In this retrospective cohort study, we analysed the incidence and functional outcome of a distal tibiofibular synostosis. Patients with an isolated AO type 44-B or C fracture of the ankle who underwent surgical treatment between 1995 and 2007 were invited for clinical and radiological review. The American Orthopaedic Foot and Ankle Society score, the American Academy of Orthopaedic Surgeons score and a visual analogue score for pain were used to assess outcome.

A total of 274 patients were available; the mean follow-up was 9.7 years (8 to 18). The extent of any calcification or synostosis at the level of the distal interosseous membrane or syndesmosis on the contemporary radiographs was defined as: no or minor calcifications (group 1), severe calcification (group 2), or complete synostosis (group 3).

A total of 222 (81%) patients were in group 1, 37 (14%) in group 2 and 15 (5%) in group 3. There was no significant difference in incidence between AO type 44-B and type 44-C fractures (p = 0.89). Severe calcification or synostosis occurred in 21 patients (19%) in whom a syndesmotic screw was used and in 31 (19%) in whom a syndesmotic screw was not used.(p = 0.70). No significant differences were found between the groups except for a greater reduction in mean dorsiflexion in group 2 (p = 0.004).

This is the largest study on distal tibiofibular synostosis, and we found that a synostosis is a frequent complication of surgery for a fracture of the ankle. Although it theoretically impairs the range of movement of the ankle, it did not affect the outcome.

Our findings suggest that synostosis of the distal tibiofibular syndesmosis in general does not warrant treatment.

Cite this article: Bone Joint J 2015;97-B:945–9.

Introduction

It is recommended that the ankle be held in dorsiflexion at the time of placement of syndesmosis screw. We assessed the validity of this recommendation.

Introduction: Diagnosis of syndesmotic injuries is primarily based upon the assessment of ankle radiographs. Earlier studies examining normal radiographs are limited by small sample size and methodological issues.

Materials and Methods: One thousand four hundred and fifteen consecutive patients with ankle radiographs were reviewed. 1023 patients were excluded as a result of a history of ankle/hindfoot pain, trauma, or surgery; or radiographic evidence of ankle/hindfoot pathology. 392 patients (218 females, 174 males) with normal ankle radiographs were included. 83 of 392 patients had bilateral normal radiographs. All radiographs were reviewed independently by a fellowship-trained foot and ankle surgeon and a fellowship-trained musculoskeletal radiologist. Tibiofibular overlap and tibiofibular clear space were measured on anteroposterior (AP) and mortise radiographs. These four measurements were analyzed.

Results: Mean AP overlap was 8.3 mm (±2.5). Mean mortise overlap was 3.5 mm (±2.1), 7.7% patients had < 1 mm overlap and 4.9% of patients had < 0 mm overlap. Mean AP clear space was 4.6 mm (±1.1), 7.1% patients had > 6 mm clear space. Mean mortise clear space was 4.3 mm (±1.0), 4.3% patients had > 6 mm clear space. All measurements were significantly different between females and males (p < 0.001). Mortise clear space is the most accurate measure when obtaining contralateral radiographs. Intraobserver and interobserver reliabilities of all measurements were high (intra-class correlation coefficient range 0.820–0.983).

Discussion and Conclusion: Our data unequivocally demonstrates that basing treatment of syndesmotic injuries on previously reported radiographic criteria can lead to unnecessary operative intervention or failure to treat. Lack of overlap on the mortise view can represent a normal variant, which has not been definitively reported in prior investigations. Our data forms the basis for new radiographic criteria to evaluate syndesmotic disruption.