title: Peroneus quartus and functional ankle instability.
abstract: BACKGROUND
  Physical and rehabilitation medicine physicians commonly see patients with chronic functional ankle instability. The main anatomical structures involved in ankle stability are the peroneus (fibularis) brevis and peroneus longus muscles. Several anatomical muscle-tendon variations have been described in the literature as being sometimes responsible for this instability, the peroneus quartus muscle being the most frequent. The objective of this clinical study is to discuss the implication of the bilateral peroneus quartus muscle in functional ankle instability.
  
  
  METHODS
  This 26-year-old patient was seen in PM&R consultation for recurrent episodes of lateral ankle sprains. The clinical examination found a moderate hyperlaxity on the right side in bilateral ankle varus. We also noted a bilateral weakness of the peroneus muscles. Additional imaging examinations showed a supernumerary bilateral peroneus quartus. The electroneuromyogram of the peroneus muscles was normal.
  
  
  CONCLUSIONS
  In the literature the incidence of a supernumerary peroneus quartus muscle varies from 0 to 21.7%. Most times this muscle is asymptomatic and is only fortuitously discovered. However some cases of chronic ankle pain or instability have been reported in the literature. It seems relevant to discuss, around the clinical case of this patient, the impact of this muscle on ankle instability especially when faced with lingering weakness of the peroneus brevis and longus muscles in spite of eccentric strength training and in the absence of any neurological impairment. One of the hypotheses, previously described in the literature, would be the overcrowding effect resulting in a true conflict by reducing the available space for the peroneal muscles in the peroneal sheath.
authors.affiliation: Pôle intersites de médecine physique et de réadaptation médecine et traumatologie du sport, hôpital La Timone, Marseille, France. guillaume.lotito@ap-hm.fr
authors.forename: G
authors.initials: G
authors.lastname: Lotito
authors.forename: J
authors.initials: J
authors.lastname: Pruvost
authors.forename: H
authors.initials: H
authors.lastname: Collado
authors.forename: J-M
authors.initials: JM
authors.lastname: Coudreuse
authors.forename: L
authors.initials: L
authors.lastname: Bensoussan
authors.forename: G
authors.initials: G
authors.lastname: Curvale
authors.forename: J-M
authors.initials: JM
authors.lastname: Viton
authors.forename: A
authors.initials: A
authors.lastname: Delarque
mesh_terms: D000328:Adult; D016512:Ankle Injuries / Q000209:etiology / Q000534:rehabilitation; D000843:Ankle Joint / Q000000981:diagnostic imaging / Q000473:pathology / Q000503:physiopathology*; D004576:Electromyography; D005413:Flatfoot / Q000150:complications; D056305:Genu Varum / Q000150:complications; D006801:Humans; D007593:Joint Instability / Q000000981:diagnostic imaging / Q000209:etiology* / Q000473:pathology / Q000534:rehabilitation / Q000628:therapy; D008279:Magnetic Resonance Imaging; D008297:Male; D018482:Muscle, Skeletal / Q000002:abnormalities* / Q000000981:diagnostic imaging / Q000473:pathology / Q000503:physiopathology; D009989:Orthotic Devices; D010146:Pain / Q000209:etiology; D012008:Recurrence; D055070:Resistance Training; D013180:Sprains and Strains / Q000209:etiology / Q000534:rehabilitation; D013717:Tenosynovitis / Q000150:complications; D014463:Ultrasonography