Major Shortening of the Patellar Tendon During Septic Two-Stage Knee Arthroplasty Revision Using Static Spacers

Abstract

BackgroundTwo-stage septic revision knee arthroplasty (TKA) often results in inferior functional outcome after reimplantation, which might be due to impairments of the extensor mechanism. The aim of the current study was to elucidate possible alterations in extensor mechanisms during septic two-stage revision of TKA treated with a static spacer. MethodsThis retrospective study included 87 patients (42 women, 45 men, age 64.5 ± 10.5; range, 29-85 years) undergoing septic two-stage TKA revision using a static spacer. The modified Insall Salvati ratio (mISR) was calculated via calibrated true lateral radiographs by two independent orthopedic surgeons before TKA explantation (G0), 6-8 days after TKA removal (G1), one day before TKA reimplantation (G2) and 6-8 days after TKA reimplantation (G3). Age, sex, body mass index (BMI), index C-reactive protein level, and number of previous surgeries were evaluated to identify the possible correlations. ResultsOverall, mISR significantly decreased within the first 6 days after index surgery from 1.71 ± 0.41 to 1.63 ± 0.41 (G0 versus G1, P < .001) and showed a further decline within the next 6 weeks to 1.54 ± 0.39 (G1 versus G2, P = .002). Conversely, mISR increased after reimplantation of TKA to 1.6 ± 0.43 (G3 versus G2, P = .08), though it did not regain preoperative baseline levels (G0 versus G3, P < .001). The subgroup with mISR decrease ≥10% experienced patellar tendon shortening of 16% between G0 and G1, 19% between G0 and G2 and up to 20% between G0 and G3. There were weak correlations concerning age (r = −0.240, P = .038), preoperative C-reactive protein level (r = 0.239, P = .04) and patellar tendon shortening. Intraclass correlation coefficient (ICC)was 0.88 concerning radiographic measurement. ConclusionSeptic two-stage TKA revision using static spacers leads to irreversible alterations of the extensor mechanism, specifically a major shortening of the patellar tendon, in one out of 3 patients. Level of evidenceII.