Purpose: The Less Invasive Stabilization System (LISS), Dynamic Condylar Screw (DCS) and Condylar Buttress Plate (CBP) are three common fixation methods for supracondylar femur fractures. The DCS and CBP are compression plates while the LISS uses locking screws to transfer load from bone to plate without compression. We developed a study to determine if the theoretical biomechanical advantages of the LISS would be evident in laboratory testing.

Methods: Identical AO type C fractures were created in eighteen composite femurs and fixed with either LISS, CBP, or DCS (6 each). Roentgen Stereophotogrammetric Analysis (RSA) was used for analysis. Reference markers were implanted into each bone segment. Biplanar x-rays were taken to give a three-dimensional representation of the fracture. The femurs were loaded axially in an Instron 1350 and subjected to cyclic loading (50kg ± 25 for 50000 cycles). After loading, the bones were x-rayed to determine relative motion between fracture segments. To examine inducible displacement under static loading, the femurs were x-rayed in an unloaded and loaded (50 kg) condition. Again, RSA was used for analysis.

Results: RSA-CMS software was used to analyze relative motion between the bone segments. After cyclic loading, the condylar buttress plate showed significantly more permanent deformation between the medial condyle and shaft of the femur than the DCS or LISS. Under static load, the LISS showed greater displacement than the other devices between the medial condyle and shaft, and between the lateral condyle and shaft.

Conclusions: The LISS demonstrated less permanent deformation but greater inducible deformation between the medial femoral condyle and femoral shaft, compared to the DCS and CBP. The results were statistically significant. These results may have clinical implications regarding the choice of fixation devices for this difficult fracture pattern.

Funding : Other Education Grant

Funding Parties : Capital Health Research Grant