TOTAL HIP REPLACEMENT: INFECTION
Subfascial (deep) infection, whether acute or latent, is a serious complication in joint replacement surgery. It is important to identify the type of infection because prognosis and treatment differ. Also, because any implant can become a focus for infection, patients with a hip prosthesis should be given preventive antibiotics when undergoing dental, urinary, or gastrointestinal procedures.
Any unexplained wound or hip pain in the early post-operative period should arouse suspicion. Acute infections are easiest to diagnose because they manifest classic systemic and local signs of sepsis. Diagnosis of latent infections is more difficult because clinical and radiographic signs are similar to those seen in aseptic loosening of the prosthesis.
Strong indications of a suprafascial infection are pain at the incision site, inflammation, and drainage in the first 2 weeks after surgery; fever and leukocytosis may also be present. Daily surgical wound care is therefore essential. Suprafascial infections respond well to drain- age and debridement.
Symptoms of subfascial (deep) infections may include swelling of the thigh, increased hip pain, and elevated leukocyte count with an increased proportion of neutrophils. Accurate diagnosis depends on culture of aspirated fluid to isolate the causative organism. Blood cultures are also indicated. If the culture results are positive, surgical debridement and intravenous administration of antibiotics should be instituted immediately.
Acute subfascial infections cause a variety of signs and symptoms, depending on the organism’s virulence and the patient’s immunologic status. Because long-term postoperative administration of antibiotics can mask the appearance of symptoms, preventive intravenous administration of antibiotics should not be continued for more than 48 hours after surgery.
Acute deep infections must be treated aggressively with intravenous administration of antibiotics and fluid replacement, as well as immediate open debridement of the implant site. Because most nosocomial gram-positive cocci have become resistant to penicillin, early treatment with a penicillinase-resistant synthetic penicillin or cephalosporin is necessary until the drug sensitivity of the organism is determined. If the infection is controlled early enough, it may be possible to save the prosthesis. If the infection is intractable or is due to antibiotic-resistant organisms, the prosthesis must be removed. Secondary acute hematogenous infections can occur after months or years, with or without septicemia and sudden onset of hip pain.
Latent infections do not usually become evident until at least 12 weeks after surgery. They should be suspected if the patient is not recovering normally. Delayed primary infections may be due to bacterial contamination from a remote body source (mouth, urine, bowel), in the perioperative period. There may be no fever or elevated leukocyte count, although the erythrocyte sedimentation rate and C-reactive protein level are usually elevated. In a long-standing infection, radiographs may show osteopenia and a radiolucent zone around the implant. Results of bone scans are positive for both infection and a loosened implant, but the pattern of radioisotope uptake is sometimes specific enough to differentiate between the two conditions.
Treatment. Removal of the prosthesis with a temporary hip spacer is the treatment of choice. Intravenous administration of antibiotics to establish adequate bactericidal levels as confirmed by tube dilution sensitivity studies should be instituted for 4 to 6 weeks. Before revision surgery, histologic examination of local tissue is needed to ensure that the infection has been controlled.
Some organisms are so virulent and difficult to eradicate that a new implant can never be placed for fear of recurrent infection. A Girdlestone resection arthroplasty may be the only alternative procedure. Pain, severe limb shortening, and concomitant gross instability of the hip are serious disadvantages.