HIGHLIGHTS People with diabetes may experience worse outcomes from frozen shoulder than those without diabetes; however, the certainty in evidence was moderate to low. If high-quality studies can confirm the findings of this review, then clinicians should monitor patients with frozen shoulder with diabetes more closely and offer further treatment if pain or lack of function persists long-term.

ObjectiveSummarise longitudinal observational studies to determine whether diabetes (types 1 and 2) is a risk factor for frozen shoulder.DesignSystematic review and meta-analysis.Data sourcesMEDLINE, Embase, AMED, PsycINFO, Web of Science Core Collection, CINAHL, Epistemonikos, Trip, PEDro, OpenGrey and The Grey Literature Report were searched on January 2019 and updated in June 2021. Reference screening and emailing professional contacts were also used.Eligibility criteriaLongitudinal observational studies that estimated the association between diabetes and developing frozen shoulder.Data extraction and synthesisData extraction was completed by one reviewer and independently checked by another using a predefined extraction sheet. Risk of bias was judged using the Quality In Prognosis Studies tool. For studies providing sufficient data, random-effects meta-analysis was used to derive summary estimates of the association between diabetes and the onset of frozen shoulder.ResultsA meta-analysis of six case–control studies including 5388 people estimated the odds of developing frozen shoulder for people with diabetes to be 3.69 (95% CI 2.99 to 4.56) times the odds for people without diabetes. Two cohort studies were identified, both suggesting diabetes was associated with frozen shoulder, with HRs of 1.32 (95% CI 1.22 to 1.42) and 1.67 (95% CI 1.46 to 1.91). Risk of bias was judged as high in seven studies and moderate in one study.ConclusionPeople with diabetes are more likely to develop frozen shoulder. Risk of unmeasured confounding was the main limitation of this systematic review. High-quality studies are needed to confirm the strength of, and understand reasons for, the association.PROSPERO registration numberCRD42019122963.