Traumatic high-load injuries in the adolescent spine. Clinical, radiological and experimental studies
Abstract: Background: Disc degeneration and other radiological abnormalities are highly frequent among young athletes in sports with great demands on the back. It has also been reported that athletes with these abnormalities have more back pain than other athletes and non-athletes. There is, however, incomplete knowledge regarding the effect of intensive physical loading on the spine, at what age various abnormalities occur and regarding the long-term effects on the morphological abnormalities and on the occurrence of back pain. Aims: It was hypothesised that high loads on the spines of athletes are correlated to an increased frequency of abnormalities and to back pain. The aim was to study the long-term outcome with regard to MRI-abnormalities and back pain. With the aid of an experimental porcine model, an aim was also to try to elucidate the mechanisms behind traumatic displacement of the ring apophysis, disc degeneration and endplate injuries found in adolescent athletes.Methods: Clinical studies: Twenty young elite divers were studied longitudinally (5 years) regarding MRI changes in the thoracolumbar spine and back pain symptoms. The frequency of MRI changes and back pain were also studied longitudinally (15 years) in 71 athletes (weight-lifters, wrestlers, orienteers, ice-hockey players) and 21 non-athletes. Back pain was assessed by questionnaires. Experimental studies: Normal discs and discs with experimentally-induced degeneration from young pigs were mechanically loaded in axial compression, flexion compression and extension compression to failure. The compression load and angle at failure were measured. The segments were then examined for injuries using X-ray, MRI and morphological and histological techniques. Additionally, a group of intervertebral discs with experimentally-induced degeneration were histologically examined regarding reactive and degenerative changes. Results and conclusions: Clinical studies: At the baseline assessment, MRI changes (primarily reduced disc signal) were found in 65% of the young elite divers and at 5 year follow-up deterioration had occurred in half the cases. New abnormalities in previously unaffected individuals occurred in only one case. Current or previous back pain was reported in 89%. Among the four groups of athletes, an even higher prevalence of MRI changes (91%) was found, while back pain was found in 78%. Disc degeneration was the most prevalent abnormality, and it progressed in a large proportion. Experimental studies: The spine in this porcine model was more susceptible to trauma in extension compression than in flexion compression Flexion compression and extension compression caused a fracture or separation of the endplate from the vertebral body in the growth zone in both normal and degenerated discs from young pigs. Axial compression of degenerated discs caused a fracture through the endplate and dorsal part of the vertebral body. In the histological study, the main finding was the demonstration of reactive repair processes that had replaced injured and degenerative structures with vascularised scar tissue. In conclusion, elite athletes run a high risk of developing disc degeneration and back pain. The growth zone and the endplate are the weakest parts in both normal and degenerated discs in growing porcine lumbar spines, when loaded in axial compression, flexion compression and extension compression. Neo-vascularisation of the central parts of the disc is likely to be of key importance in turning the degenerative features of the remaining tissue into reactive more normal structures.
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