Richard J Herzog

Hospital for Special Surgery, New York, New York, United States

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Publications (42)107.83 Total impact

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    ABSTRACT: Spinal subdural hematoma (SSDH) following spine surgery is an extremely rare condition, with only three cases being reported in the literature. Unintended durotomy has been associated with SSDH due to alterations of pressures in the dural compartments. The objective of the present report was to report two rare cases of acute SSDH developed after lumbar decompressive surgery. In one of the patients, the diagnosis of SSDH was followed by urgent hematoma evacuation via durotomy due to the patient's worsening neurological symptoms. In the second patient, the SSDH was treated conservatively due to the absence of severe or progressive motor or sensory deficits. In conclusion, emergency evacuation via durotomy is the treatment of choice for patients with SSDH and neurologic impairment. Conservative management may be indicated in selected cases with absent motor and sensory deficits.
    Wiener klinische Wochenschrift 11/2014; 127(1-2). DOI:10.1007/s00508-014-0632-3 · 0.84 Impact Factor
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    ABSTRACT: PURPOSE: Anatomical landmarks and their relation to the lumbar vertebrae are well described in subjects with normal spine anatomy, but not for subjects with lumbosacral transitional vertebra (LSTV), in whom correct numbering of the vertebrae is challenging and can lead to wrong-level treatment. The aim of this study was to quantify the value of different anatomical landmarks for correct identification of the lumbar vertebra level in subjects with LSTV. METHODS: After IRB approval, 71 subjects (57 ± 17 years) with and 62 without LSTV (57 ± 17 years), all with imaging studies that allowed correct numbering of the lumbar vertebrae by counting down from C2 (n = 118) or T1 (n = 15) were included. Commonly used anatomical landmarks (ribs, aortic bifurcation (AB), right renal artery (RRA) and iliac crest height) were documented to determine the ability to correctly number the lumbar vertebrae. Further, a tangent to the top of the iliac crests was drawn on coronal MRI images by two blinded, independent readers and named the 'iliac crest tangent sign'. The sensitivity, specificity and the interreader agreement were calculated. RESULTS: While the level of the AB and the RRA were found to be unreliable in correct numbering of the lumbar vertebrae in LSTV subjects, the iliac crest tangent sign had a sensitivity and specificity of 81 % and 64-88 %, respectively, with an interreader agreement of k = 0.75. CONCLUSION: While anatomical landmarks are not always reliable, the 'iliac crest tangent sign' can be used without advanced knowledge in MRI to most accurately number the vertebrae in subjects with LSTV, if only a lumbar spine MRI is available.
    European Spine Journal 09/2014; 24(3). DOI:10.1007/s00586-014-3573-7 · 2.07 Impact Factor
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    ABSTRACT: OBJECTIVE: Sufficiently sized studies to determine the value of the iliolumbar ligament (ILL) as an identifier of the L5 vertebra in cases of a lumbosacral transitional vertebra (LSTV) are lacking. METHODS: Seventy-one of 770 patients with LSTV (case group) and 62 of 611 subjects without LSTV with confirmed L5 level were included. Two independent radiologists using coronal MR images documented the level(s) of origin of the ILL. The interobserver agreement was analysed using weighted kappa/kappa (wκ/κ) and a Fischer's exact test to assess the value of the ILL as an identifier of the L5 vertebra. RESULTS: The ILL identified the L5 vertebra by originating solely from L5 in 95 % of the controls; additional origins were observed in 5 %. In the case group, the ILL was able to identify the L5 vertebra by originating solely from L5 in 25-38 %. Partial origin from L5, including origins from other vertebra was observed in 39-59 % and no origin from L5 at all in 15-23 % (wκ = 0.69). Both readers agreed that an ILL was always present and its origin always involved the last lumbar vertebra. CONCLUSION: The level of the origin of the ILL is unreliable for identification of the L5 vertebra in the setting of an LSTV or segmentation anomalies. KEY POINTS: • The origin of the ILL is evaluated in subjects with an LSTV. • The origin of the ILL is anatomically highly variable in LSTV. • The ILL is not a reliable landmark of the L5 vertebra in LSTV.
