A NAVIGATED 8 IN 1 FEMORAL CUTTING GUIDE FOR TKA-TECHNICAL DEVELOPMENT AND ACCURACY STUDY

Abstract

Background: A navigated 8 in 1 femoral cutting guide for TKA that does not require primary fixation or intramedullary guides was developed. The hypothesis of our study were twofold: 1) the navigation system allows for precise alignment and adjustment of a new femoral 8 in 1 cutting guide with negligible variance in the initially planned vs. achieved implant position; 2) resulting femoral cuts are very accurate without relevant cutting errors.

Material and Methods: We demonstrate our approach with the Universal Knee Instrument (UKI, Precimed Inc. USA), a versatile 8 in 1 TKA guide designed to perform all femoral cuts with a single jig. We integrated an array of “adjustable constraints” into the UKI by machining four threaded holes directly through the template. Adaptation to a navigation system has been performed by integrating the adjustable constraints protocol on the open platform Surgetics Station (PRAXIM-medivision, France), which uses image-free BoneMorphing technology. Based on navigated bone morphing the required preadjustment of the guide was done mechanically, with depth control by mini screws. Testings on 10 cadavers compared the planned vs. achieved positions of the jig before, after fixation, final implant position and planned vs. achieved cutting procedures.

Results: Results revealed for valgus/varus deviations before fixation −0.1°±0.7°, after 0.0°±0.8° (p=0.51), final implant position 0.9°±1.7° (p=0.93). For flexion before fixation −0.3°±1.3° after −0.3°±1.8° (p=0.44), final position 2.9°±2.5° (p=0.65). Distal cut height before fixation 0.0°±0.4°, after 0.1°±0.3° (p=0.61), final position 0.3°±1.0° (p=0.1). Axial rotation before −0.3°±1.1°, after fixation 0.2°±1.4° (p=0.57), final implant position 0.8°±2.7° (p=0.89). Anterior-posterior positions before fixation 0.7°±1.4°, after 1.0°±1.6° (p=0.27), final position 3.4°±1.3° (p=0.13). Highest deviations in the planned vs. actual cut position was found for the posterior cut −3.1°±2.4° in sagittal and anterior cut 0.8°±1.9° in the coronal plane. The highest mean errors in the final implant position where on the order of 3 degrees/mm in flexion and anterior-posterior positioning.

Conclusion: A novel ‘CAS-enabled 8 in 1 jig’ has been developed and validated. The system allows for direct execution of a complex, multi-planar CAS plan with single navigated device. The instrumentation is considerably simplified and eliminates the problems associated with sequential jigs.