Making minimally invasive THR safe: conclusions from biomechanical simulation and analysis.

The use of smaller surgical incisions has become popularized for total hip arthroplasty (THR) because of the potential benefits of shorter recovery and improved cosmetic appearance. However, an increased incidence of serious complications has been reported. To minimize the risks of minimally invasive approaches to THR, we have developed an experimental approach which enables us to evaluate risk factors in these procedures through cadaveric simulations performed within the laboratory. During cadaveric hip replacement procedures performed via posterior and antero-lateral mini-incisions, pressures developed between the wound edges and the retractors were approximately double those recorded during conventional hip replacement using Charnley retractors (p < 0.01). In MIS procedures performed via the dual-incision approach, lack of direct visualisation of the proximal femur led to misalignment of broaches and implants with increased risk of cortical fracture during canal preparation and implant insertion. Cadaveric simulation of surgical procedures allows surgeons to measure variables affecting the technical success of surgery and to master new procedures without placing patients at risk.

Prolonged enoxaparin therapy to prevent venous thromboembolism after primary hip or knee replacement. Enoxaparin Clinical Trial Group.

BACKGROUND: Patients undergoing hip or knee joint replacement are at risk for venous thromboembolic complications for up to twelve weeks postoperatively. We evaluated the efficacy and safety of a prolonged post-hospital regimen of enoxaparin, a low-molecular-weight heparin, in this patient population. METHODS: Following elective total hip or knee replacement, 968 patients received subcutaneous enoxaparin (30 mg twice daily) for seven to ten days, and 873 were then randomized to receive three weeks of double-blind outpatient treatment with either enoxaparin (40 mg once daily) or a placebo. The primary efficacy end point was the prevalence of objectively confirmed venous thromboembolism or symptomatic pulmonary embolism during the double-blind phase of treatment. RESULTS: Of the 873 randomized patients, 435 underwent elective total hip replacement and 438 underwent elective total knee replacement. Enoxaparin was superior to the placebo in reducing the prevalence of venous thromboembolism in patients treated with hip replacement: 8.0% (eighteen) of the 224 patients treated with enoxaparin had venous thromboembolism compared with 23.2% (forty-nine) of the 211 patients treated with the placebo (p < 0.001; odds ratio, 3.62; 95% confidence interval, 2.00 to 6.55; relative risk reduction, 65.5%). Enoxaparin had no significant benefit in the patients treated with knee replacement: thirty-eight (17.5%) of the 217 patients treated with enoxaparin had venous thromboembolism compared with forty-six (20.8%) of the 221 patients treated with the placebo (p = 0.380; odds ratio, 1.24; 95% confidence interval, 0.76 to 2.02; relative risk reduction, 15.9%). Symptomatic pulmonary embolism developed in three patients, one with a hip replacement and two with a knee replacement; all had received the placebo. There was no significant difference in the prevalence of hemorrhagic episodes or other types of toxicity between the enoxaparin and placebo-treated groups. CONCLUSIONS: Prolonging enoxaparin thromboprophylaxis following hip replacement for a total of four weeks provided therapeutic benefit, by reducing the prevalence of venous thromboembolism, without compromising safety. A similar benefit was not observed in patients treated with knee replacement.

Anti-infective efficacy of antiseptic-coated intramedullary nails.

The coating of medical devices with antimicrobial agents has recently emerged as a potentially effective method for the prevention of device-related infections. We examined the anti-infective efficacy of intramedullary nails coated with an antiseptic combination of chlorhexidine and chloroxylenol in a rabbit model of device-related infection after fixation of an open tibial fracture. The rabbits were randomized to receive 2.8-by-100-millimeter stainless-steel tibial intramedullary nails that either were uncoated or were coated with antiseptic. After administration of anesthesia and preoperative antibiotic prophylaxis, a tibial fracture was created and then reduced with insertion of the intramedullary nail. A bacterial inoculum of 10(6) colony-forming units of Staphylococcus aureus was injected into the intramedullary canal, and the wound was sutured. Radiographs of the tibiae were made postoperatively, and the rabbits were monitored daily. They were killed at six weeks, or earlier if there was dehiscence of the wound, the fracture became grossly unstable, or the rabbit failed to thrive. The use of the antiseptic-coated nails was associated with a significantly lower rate of device-related osteomyelitis (two of twenty-two; 9 per cent) than the use of the uncoated nails (thirteen of twenty-one; 62 per cent) (p = 0.0003). The radiographic and histopathological findings were generally similar in the two groups of rabbits. Antiseptic agents were not detected in serum. The results suggest that antiseptic-coated fracture-fixation devices provide significant local protection against Staphylococcus aureus, which is the most common cause of infections related to orthopaedic devices.

