Isokinetic muscle strength test implemented by the Biodex system is a method used for evaluating muscle function that has been applied clinically in the field of sports and rehabilitation medicine. However, information on its application on Haglund's deformity remain insufficient. Therefore, the present study is designed to examine the effectiveness of the muscle strength test using the Biodex system in evaluating the recovery of athletic capacity in patients with Haglund's deformity following endoscopic surgery.

Patients. A retrospective (medical records), level 3 evidence study was designed to evaluate the outcomes of patients who underwent endoscopic surgery for Haglund's deformity. The present study was approved by the Peking University Third Hospital's ethics committee. Written informed consent was obtained from all patients, parents or guardians of the patients prior to the present study. The rights of the patients were protected.

Diagnosis. Patients were designed to be diagnosed based on subjective complaints, combined with clinical and radiological examinations. Radiological measurements for this disease include the Fowler-Phillip angle, calcaneal pith angle, parallel pitch lines, Chauveaux-Liet angle and the X/Y ratio.

Inclusion Criteria:

• Patients who underwent endoscopic surgery for Haglund's deformity

Exclusion Criteria:

• None

The study included 42 cases of 37 patients diagnosed with Haglund disease treated by the author from 2012 to 2018 treated with endoscopic surgery (5 of whom were patients with left and right feet, 33 men, 4 women, average age 32.3 (range:15 to 62, SD=13.6) years, 2 of whom are professional athletes.