OUTCOMES AND CLINICAL SIGNIFICANCE OF POSTERIOR MALLEOLAR FRACTURES ASSOCIATED WITH DIAPHYSEAL TIBIAL FRACTURE

Recent studies demonstrate high incidence of occult posterior malleolar fractures (PMFs) associated with tibial shaft fractures (TSFs) that cannot be identified using plain radiographs. Computed tomography (CT) scans are effective in identifying occult PMFs but expose patients to greater radiation, are expensive, may delay surgery, and are not readily available in all resource settings. Pre-operative PMF identification allows the opportunity for “malleolus-first” fixation, an operative strategy to mitigate risk of articular displacement when inserting a tibial nail. Our aim was to assess PMF morphology, treatment and outcomes when associated with TSFs, as there is little in the published literature regarding the clinical significance of this injury. This is a multi-centre, retrospective, observational cohort study based on a provincial data base. Skeletally-mature patients with an acute TSF and associated PMF on plain radiographs or cross- sectional imaging were included. Fracture-, injury- and patient-factors were assessed. Differences and outcomes of different PMF treatment strategies were evaluated using descriptive statistics when associated with a TSF. All available post-operative radiographs were studied unless PMF union was confirmed on serial films prior to discharge from the surgeons’ practice. We assessed 500 patients with TSFs, of whom 29% (n=145) met inclusion criteria. 76/145 of these fractures had CTs to rule in/out PMFs, the remaining 69/145 had PMFs observed on plain radiographs. The average patient age was 43 years old (range: 16 to 100) and 58% (n=84) were male. The most common location of fracture was distal third (79%), the most common TSF pattern was spiral (49%), and posterolateral oblique was the most common PMF morphology observed on axial CT (60%). Low energy trauma comprised two thirds of the documented injury mechanisms. Sixty-six percent (n=95) of the TSFs which met inclusion criteria had associated PMFs identified. Of those with no overlying fibular plate obscuring visualization (n=16), 92% were united by the final follow-up, with an average time to union of 2.6 months post-operatively. Thirty-one percent (n=30) of PMFs underwent posterior “malleolus first” fixation and in this group, anterior to posterior screws was the most frequent fixation strategy (77%). PMFs that were not treated with “malleolus first” fixation comprised an average of 26% of the articular surface on lateral/sagittal imaging, were displaced 0.9mm at the time of injury and 1.0mm postoperatively. In the “malleolus-first” fixation group, the average fragment size was 40% of the articular surface on lateral/sagittal imaging, the average displacement at the time of injury was 1.0mm and post operatively was 0.2mm. Contrary to publications advocating “malleolus-first” fixation, our analysis demonstrates PMFs associated with TSFs on average only displace 0.1mm when an intramedullary nail is inserted in the absence of preliminary articular fixation. Furthermore, almost all PMFs associated with TSFs achieved uncomplicated union at an average of less than three months following injury, regardless of whether malleolar fixation was performed.