Shaft of the Humerus

Gross Anatomy

• 3 borders: anterior, medial, lateral
• 3 surfaces: anterolateral, anteromedial, posterior

Key Surface Markings

Important Relations

Radial Groove

• Radial nerve (posterior cord of brachial plexus, C5-C8, T1)
• Profunda brachii artery (deep brachial artery)

Intermuscular Septa

Muscle Attachments (Summary)

Fracture Displacement Patterns

• Above pectoralis major insertion: proximal fragment abducted + externally rotated by rotator cuff; distal fragment pulled medially by pectoralis major
• Between pectoralis major and deltoid insertions: proximal fragment adducted by pectoralis major; distal fragment pulled laterally and superiorly by deltoid
• Below deltoid insertion: proximal fragment abducted by deltoid; distal fragment pulled superiorly by biceps and triceps

Clinical: Humeral Shaft Fractures

Mechanism

• Most common: direct blow, severe twist, or fall on outstretched hand
• Rare: abrupt muscle contraction (e.g., throwing a javelin or baseball)
• Most commonly fracture in the middle third, in a transverse pattern

Clinical Features

• Localized severe pain, arm swelling, inability to use the arm
• Bony crepitus with any manipulation in complete fractures
• Shortening or rotation depending on displacement
• Incomplete fractures show only tenderness and swelling without deformity

Holstein-Lewis Fracture

• Radial nerve palsy occurs in 5-10% of humeral shaft fractures overall, but up to 22% in distal-third fractures
• Up to 92% of radial nerve palsies in closed fractures resolve with 3-4 months of observation

Treatment

Non-operative (preferred for most closed fractures)

• Acceptable if: <20° anterior angulation, <30° valgus/varus, <3 cm shortening
• Coaptation ("sugar-tong") splint + sling-and-swathe initially
• Replaced by a functional brace at 10-14 days
• Hanging cast for grossly displaced or spiral fractures
• Radial nerve palsy alone is NOT an indication for surgery - observe for 3-4 months

Operative Indications (ORIF)

• Polytrauma - facilitates early mobilization
• Gross mobility at 6 weeks (predicts nonunion)
• Floating elbow
• Pathologic fracture
• Open fracture
• Secondary (post-manipulation) radial nerve palsy - controversial

Fixation Options

Radial Nerve Palsy - Recovery Milestones

1. Brachioradialis - first to return
2. Extensor carpi radialis longus (wrist extension in radial deviation)
3. Extensor pollicis longus and extensor indicis proprius - last to return

Fractures of the Shaft of the Humerus

Epidemiology

• Account for 1-2% of all fractures and 13-14% of all humeral fractures
• Bimodal age distribution:
  • Young males: high-energy trauma (e.g., road traffic accidents, sports)
  • Elderly females: low-energy fall from standing height
• After age 60, fractures are more common in women following a simple ground-level fall
• Annual incidence: 10-20 per 100,000 population
• Location: Middle third most common (47-64%), followed by proximal third (15-30%), then distal third (11-35%)

Mechanism of Injury

Classification

By Location

• Proximal third - typically oblique
• Middle third - typically transverse (most common)
• Distal third - often oblique/spiral; highest risk of radial nerve injury

AO/OTA Classification

• Type A: Simple (A1 = spiral, A2 = oblique ≥30°, A3 = transverse <30°)
• Type B: Wedge (B1 = spiral wedge, B2 = bending wedge, B3 = fragmented wedge)
• Type C: Complex/comminuted (C1 = spiral, C2 = segmental, C3 = irregular)

Displacement Patterns (Depend on Level Relative to Muscle Insertions)

Clinical Features

• Severe, localized arm pain; arm hangs useless
• Swelling and ecchymosis over the arm
• Visible deformity - shortening or rotational malalignment in displaced fractures
• Bony crepitus with the slightest manipulation (complete fractures)
• Incomplete fractures: local tenderness + swelling without deformity
• Always examine radial nerve - check wrist and finger extension before and after any manipulation or splinting

Associated Injuries

Radial Nerve Palsy (Most Important Complication)

• Occurs in 10-12% of closed humeral shaft fractures overall
• Up to 22% with distal-third fractures

• Wrist drop (inability to dorsiflex wrist and digits)
• Numbness over dorsoradial hand and dorsal aspect of radial 3.5 digits

Holstein-Lewis Fracture

Vascular Injury

• Brachial artery injury is uncommon but can occur, particularly with high-energy trauma or open fractures
• Always check distal pulses

