Tomonori Tabata

Influence of the volume of bone defect, bone grafting methods, and hook fixation on stress on the Kerboull-type plate and screw in total hip arthroplasty: three-dimensional finite element analysis.

For total hip arthroplasty or revision surgery using acetabular reinforcement cross-plates, choosing between bulk and morselized bone grafts for filling acetabular defects is challenging. We used finite element model (FEM) analysis to clarify various stresses on the cross-plate based on bone defect size, bone graft type, and presence or absence of hook fixation to the bone. We constructed 12-pattern FEMs and calculated the maximum stress generated on the Kerboull-type (KT) plate and screw. Bone defects were classified into four patterns according to the volume. Regarding the bone graft type, bulk bone grafts were considered as cortical bone, and morselized bone grafts were considered to consist of cancellous bone. Models were compared based on whether hook fixation was used and whether a gap was present behind the plate. The upper surface of the host bone was fixed, and a 1,000-N load was imposed on the horizontal axis at 71°. Larger bone defects increased the stress on the KT plate and screws. This stress increased when no bone was grafted; it was lower when bulk cortical bone grafts were used for filling than when morselized cancellous bone grafts were used. For cortical bone grafts, the increased stress on the KT plate and screws was lowered with hook removal. Attaching the hook to the bone and filling the gap behind the KT plate with an adequate bone graft reduced the stress on the KT plate and screws, particularly for large bone defects filled by bulk bone grafting.

Bilateral Greater Trochanteric Avulsion Fractures after Bilateral Simultaneous Total Hip Arthroplasty

We report a case of bilateral spontaneous greater trochanteric fracture after bilateral simultaneous total hip arthroplasty (THA) performed via the posterolateral approach during the early postoperative phase. A 75-year-old woman underwent bilateral simultaneous THA (BS-THA) for severe osteoarthritis with developmental dysplasia of the hip; she also presented a limited range of adduction. BS-THA was successful without any intraoperative complications. Rehabilitation with full weight-bearing exercises was initiated the day after the surgery. On the 14th postoperative day, she experienced a spontaneous left greater trochanteric fracture during a walking exercise without any trauma. Osteosynthesis was performed for the fracture on the 18th postoperative day. On the 20th postoperative day, a right spontaneous greater trochanteric avulsion fracture occurred during a transfer exercise without any trauma; this was treated on the 27th postoperative day. In the 18th postoperative month, although the right fragment showed slight upper migration, the patient had no complaints of coxalgia and both hip joints showed an excellent range of motion.

Relationship between pull-out strength and oscillation angle in bipolar cups: an in vitro study

Purpose To compare the past and present bipolar hip arthroplasty (BHA) models in terms of balance between pull-out strength and oscillation angle (OA). Methods The pull-out strength and OA of 8 BHA models were compared: UPF-II, IBC, and Tandem XLPE (Smith & Nephew); Ringloc x (Biomet); J-FX (DePuy); Bipolar (Nakashima Medical); Multipolar (Zimmer); and Centrax (Stryker). Results Respectively for the UPF-II, IBC, Tandem, Ringloc, J-FX, Nakashima Bipolar, Multipolar, and Centrax, the mean pull-out strength was 2219 N, 3303 N, 1503 N, 951 N, 1453 N, 1856 N, 1536 N, and 753 N, whereas the mean OA was 54.2°, 53.8°, 64.0°, 73.2°, 63.0°, 65.4°, 55.6°, and 75.4°. The OA was lower in the integrated types. For pull-out strength of the locking mechanism, the integrated type (IBC and Nakashima) was stronger than the metal or polyethylene ring-lock type (all others). The pull-out strength and OA were negatively correlated (r= −0.881, p=0.007), and the balance between the 2 varied for different models. Conclusion There is a trade-off between the pull-out strength and OA; optimal balance between the 2 should be based on each patients need.

Contact between the acetabulum and dome of a Kerboull-type plate influences the stress on the plate and screw

Abstract We used a three-dimensional finite element method to investigate the conditions behind the Kerboull-type (KT) dome. The KT plate dome was divided into five areas, and 14 models were created to examine different conditions of dome contact with the acetabulum. The maximum stress on the KT plate and screws was estimated for each model. Furthermore, to investigate the impact of the contact area with the acetabulum on the KT plate, a multiple regression analysis was conducted using the analysis results. The dome–acetabulum contact area affected the maximum equivalent stress on the KT plate; good contact with two specific areas of the vertical and horizontal beams (Areas 3 and 5) reduced the maximum equivalent stress. The maximum equivalent stress on the hook increased when the hardness of the bone representing the acetabulum varied. Thus, we confirmed the technical importance of providing a plate with a broad area of appropriate support from the bone and cement in the posterior portion of the dome and also proved the importance of supporting the area of the plate in the direction of the load at the center of the cross-plate and near the hook.

Fixation strength at the interface between Kerboull-type plate and bone cement

Purpose. To evaluate the fixation strength at the interface between the Kerboull-type plate and bone cement in 6 experimental conditions. Methods. Experimental materials comprised a simulated acetabular block, a simulated Kerboull-type plate, a pressuriser cover, a pressuriser arm, and bone cement. The simulated Kerboull-type plate was placed on the simulated acetabular block, with the pressuriser cover. Bone cement was added and the pressuriser arm was inserted. After 6 days of curing, pulling tests were performed to measure the fixation strength at the interface between the plate and the bone cement. Six experimental conditions were evaluated. In condition 1, a 1-mm plate was used with no gap between the plate and the acetabular block. In condition 2, a 2.5-mm plate was used with no gap. In condition 3, a 2.5-mm plate was used with a 2-mm gap. In condition 4, the plate was not used. In condition 5, condition 2 was tested with the model rotated 45°. In condition 6, condition 3 was tested with the model rotated 45°. Results. The maximum fixation strengths in conditions 1, 2, 3, 5, and 6 were 44.4 N, 59.1 N, 122.5 N, 86.9 N, and 185.2 N, respectively. The most important factor affecting the maximum fixation strength was bone cement at the interface between the plate and the acetabular block, followed by 45° rotation during testing, and then thickness of the plate. Conclusion. To enhance fixation of the Kerboull-type plate with cemented acetabular cup, penetration of cement into the outer side of the Kerboull-type plate should be minimised.