Despite extensive research and clinical investigations, the exact cause of frozen shoulder is not known. Investigators have agreed that the condition is mainly multi-factorial in origin (i.e. more than one causative agent is responsible for the pathogenesis of adhesive capsulitis (otherwise known as frozen shoulder).
It is imperative to keep in mind that frozen shoulder should not be confused with shoulder joint arthritis or other disorders of shoulder joint. Frozen shoulder is caused by constriction or stiffening of the capsule of shoulder joint and intercapsular space; whereas arthritis (or arthralgia) involves the joint or articulating bones.
Pathophysiology of Frozen Shoulder:
The shoulder joint offers 3-dimensional movement owing to the characteristic ball-and socket like arrangement of scapula, humerus and clavicle. The shoulder joint is supported, strengthened and stabilized by strong fibrous ligaments, tendons and antagonizing group of muscles to maintain normal anatomy and physiology of the joint cavity. The shoulder joint capsule is in turn made up of strong connective tissue fibers.
However, with physiological aging, the connective tissue components loses its flexibility and strength. The resultant effect is thinning of connective tissue capsule and stiffness of joint elements; that increases the risk of wear and tear related damage and adhesive capsulitis (thickening and tightening of joint capsule). There are a number of pathological factors that may deteriorate shoulder joint strength and flexibility; but based on extensive research and clinical analysis; the most notable ones are:
- Injury to the shoulder joint (strain or sprains that are usually not detected by patients). It is imperative to keep in mind that the injury process is not always severe or significant. In fact most patients tend to forget the inciting source of injury (that could be lifting a heavy suitcase, lawn mowing or vigorous gym workout).
- Ongoing musculoskeletal or nervous condition that affects the integrity of neuronal connectivity. This includes muscle contractile disorders, nerve compression syndromes (like thoracic outlet syndrome) and spinal disc degeneration. In most cases, the neuronal disruption or weakness is the primary source of immune hyperactivity or exaggerated response.
- Personal history of hormonal imbalance such as testosterone deficiency, estrogen deficiency (physiological as in menopause or pathological), adrenal disorders, thyroid dysfunction and diabetes. Hormonal imbalance is almost always implicated in the setting of frozen shoulder and should be address adequately in order to minimize the risk of recurrence.
Since these three elements co-exists in over 90% cases, these three causative agents can also be referred to as “Etiology Triad of Frozen Shoulder”
Risk Factors That May Lead to Frozen Shoulder:
Clinical data and experimental research studies suggests that certain risk factors can increase the chance of wear and tear related damage to joint capsule. These risk factors are:
- Injury or surgery of Upper limb: Individuals who are recovering from an acute injury or surgical procedure involving the upper limb are at much higher risk of developing frozen shoulder due to inflammatory response, poor mobility and restricted range of motion (all these factors strongly favors the development of frozen shoulder.Restricted mobility of shoulder joint is also seen in other situations; such as:
- Rotator cuff injury
- Systemic Disease:Individuals who are suffering from chronic health or medical issues are more likely to develop frozen shoulder. Most frequently reported medical conditions that may play an integral role in the pathogenesis of frozen shoulder are:
- Cardiovascular disease
- Parkinson’s Disease
- Hyperthyroidism (overactive thyroid gland)
- Hypothyroidism (Underactive thyroid gland)
- Cervical cancer
- History of autoimmune diseases/ disorders
- Age and Gender:Physiological aging favors the degeneration of cartilage and other connective tissue elements; thereby significantly compromising the healing and regeneration process after an injury. Elderly females are more likely to develop frozen shoulder due to weakening and fibrosis of joint connective tissue.
Other risk factors include:
- Repetitive stress and strain involving the shoulder joint
- Chronic inflammation of joint capsule due to circulatory or immune dysfunction
Frozen shoulder often resolves spontaneously over a period of 1-2 years; however, certain treatment modalities can be used to enhance the pace of recovery. Investigators and healthcare professionals prefer conservative options to minimize the risk of recurrence.