2 REVIEW OF THE LITERATURE
2.1 Surgical anatomy and exposures of the humeral shaft
Surgical anatomy of the humerus is generally divided into proximally located head, shaft, and distal end. The head articulates with the glenoid fossa of the scapula, and the distal part forms the elbow joint together with the ulna and radius. This section focuses on surgical anatomy related to humeral shaft fractures. Important structures around the humerus are the brachial plexus and the brachial artery running medially along the humeral shaft, and the radial nerve running with the deep brachial artery around the radial groove of the humerus through the intermuscular septum.
Surgical exposures of the humeral shaft are generally divided into anterior, lateral, posterior, and (rarely used) medial approaches. The approach used depends on the location of the fracture, condition of the soft tissues, and the surgeon’s preference. Here, the three most common approaches for open reduction and internal fixation (ORIF) are described.
Anterior
The anterior approach to the humeral shaft was first described by Arnold Henry in 1924 (Henry 1924). The incision starts from the coracoid process, following the course of the cephalic vein to the anterior aspect of the cubital fossa. The biceps brachii muscle is moved medially with the accompanying musculocutaneous nerve in the posterior aspect of the muscle belly. The brachialis muscle is divided longitudinally at the outer fourth of the muscle, exposing the humeral shaft. The radial nerve stays protected on the lateral side of the brachialis muscle fibers, but it is easily found if necessary (Fig. 1 A). The term ‘anterolateral approach’ is commonly used in conjunction with the anterior approach in the literature. The distinction can be made according to how the humeral shaft is exposed at the distal end of the exposure. In the anterolateral approach (Fig. 1 B), the plane between the brachialis and brachioradialis is used, instead of splitting the brachialis muscle (true anterior approach). Recently, a modification of the approach was introduced to prevent unnecessary transection of diagonally oriented superficial head fibers of the brachialis muscle at the distal end of the humeral shaft (Chang et al. 2019).
The anterior approach is a useful option in the treatment of proximal and middle third fractures of the humeral shaft.
Lateral
The lateral approach (Fig. 2) was described in the context of humeral shaft fractures rather recently (Mills et al. 1996). The incision starts from the lateral epicondyle of the humerus proximally towards the deltoid insertion. The plane between the brachioradialis and triceps muscles is divided, and the humeral shaft is exposed. It is paramount to locate and protect the radial nerve as it pierces the lateral intermuscular septum within 5 mm from a junction of the middle and distal thirds of the line running from the lateral border of the acromion to the lateral epicondyle (Fleming et al. 2004). The lateral approach is mainly used in distal third shaft fractures.
A. B.
Fig. 2. Lateral approach to the humeral shaft. Copyright by AO Foundation, Switzerland. Source: AO Surgery Reference, www.aosurgery.org.
Fig. 1.
A. Anterior approach to the humerus, where the brachialis muscle is split.
B. Anterolateral approach, where the brachialis muscle is retracted medially.
Copyright by AO Foundation, Switzerland. Source: AO Surgery Reference, www.aosurgery.org.
Posterior
The posterior approach gives good exposure of middle and distal third shaft fractures. The bone can be exposed either around the lateral and medial border of the triceps muscle (paratricipital approach, Fig. 3) or by splitting the muscle longitudinally (triceps splitting approach, Fig. 4) (Gerwin et al. 1996). This approach gives good visibility to the radial nerve, which should always be visualized and protected before exposing the humeral shaft. This approach allows placing of the implant to either the medial, posterior, or lateral border of the humerus. This approach is useful especially in the cases having both distal intra-articular humeral fracture and ipsilateral shaft fracture.
Fig. 4. Posterior triceps splitting approach to the humeral shaft. Copyright by AO Foundation, Switzerland. Source: AO Surgery Reference, www.aosurgery.org.
Fig. 3. Posterior paratricipital approach to the humeral shaft with radial (left) and ulnar (right) windows around the triceps muscle. Copyright by AO Foundation, Switzerland. Source: AO Surgery Reference, www.aosurgery.org.
Approach for minimal invasive plate osteosynthesis
Two separate incisions are made to enable plate fixation above and below the fracture. The proximal part can be made either through the deltoid muscle (transdeltoid approach) or using the upper part of the anterior approach proximally (deltopectoral interval) and the anterolateral approach distally (Fig. 5). Care must be taken at the distal part to protect the radial nerve on the lateral side of the incision.
Approaches for intramedullary nailing
An intramedullary nail is introduced to the medullary canal from either the proximal (antegrade, Fig. 6) or distal (retrograde, Fig. 7) direction. For antegrade nailing, an approximately 4 cm incision is made from the anterolateral border of the acromion downwards. The muscle fibers of the deltoid muscle are split, and the rotator cuff interval is opened. Care must be taken to avoid excessive opening of the deltoid muscle, as the axillary nerve runs approximately 7 cm below the edge of the acromion. For retrograde nailing, a longitudinal midline incision is made over the tendinous part of the triceps right above the olecranon. Sharp dissection is carried out through the tendon by splitting the tendon fibers going towards the upper part of the olecranon fossa.
Fig. 5. Anterior approach for minimal invasive plate osteosynthesis. Copyright by AO Foundation, Switzerland. Source: AO Surgery Reference, www.aosurgery.org.
Fig. 6. Approach for antegrade nail insertion. Copyright by AO Foundation, Switzerland.
Source: AO Surgery Reference, www.aosurgery.org.