O'Driscoll (1992) — Elbow subluxation and dislocation. A spectrum of instability.

Elbow Subluxation and Dislocation. a Spectrum of Instability.

·Clin Orthop Relat Res·1992·556 citations·Shoulder & Elbow

This cadaveric biomechanical study used sequential ligament releases and 3D electromagnetic kinematic tracking in 13 fresh-frozen elbows. It tested whether the elbow can dislocate posteriorly with the AMCL intact, and defined the mechanism and stages of progressive instability. The study directly challenged the prior dogma that AMCL disruption is required for posterior dislocation.

Study Snapshot

Design

Cadaveric biomechanical study

Setting: Single center, Mayo Clinic, Rochester

Funding: NIH; McLaughlin Foundation

Objective

Whether elbow can dislocate posteriorly with anterior medial collateral ligament intact

Outcome(s)

AMCL functional integrity after posterior elbow dislocation

Subjects

13 fresh cadaveric upper extremities (11 donors)

Sequential ligament/capsule release + manual posterolateral rotatory dislocation

Exclusion

Coronoid osteophyte (n=1, excluded from dislocation analysis)

Statistics

Paired two-tailed t-testSign testPower analysis

Key Findings

Posterior dislocation occurred with the AMCL functionally intact in 12 of 13 specimens — overturning the prior dogma that AMCL disruption is required for posterior dislocation, and explaining why most simple dislocations are stable after closed reduction.
Dislocation requires traversal of a kinematic threshold — the coronoid must clear the trochlea via ~41° external rotation and ~15° valgus at ~80° flexion. The elbow pivots on the AMCL rather than rupturing it; AMCL origin-to-insertion distance never exceeded intact values throughout the dislocation arc (p < 0.05).
Instability follows the circle concept: sequential lateral-to-medial capsuloligamentous disruption across four stages.
–Stage 1: LUCL tear → posterolateral rotatory subluxation (PLRI), positive pivot-shift test
–Stage 2: + anterior/posterior capsule → perched dislocation; varus instability, valgus stable
–Stage 3a: + PMCL → posterior dislocation; AMCL still intact, valgus stable in pronation
–Stage 3b: + AMCL → complete instability, gross valgus laxity
Post-reduction valgus laxity was not significantly greater than intact elbows (maximum increase 1.1° ± 0.9°, range -0.3° to 2.4°; p > 0.05) — the biomechanical basis for immediate hinged-brace rehabilitation when the AMCL is preserved.
Recurrent instability responds to lateral-only ligament reconstruction without medial repair, consistent with the LUCL as the primary and initiating lesion across the entire instability spectrum.

Board PearlPosterior elbow dislocation progresses lateral-to-medial in three stages; an intact AMCL after reduction means early hinged-brace mobilization in pronation is safe.

Clinical Relevance

Two clinical decisions come directly from this paper: how you reduce a dislocated elbow, and what you do immediately after. Reduce in supination — this allows the coronoid to clear back under the trochlea and avoids stripping the medial soft tissues that may still be intact.

After reduction, test valgus stability with the forearm in full pronation (pronation compensates for the absent LUCL). If the elbow is stable, the AMCL is intact and you can start hinged-brace rehab in pronation immediately without fear of redislocation.

This paper is also the foundation of the O'Driscoll instability staging system and explains why PLRI. A lateral-only lesion. Can present as a spectrum from subtle snapping to frank recurrent dislocation. Recognizing which stage a patient occupies tells you exactly which structures need repair.

Elbow Subluxation and Dislocation. a Spectrum of Instability.

Study Snapshot

Key Findings

Clinical Relevance

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Elbow Subluxation and Dislocation. a Spectrum of Instability.

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Key Findings

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Elbow Subluxation and Dislocation. a Spectrum of Instability.

Study Snapshot

Key Findings

Clinical Relevance

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Elbow Subluxation and Dislocation. a Spectrum of Instability.

Study Snapshot

Key Findings

Clinical Relevance

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