    European Radiology 06/2014; 24(10). DOI:10.1007/s00330-014-3277-8 · 4.01 Impact Factor
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    ABSTRACT: Evolution and progression of disc and endplate bone marrow degeneration of the lumbar spine are thought to be multifactorial, yet, their influence and interactions are not understood. The aim of this study was to find association of potential predictors of evolution of degeneration of the lumbar spine. Patients (n = 90) who underwent two lumbar magnetic resonance imaging (MRI) exams with an interval of at least 4 years and without any spinal surgery were included into the longitudinal cohort study with nested case-control analysis. Disc degeneration (DD) was scored according to the Pfirrmann classification and endplate bone marrow changes (EC) according to Modic in 450 levels on both MRIs. Potential variables for degeneration such as age, gender, BMI, scoliosis and sagittal parameters were compared between patients with and without evolution or progression of degenerative changes in their lumbar spine. A multivariate analysis aimed to identify the most important variables for progression of disc and endplate degeneration, respectively. While neither age, gender, BMI, sacral slope or the presence of scoliosis could be identified as progression factor for DD, a higher lordosis was observed in subjects with no progression (49A degrees A A +/- A 11A degrees vs 43A degrees A A +/- A 12A degrees; p = 0.017). Progression or evolution of EC was only associated with a slightly higher degree of scoliosis (10A degrees A A +/- A 10A degrees vs 6A degrees A A +/- A 9A degrees; p = 0.04) and not to any of the other variables. While a coronal deformity of the lumbar spine seems associated with evolution or progression of EC, a higher lumbar lordosis is protective for radiographic progression of DD. This implies that scoliotic deformity and lesser lumbar lordosis are associated with higher overall degeneration of the lumbar spine.
    European Spine Journal 06/2014; 23(9). DOI:10.1007/s00586-014-3382-z · 2.07 Impact Factor
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    ABSTRACT: It is questionable whether an annular tear (AT) is a predictor for accelerated degeneration of the intervertebral discs. The aim of the present study was to answer this question via a matched case-control study design that reliably eliminates potential confounders. Presence or absence of AT, defined as a hyperintense lesion within the annular fibrosus on T2-weighted non-contrast MRI images, was documented in 450 intervertebral lumbar discs of 90 patients who could be followed up for at least 4 years with MRI. Discs with an AT (n = 36) were matched 1:1 to control discs according to the level, degree of initial disc degeneration on MRI (both Pfirrmann grade median 4, range 3-4), age (59.5 ± 15.0 versus 59.3 ± 14.6 years), BMI (26.7 ± 4.4 versus 26.9 ± 4.4 kg/m(2)) and interval to the follow-up MRI (4.8 ± 0.9 versus 5.1 ± 0.8 years). The degree of disc degeneration after a minimum of 4 years was graded on the follow-up MRI in both groups according to the Pfirrmann classification. One-fourth (25 %) of the 36 discs with an AT on the initial MRI exam progressed in degeneration. This was similar to the rate of the matched control discs with no AT, in which also around one-fourth (22 %) showed a progression of degeneration (p = 1.00), also without any difference in the degree of degeneration. Discs with a Pfirrmann grade >2 with an AT, defined by a hyperintense signal intensity on MRI, are not prone to accelerated degeneration if compared to discs without an AT. Therefore, the presence of an AT per se does not predict accelerated disc degeneration.
