Continued Stabilization of a Cementless 3D-Printed Total Knee Arthroplasty: Five-Year Results of a Randomized Controlled Trial Using Radiostereometric Analysis

Abstract

Background: Three-dimensional (3D) printing of highly porous orthopaedic implants aims to promote better osseointegration, thus preventing aseptic loosening. However, short-term radiostereometric analysis (RSA) after total knee arthroplasty (TKA) has shown higher initial migration of cementless 3D-printed tibial components compared with their cemented counterparts. Therefore, critical evaluation of longer-term tibial component migration is needed. We investigated migration of a cementless 3D-printed and a cemented tibial component with otherwise similar TKA design during 5 years of follow-up, particularly the progression in migration beyond 2 years postoperatively.

Methods: Seventy-two patients were randomized to a cementless 3D-printed Triathlon Tritanium (Stryker) cruciate-retaining (CR) TKA or a cemented Triathlon CR (Stryker) TKA implant. Implant migration was evaluated with RSA at baseline and postoperatively at 3 months and at 1, 2, and 5 years. The maximum total point motion (MTPM) of the tibial component was compared between the groups at 5 years, and progression in migration was assessed between 2 and 5 years. Individual implants were classified as continuously migrating if the MTPM was ≥0.1 mm/year beyond 2 years postoperatively. Clinical scores were evaluated, and a linear mixed-effects model was used to analyze repeated measurements.

Results: At 5 years, the mean MTPM was 0.66 mm (95% confidence interval [CI], 0.56 to 0.78 mm) for the cementless group and 0.53 mm (95% CI, 0.43 to 0.64 mm) for the cemented group (p = 0.09). Between 2 and 5 years, there was no progression in mean MTPM for the cementless group (0.02 mm; 95% CI, -0.06 to 0.10 mm) versus 0.07 mm (95% CI, 0.00 to 0.14) for the cemented group. One implant was continuously migrating in the cementless group, and 4 were continuously migrating in the cemented group. The clinical scores were comparable between the groups across the entire time of follow-up.

Conclusions: No significant difference in mean migration was found at 5 years between the cementless and cemented TKA implants. Progression of tibial component migration was present beyond 2 years for the cemented implant, whereas the cementless implant remained stable after initial early migration.

Level of evidence: Therapeutic Level I . See Instructions for Authors for a complete description of levels of evidence.

Fig. 1

CONSORT (Consolidated Standards of Reporting Trials) flow diagram. TKA = total knee arthroplasty.

Fig. 2

MTPM during the 5-year follow-up. The solid lines represent the mean MTPM of the groups, with 95% confidence intervals for all patients. Separate lines are presented for the individual revised, continuously migrating, and stabilized implants.

Fig. 3

Spaghetti plot showing the individual implant-migration profiles.

Fig. 4

Figs. 4-A, 4-B, and 4-C RSA images of a cemented TKA implant. Fig. 4-A Biplanar (lateral and anteroposterior) views with markers inserted in the polyethylene insert and tibial bone. Fig. 4-B Lateral radiograph of the same implant, which was classified as continuously migrating. Fig. 4-C Anteroposterior radiograph of the same implant.

Fig. 5

Mean clinical scores with 95% confidence intervals. KSS = Knee Society Score, KOOS = Knee injury and Osteoarthritis Outcome Score, ADL = activities of daily living, QoL = quality of life, and FJS = Forgotten Joint Score.