JIANG Xin, ZHANG Yi-min ,LIU Jian-yong

      Patella infera is a rare condition caused by pathological shortening of the patellar tendon. The term “patella infera” was coined by Caton et al1 in 1982 and the condition can severely affect knee function. Patella infera has been reported as a complication of non-operative treatment for patellar fracture;2 anterior cruciate ligament reconstruction; tibial tubercle osteotomy; surgically-treated patellar fracture; unicompartmental and total knee replacement; high tibial osteotomy; surgically-treated habitual dislocation with coexistent patella alta; and retrograde nail insertion for femoral shaft fracture. Traumatic causes of patella infera include quadriceps tendon rupture, femoral shaft fracture, and intraarticular fracture of the knee.3 Our case occurred because of closed trauma on the patellar tendon leading to partial cicatricial contracture of the patellar tendon and eventual patella infera. Z-plasty lengthening of the patellar tendon and post-operative rehabilitation were effective treatments. Despite its association with other injuries and surgeries around the knee, no previous report has discussed the connection between closed traumatic contracture of the patellar tendon and patella infera.
        A 37-year-old woman fell suddenly on her right knee while walking. She experienced marked pain in her injured knee and was sent to a local hospital. There was a painful, bruised and swollen area of skin on the anteroinferior part of the knee with no radiographic indication of fracture or other anomalies. The diagnosis was local soft tissue injury and the patient was discharged without further intervention.The patient began weight-bearing 3 days later when the local pain and swelling decreased, and had good function for approximately 2 months. Subsequently, the patient complained of chronic disability of the affected knee, with weight-bearing pain; difficulty in extending the knee; quadriceps muscle weakness; and aggravating pain in the anterior part of the knee when going upstairs and squatting. X-rays of the right knee taken 2 months after the closed trauma appeared normal with Insall-Salvati ratio4 of 1.1 (Figure 1A). The patient came to our hospital 5 months later. On physical examination, local tenderness was obviously palpable on the middle part of the patellar tendon, and the patella moved to a lower position with knee flexion.