Postoperative Deep Wound Infection Research Articles

Implant Removal for the Management of Infection After Instrumented Spinal Fusion

We operated on 21 patients with a postoperative deep wound infection. All the patients underwent implant removal and wide debridement. One patient lost to follow-up was excluded. To reduce the number of debridements and manage uncontrolled spine infection. There are a few reports on the treatment for postoperative spinal infection after instrumented spine fusion with implant removal and wide debridement. The clinical outcomes were assessed using the Oswestry disability index, visual analog scale of pain and patients' satisfaction. The functional outcomes of the Oswestry disability index were minimal in 13 patients and moderate in 7 at final follow-up. The serial changes of visual analog scale score of pain in the back and leg showed statistically significant decline after operation. Patients' satisfaction outcomes were better in 16 patients and unchanged in 4. Six patients of the preoperative spinal fusion group included the patients that already had fusion mass well developed by the time of implant removal. Bony union was not achieved in any patient of the preoperative nonspinal fusion group (n=14) by the last follow-up. In nonspinal fusion group, mean lordotic angle before the operation was 41 degrees decreasing after the operation to 39 degrees. At the final follow-up it was 30 degrees. Mean disc space height before the operation was 11.1 mm and it decreased to 8.1 mm at the final follow-up. The mean lordotic angle and disc space height at last follow-up was larger in the spinal fusion group than in the nonspinal fusion group. Our results indicate that implant removal and wide debridement for postoperative infection after posterior instrumented spine fusion can provide satisfactory results and could be one treatment option. However, the collapse of the disc space, loss of normal lordosis, and pseudoarthrosis are inevitable in patients with early postoperative infection.

Complications associated with subpectoral biceps tenodesis: Low rates of incidence following surgery

Tenodesis of the long head of the biceps tendon is a common procedure used to alleviate pain caused by instability or inflammation of the tendon. The purpose of this study is to report on the incidence and types of complications following an open subpectoral biceps tenodesis (OBT) procedure. Our hypothesis was that the rate of adverse events after OBT was low. From January 2005 to December 2007, all patients that underwent an OBT with bioabsorbable interference screw fixation performed by 1 of the 2 senior authors for biceps tendonitis were reviewed, excluding tenotomy, revision cases, or fixation methods other than interference screw fixation. Over a 3-year period, 7 of 353 patients had complications with OBT with an incidence of 2.0%. The mean age of patients with complications was 44.67 years, with 57.1% males and 42.9% females. There were 2 patients (0.57%) with persistent bicipital pain. Two patients (0.57%) had failure of fixation resulting in a Popeye deformity. One patient (0.28%) presented with a deep postoperative wound infections that necessitated irrigation and debridement with intravenous antibiotics. Another patient (0.28%) developed a musculotaneous neuropathy. Another patient (0.28%) developed reflex sympathetic dystrophy necessitating pain management and stellate ganglion block. The incidence of complications after subpectoral biceps tenodesis with interference screw fixation in a population of 353 patients over the course of 3 years was 2.0%.

Current Concepts in Perioperative Care for the Prevention of Deep Surgical Site Infections in Elective Spinal Surgery

Postoperative deep wound infections are the third most common reason for nosocomial infections after pneumonia and urinary tract infections. Deep wound infections lead to higher rates of morbidity and mortality and increased costs of treatment. Infection rates following spinal surgery are reported to lie between 1.9 and 10%. This study was carried out to prove whether a new internal concept for perioperative management could reduce the infection rates following spinal surgery. Based on the current literature we developed a concept for perioperative care in spinal surgery in order to prevent postoperative deep wound infections. We retrospectively compared infection rates of 2006 and 2007 after the implementation of our perioperative care concept in spinal surgery patients. Total annual operations were comparable. After the introduction of our predominantly evidence-based concept of perioperative care for spinal surgery patients, we found a considerable decrease in infection rates from 0.6% in 2006 to 0% in 2007. A new concept for perioperative care in spinal surgery for the prevention of deep wound infections was found to effectively reduce infection rates. Due to the limitations of our single-center retrospectively selected cohort, further research is necessary to support our results.

