%. Harris hip score improved from preoperative (67.1 ± 8.7) points to (88.1 ± 7.3) points; postoperative AHI increased an average of 39.6%, CE angle increased an average of 33.2 ° and sharp angle reduced an average of 9.6 °. Conclusions. Both biomechanical study and preliminary clinical observation show that ERAO has the ability to correct the deformity of acetabulum. It enlarges the acetabular coverage of the femoral head and thus corrects the abnormal stress pattern. No bone graft is needed during the operation and postoperative rehabilitation is short, therefore, ERAO may have good curative effect when treating the DDH

Stress shielding of the proximal femur occurs in stemmed implants. Resurfacing implant does not invade the intramedullary region. We studied the stress patterns in conventional and nonstemmed designs. Methods. FE model geometry was based on standard femur from the international Society of Biomechanics Mesh Repository. Loading simulated for one- legged stance with body weight of 826 N. 2 regions were defined, R1 (40 mm from tip of head) and R2 41 mm–150 mm) of the intramedullary part of the stemmed model's interface with bone. 2 different loading conditions bending and torsion were compared for stress and strain. The FE model was solved with ANSYS version 6.1 on a single processor NT station. Results. With conventional implants, stem shields cortical bone from being loaded. In nonstemmed implants, Von Misses stress contours show a similar distribution as intact bone, transferring loads to the cortical shell but with higher stresses and a maximum displacement of 17.39% higher than that of intact bone. 15–23 mm proximal to R2 and around 110 mm, region of the stem tip, there were higher stress and strain concentrations. Conclusion. Based on simulations, nonstemmed implants provide more physiological loading compared to conventional implants though stress shielding increases in region of the stem in resurfacing implant

Introduction. Total hip replacement is an established surgical procedure done to alleviate hip pain due to joint diseases. However, this procedure is avoided in yonger patients with higher functional demands due to the potential for early failure. An ideal prosthesis will have have a high endurance against impact loading, with minimal micromotion at the bone cement interface, and a reduced risk of fatigue failure, with a favourable stress distribution pattern in the femur. We study the effect of varying the material properties and design element in a standard cemented total hip using Finite Element Analysis. Methods. A patient-specific 3D model of femur will be constructed from CT scan data, while a Summit® Cemented Hip System (DePuy Orthopedic) will be used to as a control for comparative evaluation. We vary the material stiffness of different parts of the prosthesis(see Fig.1) to formulate a design concept for a new total hip prosthesis design; and use Finite Element Method to predict the micromotion of the hip prosthesis at the bone cement interface, as well as the stress distribution in the the femur. Result. Validation of computational protocol was being done by comparing the principal maximum strain of the femoral cortex along the diaphysis, and the amount of deflection, with published literature, similarly, contact modelling validation was also done. Model 1–4 induced lower peak Von Mises stress in the cement, which takes a much lower value than any of the cement mechanical limits postulated. Therefore, the risk of cement failure is greatly reduced in Model 1–4. However, the effect of varying stiffness in different regions is not significant in terms of load transmission to the cement. Micromotion at the bone-cement interface was studied via two approaches: Peak micromotion at the bone cement interface; and the micromotion data at 12 Regions of Interest (ROI)s. Both results showed that model 2 and 3 are capable of reducing micromotion at bone-cement interface, in comparison with the Summit® Cemented Hip System. By comparing the Von Mises Stress distribution in the proximal femur; model 1 is found to result in a significantly reduced stress shielding effect, while model 2–4 are also favourable in comparison to the standard Summit® prosthesis in terms of stress distribution in the femur. Figure 2 shows the effects of the performance of model 1–4, presented as percentage difference from the Summit® prosthesis. Model 1 is unfavourable, despite its favourable stress distribution, because its peak and overall micromotion at the bone-cement interface is greatly increased. Conclusion. Model 2 and 3 have favourable design elements. They both have reduced micromotion at the bone-cement interface; and a favourable stress distribution in the femur. Further refining and testing of model 2 and 3 should done, as these models may provide information which may be useful in improving the performance of the current range of total hip replacement prostheses