There are two basic implantation philosophies in total knee arthroplasty that essentially determine the rotational alignment of the femur. One method, the measured resection technique, uses bony landmarks to determine alignment, while the other, the gap-balancing technique, uses soft-tissue tension as the reference. The use of patient-specific instrumentation (PSI) has so far only been employed in cases where alignment is based on bony landmarks; alignment of the femoral rotation applying the gap-balancing technique is not currently possible.
This paper describes the use of PSI with alignment using a balancer device in 25 patients, corresponding to the gap-balancing technique. The average age of the study population was 67.6±6.7 yr. The Knee Society Score (KSS) and flexion of the knee joint were recorded preoperatively and then at 3 and 12 mo postoperatively. Postoperatively, function was determined based on the Forgotten Joint Score (FJS), and any complications were documented. Deviation to the neutral mechanical leg axis also was determined based on long-standing radiographs of the lower extremity.
The KSS and flexion improved after 3 and 12 mo compared with preoperative results. The FJS was 34.4±4.2 points after 3 mo and 57.8±8.4 points after 12 mo. There were no complications. The deviation of the neutral mechanical axis averaged 1.5 degrees±1.8 degrees.
The data show that the alignment of the PSI also can be achieved functionally, which will extend the range of application of PSI, especially in complex anatomical situations and after previous surgery.