A novel experimental human hip pain model provides new insights into the pain mechanism and the structures generating specific pain patterns in hip disorder patients.
Hip disorder patients typically present with extensive pain referral and hyperalgesia. To better understand underlying mechanisms, an experimental hip pain model was established in which pain referrals and hyperalgesia could be studied under standardized conditions. In 16 healthy subjects, pain was induced by hypertonic saline injection into the gluteus medius tendon (GMT), adductor longus tendon (ALT), or gluteus medius muscle (GMM). Isotonic saline was injected contralaterally as control. Pain intensity was assessed on a visual analogue scale (VAS), and subjects mapped the pain distribution. Before, during, and after injections, passive hip joint pain provocation tests were completed, together with quantitative sensory testing as follows: pressure pain thresholds (PPTs), cuff algometry pain thresholds (cuff PPTs), cutaneous pin-prick sensitivity, and thermal pain thresholds. Hypertonic saline injected into the GMT resulted in higher VAS scores than hypertonic injections into the ALT and GMM (P < .05). Referred pain areas spread to larger parts of the leg after GMT and GMM injections compared with more regionalized pain pattern after ALT injections (P < .05). PPTs at the injection site were decreased after hypertonic saline injections into GMT and GMM compared with baseline, ALT injections, and isotonic saline. Cuff PPTs from the thigh were decreased after hypertonic saline injections into the ALT compared with baseline, GMT injections, and isotonic saline (P < .05). More subjects had positive joint pain provocation tests after hypertonic compared with isotonic saline injections (P < .05), indicating that this provocation test also assessed hyperalgesia in extra-articular soft tissues. The experimental models may open for better understanding of pain mechanisms associated with painful hip disorders.
aLaboratory for Musculoskeletal Pain and Motor Control, Center for Sensory-Motor Interaction (SMI), Department of Health Science and Technology, Faculty of Medicine, Aalborg University, Aalborg, Denmark
bDepartment of Orthopedic Surgery, Kochi University, Kochi, Japan
* Corresponding author. Address: Laboratory for Musculoskeletal Pain and Motor Control, Center for Sensory-Motor Interaction (SMI), Department of Health Science and Technology, Faculty of Medicine, Aalborg University, Frederik Bajers Vej 7D-3, Aalborg E 9220, Denmark. Tel.: +45 9940 9832; fax: +45 9815 4008.
Received 26 August 2013
Received in revised form 6 December 2013
Accepted 14 January 2014
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