74 - An Extensive Review of the Fibularis Quartus Muscle – a Supernumerary Muscle of the Lateral Leg Compartment

Poster Board Number: 74
There are separate poster presentation times for odd and even posters.
Odd poster #s – first hour
Even poster #s – second hour

Co-authors:

Lienne Russell - Undergraduate Student, Pathology, Anatomy, and Laboratory Medicine (PALM), West Virginia University School of Medicine; Allison Ralston - Undergraduate Student, Pathology, Anatomy, and Laboratory Medicine (PALM), West Virginia University School of Medicine; Reagan Martignetti, B.Sc. - Graduate Student, Pathology, Anatomy, and Laboratory Medicine (PALM), West Virginia University School of Medicine; B. Diane Gillis, B.Sc. - Medical Student, Pathology, Anatomy, and Laboratory Medicine (PALM), West Virginia University School of Medicine; Allison Angilello - Undergraduate Student, Pathology, Anatomy, and Laboratory Medicine (PALM), West Virginia University School of Medicine; Jesse Burkett, B.Sc. - Graduate Student, Pathology, Anatomy, and Laboratory Medicine (PALM), West Virginia University School of Medicine; Matthew Zdilla, D.C. - Associate Professor, Pathology, Anatomy, and Laboratory Medicine (PALM), West Virginia University School of Medicine; H. Wayne Lambert, Ph.D. - Professor and Vice Chair, Pathology, Anatomy, and Laboratory Medicine (PALM), West Virginia University School of Medicine

Abstract Body : The presence of the fibularis (peroneus) quartus, a supernumerary muscle within the lateral leg compartment, has been associated with ankle instability, lateral leg pain, fibular tenosynovitis, longitudinal splitting of the fibularis brevis tendon, and subluxation of the fibular tendons, often following inversion ankle sprains. This variant leg muscle is present in approximately 11.5% of legs as determined by MRI, ultrasound, and whole-body donor studies. The fibularis quartus muscle travels posterior to the lateral malleolus of the fibula after arising proximally from the fibula, fibularis longus, and/or fibularis brevis muscle. The distal insertion of the fibularis quartus muscle varies greatly, most often inserting upon the lateral surface of the calcaneus into either the retrotrochlear eminence or the fibular (peroneal) trochlea. When this supernumerary muscle inserts into the lateral calcaneus, it is called a fibulocalcaneus (peroneocalcaneus) externum muscle because fibularis quartus variants are, in most cases, named due to the location of their distal insertion. However, when the distal insertion travels distal to the calcaneus, the name of the fibularis quartus variants changes. A distal insertion into the cuboid bone results in a muscular variant named the fibulocuboideus muscle. Insertion into an aspect of the fifth (or little) toe results in a fibularis quartus variant called the fibularis digiti minimi, which can insert into extensor (dorsal) aponeurosis of the fifth toe, the base of the dorsal surface of the fifth metatarsal, or the base of the fifth proximal phalanx. Another fibularis quartus variant is termed the fibularis (peroneus) accessorius muscle, and this muscle results when the fibularis brevis or fibularis longus muscle splits and inserts distally into either the tendon of the fibularis longus or the fibularis brevis. This study will discuss the confusion in the nomenclature of these supernumerary muscles and how this confusion has led to great disparities in the reported prevalence of these lateral leg muscle variants. It will also present examples of fibularis quartus variants, and show novel and exceedingly rare fibularis quartus variants, such as the fibulotalocalcaneus, the fibulocalcaneocuboideus, and the fibulocalcaneus externum invertus muscles. In some cases, surgical removal of the fibularis quartus muscle is necessary to relieve ankle pathology and instability issues; however, most fibularis quartus variants are found during imaging, anatomical dissection, or surgery in asymptomatic individuals.