A 25-year-old man was referred after excision of a painful 2-cm nodule in the left infrapatellar region. Pathological diagnosis was synovial sarcoma (Fig. 1a). Because of positive margin, pre-operative radiotherapy and subsequent re-excision were performed. The whole patellar tendon, infrapatellar fat pad, inferior one-third of the patella, and the tibial tuberosity were removed together with 6 x 12 cm of the skin including previous operation scar. Using an oblique osteotomy, nearly the whole original patellar-femoral joint surface of the patella was preserved. Following resection, BPTB allograft was harvested and shaved to fit the osteotomy sites. Then, the allograft was fixed to the residual patella and proximal tibia with screws and a stainless steel Dall-Miles 2-mm Cable and Sleeve Set (Stryker Australia Pty., Ltd.) tightened at 30  knee flexion (Fig. 1b). The soft tissue defect was covered with a free ipsilateral antero-lateral thigh (ALT) flap.
Post-operative course was uneventful without wound complication or infection. The operated knee was kept straight in splint for the first 3 months, and then gentle passive and active range-of-motion (ROM) exercise was started. Full weight bearing (FWB) was tolerated immediately after surgery but only in the setting of using crutches for the first 6 weeks. Three months after surgery, progressive ROM exercise and FWB without splint were allowed. Both bone-bone junctions were united 11 months post-operatively (Fig. 1c). After both bone-bone junctions were united, sports activity, including fun skiing, was permitted. At 67 months after surgery, the patient was continuously free of disease. His left knee function was virtually normal, with no extension lag and knee flexion of 130  (Fig. 2; Additional file 1: Movie S1). Quadriceps manual muscle test was 5/5. Musculoskeletal Tumor Society (MSTS) score was 30/30 (Enneking et al.).