Working Diagnosis:
An acute burst fracture at L1 with posterior displacement of the vertebral body and fracture fragments into the spinal canal resulting in a severe central spinal stenosis

Treatment:
Steroid protocol was initiated. Patient underwent left thoracotomy with left 10th rib resection, division of diaphragm and repair, L1 corpectomy with decompression of the thecal sac and nerve roots, L1-L2 and L2-L3 arthrodesis with autograft, T12, L1-L2 interbody arthrodesis with arthrograft, and placement of T12-L2 lateral plate. Case Photo #5

Outcome:
L1 ASIA D. Patient currently ambulatory 1 year post injury with residual neurogenic bowel and bladder.

Author's Comments:
Resistance training is a popular form of exercise. Studies have shown that resistance training is an effective method of exercise which can lead to increased muscle mass, increased strength, increased bone density, and may even be more beneficial than aerobic exercise for weight loss(1). The squat has biomechanical and neuromuscular similarities to a wide range of athletic movements and thus is included as a core exercise in many sports routines designed to enhance athletic performance (2). The squat can be performed as a free weight exercise and on the Smith Machine. The Smith Machine is a device commonly found in gyms that consists of a barbell fixed in a vertical or near vertical plane (Photo 6). Low back injuries are common among weight lifters, where the incidence of back pain approaches 40%. The most common injuries are spondylolisthesis, spondylolysis, herniated nucleus pulposis and various strains and sprains of spinal muscles and ligaments(4). In the literature, there have been reports of flexion-distraction injury of the thoracolumbar spine during the squat exercises on the Smith Machine but no known documented cases of burst fractures(5). The burst fracture is a type of compression fracture of the vertebral body where a fragment arising from the posterosuperior margin of the vertebral body is displaced into the spinal canal. The burst fracture results from axial compressive forces the anterior and middle spinal column. The retropulsed fragment may result in neurological injury to the spinal cord, conus medullaris, or cauda equina. One study showed that neurological injury occurred with 65% of all burst fractures and L1 was by far the most commonly fractured segment(6). When performed properly, squat related injuries are relatively uncommon. Poor technique can lead to injury, especially in combination with heavy weights (7). It is a common misconception that the Smith Machine is safer to use, as it is believed that the device inherently reduces the need for balance and can therefore be used without a spotter. The squat naturally places a large load on all components of the spinal column below the barbell. Studies have shown that compressive loads of 0.8-1.6 times body weight exhibited loads on the L3-L4 segment of 6-10x the body weight(7). Studies have also shown that lumbar forces are increased with intensified flexion. A flexed lumbar spine decreases the moment arm for the erector spinae reducing tolerance to compressive loads. Compressive forces may double if weights are lifted rapidly(8). Weight lifters of all ages and experience levels should be instructed on proper form, exercise prescription, and the strict use of a spotter with all exercises.

Editor's Comments:
This case underscores the importance of learning proper weightlifting form and having spotters present. As the author points out, machines are often thought of as being safer than free weights alone. However, safety precautions are a necessity with all types of weight training.

References:
1. Sundell, J. Resistance training is an effective tool against metabolic and frailty syndromes. Advances in Preventive Medicine. 2011
2. Schoenfeld, BJ. Squatting kinematics and kinetics and their application to exercise performance. J Strength Cond Res 24(12): 3497-3506, 2010
3. Kim, T, Lee, K, Kwon, J. Design improvement of the smith machine using simulation on musculoskeletal model. International Journal of CAD/CAM vol 11. No 1. pp 00-00, 2011
4. Aggrawal ND, Kaur R, Kumar S, et al. Study of changes in weightlifters and other athletes. BR J Sports Med. 1979; 13:58
5. Gallo A, Reitman R, Althman D, et al. Flexion-distraction injury of the thoracolumbar spine during squat exercise with the Smith Machine. American Journal of Sports Medicine 32(8), 1962-1967, 2004
6.Atlas, S, Regenbogen, V, Rogers, L, et al. The Radiogaphinc Characterization of Burst Fractures of the Spine. AJNR 7:675-682, July/Aug 1986
7. Cappozzo, A, Felici, F, Figura F, and Gazzani, F. Lumbar spine loading during half squat exercises. Med Sci Sports Exerc 17: 613-620, 1985
8. Vakos, JP, Nitz, AJ, Threlkeld, AJ, Spairo, R, and Horn, T. Electromyogaphic activity of select trunk and hip muscles during a squat lift. Effect of varying lumbar posture. Spine 19: 687-695, 1994

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