Minimally Invasive Anterolateral Proximal Humerus Approach for IMN: A Comprehensive Surgical Guide

Minimally Invasive Proximal Humerus Approach: Techniques Explained

Introduction & Epidemiology

The minimally invasive anterolateral approach to the proximal humerus represents a refined surgical strategy, primarily utilized for the insertion of intramedullary nails (IMN) to treat a spectrum of humeral fractures and their sequelae. This approach is distinguished by its emphasis on preserving soft tissues, particularly the deltoid and rotator cuff, minimizing devascularization of bone fragments, and potentially facilitating earlier rehabilitation and reduced surgical morbidity compared to more extensive open techniques.

Historically, surgical management of proximal humeral and humeral shaft fractures involved significant soft tissue stripping to achieve open reduction and internal fixation with plates. While plating remains a robust option for many fracture patterns, the biomechanical advantages of intramedullary nailing, such as load sharing and central fixation, coupled with the desire for less invasive techniques, have driven the adoption of approaches like the anterolateral method. This technique aims to navigate critical neurovascular structures while providing adequate access for implant insertion and fracture reduction.

Epidemiologically, humeral shaft fractures account for approximately 1-3% of all fractures, with a bimodal distribution affecting young males in high-energy trauma and elderly osteoporotic females. Proximal humerus fractures are also common, particularly in the elderly, and sometimes extend distally to involve the shaft or require a proximal entry point for IMN. Pathologic fractures, often secondary to metastatic disease, and cases of delayed union or nonunion of humeral shaft fractures, also frequently necessitate intramedullary fixation via a proximal approach. The choice of a minimally invasive technique is particularly relevant in these patient populations, where comorbidities or compromised bone quality may benefit from a less disruptive surgical footprint.

Surgical Anatomy & Biomechanics

A thorough understanding of the surgical anatomy of the proximal humerus and humeral shaft is paramount for successful and safe application of the minimally invasive anterolateral approach.

Bony Anatomy

The proximal humerus consists of the humeral head, anatomical neck, surgical neck, greater tuberosity, and lesser tuberosity. The greater tuberosity serves as the insertion site for the supraspinatus, infraspinatus, and teres minor, while the lesser tuberosity accepts the subscapularis tendon. Distal to the tuberosities lies the surgical neck, a common site for fractures. The humeral shaft extends from the surgical neck to the supracondylar region, characterized by the deltoid tuberosity on its lateral aspect. The articular cartilage of the humeral head covers the superior aspect, making entry portal selection critical to avoid iatrogenic damage.

Muscular Anatomy

The deltoid muscle covers the entire proximal humerus, originating from the clavicle, acromion, and spine of the scapula, and inserting on the deltoid tuberosity. The anterolateral approach typically involves a limited deltoid-splitting incision. Beneath the deltoid lie the rotator cuff muscles. The supraspinatus tendon inserts on the superior facet of the greater tuberosity, the infraspinatus on the middle facet, and the teres minor on the inferior facet. The subscapularis inserts on the lesser tuberosity. The interval between the supraspinatus and subscapularis, known as the rotator interval, is a potential area for entry, although the standard anterolateral entry is often more lateral to this.

Neurovascular Structures

The axillary nerve is a critical structure, originating from the posterior cord of the brachial plexus (C5-C6). It courses inferiorly and posteriorly, exiting the quadrangular space with the posterior circumflex humeral artery. It wraps around the surgical neck of the humerus approximately 5-7 cm distal to the lateral acromial edge, innervating the deltoid and teres minor muscles. Care must be taken during deltoid splitting to remain anterior and avoid injury to this nerve, particularly with more extensive splits or overly aggressive retraction.
The radial nerve , another major branch of the posterior cord (C5-T1), spirals around the humeral shaft in the spiral groove, typically 10-14 cm distal to the greater tuberosity, innervating the triceps and wrist extensors. While not directly in the path of a proximal approach entry, its location must be respected during distal locking procedures or when addressing mid-shaft components of the fracture.
The anterior and posterior circumflex humeral arteries also course around the surgical neck, supplying the humeral head, and are vulnerable during approaches that expose this region.

