The Presence of An Avulsion Fracture of the 1st Tarso-Metatarsal Joint in Lisfranc Injuries is a Useful Adjunct in Detecting 1st TMTJ Instability

Abstract

Category: Midfoot/Forefoot; Trauma Introduction/Purpose: Lisfranc fracture-dislocations are uncommon injuries that are often missed or diagnosed late. The consequences of this include post-traumatic osteoarthritis and deformity. Injuries with ligamentous involvement injuries often have avulsion fractures at the level of the tarso-metatarsal joint (TMTJ) on either plain radiographs or CT scan. A proportion of these will have a congruent TMTJ joint on initial imaging. However, it has been suggested that many of these patients will have an unstable TMTJ which requires stabilisation. The purpose of this study was to determine the relationship between the presence of an avulsion fracture on initial imaging and instability or incongruence of the first TMTJ. Methods: A prospectively maintained database of all Lisfranc fracture-dislocations presenting to our centre was collected. Initial plain radiographs and CT scans were analysed for the presence of 1st TMTJ avulsion fractures independently by two senior authors. Data were collected regarding the initial mechanism of injury, fracture classification (Myerson and Qenu). Injuries which were managed non-operatively were excluded from the study. All included cases were managed with examination under anaesthesia (EUA) and intra-operative screening with stress testing under image intensification prior to fixation or arthrodesis surgery. The rate of instability for each fracture classification type was also determined. The sensitivity and specificity of the presence of an avulsion fracture of the 1st TMTJ in detecting an unstable joint was determined. Results: 153 patients with a Lisfranc injury were included. The mean age was 35.2 years, and 68% of patients were male. 99 injuries (64.7%) were identified as having an avulsion fracture at the level of the 1st TMJ on either plain radiographs or CT scan. Of these, 76.7% were found to have a congruent joint on XR or CT scan. 91.9% of patients with an avulsion fracture of the 1st TMTJ were found to have instability on EUA stress testing. Amongst the 54 patients who had no avulsion fracture, 23 (42.6%) demonstrated instability of the 1st TMTJ on EUA. The presence of an avulsion fracture of the 1st TMTJ had a sensitivity of 79.8% and a specificity of 79.5% in the detection of an unstable joint. Conclusion: The presence of an avulsion fracture of the 1st TMJ is highly suggestive of instability of the joint and may be a useful adjunct in assessment and decision making for Lisfranc injuries. This finding on pre-operative radiographs should alert clinicians to have a low threshold to perform further imaging in the form of CT scanning or EUA and dynamic stress testing of the 1st TMTJ. A high proportion of Lisfranc injuries without avulsion fractures have instability at the level of the 1st TMTJ, and therefore the absence of this finding does not provide a reliable indication of joint stability.