Sina Pourtaheri, Akshay Sharma, Jason Savage, Iain Kalfas, Thomas E. Mroz, Edward Benzel and Michael P. Steinmetz
The flexed posture of the proximal (L1–3) or distal (L4–S1) lumbar spine increases the diameter of the spinal canal and neuroforamina and can relieve symptoms of neurogenic claudication. Distal lumbar flexion can result in pelvic retroversion; therefore, in cases of flexible sagittal imbalance, pelvic retroversion may be compensatory for lumbar stenosis and not solely compensatory for the sagittal imbalance as previously thought. The authors investigate underlying causes for pelvic retroversion in patients with flexible sagittal imbalance.
One hundred thirty-eight patients with sagittal imbalance who underwent a total of 148 fusion procedures of the thoracolumbar spine were identified from a prospective clinical database. Radiographic parameters were obtained from images preoperatively, intraoperatively, and at 6-month and 2-year follow-up. A cohort of 24 patients with flexible sagittal imbalance was identified and individually matched with a control cohort of 23 patients with fixed deformities. Flexible deformities were defined as a 10° change in lumbar lordosis between weight-bearing and non–weight-bearing images. Pelvic retroversion was quantified as the ratio of pelvic tilt (PT) to pelvic incidence (PI).
The average difference between lumbar lordosis on supine MR images and standing radiographs was 15° in the flexible cohort. Sixty-eight percent of the patients in the flexible cohort were diagnosed preoperatively with lumbar stenosis compared with only 22% in the fixed sagittal imbalance cohort (p = 0.0032). There was no difference between the flexible and fixed cohorts with regard to C-2 sagittal vertical axis (SVA) (p = 0.95) or C-7 SVA (p = 0.43). When assessing for postural compensation by pelvic retroversion in the stenotic patients and nonstenotic patients, the PT/PI ratio was found to be significantly greater in the patients with stenosis (p = 0.019).
For flexible sagittal imbalance, preoperative attention should be given to the root cause of the sagittal misalignment, which could be compensation for lumbar stenosis. Pelvic retroversion can be compensatory for both the lumbar stenosis as well as for sagittal imbalance.
Jeffrey P. Mullin, Breanna Perlmutter, Eric Schmidt, Edward Benzel and Michael P. Steinmetz
In 2009, Santoni and colleagues described a novel technique of posterior instrumentation; the cortical bone trajectory (CBT) was described as a caudocephalad and medial-to-lateral trajectory. Reported indications for CBT fixation include patients with osteoporosis, single-level degenerative disease, or adjacent-segment disease (ASD). In cases of revision surgery, it is technically possible and beneficial to place a traditional pedicle screw and a CBT screw at the same spinal level and side. It remains unclear as to the feasibility of placing both a traditional and a CBT screw at all levels of the lumbar spine and with varying trajectories of the preexisting traditional pedicle screws. Therefore, the authors conducted a study to radiographically assess the feasibility of using CBT and traditional pedicle screws at the same level in a large patient population.
Using a 3D Spine Navigation WorkStation, the authors assessed 47 lumbar spine CT scans. These images were obtained from 2 disparate groups of patients: those who had previously undergone traditional pedicle instrumentation (prior surgery group) and those who had not (no prior surgery group). The authors virtually placed traditional pedicle and CBT screws at each lumbar level bilaterally. It was then determined if the dual trajectories were feasible, as defined by the presence or absence of a collision of the screw trajectories based on 3D imaging.
Overall, the authors evaluated 47 patients and were able to successfully plan dual trajectories in 50% of the pedicles. The no prior surgery group, compared with the prior surgery group, had a significantly greater success rate for dual trajectories. This difference was most significant in the lower lumbar levels (L3–5) where the prior instrumented group had success rates lower than 40% compared with the no prior surgery group's success rate, which was greater than 70%. There was a significant difference between each lumbar level in the lower spine.
There is a significant difference in the feasibility of planning CBT screws in patients who have undergone prior pedicle instrumentation compared with placing CBT and traditional pedicle screws simultaneously, but dual trajectory pedicle screws are a feasible option for posterior lumbar spinal instrumentation, especially as a de novo option in osteoporotic patients or in patients with ASD who underwent previous pedicle instrumentation. Ultimately, the practical clinical utility and biomechanical effects on the spine and instrumentation construct would require additional study.
Adam Bartsch, Edward Benzel, Vincent Miele and Vikas Prakash
Matthew J. Grosso, Roy Hwang, Thomas Mroz, Edward Benzel and Michael P. Steinmetz
Reversal of the normal cervical spine curvature, as seen in cervical kyphosis, can lead to mechanical pain, neurological dysfunction, and functional disabilities. Surgical intervention is warranted in patients with sufficiently symptomatic deformities in an attempt to correct the deformed cervical spine. In theory, improved outcomes should accompany a greater degree of correction toward lordosis, although there are few data available to test this relationship. The purpose of this study is to determine if the degree of deformity correction correlates with improvement in neurological symptoms following surgery for cervical kyphotic deformity.
A retrospective review of 36 patients with myelopathic symptoms who underwent cervical deformity correction surgery between 2001 and 2009 was performed. Preoperative and postoperative radiographic findings related to the degree of kyphosis were collected and compared with functional outcome measures. The minimum follow-up time was 2 years.
A significant relationship was observed between a greater degree of focal kyphosis correction and improved neurological outcomes according to the modified Japanese Orthopaedic Association (mJOA) score (r = −0.46, p = 0.032). For patients with severe neurological symptoms (mJOA score < 12) a trend toward improved outcomes with greater global kyphosis correction was observed (r = −0.56, p = 0.057). Patients with an mJOA score less than 16 who attained lordosis postoperatively had a significantly greater improvement in total mJOA score than patients who maintained a kyphotic position (achieved lordosis: 2.7 ± 2.0 vs maintained kyphosis: 1.1 ± 2.1, p = 0.044).
The authors' results suggest that the degree of correction of focal kyphosis deformity correlates with improved neurological outcomes. The authors also saw a positive relationship between attainment of global lordosis and improved mJOA scores. With consideration for the risks involved in correction surgery, this information can be used to help guide surgical strategy decision making.