Untitled Quiz

Biomechanics of Elbow Joint (Part 1)

Dr. Ahmed Abd El-Moneim is a lecturer in Physical Therapy & Osteopathic Medicine at Beni-Suef University
He coordinates the Prosthetics & Orthotics Technology Program (BTU)
He holds a Diploma in Osteopathic Medicine from IAO (Belgium) and a Diploma in Therapeutic Nutrition from NNI

Elbow and Forearm Complex

The elbow and forearm complex has three bones and four joints
The humero-ulnar and humeroradial joints form the elbow
Elbow flexion and extension adjust the overall functional length of the upper limb (UL). This is used in activities like feeding, reaching, and personal hygiene
The radius and ulna connect at the proximal and distal radio-ulnar joints
This allows the palm to turn up (supination) or down (pronation) without shoulder movement

Supination and Pronation

Supination and pronation can occur simultaneously or independently from elbow flexion and extension
The interaction between the elbow and forearm joints provides versatility in hand placement, enhancing the overall UL function

Four Articulations

Humero-ulnar joint
Humeroradial joint
Proximal radio-ulnar joint
Distal radio-ulnar joint

Humeroulnar & Humeroradial Joints

Both joints contribute to flexion and extension kinematics
Each joint plays a role in maintaining the overall three-dimensional stability of the elbow
The humero-ulnar joint's stability comes from a tight fit between the trochlea and trochlear notch
The humeroradial joint (less congruous), provides stability by the radial head against the capitulum with many capsuloligament connections
Anatomically classified as a 'ginglymus' or hinged joint due to predominant uniplanar motion of flexion and extension
Called a 'modified hinge joint' because the ulna experiences slight axial rotation and sideways motion during flexion and extension

Valgus Angle of the Elbow

Elbow flexion/extension occurs around a medial-lateral axis
The axis passes near the lateral epicondyle and convex members of the articulation
From medial to lateral, the axis courses slightly superiorly, due to distal prolongation of the medial lip of the trochlea
This causes the ulna to deviate laterally relative to the humerus
The natural frontal plane angle of an extended elbow is normal cubitus valgus
The carrying angle = valgus angle tends to keep carried objects away from the thigh during walking
Average in healthy men and women = 13 degrees
Women have about 2 degrees greater valgus angulation than men
Regardless of gender, the valgus angle is larger on the dominant arm
The carrying angle naturally increases with age
Excessive cubitus valgus (over 20-25 degrees)
Excessive cubitus varus (forearm deviated toward the midline): rare
Marked deformities can result from trauma (e.g., distal humerus fracture in children)
Excessive valgus can overstretch and damage the ulnar nerve (crosses medial to the elbow)

Periarticular Connective Tissue

The articular capsule encloses the humeroulnar, humeroradial, and proximal radioulnar joints
The capsule is thin and reinforced anteriorly with oblique and vertical fibrous bands
A synovial membrane lines the capsule's inner surface
Collateral ligaments strengthen the capsule, offering multiplanar stability, mainly within the frontal plane
The medial collateral ligament (MCL) has anterior, posterior, and transverse fiber bundles
Anterior fibers are strongest and stiffest, resisting valgus forces to the elbow
These fibers arise from the medial epicondyle and insert on the coronoid process of the ulna
The posterior fibers are less defined, fan-shaped thickenings, attaching to the medial epicondyle and olecranon process
Posterior fibers also resist valgus forces and become taut during elbow flexion
Transverse fibers connect the olecranon to the coronoid process of the ulna, with limited stability due to connecting to the same bone
The proximal fibers of wrist flexor and pronator muscles (e.g., flexor carpi ulnaris) are considered dynamic medial stabilizers of the elbow
MCL can be injured via excessive valgus force during a fall (e.g., stretched/torn ligament, compression fracture of the humeroradial joint/radius, injury to the ulnar nerve/pronator-wrist flexor muscles, or elbow hyperextension)
MCL injury can happen due to non-weight-bearing, repetitive valgus strains (e.g., athletes in overhead activities, like baseball pitchers). Pain and valgus instability are evident during late cocking and acceleration phases
The lateral collateral ligament complex originates on the lateral epicondyle, splitting into two bundles:
- Radial collateral ligament: fans out to merge with the annular ligament, and some fibers blend with supinator and extensor muscles
- Lateral (ulnar) collateral ligament (LUCL): attaches to the supinator crest of the ulna
The lateral location of both provides resistance to varus force
LUCL's posterior position causes it to be taut during full flexion and works with MCL to provide both frontal and horizontal plane stability to the elbow, and this also helps support the radial head from excessive external rotation