Enhance Recovery: Humeral Plate Fixation for Brachialis & Brachioradialis

Introduction and Epidemiology

Humeral shaft fractures represent a significant portion of orthopedic trauma, accounting for approximately 3 percent of all adult fractures. These injuries typically exhibit a bimodal distribution, occurring in young males following high energy trauma such as motor vehicle collisions, and in older females following low energy falls due to osteoporotic bone. The humerus is the most freely movable long bone in the human body, which affords it a high degree of compensatory motion. Consequently, strict anatomic reduction is not universally required for satisfactory functional outcomes.

Historically, these injuries have been managed nonoperatively with a high degree of success using functional bracing principles popularized by Sarmiento. Patients can often tolerate up to 20 degrees of anterior angulation, 30 degrees of varus angulation, and up to 3 centimeters of shortening without experiencing a significant loss of upper extremity function or noticeable cosmetic deformity. However, modern orthopedic traumatology has seen a paradigm shift toward surgical intervention in specific clinical scenarios to enhance recovery, facilitate early mobilization, and avoid the prolonged morbidity associated with conservative management.

Pathogenesis and Injury Mechanisms

Humeral shaft fractures occur secondary to both direct and indirect injury mechanisms. Direct blows to the brachium typically impart a bending force that fractures the humeral shaft in a transverse or short oblique pattern, frequently resulting in a butterfly fragment. High energy direct injuries, such as crush injuries or ballistic trauma, often yield a greater degree of fracture comminution and severe soft tissue compromise.

Indirect injuries frequently occur during activities that apply extreme rotational forces to the arm, such as arm wrestling or throwing. These twisting mechanisms generate torsional stress that predictably results in a spiral fracture pattern. In higher energy indirect injuries, the violent displacement of fracture fragments can result in muscle interposition—commonly the brachialis or triceps—between the bony ends. This interposition mechanically blocks closed reduction efforts and significantly increases the risk of delayed union or nonunion if managed nonoperatively.

Surgical Anatomy and Biomechanics

A profound understanding of the cross sectional and longitudinal anatomy of the brachium is mandatory for safe surgical intervention. The humeral shaft is anatomically defined as the region between the upper margin of the pectoralis major tendon insertion proximally and the supracondylar ridge distally. The shaft itself possesses anteromedial, anterolateral, and posterior surfaces, which dictate the placement of fixation constructs. Proximal and midshaft fractures are highly amenable to plating on the anterolateral surface, whereas distal third fractures often necessitate posterior plate fixation due to the contour of the olecranon fossa and the distal trajectory of the radial nerve.

Osteology and Vascular Supply

The diaphyseal blood supply of the humeral shaft is derived primarily from the posterior humeral circumflex vessels proximally and branches of the brachial and profunda brachii arteries distally. The nutrient artery typically enters the anteromedial cortex of the middle third of the diaphysis and is directed distally. Surgical approaches must respect the periosteal blood supply, utilizing minimally invasive or careful subperiosteal dissection techniques to preserve the vascularity necessary for secondary bone healing. Concomitant macroscopic vascular injuries to the brachial artery are present in approximately 3 percent of patients with humeral shaft fractures and require immediate multidisciplinary intervention.

Neuromuscular Anatomy and the Radial Nerve

The radial nerve is the most critical anatomical structure at risk during both the initial injury and subsequent surgical approaches to the humerus. The nerve, accompanied by the profunda brachii artery, exits the axilla and passes through the triangular interval. This interval is bordered superiorly by the teres major, medially by the long head of the triceps, and laterally by the humeral shaft.

From the triangular interval, the radial nerve transverses from medial to lateral along the posterior aspect of the humeral shaft within the spiral groove. It pierces the lateral intermuscular septum approximately 10 to 12 centimeters proximal to the lateral epicondyle to enter the anterior compartment of the arm. Distally, the nerve travels in the anatomic interval between the brachialis muscle medially and the brachioradialis muscle laterally. This specific interval is the foundation of the distal anterolateral approach to the humerus.

The musculocutaneous nerve also requires consideration during the anterior approach. It pierces the coracobrachialis proximally, lies on the undersurface of the biceps brachii muscle, and rests superficially on the brachialis muscle. It provides motor innervation to the medial portion of the brachialis before terminating distally as the lateral antebrachial cutaneous nerve. The dual innervation of the brachialis—medial half by the musculocutaneous nerve and lateral half by the radial nerve—permits longitudinal splitting of the brachialis muscle during the anterolateral approach without causing complete denervation.

Biomechanical Considerations in Fixation

The humerus is subjected to complex biomechanical forces, including axial loading, bending, and significant torsion. Open reduction and internal fixation utilizing plate osteosynthesis must neutralize these forces. Plate fixation offers distinct biomechanical and functional advantages over intramedullary nailing. Most notably, plating avoids violation of the rotator cuff, which consistently leads to improved postoperative shoulder function and decreased incidence of chronic shoulder pain.

Construct rigidity depends on the working length of the plate, the number of cortices engaged, and the utilization of compression versus bridge plating techniques. For simple transverse or short oblique fractures, absolute stability is achieved via interfragmentary lag screws and dynamic compression plating. For highly comminuted segmental fractures, relative stability via bridge plating is preferred to preserve the fracture hematoma and promote callus formation.