Closed Suction Irrigation for the Treatment of Postoperative Wound Infections Following Posterior Spinal Fusion and Instrumentation

Retrospective review of clinical cases. This study describes the success rate of closed suction irrigation system (CSIS) in the treatment of post operative spinal infections. Given the widening use of spinal instrumentation, the management of related postoperative deep wound infections has become increasingly important. In the literature, there have been reports of several treatment methods yet no firmly established protocol for management of postoperative deep wound infections exists. The goal of this study was to determine the effectiveness of our protocol employing (CSIS) in the treatment of postoperative deep wound infections. A retrospective record review of 500 posterior instrumented fusions between 1990 and 2002. Twenty-eight consecutive infections (5%) were diagnosed and treated by a standardized treatment protocol of Incision and Drainage, and CSIS. Cultures were obtained, wounds closed primarily, and appropriate intravenous antibiotic treatments initiated. For statistical evaluation, patients were assigned a risk factor (RF) described by Levi et al (J Neurosurg. 1997;86:975-980). Point values were assigned to medical comorbidities that may contribute to postoperative infection risk; higher RF values indicate an increased risk. Twenty-one acute and 7 late (>6 months) infections were followed for 22.3 months (1-86 months), post-CSIS treatment. Twenty-one (75%) resolved without recurrence with one CSIS treatment. Seven acute infections (25%) required a second course of treatment. Hospitalization for the index procedure averaged 15.4 days; 28.9 days for reinfections. No patient with an acute infection required implant removal. The reinfection group had higher blood loss, more levels fused, and longer hospitalization. The reinfection group was comprised entirely of pediatric patients. No correlation was found between RF values and greater risk of recurrent infection. Removal of implants is unnecessary in acute infections, provided the infection does not return. CSIS is an effective method for treatment of postoperative wound infections following instrumented spinal fusion avoiding the need for secondary closure.

Is Aggressive Surgery Necessary for Acute Postoperative Deep Spinal Wound Infection?

A retrospective study of the clinical results of conservative treatment of patients with acute postoperative deep spinal infection. To determine the efficacy of antibiotic only treatment of postoperative deep spinal infection. Traditionally, aggressive surgical treatment combined with antibiotics has been viewed as the gold standard for treating postoperative deep spinal infection. There are, however, disadvantages to surgical treatment including higher treatment cost, multiple anesthesia and surgeries, and the risk of perioperative morbidity and mortality particularly in immunocompromised patients. Although many new antibiotics and new methods of antibiotic treatment have recently become available, the role of conservative treatment using antibiotics alone to treat postoperative acute infection has not yet been determined. Ten consecutive patients with acute postoperative spinal infection were treated using antibiotics alone. The mean onset of the symptoms of infection after surgery was 15.4 days (range, 5-18 days). Seven patients had purulent wound drainage; 3 had healed wounds without discharge. Bacterial culture of the discharge showed methicillin-resistant Staphylococcus aureus (1 patient), methicillin-resistant coagulase negative Staphylococcus (4 patients), methicillin-sensitive coagulase negative Staphylococcus (1 patient). One patient had a negative culture. Patients with wound drainage were treated with intravenous vancomycin or teicoplamin for 4 to 6 weeks followed by oral antibiotics (quinolone with/without rifampin) for 1 to 3 months. All other patients were treated with oral antibiotics for 3 months. One patient could not complete treatment because of allergy to antibiotics. Infection was controlled in the remaining patients without surgical intervention and did not reoccur. All wound drainage ceased within 2 weeks. The C-reactive protein level of most patients returned to normal range within 10 weeks. Antibiotic treatment alone may be effective in the treatment of acute postoperative spinal infection when diagnosis is prompt. Aggressive surgery may be not necessary and may be reserved for patients who fail conservative treatment.

A new method for sternal closure after vacuum-assisted therapy in deep sternal infections following cardiac surgery

The treatment of nonhealing and infected sternotomies following cardiac surgery is a challenging task, with increased rates of mortality and morbidity, as well as high costs. Local vacuum therapy (VAC. sytem) permits the treatment of deep sternal infections due to continuous aspiration and a sealed dressing which stimulates granulation tissue formation. Aggressive vacuum-assisted closure treatment of the sternum in postoperative deep wound infection enhances sternal preservation and the speed of potential rewiring. After some weeks of VAC-therapy a complete preparation of the substernal structures is necessary. In this context laceration of the right ventricle is a rare, but life-threatening complication. We present a new technique for sternal closure after vacuum-assisted wound treatment using Nitinol clips which can prevent these severe complications. Without any preparation of the substernal tissue the clips can be inserted in the parasternal space with consecutive proper stabilization of the sternum. This new method represents an easy, low-cost and complication-free procedure.

