Unicameral Bone Cyst 

Updated: May 03, 2017
Author: Charles T Mehlman, DO, MPH; Chief Editor: Harris Gellman, MD 

Overview

Background

A unicameral bone cyst (UBC) is a common, benign, fluid-filled lesion found almost exclusively in children. The orthopedic entity called a UBC is not believed to be a new phenomenon. Lagier et al identified a UBC in the femur from the remains of a child from medieval times.[1] Virchow also recognized such bone cysts in humans in the late 1870s.[2]  In 1942, Jaffe and Lichtenstein published their classic paper concerning solitary UBCs,[3]  emphasizing the distinctiveness of UBC as follows:

Solitary unicameral bone cyst is a lesion sui generis. It bears no relation whatever to giant cell tumor of bone, and in particular it does not represent a cystic-healing phase of this tumor. Nor is it to be linked with enchondroma, fibroma or focus of fibrous dysplasia of bone that has undergone partial or extensive cystic degeneration. Further, it should not be regarded as representing cystic expression of osteitis fibrosa, since to throw it into this wastebasket category (one which to us is also meaningless) is to obliterate its distinctiveness. Correspondingly, solitary unicameral bone cyst ought no longer to be classed as an expression of localized fibrocystic disease of bone or localized fibrous osteodystrophy—likewise blanket designations dating from a more primitive era of bone pathology.

Much has been written about the diagnosis and management of UBCs, and evidence of a variety of successful treatment approaches can be found in the literature. Despite abundant clinical confidence in managing these lesions, many basic questions remain concerning their etiology and pathophysiology. As Bensahel stated, "[t]he solitary bone cyst has not revealed all its secrets."[4]  Among the questions that remain to be answered are the following:

  • What is the root cause of the UBC lesion?
  • Does a genetic basis to the problem exist?
  • Should pathologic fractures of the long bones (secondary to a UBC) be treated via immediate flexible intramedullary nailing?

Answering these and similar questions will require a far more coordinated research effort than has been made to date. A multicenter study (a combined effort of the Shriner's Hospital System and the Pediatric Orthopaedic Society of North America) holds some promise of refining the treatment approach to a UBC.

This article offers a comprehensive review of the present state of knowledge of a UBC, highlighting aspects of the pathophysiology, the clinical presentation, and the most commonly used treatment strategies.

Anatomy

The anatomy that is relevant to UBCs is mainly that of the proximal humerus and proximal femur. Percutaneous approaches to the proximal humerus require the surgeon to avoid injury to the biceps tendon as well as the axillary nerve as it innervates the deltoid musculature. The standard deltopectoral approach is the most common open surgical approach for proximal humeral lesions.

Key points of this approach include preservation of the cephalic vein as well as careful medial retraction of the conjoined tendon (coracobrachialis and short head of the biceps) to avoid injuring the musculocutaneous nerve. Dissection in the region of the bicipital groove should be minimized; such dissection may injure the anterolateral ascending branch of the anterior humeral circumflex artery, which provides the bulk of the blood supply for the humeral head.

Pathophysiology

A UBC may appear in virtually any bone, but typically, it is found in either the proximal humerus or proximal femur. (See the images below.) A UBC often leads to thinning of adjacent areas of bone, such that fracture or pain from microfracture may occur.

Large proximal humeral unicameral bone cyst demons Large proximal humeral unicameral bone cyst demonstrates early cortical healing following pathologic fracture.
Large unicameral bone cyst of pelvis. Pathologic f Large unicameral bone cyst of pelvis. Pathologic fracture is depicted. Note extension of cyst into region of proximal femoral physis.

When UBCs are immediately adjacent to a growth plate, they are referred to as active cysts, and when they have achieved some distance from the growth plate, they are considered to be latent cysts. This distinction has been used in the past; it was believed to have prognostic significance. A UBC usually presents as a unifocal (one bone) problem, affecting patients who are skeletally immature.

Komiya and Inoue carried out a longitudinal study (with serial radiographs over 6 years) that documented the development of a UBC over time.[5]  Initially, a small erosive lesion of the endosteal humeral metaphysis appeared, and over time, the lesion progressively enlarged into a typical UBC. The lesion analyzed by these authors was somewhat unusual, in that it was located in the distal humerus. In addition, the lesion appeared following notation of a previous UBC in the proximal aspect of the same bone.

