30-Second Snapshot
- Three joints, one capsule: ulno-humeral (hinge) | radio-capitellar (hinge/pivot) | proximal radio-ulnar (pivot).
- Key motions: 0-150 ° flex-ext (functional 30-130 °) + 180 ° pro/sup (functional 50/50 °).
- Stability “fortress”: ulno-humeral fit ► MCL ► LCL-complex ► radial-head, capsule & dynamic muscles.
- Carrying angle: 5-10 ° men | 10-15 ° women – created by trochlear tilt.
- Big forces, small levers: up to ½ body-weight across joint in routine falls.
Osteology Cheat-Sheet
|
Bone |
Hallmark geometry |
Clinical pearl |
|
Distal humerus |
40 ° anterior capitellar tilt • 10 ° posterior shaft bow • flex-ext axis 3-5 ° IR |
Trans-epicondylar line ≈ surgical axis |
|
Olecranon |
Blocks anterior ulna shift |
Loss > 25 % → varus rot. laxity |
|
Coronoid |
15 mm high, 42 % ulna • sublime tubercle (AMCL) |
“Most valuable real-estate” – fix if ≥ 50 % |
|
Radial head |
Elliptical; 240 ° thick cartilage; non-articulating 120 ° safe zone |
Screw heads here; replacement restores valgus buttress |
Ligament Big-3
|
Complex |
Components |
Primary job |
|
MCL / UCL |
Anterior-bundle (work-horse) • posterior • transverse |
Blocks valgus & distraction |
|
LCL |
Radial-collat. • LUCL (key) • annular • accessory |
Blocks varus & posterolateral rot. |
|
Annular |
Fibro-osseous collar round radial head |
Keeps radius on ulna during spin |
Rule-of-thumb: AMCL taut 30-120 °; LUCL failure = PLRI every time.
Capsule & Sensors
- Anterior & posterior bands, maximal volume at 70-80 ° flex.
- Ruffini & Pacinian corpuscles → proprio feedback → reflex muscle firing.
Dynamic Muscle Guards
|
Group |
Key fibres |
Stabilising trick |
|
Flexors |
Biceps, brachialis, brachioradialis |
Compression in flexion; biceps = power supinator |
|
Extensors |
Triceps, anconeus |
Triceps counters valgus; anconeus curbs varus/PLRI |
|
Flexor-pronator mass |
PT, FCR, FCU etc. |
Dynamically relieves AMCL in pitchers |
Biomechanics Highlights
- Flex-ext axis: loose-hinge; migrates 1-2 mm, rotated 4-8 ° valgus.
- Pro/sup axis: radial-head centre → distal ulna; radius glides proximal in pronation.
- Forearm position & laxity:
- MCL-deficient elbow safer in supination.
- LCL-deficient elbow safer in pronation.
- Both positions ↓ valgus gap via radiocapitellar compression.
- Load split (extension): 40 % ulno-humeral | 60 % radio-humeral. Peaks RC-joint 0-30 ° & in pronation.
Common Pathology Fast-List
|
Injury |
Mechanism |
Key point |
|
Terrible triad |
Posterior dislocation + radial-head + coronoid tip |
Fix coronoid & radial-head, repair LCL-complex. |
|
PLRI |
LUCL failure (fall, iatrogenic) |
Pivot-shift test + surgical LUCL recon (docking). |
|
MCL sprain (thrower’s) |
Repetitive valgus |
MRI + AMCL recon “Tommy John”. |
|
Epicondylitis |
Over-use flexor/extensor tendons |
ECRB (lateral) vs PT/FCR (medial); load-mod + rehab. |
|
Cubital tunnel |
Ulnar-nerve entrapment |
Paraesthesiae 4th/5th digits; decompression if persistent. |
- Key Surgical Takeaways
- Re-establish axis, angles & articular congruity – especially coronoid & radial-head geometry.
- Respect isometric points: AMCL origin posterior to flex-ext axis; LCL origin inferior lat-epicondyle.
- Plate/screw paths must track prox-ulnar varus & torsion (“rule of 8”).
- Muscle rehab: early motion 30-100 °, avoid varus valgus loads until ligamentous healing (6-8 wks).
Call to Action
If you have pain, book an appointment to be reviewed by Prof Imam or another member of our specialist team at The Arm Clinic. Early specialist care helps prevent long-term issues. Visit www.TheArmDoc.co.uk or book your consultation today. Phone: 020 3384 5588 | Email: Info@TheArmDoc.co.uk
Disclaimer
This information is for general educational purposes and should not be used as a substitute for professional medical advice. Consult a healthcare professional for individual guidance on your condition and treatment options.
This page was last clinically updated in May 2025
Last reviewed: July 2024. For professional education, not a substitute for clinical judgment.