Arthroscopic Decompression and Grafting of a Symptomatic Posterior Talar Body Bone Cyst: Case Report and Literature Review
Sara Yancovitz, DPM (1)
Nathaniel Preston, DPM, FACFAS (2)
(1) Resident Physician, Grant Medical Center, Columbus, OH, USA
(2) Executive Director, Foot & Ankle Specialists Australia, Melbourne, Australia
Unicameral bone cysts (UBC) are common benign non-neoplastic lucent bone lesions filled with fluid that enlarge over time and thin the adjacent bone cortices (1, radiopaedia.org) These lesions are almost exclusively found in children and adolescents between the ages of 3 to 14 years of age, and are over twice as frequent in males than females (Mascard). UBCs are typically found in the metaphysis of long bones with an open physis especially the proximal humerus and femur; however, they have been diagnosed in almost every bone including tarsal bones and the calcaneus. (2) Though rare, UBCs can be seen in unusual locations such as the talus (radio*).
UBCs are most often asymptomatic and are incidental findings and may resolve on their own as a patient approaches skeletal maturity. The most frequent clinical presentation of a symptomatic UBC is pain, stiffness, swelling, with a concomitant pathologic fracture (Mascard). The pathogenesis of this cyst is largely unknown, though it is postulated to arise as a defect during bone growth that creates a cavity filled with fluid. The cyst is located adjacent to the physis during its active phase, and migrates away when it is latent (**). Because the cortical bone is weakened by the cyst, a traumatic event can result in a pathologic fracture.
These lesions are radiographically characterized as well-defined, expansive, unifocal, radiolucent lesions and centered along the longitudinal axis of the metaphysis with a thin sclerotic margin without periosteal reaction. A pathologic fracture through the lesion with a dependent bony fragment -- known as the “fallen fragment sign” -- is pathognomonic of a UBC. Magnetic resonance imaging (MRI) of a UBC demonstrates decreased signal intensity on T2, and high signal intensity on T2 with classic rim enhancement of a cystic lesion. It is often used to rule out an aneurysmal bone cyst. Other differentials include fibrous dysplasia, non-ossifying fibroma, eosinophilic granuloma, enchondroma, chrondromyxoid fibroma.
Non-surgical management modalities include immobilization and aspiration with methylprednisolone acetate injection. Surgical management is indicated when symptomatic cysts do not respond to steroid injections or structural cysts are at risk for fracture. This routinely includes curettage of the bone cyst with use of bone graft -- either autograft or allograft -- and internal fixation dependent on tumor location. The outcome for surgical intervention is favorable, with a healing rate of 90% (Kadim).
UBCs of the talus can be surgically managed through an open incision or arthroscopically. Open incisions require a malleolar osteotomy for access to the lesion. Ankle arthroscopy has become more popular in recent times as it provides adequate visualization, minimizes soft tissue dissection, negates the need for a malleolar osteotomy, and provides a better cosmetic result as compared to an open approach.
We present the case of a 25 year old active duty military male with no significant past medical history who presented as a referral from his physical therapist with chief complaint of pain to the right posterior ankle joint unresponsive to conservative treatment options. At time of initial presentation the pain had been persisting for approximately 8 months and began after the patient fell from a ladder landing predominantly on his right foot. At the time of injury he had pain involving the medial midfoot in addition to the posterior ankle however after RICE and subsequent physical therapy the pain to the medial midfoot entirely resolved. At time of presentation he described a deep aching pain to the posterior ankle which he rated as 5/10 exacerbated with prolonged weight bearing and high impact activity.
On exam the patient demonstrated 5/5 muscle strength to all quadrants bilateral lower extremity. Ankle joint ROM was full to right lower extremity however pain was elicited in the position of maximal plantarflexion in combination with axial load. Subtalar joint ROM was full and free of any pain or crepitation. The patient was able to perform a single limb heel rise however significant pain was elicited to the posterior right ankle. The postero-medial ankle joint, anterior to Kager's triangle, was noticeably tender to palpation. The remaining physical exam was free of any other pertinent clinical findings.
Initial plain-film radiographs demonstrated a well-defined lesion within the posterior aspect of the talus with a thin sclerotic rim. An irregular contour was appreciated to the posterior aspect of the talar dome on the lateral film however there were no overt signs of cortical collapse. (Figure 1) Incidentally there was noted to be an age indeterminate avulsion fracture to the distal anterior fibula which was asymptomatic on physical exam. Subsequent CT and MRI imaging again demonstrated an oval 2.1 x 1.5 x 1.9 cm cystic lesion with benign appearing non-aggressive features and a well-circumscribed thin cortical margin within the posterior talus. (Figure 2 a-c) Given the location, no fluid-fluid levels and no bony expansion, this was favored to represent a benign structure such as a unicameral or simple bone cyst.
The patient was informed of the results of the advanced imaging and educated on the benign appearing nature of the lesion. Given the recalcitrant nature of the pain however, the patient opted for surgical treatment.
