Refractory Ankle Pain: A Case of Septic Arthritis
Vignette
A 51-year-old male with a history of uncontrolled Type 2 Diabetes presents to the ED with refractory left ankle pain. The patient had been evaluated in an urgent care three days prior and discharged with a steroid pack and NSAIDs, however, his pain continued to worsen. His vital signs are stable, however he reports subjective fevers. On physical exam, his left ankle is warm, swollen, with exquisite tenderness and limited range of motion in all planes. What is the gold standard test for the suspected diagnosis?
A. Bone biopsy
B. MRI with contrast
C. Arthrocentesis
D. Medical history and physical exam
Introduction
Septic arthritis is a painful infection involving the joints of the body that may stem from a local penetrating injury (bite, drug injection, prior joint replacement, trauma, etc.) or another infection in the body, such as a urinary tract infection or bacteremia, that spreads through the bloodstream to seed a joint. While uncommon (2-10 cases per 100,000 per year), the incidence of septic arthritis appears to be increasing, possibly due to an aging population, increased antibiotic resistance, and the use of immunosuppressive agents.[1]Kalagate R, Rivera A, Pritchard CH, Brent LH. Thu0369 septic arthritis: Changing trends in epidemiology over two decades. Annals of the Rheumatic Diseases. … Continue reading Septic arthritis is a must rule out diagnosis, especially when accompanied by cardinal signs of inflammation, including redness (rubor), swelling (tumour), heat (calor), pain (dolor) and loss of function (functio laesa). The ankle (8.6%) is the fourth most involved joint in septic arthritis, following the knee (45.7%), hip (31.4%), and shoulder (11.4%).[2]Mue D, Salihu M, Awonusi F, Yongu W, Kortor J, Elachi I. The epidemiology and outcome of acute septic arthritis: A hospital based study. Journal of the West African College of Surgeons. … Continue reading If left untreated or treatment is delayed, septic arthritis can lead to joint degeneration and permanent damage.
Differential Diagnosis
- Musculoskeletal: fracture, ligament sprain, tendon strain/tendinitis, muscular strain, arthritis
- Integumentary: cellulitis
- Lymphatic: lymphedema
- Hematologic: hematoma
- Infectious: septic arthritis, osteomyelitis
- Autoimmune: rheumatoid arthritis
- Inflammatory: gout, pseudogout
Diagnosis
The gold standard test for diagnosing septic arthritis is arthrocentesis, also known as a joint aspiration of synovial fluid. Joint aspiration allows for the evaluation of joint white blood cell count (jWBC), differential count, cultures, Gram stain, and crystals in the synovial fluid.
Joint WBC (specificity of 0.88) has the best diagnostic value for septic arthritis(jWBC≥50,000/μL). WBC and ESR are poor tests with specificities of 0.55 and 0.11 respectively.[3]Li SF, Cassidy C, Chang C, Gharib S, Torres J. Diagnostic utility of laboratory tests in septic arthritis. Emergency medicine journal : EMJ. https://www.ncbi.nlm.nih.gov/pmc/article/PMC2658211/.
Point of care synovial lactate has been shown to perform similarly to the classic diagnostic marker of jWBC ≥50,000/μL with the added benefit of shorter time to diagnosis, however explicit guidelines with diagnostic cutoff values still have not been clearly established.[4]Shu E, Farshidpour L, Young M, Darracq M, Ives Tallman C. Utility of point-of-care synovial lactate to identify septic arthritis in the emergency department. The American Journal of Emergency … Continue reading
| Lab Marker[5]Luo TD, Jarvis DL, Yancey HB, Zuskov A, Tipton SC, Langfitt MK. Synovial cell count poorly predicts septic arthritis in the presence of crystalline arthropathy. Journal of Bone and Joint Infection. … Continue reading | Lab Value | PPV | NPV | Sensitivity | Specificity |
|---|---|---|---|---|---|
| Joint/Synovial WBC[6]Luo TD, Jarvis DL, Yancey HB, Zuskov A, Tipton SC, Langfitt MK. Synovial cell count poorly predicts septic arthritis in the presence of crystalline arthropathy. Journal of Bone and Joint Infection. … Continue reading | >50k or <50k | 32.6% | 92.9% | 61.2% | 79.9% |
| Gram Stain[7]Luo TD, Jarvis DL, Yancey HB, Zuskov A, Tipton SC, Langfitt MK. Synovial cell count poorly predicts septic arthritis in the presence of crystalline arthropathy. Journal of Bone and Joint Infection. … Continue reading | +/- | 82.4% | 89.7% | 28.6% | 99% |
| Synovial Lactate[8]Shu E, Farshidpour L, Young M, Darracq M, Ives Tallman C. Utility of point-of-care synovial lactate to identify septic arthritis in the emergency department. The American Journal of Emergency … Continue reading | >5 mmol/L >10 mmol/L | - | - | 55% 26% | 76% 97% |
| CRP[9]Hariharan P, Kabrhel C. Sensitivity of erythrocyte sedimentation rate and C-reactive protein for the exclusion of septic arthritis in emergency department patients. The Journal of Emergency Medicine. … Continue reading | >20 mg/L | - | - | 92% | - |
| ESR[10]Hariharan P, Kabrhel C. Sensitivity of erythrocyte sedimentation rate and C-reactive protein for the exclusion of septic arthritis in emergency department patients. The Journal of Emergency Medicine. … Continue reading | >10 mm/h >15 mm/h | - | - | 98% 94% | - |
Lateral ankle radiograph shows a large tibiotalar joint effusion (arrows).Lin, Hank M., et al. “Emergency joint aspiration: a guide for radiologists on call.” Radiographics 29.4 (2009): 1139-1158.
