Abstract
Purpose
The purpose of this study was to clarify the relationship between the laxity of surrounding soft tissue and artificial joint kinetics during knee articulation, where total knee arthroplasty had been performed using ceramic LFA artificial knee joints (LFA-TKA below) from Japan Medical Materials (JMM).
Materials Methods
The subjects of the study were 47 knees in 40 LFA-TKA recipients whose cooperation could be obtained. The CR type joint (posterior cruciate retention design) was used in 33 knees in 27 recipients and the PS type joint (posterior cruciate stabilizer design) was used in 14 knees in 13 recipients. OA patients received 30 CR type and 8 PS type joints while RA patients received 3 CR type and 6 PS type joints. For analysis of post surgery knee joint kinetics, using digital fluoroscopy, lateral images were taken of knee motion from a loaded squat position to the erect standing position. Using Knee Motion® software the imaging data was evaluated for 1) femoral rollback, 2) tibial axial rotation patterns, and 3) pivot center position, from analysis of lateral and medial condylar translation (femoral components) at the point of contact with the tibial insert, starting from the extended position. Subsequent imaging under medial-lateral and posteroanterior stress was performed to measure the medial-lateral dihedral angle changes and posteroanterior movement, and the relationship of those factors to the dynamic patterns was evaluated.
Results
-
No definite tendency was noted in Rollback of the CR type femoral components and no relationship to the laxity of surrounding soft tissue was found. For PS type joints both medial and lateral movement (average±standard deviation) was 5.4±8.0 and 16.0±3.7 respectively so that significant rollback was noted when flexed past 120°.
-
As for tibial axial rotation patterns, of CR type joints 48% rotated outward and 52% rotated inward while of the PS type joints 33% rotated outward and 67% rotated inward, such that no definite tendency was determined.
-
As for the pivot center, among CR type joints 27% were medial, 42% were lateral and 33% were other, and among PS type joints 78% were medial, 14% lateral and 8% other, with large individual differences but no definite tendency. Stress imaging showed significantly greater medial-lateral dihedral angles for CR type joints, and equal posteroanterior movement for both CR and PS joints, but no clear relationship was found between the laxity of surrounding soft tissue and the kinetics of artificial knee joints.
Discussion
Knees with degenerative and rheumatoid arthritis that do not exhibit normal kinetics prior to surgery are not uncommon. Then since the ACL must be sacrificed in the TKA process, knee area soft tissue balance is not uniform between cases. The possibility is suggested that artificial knee joint kinetics are influenced more significantly by factors other than the design of the implant.
Conclusion
While rollback was verified with PS type LFA-TKA, there were such large individual differences for both PS and CR cases that normal knee kinetics were not reproducible.
