The Role of the Flexor Hallucis Longus in the Treatment of the Painful Hallux Metatarsophalangeal Joint.

Background: Pain in the hallux metatarsophalangeal joint (MTPJ) is very common, yet the underlying etiology remains unknown. Previous clinical research and biomechanical research has implicated stenosing flexor hallucis longus (FHL) tendonitis as a possible cause. The hypothesis of this study was that treatment solely focusing on alleviating restricted FHL excursion would be beneficial in patients with hallux MTPJ pain.

Methods: This is a retrospective study of those treated in the Foot & Ankle Division between January 2009, and December 2018, who were diagnosed with FHL tendonitis with associated pain in the hallux MTPJ. Demographics, comorbidities, examination findings, imaging results, pain scores, treatment instituted, and outcome was obtained from the electronic medical record. The primary outcome was the improvement in the pain score (visual analog scale [VAS]). The surgical patients were included if their procedure was solely related to the FHL (posteromedial ankle release ± os trigonum resection). The decision to have surgery was analyzed by univariate and multivariable statistics using demographics, comorbidities, and clinical findings as potential factors (P < .05).

Results: In 75% (59 of 79 feet), nonoperative treatment of FHL stenosis resulted in a decrease in pain scores that the patients felt was satisfactory. The operative group that had an FHL release showed decreased pain in 90% (18 of 20 feet). Multivariable analysis identified the need for immobilization (OR 9.8, 95% CI 1.8-55.2, P = .009), participating in athletics (OR 8.7, 95% CI 1.8-42.2, P = .007), and higher initial VAS (OR 1.7, 95% CI 1.3-2.3, P < .001) as being associated with the decision for surgery.

Conclusion: Previous biomechanical studies have suggested that stenosing FHL synovitis can cause increased intraarticular loading in the hallux MTPJ. The current clinical study supports this hypothesis, demonstrating that treatment focused on relieving restricted FHL excursion can ameliorate pain in the hallux MTPJ in select cases.