The diagnosis and management of infection following instrumented spinal fusion

A 10-year retrospective audit. (1) The incidence of infection; (2) causative organisms; (3) whether eradication of infection is achievable with spinal implant retention; (4) patient outcome. The reported incidence of infection following posterior spinal instrumentation is between 2.6 and 3.8%. Management of infection is controversial, with some advocating serial wound debridement while others report that infection cannot be eradicated with retention of implants. There are no published data demonstrating that propionibacteria are associated with early postoperative infection. The management of infected cases at our institution includes eventual removal of their implants. Our population was identified by studying the case notes of all patients who had undergone removal of spinal implants and cross-referencing this population with positive microbiology or histology reports. The incidence of infection was 3.7%. Propionibacteria were isolated in 45% of cases. The diagnosis of infection was unexpected in 25% of patients, following removal of implants for prominence of implants or back pain. Sixty per cent of patients with acute postoperative deep wound infection had continuing active infection on subsequent removal of implants, despite long-term antibiotics and wound debridement. Fourty-six per cent of patients had a stable, pain-free spine at the end of their treatment. This is the largest reported series of infections following posterior spinal instrumented fusions of which we are aware. Propionibacteria are a common cause of infection and successful eradication of infection cannot be reliably achieved with antibiotics and wound debridement alone.

Do silver-impregnated dressings limit infections after lumbar laminectomy with instrumented fusion?

Background Silver has been used to reduce infection for centuries. This study retrospectively analyzed whether the introduction of silver-impregnated dressing (SD; Silverlon, Argentum Medical, LLC, Lakefront, GA) rather than RD (iodine- or alcohol-based swab and dry 4 × 4 gauze) would reduce the risk of superficial or deep infection after lumbar laminectomy with instrumented fusion. Methods The first 128 patients had RD applied postoperatively, whereas the second population of 106 patients received SD. These dressings were used for the first 2 weeks after surgery. Other clinical, surgical, and outcome data were comparable for both groups. Results Three of 128 patients who underwent multilevel laminectomies with instrumented fusions receiving RD developed deep postoperative wound infections (culture confirmed). All were successfully managed with 6 weeks of postoperative antibiotics, and none required secondary surgery. In addition, 11 patients who had RD developed superficial infection/irritation; 7 required oral antibiotics (7-10 days) alone, whereas 4 were referred to plastic surgeons for superficial wound revision. Alternatively, there were neither deep nor superficial wound infections/irritation among the 106 patients who received SD. Although the number of cases in each series was small, there appeared to be a positive trend toward a reduction in postoperative wound infection using SD. Conclusions Use of SD for application on lumbar wounds after laminectomies with instrumented fusions appeared to limit/reduce the incidence of both postoperative deep and superficial wound infections.

New Method for Sternal Closure After Vacuum-Assisted Therapy in Deep Sternal Infections After Cardiac Surgery

The treatment of nonhealing and infected sternotomies after cardiac surgery is a challenging task with increased rates of mortality and morbidity, as well as high costs. A local vacuum therapy (ie, the vacuum-assisted closure system) permits the treatment of deep sternal infections due to continuous aspiration and a sealed dressing that stimulates granulation tissue formation. Aggressive vacuum-assisted closure treatment of the sternum in postoperative deep wound infection enhances sternal preservation and the speed of potential rewiring. After some weeks of vacuum-assisted closure therapy, a complete preparation of the substernal structures is necessary. In this context, laceration of the right ventricle is a rare but life-threatening complication. We describe a new technique for sternal closure after vacuum-assisted wound treatment using Nitinol clips (Praesidia, Bologna, Italy), which can prevent these severe complications. Without any preparation of the substernal tissue the clips can be inserted in the parasternal space with consecutive proper stabilization of the sternum. This new method represents an easy, low-cost and complication-free procedure.

