What are the limitations of the on-track and off-track concept of the glenoid in shoulder instability?

Limitations of the On-Track and Off-Track Concept of the Glenoid in Shoulder Instability

The glenoid track concept has significant limitations in clinical practice, including moderate accuracy and reliability when compared to dynamic arthroscopic assessment, making it an imperfect tool for surgical decision-making in shoulder instability cases. 1

Key Limitations of the Glenoid Track Concept

Diagnostic Accuracy Issues

• 3D CT-based measurements for determining glenoid track status show only moderate accuracy (65%) when compared to dynamic arthroscopic assessment 1
• Static arthroscopic measurements have even lower accuracy (59%) compared to dynamic assessment 1
• The positive predictive value of 3D CT-based measurements is only 66%, meaning one-third of "off-track" designations may be incorrect 1

Reliability Concerns

• Interrater reliability for determining glenoid track status using 3D CT is only "fair" (Krippendorff α = 0.368) 1
• Static arthroscopic measurements show slightly better but still only "moderate" interrater reliability (Krippendorff α = 0.523) 1
• Intrarater reliability is "moderate" for 3D CT measurements (ICC = 0.660) and "good" for static arthroscopic measurements (ICC = 0.769) 1

Technical Challenges

• The medial margin of the footprint (lateral margin of the glenoid track) is often difficult to identify when a Hill-Sachs lesion is overriding the footprint 2
• While 3D CT is considered the most accurate method for assessment, there is increasing interest in MRI methods which have no radiation concerns, but these techniques are still under development 2

Conceptual Limitations

• The glenoid track concept addresses only one factor in shoulder instability (bony lesions) while ignoring other important risk factors 2
• The concept uses a fixed value of 83% of the glenoid width to determine the track width, which may not be appropriate for all patients 2
• There is a "gray zone" (peripheral-track lesion) that is not clearly defined in the current concept 2

Improving the Glenoid Track Concept

Individualized Assessment

• Using custom-made glenoid track width measurements based on individualized values obtained by measuring the active horizontal extension angle of the opposite shoulder in sitting position, rather than using the fixed 83% value 2
• Incorporating other risk factors beyond bony lesions into the assessment 2

Combined Assessment Tools

• The Glenoid Track Instability Management Score (GTIMS) combines the glenoid track concept with the instability severity index score to enhance clinical decision-making 2
• This approach may increase the predictive potential of the assessment by incorporating multiple risk factors 2

Imaging Considerations

• 3D CT remains the gold standard for assessment, but MRI methods are being developed to reduce radiation exposure 2
• Surgeons should be aware that both 3D CT and static arthroscopic measurements should be used with caution when making surgical decisions 1

Clinical Implications

• Despite limitations, the glenoid track concept remains useful for evaluating patients with anterior shoulder instability 3
• Shoulders classified as "off-track" have significantly higher failure rates after isolated arthroscopic Bankart repair (75% vs 8% for "on-track" lesions) 4
• The positive predictive value of an "off-track" measurement (75%) is superior to using glenoid bone loss of >20% alone (44%) for predicting postoperative instability 4
• For "off-track" lesions, either remplissage or Latarjet procedure may be indicated, depending on glenoid defect size and recurrence risk 5

The glenoid track concept provides valuable information but should be used as part of a comprehensive assessment rather than as the sole determinant for surgical decision-making in shoulder instability cases.