The Radial Head: Anatomy, Fractures, and Replacement
The radial head is the proximal, disk-shaped articular surface of the radius that articulates with the capitellum of the humerus (radiocapitellar joint) and the lesser sigmoid notch of the ulna (proximal radioulnar joint). It is a critical stabilizer of the elbow, transmitting ~60% of axial load and enabling forearm rotation.
Anatomy & Biomechanics
- Articular surfaces: Concave superior (capitellum), circumferential (lesser sigmoid notch).
- Ligamentous attachments: Annular ligament (encircles head, stabilizes PRUJ), radial collateral ligament, quadrate ligament.
- Key relationships: Posterior interosseous nerve (PIN) winds around neck — at risk in fractures/surgery.
- Load transmission: Valgus stress → radial head compression; longitudinal load → 60% through radiocapitellar joint.
Radial Head Fractures (Mason Classification)
| Type | Description | Treatment |
|---|
| I | Non-displaced (<2 mm), <30% involvement | Non-op: splint 3-5 days, early ROM |
| II | Displaced (>2 mm) or >30% articular; no comminution | Non-op if <2 mm, <30%, no mechanical block. ORIF if displaced/block. |
| III | Comminuted, entire head | IIIa: ORIF possible. IIIb/c: Radial head arthroplasty. |
| IV | Fracture + elbow dislocation | ORIF or arthroplasty + ligament repair. |
Associated Injuries (The "Terrible Triad")
Radial head fracture + coronoid fracture + elbow dislocation. Requires ORIF/arthroplasty + LCL repair ± MCL repair ± external fixator. High stiffness/arthritis risk.
Radial Head Arthroplasty (RHA)
Indications
- Mason III/IV fractures not reconstructible
- Essex-Lopresti (radial head fracture + interosseous membrane tear + DRUJ disruption)
- Failed ORIF, nonunion, post-traumatic arthritis
Implant Types
- Monoblock (metal): Fixed size/height. Simple, risk of overstuffing.
- Modular (metal/PyroCarbon): Adjustable stem/head/neck. Better fit, restore height.
- PyroCarbon: Elastic modulus similar to bone; may reduce capitellar wear.
Surgical Pearls
- Restore radial length (prevent proximal migration → wrist pain/DRUJ arthritis).
- Size head to match native (caliper measurement).
- Repair LCL/MCL ± annular ligament.
- PIN protection: Posterior approach (Kocher) with PIN identification.
Rehabilitation & Outcomes
- Early motion (Day 1-3): CPM or active-assisted flexion/extension, pronation/supination.
- Avoid forced hyperextension/varus stress early.
- Strengthening at 6-8 weeks.
- Outcomes: 80-90% good/excellent (MEPS, DASH). Complications: stiffness, loosening, capitellar wear, heterotopic ossification, PIN palsy.
The radial head is the "keystone" of elbow stability. Anatomic restoration—whether by fixation or arthroplasty—is essential for long-term function.
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