Imaging
Imaging is a standard part of any joint evaluation. The optimal imaging choice will depend on a multitude of factors, however plain radiographs and ultrasound are probably the most practical when evaluating a patient with suspected septic arthritis.
The following table demonstrates common findings seen on different imaging modalities when evaluating for septic arthritis:
Risk Factors
Risk factors for septic arthritis include, but are not limited to age >80 years, diabetes mellitus, rheumatoid arthritis, hip/knee prosthesis, joint surgery, and skin infection.[11]Kaandorp CJ, Schaardenburg DV, Krijnen P, Habbema JD, Van De Laar MA. Risk factors for septic arthritis in patients with joint disease. Arthritis & Rheumatism. 1995;38(12):1819-1825. … Continue reading
It is proposed that diabetes causes a functional immune deficiency that directly reduces immune cell function, therefore diminishing bacterial clearance and increasing infectious complications.[12] Frydrych LM, Fattahi F, He K, Ward PA, Delano MJ. Diabetes and sepsis: Risk, recurrence, and Ruination. Frontiers in endocrinology. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5670360/.
Management
Management includes early recognition and diagnosis with arthrocentesis. This allows for timely treatment with antibiotics and orthopaedic surgery consultation for surgical intervention. Due to the potential for rapid joint destruction, broad-spectrum antibiotics should be initiated early on pending cultures and sensitivities.[13]Long B, Koyfman A, Gottlieb M. Evaluation and management of septic arthritis and its mimics in the emergency department. Western Journal of Emergency Medicine. 2019;20(2):331-341. … Continue reading
Ankle Arthrocentesis
Illustration of palpation guided ankle arthrocentesis. The needle should be medial to the tibialis anterior tendon.[14]Image courtesy of merckmanuals.com, “How To Do Ankle Arthrocentesis”
Two approaches may be used for joint aspiration of the ankle: an anatomical approach and an ultrasound guided approach. For anatomical joint aspiration, two structures of the ankle must be identified: the anterior border of the medial malleolus and the tibialis anterior tendon.
The anatomical approach is discussed below:
- Palpate the anterior border of the medial malleolus and tibialis anterior tendon. The needle should be introduced between these two structures. To make the tibialis anterior tendon more prominent, dorsiflex the ankle and extend the toes.
- Mark your injection site before cleaning the area. Apply several layers of iodine, followed by alcohol to prepare the space. Use of sterile gloves is recommended.
- Use a 25-to-27-gauge needle to create a wheal of local anesthetic. Proceed to keep injecting down to the area of the joint capsule. Coolant may be used to alleviate the pain from the initial introduction of the needle.
- Introduce a 20-to-22-gauge needle in a perpendicular fashion to the shaft of the patient’s tibia. You may meet resistance with bone. In this case, withdraw slightly and redirect at a different angle. As you advance your needle past the half-inch mark, begin aspirating. Once fluid is aspirated into the syringe, the correct spot has been identified. If the fluid stops or slows down, consider advancing the needle more or retracting the needle and going at a slightly altered angle.
Case Conclusion
On admission, this patient’s plain radiograph imaging showed moderate soft tissue swelling with no soft tissue gas or radiographic evidence of osteomyelitis. CT of the lower extremity showed a fluid collection posterior to the lateral half of the subtalar joint with diffuse subcutaneous edema.
Synovial fluid analysis showed a jWBC of 76360 /mm3 with no crystals. Synovial lactate was not obtained. Gram stain showed many WBCs and few gram-positive cocci and aerobic body fluid cultures and wound cultures grew MSSA. His white count was elevated to 23.4 K/uL with a neutrophilic predominance (19.2 K/uL). CRP was elevated to 273.8 mg/L and SED rate of 67 mm/hr.
Ankle appearance after surgical intervention.
He was admitted to the medical team with orthopaedic and infectious disease consultation, received two I&D washouts, and had a PICC placed for 6 weeks of IV antibiotic administration upon discharge. At his one month follow up, he had reported significant improvements in pain, swelling, and range of motion.
– More Ankle Pain from Sports Medicine Review: https://www.sportsmedreview.com/by-joint/ankle/
– Read More @ Wiki Sports Medicine: https://wikism.org/Septic_Arthritis
Vignette Answer
In a patient with suspected septic arthritis, arthrocentesis of the joint is the diagnostic gold standard. Although imaging such as MRI and ultrasound are useful, they can not confirm the diagnosis. History and physical exam will increase or decrease your suspicion of SA. Bone biopsy is not indicated for SA, but may be used to help diagnose osteomyelitis in some patients.
References
