Two ankles, the same deformity. One gets replaced, one gets fused.
Put twenty-one degrees of coronal burden and nine degrees of residual into this tool twice. The first time, say the hindfoot gives most of it back on a Coleman block. The second time, say it does not. Same numbers, different operation. The ankle is the hip's problem one segment down: there is a joint below that either shares the load or refuses to, and a block under the forefoot is what tells you which.
The ankle's adjacent segment is the hindfoot.
In the hip, the pelvis either rotates when the patient sits or it does not, and that decides how much the cup has to carry. In the ankle, the subtalar joint either gives the deformity back or it does not, and that decides whether the residual takes an osteotomy or a fusion. The Coleman block is this joint's second film.
The deformity
The block, and the joint below
Needs work below the joint.
Same burden. Same residual. Different operation.
These two ankles produce identical arithmetic. Twenty-one degrees of total coronal burden, twelve absorbed inside the joint, nine left over. Everything the films measure agrees. The only thing that differs is what the hindfoot does on the block, and it changes the operation.
| Flexible hindfoot | Rigid hindfoot | |
|---|---|---|
| Talar tilt | 14° | 12° |
| Hindfoot deformity beyond physiologic | 7° | 9° |
| Total coronal burden | 21° | 21° |
| Absorbed inside the joint | 12° | 12° |
| Residual | 9° | 9° |
| Gives back on the block | 7° | 1° |
| Answer | Tier C — replace it, and correct the residual with an osteotomy below the joint | Tier D — the residual cannot be given back without fusing something. Fusion territory |
The residual decides whether you go below the joint. The block decides what you can do there.
Nothing below to fix.
Small burden, hindfoot inside the physiologic range. Replace and balance. Deformity under ten to fifteen degrees generally does well.
Staged correction case report →The joint takes all of it.
A real deformity that the implant and intra-articular balancing absorb on their own. Correct it at the joint, then confirm the hindfoot actually followed on the post-operative alignment view.
Hindfoot alignment change after TAR →Correctable, but it is still an operation.
More than the ankle should carry, with a hindfoot supple enough to be brought back. The residual belongs to a calcaneal or first-ray osteotomy and a ligament reconstruction, staged or concurrent. Flexible does not mean free.
The Coleman block test →Fusion territory.
Either the hindfoot is rigid under a real residual, or too much is left after everything the joint and the hindfoot can give. Coronal deformity over fifteen degrees carried roughly seven times the failure risk in one series, and an uncorrected replacement here edge-loads.
Pre-operative tibiotalar alignment and outcome →One of these is a cliff. The rest are planning assumptions.
Measure the envelope, absorb what you can, escalate only on the residual.
| Knee | Hip | Shoulder | Ankle | |
|---|---|---|---|---|
| The envelope | Opening under load, across flexion | Pelvic tilt, across posture | Distance from the premorbid glenoid | What the hindfoot gives back |
| Adjacent segment | — | Pelvis | — | Subtalar joint |
| The second look | Stress at each flexion angle | The seated film | The vault reconstruction | The Coleman block |
| The residual | Laxity positioning cannot balance | Postures no cup satisfies | Degrees the reamer should not take | Degrees the joint cannot absorb |
| The escalation | Conformity, lip, step | Dual mobility | Augment, graft, reverse | Osteotomy, or fusion |
| Mandatory episode | TEAM | TEAM | none | TEAM |
The knee.
Ten-item clinic rating; functional alignment first, geometry only on the residual.
The knee instrument →The hip.
Two lateral films give the cup window. A stiff pelvis collapses it to a few degrees.
The hip instrument →The shoulder.
The correction budget: degrees needed against degrees safely reamable, under a soft-tissue gate.
The shoulder instrument →Watch a residual become geometry.
The knee studio shows what the residual actually does to an implant surface.
Envelope studio →Put the first row in.
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