Every glenoid has a correction budget. Does this plan state it?
The glenoid has travelled some number of degrees from where it started. The reamer can bring back ten to fifteen of them before you are medialising into the vault. The difference between those two numbers decides the case, and it is the number that usually goes unwritten: it is what tells you whether this is a standard glenoid, an augment, or a reverse.
The shoulder's envelope is distance travelled, not motion.
The knee measures opening across flexion and the hip measures tilt across posture. The shoulder measures something static: how far the glenoid has eroded away from the premorbid surface it started as. That premorbid glenoid, reconstructed from the vault, is this joint's fixed reference.
The glenoid
The reference and the gate
Beyond the reamer.
The bone decides the case only when the cuff works.
This is where the shoulder genuinely differs from the knee and the hip. Those two are decided by geometry. The shoulder has a soft-tissue gate sitting above the geometry: an incompetent cuff sends the case to a reverse no matter how correctable the glenoid is. The budget matters underneath that gate, not above it.
Nothing to correct.
Centred head, version near premorbid, cuff intact. A standard glenoid on an anatomic reconstruction. The Walch A shoulder is the one that behaves.
The Walch classification →The reamer reaches it.
Deformity inside the safe limit and inside the threshold where most surgeons still ream rather than augment. Anatomic, with the version corrected on the way in.
Eccentric reaming for posterior wear →The construct supplies the rest.
Correcting this much by reaming alone medialises into the vault. An augmented baseplate or graft carries the correction the reamer should not. Anatomic only if the cuff is genuinely intact and the residual is small.
Vault perforation after eccentric reaming →Either the cuff is gone or the residual is.
Anatomic reconstruction on a B2 glenoid carries about a 10.5% complication rate, most often recurrent posterior subluxation, even where revision stays near 2.4%. When the numbers do not close, the reverse is the honest answer.
Anatomic versus reverse for B2 →Where each threshold comes from, and how firm it is.
Measure the envelope, position first, escalate only on the residual.
| Knee | Hip | Shoulder | |
|---|---|---|---|
| The envelope | Compartment opening under load, across flexion | Functional pelvic tilt, across posture | Distance travelled from the premorbid glenoid |
| The fixed reference | Constitutional alignment | Pelvic incidence | Premorbid (paleo) glenoid |
| Position first | Component angles inside the alignment boundaries | Cup anteversion inside the functional window | Eccentric reaming inside the safe limit |
| The residual | Laxity positioning cannot balance | Postures no cup orientation satisfies | Degrees the reamer should not take |
| The escalation | Conformity, lip, step | Dual mobility | Augment, graft, or reverse |
| Mandatory episode | TEAM | TEAM | none |
Put the first row in.
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