Measure how the joint actually behaves under load across its arc, then let that measurement drive the plan, the geometry and the device — instead of referencing static anatomy or a fixed alignment target.
Written by an MD with deep clinical training. Not a practising surgeon and not a licensed physician — which is a real limitation on everything below, and also the reason the observation was available at all. Nobody who spends a career inside one subspecialty is standing where three of them can be seen failing the same way.
That is the whole claim. The instruments exist to test it.
Each of these fields had a universal anatomical target. Each discovered the target was wrong — not badly measured, but wrong in kind, because it imposed a population average on an individual. Each replaced it with a patient-specific reference. And they did it separately, in their own journals, without a shared vocabulary.
| Field | Universal target | How it failed | Replaced by |
|---|---|---|---|
| Knee | Neutral mechanical axis | Imposed an average on constitutionally non-neutral knees | Constitutional alignment |
| Hip | Lewinnek safe zone | 58% of dislocated hips were inside it | Spinopelvic planning |
| Spine | Neutral sagittal alignment | Achieving it overcorrects the elderly → PJK | Age-adjusted targets |
| Shoulder | Generic version target | Ignores distance already travelled | Premorbid glenoid |
| Ankle | Tibiotalar angle alone | Ignores whether the joint below shares it | Hindfoot behaviour |
The contribution here is not any individual fix — every one of those was made by the people who own that field. It is naming the shared error, and then asking what transfers. Three things do, immediately: the hip's two-position protocol is the ankle's Coleman block asking the identical question in a different vocabulary; the spine's age-indexing exists nowhere else and probably should; and the hip's finding that a good target lets you decline the bailout — dual mobility falling from 100% to 37% of cases — is a general result currently stated only in the hip.
Find the envelope. Fix the reference. Correct by position first, and escalate to geometry only on the residual.
Same six questions asked of every joint, so that they read against each other rather than as eleven separate essays. Each is a working tool, not a diagram.
The colour on the left edge is not decoration — it is the family the joint turned out to belong to, which is a result that emerged from building them and is explained in § 3.
Compartment opening under load, measured across the flexion arc, driving component geometry rather than only component position. The origin instance: functional-alignment-first, with the soft-tissue envelope read per structure and a pre-op clinic rating that predicts the tier before anyone opens anything.
Valgus and varus fail differently and the geometry should answer differently — laxity appearing after the bone cuts is not the same problem as posterior osteophytes producing a fixed flexion contracture.
Spinopelvic mobility: functional pelvic tilt read supine, standing and seated. The instrument returns not a target angle but the width of the window in which a cup is safe for this particular pelvis.
The finding that matters clinically: immobility narrows the window, deformity does not. A stiff spine — not a deformed one — is what removes your margin. A 1A pelvis leaves 14.5° to work in; a 2B leaves 2.5°.
How far the glenoid has travelled from its premorbid position, set against how far a reamer may safely go. What will not fit inside that budget is the residual, and the residual is what the construct has to supply — augment, graft, or a different operation.
The soft-tissue gate sits above the geometry, not beside it: if the envelope will not tolerate the correction, the arithmetic never runs.
The hip one segment down. The subtalar joint is the adjacent segment and the Coleman block is the seated film — the same two-position question, asked in a vocabulary that has no idea the hip is asking it too.
The result worth the build: the same deformity burden and the same residual can demand a different operation, depending entirely on what the hindfoot is willing to give back.
First MTP dorsiflexion available under load against roughly the 55° a gait cycle demands. Two nested two-position tests: Jack's test below for the windlass, Silfverskiöld above — because the calf loads the forefoot and the toe is downstream of it. Mid-range pain overrides the arithmetic entirely.
The thumb CMC joint, and what the MCP is doing about it. As the base collapses into adduction the MCP hyperextends to keep the web open. Rebuild the base alone and the reconstruction inherits that compensation. The gate is clinical — failed non-operative management — not radiographic.
The same spinopelvic films as the hip, read in the opposite direction. The hip asks will this pelvis move? The spine asks how much of that motion am I about to remove? A stiff spine is the hip's hazard and this operation's product.
Two patients, identical radiographs — PI−LL 43°, SVA 115 mm, PT 34°, all modifiers ++. At 78 the age-adjusted target demands 26.3° of correction. At 34 it demands 53.5°. A universal neutral target demands 43° of both: it undershoots the young man by 10.5° and overshoots the elderly woman by 16.7°.
A 27° swing on date of birth alone — and the asymmetry is the point. One ideal number is wrong in both directions but only dangerous in one, where junctional failure already runs near 50% and where the patients who failed had been overcorrected.
The forearm is a ring: proximal joint, interosseous membrane, distal joint. The radial head is a secondary valgus stabiliser — expendable only while the coronoid and MCL are intact and the membrane holds.
