Patient specific cutting guides versus an imageless, computer-assisted surgery system in total knee arthroplasty

Patient specific cutting guides (PSC) in total knee arthroplasty (TKA) have recently been introduced, in which preoperative 3-dimensional imaging is used to manufacture disposable cutting blocks specific to a patient's anatomy. The purpose of this study was to compare the alignment accuracy of PSC to an imageless CAS system in TKA.

Thirty-seven patients (41 knees), received a TKA using an imageless CAS system. Subsequently, 38 patients (41 knees), received a TKA using a MRI-based, PSC system. Postoperatively, standing AP hip-to-ankle radiographs were obtained, from which the lower extremity mechanical axis, tibial component varus/valgus, and femoral component varus/valgus mechanical alignment were digitally measured. Each measurement was performed by two blinded, independent observers, and interclass correlations were calculated. A student's two-tailed t test was used to compare the two cohorts (p-value<0.05=significant).

In the PSC cohort, 70.7% of patients had an overall alignment within 3° of a neutral mechanical axis (vs. 92.7% with CAS, p=0.02), 87.8% had a tibial component alignment within 2° of perpendicular to the tibial mechanical axis (vs. 100% with CAS, p=0.04), and 90.2% had a femoral component alignment within 2° of perpendicular to the femoral mechanical axis (vs. 100% with CAS, p=0.2). Interclass correlation coefficients were good to excellent for all radiographic measurements.

While PSC techniques appear sound in principle, this study did not demonstrate patient specific cutting guides to obtain the same degree of overall mechanical and tibial component alignment accuracy as a CAS technique.

III: Retrospective cohort study.