A 28 year old woman, nursing assistant, attended the emergency trauma department because she reported that for two days she had been experiencing pain in the subpatellar region of the right knee which had been worsening and she was currently having difficulty moving the joint.
Physical examination revealed an erythematous lesion in the right subpatellar region, with pain on palpation and a small incised-contuse wound a few millimetres long. Active and passive mobilisation is partially limited by the pain, with no other accompanying symptoms.
The worker refers that in childhood she had an osteochondroma in the same knee, currently cured and without sequelae, with the last control X-ray taken two months ago, which was completely normal.
The worker relates this episode to a work-related accident suffered two days ago, in which she slipped and fell to the floor while carrying a box of 32 mercury thermometers in her hand. Some of the mercury thermometers fell on her right knee and caused an incised-contuse wound, which we observed on examination still healing.
The nursing assistant acknowledges that she was overworked at her workplace. The box in which she was transporting the thermometers was not closed, the worker was not wearing gloves and the work clothes were not removed after the accident at work. Subsequently, no hygienic-sanitary measures were taken and no appropriate action was taken to deal with the mercury spillage.
In the emergency department, the next step was to take an X-ray of the knee, which revealed a metallic foreign body in the patellar bursa, corresponding to mercury.

After the diagnosis of chemical bursitis due to mercury, and taking into account the toxicity of the metal, the patellar bursa was removed urgently in the operating theatre under scopia, in order to avoid mercury remains in the worker's joint.
Currently, the auxiliary has no sequelae and has fully recovered from her injury.