Pathology and Biomechanics of the unstable elbow
Authors: S. Lichtenberg
References: SECEC 2005, Rome
- Anatomy
- Osseous constraints
- Soft tissue constraints
- Muscles
- Osseous constraints
- Ulnohumeral articulation: olecranon
- Serial resection of olecranon in extension and 90° flexion
- Excision of 25% of proximal olecranon reduces stability by 25%
- 50% of proximal olecranon can be removed without adverse effect on stability (1)
- Coronoid
- Resultant muscle force directed posteriorly
- Elbow most stable in flexion
- 50% of coronoid are necessary to provide stability near extension
- Coronoid is major stabiliser of ulnohumeral joint
- Type I (tip of coronoid) stable
- Type II (up to 50% of coronoid) stable, unless antero-medial facet is involved, because then insertion of anterior bundle of MCL is insufficient
- Type III unstable
- Radiohumeral joint
- Radial head is a secondary constraint to valgus instability (9)
- Resection alone does only alter valgus displacement a little
- Important stabiliser, when MCL is cut (7)
- Important stabiliser for varus instability and external rotation when LUCL is gone
- Plays its role by tensioning the LCL (6)
- Soft tissue constraints
- Medial
- Medial collateral ligament (MCL)
o Anterior bundle: strongest (260 N load to failure)
o Posterior bundle
- Anterior bundle composed of anterior and posterior band
- Anterior band taut 0-60° of flexion
- Posterior band taut 60-120° of flexion
- Posterior bundle is fan-shaped
- Transvers ligament (Cooper’s ligament)
- MCL withstands valgus stress
- Lateral
- Lateral collateral ligament (LCL)
- Lateral radial collateral ligament (RCL)
- Anular ligament (
- Lateral ulnar collateral ligament (LUCL)
- Accessory lateral collateral ligament (ALCL)
Biomechanics:
- Medial instability
- Normal valgus laxity 3.6-5 mm (3, 8)
- Valgus resistance in extension 31% UCL, 38% bone, 31% ant. capsule
- Valgus resistance in 90° flexion 54% UCL, 36% bone, 10% ant. capsule
- Release of ant. bundle increase in laxity to 14°, muscle activity restored normal pattern
- Additional resection of radial head led to gross valgus and internal rotational instability, increasing flexion increase rotational laxity with subluxation at 120°
- Valgus laxity greatest at 90° flexion, valgus stress test in that position (3)
- Internal rotation laxity greatest at 60° of flexion with ant. bundle cut
- Lateral Instability
- 50% contribution of ligaments in extension
- 75% contribution of ligaments in 90° flexion
- LUCL primary constraint against rotatory instability (10)
- Laxity increases with insufficient LCL and increasing flexion (max. at 110°) (11,12)
- Laxity greater when disruption proximal (tear of the humeral insertion) (14)
- Muscles
- Medial:
- Pronator teres, flexor digitorum superficialis, flexor carpi ulnaris, flexor carpi radialis apply varus moment to resist valgus force independent from forearm rotation (2)
- Throwers present with tendinitis/epicondylitis
- Flexor carpi ulnaris is optimally positioned to provide secondary valgus support in overhead throwers (4)
- No compensatory increase of muscle activita in baseball pitchers with MCL insufficiency (5)
- Lateral
- Extensor digitorum communis, extensor carpi radialis brevis et longus, anconeus and extensor carpi ulnaris apply valgus moment to resist varus force, it is greatest in neutral rotation (2)
- Add stability by compressing the congous joint
Clinical Presentation:
- Medial
- Subtle pain while throwing
- Tenderness on palpation
- Irritation of ulnar nerve
- Gross valgus instability
- Lateral
- Minor pivoting
- Unable to push up
- Gross postero-lateral rotatory instability
- Recurrent dislocations/subluxations
- Evaluation of involved structures
- Medial instability
- Radial head fracture (Mason I-III)
- MCI tear (stress radiographs and/or MRI)
- Coronoid fracture after complete dislocation (x-ray, CT-scan)
- Lateral instability
- Fractures of the olecranon (type III unstable, because ligament insertion involved)
- Fractures of the coronoid Type I-III (x-ray, CT)
- Lateral stress radiographs, MRI
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