A new cementless tibial baseplate in kinematically aligned total knee arthroplasty has low migration and stabilizes at 3 months: A cohort study using radiostereometric analysis
Rubiana Monteiro, Ali Mohammadi, Alexander J. Nedopil, Stephen M. Howell, Maury L. HullAbstract
Purpose
Introduction of new components in total knee arthroplasty (TKA) should be assessed for long‐term stability. The primary objective was to determine whether migration of a new cementless tibial baseplate in kinematically aligned (KA) TKA is below the 6‐month threshold where baseplates have a low incidence of long‐term loosening. Other objectives were to determine when stability occurred, whether stability was associated with varus angles in knee and limb alignments, and whether a recut of the tibia affected migration.
Methods
New cementless components were implanted in 45 patients, of which 38% had a tibial recut. Baseplate migration was assessed using model‐based radiostereometric analysis with radiographs obtained post‐operatively and at 6 weeks, 3 months and 6 months. Mean maximum total point motion (MTPM) at 6 months was compared to a 6‐month threshold where baseplates have low incidence of long‐term loosening. An equivalence analysis determined when stability occurred. Correlation analyses related MTPM at 6 months to the medial proximal tibial angle (MPTA) and the hip–knee–ankle angle (HKAA). A two‐sample t test determined whether mean MTPM differed between recut and non‐recut groups.
Results
Mean 6‐month MTPM of 0.93 mm was significantly below the 6‐month stability threshold of 1.15 mm ( p = 0.015), and stability was achieved by 3 months. There was no significant relationship between MTPM and MPTA ( ρ = 0.050, p = 0.77) or HKAA ( ρ = 0.060, p = 0.72). Mean MTPM did not differ between recut (0.85 ± 0.56 mm) and non‐recut (0.97 ± 0.64 mm) groups ( p = 0.57).
Conclusion
The new cementless tibial baseplate has migration significantly below the 6‐month threshold where baseplates have a low incidence of long‐term loosening and migration stabilizes early at 3 months. Varus alignment of the baseplate and the limb as well as tibial recuts were not associated with increased migration.
Level of Evidence
N/A.