Antibiotic therapy for diabetic foot infections: comparison of two parenteral-to-oral regimens.

This prospective, randomized, multicenter trial compared the efficacy of two antibiotic regimens for treatment of foot infections in diabetic adults. Patients with infections requiring hospitalization were randomized to receive either intravenous ofloxacin followed by oral ofloxacin or intravenous ampicillin/sulbactam followed by oral amoxicillin/clavulanate (the aminopenicillin regimen) for 14-28 days. Patients with osteomyelitis were eligible for the study if the infected bone was to be removed. Of 108 patients enrolled in the study, 88 who were evaluable had various skin and soft-tissue infections, and 24% had osteomyelitis. For the ofloxacin and aminopenicillin regimens, the mean duration of intravenous therapy was 7.8 and 7.1 days, respectively, the mean duration of oral therapy was 13.2 and 12.0 days, respectively, the rate of eradication of pathogens was 78% and 88%, respectively, and the overall rate of clinical cure or improvement was 85% and 83%, respectively. Thus, about 3 weeks of therapy with either regimen was well tolerated and effective in treating these diabetic foot infections.

Role of Staphylococcus aureus surface adhesins in orthopaedic device infections: are results model-dependent?

Bacterial colonisation of prosthetic material can lead to clinical infection or implant failure, or both, often requiring removal of the device. Adherence of Staphylococcus aureus to bioprosthetic materials is mediated by adhesins belonging to the MSCRAMM (microbial surface components recognising adhesive matrix molecules) family of microbial cell surface proteins. The objective of this study was to compare the virulence of a mutant strain of S. aureus Newman that possesses all three fibrinogen-, fibronectin- and collagen-binding MSCRAMMs (MSCRAMM-positive strain) with that of a mutant strain that lacks all three types of MSCRAMMs (MSCRAMM-negative strain) in a rabbit model of orthopaedic device-related infection. After a hole was drilled into the knee joint of each animal, a group of 10 rabbits was inoculated with the MSCRAMM-positive strain and another group of 10 rabbits received the MSCRAMM-negative strain. A stainless steel screw was then placed into the drilled hole. Two weeks later, the rabbits were killed and serum samples, bone tissue and implants were harvested for bacteriological and histopathological evaluation. No significant difference in infection rates was demonstrated between the two groups. The ability to delineate the role of S. aureus surface adhesins in causing orthopaedic device-related infection could be model-dependent.

Efficacy of antibiotics alone for orthopaedic device related infections.

Treatment of orthopaedic device related infections with antibiotics alone generally has been thought to be inadequate. A rabbit model was used to compare the efficacy of 4 different antibiotic regimens for treating orthopaedic device related infection caused by slime producing Staphylococcus epidermidis. After bacterial inoculation of a hole drilled through the intercondylar notch, a stainless steel screw was placed into the femur. Two weeks later, rabbits were randomized to receive a 2-week course of antibiotics: (1) 9 rabbits received vancomycin alone; (2) 10 rabbits received minocycline alone; (3) 10 rabbits received vancomycin plus rifampin; and (4) 10 rabbits received minocycline plus rifampin. Quantitative bone cultures were performed, and antibiotic levels in serum, bone, and biofilm were determined. Despite high levels of vancomycin in biofilm, infection was never cured by vancomycin alone and was eradicated in only 20% of rabbits that received minocycline alone. The highest cure rate (90%) was achieved with the combination of vancomycin and rifampin, whereas the combination of minocycline and rifampin yielded a cure rate of 70%. These results encourage the clinical evaluation of the combination of vancomycin and rifampin in patients in whom infected orthopaedic device cannot be removed.

