A New Simple and Practical Clinical Classification for Tenosynovial Giant Cell Tumors of the Knee

OBJECTIVE: To propose a simple and practical clinical classification for tenosynovial giant cell tumor (TGCT) of the knee. METHODS: A retrospective study was conducted to verify the value and significance of this clinical classification. TGCT growth patterns, knee joint capsule, and bone erosion were applied to establish this novel clinical classification. Seventy‐eight patients who underwent surgery for TGCT from 2008 to 2016 were identified. This novel clinical classification was retrospectively applied to patients' existing classification, and patients with different TGCT types were statistically compared to verify the significance of the clinical classification. RESULTS: The clinical classification included three types and four subtypes. Type 1: localized TGCT, Subtype 1a: localized intra‐articular TGCT, Subtype 1b: localized extra‐articular TGCT. Type 2: diffuse TGCT, Subtype 2a: diffuse intra‐articular TGCT with bone normal, Subtype 2b: diffuse intra‐articular TGCT with bone destruction. Type 3: diffuse TGCT across the knee joint capsule. The mean follow‐up time for the 78 patients was 59.6 months. Twenty‐one patients were in Subtype 1a, four were Subtype 1b, 38 were Subtype 2a, seven were Subtype 2b, and eight were Type 3. Oncological results and surgical complications differed significantly (P = 0.000, P = 0.000). The mean Musculoskeletal Tumor Society functional scores differed significantly at 27.8 for Type 1 patients, 22.9 for Type 2 patients, and 17.0 for Type 3 patients (P = 0.000). CONCLUSIONS: This clinical classification can be easily used to evaluate TGCT of all knees prior to surgery or other treatments and can help determine surgical options.