Preliminary One-Year Observational Outcomes After GPS Leukocyte-Rich Platelet-Rich Plasma Injection for Kellgren-Lawrence Grade II and III Knee Osteoarthritis: A Japanese Real-World Case Series

Background Platelet-rich plasma (PRP) is used as an orthobiologic injection therapy for knee osteoarthritis (OA), but reported outcomes vary according to PRP formulation, injection protocol, comparator, and patient selection. Real-world data describing the Zimmer Biomet GPS leukocyte-rich PRP system in Japanese clinical practice remain limited. Purpose To describe 1-year patient-reported outcomes after a single intra-articular GPS leukocyte-rich PRP injection in patients with Kellgren-Lawrence (KL) grade II or III knee OA. Methods This retrospective single-center case series included patients with symptomatic Kellgren-Lawrence (KL) grade II or III knee osteoarthritis (OA) who underwent GPS leukocyte-rich platelet-rich plasma (PRP) injection. During the study period, 20 patients/knees received an initial GPS L-PRP injection; 5 could not be followed at 1 year and were excluded from the paired 1-year analysis. The final analysis included 15 knees with paired baseline and 1-year numeric rating scale (NRS) pain data. Radiography and magnetic resonance imaging were used to support baseline diagnosis and eligibility; MRI was not analyzed as a longitudinal structural outcome. The primary outcome was change in NRS pain. Secondary outcomes included Knee injury and Osteoarthritis Outcome Score (KOOS), Locomo-25, responder status, and adverse events. Results Of 20 patients/knees treated with an initial GPS L-PRP injection, 5 were lost to 1-year follow-up or had unavailable 1-year outcome data; 15 knees from 5 male and 10 female patients were included in the final paired analysis. NRS pain improved from 4.6 ± 2.4 at baseline to 2.7 ± 2.1 at 1 year (mean change, -1.9 points; 95% CI, -3.4 to -0.4; P = 0.015). KOOS quality of life improved from 30.0 ± 17.1 to 45.4 ± 23.8 (mean change, 15.4 points; 95% CI, 4.8 to 26.0; P = 0.010). Other KOOS domains and Locomo-25 showed numerical improvement but did not reach statistical significance. A ≥30% NRS pain reduction occurred in 7 of 15 knees (46.7%), and pain worsened in 2 of 15 knees (13.3%). Conclusions In this small uncontrolled retrospective case series, GPS leukocyte-rich PRP injection was associated with improved NRS pain and KOOS quality of life at 1 year. These findings should be interpreted as preliminary observational associations and cannot establish treatment efficacy or safety. Larger prospective controlled studies with standardized PRP characterization are needed.