Active Muscle Trigger Points Are Associated with Pain and Related Disability in Patients with Plantar Heel Pain: A Case-Control Study

Objective. Pain experienced by patients with plantar heel pain has been associated with fascia thickness. It is possible that referred muscle pain may also be related to symptoms experienced by these patients. Our aim was to systematically investigate if the referred pain elicited by trigger points in the leg and foot musculature reproduces the symptoms in individuals with plantar heel pain and to determine the association of trigger points (TrPs) with pain and related disability. Methods. A case-control study was conducted. Thirty-five individuals with unilateral chronic plantar heel pain and 35 matched comparable healthy controls participated. An assessor blinded to the subject's condition explored TrPs in the flexor hallucis brevis, adductor hallucis, quadratus plantae, and internal gastrocnemius. Pain and related disability were assessed with a numerical pain rating scale (0-10), the Foot Function Index, and the Foot Health Status Questionnaire. Results. The number of TrPs for each patient with plantar heel pain was 463 (2.5 +/- 2 active TrPs, 1.5 +/- 1.8 latent TrPs). Healthy controls only had latent TrPs (mean = 161). Active TrPs in the quadratus plantae (N = 20, 62.5%), and flexor hallucis brevis (N = 19, 59%) were the most prevalent in patients with plantar heel pain. A greater number of active, but not latent, TrPs was associated with higher foot pain variables (0.413 < r(s) < 0.561, P< 0.01), higher impact of foot pain (0.350 < r(s) < 0.473, P< 0.05) and worse related disability (-0.447 < r(s) < -0.35456, P< 0.05). Conclusions. The referred pain elicited by active TrPs in the foot muscles reproduced the symptoms in patients with plantar heel pain. A greater number of active TrPs was associated with higher pain and related disability in patients with plantar heel pain.