Low back pain and osteoarthritis pain:a perspective of estrogen

Low back pain(LBP)is the world's leading cause of disability and is increasing in prevalence more rapidly than any other pain condition.Intervertebral disc(IVD)degeneration and facet joint osteoarthritis(FJOA)are two common causes of LBP,and both occur more frequently in elderly women than in other populations.Moreover,osteoarthritis(OA)and OA pain,regardless of the joint,are experienced by up to twice as many women as men,and this difference is amplified during menopause.Changes in estrogen may be an important contributor to these pain states.Receptors for estrogen have been found within IVD tissue and nearby joints,highlighting the potential roles of estrogen within and surrounding the IVDs and joints.In addition,estrogen supplementation has been shown to be effective at ameliorating IVD degeneration and OA progression,indicating its potential use as a therapeutic agent for people with LBP and OA pain.This review comprehensively examines the relationship between estrogen and these pain conditions by summarizing recent preclinical and clinical findings.The potential molecular mechanisms by which estrogen may relieve LBP associated with IVD degeneration and FJOA and OA pain are discussed.

Stiffness of individual quadriceps muscle assessed using ultrasound shear wave elastography during passive stretching

Background: Until recently it has not been possible to isolate the mechanical behavior of individual muscles during passive stretching. Muscle shear modulus(an index of muscle stiffness) measured using ultrasound shear wave elastography can be used to estimate changes in stiffness of an individual muscle. The aims of the present study were(1) to determine the shear modulus—knee angle relationship and the slack angle of the vastus medialis oblique(VMO), rectus femoris(RF), and vastus lateralis(VL) muscles;(2) to determine whether this differs between the muscles.Methods: Nine male rowers took part in the study. The shear modulus of VMO, RF, and VL muscles was measured while the quadriceps was passively stretched at 3°/s. The relationship between the muscle shear modulus and knee angle was plotted as shear modulus—knee angle curve through which the slack angle of each muscle was determined.Results: The shear modulus of RF was higher than that of VMO and VL when the muscles were stretched over 54°(all p < 0.01). No significant difference was found between the VMO and VL(all p > 0.05). The slack angle was similar among the muscles: 41.3°± 10.6°, 44.3°± 9.1°, and 44.3°± 5.6° of knee flexion for VMO, RF, and VL, respectively(p = 0.626).Conclusion: This is the first study to experimentally determine the muscle mechanical behavior of individual heads of the quadriceps during passive stretching. Different pattern of passive tension was observed between mono-and bi-articular muscles. Further research is needed to determine whether changes in muscle stiffness are muscle-specific in pathological conditions or after interventions such as stretching protocols.