Position Sense in Chronic Pain: Separating Peripheral and Central Mechanisms in Proprioception in Unilateral Limb Pain.

Abstract

Awareness of limb position is derived primarily from muscle spindles and higher-order body representations. Although chronic pain appears to be associated with motor and proprioceptive disturbances, it is not clear if this is due to disturbances in position sense, muscle spindle function, or central representations of the body. This study examined position sense errors, as an indicator of spindle function, in participants with unilateral chronic limb pain. The sample included 15 individuals with upper limb pain, 15 with lower limb pain, and 15 sex- and age-matched pain-free control participants. A 2-limb forearm matching task in blindfolded participants, and a single-limb pointer task, with the reference limb hidden from view, was used to assess forearm position sense. Position sense was determined after muscle contraction or stretch, intended to induce a high or low spindle activity in the painful and nonpainful limbs, respectively. Unilateral upper and lower limb chronic pain groups produced position errors comparable with healthy control participants for position matching and pointer tasks. The results indicate that the painful and nonpainful limb are involved in limb-matching. Lateralized pain, whether in the arm or leg, does not influence forearm position sense. Painful and nonpainful limbs are involved in bilateral limb-matching. Muscle spindle function appears to be preserved in the presence of chronic pain.