Regional assessment of joint position sense in the spine.

Study Design: A test-retest design was used to assess the reproducibility of position sense measurements of the spine recorded at T1, T7, L1, and S2.
Objectives: To measure position sense at four spinal levels in healthy volunteers and to determine if this varies on a day-to-day basis. The overall purpose is to provide baseline data for studying position sense of the spine in patients with spinal lesions.
Summary of Background Data: Position sense, which is one component of proprioception, is assessed by the ability to reposition the body after displacement. In peripheral joints, position sense is accurate to within a few degrees. Studies on the spine suggest similar accuracy, but most have used indirect methods of measurement that often incorporate unusual extraneous cues.
Methods: Spinal position sense was assessed in 20 healthy volunteers using an electromagnetic movement sensor system, the 3-Space Fastrak (Polhemus, Colchester, VT), to measure absolute error in actively reproducing upright and flexed positions during movements in both coronal and sagittal planes. Three randomized measurements were taken for each position in one testing session, and measurements were repeated in all participants 2 weeks later.
Results: Same-day measurements indicate that spinal position sense is reproducible in upright postures to within a mean of 3.79 +/- 2.56 for movements in the sagittal plane and 2.26 +/- 1.59 degrees for movements in the coronal plane. Corresponding measurements for flexed postures are 5.27 degrees +/- 3.47 degrees and 3.70 +/- 2.62 degrees, respectively. Intraclass correlation coefficients between repeated measurements are generally good in the sagittal plane but are affected by side dominance in the coronal plane. Also, repositioning errors tend to increase on ascending the spine. Repeat measurements taken 2 weeks later show similar values.
Conclusions: 1) Healthy volunteers were able to reposition their spine with considerable accuracy as measured with the 3-Space Fastrak; 2) this ability does not change significantly on a day-to-day basis; and 3) the 3-Space Fastrak offers a noninvasive and accurate method for the measurement of spinal position sense.