## 1 Introduction  
Peroneal tendon dislocation is a rare condition, often initially misdiagnosed as a lateral ankle sprain during initial medical evaluation. Tendon tears are frequently associated with this condition. Acute injuries are more prevalent among athletes engaged in sports such as soccer and skiing, while chronic injuries are linked to a history of repetitive ankle sprains resulting in functional instability [1; 2]. Nonetheless, subluxation or dislocation may also arise as secondary effects of neurological disorders and calcaneal fractures [3]. Risk factors for subluxation or full dislocation include retromalleolar groove dysplasia, characterized by a convex or flat fibular groove, superior peroneal retinaculum incompetence, posterior lateral fibular spurring, low-lying brevis and quartus anomalies, and a high-arch foot type [1; 4; 5; 6]. Prior research has examined the configuration of the retromalleolar groove and its significant role in maintaining tendon stability. It has been observed that the shape of this groove can vary among individuals. [PERSON] conducted a study on cadavers and categorized the shape of the groove as follows: concave in 82% of cases, flat in 11%, and convex in 7%. The average depth of the groove ranged from 2 to 4 mm, while the typical width was around 9 mm. Additionally, there is a fibrocartilaginous ridge present that extends the surface area laterally [4; 7; 8]. Different authors have demonstrated how the low-lying brevis and quartus anomalies have the capacity to congest the retromalleolar groove, resulting in the relaxation of the SPR (short peroneal retinaculum). This relaxation is correlated with the occurrence of longitudinal splitting, tenosynovitis, and tendon dislocation [5]. The mechanism of dislocation typically involves a forceful contraction of the peroneal muscles during sudden dorsiflexion and inversion of the foot, resulting in the disruption of the superior peroneal retinaculum (SPR) [9]. The primary structure preventing the subluxation of peroneal tendons within the fibular groove is the superior band of the SPR. In 1987, [PERSON] introduced a fourth grade to the classification system for peroneal instability, which was originally proposed by [PERSON] and [PERSON] in 1976 [10]. From a clinical perspective, patients often describe a sensation of popping or snapping in the ankle region and a feeling of instability, especially when walking on uneven surfaces or during rotational movements of the ankle [11]. Some patients can replicate this instability during a clinical examination by actively circumventing the foot, starting in plantar flexion and proceeding into active evasion, which may not necessarily cause pain [12; 13]. Once more, a physician can intentionally induce tendon subluxation or dislocation during a clinical examination by applying resistance while the patient performs plantar flexion combined with version or by forcibly dorsiflexing the foot. As the patient walks, the peroneal tendons may be observed dislocating anteriorly or laterally along the distal fibula. The role of imaging in diagnosis and management is a subject of debate, with clinical evidence being the primary basis. Conventional radiography is typically used in acute cases. The presence of the 'fleck' sign on radiographs is a clear indicator of SPR avulsion and may suggest tendon subluxation or dislocation. Ultrasound imaging provides the advantage of real-time, dynamic visualization of peroneal tendon dislocation [14]. For a comprehensive assessment of peroneal tendon integrity, SPR condition, and tenosynovitis, MRI is considered the preferred imaging modality [15]. Computed tomography (CT) is useful for evaluating osseous anatomy, such as the morphology of the retromalleolar groove, hypertwrophied peroneal tubercle, or lateral wall impingement, especially following calcaneal fractures. [PERSON] et al. adapted a CT assessment of the retromalleolar groove to MRI and identified four distinct types [16].