Interactive Glenoid Track Calculator
Enter measurements from imaging (typically CT or MRI) to estimate whether a Hill-Sachs lesion is on-track or off-track.
For educational use only. Clinical decisions should be made by qualified orthopedic specialists using full patient context.
What is the glenoid track?
The glenoid track is a biomechanical concept used in shoulder instability to predict whether a Hill-Sachs lesion is likely to engage the anterior glenoid rim during abduction and external rotation. Engagement risk increases when the humeral head defect extends beyond the available glenoid track.
In practical terms, this helps surgeons and sports medicine teams estimate recurrence risk after dislocation and choose between soft tissue stabilization alone versus additional bony or remplissage procedures.
Core formulas used in this calculator
1) Glenoid track width (GT)
GT = 0.83 × D − d
- D = intact glenoid diameter
- d = measured anterior glenoid bone loss
2) Hill-Sachs interval (HSI)
HSI = Hill-Sachs defect width + bone bridge
- Hill-Sachs defect width = width of humeral head impression defect
- Bone bridge = interval between the lateral margin of the defect and cuff insertion footprint
3) On-track vs off-track interpretation
- On-track: HSI ≤ GT
- Off-track: HSI > GT
How to use the calculator correctly
Measurement quality is everything. Use consistent imaging planes, magnification standards, and an agreed method within your team. A few millimeters can change classification at the threshold.
- Use the same modality and protocol whenever serially following an athlete.
- Confirm that glenoid bone loss is measured as linear loss in the same orientation as D.
- Double-check Hill-Sachs width and bone bridge values before final interpretation.
Clinical context matters
The glenoid track model is extremely useful but should never be interpreted in isolation. Instability risk and treatment planning also depend on:
- Patient age and activity level
- Collision or overhead sport demands
- Ligamentous laxity and soft tissue quality
- Number of prior dislocations and failed surgeries
- Associated lesions (Bankart, ALPSA, HAGL, etc.)
Interpreting bone loss percentage
This page also reports glenoid bone loss percentage (d / D × 100) to provide additional context. In many practices:
- < 13.5% is often considered lower-risk bone loss
- 13.5%–20% may be viewed as subcritical bone loss
- ≥ 20% is frequently treated as critical in many algorithms
These ranges vary by institution, imaging method, and surgical philosophy. Always use local protocols and specialist judgment.
Example scenario
Suppose D = 30 mm and d = 5 mm. Then GT = 0.83 × 30 − 5 = 19.9 mm. If Hill-Sachs width is 13 mm and bone bridge is 8 mm, HSI = 21 mm. Since 21 > 19.9, this is off-track.
Off-track findings may influence surgical planning, potentially adding procedures that reduce engagement risk.
Limitations of any calculator
A calculator simplifies a complex 3D pathology into a few numeric inputs. It cannot replace image review, exam findings, and multidisciplinary discussion. Think of it as a decision-support tool, not a diagnosis engine.