The rarity of UBCs in adults supports a hypothesis of spontaneous resolution. In the absence of fracture through the cyst (or impending fracture), UBCs are asymptomatic. They are, at times, found serendipitously when radiographs are taken for other reasons. In the absence of symptoms and in the absence of mechanical compromise of the involved bone (eg, extensive cortical thinning), no treatment may be necessary other than observation.

However, treatment should be strongly considered for lesions that have resulted in a fracture or marked weakening of bone. Some evidence exists that spontaneous healing of a UBC may occur following fracture. Such healing occurs in only a minority of cases. Growth disturbance secondary to a UBC is also a concern.[6]

At least two case reports exist in which a chondrosarcoma was found to arise within the same area as a previous histologically proven UBC.[7]  In a separate case, an 8-year-old boy was reported to have sustained a pathologic fracture of the distal fibula that was believed to have resulted from a Ewing sarcoma infiltrating a UBC.[8]

The precise relation between such rare instances of apparent malignant transformation and the thousands (if not millions) of UBCs that have not demonstrated such behavior remains unclear. At any rate, a UBC is not considered to be a malignant or premalignant lesion; accordingly, routine biopsy or other treatment of asymptomatic and nonproblematic lesions based on a patient's or family's fear of cancer should not be undertaken.

Etiology

The specific etiology of a UBC has not been elucidated. Many theories have been proposed. One commonly quoted theory was proposed in 1960 by Cohen,[9] who studied the cyst fluid from six children undergoing treatment for UBCs and found four to resemble plasma and two to resemble blood. Cohen proposed that the principal etiologic factor is blockage of the drainage of interstitial fluid in a rapidly growing and rapidly remodeling area of cancellous bone.

Chigira et al studied the internal pressure of seven patients with UBCs and found them to be higher (2-7 mm Hg range) as compared to the contralateral normal bone marrow pressures.[10] The arterial oxygen tension (PaO2) in the fluid from these same cysts was found to be impressively lower than that in venous or arterial samples taken at the same time. These authors suggested that venous obstruction within the bone appears to be a likely cause of such simple bone cysts.

Such vascular theories have been supported by other authors.[11] Mirra et al suggested that a UBC represents an area of a congenital rest of synovial tissue and was able to demonstrate both synovial type A (macrophagelike) and type B (fibroblastlike) cells in the lining of such cysts.[12] This description resembles that of an intraosseous synovial cyst. Yu et al also demonstrated how methylprednisolone influences the cellular physiology of synovial cells in culture, thus establishing a theoretic basis for steroid injection treatments for a UBC.[13]

Shindel et al reported increased prostaglandin E2 levels in the cyst fluid from seven of their patients and theorized that this may help explain the beneficial effect of steroid injection of such lesions.[14] Gerasimov led a group of Russian researchers who stressed that the fluid from UBCs possesses increased lysosomal enzyme activity regardless of the UBCs' status as active or latent.[15] These authors emphasized the role such enzymatic activity might play in permanent corrosion of the cyst cavity, as well as increasing osmotic pressure within the cyst.

High levels of cytotoxic oxygen free radicals have also been found in the fluid from UBCs.[16] Such free radicals are not only cytotoxic; they might be generated during the ischemic state following blockage of interstitial fluid drainage from UBCs. The Japanese researchers suggested that such oxygen scavengers may contribute to the bone destruction associated with UBCs. Reproduction of these results in other centers has not yet occurred.

In the past several years, a group of Brazilian researchers have reported specific genetic abnormalities in a pediatric patient with a UBC of his right distal femur. Vayego et al made their first report in 1996.[17] Cytogenetic analysis of the resected cyst initially demonstrated complex aberrations of chromosomes 4, 6, 8, 12, 16, and 21. Further study of the same patient (following bone cyst recurrence) later revealed specific mutations associated with amino acid substitutions (arginine for tryptophan, arginine for serine).[18]

More study in this area clearly is indicated, and the potential for future gene-based therapies is seemingly apparent.

Epidemiology

A UBC occurs most frequently in children aged 5-15 years (average age, ~9 years).[19, 20] Many authors consider cysts that present in the first decade of life to be more aggressive.[19, 20] A UBC affects males approximately twice as often as females. These lesions constitute approximately 3% of all bone tumors.

