Impact of medial versus lateral knee pain on deep tissue hyperalgesia and muscle strength.

Abstract

Accumulating evidence indicates that knee pain gives rise to sensory and motor alterations, however, whether different profile of knee pain causes different alterations has not been investigated. The purpose of this experimental study is to clarify characteristics of medial and lateral knee pain and its potential for modulating sensory and motor function in humans. Fourteen healthy men were included. Medial knee pain (MP) was induced by injection of hypertonic saline (0.5mL) into the tibial insertion of the medial collateral ligament. For comparison, lateral knee pain (LP) was induced by injection of hypertonic saline identically into the iliotibial tract. Isotonic saline was injected contralaterally as control. Pain intensity was assessed on a continuous electronic visual analogue scale (VAS). Before, during and after the painful state, pressure pain thresholds from the knee (PPTs), maximal isometric muscle strength of the quadriceps and grip power were assessed bilaterally. MP demonstrated significantly higher VAS scores than LP and compared with control. PPTs decreased on medial and lateral knee in MP but only on the lateral knee in LP. Quadriceps muscle strength and grip power reduced bilaterally in both models, however, MP caused significantly greater reduction of ipsilateral quadriceps strength compared with LP. Medial knee pain has a greater impact on deep tissue hyperalgesia and reduction of the muscle strength compared with lateral knee pain. This is a novel finding that should be taken into consideration in a treatment strategy for painful knee patients. The experimental medial knee pain model demonstrated higher pain intensity, more localized pain distribution, widespread deep tissue hyperalgesia and more severe inhibition of muscle strength compared with the lateral knee pain model.