In vivo kinematics after a cruciate-substituting TKA

Abstract

Patterns of motion in the native knee show substantial variability. Guided motion prosthetic designs offer stability but may limit natural variability. To assess these limits, we therefore determined the in vivo kinematic patterns for patients having a cruciate-substituting TKA of one design and determined the intersurgeon variability associated with a guided-motion prosthetic design. Three-dimensional femorotibial contact positions were evaluated for 86 TKAs in 80 subjects from three different surgeons using fluoroscopy during a weightbearing deep knee bend. The average posterior femoral rollback of the medial and lateral condyles for all TKAs from full extension to maximum flexion was -14.0 mm and -23.0 mm, respectively. The average axial tibiofemoral rotation from full extension to maximum flexion for all TKAs was 10.8 degrees. The average weightbearing range of motion (ROM) was 109 degrees (range, 60 degrees-150 degrees; standard deviation, 18.7 degrees). Overall, the TKA showed axial rotation patterns similar to those of the normal knee, although less in magnitude. Surgeon-to-surgeon comparison revealed dissimilarities, showing the surgical technique and soft tissue handling influence kinematics in a guided-motion prosthetic design.

Level of evidence: Level III, therapeutic study. See Guidelines for Authors for a complete description of levels of evidence.

Fig. 1

The dual cam mechanism of the implant substituting for ACL and PCL function is shown. The posterior cam is asymmetric, driving the internal rotation of the tibia with increasing flexion [35].

Fig. 2

The average medial AP position for all TKAs and groups by surgeon are shown. The error bars indicate one standard deviation for all surgeon groups, showing the differences between these groups. The medial AP movement from 0° to maximum flexion for patients from Surgeon 3 (green) was different from patients from Surgeon 1 (blue) (p = 0.0139).

Fig. 3

The average lateral AP positions for all TKAs and groups by surgeon including error bars for the patient group from Surgeon 3 are shown. All surgeon groups were similar (p > 0.05) in AP movement on the lateral side from 0° to maximum flexion. At maximum flexion, the lateral condylar position of Surgeon’s 3 group was more anterior than for the groups of Surgeons 1 and 2 (p = 0.0042 and p = 0.0034, respectively).