A UBC probably represents the third or fourth most common benign bone tumor that the orthopedic surgeon confronts (osteochondromas are commonly considered to be the most frequently encountered benign bone tumors in children, followed by fibromas and/or fibrous cortical defects). The lesion may occur in conjunction with other benign bone tumors, such as a nonossifying fibroma.[21]

By far, the most common location for the lesion is the proximal humerus, followed by the proximal femur. The proximal humerus and femur together account for nearly 90% of all UBC sites.[19, 20] However, virtually any bone may be affected, with the calcaneus being one of these notable alternative locations.[22, 23, 24, 25, 26, 27]

Prognosis

The overall outcome and prognosis of a UBC is good. The lesion is believed to resolve spontaneously in most cases if given enough time.

Cases that present to the orthopedic surgeon typically involve patients who demonstrate a combination of a cyst that has caused cortical thinning and the right stressful event (eg, being tackled while playing football). In general, treatment may be summarized as doing nothing more than trying to promote natural healing. Flexible intramedullary nailing may do nothing more than mechanically support the bone while the natural healing process occurs.

Few comparative studies have been conducted regarding the various treatment alternatives for individuals with UBCs.[28, 29, 30, 31]  Some of the more important ones are summarized below.

In a retrospective study of 36 patients with UBCs who were surgically treated over a period of 45 years,[28]  Farber et al found that curettage and bone grafting (with some patients receiving allograft and others receiving autograft) yielded a 53% (10/19) healing rate, whereas aspiration and injection with steroid yielded a 70% (12/17) success rate. In 25% (3/12) of the patients, only one injection was required. Although this difference in overall healing rates might appear clinically significant, it was not statistically significant.

Farber et al also did not explicitly define their criteria for success.[28]  Because of the similar healing rates and the lower morbidity of the steroid injection, the authors concluded that they favored the percutaneous approach over traditional open curettage and bone grafting.

In a retrospective review, Canavese et al compared the outcomes of percutaneous curettage, intralesional injection of methlyprednisolone, and intralesional injection of bone marrow.[32]  The three treatment groups included 46 patients with radiologically confirmed unicameral bone cysts and at least 2 years of follow-up. Results showed that the rate of satisfactory healing was 70% in the percutaneous curettage group, 21% in the bone marrow injection group, and 41% in the methylprednisolone group.

Oppenheim et al evaluated 37 patients treated via open surgical techniques (35 with curettage and bone grafting and two with subperiosteal total or subtotal resection) against 20 patients treated via steroid injection.[33]  They found a 40% recurrence rate and a 15% major complication rate in their open group, whereas the steroid injection group had only a 5% recurrence rate and a 5% major complication rate.

Although not calculated by the authors, this difference in recurrence rates was statistically significant (P <0.02 via the Fisher exact test).[33]  These same authors used reconstitution of cortical thickness as their endpoint of healing rather than cyst obliteration.

Glaser et al published a comparative multicenter study focused on calcaneal UBCs.[23]  The calcaneus is a somewhat uncommon (ie, the third to sixth most common) site for UBC.[22, 23, 27, 34]  The study by Glaser et al suggested that percutaneous steroid injection procedures were less effective in the calcaneal lesions and that curettage and bone grafting may be a more predictable and successful procedure for simple bone cysts in this location.[23]

Flexible intramedullary nailing of UBCs in long bones, though not a new concept by any means, has been reported to yield good results.[35, 36]  Roposch et al documented a 94% (30/32) good response rate to flexible nailing of UBCs of the long bones.[36]  Complete cyst healing or healing with minor residual lucent areas occurred at an average of 36 months. Thus, this technique appears to support the compromised bone while the UBC follows its natural history and spontaneously resolves.

Some authors have stated that they believe such flexible nails allow continuous decompression of the UBC, with a resulting decrease in intralesional pressure.[36, 37, 38]  However, 28% of patients in a study by Roposch et al required at least one further operation because of inadequate nail length in the face of continued bone growth.[36]

In a systematic review and meta-analysis by Kadhim et al that included 62 studies and 3211 patients with 3217 UBCs, active treatment of these lesions (eg, curettage, grafting, injection of steroid or bone marrow, flexible intramedullary nailing, and continuous decompression with cannulated screws) was associated with variable healing rates, and the outcomes were favorable in comparison with conservative treatment.[39]

In a smaller study (N=68; 54 boys, 14 girls) focused specifically on humeral UBCs in children, Kadhim et al found that whereas complete healing was a challenge with any treatment modality, better healing was generally achieved when these lesions were treated surgically.[40]

 

Presentation

History and Physical Examination

Most patients with a unicameral bone cyst (UBC) present to the orthopedic surgeon after sustaining a pathologic fracture. Such fractures most commonly involve either the proximal humerus or the proximal femur. The events leading up to the fracture may range from fairly trivial (eg, throwing a ball) to more substantial (eg, a hard fall while playing soccer). As with all patients who have sustained a fracture, a careful physical examination of the patient should include efforts to exclude the possibility of an open fracture and a neurocirculatory insult.