Vancomycin penetration into biofilm covering infected prostheses and effect on bacteria.

To evaluate the adequacy of penetration of antibiotics into biofilm, a novel in vitro model for prosthesis-related infection was developed. Sterile stainless steel orthopedic nuts were incubated with slime-producing Staphylococcus epidermidis. Biofilm-covered nuts were exposed to varying concentrations of vancomycin; then biofilms were harvested. Vancomycin levels in biofilm, as measured by fluorescent polarization immunoassay, far exceeded the MIC and MBC of vancomycin for the organism. Bacterial growth in biofilm was inversely related to vancomycin concentration in biofilm, but even extremely high drug concentrations did not eradicate bacteria embedded in biofilm. The MICs and MBCs for bacteria recovered from biofilm did not differ from those for incubating organisms. Thus, failure of glycopeptide antibiotics to cure prosthesis-related infection is not due to poor penetration of drugs into biofilm but likely due to diminished antimicrobial effect on bacteria in the biofilm environment.

The current spectrum of Staphylococcus aureus infection in a tertiary care hospital.

Staphylococcus aureus remains a prominent cause of community- and hospital-acquired infection. This study reviewed 162 cases of S. aureus infection occurring in 120 adults who were hospitalized at a Veterans Affairs Medical Center and referred for consultation to the Infectious Disease Service. There were 37 cases of skin and soft tissue infection, 5 pyomyositis, 34 osteomyelitis, 13 septic arthritis, 19 pneumonia, 3 empyema, 5 pyelonephritis, 37 vascular infection, 3 epidural abscess, and 6 miscellaneous infections. Bacteremia was documented in 56 of 119 (47%) cases in which blood cultures were obtained, indicating the serious nature of the infections in many cases. Staphylococcus aureus is widely prevalent in healthy persons. Given its ubiquity and the capacity to cause a broad array of infections, an effective host response must play an important role in preventing infection. This host response is immunologically nonspecific, in that it depends upon the effectiveness of mechanical barriers to invasion and, once invasion takes place, the interaction of PMN, complement, and antibody that is probably present in serum of all immunologically competent adults rather than sensitization of B or T lymphocytes by any identifiable antigens specific to S. aureus. Analysis of the present cases calls attention to S. aureus as an opportunistic pathogen, 1 that only infrequently causes serious infection in otherwise healthy persons. Nearly every patient in this series had 1 or more medical condition thought to predispose to infection; 279 such conditions were identified, representing an average of 2.3 per person. A break in the natural barrier to infection was also present in the majority of cases, for example, trauma, wound, or pre-existing decubitus ulcer in skin and soft tissue infections; endotracheal tube in pneumonia; and a catheter bypassing urethra or skin in urinary and vascular infections, respectively. The tendency for patients to be infected with S. aureus repeatedly (mean number of infections, 1.4 per patient) reflects the chronicity of many predisposing factors and, perhaps, of colonization as well. Staphylococcus aureus has a special predilection to cause infections involving prosthetic devices, perhaps related to its affinity for fibronectin, laminin, and other serum proteins that can mediate attachment to foreign material; 46 of 162 (28%) infections were associated with the presence of a foreign body. Such infections are difficult to eradicate with antibiotic therapy alone, perhaps because of a change in the metabolic state of adherent bacteria, and removal of the foreign body is generally required for cure.(ABSTRACT TRUNCATED AT 400 WORDS)

Osteomyelitis associated with pressure sores.

