High-yield overview
Glenoid Track in Shoulder Instability
BipolarGlenoid + Hill-Sachs loss together
3D CTGold standard (en-face); 3D MRI validated
Glenoid trackOn-track vs off-track Hill-Sachs
Drives surgeryBankart / remplissage / Latarjet
Key features
Bipolar concept
PatternBone loss in anterior instability is BIPOLAR - it involves BOTH the anterior GLENOID (bony Bankart / attritional loss) AND the posterosuperior humeral head (HILL-SACHS lesion) - and the two interact, so both must be assessed together.
Treatment
Quantify
PatternGLENOID bone loss is quantified on an EN-FACE (Sagittal-oblique) 3D CT using a best-fit circle of the inferior glenoid (3D CT is the GOLD STANDARD; 3D MRI is a validated alternative); thresholds: SUBCRITICAL (~13.5-20%) and CRITICAL (~20-25%) glenoid bone loss.
Treatment
Glenoid track
PatternThe GLENOID TRACK is the contact zone of the glenoid on the humeral head in abduction-external rotation; if the Hill-Sachs lesion extends MEDIAL to the medial margin of the track it is OFF-TRACK (engages -> high recurrence); if not, ON-TRACK. This dynamic, bipolar assessment guides surgery.
Treatment
Critical Must-Knows
- Bone loss in anterior shoulder instability is BIPOLAR: it involves both the anterior GLENOID (a bony Bankart fragment or attritional/erosive loss) and the posterosuperior humeral head (a HILL-SACHS impaction lesion), and because the two interact during instability, both must be assessed TOGETHER rather than in isolation.
- GLENOID bone loss is quantified on an EN-FACE (sagittal-oblique) reconstruction using a best-fit circle of the inferior glenoid (the inferior glenoid is normally a near-perfect circle), expressing the defect as a percentage of the circle; 3D CT is the GOLD STANDARD for this static assessment, and 3D MRI has been validated as a reliable alternative (with the advantage of also assessing soft tissues).
- Recognised THRESHOLDS guide management: 'critical' glenoid bone loss is classically around 20-25% (above which an isolated soft-tissue Bankart repair has unacceptably high failure), and there is now emphasis on 'SUBCRITICAL' bone loss (around 13.5-20%), where outcomes of isolated Bankart repair are already compromised and augmentation should be considered.
- The GLENOID TRACK concept (Yamamoto/Di Giacomo) is the key dynamic, bipolar tool: the glenoid track is the zone of contact of the glenoid on the humeral head in the provocative abduction-external rotation position (its width is approximately 0.83 times the glenoid diameter minus the glenoid bone-loss width); if the Hill-Sachs lesion extends MEDIAL to the medial margin of the track it is 'OFF-TRACK' and will ENGAGE the glenoid rim (high recurrence risk), whereas if it stays within the track it is 'ON-TRACK'.
- These measurements DRIVE the surgical choice: an ON-TRACK lesion with minimal glenoid bone loss is suitable for an isolated arthroscopic BANKART repair; an OFF-TRACK Hill-Sachs (or significant bipolar loss) needs the Hill-Sachs addressed - typically a Bankart plus REMPLISSAGE (filling the Hill-Sachs with posterior capsule/infraspinatus) - and significant GLENOID bone loss (around 20% or more, or subcritical loss with an off-track lesion or other risk factors) needs a BONY procedure such as a LATARJET (coracoid transfer) or bone block.
- Accurate, reproducible assessment matters because under-estimating bone loss leads to recurrent instability after an inadequate soft-tissue repair: 3D CT (or validated 3D MRI) should be used to measure glenoid bone loss and the Hill-Sachs and to compute the glenoid track / on-off-track status as part of preoperative planning, integrated with clinical risk factors (age, sport, hyperlaxity) and instability scores.
Clinical Pearls
- “Bone loss is BIPOLAR: anterior GLENOID (bony Bankart) + posterosuperior humeral head (HILL-SACHS) - assess BOTH together.
- “Quantify glenoid loss on EN-FACE 3D CT (gold standard; 3D MRI validated) with a best-fit inferior-glenoid circle; subcritical ~13.5-20%, critical ~20-25%.
