Biomechanical properties of a new anatomical locking metal block plate for opening wedge high tibial osteotomy: uniplane osteotomy

Abstract

Purpose: The purpose of this study was to evaluate the biomechanical properties of a new anatomical locking metal block plate by comparing the initial biomechanical stability of three different fixation constructs for open wedge high tibial osteotomy (HTO).

Materials and methods: Sawbones composite tibiae were used to make a 10-mm opening osteotomy model with uniplane technique. The osteotomy was secured with three different types of plates: Group I, new osteotomy plate without a metal block (n=5); Group II, new osteotomy plate with a 10-mm metal block (n=5); and Group III, two short metal block plates (n=5). Single load to failure test and staircase load-controlled cyclical failure test were performed. In the single load to failure test, the yield load, maximum failure load, and the displacement of the osteotomy gap were measured. In the staircase cyclical load to failure test, the total number of cycles to failure was recorded. Failure modes were observed during both single and cyclic load tests.

Results: Group II showed the highest yield and ultimate loads (1829±319 N, 3493±1250 N) compared to Group I (1512±157 N, 2422±769 N) and Group III (1369±378 N, 2157±210 N, p<0.05). The displacement of the opening gap in Group II (0.34±0.35 mm) was significantly lesser than the other groups (p<0.05). In the staircase cyclical load to failure test, the total number of cycles to failure was 12,860 at 950 N in Group III, 20,280 at 1,140 N in Group I, and 42,816 at 1,330 N in Group II (p<0.05). All the specimens showed complete fracture of the intact lateral sawbones area and slight displacement of the distal fragment of the specimens in the single load to test. None of the specimens showed deformed or broken screws and plates during the single load to test. During the fatigue test with staircase cyclic loading, no fracture of the lateral sawbones area was observed.

Conclusions: This study demonstrated that the new anatomical locking metal block plate could provide sufficient primary stability for open wedge HTO. The addition of a metal block to this new plate can increase the stability of the osteotomy compared to the one without a metal block.

Keywords: Anatomical locking metal block plate; High tibial osteotomy; Knee; Stability.

Fig. 1

The new anatomical locking metal block plate. (A) The upper end of the plate has a 5-degree posterior slope for better placement onto the proximal tibia. (B) The shape of the sliding hole is oblong to adjust to the location of a metal block depending on the osteotomy site. (C) The anterior height of the metal block is two thirds of the posterior height to create a wedge-shaped opening gap. L: plate for the left knee.

Fig. 2

Three different types of plates are used in sawbones tibia models: (A) Group I, new osteotomy plate without a metal block; (B) Group II, new osteotomy plate with a 10-mm metal block; and (C) Group III, two short spacer plates.

Fig. 3

(A) In the biomechanical testing set-up, the sawbones composite tibia is mounted in a specially designed fixture connected to an MTS machine. (B) Compression loading axis test set-up is created.

Fig. 4

The bar graph shows the averages of the yield load and maximum failure load. Group 1: new osteotomy plate without a metal block, Group 2: new osteotomy plate with a 10-mm metal block, Group 3: two short spacer plates. ^*p<0.05, compared to either group 1 or group 3.

Fig. 5

The graph shows the average displacement of the medial opening gap in the single-load test. Group 1: new osteotomy plate without a metal block, Group 2: new osteotomy plate with a 10-mm metal block, Group 3: two short spacer plates. ^*p<0.05, compared to either group 1 or group 2, ^**p<0.05, comparison between group 1 and group 2.