Pain referral and regional deep tissue hyperalgesia in experimental human hip pain models

Abstract

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.

Resisted adduction in hip neutral is a superior provocation test to assess adductor longus pain: An experimental pain study

“…This study indicates that the 0° test optimizes the diagnostic procedure without compromising diagnostic capacity to identify experimental AL tendon pain. Clinical tests for the groin area can be affected by pain alone in the absence of pathology, which is consistent with findings from other studies (Palsson & Graven‐Nielsen, ; Izumi et al., ; Palsson et al., ) highlighting that positive provocation tests may be induced by the presence of pain in the absence of pathology per se. Explorations beyond patho‐anatomical diagnoses of groin patients are warranted.…”

“…When interpreting the results of the study, two considerations must be accounted for: (a) pain generated from an experimental model differs from clinical pain (Palsson & Graven‐Nielsen, ; Izumi et al., ); and (b) the negative likelihood ratio of zero is likely to be artificially low and unlikely to be seen clinically. In our criteria, for a positive response to be recorded, the subject had to report a change in their resting pain and they had to indicate pain in the groin region.…”

“…However, these tests have not been evaluated against a consistent reference standard and therefore it remains unclear to what extent the outcome of the tests is related to pain and sensitivity of the structures in the region. By using experimental pain models, it has been demonstrated how pain in the sacroiliac (Palsson & Graven‐Nielsen, ; Palsson et al., ) and hip joint (Izumi et al., ) affects the outcome of clinical diagnostic tests. Whether the same applies for the adductor muscles is however unknown.…”

Acute experimental hip muscle pain alters single-leg squat balance in healthy young adults

“…Pain induced by hypertonic saline injections into gluteus medius muscle and tendon, is associated with similar patterns of referred pain, regional deep tissue hyperalgesia, and pain provocation test responses, as observed in clinical populations with hip pathology [13]. Unilateral injections of hypertonic saline into the quadriceps, hamstrings, dorsiflexors and plantarflexors are associated with increased anterior-posterior (AP) and medio-lateral (ML) displacement of the centre of pressure (CoP) during bilateral standing and following platform perturbations [10,12]: interpreted to indicate a decline in balance performance.…”

The effects of acute experimental hip muscle pain on dynamic single-limb balance performance in healthy middle-aged adults

“…To isolate the effect of nociceptive stimulation from structural impairments, pain was induced experimentally by injection of hypertonic saline. At the hip, injections of hypertonic saline into gluteus medius have led to patterns of referred pain, regional deep tissue hyperalgesia, and pain provocation test responses, similar to those observed in hip pathologies [16]. We used a within-subject repeated measures design with two groups.…”