Equivalent Six-Week Knee Motion and Patient-Reported Outcome Scores After Cementless and Cemented Total Knee Arthroplasty with a Kinematic Alignment Optimized Implant.

Introduction: Cemented kinematic alignment (KA) total knee arthroplasty (TKA) is popular due to its superior patient-reported outcome scores (PROs). A new cementless version of a KA-optimized implant is available. The femoral component features a 20° trochlear groove and medial spherical articulation. The tibial insert features a medial socket, creating native anterior-posterior stability and a lateral flat articular surface promoting native medial pivot rotation. The present study aimed to determine whether clinical outcomes for patients receiving the cementless KA-optimized implant are equivalent to those receiving the cemented version after six weeks. This comparison is essential because lower PROs could indicate delayed osteointegration of the components, like dysfunction associated with delayed fracture union.

Materials and methods: The study included 95 cementless KA TKAs matched 1:1 with 95 cemented KA TKAs based on surgery date, age, preoperative knee deformity, sex, and surgeon. Patients completed the Oxford Knee Score (OKS) and the Knee Injury and Osteoarthritis Outcome Score for Joint Replacement (KOOS JR) both preoperatively and at six weeks, as well as the Forgotten Joint Score (FJS) at six weeks. A Wilcoxon two-sided equivalence test was used to test the null hypothesis that results were comparable for the cementless and cemented KA TKAs.

Results: The analysis included 114 females and 76 males, with a mean age of 68 years and a body mass index (BMI) of 31kg/m². Preoperatively and at six weeks, the age, sex distribution, BMI, knee extension and flexion, OKS, and KOOS JR scores for cementless and cemented KA TKAs were equivalent. At six weeks, the FJS scores were also equivalent.

Conclusion: The KA-optimized implant closely resembling native knee morphology did not show evidence of delayed osteointegration. After six weeks, knee motion and PROs were equivalent to those of the cemented implants. However, longer-term monitoring of this new cementless implant is necessary.