Chronic shoulder pain is a leading cause of musculoskeletal disability in the United States and affects up to 8% of all adults. A significant number of those affected are of working age, leading to lost productivity and substantial direct and indirect costs to the healthcare system. Disorders of the shoulder may include tendinopathies, instability, arthritis, and pathologic adaptations of the throwing shoulder. Treatment with both nonsurgical and surgical interventions generally results in favorable outcomes.

In the United States alone, more than 4.5 million patient visits due to shoulder pain occur each year.¹ Tears of the rotator cuff can occur from traumatic injuries or chronic degeneration. Degenerative tears are more common and increase with age. More than 50% of asymptomatic patients older than 60 years have a full-thickness or partial-thickness rotator cuff tear on MRI.² Additionally, the size of tears progresses over time although it is difficult to predict which tears progress and how quickly. A 2021 systematic review showed that partial-thickness tears progress to full-thickness tears at a rate of 3% per year with no difference in symptomatic
or asymptomatic tears.³ Full-thickness tears progress over time as well and possibly at an accelerated rate. A study of 34 patients with symptomatic full-thickness tears treated without surgery showed progression in 82% of patients after a minimum follow-up of 6 months⁴ (Figure 1).

Calcific tendinitis is a painful shoulder condition affecting between 3% and 7% of adults. It is most commonly seen in females aged 30 to 60 years and has an association with diabetes and thyroid disorders.²¹ The etiology is controversial though the stages of progression—formative, resting, and resorptive—are well accepted²² (Figure 4). The mainstay of treatment is nonsurgical, including activity modification, rest, physical therapy, and anti-inflammatory medications. In refractory cases, more invasive options may be considered such as injections, ultrasound-guided pulse lavage and needling, or extracorporeal shock wave therapy. Surgical intervention remains the last option. Evaluation with plain radiographs is usually sufficient; however, a 2020 MRI study found that 56% of calcium lesions were associated with partial-thickness (93%) or full-thickness (7%) rotator cuff tears, specifically lesions classified as cloudy with soft contour.²³ A 2020 randomized controlled trial compared ultrasound-guided needling (UGN) with subacromial corticosteroid injection (CSI) versus high-energy extracorporeal shock wave therapy in 82 patients. At 1 year, there were no differences in Constant scores, Disabilities of the Arm, Shoulder and Hand scores, or visual analog scale for pain; however the UGN group had more radiographic resorption of the calcific lesion and required less additional treatment during the follow-up period.²⁴ The addition of a CSI to the UGN procedure has been shown to improve pain at 6 weeks and function at 3 months versus saline injection control but had no effect on calcium resorption.²⁵ Platelet-rich plasma injection after UGN was found to have no benefit over CSI at 1 and 2 years.²⁶ Although nonsurgical treatment is frequently successful, patients with calcific lesions larger than 1 cm had a 2.8-fold increased likelihood of requiring surgical treatment.²⁷

Adhesive capsulitis, or frozen shoulder, begins as an inflammatory reaction and synovitis that progresses to fibrotic contracture of the shoulder capsule.²⁸ The pathophysiology is poorly understood but thought to be driven by increased recruitment of inflammatory cytokines. Elevated fasting glucose levels, hypercholesterolemia, thyroid disorder, and increased high-sensitivity C-reactive protein all have been associated with adhesive capsulitis. In a case-control study of 202 patients, serum high-sensitivity C-reactive protein was independently associated with adhesive capsulitis when controlling for diabetes, dyslipidemia, and
thyroid-stimulating hormone.²⁹ Interestingly, a 2021 report has also suggested a link between severe acute respiratory syndrome-coronavirus-2 (SARS-CoV-2) and adhesive capsulitis.³⁰ In refractory cases, more invasive treatments can be considered. Extracorporeal shock wave therapy has shown benefit in diabetic patients compared with intra-articular CSIs at short-term follow-up.³¹ More recently, alternative minimally invasive treatments such as collagenase Clostridium histolyticum injections and ultrasound-guided percutaneous sectioning of the coracohumeral ligament have shown early encouraging results, although further study is needed.³²,³³ Studies have shown that although capsular release and manipulation under anesthesia provide similar functional outcomes, arthroscopic capsular release results in improved range of motion including forward flexion, abduction, and external rotation.³⁴

The overhead throwing motion generates substantial force across the glenohumeral joint. The repetitive stress and microtrauma lead to adaptive changes in a thrower’s dominant arm and can lead to various pathologic conditions. These changes include increased external rotation, decreased internal rotation, increased glenoid and humeral head retroversion, and posterior capsular hypertrophy.