The anatomic rationale for transforaminal endoscopic interbody fusion: a cadaveric analysis.

OBJECTIVE The authors describe a cadaveric analysis to determine the ideal dimensions and trajectory for considering endoscopic transforaminal interbody implantation. METHODS The soft tissues of 8 human cadavers were removed from L-1 to the sacrum, exposing the posterior bony elements. Facetectomies were performed bilaterally at each lumbar level with resection of the pars interarticularis, revealing the pedicles, nerve roots, and interbody disc space. Each level was digitally photographed with a marker for scale and evaluated with digital analysis software. The traversing and exiting nerve roots and pedicle margins were identified, and the distances between these structures and their relationships to the surrounding structures were documented. RESULTS The dimensions of 2 areas were measured: the working triangle and safe zone. The working triangle is the triangle between the exiting and traversing nerve roots above the superior margin of the inferior pedicle. The safe zone is the trapezoid bounded by the widths of the superior and inferior pedicles between the exiting and traversing nerve roots. The mean surface area for the working triangle was 1.83 cm(2), with L5-S1 having the largest area at 2.19 cm(2). The mean surface area of the safe zone was 1.19 cm(2), with L5-S1 having the largest area at 1.26 cm(2). At the medial border of the pedicle extending superiorly, there were no nerve structures within 1.19 cm at any level. On the lateral border of the pedicle, the exiting nerve root was closer superiorly, with the closest being 0.3 cm. CONCLUSIONS The working triangle is a relatively large area. The safe zone, just superior to the pedicle, is free of nerve structures. By utilizing the superior border of the pedicle, the disc space can be accessed within this safe zone without risk of injury to the nerves. A thorough understanding of foraminal anatomy is fundamental for considering how to safely access the disc space, thereby utilizing less invasive endoscopic techniques, and is an important first step in considering what shapes and sizes of interbody implants and retractors are feasible for use in the foramen.

Spinous process fixation devices for instrumented spinal fusion.

Lumbar spinal fusion is a well-established surgical procedure for many spinal conditions. Posterior instrumentation may be added to provide immediate stabilization and improve fusion rates. Spinous process fixation, a type of posterior fixation, offers a less-invasive option to pedicle or facet screws with quantitative evidence of similar biomechanical stabilization; however, little has been published on the use of these devices. Further, there has been confusion about the use of spinous process fixation devices versus spinous process spacers. Spinous process fixation devices provide spine surgeons with another option for instrumented fusion, offering potential advantages for select patients. Biomechanical data suggest that relative to pedicle screws, modern spinous process fixation devices provide equivalent stability with reduced clinical risk and a less-invasive surgical procedure. These devices need to be distinguished from spacers, which are non-fixation devices.

Assessment of pedicle screw placement accuracy, procedure time, and radiation exposure using a miniature robotic guidance system.

STUDY DESIGN: Controlled, cadaveric implantation trial. OBJECTIVE: To evaluate the effect of a robotic guidance system on screw placement accuracy, amount of radiation exposure, and length of procedure time during percutaneous pedicle screw implantation. SUMMARY OF BACKGROUND DATA: Pedicle screws are associated with low complication rates, and several computer-assisted image guidance systems exist that facilitate accurate screw placement. However, these systems may represent substantial radiation exposure risk to patients and surgeons. METHODS: We implanted 234 pedicle screws in 12 cadavers (study group: 15 surgeons, 197 screws, and 10 specimens; control group: 2 surgeons, 37 screws, and 2 specimens). We measured procedure time, fluoroscopy time, and radiation exposure and evaluated screw placement accuracy with computed tomography scans. To evaluate the learning curve, we compared measurements with those of an experienced robotic guidance user through the 2-sample (heteroscedastic), 1-tail t test (P< 0.05). RESULTS: Relative to control, the study group had fewer screw placement deviations (average, 2.6±0.7 mm vs. 1.1±0.4 mm; P<0.0001), fewer pedicle wall breaches of 4 mm or greater (average, 5.4% vs. 1.5%), lower surgeon radiation exposure (average, 136 mrem vs. 4.2 mrem), lower fluoroscopy time per screw (average, 33.0 s vs. 0.9 s), and shorter procedure time (average, 1.98 h vs. 1.23 h). Use of robotic guidance increased the accuracy of percutaneous pedicle screw placement by 58%, thereby reducing the risk of neurologic injury (as measured by breaches >4 mm), new-user radiation exposure (by 98.2%), and procedure time (by 36%). CONCLUSIONS: The advantages associated with a robotic guidance system may make the surgeon more at ease about offering minimally invasive or percutaneous surgical options to patients and more comfortable about implementing pedicle-based fixation in general. This advanced technology may also allow inclusion of patients with complicated anatomic deformities, who are often excluded from pedicle screw-based surgery options.

