Unicameral Bone Cysts: Review of Etiopathogenesis and Current Concepts in Diagnosis and Management

Objective

This article aims to review the epidemiology, etio-pathogenesis and updates in clinical diagnostics and management of unicameral bone cysts (UBC).

Methods

A computerized literature search using Cochrane database of systematic reviews, EMBASE and PubMed was performed. MeSH (Medical Subject Headings) terms used in searches included the following sub-headings: "unicameral bone cyst", "epidemiology", "etiology", "pathogenesis", "diagnosis", "management" and "surgery". Studies were analyzed based on clinical relevance for the practicing orthopedic surgeon.

Results

UBC accounts for 3% of all bone tumors and is asymptomatic in most cases. Nearly 85% of cases occur in children and adolescents, with more than 90% involving the proximal humerus and proximal femur. Despite multiple theories proposed, the exact etiology is still unclear. Diagnosis is straightforward, with radiographs and MRI aiding in it. While non-surgical treatment is recommended in most cases, in those warranting surgery, combined minimal-invasive techniques involving decompression of cyst and stabilization have gained importance in recent times.

Conclusion

There is variation in the diagnosis and treatment of UBCs among surgeons. Due to the vast heterogeneity of reported studies, no one method is the ideal standard of care. As most UBCs tend to resolve by skeletal maturity, clinicians need to balance the likelihood of successful treatment with morbidity associated with procedures and the risks of developing a pathological fracture.

Study Design

Review Article.

Understanding Unicameral and Aneurysmal Bone Cysts

Bone cysts in the pediatric population are often found incidentally on radiographs or after a cyst has created cortical weakness leading to a pathologic fracture. Most bone cysts are benign, are pain free, and resolve spontaneously. The most common bone cyst is unicameral 1-chamber bone cyst, also known as simple bone cyst. General practice pediatricians may be the first to encounter these lesions, and this article aims to help elucidate their incidence, etiology, clinical findings, radiologic findings, and modern treatment approaches. The other differential diagnoses that should be considered, specifically, aneurysmal bone cyst, are also explored. This summary is not all inclusive, and it is recommended that all patients be referred to a pediatric orthopedist.

Investigating a potential biological treatment to prevent pathological fractures caused by unicameral bone cysts in children under 8 years

INTRODUCTION

There is no consensus on when and how to treat unicameral bone cysts (UBCs), partly because of a lack of knowledge of the aetiology.

PURPOSE

To review the different treatment techniques for UBCs and to describe our results with a single injection of autogenous bone marrow (BM) mixed with demineralised bone matrix (DBM) in very young children.

PATIENTS AND METHODS

We reviewed five patients under the age of 8 years with UBCs treated by percutaneous aspiration and a single injection of BM associated with DBM. The cyst was located in the proximal humerus in four patients and in the proximal femur in one patient. Assessment of the need for surgery was based on the clinical and radiographic suspicion of new pathological fractures. The administration of a second injection, when necessary, was based on the surgeon's judgement regarding the risk of fracture. The mean follow-up after first injection was 41 months.

RESULTS

There were no complications related to the procedure, except a non-displaced fracture, which healed without problems. All patients were pain free and progressively resumed their activities without restriction until a new fracture occurred in two cases. According to Capanna's classification, only one case healed completely (grade 1), one lesion was classified as grade 2, and there were three recurrences at 11, 12 and 27 months after initial treatment (grade 3). The final outcome was treatment failure for three out of the five patients. Two patients were treated with a second injection and one patient is waiting for surgery.

CONCLUSION

A single injection of aspirated autogenous BM mixed with DBM in very young children with active UBCs at risk of fracture is very simple, comfortable and safe. Nevertheless, the results seem to be unpredictable and are probably more dependent on the natural evolution of the cyst than on the treatment. Further comparative studies with larger sample numbers are needed.

Unicameral bone cysts: general characteristics and management controversies

Unicameral bone cysts are benign bone lesions that are often asymptomatic and commonly develop in the proximal humerus and femur of skeletally immature patients. The etiology of these lesions remains unknown. Most patients present with a pathologic fracture, but these cysts can be discovered incidentally, as well. Radiographically, a unicameral bone cyst appears as a radiolucent lesion with cortical thinning and is centrally located within the metaphysis. Although diagnosis is frequently straightforward, management remains controversial. Because the results of various management methods are heterogeneous, no single method has emerged as the standard of care. New minimally invasive techniques involve cyst decompression with bone grafting and instrumentation. These techniques have yielded promising results, with low rates of complications and recurrence reported; however, prospective clinical trials are needed to compare these techniques with current evidence-based treatments.

Treatment of unicameral bone cyst: systematic review and meta analysis

PURPOSE

Different treatment modalities have been utilized to treat unicameral bone cyst (UBC), but evidence has not been fully described to support one treatment over another and the optimal treatment is controversial. The aim of this quantitative systematic review was to assess the effectiveness of different UBC treatment modalities.

METHODS

We utilized Pubmed to isolate retrospective studies on patients with UBC who received any kind of treatment. The included studies needed to have a minimum sample size of 15 patients, and have provided data on radiographic healing outcome.

RESULTS

Sixty-two articles were selected for the meta-analysis from a total of 463 articles. The cumulative sample size was 3,211 patients with 3,217 UBC, and male to female ratio was 2.2:1. The summary or pool estimate of methylprednisolone acetate (MPA) injection resulted in a healing rate of (77.4 %) that was comparable to bone marrow injection (77.9 %). A higher healing rate was observed with MPA injection when inner wall disruption was performed. The pool estimate of bone marrow with demineralized bone matrix injection was high (98.7 %). UBC healing rate after surgical curettage was comparable whether autograft or allograft was utilized (90 %). UBC treatment with flexible intramedullary nails without curettage provided almost 100% healing rate, while continuous decompression with cannulated screws provided 89 % healing rate. Conservative treatment indicated a healing rate of 64.2, 95 % CI (26.7-101.8).

CONCLUSIONS

Active treatment for UBC provided variable healing rates and the outcomes were favorable relative to conservative treatment. Due to the heterogeneity of the studies and reporting bias, the interpretation of these findings should be handled with caution.