Case Presentation: A 69-year-old male with hypertension and chronic hip osteoarthritis (OA) was presented to the ED with worsening hip pain, lower back pain, and recurrent falls after he slipped in the shower and fell on his buttocks and back 3 weeks ago. CT of the lumbar spine and pelvis showed severe spinal stenosis in L3-4 and L4-5, and severe OA in both hips without effusion. His ESR was mildly elevated at 22mm/hr, with CRP at 181mg/L (normal range < 20). One isolated fever quickly resolved without evidence of infection being found, with normal WBC and Lactate at 4.4, which was back to normal level quickly without fluids or antibiotics given. All other labs were unremarkable, and he was admitted for pain control. His condition remained well and afebrile until 4 days later when he became lethargic and had less urine output. Repeated blood work found WBC at 20K/µL, lactate at 2.9mmol/L, total bilirubin at 5.7mg/dL, Creatinine up to 2.1mg/dl, CRP significantly increased to 404mg/L, and ESR at 50mm/hr. CT head/chest/abdominal and MRI hips were both unremarkable except for severe OA in both hips without effusion. Urgent bilateral hip aspiration turned out to be a “dry tap”, which requires saline injected into the joints, and broad antibiotics were started. Blood culture and fluid culture showed Streptococcus dysgalactiae. Surgery took him for left hip irrigation and debridement and found “very scant amount of purulence upon entering the joint capsule”. Hospitalization was complicated with respiratory failure requiring intubation, renal failure requiring hemodialysis, Psoas hematoma, and persistent encephalopathy slowly improving. His ambulatory function and mentation slowly improved 2 weeks after surgery.
Discussion: This report describes an unusual presentation with painful hips without signs of joint effusion on physical exam, CT, MRI, and “dry tap” on joint aspiration, as well as a normal WBC count and is afebrile. All the above makes the diagnosis of septic arthritis least likely. The only unexplainable work-up is elevated ESR and severely elevated CRP, which made his admission VS discharge debatable. Septic arthritis has been considered an urgent surgical indication to avoid permanent damage and disability. Sometimes it is hard to tell the difference between OA, inflammation, and infection purely based on clinical findings; so, imaging looking for joint effusion [1], or other signs such as pseudocapsule dehiscence and sinus tract, have been used frequently by clinicians to screen patients for joint aspiration to rule out septic arthritis. Although it is not rare to find “dry” septic arthritis in periprosthetic hip (physical exam, imaging, and joint aspiration), a “dry” joint in a native hip usually rules out septic arthritis in practice. Recently, a 10‑year retrospective study[2] including 215 patients with dry-tap hip aspiration showed that most patients with native hip who underwent joint aspiration with a dry tap were not infected. Both ESR and CRP being normal were only seen in 14.6% (27/185) of noninfected patients and no patients with an infected hip in the native hip group and periprosthetic group.
Conclusions: “Dry” septic arthritis in native hips is rare and not as well-known as in Periprosthetic hips. If septic arthritis of the native hips is suspected clinically, even if there is no evidence of joint effusion clinically or on imaging (CT, MRI) or aspiration, biomarkers including CRP and ESR are indicators that septic arthritis is likely. If both CRP and ESR are negative, it may help to rule out Septic arthritis.