Chapter Synopsis

Patients with infection after total hip arthroplasty can present with a wide spectrum of symptoms and findings. Evaluation of the patient with a potentially infected total hip arthroplasty includes a clinical history, physical examination, laboratory and imaging studies, aspiration, and intraoperative soft tissue frozen sections. Early postoperative or acute hematogenous infection can be treated with incision and drainage, whereas late infection requires removal of the components. Two-stage revision total hip arthroplasty is an effective treatment for chronic infection, with success rates of 80% to 95%.

Important Points:

• 1
  

  Serous drainage after total hip arthroplasty does not necessarily indicate infection, but is associated with an increased risk of developing infection. If infection develops after total hip arthroplasty, early incision and drainage can be effective to salvage the total hip arthroplasty.

  
  
• 2
  

  Patients with infection after total hip arthroplasty may present with a wide spectrum of symptoms. Erythrocyte sedimentation rate and C-reactive protein levels should be obtained in patients suspected of having infection. If these levels are elevated, additional testing with nuclear imaging studies, aspiration, and intraoperative soft tissue frozen section analysis should be considered. Multiple testing modalities often are needed to establish the presence or absence of infection.

  
  
• 3
  

  Treatment of chronic infection after total hip arthroplasty requires removal of the implants to eradicate infection. Revision can be performed in one or two stages.

  
  
• 4
  

  Two-stage revision total hip arthroplasty permits use of cementless implants and is associated with success rates of 80% to 95%.

Clinical/Surgical Pearls:

• 1
  

  Incision and drainage with retention of the components is most effective if treatment is performed very soon after the onset of infection. The acetabular liner should be exchanged during incision and drainage to provide more thorough debridement without removal of the metallic components.

  
  
• 2
  

  Extended trochanteric osteotomy is helpful to permit wide exposure of the intramedullary canal for complete removal of the femoral implant and cement. Suture closure of the vastus lateralis provides adequate stability of the osteotomy in between the first and second stages of revision total hip arthroplasty. Delayed cerclage fixation of the osteotomy at second-stage revision total hip arthroplasty is associated with a high rate of healing.

  
  
• 3
  

  An antibiotic-impregnated cement spacer permits patient mobility in between the first-stage implant removal and second-stage revision total hip arthroplasty and provides local delivery of antibiotics. Larger doses of antibiotics can be used in handmade spacers compared with commercially available cements that contain antibiotics.

Clinical/Surgical Pitfalls:

• 1
  

  If wound drainage occurs and is increasing after total hip arthroplasty, early incision and drainage should be performed.

  
  
• 2
  

  None of the laboratory or imaging studies is completely accurate in establishing or ruling out infection. Multiple testing modalities should be considered when infection is suspected after total hip arthroplasty.

  
  
• 3
  

  Intraoperative periarticular soft tissue frozen section analysis is effective to determine the presence or absence of infection after total hip arthroplasty. However, frozen section analysis at the time of second-stage revision total hip arthroplasty (conversion of the spacer to total hip arthroplasty) is less accurate in determining if infection is still present.

Video Available:

“Antibiotic Cement Spacer Technique” (3:57)

INTRODUCTION

Postoperative infection is an inherent risk of any surgical procedure. The risk of infection after total hip arthroplasty (THA) is approximately 1%. Early postoperative infection can develop from wound contamination during surgery, whereas late infection typically results from hematogenous spread of bacteria. Many factors influence the risk of developing infection after THA. Lengthy surgical times and high traffic volume in the operating room have been implicated as sources of increased risk of infection; laminar air flow, ultraviolet lights, body exhaust suits, and preoperative antibiotics have been recommended to reduce the risk of infection. Patients with poor nutrition, immunosuppression, diabetes mellitus, prior infection, or obesity have an increased risk of developing postoperative infection. Patients who develop infection after THA may present with a wide spectrum of clinical symptoms, physical examination findings, and radiographic and laboratory studies, which can make the diagnosis of infection difficult to establish.

