获得性低位髌骨的研究进展

Literature review of acquired patella baja

低位髌骨是全膝关节置换术（total knee arthroplasty，TKA）的一种并发症。低位髌骨是指髌韧带缩短或髌骨远离股骨滑车而引起的髌骨位置过低，分为先天性低位髌骨、获得性低位髌骨及混合性低位髌骨。获得性低位髌骨最常见，常继发于创伤或手术。因TKA术后关节线抬高而引起的低位髌骨称为假性低位髌骨。低位髌骨病因尚未明确。有学者认为股四头肌及其肌腱的伸长，髌韧带、髌下脂肪垫及其他软组织挛缩，关节纤维化等可导致低位髌骨。低位髌骨的诊断多借助膝关节侧位x线片，主要指标包括Insall-Salvati指数、改良Insall—Salvati指数、Blackbume—Peel指数、Caton-Des—champs指数和胫骨平台一髌骨角。随着影像学技术的进展还出现了基于MRI图像的诊断方法。但目前的诊断方法仍然不够完全准确。低位髌骨可导致膝关节活动度降低、伸肌力臂减小、髌骨对胫骨平台或聚乙烯衬垫的持续碰撞，继而出现膝前疼痛，严重者甚至出现髌腱或股四头肌肌腱断裂。对低位髌骨的治疗，应首先区分真性低位髌骨和假性低位髌骨，对症状严重或保守治疗无效者需手术治疗。若为真性低位髌骨，改善髌腱挛缩状态和将胫骨结节近移为主要方法；若为假性低位髌骨，则应重建关节线、更换垫片或假体。

Patella baja is one of the complications after total knee arthroplasty （TKA）. It refers to an abnormal location of patella occurred secondary to shortening of the pateUar tendon or distal positioning of the patella relative to the femoral trochlea. Clinically, it can be classified into congenital, acquired, and a combination of the above two types. Acquired patella baja is the most common type and usually occur as a result of trauma or surgery. Acquired patella baja is also caused by elevation of the joint line after TKA, which refers to pseudo-patella baja. Presently, its etiology is still uncertain. Some studies report the following causes of patella baja, including extending of quadriceps femoris, contracture of patella tendon or patellar fat pad, and fibrosis of joint. The diagnosis is mostly based on the lateral roentgenogram. The following parameters, including Insall-Salvati ratio, Modi- fied Insall-Salvati ratio, Blackburne-Peel ratio, Caton-Deschamps ratio and Plateau-Patella angle, are used to assist diagnosis for patella baja. With the progress of imageology, some literatures describe several methods based on magnetic resonance imaging （MRI）. However, the diagnostic methods of patella baja are not entirely precise. Patella baja can lead to decreased range of motion （ROM）, a decreased lever ann, impingement of the patella against the tibial polyethylene or tibial plate, which may resuh in anteri- or knee pain, rupture of the patellar or quadriceps tendons. The treatment of patella baja depends on determining the cause and distinguishing between patella baja and pseudo-patella baja. Patients with severe symptom or failed for conservative treatment should receive surgery. The corrective measures for patella baja include lengthening of the patellar tendon and proximalize osteoto- my of tibial tuberosity. In addition, the therapies for pseudo-patella baja include reestablishing the joint line by use of distal femo- ral augment, replacement of the patellar implant or polyethylene insert.