Segmental hypermobility in lumbar spine and entrapment of dorsal rami.

Low back pain patients (N = 18) having segmental hypermobility in one lumbar segment and healthy controls (N = 13) were chosen for this study. Patients had no other structural spinal pathology except displacement of one vertebra to another in lateral X-ray bending pictures. Kinetic intramuscular EMG-activity from paraspinal muscles was studied off-line during back flexion and reextension. Routine needle EMG study of paraspinal muscles was also performed in addition to measurements of the tibial nerve H-reflexes and peroneal F-responses. Results showed that the number of MUAPs in erector spinae muscle on voluntary efforts was rarefied at hypermobile levels, and spontaneous activity, positive sharp waves and high frequency discharges were found in more than half of the patients in paraspinal muscles, usually at hypermobile levels only. No signs of proximal nerve root compression were found. This indicates neuropathy of dorsal rami at the instable level.