CASE 110

By: Dr. Nizar Al-Nakshabandi MD, FRCPC

HISTORY: 29-year-old male with left hip pain. On examination, he has marked limitation of the left hip movement with crepitus and fever.

What are your findings?

What is the differential diagnosis?

What are the causes?

FINDINGS:

The plain radiograph (A) demonstrates a normal bilateral hip joint and femoral heads. However, the left sacroiliac joint demonstrates widening of the joint space when compared to the right side likely with an effusion present.

T1 axial oblique weighted image of the sacroiliac joints (B) demonstrates widening of the left sacroiliac joint with low signal edematous bone marrow changes. It involves the left sacroiliac joints as well as the left sacrum and ilium.

T1- axial oblique weighted images fat sat post gadolinium demonstrates avid enhancement of the left sacroiliac joint and synovium with a collection anterior to the left sacroiliac joint measuring at least 2 x 1 cm. In addition, there is evidence of enhancement of the left side of the sacrum.

DIAGNOSIS:

Left septic arthritis with secondary left sacral osteomyelitis.

PEARLS AND DISCUSSION:

Septic arthritis is infectious arthropathy where there is evidence of bacteria within the joint lining that is causing destruction of the joint space that may or may not extend into the bone. This is considered a radiological emergency. Prompt action should be taken. The first and immediate step to be taken before an MRI if you suspect septic arthritis is to aspirate the joint and send the fluid for culture/sensitivity and Gram stain, followed by starting the patient on antibiotics empirically. It is important that you stress this point to the examiner during the examination process. MRI may follow that crucial step. However, it should not delay the aspiration. Logistics and hospital scheduling may delay an emergency MRI anywhere from 24-48 hours, by that time the joint will be completely destructed and non-repairable.

Large joints are a favored location for septic arthritis. The reason is abundant blood supply. Therefore, they are more prone to bacterial infection. The most common joint infection is the shoulder, hip and knee.

Be aware that in IV drug abuse is as a sternoclavicular joint and sacroiliac joint are favorable in these types of patient’s.

Also, Brucellosis has an affinity to affect the sacroiliac joint. If there is no evidence of direct trauma or recent procedure, staph aureus is the most commonly isolated agent in approximately 32% of cases.

The plain radiographs demonstrate no significant abnormality at the beginning of the disease. However, joint effusion may be seen on as well as juxta-articular osteoporosis due to increased blood supply. At the beginning of the process, there is narrowing of the joint space which appears due to cartilage destruction. However, later as in our case, subchondral bone destruction occurs leading to a widened sacroiliac joint.

MRI is sensitive and more specific for early cartilaginous involvement as well as delineating any collection if present. In our case, low signal intensity in the subchondral bone from edema is noted. Synovial collection anterior to the joint is seen.

Irreversible joint damage will occur if the patient is left for more than 48 hours as the proteolytic enzymes of the white blood cells start destructing the synovial space and into the bone. Eventually, osteonecrosis will be the sequela from the large effusion and increased intra-articular pressure that compromises the blood circulation. When treated quickly and effectively 90% of the patient’s result in recovery.

FURTHER READING:

1.      Karchevsky M, Schweitzer ME, Morrison WB et-al. MRI findings of septic arthritis and associated osteomyelitis in adults. AJR Am J Roentgenol. 2004;182 (1): 119-22. 

2.      Weissleder R, Wittenberg J, Harisinghani MG. Primer of diagnostic imaging. Mosby Inc. (2003) ISBN:0323023282. 

3.      Al-Nakshabandi N. The spectrum of Imaging findings of Brucellosis: A Pictorial essay. Canadian Association of Radiologist Journal63(2012) 5-11.