Brachial Plexus Injury

• Can be associated, especially with high-energy trauma

Investigations

• X-rays: AP + lateral views of the entire humerus including the shoulder and elbow joints (mandatory)
• Look for pathologic features: cortical thinning, abnormal osteoblastic/osteoclastic activity - consider bone metastasis (humerus is a common site)
• CT: Useful for complex or comminuted fractures or pre-operative planning
• MRI/bone scan: If pathologic fracture is suspected
• EMG/nerve conduction: Baseline and to monitor recovery of radial nerve palsy at 3-4 weeks, then serially

Treatment

Acceptable Alignment (for Non-operative Management)

• < 20° anterior angulation
• < 30° varus/valgus angulation
• < 3 cm shortening

Non-operative Treatment (First-Line for Most Closed Fractures)

• Gentle motion exercises begin within 1-2 weeks
• Serial radiographs to verify healing
• Radial nerve palsy alone is NOT a contraindication to conservative treatment - up to 92% resolve spontaneously within 3-6 months

Operative Indications

Fixation Options

• Weight bearing to tolerance is safe after plate fixation
• Allows early mobilization

• Consider for: pathologic fractures, segmental fractures
• Disadvantages vs. plate:
  • More shoulder pain (from proximal nail entry)
  • Risk of radial nerve injury with lateral-to-medial distal locking screw
  • Risk of musculocutaneous nerve with AP distal locking screw

Radial Nerve Palsy - Management

Recovery Order (Proximal to Distal)

1. Brachioradialis (first)
2. Extensor carpi radialis longus (wrist extension in radial deviation)
3. Extensor carpi radialis brevis
4. Extensor pollicis longus + extensor indicis proprius (last)

Complications

Special Situations

Children

• Humeral shaft fractures in children are uncommon (<10% of all humeral fractures)
• Peak in <3 years or >12 years
• Nearly all treated non-operatively given remodeling potential
• Acceptable angulation: up to 70° in children <5 years, 30° in ages 12-13
• Radial nerve entrapment can occur after closed reduction - loss of radial nerve function after reduction = urgent nerve exploration (Campbell's Operative Orthopaedics, 15th ed.)

Pathologic Fractures

• Humerus is a common site for bone metastases, unicameral bone cysts, and primary bone tumors
• Cortical thinning and abnormal bone activity on X-ray are warning signs
• Require multidisciplinary management with oncology
• Stabilization options: plates, IM nails, cement, joint replacement - but underlying pathology must be treated concurrently for healing

Triceps-Splitting Approach to the Humerus

Overview

Indications

• Humeral shaft fractures of the middle third and distal third
• Distal humeral fractures requiring ORIF
• Can be used as a preliminary to Total Elbow Arthroplasty (TEA) - the ability to convert from ORIF to TEA intraoperatively is a major advantage
• Outerbridge-Kashiwagi procedure (ulnohumeral arthroplasty) for elbow arthritis
• Bridge plating for complex distal humerus/periarticular fractures
• Preferred over anterolateral approach for fractures of the distal half of the humeral shaft

Positioning

• Prone or lateral decubitus position
• Arm abducted 90° on a radiolucent arm support
• This allows the elbow to flex freely during the approach, which is important for improving exposure

Surgical Technique (Step by Step)

Skin Incision

Step 1 - Identify the Interval (Superficial Dissection)

Key landmark: As you retract the lateral head laterally and the long head medially at the proximal part, the radial nerve and profunda brachii artery are exposed as they run together in the spiral groove.

• The radial nerve lies approximately 39 ± 2.1 mm from the point of confluence between the long and lateral heads of the triceps and the triceps aponeurosis.
• The first branch identifiable at the lateral septum is the lateral sensory branch of the radial nerve - trace it proximally to find the main radial nerve.

Step 2 - Deep Dissection (Midline Split)

• The medial head originates just distal to the spiral groove and is the deepest layer
• Longitudinal midline dissection through it reveals the periosteum of the posterior humeral shaft

Step 3 - Periosteal Elevation

• The medial and lateral columns of the distal humerus are exposed
• Periosteal retraction also protects the radial, ulnar, and lateral brachial cutaneous nerves

Step 4 - Distal Extension (if needed)

• Release Sharpey fibers to create medial and lateral fasciotendinous sleeves
• This allows access to the olecranon fossa and articular surface

Tip: Visualization of the articular surface of the distal humerus can be improved by partial excision of the olecranon tip and flexion of the elbow.

