Summary

In our hands, patient specific instrumentation did not provide superior results to conventional instrumentation with regard to tibial component positioning.

Abstract

Purpose

Component malposition remains a leading cause of early implant failure. The authors sought to reduce the variance observed in tibial component placement utilizing standard instrumentation. Our purpose was to evaluate the effect of patient specific instrumentation (PSI) on tibial component positioning in total knee arthroplasty.

Hypothesis

The utilization of Patient Specific Instrumentation would lead to improved component positioning on plain radiographs.

Study design: Cohort study (prognosis); Level of evidence: 2

Methods

The authors reviewed a consecutive series of 113 total knee arthroplasties that were performed by the same surgeon. Post-operative radiographs consisting of AP, Rosenberg, lateral and merchant views were obtained for each patient by the same technologist. These were analyzed for degree of varus/valgus angulation and tibial slope utilizing a Digital x-ray management system (AGFA, Mortsel Belgium). An independent author, blinded to the surgical technique utilized, reviewed all X-rays. Three measurements were taken for each X-ray at separate sittings and the results averaged to minimize intraobserver error. Means were determined for both PSI and conventional instrumentation with regard to angulation and slope. A t-test was utilized to compare the means. A power analysis conducted prior to data collection indicated the study was adequately powered.

Results

64 patients had a TKA with PSI. 51 patients had a TKA with conventional instrumentation. Patients undergoing TKA with conventional instrumentation averaged 2.3. degrees of varus/valgus (range= 0.5 to 6.2) and 5.9 degrees of tibial slope (range= 3.5 to 10.9). Patients undergoing TKA with PSI averaged 2.6 degrees of varus/valgus (range= 0.3 to 12.4) and 6.4 degrees of tibial slope (range= 2.5 to 12.4). There was no statistically significant difference in tibial component positioning with regard to angulation in the AP plane (p=0.136) or tibial slope (p=0.121).

Conclusion

Utilization of patient specific instrumentation did not improve tibial component positioning with regard to varus/valgus and posterior slope on plain radiographs. The authors found no significant difference between knees replaced with conventional instrumentation and those replaced with patient specific instrumentation. While the authors acknowledge reduction in OR time with PSI utilization, the increased cost of the molds and models may not warrant widespread utilization for all patients.

Keywords: Case series with retrospective collection of data; knee; arthroplasty; tibial component; patient specific instrumentation.