Excise it with an incompetent membrane and the radius migrates proximally. The failure presents as ulnar-sided wrist pain, months later, at a joint nobody operated on, often to a different surgeon. Adjacent-segment coupling at maximum displacement — a whole limb segment away, and displaced in time as well as space.
Built expecting an envelope. Found a gate. No neighbour compensates, there is no second position, and the midcarpal joint is resected rather than recruited.
What actually decides the operation is which articular surfaces have survived: a proximal row carpectomy makes the capitate articulate with the lunate fossa, so both must be intact, and stage III degeneration of the proximal capitate excludes the operation rather than making it harder.
The scapulothoracic share of elevation — judged against the share expected for that segment of the arc, not against one taught ratio.
Scapulohumeral rhythm is taught as 2:1. No increment is 2:1. The scapula supplies about 2.5% of the first 30° and about 52.7% of the arc from 90° to 120°. In the cited inclinometer series the ratio between 30° and 90° ran from 1.64:1 to 3.76:1 and never once equalled 2:1.
That is § 1's error in miniature, arrived at independently: a whole-arc population average taught as a per-patient, per-segment target.
T1 slope behaves as the cervical pelvic incidence — the fixed reference the lordosis must be built to match, correlating at about r = 0.89 with C0–C7 lordosis. The instrument reads the T1S−CL mismatch and the C2–C7 sagittal axis against a 40 mm threshold.
This is the only joint in the programme where the adjacent segment is an output of the operation with a published rate, rather than an input you measure beforehand. Symptomatic adjacent-segment disease runs at 2.9% per year and 25.6% at ten years. The model reproduces that ten-year figure to within a tenth of a point — the only external calibration any instrument here has.
Two patients with identical radiographs, three levels: at 45 the projection is about 76%, at 75 about 24%. The target does not move. The exposure does. Age therefore enters the spine twice for entirely unrelated reasons — changing the target in the lumbar spine, and the exposure here.
Every one of the eleven above depends on a joint being loaded — under body weight, under an examiner's hand, under a block. Nothing in orthopaedics standardises that force. "Stress the joint" means whatever the examiner's grip means that afternoon.
A calibrated stress applicator with a load indicator would put a number under all eleven instruments at once. It is the highest-value missing piece in the programme and it does not exist here — only a note that it should.
Which is worth considerably more than a confirmation would have been.
The written thesis listed six conditions under which it should be considered false. The fourth was: examine joints with obvious neighbours — the elbow, the wrist — and see whether the neighbour dominates. Both were then built, without softening the prediction first. The result was mixed.
The ring holds. The neighbour does not merely participate — it determines whether a structure is expendable at all, and it registers the failure at a different joint, months later, in front of a different surgeon.
There is no neighbour to ask. Applying the adjacent-segment question to this joint produced nothing — which is exactly what happened during the build: an envelope was expected and a gate was found.
The original rule was simply too broad. What replaced it is a distinction the programme did not have when it started:
| Family | Joints | Coupling | The question to ask |
|---|---|---|---|
| Coupled | hip · ankle · thumb · elbow · girdle · cervical | chain, linkage, ring | What is the neighbour doing? |
| Attrition | shoulder · wrist | none — local surface loss | What is left to build on? |
| Neither cleanly | knee · foot · lumbar spine | load and posture | Deviation from its own reference |
Families are properties of the question, not of the joint. The same shoulder is an attrition problem when you are asking about the glenoid surface and a coupled problem when you are asking about the girdle. The table above assigns families to joints, which is a convenience; the honest version assigns them to questions.
There is a third pattern: displaced failure. The elbow and the cervical spine share something neither the coupled nor the attrition family captures — the harm lands at a joint nobody operated on. In the cervical spine, that pattern even comes with a price list.
The book was rewritten rather than left standing. The chapter that stated the hypothesis now carries the result and the two-family table; the falsification chapter marks condition four tested, and partly true, and states plainly that the claim as first published was wrong.
Kept as a standing list, because a model that does not say which numbers it made up is not a model.
Anchored in published work: the Lewinnek failure rate, the hip-spine classification, Walch glenoid types, the Coleman block, Jack's and Silfverskiöld's tests, the 30° MCP decision point, SRS-Schwab modifiers and age-adjusted alignment, the radius pull test thresholds, proximal row carpectomy staging, scapular share by arc segment, and the Hilibrand adjacent-segment rate.
Invented here, and marked as such on every page that uses them: conformity slopes, step gain, cup window widths, the ankle's 12° capacity, cheilectomy gains, the 20° MCP watch level, the spine's age brackets, and the assumptions of additivity and linearity throughout.
Eleven instruments, built to test one sentence. One of them refuted the rule the others were built on, two more corrected the correction, and the twelfth — the one that would put a number under all of it — was never built.
None of them has been used to plan an operation on a living person. That is the honest state of it, and it is stated here rather than at the bottom of a disclaimer.