Reliability of ultrasound measures of the transversus abdominis: effect of task and transducer position.

Objective: To assess the reliability of ultrasound (US) measures of the transversus abdominis (TrA) muscle in a sample of subjects with and without specific chronic low back pain and to test whether reliability is enhanced by using different abdominal muscle activation tasks, with use of a foam cube for US transducer stabilization or by averaging 3 measures on the same image.

Design: Cross-sectional repeated-measures design.

Setting: Laboratory setting.

Patients: Fifteen subjects with chronic low back pain and 15 control subjects.

Methods: Subjects (n = 30) performed 3 tasks in the supine position: (1) contralateral straight leg raise (SLR), (2) bilateral hook-lying leg raising (HLR), and (3) abdominal drawing-in maneuver (ADIM) (control subjects only). Two 7-second videos of the right and left abdominal wall (from rest to contraction) were collected, with and without use of the foam cube. One of the 2 raters repeated the testing 7 to 14 days later to assess intrarater reliability.

Main Outcome Measurements: US imaging of abdominal muscles thickness.

Results: The TrA muscle was recruited preferentially in the ADIM task compared with the automatic tasks (SLR and HLR). The reliability was comparable among the 3 tasks, with intrarater reliability results being better than interrater reliability results. The use of the foam cube or averaging measures on the same image was generally not effective to increase reliability.

Conclusions: Although they are not as preferential in TrA recruitment as the ADIM, the SLR and HLR tasks showed comparable reliability results. The foam cube used to control transducer orientation and pressure and averaging measures on the same image had limited effect on reliability.