Discussion
We presented a case report of a fractured, unicameral bone cyst at the distal. The fracture was successfully treated by open reduction, internal fixation and autologous bone grafting. A surgical approach without prior biopsy was chosen based on the patient’s age and the extended radiographic diagnostics revealing a unicameral, cystic lesion with a positive ‘fallen fragment sign’. The ‘fallen fragment sign’ in combination with a unicameral, cystic lesion is almost diagnostic for a UBC [
5‐
9].
The differential diagnosis includes aneurysmatic bone cysts (ABC), giant cell tumors (GCT), non-ossifying fibromas, post-traumatic bone cysts and malignant tumors or metastases. ABC are usually characterized by several blood- or serum-filled cavities of varying diameters. They tend to grow expansively beyond the natural margins of the affected bone thus producing defects within the cortical bone [
10]. In plain radiographs, GCT appear as lytic lesions with well-defined but nonsclerotic margins. They are eccentric and also exceed the cortical borders [
11]. A definitive diagnosis is obviously only possible upon histopathological examination.
In the literature, the terms juvenile bone cysts or simple bone cysts are synonymously used for UBC. They are unicameral, expansively growing, osteolytic, non-tumorous bone lesions not affecting the cortical bone. UBC are rare, accounting for only 5% of all non-malignant pathological fractures [
6,
8]. Typical locations are the metaphyseal-diaphyseal region of long bones. The most commonly affected bones are the humerus (23-70%), the femur (23-33%), the calcaneus (11%), the tibia (11%) and the pelvis (10%) [
12,
13]. Only two papers mention UBC at the distal radius (less than 2,5%) [
12,
13]. To the authors’ best knowledge, this is the first detailed report on an UBC at the distal radius causing a pathologic DRF in an adult patient.
UBC are usually treated conservatively as they heal spontaneously with skeletal maturity. Although their etiology is unknown, the venous obstruction theory is one of the most accepted models [
14,
15]. Selected cases, dependent on the location and size of the cyst, may require prophylactic treatment in order to prevent fracture and related complications. For those cases, a variety of treatment approaches has been recommended, including protective bracing, aspiration, local steroid injection, ethanol cauterization, open curettage and bone-grafting or continuous decompression [
13,
16,
17]. Overall, healing rates range between 12% and 92% [
12,
13,
16,
17]. There is almost no recommendation for treatment of fractures due to UBC in the literature. Hagmann et al. [
18] in 2011 retrospectively analysed 46 cases of UBC, 21 of which resulted in a pathological fracture. UBC were treated either by curettage and bone grafting, corticoid instillation or decompression using cannulated screws with an overall recurrence rate of 39%. They did not specify their treatment regimen for pathologic fractures.
The pathologic fracture presented here required open reduction and internal fixation. The UBC was addressed by curettage and autologous bone grafting harvested by RIA from the ipsilateral femur. Because of the cyst-size and the resulting bone defect we reasoned that filling the defect was essential to ensure stability. Autologous bone graft was chosen because it possesses biomechanical advantages over synthetic bone substitutes and carries no risk of immunogenic reaction or transmission of infectious diseases in contrast to cadaveric allografts or xenografts [
19,
20].
Intramedullary autologous bone grafts have been shown to yield comparable results regarding stiffness, bone healing and osteoinductive factors when compared to bone grafts from the iliac crest [
21]. In a recent prospective study, Sagi et al. [
22] showed reduced donor site morbidity for RIA compared to iliac crest grafts. Only limited data is available on how autologous bone grafting harvested by RIA promotes fracture healing [
21].
Retrospectively, arthroscopically assisted fracture repair may have prevented the need for revision surgery. To rule out SL-ligament tears, dynamic arthroscopic testing is a validated method [
23]. Arthroscopically assisted DRF repair was shown to significantly improve the quality of reduction of the joint surface compared to fluoroscopically guided reduction [
24]. Yet to date, no study has proven that arthroscopically assisted fracture repair in DRF results in better long-term clinical outcome. Although there is not enough evidence to support this hypothesis, it seems reasonable to consider wrist arthroscopy whenever difficult intra-articular fragments or co-pathologies such as SL-ligament tears are suspected [
25,
26].
Competing interests
The corresponding author confirms that there are no competing interests.
Authors’ contributions
FM drafted and wrote the manuscript, wrote the revision, did the literature research and made all the follow up examinations of the patient and the documentation of all data. SFB assisted drafting and writing the manuscript, assisted in writing the revision and was responsible for informed consent of the patient. EV was responsible for reviewing the manuscript and substantially contributed to the structure of the manuscript. He finally proof-read and edited the manuscript together with a native English speaker. WM was responsible for the final revision of the manuscript and contributed lots of knowledge and experience concerning cyst-like bone tumors to the case report. SG revised the manuscript and was basically involved in treating the patient and initiating the case report. All authors read and approved the final manuscript.