    European Spine Journal 03/2014; 23(9). DOI:10.1007/s00586-014-3260-8 · 2.07 Impact Factor
  • Alexander Aichmair · Richard J Herzog · Giorgio Perino · Darren R Lebl
    HSS Journal 02/2014; 10(1):83-87. DOI:10.1007/s11420-013-9364-6
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    ABSTRACT: The relation between specific types of lumbosacral transitional vertebra and the degree of degeneration at and adjacent to the transitional level is unclear. It is further unknown whether the adjacent cephalad segment to a transitional vertebra is prone to greater degeneration than a normal L5/S1 level. To evaluate the relation between specific lumbosacral transitional vertebra subtypes according to the Castellvi classification and the severity of degeneration at the transitional level and the adjacent cephalad segment. Retrospective review. 92 subjects with lumbosacral transitional vertebra grade 2 or higher and 94 controls without were retrieved from a PACS search. Disc degeneration parameters at the transitional and at the adjacent cephalad level. After IRB approval, 92 (42 male; mean age 57±16 years) subjects with lumbosacral transitional vertebra grade 2 or higher and 94 (41 male; 51±16 years) controls without were retrieved from a PACS search. Degeneration of the last two segments of the lumbar spine was quantified using the Pfirrmann, and Modic classifications, along with documentation of annular tears, disc herniations and disc heights, and compared between the two groups. Further, L5/S1 levels of the controls were compared to the adjacent cephalad segments of the transitional vertebrae for the same parameters. While the controls at L5/S1 had moderate to severe degeneration by Pfirrmann grades (31%) and Modic changes (MC: 20%), compared, the discs at the transitional level of the lumbosacral transitional vertebra group demonstrated significant less degeneration (3% and 1%,each p<0.05). The adjacent cephalad segments of the lumbosacral transitional vertebra group showed significantly greater degeneration (Pfirrmann grade 5: 39%; MC: 30%) compared to the L4/5 level in controls (16%; 11%; each p<0.05). The severity of disc degeneration using all parameters correlated with the type of lumbosacral transitional vertebra. The degree of degeneration of L5/S1 in controls was similar to the adjacent cephalad segment in lumbosacral transitional vertebrae. Increasing mechanical connection of a lumbosacral transitional vertebra protects the disc at the transitional level and predisposes the adjacent cephalad segment to greater degeneration. The adjacent cephalad segment had comparable degree of degeneration as the L5/S1 level of controls.
    The spine journal: official journal of the North American Spine Society 11/2013; 15(6). DOI:10.1016/j.spinee.2013.10.029 · 2.43 Impact Factor
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    ABSTRACT: The purpose of this study was to devise a simple but reliable radiological method of identifying a lumbosacral transitional vertebra (LSTV) with a solid bony bridge on sagittal MRI, which could then be applied to a lateral radiograph. The vertical mid-vertebral angle (VMVA) and the vertical anterior vertebral angle (VAVA) of the three most caudal segments of the lumbar spine were measured on MRI and/or on a lateral radiograph in 92 patients with a LSTV and 94 controls, and the differences per segment (Diff-VMVA and Diff-VAVA) were calculated. The Diff-VMVA of the two most caudal vertebrae was significantly higher in the control group (25° (sd 8) than in patients with a LSTV (type 2a+b: 16° (sd 9), type 3a+b: -9° (sd 10), type 4: -5° (sd 7); p < 0.001). A Diff-VMVA of ≤ +10° identified a LSTV with a solid bony bridge (type 3+4) with a sensitivity of 100% and a specificity of 89% on MRI and a sensitivity of 94% and a specificity of 74% on a lateral radiograph. A sensitivity of 100% could be achieved with a cut-off value of 28° for the Diff-VAVA, but with a lower specificity (76%) on MRI than with Diff-VMVA. Using this simple method (Diff-VMVA ≤ +10°), solid bony bridging of the posterior elements of a LSTV, and therefore the first adjacent mobile segment, can be easily identified without the need for additional imaging.
    Bone and Joint Journal 11/2013; 95-B(11):1533-7. DOI:10.1302/0301-620X.95B11.32331 · 1.96 Impact Factor
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    ABSTRACT: A feared complication of spinal or epidural anesthesia is the development of epidural or spinal hematoma with subsequent neural element compression. Most available data are derived from the obstetric literature. Little is known about the frequency of hematoma occurrence among patients undergoing orthopedic joint arthroplasty, who are usually elderly and experience significant comorbidities. We sought to study the incidence of clinically significant lesions after spinal and epidural anesthesia and further describe their nature. We retrospectively analyzed a database of all patients who underwent total hip or total knee arthroplasty under neuraxial anesthesia at our institution between January 2000 and October 2010. Patients with radiographically confirmed epidural lesions were identified and further analyzed. A total of 100,027 total knee and hip replacements under neuraxial anesthesia were performed at our institution. Ninety-seven patients underwent imaging studies to evaluate perioperative neurologic deficits (0.96/1000; 95% confidence interval, 0.77-1.16/1000). Eight patients were identified with findings of an epidural blood or gas collection (0.07/1000; 95% confidence interval, 0.02-0.13/1000). No patients receiving only spinal anesthesia were affected. All patients diagnosed with hematoma took at least 1 drug that potentially impaired coagulation (5 nonsteroidal anti-inflammatory agents, 1 a tricyclic antidepressant, and 1 an antiplatelet drug). No patient incurred persistent nerve damage. The incidence of epidural/spinal complications found in this consecutive case series is relatively low but higher than previously reported in the nonobstetric population. Further research using large data sets could quantify the significance of some of the potentially contributing factors observed in this study.
