No shortening of the patellar tendon during two-stage total knee arthroplasty revision using articulating spacers

Background Surgical techniques in two-stage revision total knee arthroplasty (rTKA) include the use of articulating spacers and static spacers. Shortening of the patellar tendon could be a reason for inferior functional outcomes in two-stage septic rTKA . The aim of this study was to determine if articulating spacers also have negative effects on the extensor mechanism in rTKA. Methods This retrospective study includes 65 consecutive patients (23 women, 42 men, age 71.3 +/- 1.2; range, 51.2-88.6 years) undergoing septic two-stage rTKA using an articulating spacer between 2014 and 2021 in a single orthopedic center. For all patients, calibrated true lateral radiographs before total knee arthroplasty (TKA) explantation (T0), directly after TKA explantation (T1), shortly before TKA reimplantation (T2) and 6-8 days after TKA reimplantation (T3) were used to calculate the modified Insall Salvati ratio (mISR). Results Overall, the mISR decreased significantly immediately after explantation (T0 vs. T1, p = 0.002) from 1.43 +/- 0.03 to 1.36 +/- 0.03 and remained stable until T2 (1.37 +/- 0.02, p = 0.74). Following TKA reimplantation, the mISR increased again to 1.43 +/- 0.03 (T3). There were no significant differences between T0 and T3 (p = 0.88). Six out of 65 patients (9%) experienced patellar tendon shortening > 10% at T3. Conclusions Septic two-stage revision TKA using an articulating spacer does not lead to patellar tendon shortening in the majority of cases. This study suggests that one reason for the improved range of motion after reimplantation may be the use of articulating spacers compared to static spacers.