Management of Deep Wound Infection After Posterior Lumbar Interbody Fusion With Cages

To evaluate long-term treatment outcome of patients with infected posterior lumbar interbody fusion (PLIF) managed with surgical debridement and or prolonged antiobiotic treatment without removal of the interbody cages. Between 1996 and 1999, 8 out of 111 patients who underwent PLIF were diagnosed with deep wound infection (7.2%). All infected patients were clinically followed for at least 2 years after completion of the antibiotic treatment. Longer follow-up of at least 6 years duration was performed by a telephone interview. Six patients were managed with surgical debridement, wound irrigation, and primary closure of the wound. None of the patients required removal of the instrumentation. In 2 patients, the PLIF cages were repositioned in the face of infection. All 8 patients received 4 to 6 weeks of intravenous antibiotic therapy followed by another 6 to 9 weeks of oral antibiotic administration. At 2-year follow-up, no clinical or laboratory signs of recurrent infection were evident. Four of the 8 patients reported improved clinical status compared with their prefusion status. At 6-year follow-up, 3 patients had minimal disability according to the Oswestry Disability Index and 2 patients had moderate disability with residual leg pain. In cases of postoperative deep wound infection after PLIF with cages, removal of the interbody implants is not necessary. Treatment is composed of prolonged antibiotic therapy guided by antimicrobial susceptibility of the isolated bacteria and supplemented with extensive surgical debridement if needed.

Vacuum-assisted wound closure of deep infections after instrumented spinal fusion in six children with neuromuscular scoliosis

Background context The rate of infection after spinal fusion in neuromuscular scoliosis is reported to range from 4% to 20%. Infection persists in about 50% after traditional treatment including debridement and closure. Instrumentation removal is necessary in up to 28%. Purpose To analyze the outcome of vacuum-assisted wound closure (VAC) in combination with antibiotics for the treatment of deep wound infection after instrumented spinal fusion in pediatric neuromuscular scoliosis. Study design Six prospective consecutive neuromuscular patients with scoliosis. Patient sample Between 2001 and 2005, six consecutive pediatric patients (average age, 12.6 years) with neuromuscular scoliosis with a postoperative deep wound infection after instrumented spinal fusion were included in the study. Outcome measures Measurement of the duration of wound closure and infection parameters during treatment. Methods The patients were treated with a VAC system in combination with antibiotics. Results Wound closure averaged 3 months. Infection parameters were normalized within 6 weeks. Removal of the instrumentation was not necessary in any patient, and there were no signs of infection at follow-up ranging from 9 to 42 months. Conclusion The VAC system, in combination with antibiotic therapy, seems to be a useful method for treatment of deep wound infections after spinal fusion in pediatric neuromuscular scoliosis. It may prevent removal of the instrumentation and multiple surgery for irrigation and closure of the wound.

Mycoplasma hominis deep wound infection after neuromuscular scoliosis surgery: the use of real-time polymerase chain reaction (PCR)

Mycoplasma hominis is a commensal of the genitourinary tract. It mostly causes infections to associated structures of this system; however, occasionally it is a pathogen in nongenitourinary tract infections. Since, M. hominis strains require special growth conditions and cannot be Gram stained, they may be missed or delay diagnosis. This report describes a deep wound infection caused by M. hominis after neuromuscular scoliosis surgery; M. hominis was recovered by real-time polymerase chain reaction (PCR). An awareness of the role of M. hominis as an extragenital pathogen in musculoskeletal infections, especially in neuromuscular scoliosis, being a high-risk group for postoperative wound infection, it is necessary to identify this pathogen. Real-time PCR for postoperative deep wound infection, in patients with a history of genitourinary infections, decreases the delay in diagnosis and treatment. In these cases rapid real-time PCR on deep cultures should be considered.

Monitoring Method for Deep Infection after TKA: Significance of Intraoperative Synovial Fluid Culture and Postoperative Suction Drainage Tip Culture

