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



  1. An KN, Morrey BF, Chas EYS (1986) The effect of partial removal of proximal ulna on elbow constraint.  Clin Orthop 209:270-279
  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
  4. Davidson PA, Pink M, Perry J, Fobe FW (1995) Functional anatomy of the flexor pronator muscle group in relation to the medial collateral ligament of the elbow.  Am J Sports Med 23:245-250
  5. Hamilton CD, Glousman RE, Jobe FW (1996) Dynamic stability of the elbow: electromyographic analysis of the flexor pronator group and extensor group in pitchers with valgus instability.  J Shoulder Elbow Surg 5:347-354
  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
  7. Morrey BF, An KN (2005) Stability of the elbow: osseous constraints.  J Shoulder Elbow Surg 14:174S-178S
  8. Morrey BF (1997) Complex instability of the elbow.  J Bone Joint Surg 79-A: 460-469
  9. Morrey BF, Tanaka S, An KN (1991) Valgus stability of the elbow.  A definition of primary and secondary constraints.  Clin Orthop 265:187-195
  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



This website is certified by Health On the Net Foundation. Click to verify. This site complies with the HONcode standard for trustworthy health information:
verify here. satisfies the INTUTE criteria for quality and has been awarded 'editor's choice'.

The material on this website is designed to support, not replace, the relationship that exists between ourselves and our patients. Full Disclaimer