Reliability and agreement in measurement of cervical spine joint repositioning error in the retraction-protrusion plane

Joint position error (JPE) occurring with retraction and protrusion movements of the cervical spine remains uninvestigated. This study examined reliability and agreement of JPE measurement in the retraction-protrusion plane and the impact of sagittal displacement on rotation JPE estimates. In a single session repeated measurement study, JPE was assessed in 20 asymptomatic individuals following retraction, protrusion and axial rotation in retracted and protruded positions. Movements were measured three times using an electromagnetic tracking system. Constant, absolute and variable JPE was recorded for each movement relocation. Intraclass correlation coefficients (ICC_2,3), standard error of measurement and minimal detectable change was calculated for the repositioning error of each movement. For constant error, ICC for JPE for retraction was 0.80 and protrusion 0.89. ICCs for relocation in the transverse plane to protrusion or retraction ranged from 0.75 to 0.88. For absolute error, ICC for JPE following retraction was 0.34 and protrusion 0.79. ICCs for relocation in the transverse plane to protrusion or retraction ranged from 0.69 to 0.89. Relocation following protrusion can be measured with moderate reliability. Whilst constant repositioning error for measurement following retraction displays substantial agreement, repositioning absolute error cannot be measured with adequate agreement. No effect on axial rotation JPE due to protrusion/retraction plane positioning was evident.