**4.4 Musculoskeletal involvement**

The most common involvement of the musculoskeletal system in SSc are tendinopathy, joint contractures, and in some cases arthritis. In 45–90% of patients, arthralgia and arthritis of the small joints of the wrist, knees, and ankles occur [31].

Tenosynovitis and tendon ruptures are frequently detected in SSc. Tendon friction sound that can be detected by physical examination is caused by fibrotic deposits in the tendon sheath [32].

Calcinosis and acroosteolysis in the bones (resorption of terminal phalanx) can be seen in SSc patients. These changes are related to digital ischemia [31].

In addition, muscle weakness and pain, which mainly affects the proximal muscles, is another common symptom in SSc. Muscle involvement may occur in the form of myopathy or myositis, and patients should be evaluated from this angle [31]. Muscle weakness may result from nonuse, sedentary life, or joint/tendon involvement or sometimes as a side effect of treatment.

Although respiratory muscle involvement is not common in SSc, respiratory muscles may be affected in SSc-polymyositis/dermatomyositis overlap syndrome [31].
