Posterior Leg Compartment Abscess Following Rupture of Infected Baker's cyst: A Complication of Intra-articular Corticosteroid Injection

摘要

We report a case of a left leg posterior compartment abscess, developing from a ruptured Baker's cyst following intra-articular Depo-medrone injection into the knee. Initially the patient developed a suspected pyarthrosis following the Depomedrone injection, where S. aureus was grown on culture. The initial treatment with arthroscopy did not address the patients Baker's cyst which subsequently ruptured causing an abscess. The diagnosis was confirmed on an ultrasound scan and with magnetic resonance imaging. The patient was treated with incision and drainage of the abscess, which resulted in resolution of the problem over the following two months. Case Report A 77 year old lady presented to her general practitioner with longstanding left-sided knee pain. She was known to have tricompartmental osteoarthritis which had been deteriorating clinically. Clinical examination was unremarkable and conservative treatment was instituted. Her knee was injected by her general practitioner with 80mg Depo-medrone with 1mg Lidocaine. Over the next three days the patient began to develop increasingly severe knee pain and returned to her general practitioner unable to weight-bare. The movements of her knee had become restricted and was therefore referred to secondary care for further investigation and management.On admission to hospital, the patient was pyrexial (38.9°C). Examination of the knee revealed a moderate effusion with swelling in the popliteal fossa. The knee was slightly warm to the touch with tenderness over the posteromedial joint line and proximal calf with a constrained range of movement (30-80 ° ). Differential diagnosis of deep vein thrombosis was excluded with a doppler ultrasound scan. Blood tests revealed a white cell count of 12.8 x 10 9 /l and elevated inflamatory markers (erythrocyte sedimentation rate 115 mm in first hour and C-reactive protein >450 mg/l). Approximately 15mls was aspirated from the knee and sent for microscopy and culture. It revealed 10,000/mm 3 leucocytes (90% polymorphs, 10% lymphocytes), no organisms and no crystals. There were no organisms grown on culture.Clinical outlook necessitated the patient undergoing an urgent arthroscopic washout of her knee. This revealed a large quantity of pus like fluid, which was again sent for microscopy, culture and sensitivity along with synovial tissue. This grew Staphylococcus aureus, and intravenous antibiotics were instituted (Benzyl penicillin 1.2g QDS and Flucloxacillin 1g QDS). Postoperatively the patient was slow to improve clinically, with limited ability to weight-bare and a reduced range of movement. Six days following arthroscopy the patient developed a very tender, swollen and erythematous proximal calf. The inflammatory markers had failed to settle (ESR 116 mm in first hour and CRP 206 mg/l). An ultrasound scan was organised, which revealed a 3 cm superficial abscess communicating with a deeper larger abscess in the posterior compartment of the left leg. Magnetic resonance imaging (Figure 1, 2 and 3) confirmed a loculated abscess with a superficial component overlying the medial aspect of the tibia and a deeper component superficial to the medial head of gastrocnemius. The loculi communicated via a small channel. The abscess was treated with incision and drainage and was left to heal by secondary intention over the next two months.