Session IX - Tibia

Low-Profile Fixation of Tibial Plateau Fractures

George E. Herriott, MD; David F. Hubbard, MD, West Virginia University Hospital, Morgantown, WV

Conventional fixation of lateral tibial plateau fractures with a large fragment buttress plate and 6.5mm cancellous screws can result in prominent hardware that may become symptomatic. Low-profile fixation with small fragment 3.5mm screws and a T-plate has been advocated by other authors as an alternative, offering the advantage of less prominent hardware postoperatively and, unlike "standard" methods, supports the subchondral bone with four parallel screws. A cadavaric study was designed to determine if low-profile fixation offers similar or improved biomechanical characteristics in comparison to conventional fixation in a split-depression (41-B3) lateral tibial plateau model.

Seven matched pairs of fresh frozen cadavaric proximal tibias were obtained for study. The specimens were thawed and dissected free of soft tissue. The tibiofibular joint was disarticulated and the fibula removed. A reproducible split-depression fracture was then created. The experimental groups were created by instrumenting each pair of tibias with small and large fragment fixation. After anatomic reduction of each fracture under direct vision, one tibia was fixed with a large fragment L-buttress plate, two 6.5mm cancellous screws proximally, and 4.5mm cortical screws distally. The second tibia was fixed with a small fragment T-buttress plate and all 3.5mm cortical screws. The proximal screws were placed parallel just below the subchondral bone in a "raft" configuration.

The tibias were potted in cement and mounted on a MTS machine for testing. Continually increasing compressive load was applied axially at a rate of 0.05cm per second through the fractured plateau. Loading was continued until 6mm of inferior displacement was achieved. The force required to produce 2mm and 6mm of displacement was recorded for each matched pair. Statistical analysis comparing failure strengths of the experimental groups was completed utilizing a paired Student t-test, with p<0.05 considered significant.

No statistically significant differences in fixation strength were observed between the experimental groups. The average force required to produce 2mm of displacement in the low profile group was 555 +/- 150 N, while conventionally fixed tibias averaged 642 +/- 215 N (p = 0.18). At 6mm of displacement, average force values were 1241 +/- 337 N for low-profile fixation and 1299 +/- 461 for large fragment constructs (p = 0.54).

The split-depression (41-B3) tibial plateau fracture is a common pattern, especially in the elderly population. No previous study has compared the mechanical characteristics of these two different methods in a split-depression model. The low-profile fixation method proposed in this study is attractive not only because it may result in less postoperative discomfort, but also because it provides a "raft" of support for unstable subchondral bone. This study detected no significant difference in strength of the small fragment construct when compared to conventional buttress plating techniques with axial loading.

Based on resistance to axial displacement, the results of this study support the use of small-fragment T-plates secured with 3.5mm cortical screws for fixation of split-depression lateral tibial plateau fractures.