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 (AL); ant. Part taut in supination, post. part taut in pronation

-        Lateral ulnar collateral ligament (LUCL)

-        Accessory lateral collateral ligament (ALCL)



-        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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  2. An KN, Hui FC, Morrey BF, Linscheid RL, Chao EY (1981) Muscles across the elbow joint: a biomechanical analysis.  J Biomech 14:659-669
  3. Callaway GH, Field LD, Deng XH, Torzilli PA, O’Brien SJ, Altchek DW, Warren RF (1997) Biomechanical evaluation of the medial collateral ligament of the elbow.  J Bone Joint Surg 79-A:1223-1231
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  6. Jensen SL, Olsen BS, Tyrdal S, Söjberg JO, Sneppen O (2005) Elbow joint laxity after experimental radial head excision and lateral collateral ligament rupture: efficacy of prosthetic replacement and ligament repair.  J Shoulder Elbow Surg 14:78-84
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  10. Olsen BS, Soejbjerg JO, Dalstra M, Sneppen O (1996) Kinematics of the lateral ligamentous constraints of the elbow joint.  J Shoulder Elbow Surg 5:333-341
  11. Olsen BS, Soejbjerg JO, Nielson KK, et al (1998) Posterolateral elbow joint instability: the basic kinematics.  J Shoulder Elbow Surg 7:19-29
  12. Olsen BS, Vaesel MT, Soejbjerg JO, Helmig P, Sneppen O (1996) Lateral collateral ligament of the elbow joint: anatomy and kinematics.  J Shoulder Elbow Surg 5:103-112
  13. Safran MR, Baillargeon D (2005) Soft-tissue stabilizers of the elbow.  J Shoulder Elbow Surg 14:179S-185S
  14. Seki A, Olsen BS, Jensen SL, Eygendaal D, Soejbjerg JO (2002) Functional anatomy of the lateral collateral ligament complex of the elbow: configuration of Y and its role.  J Shoulder Elbow Surg 11:53-59



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