Association between degenerative spondylolisthesis and spinous process fracture after interspinous process spacer surgery.

BACKGROUND CONTEXT: Spinous process fracture is a recognized complication associated with interspinous process spacer (IPS) surgery. Although occasionally identified by plain radiographs, computed tomography (CT) appears to identify a higher rate of such fractures. Although osteoporotic insufficiency fracture is considered a contraindication for IPS surgery, a formal risk factor analysis for this complication has not previously been reported. PURPOSE: To identify risk factor(s) associated with early spinous process fracture after IPS surgery. STUDY DESIGN/SETTING: Prospective cohort study of 39 consecutive patients with lumbar stenosis and neurogenic claudication undergoing IPS surgery at a single institution. METHODS: Patients underwent preoperative dual-energy X-ray absorptiometry (DXA) scans, lumbar spine CT, and plain radiographs. Postoperatively, patients underwent repeat CT imaging within 6 months of surgery and serial radiographs at 2 weeks, 6 weeks, 3 months, 6 months, and 1 year. Preoperative CT scans were analyzed by calculating average Hounsfield units for a 1 cm(2) area of the midsagittal reconstructed image for four separate locations: midvertebral body, subcortical bone subjacent to the superior margin of the midspinous process, subcortical bone above the inferior margin of the midspinous process, and the midspinous process. RESULTS: Thirty-eight patients underwent IPS surgery at a total of 50 levels (38 L4-L5, 12 L3-L4; 26 one-level, 12 two-level). One patient underwent laminectomy at index surgery and was excluded from the analysis. Implants included 34 titanium X-STOP (Medtronic, Memphis, TN, USA), 8 polyaryletheretherketone X-STOP (Medtronic, Memphis, TN, USA), and 8 Aspen (Lanx, Broomfield, CO, USA) devices. Eleven spinous process fractures were identified by CT in 11 patients (22.0% of levels). No fractures were apparent on plain radiographs. The rate of spondylolisthesis observed on preoperative radiographs was 100% (11 of 11) among patients with fractures compared with 33.3% (9 of 27) of patients without fracture (p=.0001). Overall, 21 of 39 patients in this series had spondylolisthesis, and the rate of fracture in this group was 52%. Among patients without spondylolisthesis, the fracture rate was 0%. A trend was observed toward decreased DXA lumbar spine and hip T-scores among fracture patients versus nonfracture patients (0.2 ± 1.7 vs. 0.8 ± 1.7; p=.389; -1.1 ± 1.4 vs. -0.3 ± 1.4; p=.201), but these differences were not significant. Similarly, bone density based on CT measurements at four different locations revealed a trend toward decreased density among fracture patients, but these differences were not significant. CONCLUSIONS: Degenerative spondylolisthesis appears strongly associated with the occurrence of spinous process fracture after IPS surgery. There is a trend toward increased fracture risk in patients with decreased bone mineral density as measured by both DXA scan and CT-based volume averaging of Hounsfield units, but osteoporosis appears to be a relatively weaker risk factor. The association between spondylolisthesis and fracture observed in this study may account for the relatively poorer outcome of IPS surgery in patients with spondylolisthesis that has been reported in previous series.

Occult spinous process fractures associated with interspinous process spacers.

STUDY DESIGN: Prospective observational study. OBJECTIVE: To provide a more accurate estimate of the rate of acute spinous process fractures associated with IPS surgery. SUMMARY OF BACKGROUND DATA: Biomechanical cadaveric studies have suggested adequate spinous process strength to support placement of interspinous process spacers (IPS). Postoperative spinous process fractures have been reported in one%-to 5.8% of patients in previous series based on routine biplanar radiographic evaluation. However, most fractures occur between the base and midportion of the spinous process in an area that is typically difficult to visualize on plain radiographs due to device design. METHODS: All patients underwent preoperative biplanar plain radiographs and computed tomography (CT) of the lumbar spine to confirm anatomy favorable for IPS placement and rule out fracture or spondylolysis. Postoperatively, all patients underwent repeat CT imaging within six months of surgery, biplanar radiographs at two weeks, six weeks, three months, six months, and one year. All studies were reviewed independently by a neuroradiologist and two orthopedic spine surgeons. RESULTS: Fifty implants (38 L4-5, 12 L3-4) were placed in 38 patients who completed follow-up and were included in final analysis. Three IPS designs were included (34 Medtronic X-STOP titanium, 8 X-STOP PEEK, 8 Lanx Aspen). Postoperative CT revealed 11 nondisplaced spinous process fractures in 11 patients (28.9% of patients, 22% of levels). Five fractures were associated with mild to moderate lumbar back pain and six fractures were asymptomatic. No patient reported a traumatic incident. No fracture was identifiable on plain radiographs. One fracture displaced during follow-up evaluation. Three patients underwent IPS removal and laminectomy. Three fractures healed by CT in one year. Overall, patients with fractures tended toward poorer outcomes by Zurich Claudication Questionnaire (ZCQ) (28.5% vs. 34.8% improvement in symptom severity, P = 0.496; 21.4% vs. 30.7% improvement in physical function, P = 0.199) and tended toward lower satisfaction rates (50% vs. 73.7%, P = 0.24) at one year compared to patients without fracture. CONCLUSION: Interspinous process spacer surgery appears associated with a higher rate of early postoperative spinous process fracture than previously reported. In all cases, in this series, plain radiographs were inadequate to identify fractures because all fractures were initially minimal or nondisplaced, many patients were osteopenic, and the metallic wings of the devices often obscured fractures. Moreover, in most patients, fractures were associated with mild or no acute localized pain. This study suggests that unrecognized spinous process fracture may be responsible for a significant number of patients who experience unsatisfactory outcome after IPS surgery. CT imaging is required to identify the vast majority of such fractures.