    Regional anesthesia and pain medicine 10/2013; 38(6). DOI:10.1097/AAP.0000000000000009 · 3.09 Impact Factor
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    ABSTRACT: Different types of lumbosacral transitional vertebra (LSTV) are classified based on the relationship of the transverse process of the last lumbar vertebra to the sacrum. The Ferguson view (30° angled anteroposterior [AP] radiograph) is supposed to have a sufficient interreader reliability in classification of LSTV, but is not routinely available. Standard AP radiographs and magnetic resonance imaging (MRI) are often available, but their reliability in detection and classification of LSTV is unknown. The purpose of this study was to evaluate the interreader reliability of detection and classification of LSTV with standard AP radiographs and report its accuracy by use of intermodality statistics compared with MRI as the gold standard. Retrospective case control study. A total of 155 subjects (93 cases: LSTV type 2 or higher; 62 controls). Interreader reliability in detection and classification of LSTV using standard AP radiographs and coronal MRI as well as accuracy of radiographs compared with MRI. After institutional review board approval, coronal MRI scans and conventional AP radiographs of 155 subjects (93 LSTV type 2 or higher and 62 controls) were retrospectively reviewed by two independent, blinded readers and classified according to the Castellvi classification. Interreader reliability was assessed using kappa statistics for detection of an LSTV and identification of all subtypes (six variants; 1: no LSTV or type I, 2: LSTV type 2a, 3: LSTV type 2b, 4: LSTV type 3a, 5: LSTV type 3b, 6: LSTV type 4) for MRI scans and standard AP radiographs. Further, accuracy and positive and negative predictive values were calculated for standard AP radiographs to detect and classify LSTV using MRI as the gold standard. The interreader reliability was at most moderate for the detection (k=0.53) and fair for classification (wk=0.39) of LSTV in standard AP radiograph. However, the interreader reliability was very good for detection (k=0.93) and classification (wk=0.83) of LSTV in MRI. The accuracy and positive and negative predictive values of standard AP radiograph were 76% to 84%, 72% to 86%, and 79% to 81% for the detection and 53% to 58%, 51% to 76%, and 49% to 55% for the classification of LSTV, respectively. Standard AP radiographs are insufficient to detect or classify LSTV. Coronal MRI scans, however, are highly reliable for classification of LSTV.
    The spine journal: official journal of the North American Spine Society 10/2013; 14(8). DOI:10.1016/j.spinee.2013.08.048 · 2.43 Impact Factor
  • European Journal of Anaesthesiology 06/2013; 30:2-3. DOI:10.1097/00003643-201306001-00006 · 2.94 Impact Factor
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    ABSTRACT: Study Design: A retrospective cohort designObjective: To determine if baseline MRI findings including central/foraminal stenosis, Modic change, disc morphology, facet arthropathy, disc degeneration, nerve root impingement, and thecal sac compression are associated with differential surgical treatment effect.Summary of Background Data: Intervertebral Disc Herniation (IDH) remains the most common source of lumbar radiculopathy treated either with discectomy or non-operative intervention. Although MRI remains the reliable gold standard for diagnosis, uncertainty surrounds the relationship between MRI findings and treatment outcomes.Methods: Three-hundred-and-seven "complete" images from patients enrolled in a previous trial were de-identified and evaluated by one of 4 independent readers. Findings were compared to outcome measures including the Oswestry Disability Index. Differences in surgery and non-operative treatment outcomes were evaluated between image characteristic subgroups and TE determined by the difference in ODI scores.Results: The cohort was comprised of 40% females with an average age of 41.5 (±11.6), 61% of which underwent discectomy for IDH. Patients undergoing surgery with Modic type I endplate changes had worse outcomes (-26.4 versus -39.7 for none and -39.2 for type 2, p = 0.002) and smaller treatment effect (-3.5 versus -19.3 for none and -15.7 for type 2, p = 0.003). Those with compression > = 1/3 showed the greatest improvement within the surgical group (-41.9 for > = 1/3 versus -31.6 for none and -38.1 for <1/3, p = 0.007), and the highest TE (-23 compared to -11.7 for none and -15.2 for <1/3, p = 0.015). Furthermore, patients with minimal nerve root impingement demonstrated worse surgical outcomes (-26.5 versus -41.1 for "displaced" and -38.9 for "compressed", p = 0.016).Conclusion: Among patients with IDH, those with thecal sac compression > = 1/3 had greater surgical treatment effect than those with small disc herniations and Modic type I changes. Additionally, patients with nerve root "compression" and "displacement" benefit more from surgery than those with minimal nerve-root impingement.