- “GLENOID TRACK: track width ~0.83 x glenoid diameter - glenoid bone-loss width; Hill-Sachs medial to the track = OFF-TRACK (engages). Drives Bankart (on-track) vs +remplissage (off-track) vs Latarjet (significant glenoid loss).
Assess Both Bones - and Whether the Hill-Sachs Engages
Quantify
Bone loss is bipolar (glenoid + Hill-Sachs). Measure glenoid loss on en-face 3D CT (gold standard) with a best-fit inferior-glenoid circle; subcritical ~13.5-20%, critical ~20-25%.
On- or off-track?
Compute the glenoid track: a Hill-Sachs medial to the track margin = OFF-TRACK (engages, high recurrence). This drives Bankart vs remplissage vs Latarjet.
Bipolar Bone Loss, Quantification & the Glenoid Track
Measure the Glenoid, Track the Hill-Sachs
Bone loss in anterior instability is bipolar - both the anterior glenoid (bony Bankart/attritional loss) and the posterosuperior humeral head (Hill-Sachs) - and the two interact, so both are assessed together. Glenoid bone loss is quantified on an en-face (sagittal-oblique) 3D CT with a best-fit circle of the inferior glenoid (3D CT is the gold standard; 3D MRI is a validated alternative); thresholds are subcritical (~13.5-20%) and critical (~20-25%). The glenoid track concept is the key dynamic tool: the track is the glenoid's contact zone on the humeral head in abduction-external rotation (width approximately 0.83 x glenoid diameter minus the glenoid bone-loss width); a Hill-Sachs lesion medial to the medial margin of the track is OFF-TRACK (it engages the rim, high recurrence) whereas one within the track is ON-TRACK. These measurements drive the surgical choice.
| Scenario | Bone status | Typical procedure |
|---|---|---|
| Minimal loss, on-track | Glenoid loss minimal; Hill-Sachs on-track | Arthroscopic Bankart repair |
| Off-track Hill-Sachs (limited glenoid loss) | Hill-Sachs engages; glenoid loss subcritical | Bankart + remplissage |
| Significant glenoid loss | Glenoid loss ~20%+ (or subcritical + off-track / high risk) | Bony procedure (Latarjet / bone block) |
| Severe bipolar loss | Large glenoid + large Hill-Sachs | Latarjet (+/- humeral-side procedure) |
How the Numbers Drive Surgery
From Measurement to Operation
- On-track, minimal glenoid loss: isolated arthroscopic Bankart repair.
- Off-track Hill-Sachs (with subcritical glenoid loss): address the Hill-Sachs - Bankart + remplissage (fill the Hill-Sachs with posterior capsule/infraspinatus) to make it functionally on-track.
- Significant glenoid bone loss (~20% or more, or subcritical loss with an off-track lesion / high-risk patient): a bony procedure - Latarjet (coracoid transfer, restoring glenoid arc + the sling effect) or a glenoid bone block.
- Integrate clinical risk: age, sport (contact/collision), hyperlaxity and instability scores modify the thresholds.
- Measure accurately: use 3D CT (or validated 3D MRI) for glenoid loss, the Hill-Sachs and the glenoid track preoperatively - under-estimating bone loss is a key cause of recurrence."
Don't Repair Soft Tissue Over Unaddressed Bone Loss
The central error in shoulder instability surgery is performing an isolated soft-tissue Bankart repair while under-estimating or ignoring bone loss, because an off-track Hill-Sachs or significant glenoid bone loss will cause the repair to fail with recurrent instability. The bone loss is bipolar, so both the glenoid and the Hill-Sachs must be measured and combined in the glenoid-track assessment: a Hill-Sachs that is off-track, or glenoid bone loss in the subcritical-to-critical range, signals that the soft-tissue repair needs augmentation - remplissage for the engaging Hill-Sachs, and a bony procedure such as a Latarjet for significant glenoid loss. Use 3D CT (or validated 3D MRI) to quantify bone loss and compute on/off-track status preoperatively, and integrate clinical risk factors, rather than deciding from a plain film alone.
