In vivo measurement of lumbar foramen during axial loading using a compression device and computed tomography.

Methods: In vivo measurement of lumbar foramen using computed tomography and an axial loading device in healthy young subjects. Objective: To investigate the effects of axial loading on the morphology of the lumbar foramen in vivo.

Background: In vitro studies have shown morphologic changes in the lumbar foramen in response to axial loading. The effects of axial loading on foraminal dimensions in vivo, however, are poorly understood.

Methods: The study population consisted of 12 asymptomatic healthy young volunteers [6 men and 6 women; age range, 22-34 y (mean, 27 y)]. Lumbar computed tomography images were compared with and without axial loading using a compression device (DynaWell), and differences in disk height (DH), foraminal height (FH), foraminal width (FW), and the cross-sectional area (CSA) of the intervertebral foramen (IVF) were determined.

Results: During axial loading, the FHs at L1/L2, L2/L3, L3/L4, and L4/L5 each decreased significantly (P<0.01 each), by 4.0%, 6.6%, 6.6%, and 5.1%, respectively. Maximum FW decreased significantly (P<0.05 each) at L2/L3 (7.2%) and L3/L4 (5.7%), and increased significantly (P<0.05) at L5/S1 (8.9%). The CSAs of the IVF decreased significantly (P<0.01 each) at L2/L3 (10.8%) and L3/L4 (10.7%) and increased significantly (P<0.01) at L5/S1 (23.3%). Changes in FH, maximum and minimum FW, and CSA of the IVF significantly (P<0.01) correlated with change in posterior DH.

Conclusions: FH, FW, and CSA of the IVF, except for L5/S1, decreased significantly during axial loading. Changes in posterior DH correlated well with the changes in foraminal dimensions.