SPINE Volume 35, Number 26S, pp S361–S367 ©2010, Lippincott Williams & Wilkins Biomechanical Analysis and Review of Lateral Lumbar Fusion Constructs Andrew Cappuccino, MD,* G. Bryan Cornwall, PhD,† Alexander W. L. Turner, PhD,† Guy R. Fogel, MD,‡ Huy T. Duong, MD,§ Kee D. Kim, MD,§ and Darrel S. Brodke, MD¶ Study Design. Biomechanical study and the review of literature on lumbar interbody fusion constructs. Objective. To demonstrate the comparative stabilizing effects of lateral interbody fusion with various supple- mental internal fixation options. Summary of Background Data. Lumbar interbody fu- sion procedures are regularly performed using anterior, posterior, and more recently, lateral approaches. The bio- mechanical profile of each is determined by the extent of resection of local supportive structures, implant size and orientation, and the type of supplemental internal fixation used. Methods. Pure moment flexibility testing was per- formed using a custom-built 6 degree-of-freedom system to apply a moment of 7.5 Nm in each motion plane, while motion segment kinematics were evaluated using an optoelectronic motion system. Constructs tested in- cluded the intact spine, stand-alone extreme lateral inter- body implant, interbody implant with lateral plate, unilat- eral and bilateral pedicle screw fixation. These results were evaluated against those from literature-reported biomechanical studies of other lumbar interbody con- structs. Results. All conditions demonstrated a statistically sig- nificant reduction in range of motion (ROM) as a percent- age of intact. In flexion-extension, ROM was 31.6% stand- alone, 32.5% lateral fixation, and 20.4% and 13.0% unilateral and bilateral pedicle screw fixation, respec- tively. In lateral bending, the trend was similar with greater reduction with lateral fixation than in flexion-ex- tension; ROM was 32.5% stand-alone, 15.9% lateral fixa- tion, and 21.6% and 14.4% unilateral and bilateral pedicle screw fixation. ROM was greatest in axial rotation; 69.4% stand-alone, 53.4% lateral fixation, and 51.3% and 41.7% unilateral and bilateral pedicle screw fixation, respec- tively. Conclusion. The extreme lateral interbody construct provided the largest stand-alone reduction in ROM com- pared with literature-reported ALIF and TLIF constructs. Supplemental bilateral pedicle screw-based fixation pro- vided the overall greatest reduction in ROM, similar among all interbody approach techniques. Lateral fixation and unilateral pedicle screw fixation provided intermedi- ate reductions in ROM. Clinically, surgeons may evaluate these comparative results to choose fixation options com- mensurate with the stability requirements of individual patients. Key words: lumbar interbody fusion, range of motion, ex- treme lateral, stability, XLIF. Spine 2010;35:S361–S367 Lumbar spine fusions, often combined with direct or in- direct neurologic decompression, are commonly per- formed to treat patients with persistent symptoms of neurologic pain due to spinal instability, spondylosis, or spinal deformities such as scoliosis and spondylolisthesis and who are refractory to nonoperative measures. Lum- bar spine surgery has been compared with other elective orthopedic procedures such as total knee and total hip replacement, and patients were found to have better clin- ical quality of life outcomes comparing pre- and postop- erative indexes with various procedures. 1 Although the posterolateral gutter remains the most common site for fusion, it is increasingly common to perform an anterior column (interbody) fusion to increase stability and the likelihood of fusion. 2,3 Several operative approaches are commonly used to access the anterior column for fusion, including posterior, transforaminal, anterior, and more recently, lateral transpsoas. Posterior approaches for lumbar spine surgery allow for placement of anterior (i.e., interbody) and posterior instrumentation through a single incision, though with a relatively small working window, risk to neural struc- tures, 4–6 and damage to posterior musculature. 7,8 Ante- rior approaches provide a broad exposure of the anterior column and use techniques familiar to most surgeons, but complications associated with the approach (e.g., vascular 9,10 and reproductive 11,12 ) as well as a high risk of vascular injury during revision procedures lessen the value of anterior approach benefits, especially at lumbar levels above L5–S1. The lateral transpsoas approach minimizes the vascular and neural complications associ- ated with anterior and posterior procedures, respec- tively. It is considered a minimally disruptive approach, and advanced neuromonitoring techniques are required to avoid lumbar plexus injuries. 13,14 From a biomechani- cal perspective, the lateral approach allows an abundant amount of disc to be removed, and placement of a large, stable interbody implant, retaining the anterior longitu- From the *Buffalo Spine Surgery, Lockport, NY; †NuVasive Inc, San Diego, CA; ‡Orthopaedic Spine Institute, San Antonio, TX; §Depart- ment of Neurological Surgery, University of California Davis, Davis, CA; and ¶Department of Orthopaedics, University of Utah, Salt Lake City, UT. Acknowledgment date: August 24, 2010. First revision date: Septem- ber 29, 2010. Second revision date: October 15, 2010. Acceptance date: October 15, 2010. The device(s)/drug(s) is/are FDA-approved or approved by correspond- ing national agency for this indication. Corporate/Industry funds were received in support of this work. One or more of the author (s) has/have received or will receive benefits for personal or professional use from a commercial party related directly or indirectly to the subject of this manuscript: e.g., honoraria, gifts, consultancies, royalties, stocks, stock options, decision making posi- tion. Address correspondence and reprint requests to Andrew Cappuccino, MD, Buffalo Spine Surgery, 46 Davison Court, Lockport, NY 14094; E-mail: andycapp46@aol.com S361