Abstract
BACKGROUND
We conducted this study to determine if the pre-surgical patient specific instrumented planning based on Computed tomography scans can accurately predict each of the femoral and tibial resections. The technique helps in optimization of component positioning and hence overall alignment thereby reducing errors. This makes it less invasive, more efficient and cost effective. The surgical plan in combination with the cutting guides determine the resection thickness, component size, femoral rotation and femoral and tibial component alignment. Several clinical studies have shown that PSI is safe, accurate and reproducible in primary TKA. Accurate preparation of the femoral and tibial surfaces will determine alignment and component positioning and this in turn reflects on function and longevity
METHODS
The study was conducted prospectively between May 2016 and December 2017 in our institution. Patients admitted over a period of these twenty months were included in the study. Patients with primary or secondary osteoarthritis (OA) and inflammatory arthritis who were suitable to undergo patient-specific TKA were included in the study. Patients with conventional instrumented TKR and those with significant deformities requiring constrain including valgus or varus of greater than 20 degrees with incompetent lateral or medial collateral ligaments were excluded from the study along with revisions of partial knee to TKA using PSI blocks.
Prophecy® Preoperative Navigation 3D printed Guides were used for the Evolution Medial Pivot knee replacement system (Microport Orthopaedics (Arlington, TN 38002, USA)) in all cases. The operating surgeon measured all the resections made (4 femoral and 2 tibial) using vernier calipers intraoperatively. These measurements were then compared with the preoperative CT predicted bone resection surgical planning.
The senior author (IN) also designed markings on the tibial cutting blocks to improve accurate placement on the tibia and further markings on the femoral cutting blocks to ensure accurate positioning and rotational alignment improving accuracy of the cuts and femoral rotation. Further markings by senior surgeon (IN) on the pre-operative plans included tibial rotational plans in relation to the tibial tubercle.
RESULTS
A total of 3618 readings were calculated from 201 knees (105 right and 96 left). There were 112 females and 76 males, and the average age was 67.72 years (44 to 90 years) and average BMI 32.3 (25.1 to 42.3). The surgical time ranged from 46 to 102 minutes with a mean operating time of 62 minutes. All Femoral and Tibial blocks sat accurately on the bony surfaces before being pinned. 94% of all collected resection readings were below the error margin of ≤1.5 mm of which 90% showed resection error of ≤1mm. Mean error of different resections were ≤0.60 mm (P ≤ 0.0001). In 24% of measurements there were no errors or deviations from the templated resection (0.0 mm).
CONCLUSION
The 3D printed cutting blocks with slots for jigs accurately predict bone resections in PSI total knee arthroplasty which would directly affect component positioning and hence longevity and function.
