gms | German Medical Science

There is strong interest to provide total knee arthroplasty (TKA) patients with a large range of knee flexion. Factors associated with component geometry and the relative position of the femoral and tibial components can affect knee flexion. Enhanced flexion has been achieved in some patient populations using knee implants specifically designed to maintain a posterior femoral position on the tibia during flexion and to restore posterior condylar offset. However, it is unknown whether the functional flexion intended by such implant designs can be achieved in patients operated using varied surgical techniques. The purpose of this study was to evaluate the in vivo flexion performance of a single implant design in patients whose posterior cruciate ligament (PCL) was either meticulously maintained or completely resected.

Thirty-three TKA (29 patients) were observed using fluoroscopy during maximum flexion kneeling and lunge activities. Twenty TKA (sixteen patients) had full maintenance of the PCL, including a bone block on the proximal tibia (PCL+ group). Thirteen TKA (13 patients) had complete PCL resection (PCL- group). All knees received the same fixed-bearing “ACL-substituting” TKA with an asymmetric tibial bearing having a sagittally curved medial compartment and a lateral compartment fully congruous with the lateral condyle in extension. Knee kinematics were determined.

For the kneeling activity, skeletal flexion averaged 131°±13° (PCL+ knees) and 124°±11° (PCL- knees) (p0.05), tibial internal rotation averaged 10°±4° (PCL+ knees) and 10°±6° (PCL- knees) (p0.05) and tibial valgus averaged -1°±2° (PCL+ knees) and 1°±3° (PCL- knees) (p=0.02). Medial contact locations during kneeling averaged -2mm±4mm (PCL+ knees) and +2mm±4mm (PCL- knees) (p=0.02), and lateral contact location averaged -10mm±4mm (PCL+ knees) and -5mm±4mm (PCL- knees) (p=0.01). For the partial weight-bearing lunge activity, skeletal flexion averaged 120°±11° (PCL+ knees) and 123°±17° (PCL- knees) (p0.05), tibial internal rotation averaged 11°±4° (PCL+ knees) and 9°±4° (PCL- knees) (p0.05) and tibial valgus averaged -1°±1° (PCL+ knees) and 1°±2° (PCL- knees) (p0.01). Medial contact locations during lunge averaged 0mm±4mm (PCL+ knees) and -2mm±3mm (PCL- knees) (p0.05), and lateral contact location averaged -8mm±4mm (PCL+ knees) and -9mm±3mm (PCL- knees) (p0.05).

There was no difference in implant flexion between PCL+ and PCL- knees, and both groups included patients with knee flexion exceeding 150°. There were no differences in tibial rotation. There were differences in tibial valgus for both activities, with three PCL- knees exhibiting a tendency for the medial compartment to “book open” with flexion beyond 130°. There was greater posterior femoral translation in the PCL+ knees during kneeling. The observed differences are consistent with the presence or absence of the PCL, but appear to have no impact on functional knee motion with this fixed-bearing TKA design.