Comminuted periprosthetic distal femoral fractures have greater postoperative extension malalignment.

Comminution is a significant aspect of periprosthetic distal femoral fracture characterization and may influence post-surgical outcomes. Existing classification systems that guide treatment decisions do not take into account comminution and current literature is unclear on which surgical approach is optimal. We hypothesize that fractures with comminution will have poorer quality post-reduction alignment, especially with a lateral approach. 37 study patients were identified with billing codes designating a distal femoral periprosthetic fracture. A retrospective chart review was performed to categorize fractures by absence or presence of comminution and medial parapatellar versus lateral surgical approach. These patients underwent an imaging evaluation for the primary outcome of reduction quality including the anatomic lateral distal femoral angle (LDFA) and the posterior distal femoral angle (PDFA). Differences in radiographic outcomes were analyzed with Wilcoxon/Kruskal-Wallis tests, and analysis by approach was through Fisher's exact test. Patients with comminuted fractures had significantly greater extension of the fragment (PDFA = 95.4° vs 90.0°, p = 0.018) and similar coronal alignment (LDFA = 85.3° vs 86.3°, p = 0.83) of the knee compared to non-comminuted fractures after surgical reduction. This difference was more prominent amongst those treated with a lateral approach (PDFA = 96.1° vs 89.4°, p = 0.032) than with a medial approach (PDFA = 93.7° vs 91.5°, p = 0.41) (Table 1). Current classification systems and treatment guidelines for periprosthetic distal femoral fractures do not adequately address several issues that may influence treatment outcomes, especially comminution. Comminuted fractures had greater post-reduction extension malalignment, falling outside the recommended PDFA range of 87-90°, especially with a lateral approach. Consideration should be given to surgical approach and techniques to reduce excessive extension when treating comminuted periprosthetic distal femoral fractures.

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Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.