Step 5 - Proximal Extension (if needed)

• With mobilization of the radial nerve, access to the posterior humerus increases from 55% to 76% of the shaft.

Closure

Anatomical Interval

Access Provided

Advantages

• Relatively technically straightforward
• Can be extended proximally and distally as needed
• Ability to convert from ORIF to TEA intraoperatively with minimal additional steps
• No bone osteotomy required (unlike olecranon osteotomy)
• McKee et al. showed no significant difference in extensor mechanism strength between triceps-splitting and olecranon osteotomy approaches

Disadvantages

• Limited visibility of the articular surface - not ideal for highly comminuted intra-articular distal humerus fractures
• Requires postoperative protection of the triceps repair - risk of extensor mechanism disruption
• No true internervous plane (working within the radial nerve's territory throughout)
• Triceps splitting at the olecranon insertion risks extensor weakness or dehiscence

Postoperative Care

• Patients with triceps-splitting approach are restricted to gravity-assisted range of motion initially (unlike paratricipital approach, where unrestricted active ROM is allowed)
• Triceps protection for approximately 6 weeks to allow tendon-to-bone healing
• Gentle flexion exercises permitted; active extension against resistance restricted early

Comparison with Other Posterior Approaches

Anterolateral Approach to the Humerus

Indications

• Humeral shaft fractures of the proximal and middle thirds (preferred approach for these levels)
• ORIF of humeral diaphyseal fractures requiring anterolateral plate placement
• Lowest incidence of iatrogenic radial nerve palsy compared to the lateral and posterior approaches
• Pathologic lesions of the humeral shaft
• Brachial artery repair (can combine with medial approach)
• Can be combined with a volar Henry approach distally to extend into the forearm

Positioning

• Supine with the arm on an arm table, or lateral decubitus
• A padded support under the shoulder allows the arm to fall into slight abduction
• Elbow flexion to 90° during the distal part of the dissection relaxes the brachialis and improves exposure

Anatomical Intervals

This approach is extensile but not truly internervous at all levels - the brachialis split in the middle third is the key "safe" plane because the dual nerve supply allows longitudinal splitting without paralysis.

Surgical Technique (Step by Step)

Skin Incision (Thompson-Henry)

Step 1 - Superficial Fascia and Cephalic Vein

Step 2 - Proximal Exposure (Deltopectoral Interval)

• Deltoid - retract laterally
• Pectoralis major / biceps long head - retract medially

Caution: Avoid excessive lateral retraction of the deltoid - the axillary nerve enters the deltoid from its deep surface and is at risk from forceful retraction.

Step 3 - Pectoralis Major Attachment (if needed)

Step 4 - Middle Third Exposure (Brachialis Split)

• Mobilize the biceps medially
• This exposes the brachialis muscle, which covers the anterior humeral diaphysis
• Split the brachialis longitudinally at its lateral third (one-third lateral, two-thirds medial)
• Retract the brachialis subperiosteally to expose the shaft

Why split at the lateral third? The brachialis is supplied by the musculocutaneous nerve medially and the radial nerve laterally. A midline or lateral-third split preserves the innervation to both halves. The lateral half of the brachialis also acts as a protective buffer for the radial nerve as it winds around the spiral groove.

Retraction is easiest when the elbow is flexed to 90°, which relaxes the brachialis tendon.

Step 5 - Distal Exposure

• Brachialis (medially)
• Brachioradialis (laterally)

At the distal end, be vigilant for:

• Radial nerve traveling deep to the brachioradialis muscle
• Lateral antebrachial cutaneous nerve (terminal branch of musculocutaneous) coursing medially to laterally under the biceps tendon as it enters the field

Step 6 - Periosteal Elevation

Access Provided

Structures at Risk

Advantages

• Truly extensile - from humeral head to coronoid fossa, and further into forearm
• Lowest incidence of radial nerve palsy among humeral shaft approaches (the lateral brachialis half provides a physical nerve shield)
• Intermuscular at most levels; brachialis dual innervation allows safe longitudinal splitting
• Can be performed supine (patient comfort, ease of anaesthesia)
• Most appropriate for proximal two-thirds of humeral shaft

Disadvantages

• Not the best approach for distal third fractures - posterior approach is preferred there
• Radial nerve still at risk with excessive dissection or screw penetration near spiral groove
• King & Johnston modification required to avoid painful neuromata from lower lateral brachial cutaneous nerve

Modifications

Comparison: Anterolateral vs. Posterior Approach