Evidence & Key Studies
Evidence
3D MRI vs 3D CT for static bone loss and dynamic bipolar (glenoid track) assessment in instability
Twomey-Kozak J, Udoh I, Briggs DV, Hurley ET, Lorentz S, Meyer A, et al. • Orthopaedic Journal of Sports Medicine (2025)
Key Findings:
- 3D CT has been the gold standard for evaluating static glenoid bone loss; 3D MRI was validated as a reliable alternative for both static bone loss and dynamic morphological variables.
- Measured variables included glenoid and humeral bone loss, Hill-Sachs occupancy, glenoid track zones and distance to dislocation; both modalities accurately identified on-track/off-track lesions.
- Inter- and intra-rater reliability was good to excellent, supporting either modality for preoperative bipolar bone-loss and glenoid-track assessment.
Evidence
Bone-loss-guided treatment: dynamic anterior stabilization with remplissage for off-track/bipolar loss
de Campos Azevedo C, Angelo AC • Arthroscopy Techniques (2025)
Key Findings:
- Soft-tissue stabilization (dynamic anterior stabilization using the biceps) is indicated for anterior instability with anterior glenoid bone loss of up to about 20%.
- In patients with bipolar bone loss who play contact/collision sports, augmenting with Hill-Sachs remplissage further increases stability and reduces recurrence.
- Treatment selection is explicitly driven by the amount of glenoid bone loss and whether the Hill-Sachs is engaging, supporting the bone-loss/glenoid-track framework.
Evidence Attribution
According to PubMed, 3D CT being the gold standard for static glenoid bone loss (with 3D MRI a validated alternative) and the measurement of glenoid/humeral bone loss, Hill-Sachs occupancy and on/off-track glenoid track zones come from the cited Twomey-Kozak study; the bone-loss-driven treatment thresholds (soft-tissue repair up to ~20% glenoid loss, augmenting with remplissage for bipolar/off-track loss in contact athletes) from the cited de Campos Azevedo technical note. The bipolar-bone-loss concept, the en-face best-fit-circle quantification, the subcritical/critical thresholds, the glenoid-track formula and the Latarjet-for-significant- glenoid-loss principle are standard, well-established teaching. (See also our Anterior Shoulder Instability and Latarjet Procedure topics.)
Clinical Decision Scenarios
Practise clinical reasoning and management decisions out loud
Viva scenarioStandard
Clinical prompt
“How do you assess bone loss in a patient with recurrent anterior shoulder instability?”
Practical approach
I assess bone loss as bipolar, because in anterior instability it involves both the anterior glenoid and the posterosuperior humeral head, and the two interact, so I evaluate them together. For the glenoid, I quantify bone loss on an en-face, sagittal-oblique reconstruction using a best-fit circle of the inferior glenoid, which is normally close to a perfect circle, and express the defect as a percentage; 3D CT is the gold standard for this, and 3D MRI has been validated as a reliable alternative with the advantage of also showing soft tissue. I interpret the result against thresholds: critical glenoid bone loss is classically around 20 to 25 percent, above which an isolated soft-tissue Bankart repair fails too often, and there is now emphasis on subcritical loss, around 13.5 to 20 percent, where outcomes are already compromised. For the humeral side I assess the Hill-Sachs lesion and then combine the two using the glenoid track concept: the glenoid track is the contact zone of the glenoid on the humeral head in abduction and external rotation, with a width of about 0.83 times the glenoid diameter minus the glenoid bone-loss width, and if the Hill-Sachs extends medial to the medial margin of the track it is off-track and will engage, which carries a high recurrence risk, whereas if it stays within the track it is on-track. I would compute all of this on 3D CT or validated 3D MRI preoperatively and integrate it with clinical risk factors such as age, sport and hyperlaxity.
