What is the most common rotator cuff injury?

Most Common Rotator Cuff Injury

The supraspinatus tendon is the most common site of rotator cuff injury, with partial-thickness tears at the articular surface being the most prevalent type of rotator cuff tear. 1

Epidemiology and Risk Factors

Rotator cuff injuries are extremely common, affecting approximately 1 in 50 adults, with prevalence increasing significantly with age:

• 13% of individuals in their 50s
• 20% in their 60s
• 31% in their 70s have rotator cuff tears 1

The prevalence of rotator cuff tears increases dramatically with age, with 54% of asymptomatic patients aged 60 years or older having rotator cuff tears 1. Studies of cadavers have shown a 19% prevalence of full-thickness tears and 32% prevalence of partial-thickness tears 1.

Risk factors include:

• Age over 40 years (primary risk factor)
• Repetitive overhead activities
• Athletes with repetitive microtrauma (tennis players, baseball pitchers)
• Occupational exposure (painters, carpenters, other overhead workers)
• Traumatic injuries in younger patients (falls, shoulder dislocations) 1

Anatomy and Pathophysiology

The rotator cuff consists of four muscles and their tendons:

• Supraspinatus (superior aspect)
• Infraspinatus (posterior)
• Teres minor (posterior)
• Subscapularis (anterior)

The supraspinatus is particularly vulnerable because:

1. It occupies a narrow space between the humeral head and the coracoacromial arch
2. It experiences repeated impingement during shoulder abduction
3. It has an area of hypovascularity near its insertion point 1

Types of Rotator Cuff Tears

Tears can be classified as:

1. Partial-thickness tears:

   • Articular surface (most common type)
   • Bursal surface
   • Intratendinous

2. Full-thickness tears:

   • Complete disruption from articular to bursal surface
   • More common in older patients (>60 years)
   • More likely to progress in size over time 2

Diagnostic Imaging

For suspected rotator cuff tears, after initial radiographs:

• MRI and ultrasound have similarly high sensitivity and specificity for full-thickness tears 1
• MR arthrography has the highest sensitivity for partial-thickness tears 1
• Ultrasound is highly operator-dependent but can be effective with experienced technicians 1

MRI findings of rotator cuff tears include:

• Increased signal intensity extending through the tendon (full-thickness)
• Focal disruption or abnormal signal intensity (partial-thickness)
• Associated findings: muscle atrophy, fatty infiltration, tendon retraction 1

Clinical Implications and Progression

Important clinical considerations:

• Not all rotator cuff tears are symptomatic - 10% are asymptomatic 1
• Full-thickness tears are more likely to progress than partial-thickness tears (52% vs. 8%) 2
• Tears in patients over 60 years are more likely to progress than in younger patients (54% vs. 17%) 2
• Presence of fatty infiltration is associated with higher likelihood of tear progression 2

Pitfalls and Caveats

1. Diagnostic challenges:

   • Physical examination tests like Hawkins' and Neer's have high sensitivity (92% and 88% respectively) but poor specificity (25% and 33%) 1
   • Partial-thickness tears are more difficult to diagnose on ultrasound with variable interobserver agreement 1

2. Management considerations:

   • Not all tears require surgical intervention - many respond to conservative treatment
   • Factors associated with poor response to conservative treatment include:
     • Full-thickness tears
     • Multiple tendon involvement
     • Significant muscle atrophy or fatty infiltration
     • Older age (>60 years) 3, 2

3. Monitoring progression:

   • Tears followed for more than 18 months are more likely to progress in size (48%) compared to those followed for less than 18 months (19%) 2
   • MRI can be used to monitor changes in tear size and guide management decisions 2

Understanding that the supraspinatus is the most commonly affected tendon, with partial-thickness articular surface tears being the most prevalent type, helps guide appropriate diagnostic and treatment approaches for patients with shoulder pain.