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Facet joint septic arthritis is a rare but severe infection with the possibility of significant morbidity resulting from local or systemic spread of the infection. Pain is the most common complaint on presentation followed by fever, then neurologic impairment. While the lumbar spine is involved in the vast majority of cases presented in the literature, the case presented here occurred in the cervical spine. The patient presented with a three week history of neck and left shoulder pain and was diagnosed by MRI when his pain did not respond to analgesics and muscle relaxants. The only predisposing factor was a history of diabetes mellitus and the infection most likely resulted from hematogenous spread. MRI is highly sensitive in diagnosing septic arthritis and it is the preferred modality for demonstrating the extent of infection and secondary complications including epidural and paraspinal abscesses as seen in this case. Without familiarity with this entity's predisposing factors, clinical symptoms and appropriate lab/ imaging work up, many patients experience a delay in diagnosis. Treatment involves long term parenteral antibiotics or percutaneous drainage. Surgical debridement is reserved for cases with severe neurologic impairment. The incidence of facet joint septic arthritis is increasing likely related to patient factors (increasing number of patients >50 yo, immunosuppressed patients, etc), advancement in imaging technology, availability of MRI, and heightened awareness of this rare infection which is the aim of this case presentation.
Septic arthritis of the facet joint is a rare clinical entity with a similar clinical presentation to spondylodiscitis. Septic arthritis most commonly affects the larger peripheral joints and rarely the facet joint, however many of the same principles apply regarding predisposing factors, clinical presentation, lab/imaging work up and treatment modalities. Without appropriate diagnosis and treatment, infection can spread to adjacent structures resulting in abscess formation, spinal cord/nerve root impingement and sepsis. Two retrospective reviews of case reports in the literature found that septic arthritis of the facet joint causes 4-20% of pyogenic spinal infections, the average patient age is 55-59 and the overwhelming majority, 86-97%, occur in the lumbar spine.1,2 While most cases are thought to occur via hematogenous spread, there are a number of case reports in the literature where septic arthritis of the facet joint resulted from iatrogenic causes including corticosteroid injection3,7and epidural catheter-ization.8,9These infections can also occur secondary to spread from adjacent infections such as spondylodiscitis, epidural or paraspinal abscess, psoas muscle abscess or other intraabdominal infections. MRI has become the imaging modality of choice for diagnosis and determining extent of the infection. Timely and accurate diagnosis of septic arthritis of the facet joint followed by definitive therapy of this entity requires a multidis-ciplinary approach. Most cases are treated with up to 6 weeks of parenteral antibiotics, percutaneous drainage or open debridement depending on clinical symptoms and severity. While most patients typically experience some delay in diagnosis, the majority of patients fully recover or experience mild residual pain/neurologic sequela following appropriate therapy.1
The patient is a 57 year old male with a past medical history significant for type 2 diabetes mellitus who presented to an outside hospital with a three week history of left shoulder and neck pain after a trial of analgesics and muscle relaxants did not improve his symptoms. The patient was afebrile with no focal neurological deficits on physical exam. He had a normal white blood cell count with elevated Erythrocyte Sedimentation Rate (ESR) of 91 (normal 0-15 MM/HR) and C-reactive protein (CRP) of 3.2 (normal <0.5 Mg/Dl). Cervical spine MRI revealed left C5-C6 facet joint septic arthritis with extension of the infection into the paraspinal musculature, prevertebral soft tissues and epidural space with abscess formation and spinal canal narrowing. (Figure 1, Figure 2, and Figure 3).
The patient was then transferred to the University of Iowa for further care. He was started on IV Vancomycin and Ceftriaxone. Cultures from a CT guided aspiration (Figure 4) revealed Staphylococcus aureus as the causative agent. As the patient had no neurolgic deficits, negative blood cultures and no signs of sepsis, he was placed on IV Vancomycin for 6 weeks followed by two weeks of oral Linezolid by the Infectious Disease service. The patient remained afebrile, his pain subsided and the ESR and CRP returned to normal within a few weeks. Six week follow up MRI showed resolution of the abscesses and decreased soft tissue enhancement. There was no evidence of infection on the six month follow up study as well.
Septic arthritis is most commonly secondary to a bacterial infection with less common, more indolent infections resulting from fungal or mycobacterial causes. Predisposing factors include elderly patients, diabetes mellitus, immunosuppressed patients, rheumatoid arthritis, skin infection, IV drug abuse, and previous joint manipulation including joint prosthesis, recent joint surgery and intra-articular corticosteroid injections.10 Septic arthritis is caused by hematogenous spread (where the presenting sign can be bacterial endocarditis), direct inoculation of the joint from corticosteroid injection, surgery or trauma, or from spread of adjacent infection into the joint space. One retrospective review of 191 cases of septic arthritis found that 72% of cases were thought to arise from hematogenous spread.nThe majority of cases in adults is caused by Staphylococcus aureus and occur in the larger peripheral joints including knees, wrists, shoulders, elbows, ankles and hips. Smaller joints are rarely affected including the sternoclavicular joint, sac-roiliac joint, pubic symphysis and the spinal facet joint.