BACKGROUND: Pressure sores may be associated with underlying osteomyelitis that is difficult to differentiate clinically from infection or colonization of adjacent soft tissue. Cultures of bone specimens are frequently contaminated with organisms residing in adjacent soft tissue. The three objectives of this cohort study were to (1) determine the accuracy of clinical evaluation for osteomyelitis; (2) evaluate the potential role of quantitative cultures of bone in differentiating osteomyelitis from soft-tissue infection or colonization; and (3) assess the impact of treating osteomyelitis on the outcome of pressure sores. METHODS: Thirty-six patients with pressure sores related to spinal cord injury or cerebrovascular accident underwent clinical evaluation for osteomyelitis, followed by percutaneous needle biopsy of bone. Routine semiquantitative and quantitative, aerobic and anaerobic cultures of bone specimens were performed. Pathologic examination of bone tissue was used as the standard criterion for diagnosing osteomyelitis. RESULTS: Six (17%) of 36 patients were diagnosed by pathologic examination as having osteomyelitis. The sensitivity and specificity of clinical evaluation were 33% and 60%, respectively. When positive, quantitative bone cultures yielded a similar number of bacterial isolates and a comparable range of bacterial concentration in patients with osteomyelitis vs those without osteomyelitis. Pressure sores healed in all six patients with osteomyelitis after appropriate therapy. CONCLUSIONS: Clinical evaluation for osteomyelitis is often inaccurate. Pathologic examination of bone tissue is required for definitive diagnosis of osteomyelitis. Quantitative bone cultures do not help differentiate osteomyelitis from infection or colonization of adjacent soft tissue. It is possible that treatment of osteomyelitis may improve the outcome of associated pressure sores.

Amputation after failed total knee arthroplasty.

From 1983 to 1992, nine above-knee amputations were performed in eight patients for complications after total knee arthroplasty. The mean time from the initial knee replacement to amputation was 9.7 years. The average age of the four men and four women was 72 years. Eight knees had chronic infection and one had intractable pain after four revision attempts for aseptic loosening. Most patients had two revision arthroplasties after the original implant. In this series, the common factors that lead to amputation were multiple revision attempts in the presence of chronic infection, severe bone loss, and intractable pain. Earlier consideration of arthrodesis rather than multiple revision attempts is recommended to avoid such a poor outcome.

Antimicrobial treatment of osteomyelitis.

Parenteral antibiotic therapy remains the mainstay of antimicrobial therapy for osteomyelitis. In acute cases, empirical treatment may be used initially, but antibiotic selection should ideally be based on deep aspiration or bone cultures with corresponding in vitro sensitivity testing. The drug exhibiting the highest bacteriocidal activity with the least toxicity and lowest cost should be chosen. Antibiotic treatment will not substitute for surgical debridement of infected devitalized bone. The length of treatment with parenteral therapy remains controversial. The six-week benchmark, which was determined largely by experience with childhood hematogenous osteomyelitis, may not be applicable to contiguous focus osteomyelitis after trauma in adults. The goal of surgical treatment is to convert an infection with dead bone to a situation with well-vascularized tissues that are readily penetrated by blood-borne antibiotics, making prolonged drug treatment unnecessary.

Total hip arthroplasty following failed internal fixation of hip fractures.

A retrospective review was performed on 27 consecutive patients with total hip arthroplasty (THA) following failure of internal fixation of fractures of the proximal femur. The results were comparable to primary THA in femoral neck fractures. Considerably less satisfactory results were obtained in THA in intertrochanteric fractures. Bone loss and medial displacement of the femoral shaft led to high incidence of intraoperative complications and postoperative dislocations. Extreme care must be taken to avoid fracture and penetration of the femoral shaft. Autograft, allograft, or head and neck replacement components should be available for reconstruction of the difficult cases.

Arthrodesis with dual plates after failed total knee arthroplasty.

Eleven patients were treated by arthrodesis with dual compression plates after failed total knee arthroplasty. All patients had a solid fusion, at an average of 5.6 months after the operation. The complications included one femoral stress fracture and one persistent infection, both of which were treated successfully. Fixation with dual compression plates is a useful technique for the salvage of a failed total knee arthroplasty, even when the patient has an infection. Staggering of the plates may help to prevent late stress fractures.

Elution of vancomycin, daptomycin, and amikacin from acrylic bone cement.

