Cobalt-chrome alloys are widely used in dentistry and Orthopaedic implant industry. Vitallium is a similar alloy which contains 60% cobalt, 20% chromium, 5% molybdenum along with traces of other substances. It has been in use along with stainless steel for the last century because of its lightweight, favourable mechanical properties and resistance to corrosion. We present an unusual case of synovial cyst formation following Vitallium plating mimicking a sarcoma. To our knowledge, we are the first to report a delayed tissue reaction to Vitallium plating 40 years after its implantation.

A 78 yrs old man had a right femoral intertrochanteric fracture 40 years ago, which was fixed with a Vitallium nail plate. His postoperative recovery was uneventful and he regained full function of his leg. 3 years prior to excision, he presented with a painless swelling around his right upper thigh to our unit. Aspiration of the swelling and investigations were requested but patient was lost to follow up due to social reasons. Seven months prior to excision, he represented as the swelling had increased to the extent that it was involving the anterior and posterior aspect of the upper thigh with pressure necrosis of skin posteriorly. Examination revealed painless, transilluminable, fluctuant multilobular swelling over the right proximal femur overlying the healed surgical scar. Compression of the larger lobe in the buttock clearly forced fluid into the anterior compartment of the thigh where again swelling was extensive. Surprisingly he had full range of movements at the hip joint.

Radiograph of the hip showed a soft tissue swelling with a healed fracture and Vitallium implant insitu. Cytology was negative. MRI scan showed multiloculated cystic lesions extending anteriorly, laterally and posteriorly into the intermuscular and subcutaneous planes around the right proximal femur. Multiple small dependent foci likely representing debris or synovial proliferation was seen within loculations.

Excision of the cystic lesions with removal of metal work was performed. The old incision was reopened in the lateral position and a large cystic lesion with a thick capsule was dissected down to the metal work. The lesion was lying superficial to the vastus lateralis but was communicating with metal work. The metal work was removed with difficulty, no visible metallosis. A second cystic lesion was located more posteriorly but its neck was communicating with the thin hole into the first lesion. The lesion was excised completely.

Macroscopic examination showed two cysts 9×8×5.5cm and 20×10×7.5cm with a smooth external surface and the lumen appeared trabecular containing numerous loose (rice) bodies. Microscopy showed a dense fibrotic cyst wall with lumen with multiple small nodules containing organised fibrinous and eosinophilic material. Several foci of cellular debris including lymphocytes and macrophages were scattered in nodules best representing a synovial cyst with loose/rice bodies. No malignancy was seen.

We recommend early removal of metal work if it shows any signs of local reaction provided fracture is united. Be aware of large foreign body/ hypersensitivity reaction and incompatible equipment for removal.

Background

Patellar instability is a complex, multi-factorial disorder. Radiological assessment is regarded as an important part of the management of this population. The purpose of this study was to determine the intra- and inter-rater reliability of common radiological measurements used to evaluate patellar instability.