Osteomyelitis of the patella: ensure a high index of suspicion and beware the negative aspirate

Abstract

We report the case of a 33-year-old man who presented several times to healthcare professionals over a 6-week period with a painful swollen right knee. He had a history of chronic osteomyelitis of the left femur and had recently stopped taking suppressive antibiotics. A joint aspirate did not demonstrate any organisms. On subsequent review by the orthopaedic team MRI was performed which revealed an isolated area of osteomyelitis and an abscess in his right patella. He underwent arthrotomy, debridement and irrigation of the joint alongside antibiotic treatment. We highlight this case, as isolated osteomyelitis of the patella is a rare condition, especially in adults. In addition, the presenting features of osteomyelitis of the patella are varied and joint fluid aspirates often do not reveal an organism. This case therefore aims to raise an awareness of this condition and thereby ensure a high index of suspicion when symptoms or signs are present and inform clinicians of the investigative steps in order to avoid a delay in diagnosis as seen in this case.

Figure 1

Anteroposterior and lateral view of the left femur demonstrating changes associated with previous osteomyelitis.

Figure 2

Initial anteroposterior and lateral view of the right knee revealing no abnormality.

Figure 3

Subsequent anteroposterior and lateral view of the right knee showing a supra-patella effusion and soft tissue thickening.

Figure 4

Anteroposterior and lateral view of the right knee demonstrating the gross swelling.

Figure 5

Coronal proton density fat saturated MRI showing collection in patella.

Figure 6

Sagittal proton density fat saturated MRI showing collection in patella.

Figure 7

Axial T2 MRI showing proximity of collection to cartilage surface.

Figure 8

Supra-patella pouch containing a collection of pus.

Figure 9

Pus swab in cavity in patella.

Figure 10

Cavity in patella.