Characteristics of flexed knee gait and functional outcome of a patient who underwent knee reconstruction with a hingeless prosthesis for bone tumor resection: a case report with gait analysis and comparison with healthy subjects.

We report on a patient after knee reconstruction for osteosarcoma in the distal femur using a hingeless prosthesis K-MAX KNEE system K-5 who walked without ipsilateral knee extension in the latter half of the stance phase (flexed knee gait). We evaluated the patient using three-dimensional gait analysis and isokinetic knee strength measurement, and compared the patient with five healthy subjects. The Musculoskeletal Tumor Society (MSTS) score was also used for evaluation. The patient kept his operated knee flexed during mid stance. The maximal ankle plantarflexion internal moment was lower on the ipsilateral side than on the contralateral side, and lower than in the healthy subjects. The negative ankle power during the stance phase was generally stronger on the ipsilateral side than on the contralateral side, and also in the healthy subjects. Unusual contralateral hip flexion occurred after the initial contact, indicating increased joint load on the ipsilateral ankle and the contralateral hip. The ratios of the peak knee extension/flexion torque were 0.7 on the ipsilateral side, 1.9 on the contralateral side, and 1.7 in the healthy subjects. The MSTS score of the patient was 23/30 (76.6%). Flexed knee gait might account for the reduction of ipsilateral hip flexion and ankle plantarflexion moment during the late stance phase. These results suggest the importance of focusing more on the ipsilateral ankle joint and the contralateral hip joint to maintain the function of the entire limb joints of the patients with flexed knee gait.