Biomechanical evaluation of locked versus non-locked proximal subchondral raft screws in a Schatzker Type II tibial plateau fracture model.

OBJECTIVE

Schatzker Type II fractures involve a lateral split and intra-articular depression and are typically managed with a periarticular plate and subchondral raft screws. While locking plate technology is common in osteoporotic bone, its biomechanical advantage over non-locking screws for proximal subchondral rafting remains unclear. We aimed to compare construct stiffness and fragment displacement in a Schatzker Type II fracture model stabilized with a periarticular plate using proximal locked versus non-locked subchondral screws.

METHODS

Six matched pairs of fresh-frozen cadaveric tibias were osteotomized to create a reproducible lateral split-depression fracture. Fractures were reduced and stabilized with a 4-hole periarticular proximal tibia plate. One tibia per pair received proximal non-locking screws - the contralateral received proximal locking screws. Specimens underwent cyclic axial loading (10-100 N), followed by stepwise increases of 200 N (10 cycles each) until failure (>5 mm articular depression or hardware failure). Construct stiffness and displacement were measured using digital motion analysis and a Microscribe.

RESULTS

During cyclic loading, no significant differences were observed between locking and non-locking constructs in stiffness or fragment displacement. However, during load-to-failure testing, the non-locking construct demonstrated significantly greater stiffness (128.4 ± 22.6 N/mm) compared to the locking construct (91.7 ± 18.7 N/mm) (p < 0.05). Average load to failure was similar: 1900 ± 309 N (locking) versus 1933 ± 154 N (non-locking) (p = 0.87).

CONCLUSION

In this cadaveric biomechanical study of Schatzker Type II tibial plateau fractures non-locking screws offered comparable stability, potentially at a reduced implant cost, which may question the routine application of more costly locking technology for this specific fracture pattern. Locking plates remain clinically indicated in scenarios outside the scope of our model, such as fractures with severe comminution of the lateral wall precluding stable cortical compression, or in cases of extreme osteoporosis where conventional bicortical screw purchase cannot be achieved.