Abstract: In this update in 2017, we did not identify any new randomised controlled trials (RCT) for inclusion. We identified one ongoing trial that we are likely to include in a future update. Accordingly, our results are unchanged. The only included trial is a multicentre RCT conducted at 24 locations in North America and India that compared bone marrow injection with steroid (methylprednisolone acetate) injection for treating simple bone cysts. Up to three injections were planned for participants in each group. The trial involved 90 children (mean age 9.5 years) and presented results for 77 children at two-year follow-up. Although the trial had secure allocation concealment, it was at high risk of performance bias and from major imbalances in baseline characteristics. Reflecting these study limitations, we downgraded the quality of evidence by two levels to 'low' for most outcomes, meaning that we are unsure about the estimates of effect. For outcomes where there was serious imprecision, we downgraded the quality of evidence by a further level to 'very low'. The trial provided very low quality evidence that fewer children in the bone marrow injection group had radiographically assessed healing of bone cysts at two years than in the steroid injection group (9/39 versus 16/38; RR 0.55 favouring steroid injection, 95% CI 0.28 to 1.09). However, the result was uncertain and may be compatible with no difference or small benefit favouring bone marrow injection. Based on an illustrative success rate of 421 children with healed bone cysts per 1000 children treated with steroid injections, this equates to 189 fewer (95% CI 303 fewer to 38 more) children with healed bone cysts per 1000 children treated with bone marrow injections. There was low quality evidence of a lack of difference between the two interventions at two years in functional outcome, based on the Activity Scale for Kids function score (0 to 100; higher scores equate to better outcome: MD -0.90; 95% CI -4.26 to 2.46) or in pain assessed using the Oucher pain score. There was very low quality evidence of a lack of differences between the two interventions for adverse events: subsequent pathological fracture (9/39 versus 11/38; RR 0.80, 95% CI 0.37 to 1.70) or superficial infection (two cases in the bone marrow group). Recurrence of bone cyst, unacceptable malunion, return to normal activities, and participant satisfaction were not reported. The available evidence is insufficient to determine the relative effects of bone marrow versus steroid injections, although the bone marrow injections are more invasive. Noteably, the rate of radiographically assessed healing of the bone cyst at two years was well under 50% for both interventions. Overall, there is a lack of evidence to determine the best method for treating simple bone cysts in the long bones of children. Further RCTs of sufficient size and quality are needed to guide clinical practice.

Plain-language summary: We searched several important medical databases in April 2016, as well as trial registers, conference proceedings and reference lists. We found only one relevant medical study in which the children participating were allocated randomly to different treatments. The study compared treatments in which the simple bone cysts were injected with bone marrow or steroid (methylprednisolone acetate). Ninety children with an average age of 9.5 years participated in this study. Results were available for 77 children. Two years after treatment, X-ray examination showed that successful healing of bone cysts was more common in children who had received steroid injections; however, we are very uncertain whether this is a true finding. Low quality evidence two years after treatment showed children in the two treatment groups had similar high levels of function (measured by the Activity Scale for Kids score) and low levels of pain (measured by Oucher score). There was very low quality evidence that there was no difference between the two interventions for adverse events, including pathological fracture after treatment. As the quality of the evidence is low, or very low, we cannot definitively conclude that there are no differences between the treatments, and we do not know whether either treatment gives better results with fewer complications. This review is based on one trial with a small number of participants. Hence, at present there is insufficient evidence to determine the best method for treating simple bone cysts in the long bones of children. More studies with larger numbers of participants and that monitor children for longer follow-up periods are needed.