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Faiz U. Ahmad, Charif Sidani, Roberto Fourzali and Michael Y. Wang

Object

Cobalt-chromium alloy (CoCr) rods haves some preferred biomechanical properties over titanium rods for spinal fixation. The use of CoCr rods in spinal fusion is relatively new, and there is no study in the existing world literature assessing the artifact caused by these rods in patients undergoing postoperative MRI. The purpose of this study is to compare the amount of imaging artifact caused by these implants and to assess its impact on the visualization of neighboring neural structures.

Methods

This study investigated MR images in patients who underwent implantation of thoracolumbar instrumentation using 5.5-mm-diameter CoCr rods between November 2009 and March 2011 and images obtained in a comparison group of patients who had 5.5-mm titanium rods implanted during the same time period. Axial measurements of the artifact created by the rods between the screw heads were compared between the groups. Two blinded board-certified radiologists performed the measurements independently. They scored the visualization of the spinal canal using a subjective scoring system of 1–3, with 1 representing very good visualization and 2 and 3 representing reduced (good or suboptimal, respectively) visualization as a result of rod-related artifact. All measurements and scores were independently provided for T1-weighted and T2-weighted fast spin echo sequences (1.5-T magnet, 5-mm slice thickness).

Results

A total of 40 levels from the CoCr group (6 patients) and 30 levels from the titanium group (9 patients) were included in the analysis. Visualization of the canal at all levels was rated a score of 1 (very good) by both evaluators for both the CoCr and titanium groups. The average artifact on T1-weighted images measured 11.8 ± 1.8 mm for the CoCr group and 8.5 ± 1.2 mm for the titanium group (p < 0.01). The corresponding measurements on T2-weighted images were 11.0 ± 2.3 mm and 8.3 ± 1.7 mm (p < 0.01), respectively. In a mixed regression model, the mean artifact measurement for the CoCr group was, on average, 3.5 mm larger than for the control group. There was no significant difference between the measurements of the 2 evaluators (p = 0.99).

Conclusions

The artifact caused by CoCr rods is approximately 3.5 mm larger than that caused by titanium rods on axial T1- and T2-weighted MRI. However, artifact from either CoCr or titanium was not found to interfere with the evaluation of the spinal canal and surrounding neural elements.

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Michael Y. Wang

Adult spinal deformities (ASD) pose a challenge for the spinal surgeon. Because the spine is often rigid, mobilization of the segments is critical for effective correction, particularly in the sagittal plane. While minimally invasive surgery (MIS) has many favorable attributes that would be of great benefit for the ASD population, improvements in lordosis and sagittal balance have remained problematic using MIS approaches, including MIS lateral methods. This video illustrates one method for achieving improvement of coronal and sagittal correction without the extensive exposure and soft tissue envelope disruption needed in open surgery, particularly for less severe deformities. By using multi-level TLIFs through a mini-open surgery, curves of less than 60° can be managed with minimal blood loss and within a reasonable surgical timeframe. While feasibility will have to be proven with larger series and improved surgical methods, this technique holds promise as a means of reducing the significant morbidity associated with surgery in the ASD population.

The video can be found here: http://youtu.be/I0rkDSAVas0.

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Christopher I. Shaffrey and Justin S. Smith

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Michael Y. Wang

Object

The treatment of adult spinal deformity (ASD) remains a challenge for the spine surgeon. While minimally invasive surgery (MIS) has many favorable attributes that would be of great benefit for the ASD population, improvements in lordosis and sagittal balance have remained elusive in cases involving the MIS approach. This report describes the evolution of an MIS method for treating ASD with attention to sagittal correction.

Methods

Over an 18-month period 25 patients with thoracolumbar scoliosis were treated surgically. The mean patient age was 72 years, and 68% of the population was female. Patients were treated with multilevel facet osteotomies and interbody fusion in which expandable cages (mean 3.2 levels) were placed and percutaneous screw fixation (mean 5.3 levels) was performed. Seven patients underwent supplemental percutaneous iliac fixation.

Results

All patients underwent MIS without conversion to a traditional open procedure. The mean operative time was 273 mins and the mean blood loss was 416 ml. There were no intraoperative complications. The Cobb angle over the scoliotic deformity improved from a mean of 29.2° to that of 9.0° (p < 0.001). Lumbar lordosis between L-1 and S-1 improved from a mean of 27.8° to one of 42.6° (p < 0.001). Sagittal vertical axis improved from 7.4 cm to 4.3 cm (p = 0.001). Numeric pain scale scores improved as well, an average of 3.3 and 4.2 for the leg and back, respectively. A mean improvement of 20.8 points on the Oswestry Disability Index was seen at 12 months. Complications included: two cases requiring hardware repositioning, one case of screw pullout, one asymptomatic pedicle screw breach, prolonged hospitalization from constipation, and one acute coronary syndrome developing 3 days after surgery without myocardial damage.

