What is the purpose of the Bigliani classification in shoulder surgery?

Purpose of the Bigliani Classification

The Bigliani classification system categorizes acromion morphology into three types (Type I: flat, Type II: curved, Type III: hooked) to identify anatomical variations theoretically associated with subacromial impingement and rotator cuff pathology, though its clinical utility is limited by poor interobserver reliability and lack of evidence supporting routine surgical intervention based on acromion type alone. 1, 2

Primary Classification System

The Bigliani classification divides acromial morphology into three distinct types 2, 3:

• Type I (flat): Represents approximately 20-26% of acromions 4, 5
• Type II (curved): The most common variant, comprising 55-60% of acromions 4, 5
• Type III (hooked): Found in approximately 18-19% of acromions 4, 5

Theoretical Clinical Rationale

The classification was developed based on the hypothesis that certain acromial shapes predispose to shoulder pathology 2, 3:

• Type III acromions show higher prevalence of subacromial enthesophytes (75%) and rough inferior surfaces (81.2%), suggesting mechanical irritation 4
• Extreme hooked acromions with slope >43° and lateral acromial angle <70° occur exclusively in patients with rotator cuff tears 3
• Type II and III morphologies have been theoretically linked to increased risk of subacromial impingement 2

Critical Limitations in Clinical Practice

Poor Reliability

The classification system suffers from significant reliability problems that undermine its clinical utility 6, 5:

• Interobserver reliability is poor to fair (kappa coefficient 0.516), with six fellowship-trained observers agreeing only 18% of the time 6
• Individual observer comparisons range from kappa 0.01 to 0.75 (mean 0.35), indicating substantial disagreement 6
• Lowest reliability occurs when distinguishing between Type II and Type III acromions, the most clinically relevant differentiation 5

Lack of Treatment Implications

The American Academy of Orthopaedic Surgeons explicitly states that routine acromioplasty is not necessary during rotator cuff repair, even in the presence of Type II or III acromion. 1, 2

• Level II randomized studies demonstrate no significant differences in functional outcomes (ASES scores, Constant-Murley scores, DASH scores) between rotator cuff repair with versus without acromioplasty, regardless of acromion type 1, 2
• One study of 47 patients with Type II acromion showed identical outcomes with or without acromioplasty 2
• Another study of 80 patients with Type II or III acromion confirmed no benefit from adding acromioplasty 2

Appropriate Use in Modern Practice

The classification serves primarily as a descriptive anatomical tool rather than a treatment decision-making instrument 1, 2:

• Standard radiographic evaluation including anteroposterior, lateral, and outlet supraescapular or Rockwood views can document acromial morphology 1, 2
• Treatment should focus on underlying pathology (rotator cuff tears, impingement symptoms) rather than acromial morphology alone 2
• Simply having a Type II or III acromion does not justify surgical intervention, as evidence does not show clinically important benefits from acromioplasty 1, 2

Common Pitfalls to Avoid

• Do not use acromion type as the primary indication for acromioplasty, as this is not supported by current evidence 1, 2
• Recognize the poor interobserver reliability when comparing studies or making clinical decisions based on reported acromion types 6, 5
• Avoid assuming causation between acromion type and rotator cuff pathology, as the association is not consistently demonstrated 3, 5
• Ensure adequate conservative treatment before considering surgery, regardless of radiographic acromial morphology 2