The personnel of the Spinal Biomechanics Laboratory study the mechanical behavior of the spine in its normal condition and after injury, disease, or surgical intervention. The lab works closely with clinical neurosurgeons in the Division of Neurosurgery. Neurosurgical residents, fellows, and Barrow staff perform experiments on specially prepared human cadaveric spines. Injuries that mimic those seen in patients are induced in the specimens, and surgical procedures identical to those in the operating room are performed.
Before and after injuring or performing surgery on a cadaveric spine, the specimen is tested mechanically by applying carefully controlled loads through a system of cables and pulleys or belt, motor, and weights while measuring the three-dimensional motion using an optical system. The loads are similar to the maximum forces a person applies to the spine during daily activities.
The laboratory’s principal goal is to improve healthcare by investigating how different surgical procedures affect the mechanical response of the spine—particularly, what effect different procedures have on spinal stability. Studies like the ones performed in our laboratory are published to help surgeons decide how best to treat patients requiring spinal surgery; these studies may lead to new and better techniques or devices for spinal surgery.
Biomechanics of Artificial Discs
Although few artificial intervertebral discs are currently on the market in the US due to the slow FDA approval process, many are under development by different companies in the US and elsewhere. The biomechanics lab initiated a number of protocols with these companies to evaluate their devices. The ultimate goal is to publish our findings to benefit patients and doctors in understanding how the spine will move differently after implantation of each device. As described on the Testing Techniques page, the BNI lab has at its disposal several advanced testing methods unavailable at other labs and is hoping to set new standards in how such experiments are performed.
Dr. Crawford published a critique of the most recently published studies on biomechanical testing of cervical artificial discs.
Ongoing research includes measurement of range of motion, zone of laxity, coupling patterns, axis of rotation, and facet loads at levels of the spine in specimens with artificial intervertebral discs implanted. One of the hypothetical benefits of implanting an artificial disc instead of fusing a level of the spine is that there is less of a “lever arm” on the adjacent normal levels, and so there is less chance of these normal levels degenerating later in life. New research in the biomechanics lab focuses on studying the biomechanical effects on adjacent levels in conditions of natural disc versus fusion versus artificial disc. This new research will make use of a complex testing apparatus recently designed in collaboration with a local engineering firm that generates external loads on spine representing both muscles and gravity.
Surgical Planning and Rapid Prototyping of the Spine
The biomechanics lab was awarded a grant from the National Institutes of Health to develop a computerized surgical planning tool, which is now in the late stages of development, utilizing a desktop haptic device. With this system, a 3D computer model of the patient’s spine and pathology is generated from the patient’s computerized tomography scan. The surgeon then performs virtual surgery to correct the pathology.
With haptics, the surgeon feels forces during simulated drilling and bone realignment that help to predict the experience that will be encountered in the operating room. After the surgeon completes the mock surgery, computerized analysis is applied to fine tune the surgical plan, and rapid-prototyped spine models help communicate surgical planning information to the patient. Rapid prototyped drill guides are also used to improve accuracy of screw insertion. (See an abstract of this grant on the NIH website)
Brian Kelly, PhD
Assistant Professor, Spinal Biomechanics
Robert H. Chamberlain Memorial
The Spinal Biomechanics Laboratory offers a one-year fellowship in biomechanics to international surgeons or surgeons-in-training. The position runs from July 1 through the following June 30 and pays a monthly stipend.
Interested applicants should send their curriculum vitae and a cover letter describing their proposed course of study to Dr. Brian Kelly for consideration.
Current Biomechanics Fellows
Former Biomechanics Fellows
Ram Kumar Menon
Mexico City, Mexico
Nestor Rodriguez, MD
Luis Pérez-Orribo, MD
Tenerife, Canary Islands, Spain
Marco Túlio Domingos Silva e Reis, MD
Belo Horizonte, Brazil
Felix Dominguez Cortinas, MD
Mexico City, Mexico
Ali A. Baaj, MD
Bruno C. R. Lazaro, MD
Rio de Janeiro, Brazil
Mehmet Senoglu, MD
Sam Safavi-Abbasi, MD
Seref Dogan, MD
Zafer Yüksel, MD
Adolfo Espinoza-Larios, MD
Hakan Bozkus, MD
Luis E. Perez-Garza, MD
Sung Chan Park, MD
Seoul, South Korea
- Newcomb GUS, Lehrman J, Crawford NR, Kelly BP. Variations among human lumbar spine segments and their relationships to in vitro biomechanics: a retrospective analysis of 281 motion segments from 85 cadaveric spines. Accepted for publication in the International Journal of Spine Surgery, December 03, 2019.
- Tumialan LM, Lehrman JN, Mulholland CB, de Andrada Pereira B, Newcomb AGUS, Kelly BP. Dimensional characterization of the human cervical interlaminar space as a guide for safe application of minimally invasive dilators. Accepted for publication in Operative Neurosurgery, December 17th, 2019.
- Lehrman JN, Narayanan M, Cavallo C, Newcomb AGUS, Zhao X, Kelly BP, Crawford NR, Nakaji P. Evaluation of abnormal styloid anatomy as a cause of internal jugular vein compression using a 3D-printed model: a laboratory investigation. J Clin Neurosci. 2019 Dec 26. pii: S0967-5868(19)31647-9. Doi 10.1016/j.jocn.2019.11.048. [Epub ahead of print] PubMed PMID: 31883814.