Purpose : The aim of this study was to evaluate the usefulness of the intra-operative synovial fluid culture and post-operative suction drainage tip culture as a method for predicting the development of a deep infection after primary TKA. Materials and Methods : Between July 1998 and July 2002, 324 primary total knee arthroplasty procedures were performed and aerobic and anaerobic bacterial cultures for intra-operative synovial fluid and post-operative suction drainage tip were obtained. The results of culture of intra-operative synovial fluid and post-operative suction drainage tip of total 324 primary TKA cases were analyzed. The sensitivity, specificity and predictive value were calculated. positive culture rate for osteoarthritis was compared with rheumatoid arthritis and the results of a single TKA was compared with both simultaneous TKA. Results : 14 out of 324 knees showed a positive intra-operative synovial fluid culture and 10 cases showed a positive post-operative suction drainage tip culture. Only 1 case out of the 4 deep infection cases showed a positive on suction drainage tip culture with S. aureus being isolated. The specificity of the intra-operative synovial culture was 95.6% and the negative predictive value was 98.7%. The sensitivity of the post-operative suction drainage tip culture was 25%, the specificity was 97%, the positive predictive value was 10% and the negative predictive value was 99%. The positive culture rate was similar in the osteoarthritis and rheumatoid arthritis cases (respectively p=0.4717, p=0.6550). However, the culture positive rate between single and both simultaneous TKA was numerically different, approximately 2 times (3.2% vs 6.31% for intra-operative synovial culture and 4.0% vs 9.47% for post-operative suction drainage tip culture) but it was not statistically significant (respectively p=0.311, p=0.1051). Conclusion : In primary TKA, a culture of intra-operative synovial fluid and post-operative suction drainage tip cannot predict a postoperative deep wound infection. It is recommended that careful observation for other signs of a deep infection be examined when a clinically significant true pathogen isisolated.

Monitoring for Deep Wound Infection after Thoracolumbar Surgery Significance of Suction Drainage Tip Culture for Early Detection of Postoperative Deep Wound Infection

Study Design: A retrospective study. Objectives: To evaluate the usefulness of postoperative suction drainage tip cultures as a method of predicting the development of deep wound infections after thoracolumbar surgery using pedicle screws. Summary of Literature Review : The primary diagnostic elements of post-operative spinal infections are a high degree of clinical suspicion by the surgeon combined with aspiration and culture of the suspected infection sites. Materials and Methods : We analyzed the results of cultures on postoperative suction drainage tips from a total of 471 thoracolumbar surgery cases. We calculated the sensitivity, specificity, and predictive value and investigated the isolated pathogens. In addition, we performed quantitative analyses of serum C-reactive protein using Turbidimetry. Results: The post-operative infection rate was 4.0%. The most common isolated pathogen of the true positive cases was staphylococcus aureus, which was found in 3 cases (methicillin-resistant staphylococcus aureus in 2 cases); and that of the false positive cases was coagulase-negative staphylococcus in 5 cases. The sensitivity of the suction drainage tip culture was 52.6%, the specificity was 96.3%, the positive predictive value was 37.0%, and the negative predictive value was 98.0%. In cases of C-reactive protein, true positive and false negative cases followed the same course, where the CRP decreased slowly for the first week but remained elevated persistently at the 14th postoperative day. Conclusions: Culture of the suction drainage tips could not predict the development of postoperative deep wound infections, but it had more significance in the exclusion of deep wound infections. We concluded that careful observation for other signs of deep wound infections are necessary when a clinically significant pathogens are isolated.

Diagnostic value of routine drain tip culture in primary joint arthroplasty

Closed suction drainage after joint arthroplasty is common practice in many institutions. The purpose of this study was to determine the correlation between routine drain tip culture and the diagnosis of superficial or deep postoperative wound infection after primary knee and hip replacement. Over a 12-month period, drain tips were retrieved and cultured in all patients who underwent unilateral primary total knee or hip replacement with the use of closed suction drainage. A total of 393 cultures was performed in 387 patients (145 hip replacements, 242 knee replacements). Patients were followed for an average of 8.9 months after surgery to assess for postoperative wound infection. Three patients had a positive drain tip culture, none of which were diagnosed with superficial or deep infection. Four patients (1%) were diagnosed with deep infection, 16 (4.1%) with superficial infection. No patient with either superficial or deep infection had a positive drain tip culture after their index procedure. The sensitivity of routine drain tip culture for the diagnosis of postoperative infection in primary joint replacement was 0% and specificity was 99.2%. These data do not support the practice of routine drain tip culture after primary hip or knee replacement for the diagnosis of postoperative infection.