In other instances, patients may present to emergency department physicians, their primary care physicians, or orthopedic surgeons for other reasons, and radiographs obtained in the workup of other complaints may identify asymptomatic UBCs. Such incidental diagnosis of "a bone tumor" may be quite disconcerting to the child's parents and family. Random bone tumor discussions with such a child's family are contraindicated. Medical personnel who eagerly deliver well-intentioned but inaccurate discussions of bone tumors often needlessly terrify families.

In either scenario, a review of the patient's past history, as well as their family's past history relative to fractures, rheumatologic conditions, bone tumors, endocrine disease, and cancer, is appropriate. Physical examination of the patient should also include a screening examination of the axial skeleton and the uninvolved extremities. Any other identified abnormalities may require further plain radiographs.[41]  Palpation of major lymph node areas (eg, the axillary and inguinal fields) is also appropriate; infection and malignancy are part of the differential diagnosis.

 

Workup

Laboratory Studies

The diagnosis of a unicameral bone cyst (UBC) is strongly suspected on the basis of the lesion's typical radiographic appearance and is confirmed when an appropriate cyst fluid is demonstrated. Specific laboratory tests are not a routine part of the workup of a UBC.[20, 42, 43, 44]

Imaging Studies

Plain radiography

Appropriate imaging studies for a UBC should always include plain radiographs. The plain radiograph appearance of the lesion is virtually diagnostic.

A particular radiographic sign (ie, the fallen-fragment sign) is, at times, very helpful in the radiographic diagnosis of a UBC. Reynolds is credited with describing this sign in 1969.[45] Typically, the sign is identified when the patient with a UBC presents with a pathologic fracture. The interior of the bone cyst may have complete or nearly complete thin bony septations within the cyst.

At the time of pathologic fracture, a portion of one of these bony segments may actually break free and float to the bottom of the cyst. This is possible because the UBC is filled with fluid and is not a solid. The fallen-fragment sign is found in approximately 20% of patients who present with a pathologic fracture secondary to a UBC.[46, 47]

Some authors have altered the original description of this sign and refer to it as the fallen-leaf sign; they choose to imagine the broken fragment of bone gently wafting down from the top of the cyst to the bottom of the cyst as if it were a leaf slowly falling to earth from a tree.

Magnetic resonance imaging

If a UBC is in close proximity to a growth plate and growth impairment is a concern, magnetic resonance imaging (MRI) may prove quite helpful.[48, 49, 50] MRI should not be a routine part of the workup of a UBC. Instead, it should be reserved for unusual or atypical situations. One such instance is a cyst in which growth-plate damage is a concern. Several authors have documented that such damage can occur about the proximal humeral growth plate.

Another situation in which preoperative MRI could be of value is in rare cases in which a more sinister diagnosis is suspected (eg, pseudocystic osteosarcoma or low-grade central osteosarcoma). In such instances, MRI is an appropriate part of preoperative staging of such a tumor.

A UBC can produce a wide variety of appearances on MRI, including rather heterogeneous fluid signals and even fluid-fluid levels (a sign much more commonly found in aneurysmal bone cysts).

 

Treatment

Approach Considerations

The decision to pursue surgical intervention in patients with unicameral bone cysts (UBCs) is a highly individualized one. An asymptomatic lesion with satisfactory maintenance of cortical thickness may require only observation. A lesion with precarious cortical thinning (with or without insufficient pain) may demand surgical intervention.

In addition, factors such as an upper extremity (lower stress) vs a lower extremity (higher stress) and younger children (more amenable to cast immobilization) vs older adolescents (less amenable to cast immobilization) may strongly influence surgical decisions. Simple treatment of the pathologic fracture may result in cyst resolution in as many as 25% of cases.[28]

Some authors have suggested the use of a cyst index aimed at predicting the future risk of a pathologic fracture. Kaelin and MacEwen discussed this concept and defined their cyst index as the area of the UBC measured via its widest dimensions divided by the diameter of the diaphysis of the same bone.[51]  On the basis of a statistical analysis of 57 patients with UBCs, they recommended mainly observation for humeral cysts with an index below 4 and femoral cysts with an index below 3.5.[51]  When either threshold was exceeded, stronger consideration regarding surgical intervention was deemed appropriate.

