Plantaris Excision Reduces Pain in Midportion Achilles Tendinopathy Even in the Absence of Plantaris Tendinosis

BACKGROUND: It is becoming increasingly apparent that the plantaris can contribute to symptoms in at least a subset of patients with midportion Achilles tendinopathy. However, the nature of its involvement remains unclear. PURPOSE: To determine whether excised plantaris tendons from patients with midportion Achilles tendinopathy display tendinopathic changes and whether the presence of such changes affect clinical outcomes. STUDY DESIGN: Case series; Level of evidence, 4. METHODS: Sixteen plantaris tendons in patients with midportion Achilles tendinopathy recalcitrant to conservative management underwent histological examination for the presence of tendinopathic changes. All patients had imaging to confirm the presence of the plantaris tendon adherent to or invaginated into the focal area of Achilles tendinosis. Visual analog scale (VAS) and Foot and Ankle Outcome Score (FAOS) results were recorded pre- and postoperatively. RESULTS: Sixteen patients (mean age, 26.2 years; range, 18-47 years) underwent surgery, with a mean follow-up of 14 months (range, 6-20 months). The plantaris tendon was histologically normal in 13 of 16 cases (81%). Inflammatory changes in the loose peritendinous connective tissue surrounding the plantaris tendon were evident in all cases. There was significant improvement in mean VAS scores (P < .05) and all domains of the FAOS postoperatively (P < .05). CONCLUSION: The absence of any tendinopathic changes in the excised plantaris of 13 patients who clinically improved suggests plantaris involvement with Achilles tendinopathy may not yet be fully understood and supports the concept that this may be a compressive or a frictional phenomenon rather than purely tendinopathic.