Description
Objective: Accessory muscles of the foot are a rare anatomical entity. Among them, the peroneocalcaneus internus (PCI) muscle is the least frequent one, with the prevalence of only 1%. When performing posterior ankle arthroscopy, the flexor hallucis longus (FHL) tendon is the main landmark since it is the medial safe boundary for arthroscopy, with the neurovascular bundle staying superficial and posteromedial to it. According to literature the finding of the PCI is of extreme importance because it may be misinterpreted for the FHL tendon due to interdigitation of the fibres between the tendons. In such cases an interval between the PCI and FHL may be accessed, causing damage to neurovascular bundle. The goal of this paper is to present a case of combined one-stage anterior and posterior ankle arthroscopy during which the peroneocalcaneus internus muscle was found.
Methods: A 49-year-old female presented herself after an inversion ankle sprain with pain in the anterior and posterior part of the ankle. After initial conservative treatment the pain was still present, mainly in the posterior part of the ankle and a magnetic resonance imaging was conducted showing the Shepherd fracture (Figure 1), after which the surgery was indicated.
Results: The patient underwent a combined one-stage anterior and posterior ankle arthroscopy. The surgery was conducted in spinal anaesthesia, without the use of the tourniquet. The patient was initially set up in prone position to conduct hindfoot endoscopy via 2-portal technique as described by van Dijk. During this part of surgery an accessory tendon and muscle was found in the posteromedial part of the ankle (Figure 2A). The muscle originated laterally in the proximal part and was directed distally towards the medial part of the calcaneus. It turned into the tendon at the level of the tibiotalar joint and was localized posteromedial to the flexor hallucis longus tendon and in contact with the fractured Stieda process. At that time dorsal and plantar flexion of the great toe was performed, causing movement of both tendons. The Stieda process was resected and the abundant peroneocalcaneus internus muscle was partially removed leaving its tendon intact (Figure 2B, 2C). The wounds were then sutured, and the patient was turned to supine position to perform anterior ankle arthroscopy. The perioperative course was uneventful, and the patient made a full recovery.
Conclusion: Although it is extremely rare, the PCI tendon, due the interdigitation fibres, may be misinterpreted for FHL tendon leading to possible iatrogenic damage of the neurovascular bundle. Surgeons performing hindfoot endoscopy should be aware of this anatomical entity to make the surgery as safe as possible.
