Five hundred and sixty-five examinations were made by flexion and extension roentgenograms of 400 consecutive patients seen in a private orthopaedic practice because of low-back pain. Ninety-two of these patients were operated on—by us in seventy-two and by others in the remainder. Of the seventy-two operated on by us, fifty-two had laminectomy and twenty spine fusion. A preoperative roentgenographic analysis of motion was made in seventeen of the patients and eighteen had a similar evaluation at intervals after operation to demonstrate progressive changes.

Measurements of motion at all five lumbar levels were made by use of the technique of Begg and Falconer. Flexion and extension roentgenograms were made with the patient standing for the flexion and kneeling for the extension roentgenograms or lying on his side on the top of the x-ray table when this position was necessary to obtain maximum flexion in the presence of pain. The examination (known as a lumbar dynamogram) provides a quantitative measurement of motion in degrees rather than an indication of qualitative changes in motion and thus makes possible more precise comparisons between joints of the same spine, as well as comparison between patients.

The findings demonstrated restriction of flexion and extension in the majority of patients who had a successful laminectomy. Persistence of mobility comparable with that expected in a normal individual was usually found in patients judged to have poor results.

Lumbar dynamograms often demonstrated increased flexion and extension of the joints adjacent to those showing restriction of motion, especially joints successfully fused.

A hypothesis is proposed: As disc degeneration progresses, an internal stiffness of the degenerated disc junction may result from fibrous replacement and marginal ossification. This stiffness may cause more motion in adjacent better preserved lumbar joints which have essentially normal internal resistance. These two effects serve together to preserve both flexibility and support of the spine despite the advance of morphological changes in some segments.