Aim

Previous studies have indicated that TNF-α and lymphotoxin-α (LTA) gene polymorphisms associate with the development of several different inflammatory diseases. However, potential associations of such gene polymorphisms with the susceptibility to extremity chronic osteomyelitis remain unknown. This study aimed to investigate potential links between TNF-α gene polymorphisms (rs1800629, rs361525, rs1799964, rs1800630, rs1799724 and rs1800750) and LTA gene polymorphism (rs909253) and the risk of developing extremity chronic osteomyelitis in Chinese population.

Impact relief ability of Metal-on-Metal artificial hip joint with multi-garter spring using drop impact tester for practical use

Toshiaki Kaneeda, Xinming Zhao and Hiroshi Matsuura

Metal-on-metal (MoM) joints can provide better wear properties than hard-on-polymer joints, leading to reducing osteolysis. However during gait, MoM hip joints have no material to relieve impact. These impacts can cause severe pain in postoperative patients. Kaneeda proposed double-shell MoM artificial hip joints in which multi garter springs were inserted between the inner and outer acetabular shell as an impact relief device. The proposed double-shell metal-on-metal artificial hip joint is composed of two layers, as shown in Fig. 11).

A garter spring is usually used when by loading and a compression stress from the outside to the center axis. In the model testing for garter spring, it is demonstrated that garter spring had impact relief ability, then using dual garter springs could lead to better impact relief ability than single one2).

In this work, the impact relief ability of model hip joint were investigated by using the Instron CEAST 9340 machine as shown in Fig. 2. The machine is a floor standing impact system designed to deliver 0.30–405J of energy and equipped with precise locating system for height. A holding device of double-shell cup was made to fix the right position. A shape of drop impact weight was modified for this experiment. The model hip joint was applied vertical load over 6000N, which is estimated to be equal to maximum vertical load during jumping. The ability in the case of single garter spring and dual garter springs was evaluated in the model hip joint, comparing with UHMWPE liner in the same size of femur head. Each testing was conducted 10 times.

Fig. 3 shows load-time curve detected. From the results, it can be seen that in both case Load L gradually rise with Time T, then reach maximum values, finally L gently drop: maximum impact load as well as maximum impact load arriving time also presented nearly the same values. Much differences in shape of the curve between model hip joint with dual garter springs and UHMWPE liner could not be recognized. The model hip joint with dual garter springs may has enough impact relief ability.

Total hip arthroplasty for developmental dysplasia of the hip (DDH) remains a difficult and challenging problem. How to reconstruct acetabular deficiencies has become increasingly important. One of the major causes inducing loosening of acetabular reinforcement ring with hook (Ganz ring) is insufficient initial stability. In this study, three-dimensional finite element models of the pelvis with different degrees of bone defect and acetabular components were developed to investigate the effects of the number of screws, screw insert position (Fig. 1), and bone graf quality on the initial stability under the peak load during normal walking. The size of pelvic bone defect, the number of screws and the position of screws were varied, according to clinical experience, to assess the change of initial stability of the Ganz ring. The Ganz ring was placed in the true acetabulum and the acetabular cup was cemented into the Ganz ring with 45 degrees abduction and 15 degrees of screws. The Insert position, nodes on the sacroiliac joint and the pubic symphysis were fixed in all degrees of freedom as the boundary condition. The peak load during normal walking condition was applied to the center of the femoral head (Fig. 2). According to the Crowe classification, as the degree of acetabular dysplasia was increased, the relative micromotion between the Ganz ring and pelvis was also increased. The peak micromotion increased as the stiffness of bone graft decreased. Increasing the numbers of screws, the relative micromotion tended to be reduced and varied the screw insertion position that affects the relative micromotion in the Ganz ring-pelvic interface (Fig. 3). This study showed that increasing the number of inserted screws can reduce the relative micromotion. Both the insert position and graft bone property affect the stability of the Ganz ring while the insert position has a greater impact. The current study is designed to lay the foundation for a biomechanical rationale that will support the choice of treatment.