Fracture obliquity angle and distance from plafond: novel radiographic predictors of posterior malleolar involvement in tibial shaft fractures.

BACKGROUND

The purpose of this study was to identify specific radiographic parameters that are predictive of associated PM fractures in TSFs.

METHODS

All TSFs presenting over a 6-year period were identified. A review of plain radiographs and CT scans included: identification of an isolated PM fracture, AO/OTA classification, measurements of the fracture obliquity angle (FOA), absolute and relative distance from distal extent of fracture to plafond (DFP and DFP%), and presence and level of associated fibular fractures. Patients with and without PM fractures were compared. Multivariate logistic regression determined independent correlates of PM fractures and cutoff values for FOA and DFP%.

RESULTS

A total of 405 TSFs in 397 patients were identified, and 94 TSFs (23.2%) had an associated PM fracture. The majority (85.1%) of TSFs with PM fractures were AO/OTA type 42-A1, 42-B1 or 42-C1 (p < 0.001). The mean FOA was 60.9 ± 12.1° in the PM group versus 40.8 ± 18.9° in the non-PM group (p < 0.001). The mean DFP was 5.9 ± 2.7 cm in the PM group versus 11.9 ± 7.9 cm in the non-PM group (p < 0.001). Multivariate regression demonstrated that AO/OTA classification type 42-A1, 42-B1 or 42-C1 (OR 4.7 [95% CI 2.4-9.8]; p < 0.001), FOA greater than 45° (OR 4.4 [95% CI 1.9-10.9]; p = 0.001) and fracture extension to the distal third of the tibia (DFP% < 33%; OR 18.3 [95% CI 3.8-330.4]; p = 0.005) were independent correlates of PMs fractures regardless of mechanism of injury or fibula fracture presence or location (AUROC 0.83 [95% CI 0.80-0.87]). Separate multivariate regression showed for every 1° increase in FOA, PM fracture odds increase 6% per degree and for every 1 cm increase in DFP odds of PM fracture decreased by 15%.

CONCLUSIONS

Spiral fractures (simple, wedge or complex), fracture angles greater than 45° and extension into the distal 1/3 of the tibial shaft are independent predictors of PM fractures in TSFs regardless of mechanism of injury.