Imaging plays a pivotal role in identifying and evaluating Bony Bankart lesions—fractures of the anteroinferior glenoid rim associated with shoulder dislocations. While plain radiographs (X-rays) are often the first step, computed tomography (CT) offers a more precise assessment. This article dives into the respective contributions of X‑ray and CT in diagnosing Bankart lesions and quantifying glenoid bone loss.
1. Role of X‑Ray in Bony Bankart Diagnosis
1.1 Standard Radiographic Views
- Anteroposterior (AP) view: May show irregularity or fragments along the inferior glenoid rim.
- Scapular Y‑view: Offers a lateral image of the scapula and can help visualize displaced fragments.
- Axillary view: Critical for detecting anterior glenoid rim defects that might be missed on AP views.
1.2 Strengths & Limitations
Strengths:
- Widely available, fast, low radiation dose.
- Helpful for initial detection and directing further imaging.
Limitations:
- Two-dimensional nature may obscure small or minimally displaced fragments.
- Inaccurate in measuring bone deficit due to overlap of structures.
2. Importance of CT in Quantifying Bone Loss
2.1 When CT Is Indicated
CT should be considered if:
- The patient has recurrent shoulder dislocations.
- X-ray findings are inconclusive.
- Surgical planning is required, as bone loss measurement guides operative strategy.
2.2 CT Protocols for Glenoid Evaluation
- Thin-slice axial scans (0.5–1 mm) with multiplanar reconstructions (MPR) in sagittal and coronal planes.
- Optional 3D reconstructions to visually assess fragment position and morphology.
2.3 Measuring Glenoid Bone Loss
- Best-fit circle method: A circle is drawn through the inferior two-thirds of the intact glenoid; bone loss is calculated by comparing missing arc length.
- Surface area comparison: Segmental glenoid surface is compared to the projected full circle, often yielding a percentage of bone loss.
- Inverted pear appearance: When bone loss exceeds ~20%, the remaining glenoid looks like an inverted pear—clinically significant and may influence surgical decisions.
3. Comparing X‑Ray vs CT
| Feature | X‑Ray | CT |
| Availability | High | Moderate, depends on setting |
| Radiation dose | Low | Moderate to high (thin slices) |
| Detection of fragments | Good for large/displaced ones | Better sensitivity for subtle lesions |
| Bone loss quantification | Poor to moderate | High precision (circle method, 3D view) |
| Role in surgical planning | Limited | Essential |
4. Imaging Workflow & Clinical Impact
4.1 Typical Workflow
- Clinical suspicion (e.g., traumatic anterior dislocation → Hill–Sachs or Bankart).
- Obtain X‑rays (AP, Y‑view, axillary).
- If positive or uncertain, proceed to CT.
- If negative but clinical suspicion persists, CT may still be warranted.
- CT scan with MPR and 3D reconstructions for accurate measurement.
- Determine bone loss percentage to guide treatment:
- < 13–15% usually managed arthroscopically.
- 20–25% often requires bony augmentation (e.g., Latarjet).
4.2 Influencing Treatment Decisions
Accurate quantification through CT helps determine whether range-limiting bone loss is present. The inverted-pear sign (> 20%) is a key threshold guiding whether to perform coracoid transfer or bone grafting.
5. Challenges & Emerging Techniques
5.1 Radiation Concerns
Repeated CT scans pose radiation exposure risks, particularly in younger patients. Ongoing research into low-dose CT protocols aims to maintain diagnostic quality while reducing dose.
5.2 MRI vs CT
While MRI excels at soft-tissue visualization (e.g., labral tears), it’s still less accurate than CT for measuring osseous defects—even with 3D sequences.
5.3 Automated Measurement Tools
Artificial intelligence is emerging in automated bone-loss quantification, offering faster, reproducible assessments. These systems show promise but require further validation.
FAQs
1. What percentage of glenoid bone loss is considered critical?
Typically, ≥ 20–25% bone loss is considered significant and may prompt bony reconstruction procedures.
2. Why is the axillary view essential on X‑ray?
It provides a clearer lateral perspective of the glenoid rim, helping detect anterior rim fractures that AP views may miss.
3. Can MRI replace CT for evaluating bone loss?
MRI is excellent for soft-tissue injuries but lacks the bony resolution of CT for quantifying glenoid defects accurately.
4. What is the “inverted-pear” sign?
A glenoid with > 20% bone loss appears narrower at the bottom, resembling an upside-down pear—indicative of clinically significant bone loss.
5. Are there ways to reduce radiation from CT?
Yes, protocols using low-dose settings and advanced image reconstruction can minimize radiation while preserving diagnostic clarity.
X‑ray and CT are complementary tools in diagnosing and managing Bony Bankart lesions. While X‑ray offers a quick, accessible first look, CT remains the gold standard for precise bone loss measurement and successful surgical planning.
