The clinical success and long-term outcomes of total knee arthroplasty (TKA) depend not only on the accuracy of femoral and tibial components positioning, but also on the restoration of a proper mechanical axis (MA). Coronal and rotational mal-alignment may affect significantly the final result of a knee replacement. Patient specific cutting guides and intra-operative Computer-Assisted Surgery (CAS) have recently been introduced as options to improve implant alignment during TKA. The purpose of this study was to compare the alignment accuracy and implant positioning of Patient Matched technique to CAS system in patients with primary TKA.

A cohort of 68 consecutive patients who underwent TKA was enrolled for this study: 34 patients received a TKA using CAS system while 34 patients received a TKA using a MRI-based Patient Matched system. Mechanical axis and kinematics were digitally measured pre- and post-operatively in all knees using the intra-operative navigation system but data were blinded for the operating surgeon in the Patient Matched group. A post-operative CT-scan evaluation was performed in all patients to analyse the prosthetic components alignment (coronal, sagittal and axial alignment according to Perth Protocol from CT-scan). CT-scan measurements were used as landmarks as this tool is considered the gold standard. MA, posterior tibial slope (PTS) and femoral component rotation (FCR) in CAS group were compared to data of Patient Matched group. All patients also underwent a clinical evaluation with Knee Society Score (KSS) and Knee injury and Osteoarthritis Outcome Score (KOOS) at 6 and 12 months of follow up.

KSS, KOOS and range of motion were comparable in the two groups after surgery. Operative time was significantly shorter in the Patient Matched group. No differences were found regarding complications rate.

Mean angles, respectively for CAS and Patient Matched groups, were the following: MA was 1,7° (SD 0,9°) vs 0.8° (SD 2.1°); PTS was 3.1° (SD 0.9°) vs 3.4° (SD 2.1°); FCR was 1.5° (SD 2.2°) vs 1.36° (DS 1.2°). The outcomes of the CT scan evaluation were the following: MA was 1.5° (SD 0.8°) vs 1.0° (DS 1.5°); PTS was 2.3° (SD 0.8°) vs 3.0° (SD 2.6°); FCR was 0.4° (SD 0.8°) vs 0.2° (SD 0.3°). MA was within 3° of neutral alignment in 94% of patients for CAS group and in 97% of knees for Patient Matched group.

After a short follow up, there weren't statistically significant differences between CAS and Patient Matched techniques as regards clinical and functional scores. Both the systems achieved the goal of neutral alignment within 3° of varus and valgus. We only observed greater precision for Patient Matched technique in optimizing femoral component rotation. Actually it is unpredictable if this difference may determine long term effects.

Patient Matched technique and CAS for TKA surgery will certainly continue to have an impact in the future. Studies are needed to define which technique is better, in terms of long term results, failure rate and cost-effectiveness.