薄筋腱によって生じた弾発膝の1例

Snapping Knee Caused by a Gracilis Tendon. Case Report

　薄筋腱による弾発膝の症例を経験したので報告する．症例は30歳の女性で，主訴は左膝関節の弾発現象である．膝関節約30°屈曲位で後内側に弾発現象が認められ，その際に疼痛の訴えがあった．臨床所見や画像所見からハムストリング腱による弾発と診断し手術を行った．術中に薄筋腱が大腿骨内側顆部で弾発していることを確認し，同部で薄筋腱の切離を行った．術後に弾発現象は消失し，術後1年の現在，日常生活に問題なく経過している．弾発現象の原因として，半月板などの関節内因子以外に，腱などによる関節外因子を念頭に置く必要がある．

　In this paper we report a case in which a snapping phenomenon was caused by the gracilis tendon flipping over the medial condyle of the femur. The patient was a 30-year-old woman with a 2-year history of intermittent pain and a snapping sensation over the medial aspect of the left knee without any history of injury. Physical examination revealed snapping at the posterior corner of the medial femoral condyle at 30 degrees of both active and passive knee flexion. Imaging studies, including MRI and CT, revealed no abnormal findings. Surgery was performed based on a preoperative diagnosis of extra-articular snapping caused by a hamstring tendon. At surgery, we found a conflict between the gracilis tendon and posterior edge of the medial femoral condyle during knee motion and dissected the gracilis tendon at that level. One year after surgery, the snapping had completely disappeared. Based on an anatomical review of MRI scans taken to assess knee injuries in our patient population, we speculated that excessively anterior location of the grasilis tendon in relation to the medial femoral condyle may have been a factor in causing the snapping of this patient. Surgeons should rule out extra-articular factors when diagnosing snapping knee.