Treatment of early postoperative or acute hematogenous infection with debridement and retention of the components followed by intravenous antibiotic therapy allows salvage of the prosthesis. However, a high rate of failure may occur, particularly if the surgical treatment is delayed until 4 weeks after the onset of the infection. Treatment of chronic infection requires removal of the prosthetic components and revision THA either as a single procedure or two staged procedures. Removal of the components, placement of an antibiotic-impregnated cement spacer followed by a 6-week course of intravenous antibiotic therapy, and delayed revision THA are associated with success rates of 80% to 95% and considered the treatment of choice for management of chronically infected THA.

ACUTE POSTOPERATIVE WOUND DRAINAGE

Blood drainage from the wound after THA is common during the first few days after surgery. Once the skin begins to heal and the wound is sealed, drainage should diminish considerably. However, serous fluid drainage may continue for more than a week in some patients. The fluid likely originates from edema, blood debris, and ischemia in the subcutaneous layer but also may represent fluid drainage from the hip joint through the fascial layer.

The management of wound drainage depends on the location of fluid accumulation (superficial or deep) and presence or absence of infection ( Table 30-1 ). Serous drainage does not necessarily represent infection, but the expression of fluid through the surgical incision indicates that the wound is not healed. Incomplete wound healing indicates that the wound does not provide a complete barrier to bacterial contamination from the skin. Sterile dressings should be maintained on the wound and changed daily as often as necessary to collect wound drainage. When drainage is present the wound is at a higher risk of developing infection. However, if the drainage volume decreases daily and clinical signs of infection (fever, erythema, induration) are absent, the drainage can be treated with dressing changes alone and without antibiotics or surgical debridement. The use of antibiotics for management of a noninfected draining surgical wound is appropriate as a prophylactic measure to prevent infection because the wound is incompletely sealed and exposed to skin contamination. However, antibiotic therapy alone for treatment of a deep postoperative infection is not an effective method to eradicate infection. If deep infection is suspected and the source of wound drainage is not clear, antibiotics may suppress an infection and make the diagnosis more difficult to establish. Therefore the distinction between a draining wound that is not infected and one that is infected and draining either from the hip joint or subcutaneous layer is important.

EVALUATION OF THE CHRONICALLY INFECTED TOTAL HIP ARTHROPLASTY

A history of pain that developed immediately after surgery and persisted (no pain-free interval) is consistent with postoperative infection. The pain typically is worse with weight-bearing activity, particularly if associated with implant loosening, which results in a coxalgic gait. However, pain also can occur at rest. Hip pain typically is reproduced by passive hip flexion and internal rotation. The appearance of the wound may be quite variable. Swelling, erythema, induration, or sinus formation can be present if abscess fluid had developed. However, the wound also may appear benign with no outward signs of soft tissue inflammation.

Erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) measurements should be obtained in any patient being evaluated for a painful THA. If these values are elevated, deep periprosthetic infection may be present and additional evaluation with aspiration, nuclear medicine imaging, or intraoperative soft tissue frozen section analysis should be performed. However, negative ESR and CRP levels reliably indicate the absence of infection. Serum interleukin-6 levels also have been found to be elevated in patients with infected THA, so this test may be helpful in establishing the diagnosis of infection.

Radiographs can demonstrate changes suggestive of infection, such as bone cement radiolucency, periosteal reaction, and cortical thickening, if the infection has been chronic ( Fig. 30-1 ). However, radiographs often appear normal. Hip aspiration should be performed in patients with a moderate to high clinical suspicion of infection. When fluid is obtained, specimens should be sent for cultures as well as a cell count with differential.

A, A 78-year-old man underwent hybrid total hip arthroplasty for osteoarthritis. The anteroposterior (AP) radiograph 6 weeks after surgery shows no significant changes indicating infection. The patient continued to have pain 3 months after surgery and underwent aspiration, which was culture negative. B, Four months after surgery the patient continued to report pain. The 4-month postoperative AP radiograph shows that the collar of the prosthesis has subsided into the calcar (1) , a radiolucency has developed at the lateral proximal portion of the implant (2) , and bone erosion is present along the lateral distal endosteal cortex of the femur (3) . Two-stage revision total hip arthroplasty was performed. Intraoperative cultures grew Staphylococcus epidermidis consistent with a chronic postoperative infection.

