Introduction: Several studies have compared various plate constructs for distal intra-articular humerus fractures. In our experience osteoporotic bone and fractures that have a transverse component close to the elbow joint have tenuous fixation with traditional plating systems due to, at most, two screws in the distal fragment through the plate. Therefore, the aim of this study was to obtain objective data on the performance of two plating systems used for fixation of intra-articular distal humerus fractures with a low transverse component with only two screws through a 3.5 LC-DCP distally. It was hypothesized that locked plating would be more stable than standard plating after cyclic loading.

Methods: Twenty pairs of fresh matched cadaver humeri of patients older than 65 years old were harvested. DEXA scans of the right forearm from each pair were obtained. Osteotomies were performed to simulate comminuted supracondylar humerus fracture with intercondylar split (OTA 13-C2.3). The specimens were then randomly assigned to locking or non-locking plate fixation.

Ten paired specimens were tested in simulated extension and the remaining ten were tested axially.

Fragment motion relative to the humeral shaft was measured using kinematic analysis at the fracture gap.

Differences in resultant fragment translations and rotations between fixation groups were checked for significance (p< 0.05) using a one-tailed paired t-test. Differences in cycles to failure were checked for significance using a Wilcoxon signed rank test.

Results: On average, during extension tests, the humeri with locking plate fixation did not survive significantly more cycles (4352) than with non-locking (4755) plate fixation. There was no significant difference in fragment translation between locking (0.8 mm) and non-locking (1.7 mm) plates. However, there was a significant difference in fragment rotation between locking (2.8 degrees) and non-locking (3.9 degrees) fixations.

On axial testing, the humeri with locking plates on average survived more loading cycles (4072) than those with non-locking plate fixation (2115), but the difference was not significant. Mean translation for locking plate fixation (3.6 mm) was significantly less than for non-locking plate fixation (5.7 mm) and mean fragment rotation was significantly less for locking plate fixation (13.3 degrees) than for non-locking plate fixation (17.8 degrees).

Conclusions: The results of this study demonstrated that the fixed-angle 3.5 mm locking plate constructs for comminuted intercondylar humerus fractures reduced fracture site motion, sometimes significantly so, relative to the non-locking constructs in osteoporotic bone. The potential benefit of increased fixation survivability and decreased fracture site motion in osteoporotic bone needs to be evaluated clinically.