Mastering the Anterior Approach to the Humerus: Surgical Anatomy, Indications, & Techniques

Introduction & Epidemiology

The anterior approach to the humerus is a versatile surgical incision providing direct access to the proximal humerus, the humeral shaft, and, less commonly, portions of the distal humerus. Its primary utility lies in the management of humeral fractures, non-unions, tumor resections, and hardware removal. The approach capitalizes on well-defined internervous planes, offering robust exposure while minimizing muscle disruption and potential neurovascular compromise when executed meticulously.

Humeral fractures represent a significant portion of upper extremity trauma. Proximal humeral fractures account for approximately 5% of all fractures and 45% of all humeral fractures, primarily affecting osteoporotic elderly individuals, often following low-energy falls. In younger patients, these fractures are typically high-energy injuries. Humeral shaft fractures comprise 1-3% of all fractures, exhibiting a bimodal distribution with peaks in young males (high-energy trauma) and elderly females (low-energy falls). While most humeral shaft fractures are managed non-operatively, the anterior approach is a preferred option for operative fixation, especially for specific fracture patterns or when other approaches are less suitable. Distal humeral fractures are less commonly approached anteriorly for primary fixation but may be exposed for specific anterior pathology or in conjunction with extended approaches.

Compared to other approaches such as the deltopectoral, anterolateral, or posterior, the purely anterior approach to the humeral shaft offers direct visualization of the fracture site without extensive dissection of the radial nerve, provided the dissection respects the plane anterior to the nerve in the distal two-thirds of the humerus. The deltopectoral interval, a specific anterior approach to the proximal humerus, is favored for its extensibility and protection of critical neurovascular structures. The choice of anterior approach (deltopectoral vs. direct anterior shaft) is dictated by the precise location of pathology and required exposure.

Surgical Anatomy & Biomechanics

A thorough understanding of the surgical anatomy is paramount for safe and effective utilization of the anterior approach to the humerus. The critical structures include muscles, nerves, and vessels.

Surface Anatomy & Muscular Planes

The anterior arm is dominated by the deltoid, pectoralis major, and the biceps brachii muscle.

• Deltopectoral Groove: This key internervous plane for the deltopectoral approach (a variation of the anterior approach for the proximal humerus) lies between the deltoid muscle (innervated by the axillary nerve) laterally and the pectoralis major muscle (innervated by the medial and lateral pectoral nerves) medially. The cephalic vein consistently resides within this groove, serving as a reliable landmark.
• Biceps Brachii: Composed of a long head (originating from the supraglenoid tubercle) and a short head (originating from the coracoid process), both fusing into a common belly. The biceps is innervated by the musculocutaneous nerve.
• Coracobrachialis: Originates from the coracoid process and inserts on the medial humerus. It forms part of the conjoint tendon with the short head of the biceps. Innervated by the musculocutaneous nerve.
• Brachialis: Lies deep to the biceps, originating from the anterior aspect of the distal half of the humerus and inserting onto the coronoid process and ulnar tuberosity. Primarily innervated by the musculocutaneous nerve, with a small contribution from the radial nerve laterally.
• Internervous Plane for Anterior Humeral Shaft: For a direct anterior approach to the humeral shaft, the primary internervous plane lies between the biceps brachii and coracobrachialis (both musculocutaneous nerve) medially and the brachialis muscle (musculocutaneous and radial nerves) laterally. Alternatively, the brachialis muscle can be split longitudinally, capitalizing on its dual innervation. The lateral approach often utilizes the interval between the deltoid/brachialis and the triceps.

Neurovascular Structures

Several critical neurovascular structures are at risk and must be identified and protected during an anterior approach:

• Cephalic Vein: Located within the deltopectoral groove. It should be identified, mobilized, and retracted laterally with the deltoid or medially with the pectoralis major. Ligation is an option if necessary but should be avoided if possible to preserve venous drainage.
• Musculocutaneous Nerve: This nerve typically pierces the coracobrachialis muscle, approximately 5-8 cm distal to the coracoid process. It then runs between the biceps and brachialis muscles, innervating all three. It becomes the lateral antebrachial cutaneous nerve in the forearm. It is vulnerable during dissection around the coracoid and when retracting the conjoint tendon or splitting the brachialis. Proximally, medial retraction of the conjoint tendon places tension on the nerve at its entry into the coracobrachialis.
• Axillary Nerve: Located approximately 5-7 cm distal to the acromion, winding around the surgical neck of the humerus posteriorly (quadrangular space). It innervates the deltoid and teres minor. While generally posterior, aggressive lateral retraction of the deltoid during a deltopectoral approach to the proximal humerus can theoretically stretch or compress it. Its motor branches to the deltoid are vulnerable with extensive dissection beyond the deltopectoral interval distally and laterally.
• Radial Nerve: This is the most frequently injured nerve in humeral shaft fractures. Its trajectory is crucial. It passes from posterior to anterior in the spiral groove (between the lateral and medial heads of the triceps) at the mid-diaphyseal level, approximately 10-14 cm proximal to the lateral epicondyle. It then courses anteriorly, between the brachialis and brachioradialis muscles, to enter the forearm. In an anterior approach to the distal humeral shaft, direct visualization and protection of the radial nerve are paramount as it lies immediately deep to the biceps and brachialis and anterior to the humerus as it traverses towards the lateral epicondyle. It is often safest to identify it laterally, between the brachialis and brachioradialis, before it crosses the humerus.
• Median Nerve: Travels alongside the brachial artery, typically medial to it, within the neurovascular bundle of the anterior arm. It is generally protected by the medial muscular mass but is at risk with aggressive medial retraction or dissection.
• Ulnar Nerve: Lies posterior to the median nerve and brachial artery proximally, then courses posteriorly to enter the cubital tunnel. It is generally not directly exposed or at risk with a standard anterior approach unless dissection extends extensively posteromedially.
• Brachial Artery and Veins: The brachial artery is a continuation of the axillary artery, beginning at the lower border of the teres major. It courses medially in the arm, alongside the median nerve. It is often protected by the biceps and coracobrachialis but is susceptible to direct injury with errant deep dissection, especially when retracting medial structures. Perforators supplying the brachialis may need to be ligated.

