Abstract
Introduction
Multiple techniques exist for performance of Total Knee Arthroplasty (TKA). In April 2010, MyKnee® Patient-Specific Instrumentation (Medacta International, SA, Castel San Pietro, Switzerland) was approved for use in TKA in the United States. The present retrospective study seeks to evaluate early results of this technique. 29 consecutive patients (30 consecutive TKA operations) underwent TKA using the MyKnee cutting-blocks. These results were compared to 30 consecutive patients utilizing Standard TKA method. The findings represent the author's first MyKnee patients, and thus early learning curve for this technique. IRB approval for retrospective research was obtained prior to the evaluation of the data.
Methods
30 consecutive patients (14 males, 16 females) underwent TKA using the MyKnee technique. Pre-operative long-standing radiographs were taken and compared to 6-week post-operative radiographs. Intraoperative data includes the femoral and tibial resections thickness: Distal Medial femoral, Distal Lateral femoral, Posterior Medial Femoral, Posterior Lateral femoral, Medial Tibia, and Lateral Tibia. These were compared to the Planned vs. Actual resections. Tourniquet time was recorded as a measure of speed of surgery. These were compared to 30 consecutive patients using Conventional TKA technique. Intraoperative complications were also recorded.
Results
For the MyKnee group, 21 patients had pre-operative varus deformities with a mechanical alignment of 7.8° (range 1.2°-15.2°). 7 patients had Pre-operative valgus deformities averaging 6.9° (range 1.3°-14.5°). 2 patients were neutral. Post-operative alignment for all patients (n=23) was varus 1.92° (range 0°-5.8°). 78% of patients were within 3° and 97% of patients were within 3.6°. Only 1 patient was outside 3.6°, measuring 5.4° valgus (Figure 3).
In comparison, the Standard TKA group had 21 patients with pre-operative varus deformities averaging 7.3° (range 0°-16.5°) while 7 knees were valgus 6.3° (range 1.2°-10.6°) and one was neutral. Post-operative alignment for these patients measured varus 1.85°. 79% of patients were within 3°; however the outliers were much more dramatic ranging 3.5°-9.2°.
30 Femora and 21 Tibial resections were available for review using the MyKnee technique. The Actual vs. Planned resections for the Distal Medial Femoral resection was 9.5 vs. 9.1mm respectively. Further Actual vs. Planned Femoral resections include Distal Lateral Femoral 8.4 vs. 6.3mm; Posterior Medial Femoral 9.3 vs. 9.5mm; and Posterior Lateral Femoral 8.6 vs. 7.0mm. The Actual vs. Planned Tibial resections recorded include Medial 6.07 vs. 6.29mm and Lateral 9.36 vs. 8.19mm.
Statistically, there is no significant difference in post-op degree (1.85° vs. 1.92°). Tourniquet time (TT) averaged 32.97 minutes in the Standard TKA group vs. 37.03 minutes in the MyKnee group, which isn't significantly different. However, the final 15 MyKnee patients had an average time of 33.46 minutes. EBL was minimal each cohort. No intraoperative complications were recorded in either group.
Discussion
Many techniques exist for performance of TKA. The present study shows definitively that Intraoperative resections and Post-operative alignments can be accurately achieved with pre-operative CT planning and using Patient-Specific Instrumentation. In conclusion, using Patient-Specific Instrumentation is safe, quick, and accurate in performance of TKA.
