Abstract
Introduction: The consequences of incorrect implant orientation and improper limb alignment in TKR surgery are: 1) accelerated implant wear; 2) early prosthesis loosening; 3) sub optimal clinical function. Although mechanical alignment guides have improved the precision of TKR surgery, it has been estimated that alignment errors of more than 3 degrees occur in at least 10% of TKR even when performed by experienced surgeons using mechanical alignment systems of modern design. The purpose of this study was to determine the accuracy of TKR surgery performed with conventional instruments using a computer assisted navigation system (OrthoPilot) as a measurement tool.
Methods: 35 patients underwent primary TKR performed with a conventional intramedullary, mechanical instrumentation system. Minimal follow-up was 1 year. The OrthoPilot was used to measure: 1) pre-operative limb alignment; 2) pre-operative medial-lateral stability; 3) pre-operative flexion; 4) post-operative alignment; 5) post-operative medial-lateral stability; 6) post-operative flexion. Patients consented to the use of the Ortho-Pilot as part of an Investigation Review Board approved study. Limb and implant alignment were measured on pre- and post-operative x-rays and compared to the alignment results measured by OrthoPilot. Knee society scores were obtained on all patients.
Results: No complications were associated with the use of the OrthoPilot. Post-operative pain and function were not affected by the use of the OrthoPilot. Pre-operative angular deformities measured by OrthoPilot ranged from 12 degrees varus to 20 degrees valgus and 12 degrees flexion to 7 degrees hyperextension. Post-operative angular deformities ranged from 2.5 degrees varus to 2 degrees valgus and 5 degrees flexion to 2 degrees hyperextension. Pre-operative medial-lateral laxity ranged from 0 to 10 degrees. Post-operative medial-lateral laxity ranged from 3–5 degrees. Pre-operative flexion ranged from 95 to 125 degrees. Post-operative flexion ranged from 115 to 136 degrees. Movement of the pins that hold the diode containing rigid bodies occurred in 5 cases. Inconsistencies of more than 3 degrees in limb registration by the OrthoPilot occurred in 7 cases. Pre- and post-operative x-ray measurements varied from OrthoPilot measurements by more than 3 degrees in 25 cases. Surgery time with OrthoPilot.
Conclusions: OrthoPilot is safe. No complications occurred attributable to the system. It took approximately 10 cases to establish a consistent registration technique using the OrthoPilot. Pin movement can occur and significantly affects the accuracy of the measurements. The OrthoPilot was useful as a measurement tool for determining the pre- and post-operative alignment, stability and range of motion of a TKR. The use of conventional intramedullary mechanical TKR instruments can result in accurate and reproducible frontal and sagittal limb alignment. X-rays are not accurate for determining pre- and post-operative limb and implant alignment.
The abstracts were prepared by Nico Verdonschot. Correspondence should be addressed to him at Orthopaedic Research Laboratory, University Medical Centre, PO Box 9101, 6500 HB Nijmegen, The Netherlands.