Surgical therapy for a UBC may be divided into open and percutaneous procedures. The success rates of such procedures have varied considerably, and the very definition of success has also varied from author to author.[19, 20, 52, 53, 33, 54, 55, 56, 57]

The main contraindication for surgical treatment of a UBC is a patient who otherwise meets indications for surgery but is unable to tolerate anesthesia. Another relative contraindication for surgery is a patient with a small asymptomatic latent cyst with a low likelihood of a pathologic fracture.

Medical Therapy

Nonoperative treatment of a UBC usually amounts to closed fracture care following pathologic fracture through the lesion. It has been suggested that in as many as 25% of cases, spontaneous healing of the cyst may occur after such pathologic fractures.[28] However, not all authors have reported such a high frequency of spontaneous healing. Thus, watchful waiting and routine fracture care only are not a universally accepted treatment option.[19, 20, 13, 52, 53, 33, 54, 58, 59, 55, 56]

Open Surgical Procedures

In a study of 144 UBCs treated by means of curettage and packing with freeze-dried, crushed, cortical-bone allograft, Spence et al demonstrated higher recurrence rates in patients younger than 10 years, female patients, those with active cysts, and those with incompletely packed cysts.[60]  Of the completely packed cysts, 88% healed. The authors suggested that freeze-dried allogeneic crushed cortical bone yielded results superior to those of similarly processed cancellous bone but comparable to those of fresh autogenous cancellous bone.

Other studies have also demonstrated multiloculated cysts and fracture immobilization as a primary treatment as associated with cyst recurrence or persistence.

Neer et al stressed that reported recurrence rates in UBC surgery could be quite misleading if complete cyst obliteration was the criterion for success.[61]  They believed that true recurrences were characterized by the cyst cavity reappearing and enlarging, causing expansion and thinning of the cortex and the threat of fracture.

The key aspects of the Neer rating system for the purposes of evaluating treatment response are as follows[53] :

  • Excellent – Complete obliteration of the cyst
  • Residual defect – One or more static cystlike areas with good reestablishment of bone strength
  • Reoperation – Subsequent operation required because of recurrence

Open techniques that have been reported include subtotal resection with and without bone grafting. Different bone-grafting materials that have been used include autograft, allograft, demineralized bone matrix, high-porosity hydroxyapatite bone grafting material, and plaster-of-paris pellets.

In 1962, Fahey and O'Brien introduced a technique for UBC treatment that they referred to as subtotal resection and grafting.[62]  This technique involved subperiosteal exposure of the cyst and a portion of the adjacent normal bone, followed by removal of two thirds to four fifths of the cyst. Cortical struts of bone graft harvested from the patient's iliac crest or tibia were then used to fill the defect. Freeze-dried allograft was also used at times.

At an average of almost 4 years' follow-up, Fahey and O'Brien reported a 95% (19/20) success rate with their technique (using the absence of a cyst as their criterion).[62]  They considered the operation to be the procedure of choice for individuals with latent primary cysts and for persons with cysts that recurred after a conventional operation. One patient required repeat grafting to achieve healing, and no other specific complications were reported with the technique.

Fifteen years later, McKay et al reported on a similar subtotal resection approach to UBCs that did not include bone grafting.[63]  Their technique yielded a 90% (19/21) success rate (also defined as complete cyst obliteration). No infectious or neurocirculatory complications were reported, but the authors did identify three patients who suffered humeral growth disturbances and seven patients whose bones fractured during the procedure (though this did not substantively affect their later outcome).

Subtotal resection and bone grafting thus remains an option for UBC treatment. The procedure certainly carries a higher level of surgical morbidity than other procedures do, and the surgeon's enthusiasm for the procedure may be directly proportional to the cyst's distance from the growth plate.

Curettage and bone grafting procedures have been used extensively in the treatment of a UBC.

Percutaneous Procedures

In 1974, Scaglietti introduced a procedure by which steroids were percutaneously instilled within UBCs (as well as other types of bone lesions).[64]  A minimum of 40 mg of methylprednisolone acetate was used for smaller cysts in young patients, and as much as 200 mg was used for larger cysts in older patients. The described technique included, on average, three or four injections in a period of 12-20 months, but as many as nine injections over 4 years were used.

Scaglietti et al reported complete healing of the bone cysts in 55% of his cases and some improvement (eg, cortical thickening within the area of the cyst or areas of new bone formation within the cyst) in 45%.[64]  Whereas 24% of their patients required only one steroid injection, 76% required multiple injections. The image below shows the typical appearance of the fluid aspirated from UBCs.

