Acute surgical treatment of peroneus longus avulsion fracture of the first metatarsal base

Discussion

The PL is an extrinsic muscle of the foot arising from the lateral compartment of the leg. It runs posterior to the lateral malleolus and then in the cuboid groove where it obliquely crosses the sole of the foot to attach on to the lateral side of the base of the first metatarsal. The tendon actions include eversion of the foot and plantar flexion of the ankle. The oblique direction of travel allows the tendon to support the longitudinal and transverse arches of the foot.1

A number of case reports have described the mechanism of injury that can result in an isolated PL tendon avulsion fracture from the base of the first metatarsal. They describe an eccentric contraction of the PL tendon, as the foot and first metatarsal are dorsiflexed and inverted.2–5 The uneven medial incline caused by the inverted position of the foot has shown to activate and stretch the peroneal muscles.6 This is in contrast to the well-known mechanism of tarsometatarsal injuries that can involve a directaxial loading of a plantar flexed forefoot combined with a rotational stress.7 The inversion injury sustained by our patient was sudden and the resistant eccentric contraction of the peroneal tendon has led to the avulsion fracture.

Pain, swelling and inability to weight bear after the injury were the prevailing symptoms in our patient. This was a common presentation seen in all case reports.2–5 8 The pain was localised to the plantar medial midfoot with an associated fusiform swelling and ecchymosis. Murakami et al also describe clinical findings of plantar ecchymosis similar to that seen in TMTJ injuries.3

It is recognised that up to one-third of tarsometatarsal injuries are missed on initial assessment.9 A high index of suspicion coupled should prompt further investigations with weightbearing radiographs of the foot. If radiographs are inconclusive, further three-dimensional imaging such as a CT scan should be sought in the acute setting. Weinberg et al reported a case where further imaging was not pursued despite pain and swelling in the foot. The patient was managed expectantly and instructed to fully weight bear. They underwent a delayed MRI after symptoms had not fully resolved. This led to a 10 week delay in the diagnosis of this patient’s the PL avulsion fracture.8 Zermatten et al describe a case where the MRI only showed bruising of the first metatarsal and partial PL tendon rupture. Pain had persisted and there was a 6 month delay in diagnosis where CT scan demonstrated a minimally displaced fracture at base of first metatarsal.4 In an acute setting, the oedema from the MRI may not demarcate the fracture and thus a CT scan is best performed to not miss the diagnosis of the fracture. An MRI is useful to assessing the soft tissue structures such as the PL and Lisfranc ligament in the absences of a fracture on CT.

Conservative treatment for an avulsion fracture of the PL from the first metatarsal has shown both good and poor outcomes. Hodor et al opted for a protected approach of NWB in a fracture fragment that was displaced by 4 mm. The patient was pain free and returned to full activity at 6 months postinjury.10 Weinberg et al pursued a more functional approach with their delayed diagnosis. The patient was instructed to full weight bear in normal footwear and asked to abstain from sporting activity for 6 weeks. At lengthy 6 months postinjury, they were pain free and demonstrated equal power in both feet.8 Zermatten et al reported on failure of conservative management with multiple contributing factors, including a high body mass index and an initial delay in diagnosis by 6 months. Despite 9 months of conservative management, this was complicated by non-union and surgical treatment involved excision of the fracture fragment and arthrodesis of the first TMTJ.4 Conservative treatment may be indicated in select patients with delayed presentation or diagnosis; however, based on reported cases, there is a risk of delayed return to baseline function compared with our case managed with acute operative treatment.

Surgical treatment has reported favourable outcomes. Various techniques of internal fixation have shown bony union, symptom improvement and patient return to activity after rehabilitation. Kwak et al demonstrated an open reduction technique and fixation with multiple buried Kirschner wires. This method required removal of wires, 4 months after surgery subjecting the patient to a second operation.2 Murakami et al conducted a less invasive image intensifier guided insertion of a cannulated cortical screw and washer without exposure of the fracture site, through a 2.5 cm incision. The patient was then instructed to heel weight bear for 2 weeks then transition to full weight bearing at 3 weeks. By 4 months, the patient had started light exercise and jogging.3 More recently, Fukutake et al reported the use of a ZipTight Fixation as an internal fixation method to allow earlier return to activity. This fixation method has demonstrated good outcomes for avulsion type fracture healing and can be performed in a percutaneous surgical approach. The patient was rehabilitated with NWB for 2 weeks, heel touch weight bearing for a further 2 weeks and then full weight bearing. They reported a return to normal activity by 3 months.5

The use of a partially threaded cancellous screw for definitive fixation has been rarely quoted and has been shown to demonstrate equivocal results with regard to pain relief and return to function. The procedure should be considered as an alternative definitive fixation of the avulsed fragment. Our patient’s fracture pattern was intraarticular and displaced. This prompted the consideration for operative fixation to restore articular congruity and reduce the risks of post-traumatic TMTJ arthritis. Following eccentric stretching, facilitated by the physiotherapist, our patient successfully returned to full function, 3 months postsurgical intervention.