A 34-year-old retired football player started to practice football in 2001 and now worked in a gym as a personal trainer. In March 2004, the patient immediately felt pain in his right knee, and his right leg was unable to take off after a quick long jump without warming up enough. There was no swelling of the knee joint at the time of the injury. The patient felt his legs were soft, unable to exert force, and felt deep in the restricted position but he could continue to train. In December 2004, an MRI examination was diagnosed with an osteochondral contusion of the lateral femoral condyle. Sodium hyaluronate was injected in 2006. On the advice of doctors, he retired in April 2006. From 2006 to 2013, the patient mainly sold sports equipment and worked as a part-time model. During the past few years, the patient did not treat with relevant functional rehabilitation and was limited to physical activities of daily life. He has been a fitness instructor since 2013, the patient has been continuously undergoing acupuncture, physiotherapy and small needle knife treatment, but the knee joint pain still exists after the treatment, and at the same time, the knee joint pain worsens after each training session. The patient complained that there was no obvious pain in the right knee in daily life, but the knee joint would be uncomfortable when it was cold. The right knee has obvious downhill pain, deep pain, blurred pain, unable to take off normally and participating in strenuous exercises of the lower limbs, fearing to be injured again, dare not do high-intensity and difficult movements in daily life and training. On April 24, 2019, a Physical and Rehabilitation Medicine (PRM) physician performed physical examinations (Figure 1), and a PRM physician experienced in musculoskeletal ultrasound diagnostic used Samsung HM70A model 5 18 Hz frequency probe to examine the patient's painful knee joint. The results showed that active range of motion (AROM) of the right hip joint: flexion-extension-abduction-adduction-external rotation-internal rotation were 110 -12 -33 -18 -40 -35 ; left side hip joint AROM flexion-extension-abduction-adduction-external rotation-internal rotation were 115 -9 -25 -20 -36 -35 . Both sides hip joint extension and abduction were insufficient; Right and left knee flexion were 115  and 121 ; right and left ankle dorsiflexion-plantar flexion were 15 -35  and 9 -30 , which indicated the left ankle AROM of the dorsiflexion joint was insufficient. The flexion and extension of the knee joints of both lower extremities were tested on grade 5 with normal muscle strength. The patient had no other medical or family history.
The musculoskeletal ultrasound examination showed that the continuity of the patellar cortex was interrupted. An echoless area (about 0.57*0.35) was visible on the deep surface of the patellar tendon (Figure 2). The inner cartilage was slightly thinner than the outer side. The diagnosis was fluid accumulation in the deep subpatellar sac and old patella fracture. The patient signed informed consent and corrective training instructions to allow the use of his personal information for this case report and promise to follow the direction of exercise intervention. The patient himself was unwilling to undergo surgical treatment and only accepted conservative treatment. The patient was approved by the ethics committee of Physical Education of Southwest University School (approval no. SWU-20180304-C1).