Successful reconstruction of distal peroneus longus tendon dislocation associated with a split lesion – a case report

The peroneal tendons are probably the most important structures in the differential diagnosis of lateral ankle and rearfoot pain [1, 2]. Specifically, peroneal tenosynovitis, longitudinal (split) lesions, and even transverse tears mainly involving the peroneus longus tendon have to be considered [3, 4]. Three distinct zones are used to anatomically locate the pathology of the peroneus longus tendon [5]. Increased shear loads result when the tendon changes its direction at the lateral malleolus (zone A), at the peroneal tubercle (= peroneal trochlea) of the calcaneus (zone B), and in the cuboid notch (zone C). Dislocation of the peroneal tendons generally occurs at the lateral malleolus (zone A) and is the result of an injury to the superior peroneal retinaculum, triggered most frequently by ankle inversion injuries [3, 6‐8]. In zone B partial tears are predominantly found, while complete tears occur in zone C [5].

In 2011 another, very rare cause of lateral rearfoot pain was introduced in the literature, resulting from dislocation of the peroneus longus tendon at the peroneal tubercle [9]. Since that case description, only four more cases have been published in two papers to describe this very rare entity [10, 11].

In contrast to tenosynovitis and tears which may be induced by chronic friction of the peroneus longus tendon at an enlarged peroneal tubercle [3, 6], dislocation occurs over normal-sized peroneal tubercles following traumatic tears of the inferior peroneal retinaculum [9‐11].

The purpose of this report is to present a previously undescribed case of an incomplete longitudinal split tear of the peroneus longus tendon, which was partially dislocated from its flat groove and entrapped over the peroneal tubercle. This pathology, mimicking an enlarged peroneal tubercle, should be kept in mind by clinicians in the differential diagnosis of lateral ankle and foot pain. The respective anatomic reconstruction addresses all three constituting components of the pathology (inferior peroneal retinaculum, shape of the groove, and peroneus longus split tear). The outcome is assessed by a standardized questionnaire.

The local Ethics Committee approved the study. Written informed consent was obtained from the patient for publication of this case report and any accompanying images. The rights of the patient were protected. The registration trial number is DRKS00014266 on DRKS. ‘Retrospectively registered’. Date of registration: 06/04/2018.

Previous reports have described either tenosynovitis, tears or, very rarely, dislocation of the peroneal tendon at the lateral calcaneal facet [5, 14, 15]. The case presented in this study is unique regarding its complexity. It combines a split lesion and entrapment of a dislocated peroneus longus tendon at the level of the peroneal tubercle in the midportion of the lateral calcaneal wall. The resulting prominence mimicked an enlarged tubercle. With six published cases, distal peroneus longus tendon dislocation is very rare. From the presented case, it can be speculated that the inferior peroneal retinaculum was overused, worn out, detached, or ruptured due to overpronation and friction of the lateral edge of the low-cut speed skating shoe. Then, the peroneus longus experienced substantial friction with the peroneal tubercle with possible dislocation during ankle motion. This frictional contact may have finally led to further degeneration and a longitudinal tear of the tendon. The initial lesion (detachment or rupture) of the inferior peroneal retinaculum seems not to be associated with tubercle enlargement, which is thought to be a predisposing factor for tendon tears [12, 15]. Intraoperatively, we found a flat peroneus longus groove below the calcaneal tubercle. In the retromalleolar area, a flat or convex groove is thought to be a predisposing anatomic factor for peroneal tendon dislocation [15]. However, there is no research available for objectively assessing the shape of the bony groove at the level of the calcaneal tubercle. Therefore, no conclusions can be made about the pathologic relevance of this finding. In addition, patients with distal peroneal tendon dislocation are younger and are more active in competitive sports than patients suffering from peroneal tendon pathology associated with tubercle enlargement [14]. Additionally, patients with distal peroneus longus tendon dislocation have normal-shaped feet (Table 1). A traumatic induction of the dislocation was not observed in the presented case. Overpronation may have played an inducing role, and one case report demonstrated an ice skater who also complained about an insidious onset of symptoms [10]. Cavovarus feet and enlarged peroneal tubercles seem to predispose patients for lateral ankle sprains and friction pathologies, respectively [3, 5, 14, 16, 17].

In contrast with previous reports of distal dislocation of the peroneus longus tendon (Table 1), the presented case is unique because the patient reported no snapping phenomenon at the lateral calcaneal wall. The reason for this is entrapment by the split lesion located over the normal-sized peroneal tubercle, mimicking enlargement of the peroneal tubercle.

Diagnosis of the described condition is made from clinical findings (Table 1). It is important that physicians are aware of this rare lesion.

As demonstrated in this case, imaging (MRI and ultrasonography) can confirm dislocation. However, if a normal-sized tendon is not actually dislocated, imaging may not be helpful. Friction-induced oedema of the lateral calcaneal wall, tenosynovitis, and tendon split lesions are unspecific findings.

All patients with distal peroneal tendon dislocation were unresponsive to conservative treatment (Table 1). Therefore, as a result of the current literature and from the presented case, surgery is recommended as the treatment of choice when conservative treatment fails [15]. The rationale against resection of the whole degenerated peroneus longus tendon and tenodesis to the peroneus brevis is provided by the principle of anatomically restoring anatomy, specifically when considering the demanding loads of top-level athlete. It is expected that the remaining peroneus longus tendon will sufficiently recover. This can be seen analogue in surgery for Achilles tendinopathy, where up to 50% of the tendon can be resected [18]. The assumption is further substantiated ex juvantibus by the excellent result obtained in the described case. The patient completely recovered and was able to compete successfully at the highest international level. He finally assessed the functional capacity of his operated foot as “normal”. When comparing the operative techniques for distal peroneal dislocation within the literature (Table 1), all authors repaired the inferior peroneal retinaculum. Additional groove deepening added stability and safety, specifically for this high-demand athlete.

The strength of the present case report is achieved by the introduction of a groove deepening technique, which provides additional security for inferior peroneal retinaculum reconstruction, and by the prospective evaluation of the patient with the administered outcome measure. It remains unclear whether the excellent result could be replicated with isolated repair, by reinsertion of the inferior peroneal retinaculum, or by groove deepening alone. This question could be answered with further comparative research. A prominent peroneal tubercle can be considered for excision in patients with associated peroneal tendon pathologies [15]. In either published case of distal peroneal dislocation, however, the peroneal tubercle was assessed as “normal” and was not resected. The results of treatment were excellent in all cases (Table 1).

Distal peroneus longus dislocation with a split lesion and entrapment over the peroneal tubercle, is a very rare sports injury. It is difficult to diagnose when the patient does not report tendon snapping. This pathology adds to the differential diagnosis of lateral ankle and rearfoot pain.

In conclusion, detachment of the inferior peroneal retinaculum, peroneus longus tendon dislocation, and entrapment by a split lesion represent a new complex entity that can effectively be reconstructed by partial resection of the split tendon, groove deepening, and transosseous reinsertion of the inferior peroneal retinaculum.