Technetium (Tc) bone scan is a highly sensitive indicator of bone turnover and activity but it has low specificity. Increased uptake on ⁹⁹ Tc MDP can be seen with various conditions, including loosening, infection, heterotopic bone formation, stress fractures, modulus mismatch, tumors, metabolic bone disease, and reflex sympathetic dystrophy, so this test is not that helpful in distinguishing infection from other causes of pain after THA. Gallium citrate ( ⁶⁷ Ga), which is preferentially taken up by leukocytes, has been used in combination with Tc bone scans to differentiate between septic and aseptic loosening, although the sensitivity is still relatively low and this testing modality has been abandoned at most centers.

The use of indium-111 ( ¹¹¹ In)-labeled leukocyte scans to identify deep infection also has yielded disappointing results that have been reported to be only slightly better than with ⁶⁷ Ga scans. Scher et al used ¹¹¹ In-labeled leukocyte scans to study 143 hips and knees that had undergone reoperation for a painful or loose total joint arthroplasty or a prior resection arthroplasty. The positive predictive value was only 54%; however, the negative predictive value was 95%, suggesting that a negative scan is quite useful in predicting the absence of infection in a patient being evaluated for a painful total joint arthroplasty. The addition of ^99m Tc-labeled sulfur colloid marrow scanning has been used at some centers in an attempt to decrease the high rate of false-positive indium scans resulting from physiologic marrow packing that can cause an accumulation, slowing, or retardation of flow of (indium-labeled) leukocytes around a prosthesis, with some improvements. However, the sensitivity is still relatively low; thus all these tests are only used as a second line of investigation when the results of other testing modalities are unclear.

Preoperative joint aspiration to obtain fluid for culture and cell count analysis requires a fluoroscopic-guided arthrogram to confirm correct needle placement within the hip joint. Although a positive culture result often is diagnostic of infection, both false-positive and false-negative results can be obtained. Barrack and Harris reported on a series of 270 consecutive patients who underwent aspiration before revision THA. Six hips were subsequently found to be infected. This series had six true-positive results, four false-negative results, and 33 false-positive results, yielding a sensitivity of 60% and a positive predictive value of only 15%. These results indicate that routine joint aspiration is not an effective test to determine the presence of infection in patients who do not have other laboratory or clinical findings suggestive of infected THA. However, in patients who are suspected of having infection, aspiration can provide important diagnostic information because a positive culture also indicates a specific causative organism and antimicrobial sensitivity. Spangehl et al reported a sensitivity of 86%, specificity of 94%, positive predictive value of 67%, and negative predictive value of 98% for joint aspiration when patients receiving antibiotics were excluded. They recommended joint aspiration for patients with a clinical suspicion of infection and ESR or CRP level.

The cell count of aspirated joint fluid can provide additional evidence about the presence or absence of infection in a total joint arthroplasty. Most of the literature on cell count analysis has been obtained from studies of total knee arthroplasty. In addition, variation in reported cell concentrations suggests that some authors may not have reported the same units of volume. However, Parvizi et al analyzed 168 synovial fluid specimens, including 23 from THAs, 16 of which were infected, and found cutoff values for optimal accuracy in diagnosing infection of 1760 white blood cells/μL and 73% neutrophils. A cell fluid count of more than 1760 cells/μL had a positive predictive value of 99% and a negative predictive value of 88%. A neutrophil proportion of more than 73% had a positive predictive value of 96% and a negative predictive value of 91%, indicating that the cell count of aspirated joint fluid can be quite helpful in establishing or ruling out the diagnosis of periprosthetic infection.

Despite thorough preoperative evaluation, the diagnosis of infection may still be difficult to establish. Periprosthetic soft tissue specimens obtained during surgery and sent for culture analysis provide the most definitive diagnosis. However, culture results are not available for several days after surgery. Intraoperative histologic analysis of periprosthetic soft tissue frozen sections obtained during surgery can provide useful diagnostic information to establish or rule out infection. Lonner et al reported that when between 5 and 10 polymorphonuclear leukocytes per high power field (PMN/hpf) were identified, the sensitivity was 84% and the specificity was 99%. When 10 PMN/hpf were identified, the positive predictive value was 89%, indicating that at least 10 PMN/hpf were predictive of infection and less than 5 PMN/hpf reliably indicated the absence of infection.