Xu Bin, Xu Wei-Xing, Lu Di, Sheng Hong-Feng, Xu Xin-Wei, Ding Wei-Guo
Department of Orthopaedics, Tongde Hospital of Zhejiang Province, 234 Gu-cui Road, Hangzhou, 310012, People's Republic of China.
J Orthop Surg Res. 2017 Dec 12;12(1):191. doi: 10.1186/s13018-017-0694-9.
One complication of total knee arthroplasty (TKA) is patella baja (PB). Patellar tendon shortening and joint line elevation are two main causes of PB. The purpose of this study was to determine the incidence of PB before and after TKA by measuring the patellar height and provide evidence for choosing a suitable index.
In total, 256 consecutive patients who underwent primary TKA were included in this study. Radiographic measurements were performed; the Insall-Salvati (IS) index, modified IS (MIS) index, Blackburne-Peel (BP) index, and Caton-Deschamps (CD) index were computed; and the incidence of PB was calculated before and after the operation. The consistency between the IS and MIS indices and between the BP and CD indices was analyzed.
The preoperative incidence of true PB (TPB) and pseudo-PB (PPB) was 9.4 and 0.8%, respectively. The postoperative incidence of TPB and PPB was 10.2 and 9.0%, respectively. The consistency between the IS and MIS indices was moderate preoperatively (pre-kappa = 0.602) and postoperatively (post-kappa = 0.742). The consistency between the BP and CD indices was moderate preoperatively (pre-kappa = 0.742) and good postoperatively (post-kappa = 0.797).
The incidence of PB, especially PPB, increased after TKA. The CD and BP indices are of greater importance for the diagnosis of PB after TKA. The MIS index is a better choice than the IS index to measure the length of the patellar tendon. To measure the height of the joint line, the BP index is better postoperatively and the CD index is better preoperatively.
全膝关节置换术（TKA）的一种并发症是低位髌骨（PB）。髌腱缩短和关节线抬高是PB的两个主要原因。本研究的目的是通过测量髌骨高度来确定TKA前后PB的发生率，并为选择合适的指标提供依据。
本研究共纳入256例连续接受初次TKA的患者。进行影像学测量；计算Insall-Salvati（IS）指数、改良IS（MIS）指数、Blackburne-Peel（BP）指数和Caton-Deschamps（CD）指数；并计算手术前后PB的发生率。分析IS与MIS指数之间以及BP与CD指数之间的一致性。
真性PB（TPB）和假性PB（PPB）的术前发生率分别为9.4%和0.8%。TPB和PPB的术后发生率分别为10.2%和9.0%。IS与MIS指数之间的一致性术前为中等（术前kappa = 0.602），术后为中等（术后kappa = 0.742）。BP与CD指数之间的一致性术前为中等（术前kappa = 0.742），术后为良好（术后kappa = 0.797）。
TKA后PB的发生率，尤其是PPB的发生率增加。CD和BP指数对TKA后PB的诊断更为重要。测量髌腱长度时，MIS指数比IS指数是更好的选择。测量关节线高度时，术后BP指数更好，术前CD指数更好。
