Total Knee Replacement Complication, ABOS Oral Boards Preparation

This is a 64-year-old male retired postal worker who I saw 14 months after his right total knee arthroplasty, which I had performed at our institution for tricompartmental osteoarthritis. He had an excellent early result, pain-free with 0 to 125 degrees of motion at his six-week visit. Then at six months, he developed insidious onset of knee pain, swelling, and stiffness. No preceding dental procedures, no remote infections, no trauma. His temperature was 99.1 degrees. That timeline, a pain-free interval followed by insidious deterioration, immediately raises my suspicion for a chronic periprosthetic joint infection.

On exam, the right knee had a moderate effusion and was warm compared to the other side. Range of motion had declined to 5 to 95 degrees. The wound was well-healed without erythema or drainage. Labs showed a CRP of 28 and an ESR of 42, both elevated.

Radiographs showed a well-fixed cemented total knee without loosening, fracture, or malposition. Normal-appearing radiographs do not rule out infection, chronic PJI can present with well-fixed components.

I held antibiotics and performed an aspiration under sterile conditions. The aspirate was sent for cell count, differential, culture, and alpha-defensin. Synovial WBC was 12,400 with 89% PMNs, both exceeding the MSIS threshold for chronic PJI. Alpha-defensin was positive. Cultures grew coagulase-negative Staphylococcus after three days. This meets the ICM criteria for periprosthetic joint infection.

I discussed the diagnosis with the patient honestly and directly. This is a complication of his surgery and I owned that conversation. I explained that a chronic infection at 14 months is best treated with a two-stage exchange arthroplasty.

First stage: I performed explantation of all components and cement, aggressive debridement, and placed an antibiotic-loaded cement spacer. I sent five tissue cultures from different locations. Intraoperative cultures confirmed coagulase-negative Staphylococcus. He was started on IV vancomycin based on sensitivities.

He completed six weeks of IV antibiotics followed by six weeks of oral suppressive antibiotics. I monitored his CRP and ESR serially, they normalized by week eight. At the pre-reimplantation visit, his knee was cool, dry, and comfortable. I re-aspirated the knee, synovial WBC was 400 with a negative culture.

I performed second-stage reimplantation with revision components. Intraoperative frozen sections showed fewer than 5 PMNs per high-power field. Final cultures were negative. At six weeks post-reimplantation, he was doing well with 0 to 110 degrees of motion. At six months, he had minimal pain, inflammatory markers remained normal, and he was satisfied with his outcome.

He was satisfied with the outcome, and I was candid with him throughout the process. Looking back, I would have aspirated the knee earlier in his course. He presented at 14 months with six months of insidious symptoms, which means the infection may have been present as early as eight months post-op. A lower threshold for aspiration at the first sign of unexplained pain and swelling, even with normal-appearing radiographs, would have allowed earlier diagnosis. I followed him with serial inflammatory markers for two years after reimplantation to confirm eradication, and he remained infection-free.