Unicameral bone cysts (UBCs) are non-neoplastic fluid-filled cavities that account for up to 3% of primary bone lesions and solely arise in children and adolescents (2, 6, 7, 10). Although the exact cause of the formation of these lesions has not been elucidated, many theories have been proposed, such as local disruption in bone formation, small trapped nests of synovial cells in bones and blockage in the venous drainage (4, 5, 20). Based on observations that have shown a slight increase in the internal pressure of the involved bone compared to the normal pressure of the bone marrow and a lower partial pressure of oxygen in the cyst fluid compared to arterial or venous blood, the most widely accepted theory is a blockage in venous drainage (20). UBCs are mainly diagnosed by clinical presentations and plain radiography, which is the imaging modality of choice and possesses high diagnostic accuracy (6). Despite the fact that both CT and MRI add little to the diagnosis, these modalities can be helpful with regards to eliminating other entities that can mimic a simple bone cyst (1, 11). UBCs of the calcaneus mostly affect the anterolateral aspect of the bone, which is far away from the area where most body weight is transmitted (8).
A variety of strategies ranging from non-operative management, intralesional steroid injection, percutaneous or open curettage with or without bone grafting, percutaneous injection of allogenic demineralized bone matrix to more invasive procedures, such as cannulated pin/screw insertion and surgical procedures have demonstrated acceptable efficacy. However, the optimal management of these lesions remains an issue of debate. In patients who are incidentally diagnosed and have no risk of pathological bone fractures, non-operative management with close follow-up is recommended. Spontaneous resolution of heel pain has been reported in 1 to 2% of patients managed non-operatively (4, 19).
Intralesional steroid injection was first introduced as a successful management strategy for simple bone cysts. Despite the reported outcomes, recent studies on calcaneal UBCs have demonstrated a high recurrence rate even after multiple steroid injections (13, 21). Scaglietti et al reported only 24% cyst healing after a single injection and incomplete healing even after multiple injections. Glaser et al (22) performed 9 steroid injections on 6 patients and curettage combined with bone grafting on 9 patients. All of their patients were asymptomatic and the study reported a 0 healing rate with persistent cysts in 2 of the cases injected which steroids and complete healing without recurrence in cases who underwent curettage with bone grafting after a minimum follow-up period of 12 months. Moreover, a few studies have suggested that the steroids have minimal effect with regards to resolving the cyst, and that the mechanical effect of punctures, which helps normalise local circulation, is the key factor.
Percutaneous or open curettage, which can be performed with or without bone grafting, is the traditional method for the management of symptomatic calcaneal UBCs. Although open curettage with bone grafting has demonstrated significant improvement in the resolution of heel pain, it has been associated with a high recurrence rate in cases where the graft had been incompletely packed (16). Innami et al (12) performed endoscopic curettage in conjunction with percutaneous injection of calcium phosphate to treat symptomatic calcaneal UBCs. Their findings showed the complete resolution of pain and radiological healing in all patients after a follow-up period of 3 years. Aiba et al (14) performed endoscopic curettage on 6 calcaneal UBCs and reported complete healing after a mean follow-up period of 4 months without cyst residue.
Abdel-Wanis et al (18) used minimal curettage, multiple drilling and continuous decompression as an alternative to autografting in children. Due to the patients’ young age, harvesting a large volume of autographs can be difficult. On the other hand, the risk of disease transmission by autografting should not be overlooked, no matter how small. This study reported complete radiographic healing in all patients and total pain relief without recurrence in 59% of cases. Other methods, such as a cannulated screw placed for continuous decompression, have demonstrated lower recurrence rates, higher rates of healing and a significant reduction in heel pain following decompression. Saraph V et al (22) treated 9 calcaneal UBCs with continuous decompression using cannulated screws, among whom 8 cases showed complete healing and one showed a residual region on imaging with complete pain relief after a minimum follow-up period of 24 months. The only complication reported in the study was irritation at the screw insertion site observed in one patient, which led to early removal of the screw. Shirai et al (24) managed 23 simple bone cysts in the calcaneus by using cannulated hydroxyapatite (HA) pins, which were used to achieve continuous decompression. After a mean follow-up period of 5 months, their results showed complete healing in all patients. In another study, Park et al (15) compared open chip allogenic bone grafting with percutaneous injection of bone powder. Complete healing was reported in 70% of open chip allogenic bone grafts and 50% of cases percutaneously injected with bone powder after a mean follow-up up of 49.4 months. Persistent cysts were reported in 15% of cases treated using open chip allogenic bone grafts and 20% of those managed by percutaneous injection of bone powder.
In this case presentation, we treated a simple bone cyst in the calcaneus with a novel technique by inserting two needles into the cyst without aspiration, and injecting cement until the cyst was completely filled. Utilizing two needles enabled us to fully drain the cysts with a radiopaque bone cement mixture in a relatively short period of time (15 minutes) without any complications.
The authors believe this novel technique has the potential to be used as a feasible minimally invasive approach to manage symptomatic simple bone cysts in the calcaneus. Nevertheless, further studies are required to validate its long-term safety and efficacy with regards to the management of symptomatic calcaneal simple bone cysts.