Postoperative Deep Wound Infections in Adults After Spinal Fusion

Vacuum-assisted wound closure (VAC) exposes the wound bed to negative pressure, resulting in removal of edema fluid, improvement of blood supply, and stimulation of cellular proliferation of reparative granulation tissue. It has been used to treat open wounds in the extremities, open sternal wounds, pressure ulcers, and abdominal wall wounds. This study retrospectively reviewed instrumented spine fusions complicated by surgical wound infection and managed by a protocol including the use of VAC in order to evaluate the efficacy of applying vacuum therapy on patients with deep spine infections and exposed instrumentation. Twenty consecutive patients with deep wound infections after undergoing spinal fusion procedures were studied. There were 12 men and 8 women with an average age of 55 years (31-81 years). Eight patients had undergone concomitant anterior and posterior arthrodesis, nine patients had a posterior spinal fusion, and three patients had a transforaminal lumbar interbody fusion. Seven patients had a decompression with exposed dura. Sixteen patients presented with a draining wound within the first 6 weeks postoperatively (average 24 days). There were four patients who presented with back pain and temperature after 1 year postoperatively (average 3 years). All patients were taken to the operating room for irrigation and debridement followed by placement of the VAC with subsequent delayed closure of the wound. There was an average of 1.8 (1-8) irrigation and debridement procedures prior to placement of the VAC. Once the VAC was initiated, there was an average of 2.2 (2-3) procedures until and including closure of the wound. The wound was closed an average of 7 days (5-14 days) after the placement of the initial VAC in the wound. All patients tolerated the VAC without adverse effects. All patients were kept on a 6-week course of intravenous antibiotic therapy. The average follow-up was 10 months (6-24 months). There were no cases of uncontrolled sepsis once the VAC was initiated. All patients achieved a clean closed wound without removal of instrumentation at a minimum follow-up of 6 months. VAC therapy is an effective adjunct in closing complex deep spinal wounds with exposed instrumentation.

Deep sternal wound infection: a sternal-sparing technique with vacuum-assisted closure therapy

Background Vacuum-assisted closure therapy is a novel treatment employed to aid wound healing in different areas of the body and recently also in sternotomy wounds. Aggressive vacuum-assisted closure treatment of the sternum in postoperative deep wound infection enhances sternal preservation and the rate of possible rewiring. Methods The records of 40 consecutive patients with deep sternal wound infection were reviewed. Sternal bone sparing was achieved by using layers of paraffin gauze (Jelonet; Smith and Nephew Medical, Hull, UK) at the bottom of the wound in order to cover and protect visible parts of the right ventricle, lung tissue, and grafts from the sternal edges. Two separate layers of polyurethane foam (KCI, Copenhagen, Denmark) were placed so as to fit between the sternal edges and subcutaneously. A continuous negative pressure of 125 mm Hg was applied and subsequent revision was made exclusively in nongranulation areas. Results There were no deaths during the 90 days of follow-up. Three late deaths unrelated to the infection and three subcutaneous fistulas occurred during the total follow-up period (3 to 41 months). The median duration of the vacuum-assisted closure therapy was 10 days (range, 3 to 34). The series represents a total of 474 days with the vacuum-assisted closure device without serious adverse events. Conclusions In our opinion this modified vacuum-assisted closure therapy is a safe and reproducible option to bridge patients with postoperative deep sternal wound infection to complete healing. Reconstruction of the sternum was achieved in all patients without the use of muscle or omental flap surgery.

Effect of Antibiotics on Cell Surface Hydrophobicity of Bacteria Causing Orthopedic Wound Infections

Background: Despite antibiotic prophylaxis and treatment, the incidence of wound infections in orthopedic surgery is significant. Postoperative wound infection is a multifactorial process, which can be modified by several bacterial factors. Cell surface hydrophobicity of bacteria is a very important physicochemical feature, which has a great influence on the ability of bacteria to adhere to the surface of host cells or medical implants. Methods: In this study, the hydrophobic properties of thirteen bacterial strains (coagulase-negative staphylococci, Staphylococcus aureus and Pseudomonas aeruginosa) isolated from patients with postoperative deep wound infections following orthopedic procedures were determined by the salt aggregation test. Results were compared to the hydrophobicity of three Hungarian standard bacterial strains. The modifying effect of four antibiotics (cefuroxime, cefotaxime, amoxicillin combined with clavulanic acid and amikacin) – applied most often in our Department for prophylaxis and treatment of patients – were analyzed. Results: The cell surface hydrophobicity of certain strains showed considerable changes after antibiotic treatment. These alterations indicated the decrease in hydrophobicity. Supra-inhibitory concentrations (2× minimum inhibitory concentrations, MIC) of the antibiotics were able to induce more frequent alterations in hydrophobicity than sub-inhibitory (0.5× MIC) levels. Conclusions: Alterations in cell surface hydrophobicity caused by antibiotics can modify the adhesion process and thus the pathogenicity of bacterial strains. These changes should be taken into consideration in the management of proper antibiotic prophylaxis and in the treatment of orthopedic patients.

