A prospective case series of autologous protein solution injection in knee osteoarthritis: two-year outcomes stratified by structural severity and inflammatory phenotype.

Abstract

Two-year durability of autologous protein solution (APS) in knee osteoarthritis stratified by Kellgren-Lawrence (KL) grade and inflammatory phenotype, and its role as a non-operative bridge for patients deferring total knee arthroplasty (TKA), remain uncharacterised. Single-arm prospective case series of 67 knees (KL 2-4) receiving a single APS injection with 2-year follow-up. VAS, KOOS Pain/ADL, OMERACT-OARSI responder rate, and Kaplan-Meier TKA-free survival. Patients were stratified by KL grade and by pre-injection synovial fluid volume (<10 vs ≥10 mL) as an index of joint inflammation. KL grade had independent dual assessment with adjudication (κ = 0.615). Subgroup analyses were exploratory. Of 67 knees, 43 (64.2%) completed 2-year PROM; TKA status was confirmed in 57 (85.1%). VAS and KOOS Pain improved significantly versus baseline at every timepoint. In KL4 (n = 17; all initially recommended for TKA), median VAS improved from 50 to 28 mm at 1 year and 30 at 2 years; KOOS ADL showed a ceiling effect. Two-year Kaplan-Meier TKA-free survival was 94.0% (95% CI 88.4-99.7%); no KL4 patient underwent TKA within 24 months (log-rank p = 0.252). The OMERACT-OARSI responder rate was 70.3%. Within KL3, patients with ≥10 mL synovial fluid showed greater VAS improvement at 6 months (p = 0.030); similar direction was seen at other timepoints but did not reach significance. No serious APS-related adverse events occurred. APS was associated with sustained pain reduction over 2 years and high observed TKA-free survival. Absence of randomisation precludes causal inference; findings are hypothesis-generating.