Anconeus Exertional Compartment Syndrome and Posterolateral Rotatory Elbow Instability: A Clinical Association and Rare Cause of Elbow Pain.

Background: Anconeus compartment syndrome is a rarely reported compartment syndrome in the anconeus muscle compartment of the forearm. It has anatomic and pathophysiological associations with posterolateral rotatory instability (PLRI) of the elbow. Purpose: To present the history, management, and outcomes of 4 patients with anconeus compartment syndrome. Secondary aims were to (1) establish normative anconeus pressures and (2) measure the volume of this compartment with and without PLRI in cadavers. Study Design: Case series; Level of evidence, 4. Methods: Four patients with clinical signs of anconeus compartment syndrome (2 gymnasts, 1 swimmer, and 1 footballer/weightlifter) were identified over a 3-year period (2015-2017 inclusive). Patient history, sporting activity, physical examination, anconeus compartment pressures, and treatment outcomes were recorded. Manometry of the anconeus compartment in 2 healthy male controls was performed to establish normative compartment pressures. Anconeus volumetric anatomy and the effect of creating PLRI on compartment volume was investigated in 4 cadaveric elbows. Results: All 4 patients had microtraumatic PLRI, and 2 patients had anconeus hypertrophy. Anconeus compartment pressures at rest and at 2-minutes postexercise were median 28.0 and 67.5 mm Hg, respectively, in the patients and mean 16.5 and 18 mm Hg, respectively, in the controls. Simultaneous fasciotomy and PLRI reconstructive procedures were performed in 2 patients, with outcomes showing full return to competition. Fasciotomy alone was performed in 2 patients to allow return to competition, with both requiring later reconstruction to address PLRI. Cadaver dissection revealed that the anconeus compartment was extremely small and that creation of PLRI reduced the direct volume of the compartment and increased the distance between the anconeus origin and insertion. Conclusion: Our case series demonstrated that anconeus compartment syndrome can occur in upper limb-dominant athletes in the presence of PLRI and anconeus hypertrophy. Pain is relieved by fasciotomy, but definitive treatment of the underlying instability prevents further symptomatology.