Conclusions

An expanding body of evidence suggests that sagittal balance remains a keystone for good outcomes after ASD surgery. Minimally invasive surgery that involves a combination of osteotomies, interbody height restoration, and advanced fixation techniques may achieve this goal in patients with less severe deformities. While feasibility will have to be proven with larger series and improved surgical methods, the present technique holds promise as a means of reducing the significant morbidity associated with surgery in the ASD population.

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Alexander A. Khalessi, Gabriel Zada, Michael Y. Wang and James Forrest Calland

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Kevin S. Cahill, Joseph L. Martinez, Michael Y. Wang, Steven Vanni and Allan D. Levi

Object

The aim of this study was to determine the incidence of motor nerve injuries during the minimally invasive lateral interbody fusion procedure at a single academic medical center.

Methods

A retrospective chart review of 118 patients who had undergone lateral interbody fusion was performed. Both inpatient and outpatient records were examined to identify any new postoperative motor weakness in the lower extremities and abdominal wall musculature that was attributable to the operative procedure.

Results

In the period from 2007 to 2011 the lateral interbody fusion procedure was attempted on 201 lumbar intervertebral disc levels. No femoral nerve injuries occurred at any disc level other than the L4–5 disc space. Among procedures involving the L4–5 level there were 2 femoral nerve injuries, corresponding to a 4.8% injury risk at this level as compared with a 0% injury risk at other lumbar spine levels. Five patients (4.2%) had postoperative abdominal flank bulge attributable to injury to the abdominal wall motor innervation.

Conclusions

The overall incidence of femoral nerve injury after the lateral transpsoas approach was 1.7%; however, the level-specific incidence was 4.8% for procedures performed at the L4–5 disc space. Approximately 4% of patients had postoperative abdominal flank bulge. Surgeons will be able to minimize these motor nerve injuries through judicious use of the procedure at the L4–5 level and careful attention to the T-11 and T-12 motor nerves during exposure and closure of the abdominal wall.

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Jocelyn Cheng, D. Ethan Kahn and Michael Y. Wang

Guillain-Barré syndrome (GBS) is the eponym used to describe acute inflammatory polyradiculoneuropathies, which manifest with weakness and diminished reflexes. Although the classic form of GBS is considered to be an ascending demyelinating polyneuropathy, several variants have been described in the literature, including the Miller-Fisher syndrome, acute panautonomic neuropathy, acute motor axonal neuropathy, and acute motor-sensory axonal neuropathy (AMSAN). Few cases of postoperative GBS have been documented, particularly for the AMSAN variant. The authors describe the case of a patient who developed AMSAN after thoracic spine surgery and highlight the importance of investigating new-onset weakness in the postoperative period.

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Matthew D. Cummock, Steven Vanni, Allan D. Levi, Yong Yu and Michael Y. Wang

Object

The minimally invasive transpsoas interbody fusion technique requires dissection through the psoas muscle, which contains the nerves of the lumbosacral plexus posteriorly and genitofemoral nerve anteriorly. Retraction of the psoas is becoming recognized as a cause of transient postoperative thigh pain, numbness, paresthesias, and weakness. However, few reports have described the nature of thigh symptoms after this procedure.

Methods

The authors performed a review of patients who underwent the transpsoas technique for lumbar spondylotic disease, disc degeneration, and spondylolisthesis treated at a single academic medical center. A review of patient charts, including the use of detailed patient-driven pain diagrams performed at equal preoperative and follow-up intervals, investigated the survival of postoperative thigh pain, numbness, paresthesias, and weakness of the iliopsoas and quadriceps muscles in the follow-up period on the ipsilateral side of the surgical approach.

Results

Over a 3.2-year period, 59 patients underwent transpsoas interbody fusion surgery. Of these, 62.7% had thigh symptoms postoperatively. New thigh symptoms at first follow-up visit included the following: burning, aching, stabbing, or other pain (39.0%); numbness (42.4%); paresthesias (11.9%); and weakness (23.7%). At 3 months postoperatively, these percentages decreased to 15.5%, 24.1%, 5.6%, and 11.3%, respectively. Within the patient sample, 44% underwent a 1-level, 41% a 2-level, and 15% a 3-level transpsoas operation. While not statistically significant, thigh pain, numbness, and weakness were most prevalent after L4–5 transpsoas interbody fusion at the first postoperative follow-up. The number of lumbar levels that were surgically treated had no clear association with thigh symptoms but did correlate directly with surgical time, intraoperative blood loss, and length of hospital stay.

Conclusions

Transpsoas interbody fusion is associated with high rates of immediate postoperative thigh symptoms. While larger, prospective studies are necessary to validate these findings, the authors found that half of the patients had symptom resolution at approximately 3 months postoperatively and more than 90% by 1 year.