In Vivo Kinematics and Cruciate Ligament Tension Are Not Restored to Normal After Bicruciate-Preserving Arthroplasty.

BACKGROUND: Whether cruciate ligament forces in cruciate-preserving designs, such as unicompartmental knee arthroplasty (UKA) or bi-cruciate-retaining total knee arthroplasty (BCR-TKA), differ from those in normal knees remains unknown. The purpose of this study was to compare the in vivo kinematics and cruciate ligament force in knees before and after UKA or BCR-TKA to those in normal knees during high-flexion activity.

METHODS: Overall, twenty normal knees, 17 knees with medial UKA, and 15 knees with BCR-TKA were fluoroscopically examined while performing a squatting activity. A two-dimensional or three-dimensional registration technique was employed to measure tibio-femoral kinematics. Ligament strains and tensions in the antero-medial and postero-lateral bundles of the anterior cruciate ligament (ACL) (aACL and pACL) and the antero-lateral and postero-medial bundles of the posterior cruciate ligament (PCL) (aPCL and pPCL) during knee flexion were analyzed.

RESULTS: Tension in both bundles of the ACL decreased with flexion. At 60° of flexion, aACL tension in postoperative UKA knees was greater than that in normal knees. At 30° of flexion, pACL tension in postoperative UKA knees was greater than that in normal knees. On the other hand, aPCL and pPCL tensions increased with flexion. From 40 to 110° of flexion, the postoperative aPCL tension in UKA knees was greater than that in normal knees. At 110° of flexion, the preoperative pPCL tension in UKA knees was greater than that in normal knees. In addition, the postoperative pPCL tension in UKA knees was larger than that in normal knees beyond 20° of flexion. Furthermore, the pPCL tension of postoperative BCR-TKA knees was larger than that in normal knees from 20 to 50° and beyond 90° of flexion.

CONCLUSIONS: The cruciate ligament tensions, especially PCL tension in knees after UKA, were greater than those in the normal knees. Surgeons performing bi-cruciat-preserving knee arthroplasties should therefore balance cruciate ligament tension more carefully in flexion and extension.