A low-lying peroneus brevis muscle belly is one that has muscle tissue extending beyond the retromalleolar groove and the distal tip of the fibula. Between ~10%-25% of patients with a peroneus longus or brevis tendon tear have a low-lying peroneus brevis muscle belly when examined by MRI, suggesting that this variant can predispose the muscle and tendon to tears. It is thought that increased muscle mass in the retromalleolar groove causes overcrowding and results in peroneal tendon injury. A similar mechanism is thought to underlie the association of the presence of a peroneus quartus muscle to peroneal tendon tears.
The main differential consideration for the appearance of a low-lying peroneus brevis muscle belly is an accessory muscle, such as the peroneus quartus.
References
- Freccero DM, Berkowitz MJ. The relationship between tears of the peroneus brevis tendon and the distal extent of its muscle belly: an MRI study. Foot Ankle Int. 2006 Apr;27(4):236-9.
- Geller J, Lin S, Cordas D, Vieira P. Relationship of a low-lying muscle belly to tears of the peroneus brevis tendon. Am J Orthop (Belle Mead NJ). 2003 Nov;32(11):541-4.
- Khoury NJ, el-Khoury GY, Saltzman CL, Kathol MH. Peroneus longus and brevis tendon tears: MR imaging evaluation. Radiology. 1996 Sep;200(3):833-41.
- Rosenberg ZS, Beltran J, Cheung YY, Colon E, Herraiz F. MR features of longitudinal tears of the peroneus brevis tendon. AJR Am J Roentgenol. 1997 Jan;168(1):141-7.
In your experience, does excising the low lying muscle belly help relieve symptoms of peroneal tendonitis? If you have a patient with subluxing as a result of a convex groove and low lying muscle on one foot, but only tendonitis with the absence of sublux in the other foot, would muscle belly excision with groove deepening possibly help both feet?
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