    Spine 02/2013; 38(14). DOI:10.1097/BRS.0b013e31828ce66d · 2.30 Impact Factor
  • Richard J Herzog
    Spine 01/2013; DOI:10.1097/BRS.0b013e318285b03f · 2.30 Impact Factor
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    ABSTRACT: STUDY DESIGN:: Cadaveric Study. OBJECTIVE:: To compare a fluoroscopic imaging system with computed tomography (CT) and radiographs in detection of spondylolysis and radiation exposure in a cadaver model. SUMMARY OF BACKGROUND DATA:: Lumbar spondylolysis is defined as a defect or fracture of the pars interarticularis and occurs with or without anterior spondylolisthesis. CT scan is the gold standard imaging study for spondylolysis but is limited by the supine position, which may cause reduction of anterolisthesis and by ionizing radiation, which limits the frequency of follow-up scans. METHODS:: Thirteen intact cadaveric lumbar spine segments with 26 pars were randomized to be left intact or to undergo simulated fracture using a 1.3 mm oscillating microsurgical saw. Fifteen pars underwent simulated fracture and 11 pars were left intact. Lumbar spine segments were imaged using plain radiographs, multiplanar fluoroscopic imaging, and conventional CT scan. The images were interpreted by 3 observers blinded to the number and location of defects. Radiation exposure and doses were recorded from all imaging units. RESULTS:: Average radiation doses were 0.0025 mSv for each radiograph, 0.23 mSv (low dose) and 0.47 mSv (high dose) for fluoroscopic imaging, and 1.5 mSv for conventional CT imaging (pediatric dose setting). Evaluation of radiographs for spondylolysis had sensitivity of 98% and specificity of 97%. Evaluation using low-dose fluoroscopic images, high-dose fluoroscopic images, and CT scan images correctly identified the status of all pars based on multiplanar images; sensitivity and specificity were 100%. Kappa analysis demonstrated a value of 0.89 for radiographic interpretation indicating excellent agreement. Kappa values describing agreement for image interpretation for fluoroscopic imaging and CT scan were equal to 1.0, representing perfect agreement. CONCLUSIONS:: Three-dimensional fluoroscopic imaging provides comparable diagnostic imaging with CT scan in an experimental cadaveric model of spondylolysis using up to 85% less radiation than conventional CT scan.
    Journal of spinal disorders & techniques 12/2011; 25(8). DOI:10.1097/BSD.0b013e318228bccc · 2.20 Impact Factor
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    ABSTRACT: Provocative discography, an invasive diagnostic procedure involving disc puncture with pressurization, is a test for presumptive discogenic pain in the lumbar spine. The clinical validity of this test is unproven. Data from multiple animal studies confirm that disc puncture causes early disc degeneration. A recent study identified radiographic disc degeneration on MRI performed 10 years later in human subjects exposed to provocative discography. The clinical effect of this disc degeneration after provocative discography is unknown. To investigate the clinical effects of lumbar provocative discography on patients subjected to this evaluation method. A prospective, ten-year matched-cohort study. Subjects (n = 75) without current low back pain problems were recruited to participate in a study of provocative discography at the L3 - S1 discs. A closely matched control cohort was simultaneously recruited to undergo a similar evaluation except for discography injections. The primary outcome variables were diagnostic imaging events and lumbar disc surgery events. The secondary outcome variables were serious low back pain events, disability events, and medical visits. The discography subjects and control subjects were followed by serial protocol evaluations at 1, 2, 5 and 10 years after enrollment. The lumbar disc surgery events and diagnostic imaging (CT or MRI) events were recorded. Additionally, the interval and cumulative lumbar spine events were recorded. Out of the 150 subjects enrolled, 71 discography subjects and 72 control subjects completed the baseline evaluation. At ten-years follow-up, 57 discography and 53 control subjects completed all interval surveillance evaluations. There were 16 lumbar surgeries in the discography group, compared with 4 in the control group. Medical visits, CT/MRI examinations, work loss, and prolonged back pain episodes were all more frequent in the discography group compared to control subjects. The disc puncture and pressurized injection performed during provocative discography can increase the risk of clinical disc problems in exposed patients. Copyright © 2015 Elsevier Inc. All rights reserved.