Institutional prescreening for detection and eradication of methicillin-resistant Staphylococcus aureus in patients undergoing elective orthopaedic surgery.

BACKGROUND: Surgical site infection has been identified as one of the most important preventable sources of morbidity and mortality associated with medical treatment. The purpose of the present study was to evaluate the feasibility and efficacy of an institutional prescreening program for the preoperative detection and eradication of both methicillin-resistant and methicillin-sensitive Staphylococcus aureus in patients undergoing elective orthopaedic surgery. METHODS: Data were collected prospectively during a single-center study. A universal prescreening program, employing rapid polymerase chain reaction analysis of nasal swabs followed by an eradication protocol of intranasal mupirocin and chlorhexidine showers for identified carriers, was implemented. Surgical site infection rates were calculated and compared with a historical control period immediately preceding the start of the screening program. RESULTS: During the study period, 7019 of 7338 patients underwent preoperative screening before elective surgery, for a successful screening rate of 95.7%. One thousand five hundred and eighty-eight (22.6%) of the patients were identified as Staphylococcus aureus carriers, and 309 (4.4%) were identified as methicillin-resistant Staphylococcus aureus carriers. A significantly higher rate of surgical site infection was observed among methicillin-resistant Staphylococcus aureus carriers (0.97%; three of 309) compared with noncarriers (0.14%; seven of 5122) (p = 0.0162). Although a higher rate of surgical site infection was also observed among methicillin-sensitive Staphylococcus aureus carriers (0.19%; three of 1588) compared with noncarriers, this difference did not achieve significance (p = 0.709). Overall, thirteen cases of surgical site infection were identified during the study period, for an institutional infection rate of 0.19%. This rate was significantly lower than that observed during the control period (0.45%; twenty-four cases of surgical site infection among 5293 patients) (p = 0.0093). CONCLUSIONS: Implementation of an institution-wide prescreening program for the identification and eradication of methicillin-resistant and methicillin-sensitive Staphylococcus aureus carrier status among patients undergoing elective orthopaedic surgery is feasible and can lead to significant reductions in postoperative rates of surgical site infection. LEVEL OF EVIDENCE: Therapeutic Level III. See Instructions to Authors for a complete description of levels of evidence.

Prospective study of iliac crest bone graft harvest site pain and morbidity.

BACKGROUND CONTEXT: Morbidity associated with autologous bone graft harvest is an important factor in determining the utility of expensive alternatives such as recombinant bone morphogenic protein. The most frequently reported complication associated with graft harvest is chronic pain. PURPOSE: To prospectively determine the degree of pain and morbidity associated with autologous iliac crest bone graft harvest and its effect on activities of daily living. STUDY DESIGN: Prospective observational cohort study. PATIENT SAMPLE: One hundred ten adult patients undergoing elective posterior lumbar spinal fusion surgery involving autologous iliac crest bone graft harvest. OUTCOME MEASURES: Patient self-reported Visual Analog Scale (VAS) scores for pain and a study-specific questionnaire regarding activities of daily living. METHODS: One hundred ten patients were prospectively enrolled. Postoperative VAS scores (0-100) for harvest site pain were obtained at 6-week, 6- and 12-month follow-up. Patients completed a 12-month questionnaire regarding the persistence of specific symptoms and resulting limitation of specific activities. RESULTS: One hundred four patients were available for 1-year follow-up. Mean VAS pain scores (scale 0-100) at 6 weeks, 6 and 12 months were 22.7 (standard deviation [SD], 25.9), 15.9 (SD, 21.5), and 16.1 (SD, 24.6), respectively. At 12 months, 16.5% reported more severe pain from the harvest site than the primary surgical site, 29.1% reported numbness, and 11.3% found the degree of numbness bothersome, whereas 3.9% were bothered by scar appearance. With respect to activity limitations resulting from harvest site pain at 1 year, 15.1% reported some difficulty walking, 5.2% with employment, 12.9% with recreation, 14.1% with household chores, 7.6% with sexual activity, and 5.9% irritation from clothing. CONCLUSIONS: There is a significant rate of persistent pain and morbidity from iliac crest bone graft harvest when associated with elective spine surgery. Mean pain scores progressively decline over the first postoperative year. Nevertheless, harvest site pain remains functionally limiting in a significant percentage of patients 1 year after surgery. Rates of functional limitation are higher than previously reported and may be because of increased sensitivity of the prospective study design and targeted investigation of these specific symptoms. Validity of these findings is necessarily limited by patient ability to discriminate harvest site pain from alternative sources of back and buttock pain.