Department of Orthopaedic Surgery, New England Baptist Hospital and Tufts University School of Medicine, 125 Parker Hill Ave., Boston, MA 02120, USA.
Spine J. 2012 Jun;12(6):466-72. doi: 10.1016/j.spinee.2012.03.034. Epub 2012 May 22.
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.
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.
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.
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.
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.
棘突骨折是与棘突间间隔物（IPS）手术相关的公认并发症。尽管偶尔通过普通 X 光片识别，但 CT 似乎能识别出更高的此类骨折发生率。虽然骨质疏松性不足骨折被认为是 IPS 手术的禁忌症，但之前没有对这种并发症的危险因素进行过正式的分析。
确定 IPS 手术后早期棘突骨折的相关危险因素。
研究设计/设置：在一家机构中对 39 例接受腰椎狭窄症和神经性跛行 IPS 手术的连续患者进行前瞻性队列研究。
患者接受术前双能 X 射线吸收法（DXA）扫描、腰椎 CT 和普通 X 光片。术后 6 个月内对患者进行重复 CT 成像，2 周、6 周、3 个月、6 个月和 1 年进行连续 X 光片检查。通过计算四个不同位置的中矢状重建图像中 1cm2 区域的平均 Hounsfield 单位来分析术前 CT 扫描：椎体中部、中棘突上缘下的皮质下骨、中棘突下缘上的皮质下骨和中棘突。
38 例患者在总共 50 个节段（38 个 L4-L5，12 个 L3-L4；26 个单节段，12 个双节段）接受 IPS 手术。1 名患者在指数手术中接受了椎板切除术，因此被排除在分析之外。植入物包括 34 个钛 X-STOP（美敦力，田纳西州孟菲斯，美国）、8 个聚芳醚醚酮 X-STOP（美敦力，田纳西州孟菲斯，美国）和 8 个 Aspen（兰克斯，科罗拉多州布鲁姆菲尔德，美国）装置。11 名患者（11 名患者中的 22.0%）在 CT 上发现 11 处棘突骨折。普通 X 光片未见骨折。与无骨折患者（33.3%，9/27）相比，骨折患者术前 X 光片上观察到的滑脱率为 100%（11/11）（p=0.0001）。在这个系列中的 39 例患者中，有 21 例有脊柱滑脱，在这个组中，骨折的发生率为 52%。在没有脊柱滑脱的患者中，骨折率为 0%。与非骨折患者相比，骨折患者的 DXA 腰椎和髋部 T 评分呈下降趋势（0.2±1.7 与 0.8±1.7；p=0.389；-1.1±1.4 与-0.3±1.4；p=0.201），但这些差异无统计学意义。同样，基于四个不同位置的 CT 测量值的骨密度也显示出骨折患者骨密度降低的趋势，但这些差异无统计学意义。
退行性脊柱滑脱似乎与 IPS 手术后棘突骨折的发生密切相关。与 DXA 扫描和基于 CT 的 Hounsfield 单位体积平均测量的骨密度降低相比，骨折患者的骨折风险呈上升趋势，但骨质疏松症似乎是一个相对较弱的危险因素。在本研究中观察到的脊柱滑脱与骨折之间的关联可能解释了先前系列报道的脊柱滑脱患者 IPS 手术结果较差的情况。
