• Masaki Nagashima, Hitoshi Abe, Kenji Amaya, Hideo Matsumoto, Hisashi Yanaihara, Yuji Nishiwaki, Yoshiaki Toyama, and Morio Matsumoto.
• Department of Orthopaedic Surgery, Keio University School of Medicine, Tokyo, Japan.
• Am J Sports Med. 2013 Sep 1; 41 (9): 2059-64.

BackgroundSeveral risk factors have been proposed for intervertebral disc degeneration (DD) among adolescent athletes. However, the causes of DD are not well understood, and there have been few prospective studies evaluating DD in adolescents.PurposeTo identify risk factors for DD among adolescent American football (AF) players.Study DesignCohort study (prevalence); Level of evidence, 2.MethodsThis study investigated the relationships between the progression of DD and the following factors: lumbar spine abnormalities on baseline radiographs, body mass index, AF position played (lineman or other), and length of playing career (2 full competitive AF seasons or <2 seasons). Included were 192 students who joined a top-ranked high school AF team from 2004 to 2008. Of these, 160 played for 2 full competitive AF seasons. The remaining 32 players, who stopped before completing 2 seasons, were used as a control group. Baseline radiographs and lumbar magnetic resonance imaging (MRI) scans were obtained when the players enrolled in the AF team in May, and follow-up lumbar MRI scans were obtained 2 years later at the end of their second academic year in March. Disc degeneration was measured by the signal intensity of the nucleus pulposus, and its progression was evaluated by multiple regression analysis of decreases in signal intensity. Also analyzed was the relationship between DD and low back pain (LBP).ResultsThe mean decrease in signal intensity of the nucleus pulposus was 4.30% ± 11.63% in players who completed 2 AF seasons and 1.41% ± 10.03% in those who did not (P = .12). Mean visual analog scale scores for LBP at follow-up were significantly higher (P = .001) in players who had played for 2 full seasons (2.67 ± 2.81) than in those with a shorter career (0.99 ± 1.61). Decreases in signal intensity of the nucleus pulposus after 2 years of playing AF related significantly to playing a lineman position (partial regression coefficient, 3.47%), the presence of Schmorl nodes (partial regression coefficient, 3.58%), and disc herniation (partial regression coefficient, 4.09%).ConclusionSignificant risk factors for DD progression in high school AF players included playing a lineman position, the presence of Schmorl nodes, and disc herniation. Continuing to play AF through 2 years of high school was a risk factor for the onset of LBP.

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