General Session: Biomechanics
Presented by: D. Hey - View Audio/Video Presentation (Members Only)
D. Hey(1), E.T.C. Lau(1), D. Choong(1), C-S. Tan(2), H-K. Wong(1)
(1) University Orthopaedics, Hand and Reconstructive Microsurgery (UOHC) National University Health System, Singapore, Orthopaedics, Singapore, Singapore
(2) Saw Swee Hock School of Public Health, National University Health System, Singapore, Public Health, Singapore, Singapore
Purpose of the Study: Flexion radiographs have been used to identify patients with spinal instability and the presence or absence of this instability often influences the surgical decision and predicts outcome. However, current methods of performing these radiographs are not standardized and are not sufficiently optimized to identify instability. Here, we introduced a novel slump sitting method for performing optimal lumbar spine flexion radiographs and compared this to the conventional method.
Methods: Sixty subjects participated in a prospective, single-blinded, randomized, controlled trial comparing the lumbar spine flexion between the conventional method and the new method. The study included patients above 45 years of age, with mechanical low back pain. All subjects are block randomized into those who did the new method first or those who did the conventional method first. Both slump sitting and conventional flexion lateral lumbar spine X-rays were performed together with a single extension lateral lumbar spine X-ray in all patients. The X-rays were taken with the central beam directed at the estimated center of L3 vertebra, with T11 vertebral body and mid-body of the sacrum serving as superior and inferior limits respectively. Radiographic measurements were performed by two independent parties and include angular and displacement measurements for the entire lumbar spine and for each levels. Paired t-test was performed to compare the differences in measured means between both methods. Multivariable linear regression modeling was performed with odds ratio computed to determine the possible predictive value of each clinical parameter.
Summary of Findings: The mean age of all subjects was 56 years (SD 8.6). There were 28 males (47%) and 32 females (53%). Both groups of patients had comparable baseline characteristics. The global lumbar spine flexion increased by a mean of 17.3° (SD 17.3°; p< 0.0001) using the new method compared to the conventional method. Segmental vertebra flexion also increased in all functional spinal units from L1/2, L2/3, L3/4, L4/5, L5/S1 by a mean of 2.0° (p=0.022), 2.2° (p=0.032), 4.3° (p< 0.001), 5.2° (p< 0.001) and 3.3° (p=0.001) respectively. There were no significant difference between both methods when measuring lumbar displacements (p=0.814) but a trend towards more displacement using the new method was observed. When applying the White and Panjabi criteria, the prevalence of segmental spinal instability increases from 2.67% to 11%. No parameter was found to predict the degree of global lumbar flexion.
Conclusions: The new method of slump sitting dynamic radiograph gives far superior stress to the lumbar spine in flexion compared to the conventional method and improves the diagnosis of spinal instability by 8.33%. It should be standardized as the optimal way to perform flexion radiographs. Moreover, it remains a truly weight bearing view and reduces the potential risks of falls, the confounding effects of hamstring tightness and the challenges required for an elderly to stand which may be encountered for the conventional method.