Increasing antibiotic resistance of bacteria that infect prosthetic joints has stimulated interest in the incorporation of more effective antimicrobial agents into polymethylmethacrylate (PMMA). Vancomycin and daptomycin are effective against nearly all staphylococci and streptococci, and amikacin has a broader spectrum against gram-negative bacilli than do other aminoglycosides such as gentamicin. These three antibiotics maintained bioactivity after incorporation into several commonly used preparations of PMMA and eluted readily into the surrounding medium. Preparing PMMA under negative atmospheric pressure, which decreases porosity, caused a 50% reduction in antibiotic release; the addition of 25% dextran, which increases porosity, greatly facilitated elution of these antibiotics. Based on their broad antibacterial effect against gram-positive and gram-negative bacteria, inclusion of vancomycin and amikacin in PMMA merits clinical study. The addition of these antibiotics to PMMA, together with dextran, may be applicable when structural integrity is unimportant but a substantial local antimicrobial effect is desired, such as in the use of antibiotic-containing beads to treat osteomyelitis.

Epithelioid sarcoma. An analysis of fifty-one cases.

Analysis of the cases of fifty-one consecutive patients who had an epithelioid sarcoma revealed the five-year rate of survival to be approximately 70 per cent and the ten-year rate, approximately 50 per cent. The five-year rate of survival was about 40 per cent for the male patients and about 80 per cent for the female patients. If the primary tumor was more than three centimeters in diameter or was deeply situated, the patients had a reduced life-span, as did the patients in whom the tumor was focally necrotic. More male than female patients had necrosis of the tumor, as seen on the pathological specimens. No significant difference in life-span was noted among the patients in whom the resection had a marginal, wide, or radical surgical margin. The data indicate that wide or radical resection should be done as soon as epithelioid sarcoma is diagnosed.

Salvage of infected total knee arthroplasty.

Between 1981 and 1986, 25 patients with 26 infected total knee arthroplasties (TKAs) were treated with complete debridement of the knee, prosthetic removal, and six weeks of intravenous antibiotics, followed by insertion of a new prosthesis. The patients were followed for 12-57 months (average, 29 months). There was no evidence of residual infection at follow-up examination in any case. Applying the Hospital for Special Surgery knee rating system, 12 patients (50%) were rated excellent, six patients (25%) good, two patients (9%) fair, and four patients (6%) poor. Of the six patients with fair and poor results, five had reduced scores due to joint problems unrelated to the infected TKA. Fourteen patients had no pain at follow-up examination, and four had only slight pain. Nine patients had no limp, ten had a slight limp, one had a moderate limp, and the remainder either had a severe limp or were bedridden due to other joint problems. Eight patients could walk an unlimited distance and four could walk at least one-half mile. Twenty-one knees had a range of flexion greater than 90 degrees. Three patients had extensor lags of 20 degrees or greater. Only one patient required bracing for ambulation.

Noncemented total knee arthroplasty.

Extensive animal experimentation has proven porous titanium fiber composite to be an effective interface for direct attachment of prosthetic devices via bone ingrowth. Titanium has demonstrated excellent biocompatibility in long-term primate experiments. Utilizing this technology, a cementless total knee system has been developed. A pilot study of 34 knees demonstrated the feasibility of anchoring the tibial component without cement. A totally cementless unconstrained total knee replacement was designed with porous titanium fiber composite interfaces. Retention of the posterior cruciate ligament was an essential part of the design. A large range of sizes was chosen to allow precise fitting of individual patients with distribution of load over the maximum surface available. Early clinical results have been very encouraging. Patients have achieved excellent pain relief, rapid return of function, and range of motion exceeding previous designs.

Essay on total knee arthroplasty.

Patient selection in total knee arthroplasty can be a difficult problem for the surgeon. It appears that more young patients are appearing with advanced arthritis of the knee than in the past. Many patients have had previous knee injuries resulting in premature development of degenerative arthritis. The authors believe that in selected cases total knee arthroplasty may be offered to younger patients. Young patients incapacitated by rheumatoid or inflammatory arthritis should not be denied reconstruction by total knee arthroplasty. The problem arises in the more active patient in his forties or fifties who has advanced arthritis of the knee not suitable for treatment by other means. The authors believe that these patients should not be treated by conventional total knee arthroplasty. On an experimental basis, the authors have been performing cementless total knee arthroplasty in younger, more active patients with disabling arthritis. Precision of surgical technique is critical with the newer cementless type of knee replacement.