In-vitro mobility of the lumbar spine.

As part of a systematic study of the spine between D11 and S1 the response to stress has been assessed by measuring radiologically the total and segmental mobility of 103 specimens. The method was shown to be reproducible to within 10% of total mobility. No significant sex difference was seen. Total mobility varied widely, but mean total mobility fell with age. All lumbar segments became less mobile up to the fifth decade. Between the fifth and the eighth decade the mobility of the fifth lumbar segment continued to fall, whereas other lumbar segments became more mobile. The mobility of each segment also varied widely, but the mean segmental mobility fell progressively from L5 to D11. However, this smooth pattern of movement was seen in only 16 cases, mostly adolescents and young adults. Among the remainder, in which movement was irregularly distributed, there were 7 cases (4 aged less than 30 years) in which the mobility of at least 1 segment was more than 2 standard deviations above the mean. The cause of this hypermobility was not evident radiologically. It is suggested that segments with abnormally high mobility may be at risk.