Results of lumbar total disc arthroplasty in military personnel.

STUDY DESIGN: Evaluation of lumbar total disc arthroplasty (TDA) in military patients. OBJECTIVE: To evaluate the clinical and radiographic outcomes of US military personnel who have undergone TDA for degenerative disc disease and to assess the retention versus discharge rate after undergoing this procedure. SUMMARY OF BACKGROUND DATA: TDA was developed as an alternative to arthrodesis for the surgical management of degenerative disc disease with the goal of preserving motion and reducing adjacent segment disease. However, the indications and optimal candidates for this procedure are uncertain. Military members must maintain a certain level of physical fitness and be capable of meeting the demands of hazardous environments. This study reviews results of TDA performed on active duty military members. METHODS: The surgery schedules from 2005 to 2008 were reviewed to identify military members who underwent single-level or 2-level TDA for degenerative disc disease after failing at least 6 months of conservative management. All patients had a minimum of 2-year follow-up. Preoperative and postoperative clinical assessments were completed using the Oswestry Disability Index (ODI) questionnaire and the numeric rating scale (NRS). Radiographs were evaluated to determine range of motion, height, and disc position at the operated levels. The retention rate of the patients in the military was also recorded. Statistical analysis of the data was carried out with significance assumed at the P < 0.05 level. RESULTS: Thirty-eight patients, implanted with a total of 56 discs, met the criteria for retrospective analysis. Twenty patients had single-level and 18 had 2-level TDA. Mean age was 35 (23 to 56 y) years. Mean follow-up was 28 months. The overall mean preoperative ODI and NRS of 53.6 and 7.3, significantly improved postoperatively to 27.7 and 3.3, respectively (P < 0.001). There was no difference in the postoperative ODI (P = 0.19) or NRS (P = 0.18) when comparing single-level and 2-level TDA. Clinical success was achieved in 79% of patients. Mean range of motion was 6.5 degrees and the mean disc height increased by 69%. Sixty-eight percent of patients returned to full active duty. CONCLUSIONS: This study showed clinical success approaching 80% in military patients who underwent lumbar TDA. Furthermore, close to 70% were able to return to their positions within the military. TDA, while more closely reapproximating the normal biomechanics of the spine, may provide patients with an improved alternative to spinal arthrodesis for degenerative disc disease.

The effect of parallax on intraoperative positioning of the Charité artificial disc.

STUDY DESIGN: Fluoroscopy imaging evaluation for total disc arthroplasty. OBJECTIVES: To describe the effect of fluoroscopic parallax on the relative position of the Charité and identify the most reliable method for evaluating intraoperative disc position. SUMMARY OF BACKGROUND DATA: Results of the Investigational Device Exemption study revealed that clinical outcomes of the Charité artificial disc correlated with accurate placement of the prosthesis. This is the first study to quantitatively evaluate the technique of intraoperative fluoroscopy during positioning of an artificial lumbar disc. METHODS: A Charité artificial disc (DePuy Spine, Raynham, MA) was implanted at the L5-S1 disc space of a radiopaque lumbar spine model in ideal position. A true anteroposterior fluoroscopic image of the L5-S1 disc space was obtained as were additional images as the central ray was moved to the left and right in 1 cm increments and with rotation at 1, 2, and 3 degrees. Images were also evaluated on a poorly placed and minimally displaced disc. Measurements of the distances from the middle tooth of the endplates to the anatomic center (spinous process) and alternative measurements for evaluating disc position were examined from computer-enhanced images. RESULTS: An ideally placed prosthesis appeared more displaced with increasing rotation and distance of the C-arm away from center when the spinous process was used as the midline reference. As little as 3 degrees of rotation of the fluoroscopic ray from the true anteroposterior image, made an ideally placed disc appear in poor position. Conversely, a poorly placed disc seemed to be in ideal position. Calculated displacement using measurements off the vertebral bodies remained more constant. Calculated displacement of an ideally placed prosthesis fell within 2 mm whereas all poorly placed discs had calculated differences greater than 4 mm. CONCLUSIONS: The spinous process is an unreliable anatomic midline marker. In contrast, the borders of the vertebral bodies can more reliably be used to calculate the displacement of the prosthesis from centerline to determine prosthesis position. Fluoroscopic parallax can cause an ideally placed prosthesis to appear more displaced with increasing rotation and distance away from the true anteroposterior image. The spinous process was determined to be an unreliable midline marker. The vertebral borders provided a more dependable anatomic reference point to establish the disc-space midline.