The patient was positioned prone on the operating room table. Two standard posterior ankle arthroscopic portals were created adjacent to the achilles tendon. The camera and arthroscopic debrider were introduced into the posterior ankle joint and a working field of view was created. The Flexor Hallucis Longus tendon was identified as the medial extent of our field of view and the posterior inferior tibiofibular ligament was identified as the proximal margin. The posterior process of the talus was readily identified and appropriate positioning was ensured using fluoroscopy in multiple views. The posterior talar body cyst was then decompressed using a 3.5 drill. With decompression the lesion correlated with preoperative imaging and was consistent with a unicameral bone cyst. The margins of the cyst were then resected using curettage. An additional working arthroscopic portal was then made laterally just posterior to the peroneal tendons. A dry field was then created and 6cc of a combination of calcium phosphate and calcium sulfate was then injected into the decompressed cyst. Fluoroscopy was used to ensure appropriate placement, however the injected graft did not appear to spread evenly throughout the defect. Additional curettage was performed and the initial injected graft was supplemented with 5cc of cancellous allograft bone chips. Appropriate placement of the graft was again confirmed on fluoroscopy. The arthroscopic equipment was withdrawn and the portals were closed superficially. The patient was placed into a well padded posterior splint and discharged to home with instructions to remain non-weight bearing to the operative extremity.
At the 2 week post-op follow up appointment sutures were removed and the patient was transitioned from a posterior splint into a short leg cast. He remained non-weight bearing to the operative extremity until his 6 week follow up appointment at which time the short leg cast was removed and he was transitioned to a CAM boot. He remained weight bearing as tolerated in the CAM boot until 8 weeks post-op at which point he returned to normal shoe wear. Imaging was performed at 8 weeks post-op and again at 4 months post-op. (Figure 3) The patient initiated physical therapy at 8 weeks post-op and returned to pre-surgery level of high-impact activity 4 months after the date of surgery. At his 6 month post-op follow up appointment he was tolerating running and full unrestricted active duty military status with no pain to the operative extremity. At 1 year follow up the patient denied any recurrence of pain.
Figure 1: Pre-operative Non-Weight Bearing Mortise and Lateral Ankle Radiographs demonstrating a well-defined lesion within the posterior aspect of the talus with thin surrounding sclerotic rim.
Figure 2a-c: CT / MRI ankle demonstrating oval 2.1 x 1.5 x 1.9 cm cystic lesion with well-circumscribed thin cortical margin within the posterior talus.
Figure 3: Post-op Weight Bearing AP and Lateral Ankle Radiographs at 4 months demonstrating post-surgical changes to the talus without acute bony findings.
Analysis and Discussion:
Although UBCs are most often asymptomatic and are incidental findings, symptomatic UBCs should be actively treated since pain, stiffness, swelling, can be a precursor to a pathologic fracture (Kadhim). The goals for treatment of UBCs are to prevent pathologic bone fractures by restoring bone strength, cortical thickness and obliteration of the cyst. A pathologic fracture of talus from a UBC can be catastrophic as it can lead to breakdown of the adjacent ankle and subtalar joints; thus it is important to aggressively treat this pathology especially in younger patients.
We present a rare case of an early pathologic fracture of a large posterior talar body UBC treated with posterior ankle arthroscopic decompression and grafting. Post-operatively, our patient was able to pre-surgical level of high activity and unrestricted active military duty pain-free. Most of the literature on talar UBCs support surgical intervention with favorable outcomes. To our knowledge, there are only a few published case reports of UBC treated through a posterior arthroscopic approach with bone grafting.
Hiranya et al. reports a case of a symptomatic UBC of talus in an adult patient who was treated surgically due to high risk of fracture. Excision curettage of the lesion with autologous iliac bone grafting was performed through an open posterolateral approach. Two years post-operatively, there was successful incorporation of the bone graft, resolution of the lesion, and the patient was pain-free with full ankle range of motion.
As alternative to an open approach, arthroscopy has become more popular when treating talar cysts as it minimizes soft tissue dissection and the need for a malleolar osteotomy to access the lesion. A recent case series by Zhu et al., demonstrated favorable outcomes for seven patients with UBC of the talus who underwent debridement and grafting through an anterior ankle arthroscopic approach. The authors argue against a posterior approach as they believe it has a higher intra-operative morbidity due to the complex anatomic structures encountered, and the iatrogenic damage caused to the articular cartilage to reveal the cyst.
Lui et al reports a large talar body cyst in an adult female patient treated with curettage and bone grafting in similar fashion to our case. This lesion was diagnosed as a subchondral cyst, it was managed similar to our case report through posterior ankle arthroscopy and autologous iliac crest bone graft with successful results at one year post-operatively.
Baliga et al. reports a case of a 12 year old male patient with a UBC of talar body and associated pathologic fracture that was treated with curettage and autologous bone grafting. Similar to our study, this was performed through a posterior ankle arthroscopic approach; however, the authors used cancellous bone graft harvested from the ipsilateral calcaneus through the osteochondral autograft transfer system. The authors argue that the calcaneus as a donor site has a lower morbidity than iliac crest. At one year, the patient was noted to have a healed lesion with incorporation of the graft and was without functional limitations.
Despite its rare occurrence, a UBC can be found in the talus and should be actively managed when symptomatic. Posterior approach for arthroscopic decompression and bone grafting of a symptomatic posterior talar body cyst is an effective surgical technique that can result in a patient’s full return to activity without pain. As the follow up period for our patient is one year post-operatively, further studies are needed to determine long term surgical outcomes.
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Financial Disclosure: None
Conflict of Interest: None
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