Typical appearance of cyst fluid is depicted. Init Typical appearance of cyst fluid is depicted. Initial aspiration often yields thin, clear, yellow fluid that rapidly becomes blood-tinged.

Simple mechanical disruption of the cyst wall has also been investigated as a treatment option. Komiya et al called this trepanation, and they reported good results in 91% (10/11) of their patients.[65]  The technique consisted of aspiration of the cyst until venous hemorrhage became visible, perfusion of the cyst with saline, and cyst wall as well as proximal and distal medullary bone drilling with a Kirschner wire (K-wire).

Chigira et al reported similar success with multiple drilling in 86% (6/7) of their patients.[10]  Their technique included leaving the 2.0-mm K-wires in place in some instances to allow drainage of the fluid through the cyst wall.

Various other authors have reported their results and suggested refinements of the percutaneous steroid technique.[54, 58, 56, 66, 67, 68, 69, 70, 71]  Rosenberg et al emphasized the importance of eliminating fibrous or osseous septa within UBCs to facilitate bathing the entire lesion with the injected steroids.[72]

Capanna et al also pointed out that contrast examination allows the surgeon to identify noncontiguous septated areas of UBCs (see the image below).[73]  This is important if optimizing the treatment response is desired.[73]

Double-cannula technique demonstrates intraoperati Double-cannula technique demonstrates intraoperative use of contrast material for evaluation of cyst's interior. In this case, large partial septum remains along inferior portion of cyst.

Injectable materials other than steroids, such as alcohol-based fibrosing agents, have also been suggested as treatment options for benign bone cysts.[74, 75]

Killian et al also reported the use of demineralized bone matrix via a similar percutaneous technique.[76]  No steroids were used. At 2-year follow-up, 82% (9/11) of their patients demonstrated completely healed cysts.

Several authors have investigated the effectiveness of autologous bone marrow injection as a treatment for UBCs.[19, 77, 78]  Spurred on by their earlier published work, a group of Israeli researchers reported marked improvement in cortical thickness and cyst remodeling in 10 of their patients following a single bone marrow injection.[79]  Highlights of their technique include the following[80] :

  • A single puncture into the cyst with a thin trocar or needle
  • Aspiration of cyst fluid, which is sent for pathologic analysis
  • Disruption of the lining and septations within the cyst using the trocar or needle
  • Contrast media examination (may be used)
  • Injection of autologous bone marrow aspirated from the iliac crest (average volume, 25 mL)

All cysts healed completely with one procedure within 6-12 months.[19]

Other authors have demonstrated similar results with the percutaneous bone marrow injection procedure.[77, 80]  Yandow noted that 83% (10/12) of patients with UBCs responded satisfactorily to the procedure,[77]  and Delloye et al had good results in approximately 88% (7/8) of their patients.[80]

Kose et al evaluated the outcome of the autologous bone marrow procedure in 12 patients.[81]  Only 42% (5/12) cases responded to the treatment, whereas 50% (6/12) recurred and 8% (1/12) exhibited no response at all. These authors concluded that the technique may be less effective in large cysts and in multiloculated cysts, and they recommended that the procedure be applied to selected patients only.

A 2017 Cochrane review concluded that the available evidence was not sufficient to allow a determination of the relative merits of bone marrow injections and steroid injections for treatment of UBCs in the long bones of children.[82]

In a small study (N=12; 10 male, two female), Fillingham et al evaluated the results of debridement and one percutaneous injection of a bioceramic bone-graft substitute for treatment of UBC.[83]  Functional outcome was excellent, and 75% of the patients experienced complete healing, with 25% having a residual cyst. The largest of the residual cysts was viewed as a local recurrence and was treated with repeat percutaneous bioceramic injection 1.5 years later; 4 years subsequently, the patient was still disease-free.

Complications

Injury to the growth plate (physis) may occur secondary to direct cyst expansion, pathologic fracture, or unintended mechanical disturbance during surgical intervention.

Direct cyst expansion across the growth plate and into the epiphysis of the proximal humerus has been well documented by Gupta et al via magnetic resonance imaging (MRI).[84] Growth arrest has also been reported following treatment either with local steroid injection or with curettage and bone grafting.[6] Growth disturbance leading to angular deformity or disturbed longitudinal growth has been estimated to occur in approximately 14% of cases.[19, 20]

Steroid injection has been a successful treatment, even in the setting of cyst extension into the epiphysis.[85]