The muscle imbalance pattern associated with upper crossed syndrome involves the upper trapezius (which helps stabilize the shoulder) as well as the levator scapula (which helps lift and lower the shoulder blades), the pectoralis major and minor (the chest muscles), and the sternocleidomastoid (lateral neck muscle). In people suffering from upper crossed syndrome, tightness in the upper trapezius and levator scapula crosses with tightness in the pectoralis major and minor. This pattern of muscle tightness, coupled with weakness in the deep cervical flexors, creates joint dysfunction that can lead to shoulder instability, pain, and injury. This dysfunction is particularly evident in the atlanto-occipital joint, C4-C5 segment, cervicothoracic joint, glenohumeral joint, and T4-T5 segment. Often, the condition results from overuse of the trapezius muscles and the neck. The overuse can stem from a variety of underlying issues, most of which have to do with posture. For example, this condition often affects people with forward head posture (i.e., the head juts out in front of the shoulders), hunchback-type posture, posture in which the shoulders round forward, and posture in which the shoulder blade bones move away from the body in a wing-type formation. If left untreated, upper crossed syndrome can develop into osteoarthritis and degenerative joint disease.