    The Spine Journal 10/2011; 11(10):S23–S24. DOI:10.1016/j.spinee.2011.08.069 · 2.43 Impact Factor
  • Joshua D Back · Richard J Herzog · Gregory E Lutz
    The spine journal: official journal of the North American Spine Society 06/2011; 11(7):681-2. DOI:10.1016/j.spinee.2011.05.006 · 2.43 Impact Factor
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    Kevin I Pak · David C Hoffman · Richard J Herzog · Gregory E Lutz
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    ABSTRACT: We report a case of an 83-year-old gentleman presenting with acute low back pain and radicular left lower extremity pain after golfing. A magnetic resonance imaging (MRI) of the lumbar spine revealed a low-signal-density lesion compressing the L5 nerve. A computed tomography scan was then ordered, confirming an extra-foraminal disc protrusion at the L5-S1 level, containing a focus of gas that was compressing the left L5 nerve root and communicating with the vacuum disc at L5-S1. After a failed left L5 transforaminal epidural steroid injection, the patient was brought back for a percutaneous intradiscal aspiration of the vacuum disc gas. This resulted in immediate relief for the patient. A follow-up MRI performed 2 months after the procedure found an approximate 25% reduction in the size of the vacuum disc herniation. Six months after the procedure, the patient remains free of radicular pain. This case report suggests that a percutaneous aspiration of gas from a vacuum disc herniation may assist in the treatment of radicular pain.
    HSS Journal 02/2011; 7(1):89-93. DOI:10.1007/s11420-010-9168-x
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    ABSTRACT: Lateral transpsoas interbody fusion (LTIF) is a minimally invasive technique that permits interbody fusion utilizing cages placed via a direct lateral retroperitoneal approach. We sought to describe the locations of relevant neurovascular structures based on MRI with respect to this novel surgical approach. We retrospectively reviewed consecutive lumbosacral spine MRI scans in 43 skeletally mature adults. MRI scans were independently reviewed by two readers to identify the location of the psoas muscle, lumbar plexus, femoral nerve, inferior vena cava and right iliac vein. Structures potentially at risk for injury were identified by: a distance from the anterior aspect of the adjacent vertebral bodies of <20 mm, representing the minimum retraction necessary for cage placement, and extension of vascular structures posterior to the anterior vertebral body, requiring anterior retraction. The percentage of patients with neurovascular structures at risk for left-sided approaches was 2.3% at L1-2, 7.0% at L2-3, 4.7% at L3-4 and 20.9% at L4-5. For right-sided approaches, this rose to 7.0% at L1-2, 7.0% at L2-3, 9.3% at L3-4 and 44.2% at L4-5, largely because of the relatively posterior right-sided vasculature. A relationship between the position of psoas muscle and lumbar plexus is described which allows use of the psoas position as a proxy for lumbar plexus position to identify patients who may be at risk, particularly at the L4-5 level. Further study will establish the clinical relevance of these measurements and the ability of neurovascular structures to be retracted without significant injury.
    European Spine Journal 10/2010; 20(4):550-6. DOI:10.1007/s00586-010-1593-5 · 2.07 Impact Factor
  • David S Cheng · Richard J Herzog · Gregory E Lutz
    PM&R 02/2010; 2(2):162-4. DOI:10.1016/j.pmrj.2009.11.009 · 1.53 Impact Factor
  • The Spine Journal 10/2009; 9(10). DOI:10.1016/j.spinee.2009.08.011 · 2.43 Impact Factor

Publication Stats

754 Citations
107.83 Total Impact Points


  • 2003–2014
    • Hospital for Special Surgery
      • Department of Orthopaedic Surgery
      New York, New York, United States
    • Weill Cornell Medical College
      New York City, New York, United States
  • 2013
    • Cornell University
      Итак, New York, United States
  • 1994–1995
    • Hospital of the University of Pennsylvania
      • Department of Radiology
      Philadelphia, Pennsylvania, United States