Silicate-substituted calcium phosphate as a bone void filler after kyphoplasty in a young patient with multiple compression fractures due to osteogenesis imperfecta variant: case report.

Kyphoplasty can be used to treat compression fractures resulting from a variety of causes. The use of polymethyl methacrylate (PMMA) in conjunction with kyphoplasty has many risks and potential complications, however, particularly in the younger patient population. Silicate-substituted calcium phosphate (Actifuse Synthetic Bone Graft; Apatech, Ltd.) is an alternative to PMMA that provides immediate pain relief and the ability to heal and incorporate within the vertebral body.

TranS1 VEO system: a novel psoas-sparing device for transpsoas lumbar interbody fusion.

Minimally invasive approaches for lumbar interbody fusion have been popularized in recent years. The retroperitoneal transpsoas approach to the lumbar spine is a technique that allows direct lateral access to the intervertebral disc space while mitigating the complications associated with traditional anterior or posterior approaches. However, a common complication of this procedure is iatrogenic injury to the psoas muscle and surrounding nerves, resulting in postsurgical motor and sensory deficits. The TranS1 VEO system (TranS1 Inc, Raleigh, NC, USA) utilizes a novel, minimally invasive transpsoas approach to the lumbar spine that allows direct visualization of the psoas and proximal nerves, potentially minimizing iatrogenic injury risk and resulting clinical morbidity. This paper describes the clinical uses, procedural details, and indications for use of the TranS1 VEO system.

Clinical acceptance and accuracy assessment of spinal implants guided with SpineAssist surgical robot: retrospective study.

STUDY DESIGN: Retrospective, multicenter study of robotically-guided spinal implant insertions. Clinical acceptance of the implants was assessed by intraoperative radiograph, and when available, postoperative computed tomography (CT) scans were used to determine placement accuracy. OBJECTIVE: To verify the clinical acceptance and accuracy of robotically-guided spinal implants and compare to those of unguided free-hand procedures. SUMMARY OF BACKGROUND DATA: SpineAssist surgical robot has been used to guide implants and guide-wires to predefined locations in the spine. SpineAssist which, to the best of the authors' knowledge, is currently the sole robot providing surgical assistance in positioning tools in the spine, guided over 840 cases in 14 hospitals, between June 2005 and June 2009. METHODS: Clinical acceptance of 3271 pedicle screws and guide-wires inserted in 635 reported cases was assessed by intraoperative fluoroscopy, where placement accuracy of 646 pedicle screws inserted in 139 patients was measured using postoperative CT scans. RESULTS: Screw placements were found to be clinically acceptable in 98% of the cases when intraoperatively assessed by fluoroscopic images. Measurements derived from postoperative CT scans demonstrated that 98.3% of the screws fell within the safe zone, where 89.3% were completely within the pedicle and 9% breached the pedicle by up to 2 mm. The remaining 1.4% of the screws breached between 2 and 4 mm, while only 2 screws (0.3%) deviated by more than 4 mm from the pedicle wall. Neurologic deficits were observed in 4 cases yet, following revisions, no permanent nerve damage was encountered, in contrast to the 0.6% to 5% of neurologic damage reported in the literature. CONCLUSION: SpineAssist offers enhanced performance in spinal surgery when compared to free-hand surgeries, by increasing placement accuracy and reducing neurologic risks. In addition, 49% of the cases reported herein used a percutaneous approach, highlighting the contribution of SpineAssist in procedures without anatomic landmarks.