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

Study Design: 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.

Summary Of Background Data: 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.

Materials And 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.