Faculty Bibliography

BACKGROUND CONTEXT/BACKGROUND:The transpsoas lateral lumbar interbody fusion (LLIF) technique is an effective alternative to traditional anterior and posterior approaches to the lumbar spine; however, nerve injuries are the most reported postoperative complication. Commonly used strategies to avoid nerve injury (eg, limiting retraction duration) have not been effective in detecting or preventing femoral nerve injuries. PURPOSE/OBJECTIVE:To evaluate the efficacy of emerging intraoperative femoral nerve monitoring techniques and the importance of employing prompt surgical countermeasures when degraded femoral nerve function is detected. STUDY DESIGN/SETTING/METHODS:We present the results from a retrospective analysis of a multi-center study conducted over the course of 3 years. PATIENT SAMPLE/METHODS:One hundred and seventy-two lateral lumbar interbody fusion procedures were reviewed. OUTCOME MEASURES/METHODS:Intraoperative femoral nerve monitoring data was correlated to immediate postoperative neurologic examinations. METHODS:Femoral nerve evoked potentials (FNEP) including saphenous nerve somatosensory evoked potentials (snSSEP) and motor evoked potentials with quadriceps recordings were used to detect evidence of degraded femoral nerve function during the time of surgical retraction. RESULTS:In 89% (n=153) of the surgeries, there were no surgeon alerts as the FNEP response amplitudes remained relatively unchanged throughout the surgery (negative group). The positive group included 11% of the cases (n=19) where the surgeon was alerted to a deterioration of the FNEP amplitudes during surgical retraction. Prompt surgical countermeasures to an FNEP alert included loosening, adjusting, or removing surgical retraction, and/or requesting an increase in blood pressure from the anesthesiologist. All the cases where prompt surgical countermeasures were employed resulted in recovery of the degraded FNEP amplitudes and no postoperative femoral nerve injuries. In two cases, the surgeons were given verbal alerts of degraded FNEPs but did not employ prompt surgical countermeasures. In both cases, the degraded FNEP amplitudes did not recover by the time of surgical closure, and both patients exhibited postoperative signs of sensorimotor femoral nerve injury including anterior thigh numbness and weakened knee extension. CONCLUSIONS:Multimodal femoral nerve monitoring can provide surgeons with a timely alert to hyperacute femoral nerve conduction failure, enabling prompt surgical countermeasures to be employed that can mitigate or avoid femoral nerve injury. Our data also suggests that the common strategy of limiting retraction duration may not be effective in preventing iatrogenic femoral nerve injuries.

OBJECTIVE: To compare the characteristics, presentation, and surgical outcome of patients with microdiscectomies at L1-L2 and L2-L3 with those we treated at L3-L4. We further sought to compare these results with those reported in the literature for discectomies at the L4-L5 and L5-S1 levels. METHODS: We reviewed the clinical data collected from 69 patients who had 72 L1-L2, L2-L3, and L3-L4 microdiscectomies performed from 1989 to 1999 at the New York University Medical Center. Patients who had surgery at L1-L2 or L2-L3 were grouped and compared with those treated at the L3-L4 level. Patients' charts were retrospectively reviewed at a mean of 12.9 months after surgery for presenting signs and symptoms, patient characteristics, and surgical outcome. Long-term follow-up via telephone interview was obtained at an average of 81.3 months after surgery. RESULTS: In the L1-L2 + L2-L3 group, 58% of the patients had previous lumbar disc surgery, compared with only 10% of those in the L3-L4 group, and 20% in the L1-L2 + L2-L3 group required a fusion during the procedure compared with only 10% in the L3-L4 group. These differences are both statistically significant. The short-term chart review demonstrates that only 58% and 53% of patients in the L1-L2 + L2-L3 group were improved with regard to radicular and back pain, respectively, whereas those in the L3-L4 group reported 94 and 87% rates of improvement in the same categories, both highly statistically significant findings. The long-term follow-up confirmed a highly statistically significantly worse outcome in the L1-L2 + L2-L3 group, with only 33% of patients reporting an improvement in their economic or functional status, compared with an 88% rate of improvement in the L3-L4 group. The outcome of our patients with L3-L4 herniations was similar to that reported in the literature for herniations at L4-L5 and L5-S1. CONCLUSION: Herniated discs at the L1-L2 or L2-L3 level are different entities from those at lower levels of the lumbar spine. The surgical outcome in terms of postoperative back and radicular pain is worse for herniated discs at L1-L2 and L2-L3 compared with those treated at L3-L4. Our patients with L1-L2 or L2-L3 surgically treated herniated discs were more likely to have had previous lumbar surgery and required a fusion more often than their counterparts with L3-L4 herniated discs

Synovial cysts emanating from the lumbar facet joints may compromise the spinal canal and produce symptoms of radiculopathy or stenosis. Good results have been reported after excision of the symptomatic lesions. There are limited data, however, on the natural history involving nonoperative management and little information to suggest that these lesions ever regress spontaneously. The authors report on three patients in whom symptomatic lumbar synovial cysts spontaneously resolved and review the relevant literature

PURPOSE. To assess the thickness and surface area of porcine sclera. METHODS. One hundred twenty-eight porcine globes were sectioned from the center of the cornea to the region of the optic nerve. Photographs of the sectioned sclera including a millimeter scale were taken. Photographic slides were projected onto blank paper, and the scleral silhouette was traced. Perpendicular thickness measurements were taken at 1-mm intervals from the limbus to the optic nerve. The sclera of 18 porcine eyes were cut into small pieces, and the surface area was calculated with computerized digital tracing software. RESULTS. The scleral thickness near the corneal scleral limbus was 0.83 +/- 0.2, 0.91 +/- 0.17, and 1.12 +/- 0.23 mm in the small-, medium-, and large-sized pigs, respectively. Thickness decreased to minimum of 0.31 +/- 0.07, 0.35 +/- 0.1, and 0.43 +/- 0.16 mm at a distance of 5 mm from the limbus in the small- and medium-sized pigs and 6 mm in the large-sized pigs, respectively. The mean scleral surface area was 7.78 +/- 0.66, 9.66 +/- 0.75, and 11.92 +/- 1.57 cm(2) in the small-, medium-, and large-sized pigs, whereas the corneal surface area was 1.09 +/- 0.07, 1.15 +/- 0.09, and 1.40 +/- 0.19 cm(2), respectively. CONCLUSIONS. Porcine scleral thickness is very similar to human scleral thickness. The porcine model is an excellent model for studying transscleral drug delivery