For the first 0-30˚ of elbow flexion, the olecranon is locked within the olecranon fossa of the posterior humerus. This provides bony stability, meaning that soft tissue stability cannot be reliably tested with the elbow in full extension. When assessing soft tissues of the elbow, varus and valgus stability should be tested at 30˚ of flexion to test the medial and lateral collateral ligaments. Stabilisers of the elbow joint are described below:
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Essential |
Supplementary |
| Static |
Radio-capitellar, ulno-trochlear and proximal radioulnar articulations |
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| Coronoid process |
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| Radial head |
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| MCL: Anterior bundle |
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| LCL: LUCL |
Joint capsule |
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| MCL: Posterior fibres |
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| LCL: RCL fibres and annular ligament |
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| Dynamic |
Common flexor attachments (esp. FCU, FDS) |
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| Anconeus |
Biceps and supinator (support radial head) |
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| Triceps |
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| Brachialis |
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| Common extensor attachments |
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Paediatric stability: In children, physeal growth plates are the weakest point of the elbow, and are often the point of failure in elbow injuries (e.g. medial epicondyle avulsion). Due to ligamentous laxity in children compared to adults, dislocations can occur with lower-energy mechanisms, and examination stress-testing is less reliable in the acute setting.
- Elbow joint reinforcing ligaments
Medial collateral ligament complex: Thick, fan-shaped ligament, formed of anterior, posterior and transverse fibres.
- Anterior fibres of MCL: The strongest and most biomechanically important medial ligament. It inserts at the sublime tubercle of the ulna, acting as the primary restraint to valgus stress —especially between 30–90° of elbow flexion. It is most often injured in overhead-throwing athletes, who frequently place the elbow under high-energy valgus stress.
- Posterior fibres: Inserts more posteriorly on the ulna, along the medial border of the olecranon. It is taut in deep flexion (>90°).
- Transverse fibres (Cooper’s ligament): Fibres run from the coronoid process of the ulna to the medial side of the olecranon. As they do not cross the elbow joint, they provide no true stabilising function.
Lateral collateral ligament complex: The LCL is comprised of four parts, and provides varus and posterolateral rotational stability. It is weaker than the MCL. Below are the LCL complex subdivisions in order of functional importance:
- Lateral ulnar collateral ligament (LUCL): LUCL is the main restraint to varus stress. It resists posterolateral rotatory instability (PLRI), especially during forearm supination combined with axial loading.
- Radial collateral ligament (RCL): Arises from the lateral epicondyle and fans into the annular ligament without direct bony insertion.
- Annular ligament: Encircles the radial head, attaching anteriorly and posteriorly to the radial notch of ulna. During pro-supination, the radial head spins within the ligament forming the proximal radio-ulnar joint. Following radial head dislocation, the annular ligament interposition can create a mechanical block to reduction. In children, laxity of the annular ligament can lead to subluxation of the radial head —known as nursemaid’s elbow.
- Accessory lateral ligament: A minor fascial thickening extending from the radial collateral fibres to the ulna. Minimal contribution to stability.