Lacey E. Bresnahan

A biomechanical evaluation of graded posterior element removal for treatment of lumbar stenosis: comparison of a minimally invasive approach with two standard laminectomy techniques.

Study Design. A validated finite element model of the intact lumbar spine (L1–S1) was modified to study the biomechanical changes as a result of surgical alteration for treatment of stenosis at L3–L4 and L4–L5 using 2 established techniques and 1 new minimally invasive technique. Objective. To investigate the impact of graded posterior element removal associated with new surgical techniques on postoperative segmental motion and loading in the annulus. Summary of Background Data. Several studies have shown that laminectomy increases and produces segmental instability unless fusion is performed. However, no data exist comparing the biomechanical impact of completely preserving the contralateral anatomy and what effect this has compared to traditional approaches. Methods. The effect of graded removal of posterior elements because of iatrogenic change associated with the 3 approaches was investigated using an 800 N compressive preload using the follower load technique and application of 8 Nm flexion, 6 Nm extension, 4 Nm torsion, and 6 Nm lateral bending moments. Results. This study shows that removal of posterior elements for treatment of stenosis at L3–L4 and L4–L5 results in increased flexion-extension and axial rotation at the surgical site. This study also shows that the segmental motion following a traditional laminectomy is greater than the minimally invasive approach in flexion, extension, left and right axial rotation. Moderate preservation of the posterior elements which occurs in the intralaminar approach generates greater segmental motion that the minimally invasive approach in extension, left and right axial rotation. Conclusion. Minimization of bone and ligament removal associated with minimally invasive procedures results in greater preservation of the normal motion of the lumbar spine after surgery. This study suggests that preservation of the posterior spinal elements associated with minimally invasive surgery could minimize the risk of developing de novo postoperative changes in spinal alignment and/or acceleration of facet and disc degeneration.

Biomechanical comparison of traditional and minimally invasive intradural tumor exposures using finite element analysis.

BACKGROUND Minimally invasive approaches to intradural pathology have evolved in part in an effort to reduce approach related destabilization of the spine. No biomechanical data exist however evaluating the effects of traditional and minimally invasive exposures. METHODS A finite element model of the lumbar spine was generated, and a simulated open laminectomy and a modified hemilaminectomy at L4 were performed. Forces were applied to assess changes in flexion, extension, axial rotation, and lateral bending. FINDINGS Open laminectomy produced much greater changes in extension, flexion, and axial rotation than the modified hemilaminectomy from the intact. Lateral bending was similarly unaffected for both exposures. INTERPRETATION The results suggest that a minimally invasive hemilaminar exposure preserves the structural integrity of the lumbar spine and minimizes alterations to segmental motion postoperatively.

Evaluation of change in muscle activity as a result of posterior lumbar spine surgery using a dynamic modeling system.

Study Design. A commercially available muscloskeletal model of the lumbar spine was modified to study the change in muscle activation as a result of posterior lumbar surgery at the L3–L4 and L4–L5 segments. Objective. To evaluate how graded resection of the lumbar paraspinal muscles as a result of posterior lumbar surgery affects muscle activity for a variety of movement tasks. Summary of Background Data. Several in vivo studies compare the change in functional outcome of the paraspinal muscles following surgery. However, due to limitations that exist with current in vivo methods no study to date has been able to quantitatively examine how the function of individual muscles in the lumbar spine change in response to different levels of injury. Methods. A multibody dynamic musculoskeletal model of the lumbar spine was modified to measure muscle activity using a parametric examination of change in the cross-sectional area of muscles affected by posterior lumbar surgery. Results. This study shows that the reduction in muscle cross-sectional area as a result of posterior lumbar surgery at L3–L4 and L4–L5 results in a change in trunk muscle activity where the greatest change occurs during axial rotation and lateral bending. The results suggest that preservation of the posterior paraspinal musculature results in greater preservation of the normal muscle activity than traditional open techniques. Conclusion. Preservation of the paraspinal musculature associated with minimally invasive surgical approaches to the lumbar better preserve postoperative muscle activity. This study suggests that there is a positive correlation between the reduction of paraspinal muscle cross-sectional area following posterior lumbar spine surgery and the alteration in trunk muscle activity.

The Microendoscopic Decompression of Lumbar Stenosis: A Review of the Current Literature and Clinical Results

Lumbar stenosis is a well-defined pathologic condition with excellent surgical outcomes. Empiric evidence as well as randomized, prospective trials has demonstrated the superior efficacy of surgery compared to medical management for lumbar stenosis. Traditionally, lumbar stenosis is decompressed with open laminectomies. This involves removal of the spinous process, lamina, and the posterior musculoligamentous complex (posterior tension band). This approach provides excellent improvement in symptoms, but is also associated with potential postoperative spinal instability. This may result in subsequent need for spinal fusion. Advances in technology have enabled the application of minimally invasive spine surgery (MISS) as an acceptable alternative to open lumbar decompression. Recent studies have shown similar to improved perioperative outcomes when comparing MISS to open decompression for lumbar stenosis. A literature review of MISS for decompression of lumbar stenosis with tubular retractors was performed to evaluate the outcomes of this modern surgical technique. In addition, a discussion of the advantages and limitations of this technique is provided.

Assessment of paraspinal muscle cross-sectional area following lumbar decompression: Minimally invasive versus open approaches

Study Design: A retrospective, blinded analysis of imaging studies. Summary of Background Data: To evaluate changes in paraspinal muscle cross-sectional area (CSA) after surgical treatment for lumbar stenosis and to compare these changes between minimally invasive and standard open approaches. The open approach to lumbar stenosis is effective, but it involves retraction and resection of muscle from the spinous process, which can result in ischemia and denervation of paraspinal musculature and may lead to muscle atrophy and pain. Objective: It is hypothesized that the microendoscopic decompression of stenosis (MEDS) technique will better preserve the paraspinal muscles compared with the open procedure. Materials and Methods: A total of 18 patients underwent a 1-level posterior decompression for lumbar stenosis, (9 open, 9 MEDS). Lumbar magnetic resonance imaging was obtained before surgery and after surgery (open approach average 16.3 mo; MEDS average 16.6 mo). CSA of paraspinal muscles were averaged over the distance of the surgical site. Results: The mean age of patients treated with the open and MEDS approaches were 55.2 and 66.4 years, respectively (P=0.07). Paraspinal muscle CSA decreased by an average of 5.4% (SD=10.6%; range, −24.5% to +7.7%) in patients treated with the open approach and increased by an average of 9.9% (SD=14.4%; range, −9.8% to +33.1%) in patients treated with MEDS (P=0.02). For the open approach, changes in CSA did not differ significantly between the left and right sides for erector spinae (P=0.35) or multifidus muscles (P=0.90). After the MEDS approach there were no significant differences between the dilated and contralateral sides with regard to change in CSA for erector spinae (P=0.85) or multifidus muscles (P=0.95). Conclusions: Compared with the open approach for lumbar stenosis, MEDS had significantly less negative impact on the paraspinal muscle CSA. Previous reports have documented negative effects of paraspinal muscle injury, including weakness, disability, and pain. Collectively, these data suggest that the MEDS approach for lumbar decompression is less destructive to the paraspinous muscles than the open approach and may facilitate better clinical outcomes.