Abstract
Introduction
Total Knee Arthroplasty (TKA) is highly successful in treatment of end-stage degenerative arthritis of the knee. CT-based Patient-Specific Instrumentation (PSI) utilizes a CT scan of the lower extremity to create a three-dimensional model of the patient's anatomy, plan the surgery, and provide unique patient-specific resection blocks for the surgery.
There are few published studies utilizing CT-PSI. The present study prospectively evaluates clinical, operative, and radiographic outcomes from 100 CT-based TKAs using this technology (MyKnee®, Medacta International S.A., Castel San Pietro, Switzerland).
Materials and Methods
100 consecutive eligible knees (94 patients) of the senior author underwent TKA using CT-based PSI technology. The primary outcome of the study was to compare the planned pre-operative femoral and proximal tibial resections to the actual intra-operative measured resections. Clinical outcomes included pre- and post-operative Knee Society Scores, Range-of-Motion (ROM, measured by goniometer), and complication data.
Pre- and 6-week post-operative long-leg standing radiographs were obtained to assess HKA alignment. The femoral component angle (FCA) in the coronal plane, the tibial component angle (TCA), and posterior slope of the tibia were also assessed. Additionally, 10 patients were selected at random to undergo a post-operative CT scan for comparison to radiographic measurements.
Results
94 patients were enrolled representing 51 left and 49 right TKAs. Average follow up was 3.9 years (range 3.5 – 4.4 years). Average Knee Society Score (KSS) improved from 44.3 to 81.8 while KSS Function Score improved from 59.1 to 81.8 at 1 year. ROM arc of the patients was 110.5 (range 0–130) pre-operatively and was 111.3 (range 0–130) post-operatively. Two patients had a post-operative infection requiring surgical intervention. There were no thromboembolic complications and no revisions in study patients. No patient required a manipulation under anesthesia for post-operative stiffness.
No intraoperative complications occurred nor were there any cases of abandoning the PSI blocks for standard technique.
The actual bony resections achieved during surgery were strongly correlated to the planned resections of all 6 bone fragments measured. Each achieved statistical significance (p<0.001).
Average post-operative alignment was 179.36° (range 175°–186°). Alignment was 180 ± 3° in 94% of patients post-operatively.
Ten patients underwent a post-operative CT scan for HKA verification. The average post-operative HKA was 179.9° (range, 176.9°–180.9°) with a standard deviation of 1.31°. When comparing our pre-operative alignment by x-ray vs. CT, we found only 0.09° (p<0.001) average difference between them. Post-operatively, we continued to show very similar results showing x-ray HKA measurement of 180.1° vs. CT measurement of 179.9° (p<0.001).
Discussion
The pre-operative CT reconstruction can accurately predict the intra-operative resection depths as demonstrated here. All 6 bony resections measured to within 1mm of the predicted value in the aggregate of our series.
The restoration of mechanical axis to 179.9° as measured by CT scans demonstrates the efficacy of the blocks.
Conclusion
The present study demonstrates efficacy in the use of CT-based PSI - showing that the planning can accurately predict bony resections, be used safely, and achieve precise radiographic outcomes. Consequently, we routinely support the use of CT-based PSI in TKA.