Key clinical points
Bone loss is bipolar - assess glenoid AND Hill-Sachs together
Glenoid loss: en-face 3D CT (gold standard; 3D MRI validated) best-fit inferior-glenoid circle; subcritical ~13.5-20%, critical ~20-25%
Glenoid track width ~0.83 x glenoid diameter - glenoid bone-loss width
Hill-Sachs medial to the track margin = off-track (engages, high recurrence)
Common pitfalls
Assessing the glenoid or Hill-Sachs in isolation
Relying on plain films / 2D to quantify bone loss
Ignoring subcritical glenoid bone loss
Further questions
“Gold-standard imaging? - 3D CT (en-face); 3D MRI validated alternative”
“What makes a Hill-Sachs off-track? - It extends medial to the medial margin of the glenoid track”
Viva scenarioStandard
Clinical prompt
“How does bone-loss assessment change your surgical choice?”
Practical approach
The bone-loss assessment directly determines the operation. If the glenoid bone loss is minimal and the Hill-Sachs is on-track, an isolated arthroscopic Bankart repair is appropriate. If the Hill-Sachs is off-track but the glenoid loss is subcritical, I need to address the engaging Hill-Sachs as well, typically with a Bankart repair plus remplissage, where the posterior capsule and infraspinatus are used to fill the Hill-Sachs and make it functionally on-track, and the evidence supports adding remplissage for bipolar or off-track lesions, especially in contact or collision athletes. If there is significant glenoid bone loss, around 20 percent or more, or subcritical loss in a high-risk patient or with an off-track lesion, I would perform a bony procedure such as a Latarjet, transferring the coracoid to restore the glenoid arc and provide the sling effect, or a glenoid bone block. For severe bipolar loss I would favour a Latarjet, sometimes with a humeral-side procedure. Throughout, I would integrate clinical risk factors - age, sport, hyperlaxity and instability scores - because they modify the thresholds, and I would emphasise that under-estimating bone loss and doing an isolated soft-tissue repair over significant or off-track bone loss is the main cause of recurrence.
Key clinical points
On-track + minimal glenoid loss -> arthroscopic Bankart
Off-track Hill-Sachs (subcritical glenoid loss) -> Bankart + remplissage
Significant glenoid loss (~20%+ or subcritical + off-track/high-risk) -> Latarjet/bone block
Integrate clinical risk; under-estimating bone loss -> recurrence
Common pitfalls
Isolated Bankart over an off-track lesion or significant glenoid loss
Not adding remplissage for an engaging Hill-Sachs
Ignoring clinical risk factors
Further questions
“Procedure for an off-track Hill-Sachs with subcritical glenoid loss? - Bankart + remplissage”
“Procedure for significant glenoid bone loss? - Latarjet / bone block”
Mnemonics & Memory Aids
Mnemonic
TRACK
T
Track = glenoid contact zone in abduction-external rotation (~0.83 x diameter - glenoid loss)
R
Reconstruct on en-face 3D CT (gold standard; 3D MRI validated)
A
Assess BOTH bones - bipolar (glenoid + Hill-Sachs)
C
Critical ~20-25% (subcritical ~13.5-20%) glenoid bone loss
K
Know the procedure: on-track Bankart, off-track +remplissage, big glenoid loss -> Latarjet
Hook:TRACK: Track width formula, Reconstruct on 3D CT, Assess both bones (bipolar), Critical 20-25%, Know procedure (Bankart/remplissage/Latarjet).
Exam day cheat sheet
Glenoid & Bipolar Bone Loss - Exam Day Cheat Sheet
Concept
- Bone loss is bipolar: anterior glenoid (bony Bankart) + posterosuperior humeral Hill-Sachs
- Assess both together (they interact)
- Under-estimating bone loss -> recurrence after isolated soft-tissue repair
Quantify glenoid loss
- En-face (sagittal-oblique) best-fit circle of the inferior glenoid
- 3D CT gold standard; 3D MRI validated alternative
- Subcritical ~13.5-20%; critical ~20-25%
Glenoid track
- Track width ~0.83 x glenoid diameter - glenoid bone-loss width
- Hill-Sachs medial to the track margin = OFF-TRACK (engages, high recurrence)
- Within track = ON-TRACK
Procedure selection
- On-track + minimal glenoid loss -> arthroscopic Bankart
- Off-track (subcritical glenoid loss) -> Bankart + remplissage
- Significant glenoid loss (~20%+ / subcritical + off-track / high-risk) -> Latarjet / bone block