Indications and Contraindications

While conservative management with a prefabricated functional fracture brace remains the standard of care for many isolated, closed humeral shaft fractures, there are several absolute and relative indications for surgical intervention. Operative management requires extensive dissection and advanced operative skill but provides immediate stability, facilitates early mobilization, and simplifies nursing care in polytraumatized patients.

Operative Versus Non Operative Decision Making

The decision to proceed with surgical fixation versus conservative management hinges on fracture morphology, patient physiology, and concomitant injuries. Transverse fractures, in particular, are notorious for their inability to maintain acceptable alignment with closed treatment due to the lack of bony interdigitation and the deforming forces of the deltoid and pectoralis major muscles.

Contraindications to surgical fixation include active localized soft tissue infection, severe medical comorbidities precluding anesthesia, and exceedingly poor soft tissue envelopes that cannot tolerate surgical incisions. In cases of severe contamination or extensive soft tissue loss, external fixation may be utilized as a temporizing or definitive measure rather than immediate internal plate fixation.

Pre Operative Planning and Patient Positioning

Thorough preoperative planning is essential for successful humeral plate fixation. This phase dictates the surgical approach, the length and type of the implant, and the anticipation of necessary adjunctive procedures such as bone grafting or nerve exploration.

Imaging and Templating

Standard orthogonal radiographs, including an anteroposterior and true lateral of the entire humerus, are mandatory. The imaging must visualize the shoulder and elbow joints to rule out intra-articular extension. Computed tomography is rarely indicated for diaphyseal fractures unless there is suspicion of occult intra-articular extension at the distal humerus.

Digital templating is performed to determine the appropriate plate length. A general biomechanical rule for diaphyseal plating is to achieve a minimum of three to four bicortical screws (six to eight cortices) in both the proximal and distal main fracture fragments. A 4.5 millimeter narrow limited contact dynamic compression plate or locking compression plate is typically selected.

Positioning and Room Setup

For the anterolateral approach, the patient is placed in the supine position on a radiolucent operating table. A radiolucent arm board is attached to the operative side. The patient is positioned close to the edge of the table to allow the shoulder to drop posteriorly, facilitating access to the lateral aspect of the arm.

A sterile tourniquet may be placed high on the brachium, though it is rarely inflated due to the proximal extent of most incisions and the robust vascularity of the arm which can typically be managed with electrocautery. The entire forequarter, from the base of the neck to the fingertips, is prepped and draped free to allow for full manipulation of the extremity and intraoperative assessment of elbow and shoulder range of motion. The C-arm fluoroscopy unit is brought in from the contralateral side or from the head of the bed, ensuring unimpeded orthogonal views of the entire humerus.

Detailed Surgical Approach and Technique

The anterolateral approach is the workhorse for midshaft and distal third humeral fractures. It exploits the internervous planes and the dual innervation of the brachialis muscle, providing excellent exposure while minimizing denervation.

The Anterolateral Approach

The skin incision is made along a line connecting the coracoid process to the lateral epicondyle of the humerus. The length of the incision is dictated by the fracture pattern and the templated plate length. Subcutaneous tissues are dissected, taking care to identify and protect the cephalic vein, which can be retracted either medially or laterally depending on the exact proximal extent of the exposure.

The deep fascia is incised in line with the skin incision. The biceps brachii muscle is identified and mobilized medially, exposing the underlying brachialis muscle. At this juncture, the surgeon must decide on the specific handling of the brachialis muscle based on the fracture location.

For midshaft fractures, the brachialis muscle is split longitudinally down its midline. Because the medial half is innervated by the musculocutaneous nerve and the lateral half by the radial nerve, this longitudinal split is an internervous plane that preserves the function of both segments. The split is carried down to the periosteum, and the muscle halves are elevated off the anterior humerus. The lateral half of the brachialis acts as a protective muscular cushion between the retractor (and subsequently the plate) and the radial nerve.

For distal third fractures, the exposure must transition to the interval between the brachialis and the brachioradialis. The radial nerve emerges from the posterior compartment by piercing the lateral intermuscular septum and travels distally in the cleft between the brachialis (medially) and the brachioradialis (laterally).

To safely exploit this interval, the fascia between the brachialis and brachioradialis is carefully incised. The radial nerve must be actively identified and protected. It is often easiest to identify the nerve distally where the interval is wider and trace it proximally to where it pierces the septum. Once identified, the nerve is gently mobilized and protected with vessel loops. Retraction of the nerve must be minimal and meticulous to prevent iatrogenic neuropraxia.

Fracture Reduction and Plate Fixation

Once the fracture site is exposed and the hematoma evacuated, reduction is achieved using longitudinal traction, rotation, and direct manipulation with bone reduction forceps. Soft tissue interposition, particularly from the brachialis or triceps, must be cleared from the fracture ends.

For simple fracture patterns (transverse or short oblique), absolute stability is the goal. If the obliquity allows, an interfragmentary lag screw is placed perpendicular to the fracture plane to generate interfragmentary compression. A 4.5 millimeter narrow plate is then contoured to the anterolateral aspect of the humerus. The plate is applied in a neutralization mode. If a lag screw cannot be placed, the plate is applied in a dynamic compression mode utilizing eccentrically drilled screws.

For comminuted or segmental fractures, relative stability is preferred. The fracture zone is bypassed without disturbing the comminuted fragments, preserving the local biology. A longer plate is utilized to span the fracture, acting as a bridge construct. Locking screws are highly beneficial in this scenario, particularly in osteoporotic bone, as they provide angular stability and reduce the risk of hardware pullout.

Clinical & Radiographic Imaging