Painful Os Peroneum Syndrome
Dr. John Goodner D.P.M.
The Os Peroneum, an accessory ossicle found in the peroneus longus tendon lateral to the cuboid, has been reported present in as high as 30% of the population. The Os Peroneum protects the Peroneus Longus from stress induced injury, however, is often overlooked as a cause of plantar lateral foot pain secondary to fracture or tendon damage. The presence of this ossicle can predispose the patient to distal rupture of the peroneus longus tendon due to potential increase in friction with adjacent cuboid.
CAUSES:
Acute - Direct trauma, or indirect trauma secondary to ankle sprain of supination injury, subsequently resulting in diastasis or fracture of Os Peroneum
Chronic - Previous trauma induced calcification or remodeling with unhealed diastasis causing inflammation of peroneus longus (tenosynovitis)
DIFFERENTIAL DIAGNOSIS:
• Dislocation or subluxation of the peroneus longus tendon
• Lateral ankle injury to the talofibular ligament or calcaneofibular ligament
• Fractures in the anterior process of the calcaneus, perineal tubercle, cuboid, or fifth metatarsal
• Lateral chronic tendinopathy or tenosynovitis of peroneal tendons
SIGNS AND SYMPTOMS:
• Swelling over the cuboid
• Pain over the cuboid during palpation.
• Pain exacerbated by plantar flexion of 1st ray and heel elevation stage during gait
X-RAYS:
• Best visualized on oblique view
• Contralateral foot X-Ray can help differentiate between bipartite normal variant and acute fracture
• Acute fracture - non sclerotic and jagged edges
• Bipartite normal variant - sclerotic and rounded edges
• Diastasis greater than 5mm indicates fracture
• Displacement of the os peroneum is an indirect sign of a peroneal tendon rupture and MRI should be ordered
MRI:
• Increased intrasubstantial signal within the peroneus longus tendon, typically close to the cuboid
• Acute fracture or os peroneum or rupture of peroneus longus can be identified
TREATMENT:
Conservative
• Initial treatment for minimally displaced fracture or painful os perineum include : Immobilization, Restricted weightbearing, Rest, NSAIDS
Surgical
• After failure of conservative care, simple excision is advised for painful os peroneum if minimal tendon involvement is identified
• Primary repair was preferred if at least 50% of the tendon remained after debridement, and tendon transfer if <50% of the tendon remained after debridement.