One or more predisposing factors was seen in 38-58% of patients diagnosed with facet joint septic arthritis with the most common being concomitant infection and im-munosuppression (most notably diabetes mellitus, liver disease, transplant patients, long-term corticosteroid use and malignancy) P Another predisposing factor is underlying joint disease which is reportedly found in almost 50% of cases of septic arthritis.12 Related to underlying facet disease, there was a retrospective study where 209 consecutive lumbar spine MRIs were reviewed regardless of patient history or clinical indication which revealed that 41% of patients were found to have facet synovitis based on signal abnormality within the joint capsule and peri-articular region.13
A high index of suspicion is needed to prevent a delay in diagnosis and therapy. Mean time from symptom onset to diagnosis has been reported to be 36-43 days with a large range from 2 days to 6 months.1,14 This delay in diagnosis can result in increased patient morbidity and highlights the need for consideration of this disease in the differential diagnosis of patients presenting with neck/back pain, fever and with any of the risk factors discussed above. Further evaluation includes lab work up (white blood cell count, ESR, CRP, and blood cultures) followed by appropriate imaging studies.
Plain radiographs are not sensitive in diagnosing early disease as radiographic findings may not be evident for weeks to months following onset of symptoms.1,14-18 However there are a few reports where facet joint space widening suggesting joint pathology was noted at 4 and 21 days after onset of symptoms.14,15 Radionuclide studies including Technitium-99m MDP bone scan, Gallium-67, and In-111 labeled white blood cell scans have shown very high sensitivity for this entity as early as one week after onset of symptoms.2 Tc-99m MDP bone scan can be helpful for assessing osteoblastic activity or bony remodeling secondary to infection. However, the low specificity of this test limits its utility in diagnosing septic arthritis. Ga-67 and more recently In-111 are being used to evaluate for infection/inflammation with very high sensitivity, more specificity than Tc-99m bone scans and improved spatial resolution with the implementation of SPECT and co-registered SPECT-CT images.
Non-contrast CT is able to show joint space widening, pre-existing joint disease, bony erosions and either a fluid collection or soft tissue air that could suggest abscess formation. CT is also very helpful for establishing the diagnosis via obtaining synovial fluid for isolation of the organism and for drainage of the affected joint. MRI is the imaging modality of choice for diagnosing facet joint septic arthritis due to its high sensitivity, specificity and soft tissue contrast.15,17,19-20 MRI is also essential for therapeutic planning.
Soft tissue gadolinium enhancement may be seen on MRI within 2 days from the onset of symptoms.17 Reportedly 81% of cases show epidural and/or paraspi-nal extension of the infection,1 and MRI is superior at demonstrating extension into the epidural or disc spaces, paraspinal soft tissues, vertebra and abscess formation. Many case reports of facet joint septic arthritis are associated with epidural or paraspinal abscesses.1,2,5-8,15,19-23 It may be difficult to distinguish on imaging whether the infection started in the facet joint or if the infection spread to the facet joint. Some authors have postulated that the incidence of this infection may be underestimated if the infection decompresses into the surrounding paraspinal tissues or epidural space prior to diagnosis.17
Facet joint septic arthritis should be considered when a patient presents with back pain, fever and elevated inflammatory markers (ESR and CRP), however the presentation and at risk populations are nearly identical to that of spondylodiscitis. Over 90% of patients present with pain, roughly 75% present with fever and about 33-50% present with neurologic symptoms. Facet joint septic arthritis may be suspected in patients with unilateral symptoms or when there is a more rapid symptom progression (4 weeks) compared to the typical presentation of the more common spondylodiscitis (2-3 months).2 Other differential diagnosis considerations include non-pyogenic infection such as Tuberculosis, degenerative or inflammatory arthritis and malignancy. Lytic or destructive lesions involving the posterior elements are most often neoplastic in etiology. One retrospective study using CT to determine infection vs. tumor in the spine noted that severe neurological impairment was more common with spinal infection (39%) than tumor (14%).24
Complications of septic arthritis of the spinal facet joint include chronic pain, joint/bony destruction, pyomyositis, abscess (epidural, psoas muscle and paraspinal), neurologic sequelae, spondylodiscitis, endocarditis, meningitis, septic emboli and rarely death. In one review of 42 patients excluding cases involving pediatric patients, IV drug users and prior surgical instrumentation/surgery, the most severe complications were paraplegia in one patient and death during surgery in another patient.1 The majority of patients in the case reports recovered fully or had minimal residual pain following treatment.
Patients are typically treated with long-term (at least 6 weeks) parenteral antibiotics followed by oral antibiotics or a combination of percutaneous drainage and long-term antibiotics. Open arthrotomy and surgical drain-age/debridement is typically reserved for the patient with infection refractory to antibiotic trial or with acute neurological compromise. MRI is less helpful in assessing for treatment response as soft tissue enhancement can persist following clearance of infection. Treatment response can be assessed using the patient's subjective improvement in symptoms and improvement in inflammatory serum markers.
In conclusion, septic arthritis of the facet joint is an uncommon infection that requires a high clinical suspicion for accurate and timely diagnosis. This infection shares many features with septic arthritis in the more commonly affected large peripheral joints as well as with spondylodiscitis. The incidence of this entity is increasing and MRI will continue to play an important role in diagnosis and surgical planning. Lastly, while most patients recover with little or no neurologic sequlae, prompt diagnosis and definitive therapy are essential for decreasing patient morbidity and mortality.