Musculoskeletal trauma and pain can sensitize central pain mechanisms, but whether these normalize on recovery is unknown. This study compared the extent of pain referral in individuals recovered from a musculoskeletal trauma and healthy controls. Twenty pain-free participants recovered from a shoulder fracture and 20 age-/sex-matched controls participated in 2 experimental sessions (day-0 and day-1) separated by 24 hours. On both days, pressure pain thresholds were measured bilaterally at infraspinatus, supraspinatus, trapezius, and gastrocnemius muscles. Referred pain towards the shoulder region was induced by a 60-second pressure stimulation (pressure pain threshold + 20%) at the infraspinatus muscle and recorded on an electronic body chart. After day-0 assessments, delayed onset muscle soreness (DOMS) was induced to challenge the pain systems by exercising the external rotators of the recovered/dominant shoulder. The size of pressure-induced pain referral on day-0 did not differ between groups, although there was a tendency for a smaller referred pain area in recovered group. Pressure pain thresholds at the infraspinatus muscle on the DOMS side were reduced on day-1 in both groups (P = 0.03). An expansion of pressure-induced pain referral was found in both groups following the DOMS protocol on day-1 (P = 0.05) with a relatively larger expansion (P = 0.05) and higher frequency of pain in the shoulder (P = 0.04) in the recovered pain group. After complete recovery and absence of pain symptoms after a fracture, central pain mechanisms seem to normalize in the region of the trauma after recovery but when sensitized a heightened response can emerge. Such mechanisms could be important for recurrence of pain conditions.
Pain-free individuals with a recovered fracture showed a heightened response after pressure-induced referred pain when the pain system was sensitized through delayed onset muscular soreness.
aDepartment of Health Science and Technology, Center for Neuroplasticity and Pain (CNAP), SMI, Faculty of Medicine, Aalborg University, Aalborg, Denmark
bFaculty of Health Sciences, iPhysio Research Group, Universidad San Jorge, Zaragoza, Spain
Corresponding author. Address: Department of Health Science and Technology, Center for Neuroplasticity and Pain (CNAP), SMI, Faculty of Medicine, Aalborg University, Fredrik Bajers Vej 7D-3, Aalborg E 9220, Denmark. Tel.: +45 9940 9832; fax: +45 9815 4008. E-mail address: email@example.com (T. Graven-Nielsen).
Sponsorships or competing interests that may be relevant to content are disclosed at the end of this article.
Received December 06, 2017
Received in revised form March 01, 2018
Accepted March 28, 2018