Abstract
Background/Purpose
Patient-specific design (PSD) total knee arthroplasty (TKA) implants are marketed to restore neutral mechanical axis alignment (MAA) and provide better anatomic fit compared to standard off-the-shelf (OTS) TKA designs. The purpose of this study was to compare the Knee-Society scores, radiographic outcomes, and complications of PSD and OTS implants.
Methods
IRB approved prospective study comparing PSD and OTS by a single surgeon. Implant design change in PSD occurred during the study leading to PSD-1 and PSD-2 subgroups. Demographic, radiographic data including MAA, coronal-tibial angle (CTA), femoro-tibial angle (FTA), tibial-slope (TS) and patella-tilt (PT), and complications were analyzed. Minimum follow-up was 2 year or until revision, and patients completed Knee-Society scores preoperatively, and postoperatively at 3-, 6-, 12-, 24 weeks and final follow up.
Results
136 patients (154 knees), average age (62.7 ± 8.4 years) and follow up (3.1 ± 1.5 years). PSD-1 (77 knees), PSD-2 (36 knees), and OTS (41 knees). PSD-2 had significantly higher early Knee-Society function scores compared to PSD-1 and OTS up to 6 months. All groups had excellent knee society scores after 6 months. PSD-2 had significantly shorter hospital stay (p<0.001), and less hemoglobin drop (p = 0.031) compared to PSD-1 and OTS. No significant difference in MAA (p=0.349) or final ROM (p=0.629). There was approximately 1 degree difference between the groups in the CTA, FTA, TS and PT. Failures requiring revision were 24% (18/75) PSD-1, 0% PSD-2, and 3% (1/35) OTS. Most common modes-of- failure were tibial subsidence (56%) and polyethylene locking mechanism failure (22%) in PSD-1.
Conclusion
PSD-2 had better early Knee-Society function scores, shorter hospital stay, lower hemoglobin drop, and no failures compared to PSD-1 and OTS. There was an unexpected high failure rate in the early patient-specific design TKA that was not seen after the manufacturer changed the design.
