Patients ≤ 55 years have a high primary TKA revision rate compared to patients >55 years. Guided motion knee devices are commonly used in younger patients yet outcomes remain unknown. In this sub-group analysis of a large multicenter study, 254 TKAs with a second-generation guided motion knee implant were performed between 2011–2017 in 202 patients ≤ 55 years at seven US and three European sites. Revision rates were compared with Australian Joint Registry (AOANJRR) 2017 data. Average age 49.7 (range 18–54); 56.4% females; average BMI 34 kg/m2; 67.1% obese; patellae resurfaced in 98.4%. Average follow-up 4.2 years; longest follow-up six years; 27.5% followed-up for ≥ five years. Of eight revisions: total revision (one), tibial plate replacements (three), tibial insert exchanges (four). One tibial plate revision re-revised to total revision. Revision indications were mechanical loosening (n=2), infection (n=3), peri-prosthetic fracture (n=1), and instability (n=2). The Kaplan-Meier revision estimate was 3.4% (95% C.I. 1.7% to 6.7%) at five years compared to AOANJRR rate of 6.9%. There was no differential risk by sex. The revision rate of the second-generation guided motion knee system is lower in younger patients compared to registry controls.

Outcomes for guided motion primary total knee arthroplasty (TKA) in obese patients are unknown. 1,684 consecutive patients underwent 2,059 primary TKAs with a second-generation guided motion implant between 2011–2017 at three European and seven US sites. Of 2,003 (97.3%) TKAs in 1,644 patients with BMI data: average age 64.5 years; 58.4% females; average BMI 32.5 kg/m2; 13.4% had BMI ≥ 40 kg/m2. Subjects with BMI ≥ 40 kg/m2 had longest length of hospital stay (LOS) at European sites; LOS similar at US sites. Subjects with BMI ≥ 40 kg/m2 (P=0.0349) had longest surgery duration. BMI ≥ 40 kg/m2 had more re-hospitalizations or post-TKA reoperations than BMI < 40 kg/m2 (12.7% and 9.2% at five-year post-TKA, P<0.0495). Surgery duration and long-term complication rates are higher in patients with BMI ≥ 40 kg/m2, but device revision risk is not elevated.