A fifty-two-year-old woman with a history of insulin-dependent diabetes mellitus and hypertension presented to the emergency department (ED) with a three-day history of acute bilateral knee pain of atraumatic onset. She had undergone bilateral total knee arthroplasty for premature osteoarthritis seven years earlier (Figs. 1-A, 1-B, and 1-C), and she had been free of knee pain since the surgery. She had no history of crystalline arthropathy in any joint. On presentation, she reported pain with weight-bearing as well as decreased knee motion bilaterally. Seven days prior to presentation, she had undergone a dental procedure, which included standard antibiotic prophylaxis with amoxicillin. That evening, she had had an initial sensation of tightness in the knees that she described as “pressure,” which subsided after some rest and nonsteroidal anti-inflammatory medication. The knee pain worsened three days later, and after she began to feel febrile, she presented to the ED for evaluation.
On evaluation in the ED, the patient’s temperature was 38.6°C. Both knees were subjectively warm to touch; there was no erythema or drainage. She had joint-line tenderness bilaterally and palpable knee effusions. She had severe pain, even with minimal passive knee motion. The left knee ranged from 0° to 45° of flexion, while the right knee ranged from 0° to 20° of flexion. This marked a dramatic change compared with the excellent baseline knee motion prior to this incident. Anteroposterior and lateral knee radiographs obtained in the ED showed no osteolysis or fractures. Knee effusions were present on radiographs in both knees (Figs. 2-A through 2-D).
Laboratory values revealed a serum white blood-cell (WBC) count of 14,300/mm3. The systemic inflammatory markers were elevated, with a C-reactive protein (CRP) level of 5.4 mg/dl (normal, <1.0 mg/dl) and an erythrocyte sedimentation rate (ESR) of 32 mm/h (normal, 0 to 20 mm/h). Aspiration resulted in 40 cc of purulent-appearing fluid from the right knee and 50 cc from the left knee. Laboratory analysis of the aspirations resulted in a WBC count of 53,000 mm3 in the left knee and 81,750 mm3 in the right knee. No bacteria were seen on the immediate Gram stain. Rare CPP crystals were seen in the fluid samples from both knees.
Despite the high WBC counts in the knee aspirates, our initial plan for irrigation and debridement of suspected septic total knee arthroplasties was suspended. This decision was made in concert with the Infectious Disease team, which was consulted for treatment of likely septic arthritis. The time course and onset of pain, the bilateral nature of symptoms, and the presence of crystals in the aspirate led to the consideration of acute CPP crystal arthritis. The patient began indomethacin therapy, and the cultures were followed for growth. She reported a dramatic clinical improvement with use of the anti-inflammatory medication. The empiric antibiotics were discontinued after two doses. She steadily improved and was discharged from the hospital after final cultures resulted in no growth by day three. On discharge, she was fully weight-bearing, with bilateral knee motion ranging from −5° to 90° of flexion. The patient’s most recent follow-up eleven months later noted no recurrence of the symptoms, good overall knee function, and excellent knee motion.
Disclosure: None of the authors received payments or services, either directly or indirectly (i.e., via his or her institution), from a third party in support of any aspect of this work. None of the authors, or their institution(s), have had any financial relationship, in the thirty-six months prior to submission of this work, with any entity in the biomedical arena that could be perceived to influence or have the potential to influence what is written in this work. Also, no author has had any other relationships, or has engaged in any other activities, that could be perceived to influence or have the potential to influence what is written in this work. The complete Disclosures of Potential Conflicts of Interest submitted by authors are always provided with the online version of the article.