The impact on lateral wall fractures by a sliding hip screw device in trochanteric fractures : a biomechanical study.

AIMS

Trochanteric fractures with a reduced lateral wall thickness and a detached lesser trochanter are unstable. These characteristics can lead to failure through a lateral wall fracture after fixation with a sliding hip screw device (SHS). However, the precise mechanism by which these characteristics contribute to lateral wall fractures remains unclear. Accordingly, we examined the impact on failure by incremental decrease of both lateral wall thickness and lesser trochanter attachment in trochanteric fracture fixation using a SHS ex vivo.

METHODS

We tested 14 pairs of embalmed femora, randomly assigned to four osteotomy groups, each representing a specific 31A1 or 31A2 fracture pattern according to the AO/Orthopaedic Trauma Association (OTA) classification. After fixation with a SHS, the specimens underwent quasi-static and dynamic axial compression until failure. Outcome measures included stiffness, deformation, load to failure, and failure pattern following a set protocol.

RESULTS

We found lateral wall fractures in ten out of 28 specimens. Specimens with a thin lateral wall and a detached lesser trochanter exhibited both a significantly higher rate of lateral wall fractures (5/7 vs 5/21, p = 0.023) and a lower load to failure than specimens with only one or none of these characteristics (1,673 N (SD 810) vs 2,922 N (SD 897), p = 0.003). The specimens with a detached lesser trochanter themselves demonstrated a significantly higher rate of lateral wall fractures than those with an attached lesser trochanter (9/14 vs 1/14, p = 0.004).

CONCLUSION

Our findings emphasize the role of a detached lesser trochanter in initiating lateral wall fractures, with a reduction in load to failure when combined with reduced lateral wall thickness. Biomechanically, this suggests a failure mechanism whereby placing a load-sharing implant could overload a fragile lateral wall in unstable trochanteric fractures.