Abstract
Introduction
From pre-operative planning to final implant cementation, total knee arthroplasty (TKA) can be defined by a succession of individual steps, each presenting potential errors that can result in devices being implanted outside the desired range of alignment.
Our study used an image-free computer-assisted orthopedic surgery (CAOS) guidance system (Exactech GPS, Blue-Ortho, Grenoble, FR) to evaluate alignment discrepancies occurring during different steps of a typical TKA procedure.
Materials and methods:
A surgical profile was established to define resection parameters and steps for proximal tibial and distal femoral cuts (see Figure 1A) to be made on seven synthetic knee models (MITA, Medical Models, Bristol, UK). First, the guidance system was used to acquire pre-identified landmarks. Next, a cutting block was adjusted to match the resection targets and then fixed to the bone using locking pins. Bone cuts were performed and then checked. Data was collected from the guidance system at three steps: (1) cutting block adjusted but not pinned to bone (see Figure 1B), (2) cutting block adjusted and pinned to bone (see Figure 1C), and (3) after checking cuts (see Figure 1D). These data were then compared to the resection target parameters to assess potential discrepancies.
Results:
Discrepancies for all cuts were minimal, as the differences in bone resection thickness and angular measurement were less than 1 mm and 1°, respectively (see Table I).
For each parameter, the mean value was close to nominal, demonstrating a well-centered distribution. This being said, there was a consistent derivative of the distal femoral parameters in extension (up to 0.9°), resulting in lower than expected amount of distal femur resection (up to 0.9 mm).
Discussion/Conclusion:
In general, discrepancies at each step seemed random, and there was no apparent accumulation trend except for the flexion/extension of the distal femoral cut. There was a slight discrepancy in extension during the pinning of the block, possibly due to the offset weight of the tracker acting on the adjustable instrumentation. There was also a consistent discrepancy in extension during the cut, likely resulting from the saw skiving during cuts. Such a discrepancy can result in a slightly tighter joint in extension than expected.
The guidance system did not exhibit substantial alignment discrepancies during procedure steps, reflecting its robustness.
