Objectives. To systematically assess the clinical effectiveness, safety, patient-centred outcomes and potential environmental advantages of upper limb orthoses manufactured from bio-sustainable materials. Methods. Randomised controlled trials (RCTs) and non-controlled clinical trials (NCCTs) that reported at least one clinical or functional outcome for any bio-sustainable orthosis applied to upper limb were eligible. Five databases (CINAHL, PubMed, Web of Science, Scopus, ProQuest) were searched; reference lists were hand-searched. Risk of bias was assessed with RoB 2 (RCTs) and the NIH Quality-Assessment Tool (NCCTs). For continuous outcomes, pooled effects were calculated as Hedges’ g or standardised mean change (random-effects DerSimonian–Laird model; Hartung–Knapp adjustment when k ≤ 2); dichotomous outcomes were expressed as risk ratios. Heterogeneity (I2, τ2) and 95 % confidence intervals were reported. Leave-one-out analysis was performed when applicable. Results. Twelve studies (4 RCTs, 8 NCCTs; n = 498 participants, mean age 35.9 ± 24.5 years) met the inclusion criteria; six were suitable for quantitative synthesis. Risk of bias was low in one RCT, showed ‘some concerns’ in two, and high in one; no NCCT achieved a ‘good’ rating. Most green orthoses were wood-composites (76.3%), with the remainder additively manufactured by 3D-printing (23.7%); within the latter, polylactic acid (PLA) was the principal material (71.1%). Additive manufacturing was used predominantly for neurological disorders (p<0.0001). Neurological conditions accounted for 16% of all indications. Pooled analysis showed no statistically difference in upper limb functional improvement between bio-sustainable and conventional orthoses (SMD=0.05, 95%CI [-0.47–0.57], p=0.85, I2=52%). A single-arm cohort study reported a moderate functional gain (SMC=0.61, SE 0.28, 95%CI [0.05-1.17], p=0.029, I2=0%). In post-stroke spasticity, bio-sustainable orthoses were associated with a higher probability of spasticity improvement (RR=2.69, 95%CI [1.66-4.36], p=0.0008, I2=49%). Reduction in pain did not differ significantly between groups (SMD=0.46, 95%CI [-0.10–1.03], p=0.11, I2=0%). Safety profiles were comparable (adverse event OR=1.31, 95%CI [0.72–2.37], p=0.60, I2=60%). Overall patient satisfaction was not significantly different (SMD=0.06, 95%CI [-0.22–0.35], p=0.67, I2=33%). Discussion. Quantitative syntheses indicate functional equivalence between biosustainable and conventional orthotic devices. Current evidence, albeit preliminary, indicates that orthoses manufactured from biosustainable materials are non inferior with regard to adverse events, analgesic efficacy and patient-reported satisfaction and may confer an additional therapeutic benefit in spasticity reduction and, to a lesser extent, hand function enhancement. Evidence is limited by small sample sizes, heterogeneous outcome reporting and methodological weakness, particularly in NCCTs. Robustly powered, prospective non-inferiority trials that incorporate standardised core outcome sets, extended follow up and embedded health-economic analyses are necessary to clarify long-term durability, environmental impact and cost-effectiveness. Other. Protocol registered in PROSPERO (CRD42024584327).