Abstract
Introduction
Custom instrumentation in TKA utilizes pre-operative imaging to generate a customized guide for cutting block placement (Figure 1). The surgeon is able to modify the plan using three-dimensional software (Figure 2). Although this technology is increasingly gaining acceptance, there is a paucity of clinical data supporting it.
Methods
One hundred and eleven patients underwent primary TKA using the Patient-Specific Instrumentation (PSI) system, in twenty-eight of the cases surgical navigation was used to validate the PSI-generated cuts. Alignment measurements included long-leg alignment and biplanar distal femoral and proximal tibial cuts. Further measurements evaluated femoral implant placement in the AP plane, femoral component rotation, measured bone resection and implant sizing accuracy.
Results
The mean final limb alignment as recorded by computer-assisted surgical (CAS) tools was 0.3° of varus. Only two limbs were malaligned by greater than 3° (Figure 3). The femoral component had a mean alignment of 0.3° of valgus and 4.5° of flexion (PSI plan 3° flexion). The predicted femoral size was accurate in 89% of cases and the anterior femoral cut was congruent with the anterior cortex in 92% of cases. The PSI-directed femoral component rotation was consistent with the surgeon's perceived rotation in 95% of cases. The posterior condylar bone resection had a mean difference of < 1mm from the predicted resection.
The tibial component had a mean alignment of 0.5° of varus and 8.5° of posterior slope (PSI plan 7° posterior slope). The only statistically significant deviation in alignment was the increased tibial slope (p=0.046) (Figure4). The tibial component size was accurately predicted in 66% of cases.
Discussion
Custom instrumentation in total knee arthroplasty accurately achieved implant and limb alignment in our study. The plan was more reproducible on the femoral slide. The overestimation of tibial slope and tibial sizing incongruity were related to some of the reference points for the software. A potential benefit of this technology is improved mid-flexion stability by accurately determining femoral component size, placement, and rotation. Further studies are needed to determine the efficiency and cost-effectiveness of this technology.
