ANGULAR STABLE HTO PLATES DIFFER IN REGIONAL STRAIN ACCORDING TO GEOMETRICAL DESIGN

Abstract

The purpose of this study was to compare regional strain in crural bones after high tibial osteotomy (HTO) using two types of angular stable plates. Eight pairs of fresh frozen crura were used (age, 76–96 years). One side was attached through a short locking plate with a spacer (Puddu) to the tibia and the other side was attached to a long T-shaped locking plate (TomoFix). Strain gauges were put on the bone at the following four points: the lateral tibial cortex under the osteotomy hinge (hinge); medial cortex of the tibial shaft just distal to the Puddu (upper tibia); medial cortex of the tibial shaft just distal to the TomoFix (lower tibia); and the fibular shaft (fibula). Axial compression load of 550 N was applied three times, then loading was applied until failure. Strain data were continuously recorded via the computer during loading. Strain values showed similar trends for both Puddu and TomoFix conditions except in one region; upper tibia strain was significantly larger with Puddu (-98.4 ± 74.4 με; mean ± standard deviation) than that with TomoFix (-19.2 ± 29.2 με). In ultimate failure loading, strain varied widely between individuals. The significantly higher strain with Puddu at the upper tibia was due to the large spacer, while the small strain with TomoFix at the lower tibia was attributed to stress dissipation by many screws and its length. Setting of both plates showed significantly larger strain at the fibula compared to other parts, suggesting that weight-bearing by the fibula after HTO is not negligible.