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Case Discussion: Pathological Fracture Through a Benign Bone Cyst in the Medial Malleolus

Mr B is a 67 year old gentleman who was referred for an orthopaedic surgical opinion by his Podiatrist and General Practitioner following a three month history of atraumatic right ankle pain.

Mr B's podiatrist trialled taping and orthotic adjustment for pain relief initially suspecting tibialis posterior tendinopathy due to his medial sided ankle pain, but importantly ordered an x-ray when the pain failed to settle after one week of non-operative treatment. This x-ray demonstrated a large cyst in Mr B's medial malleolus and the astute Podiatrist urgently contacted Mr B's General Practitioner for urgent review and referral for Orthopaedic Surgical opinion.

A SPECT scan ordered by his General Practitioner demonstrated a lytic lesion in the medial malleolus (see below).

SPECT scan of the ankle

Mr B was then referred to Dr Touzell for urgent review.

On examination, Mr B was moderately swollen to his medial malleolus and had point tenderness in this area. He had a mild planovalgus alignment to his hindfoot. His tibialis posterior tendon was also irritable to palpation. He was unable to perform a single leg heel raise due to pain. Systemically, he was well with no signs or symptoms of infection.

Although benign in appearance, it is important to exclude malignancy and infection as a cause of a lytic bone lesion. Mr B subsequently underwent blood tests (FBC, ESR and CRP) to exclude infection as well as serum and urine electrophoresis to exclude multiple myeloma. Fortunately, these tests were normal. An MRI scan (below) did not demonstrate any soft tissue changes and was supportive of a benign process.

MRI scan of the foot

Mr B had exhausted non-operative management so surgery was discussed. The goals of surgical intervention would be to relieve the pressure from the cyst and provide structural support to the thin cortex that most likely had a pathological fracture.

An open debridement was performed, including multiple samples sent for histopathology with an experienced musculoskeletal pathologist as well as microscopy and culture, followed by bone grafting to the cyst. Post-operatively, Mr B was placed in a backslab for two weeks. After his two-week wound review, he was permitted to partially weight bear in a CAM boot and was referred back to his treating Podiatrist for non weight bearing range of motion exercises and gentle stretching of his ankle out of the boot as part of a slow rehabilitation program.

There was no growth on any samples and histopathology confirmed a cyst with fibrous tissue and bone, with no malignancy.

A six-week post-operative x-ray demonstrated complete incorporation of the bone graft. He then came out of the boot, started to weight bear as tolerated and commenced a rehabilitation program progressing to single leg calf raises nine weeks following surgery.

Seven months following surgery, Mr B has returned to all his normal activities including bushwalking, gardening and riding his bike. He has very occasional pain in his ankle, but this does not limit him in any way.

Key Learning Points:

  • It is important to recognise lytic lesions in bone may rarely be a result of malignancy or infection (see Mascard 2017, below).

  • If infection or malignancy is suspected, appropriate work-up with blood tests and further imaging should be undertaken prior to proceeding with any invasive procedure due to the risk of tumuor seeding.

  • Pathological fracture can occur through a benign bone cyst resulting in pain and swelling.

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All cases have been shared with written permission from the patient involved.


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