Trunk extension effort in patients with chronic low back dysfunction.

STUDY
DESIGN: Single-session measurement was performed.
OBJECTIVE: To measure trunk extension strength and assess trunk extension effort in patients with chronic low back dysfunction using a novel test protocol and the DEC parameter. SUMMARY OF BACKGROUND DATA: In normal subjects, the DEC parameter effectively and reproducibly differentiates between maximal effort and feigned weakness of the trunk extensors, but its applicability to patients with chronic low back dysfunction has not yet been explored.
METHODS: Isokinetic trunk extension strength was measured in 44 patients with chronic low back dysfunction (22 women and 22 men) who were not involved in litigation process. Tests were conducted using a range of motion of 20 degrees, angular velocities of 10 degrees and 40 degrees per second, and an isometric preactivation force of 50 N. The average strength at these velocities served for calculation of the DEC score, which is the difference between the eccentric and concentric strength ratios at these velocities.
RESULTS: The strength scores resembled the characteristic physiologic moment-angular velocity relation, and were much reduced, as compared with the scores of normal subjects. The DEC scores for 39 patients (89%) were less than the cutoff value, which in normal subjects differentiates maximal effort (below cutoff) from feigned weakness (above cutoff) at tolerance limits of 99%. This figure was slightly lower (84%) at a corresponding 95% level. A principal finding in the false-positive cases was a particularly low concentric strength at 40 degrees per second.
CONCLUSIONS: This study indicates that under the current protocol, the large majority of patients perform at a maximal level of effort.