Asymptomatic Lisfranc dislocation: an unusual case

Clinical History

53-year-old diabetic and hypertensive male patient post renal transplant had incidental swelling of his left foot, which he had attributed to his medical condition. The asymptomatic swelling had been present, intermittently, for over a year but the patient had been mobilising with full weight bearing. Examination showed swelling and bruising of the foot.

Imaging Findings

X-ray revealed a divergent Lisfranc fracture-dislocation involving the base of all the metatarsals. Associated fractures of the neck of 2nd-4th metatarsals were also noted.

Close questioning revealed that the patient had sustained a twisting injury to his foot 15 months ago while stepping off a bus. There was no pain, swelling or discomfort at that time and he had continued to mobilise without any disability.

Discussion

Fracture-dislocations of the tarso-metatarsal joints of the foot (Lisfranc’s joint) are not very common [1]. This is due to an inherent stability provided by the bony configuration and the surrounding ligaments [2].

Lisfranc injuries are associated with low-energy sports-related trauma or high-energy motor vehicle trauma. The common injury patterns are direct blow to the joint, twisting, axial loading or crushing. Pain, disproportionate swelling, plantar ecchymosis, deformity and midfoot instability following these injuries is usually fairly significant [2].

The two radiological patterns are divergent and homolateral. In divergent Lisfranc fracture-dislocation, there is medial displacement of the 1st metatarsal and lateral displacement of the 2nd-5th metatarsals. In homolateral Lisfranc fracture-dislocation, all the metatarsals, usually 2nd to 5th, are displaced to one side, usually laterally.

This patient, reportedly, sustained an injury to the foot 15 months before presentation. Stepping off a bus may have resulted in a missed step causing axial loading on an equinus foot. With hyperextended toes, the load is transmitted through the metatarsals. This stresses the Lisfranc’s joint resulting in a fracture-dislocation.
However, the complete absence of symptoms is unusual and not often reported.

We are of the opinion that this may be related to the associated medical conditions of the patient. Diabetes mellitus is a common reason for neuropathic changes in the foot [3, 4]. The midfoot is the usual site of involvement with changes most marked at the tarso-metatarsal joints. This may result in spontaneous subluxations and pathological fractures [5]. Lack of pain in diabetic peripheral neuropathy causes the patient to continue walking on the injured foot. The changes of Charcot's arthropathy may also mimic infection with swelling, local redness and warmth; all the above changes were seen in this patient.

In summary, patients with peripheral neuropathy are prone to sustaining significant foot injuries, without any noteworthy symptoms. A high index of suspicion is essential for identification of these injury patterns. This can facilitate adequate and timely intervention preventing long-term complications. This unusual presentation reiterates this.

Differential Diagnosis List

Final Diagnosis

Lisfranc fracture dislocation

URL:	https://www.eurorad.org/case/8700
DOI:	10.1594/EURORAD/CASE.8700
ISSN:	1563-4086