- Godzik J, Pereira BA, Newcomb AGUS, Lehrman JN, Mundis GM Jr, Hlubek RJ, Uribe JS, Kelly BP, Turner JD. Optimizing biomechanics of anterior column realignment for minimally invasive deformity correction. Spine J. 2019 Sep 10. pii: S1529-9430(19)30968-4. doi: 10.1016/j.spinee.2019.09.004. [Epub ahead of print] PubMed PMID: 31518683.
- Savardekar AR, Rodriguez-Martinez NG, Newcomb AGUS, Reyes PM, Soriano-Baron H, Chang SW, Kelly BP, Crawford NR. Comparing the Biomechanical Stability of Cortical Screw Trajectory Versus Standard Pedicle Screw Trajectory for Short- and Long-Segment Posterior Fixation in 3-Column Thoracic Spinal Injury. Int J Spine Surg. 2019 Jun 30;13(3):245-251. doi: 10.14444/6033. eCollection 2019 Jun. PubMed PMID: 31328088; PubMed Central PMCID: PMC6625712.
- Snyder LA, Lehrman JN, Menon RK, Godzik J, Newcomb AGUS, Kelly BP. Biomechanical implications of unilateral facetectomy, unilateral facetectomy plus partial contralateral facetectomy, and complete bilateral facetectomy in minimally invasive transforaminal interbody fusion. J Neurosurg Spine. 2019 May 10;31(3):447-452. doi: 10.3171/2019.2.SPINE18942. PubMed PMID: 31075766.
- Godzik J, Lehrman JN, Newcomb AGUS, Menon RK, Whiting AC, Kelly BP, Snyder LA. Tailoring selection of transforaminal interbody spacers based on biomechanical characteristics and surgical goals: evaluation of an expandable spacer. J Neurosurg Spine. 2019 Apr 12:1-7. doi: 10.3171/2019.1.SPINE181008. [Epub ahead of print] PubMed PMID: 30978679.
- Bohl MA, Morgan CD, Mooney MA, Repp GJ, Lehrman JN, Kelly BP, Chang SW, Turner JD, Kakarla UK. Biomechanical Testing of a 3D-printed L5 Vertebral Body Model. Cureus. 2019 Jan 15;11(1):e3893. doi: 10.7759/cureus.3893. PubMed PMID: 30911450; PubMed Central PMCID: PMC6424546.
- Godzik J, Hlubek RJ, Newcomb AGUS, Lehrman JN, de Andrada Pereira B, Farber SH, Lenke LG, Kelly BP, Turner JD. Supplemental rods are needed to maximally reduce rod strain across the lumbosacral junction with TLIF but not ALIF in long constructs. Spine J. 2019 Jun;19(6):1121-1131. doi: 10.1016/j.spinee.2019.01.005. Epub 2019 Jan 23. PubMed PMID: 30684758.
- Hlubek RJ, Godzik J, Newcomb AGUS, Lehrman JN, de Andrada B, Bohl MA, Farber SH, Kelly BP, Turner JD. Iliac screws may not be necessary in long-segment constructs with L5-S1 anterior lumbar interbody fusion: cadaveric study of stability and instrumentation strain. Spine J. 2019 May;19(5):942-950. doi: 10.1016/j.spinee.2018.11.004. Epub 2018 Nov 9. PubMed PMID: 30419290.
In vitro testing of the spine provides valuable information to researchers and clinicians about how neurosurgical procedures affect spinal stability and motion (Crawford, 2002). The Spinal Biomechanics Laboratory has devised several novel techniques for experimentally testing cadaveric spines, enabling researchers at our institution to study spinal biomechanics in ways that were not possible at other institutions. Many of these techniques are incorporated in the custom software developed in the Spinal Biomechanics Laboratory. This software is now used not only at Barrow, but has also been provided by Barrow for use in other biomechanics laboratories at universities in the United States.
Local Coordinate Systems
In the Spinal Biomechanics Laboratory, a technique was devised to enable each level of the spine to be tracked and studied independently (Crawford and Dickman, 1997). With this technique, the researcher points to specific vertebral landmarks with a probe in which optical markers are embedded. Custom testing software performs spatial transformations to align these landmarks with appropriate Cartesian coordinate system of the vertebra. Angular data can then be plotted in real time in individual local coordinate systems of multiple spinal levels during testing.
Three-Dimensional Spinal Angle Calculation
Publications from the Spinal Biomechanics Laboratory have contributed to the understanding of how three-dimensional (3D) joint angles are best calculated. In Crawford et al, 1996, the differences and similarities of two methods for calculating 3D joint angles, projection angles and Euler angles, were described, and a method was proposed by which the most appropriate Euler angle sequence or projection angle set can be selected for the spine and other joints of the body. In Crawford et al, 1999, a new 3D angle technique, the “tilt/twist” method, which has advantages over both the projection and Euler methods, was developed. The custom software developed in the Spinal Biomechanics Lab uses this tilt/twist method technique to display spinal angles in real time during testing.
Illustrations reprinted from Human Movement Science, 15(1), Crawford NR, Yamaguchi GT, Dickman CA: Methods for determining spinal flexion/extension, lateral bending, and axial rotation from marker coordinate data: Analysis and refinement, pg.55-78, 1996, with permission from Elsevier.