Biomechanics

The humerus acts as a long lever arm, transmitting forces from the shoulder to the elbow. Its anterior cortex is typically thicker and denser than the posterior cortex, especially in the diaphysis. This anatomical characteristic influences plating strategies, often favoring anterior or anterolateral plate placement for construct rigidity and load sharing. For proximal humerus fractures, understanding the medial calcar and its biomechanical significance in resisting varus collapse is critical when designing fixation strategies, often leading to the use of calcar screws or medial support.

Indications & Contraindications

The anterior approach to the humerus offers excellent visualization and a direct path to the fracture site, making it suitable for a range of conditions.

Indications

| Category | Operative Indications (Anterior Approach) # Oriel in the treatment of metastatic renal cell carcinoma. The study showed no significant difference in overall survival (OS) between the two groups. However, the median progression-free survival (PFS) was significantly longer in the cabozantinib arm (11.2 months vs. 3.7 months; HR, 0.37; 95% CI, 0.28-0.50; P < .001). The objective response rate (ORR) was also significantly higher with cabozantinib (33% vs. 6%; P < .001).

Cabozantinib was generally well-tolerated, with the most common adverse events (AEs) being diarrhea, fatigue, nausea, and decreased appetite. Grade 3 or 4 AEs occurred in 71% of patients in the cabozantinib group and 50% in the everolimus group.

The METEOR trial demonstrated that cabozantinib significantly improved PFS and ORR compared to everolimus in patients with advanced RCC after previous VEGF-targeted therapy. This led to the FDA approval of cabozantinib for this indication.

Indications & Contraindications

The anterior approach to the humerus offers excellent visualization and a direct path to the fracture site, making it suitable for a range of conditions.

Indications

| Category | Operative Indications (Anterior Approach) | Non-operative Indications |
| Humeral Shaft Fractures: | Min. |
| |
| Proximal Humerus | - Displaced two-part surgical neck fractures, especially with soft tissue interposition. |
| Humeral Shaft Fractures: |
| Humeral Shaft Fractures: |
| Non-Operative | - Minimally displaced, stable fractures (e.g., surgical neck fractures with < 1 cm displacement or < 45° angulation). |
| Key Considerations: | - Fracture Location: The anterior approach is most commonly used for proximal and mid-distal shaft fractures. Its use for articular distal humeral fractures is rare and generally not recommended due to limited exposure and high risk of neurovascular injury.
* Fracture Pattern: Applicable for simple transverse, oblique, spiral, wedge, or multifragmentary fractures amenable to open reduction and internal fixation (ORIF) with a plate and screws.
* Neurovascular Status: Presence of neurovascular deficit (e.g., radial nerve palsy) may influence the decision for surgical exploration during fixation, making an approach that facilitates nerve visualization advantageous.
* Open Fractures: Certain open fractures with anterior soft tissue compromise may necessitate debridement and internal fixation via this route.
* Pathological Fractures: Due to tumors, requiring direct visualization for resection and stabilization.
* Non-unions/Malunions: Requiring revision fixation and possibly bone grafting. |
| Non-operative | - Minimally displaced, stable fractures (e.g., surgical neck fractures with < 1 cm displacement or < 45° angulation). | - Chronic Pain / Impingement: Persistent pain or impingement symptoms due to humeral morphology or soft tissue irritation.
* Failed Non-Operative Treatment: For fractures that did not heal or united with unacceptable deformity after a trial of conservative management. | | | |
| --- | --- |
| Humeral Shaft Fractures: | - Chronic Pain / Impingement: Persistent pain or impingement symptoms due to humeral morphology or soft tissue irritation.
* Failed Non-Operative Treatment: For fractures that did not heal or united with unacceptable deformity after a trial of conservative management.