Characterization of a developing lumbar arthrodesis in a sheep model

Mark R. Foster, PhD, MD, Pittsburgh, PA, USA; Hansen A. Yuan, MD, Matthew J. Allen, MB, PhD, Joanne E. Schoonmaker, AAS, Syracuse, NY, USAPurpose: The role of mechanical forces from spinal instrumentation to modify the biological processes ongoing in a developing lumbar arthrodesis was evaluated in a sheep model. Although the rigidity of instrumentation has been reported to influence the stiffness and rate of development of a bony fusion and considered to later shield stresses, the mechanism of healing of that fusion mass has not been well characterized. The specific aim of this study was therefore to determine the effects of mechanical instability on the healing of an intertransverse process fusion in the sheep lumbar spine.Methods: Fourteen skeletally mature Dorset ewes underwent anterior discectomy and posterior instrumentation at L4–L5. Animals were randomly assigned to one of two groups: 1) control: the anterior discectomy was stabilized with a carbon fiber interbody cage and the posterior elements rigidly fixed with pedicle screws and rods; 2) unstable: anterior discectomy defect untreated and posterior elements repaired with custom pedicle instrumentation that allowed quantitative instability (2 mm of anterior-posterior movement). Groups of animals were euthanized either 6 weeks or 12 weeks after surgery. The explanted lumbar spine was radiographed, then fixed in formalin and processed into polymethylmethacrylate. Sagittal sections (approximately 100 mm thick) were prepared from the intertransverse process fusion site. Slides were microradiographed, then stained with Sanderson's rapid bone stain. Histomorphometric analysis was used to quantify the tissue within the developing fusion mass.Results: Four animals were eliminated from the study because of either postoperative neurological deficits (three animals) or deep wound infection (one animal). The remaining animals recovered well after surgery, although the unstable group was noted to be much less active than the rigidly fixed group in the first postoperative month. None of the animals had achieved an anterior and posterior fusion by 12 weeks. Histology revealed collagen-model bone in the vicinity of the transverse process, and in a subsequent zone of influence around the adjacent bone graft. The bulk of the healing fusion in the intertransverse space was by a cartilaginous model or endochondral ossification in both the rigid and the unstable cases, as determined by quantitative histomorphometry. Microradiography and histomorphometry demonstrated that the relative amount of mineralized bone within the fusion site was significantly increased in the 12-week unstable animals as compared with the 6-week unstable animals. In contrast, most of the mineralized bone had already developed by 6 weeks in the rigidly fixed animals, so that there was no significant difference between the 6- and 12-week animals in this group.Discussion: This result demonstrates that larger species form bone from a cartilaginous anlagen, as opposed to rabbits, which have been characterized by Boden et al. as healing primarily through collagen-model bone. This large animal model therefore provides a clinically relevant system for studying the relative significance of biological and mechanical factors in spinal fusion. In this model, mineralized bone forms more rapidly with rigid fixation, and subsequently the process is of maturation, in a manner that is significantly influenced by the mechanical forces of spinal instrumentation.

Postoperative deep wound infection in adults after posterior lumbosacral spine fusion with instrumentation: incidence and management.

The authors reviewed 817 instrumented lumbosacral fusions in adults and found an incidence of 3.2% deep wound infections. The primary focus of this study was the management of these infections, with particular attention to whether the implants needed to be removed. A consulting infectious disease specialist indicated that an acute infection of a low back fusion wound could not be healed without removal of the metallic implants. This opinion was in contrast to the authors' daily experience and prompted this study. The authors identified and reviewed 817 cases of instrumented posterior lumbosacral arthrodeses in adults. A detailed analysis of any case with a deep wound infection was performed and yielded and infection rate of 3.2% (26 patients). Of these, 24 achieved a clean, closed wound without removal of instrumentation through a protocol of aggressive debridement and secondary closure. Instrumentation removal is not necessary to obtain a clean, closed wound using an aggressive approach with early diagnosis, vigorous debridement in the operative room under general anesthesia, delayed primary or secondary closure, and appropriate antibiotic coverage.