Biomechanics

Intramedullary nailing offers distinct biomechanical advantages over plating for humeral shaft fractures and certain proximal humeral patterns. IMN provides load sharing with the bone, reducing stress shielding and potentially promoting earlier weight-bearing. Its central position within the medullary canal offers inherent stability in bending and torsion, particularly with appropriate interlocking screws. For the proximal humerus, the challenge lies in achieving stable fixation within the metaphysis, which often has poorer bone quality, without compromising articular cartilage. Modern nails are designed with multiple proximal locking options and specific curvatures to address these challenges, with some having an angled proximal segment to facilitate entry lateral to the articular surface.

Indications & Contraindications

The minimally invasive anterolateral approach to the proximal humerus is primarily indicated for intramedullary nailing. The specific indications for IMN often overlap with those for plate fixation, but the choice is frequently guided by fracture pattern, patient factors, and surgeon preference.

Indications for Intramedullary Nailing via Minimally Invasive Proximal Approach:

• Acute Humeral Shaft Fractures: Transverse, short oblique, spiral, comminuted fractures of the diaphysis, especially those extending proximally.
• Pathologic Humeral Shaft Fractures: Due to metastatic disease or primary bone tumors, where IMN provides robust internal splinting and allows for earlier weight-bearing and pain relief.
• Delayed Union and Nonunion of Humeral Shaft Fractures: Particularly hypertrophic or oligotrophic nonunions where reaming and nailing can provide mechanical stability and biological stimulation.
• Segmental Humeral Fractures: Where IMN can bridge multiple fracture sites effectively.
• Proximal Humeral Fractures with Diaphyseal Extension: Where the proximal fragment is large enough to allow stable nail insertion without compromising the articular surface and distal extension requires shaft stabilization.
• Polytrauma Patients: IMN may be preferred for its less extensive soft tissue dissection and potential for faster operative time, contributing to damage control orthopedics.
• Open Humeral Shaft Fractures: After thorough debridement, IMN can be a viable option, depending on wound contamination and soft tissue injury.

Contraindications:

• Significant Articular Involvement of the Humeral Head: Comminuted or displaced articular fractures where IMN entry would further damage the cartilage or where anatomical reduction and specific articular fixation (e.g., with screws or plating) are paramount.
• Severe Proximal Metaphyseal Comminution: Insufficient bone stock in the proximal fragment to achieve stable nail purchase or interlocking screw fixation.
• Severe Glenohumeral Arthritis: Pre-existing arthritis may be exacerbated by IMN entry or shoulder stiffness post-operatively.
• Active Infection: Absolute contraindication without prior debridement and management.
• Unsuitable Nail Design/Anatomy Mismatch: When the patient's anatomy (e.g., small medullary canal, extreme humeral bowing) is not compatible with available nail designs.
• Inability to Achieve Closed or Limited Open Reduction: If the fracture cannot be adequately reduced using minimally invasive techniques, conversion to a more extensive open approach may be necessary.
• Compromised Rotator Cuff or Deltoid: Pre-existing pathology that would be worsened by the approach, though this is less common.

Table 1: Indications for Operative vs. Non-Operative Management in Humeral Fractures Relevant to Proximal IMN

Pre-Operative Planning & Patient Positioning

Meticulous pre-operative planning and precise patient positioning are critical for optimizing outcomes and minimizing complications with the minimally invasive anterolateral approach.

Pre-Operative Planning

1. Imaging Assessment:
   • Standard Radiographs: Anteroposterior (AP), lateral, and axillary views of the shoulder and entire humerus are essential to characterize the fracture pattern, comminution, and displacement. Bilateral views can assist in templating for canal diameter and length.
   • Computed Tomography (CT) Scan: Highly recommended for complex proximal humeral fractures with diaphyseal extension, severe comminution, or for identifying articular involvement. A CT scan with 3D reconstructions can aid in visualizing fracture fragments and planning reduction maneuvers.
2. Implant Selection and Templating:
   • Nail Type: Selection of an appropriate intramedullary nail (e.g., antegrade, retrograde, specific curvature, locking options) is crucial. Most nails used via this approach are antegrade.
   • Templating: As highlighted in the original seed, radiographic templating is vital. A template of the intended nail should be superimposed over pre-operative radiographs to determine the appropriate nail length, diameter, and most importantly, the optimal entry point that respects articular cartilage and tuberosities. The entry point depends on the specific design of the nail, as some nails have an angled proximal segment.
   • Working Lengths: Estimate working lengths for guidewires, reamers, and interlocking screws.
3. Evaluation of Patient Factors: Assess patient comorbidities, bone quality (e.g., osteoporosis), and functional demands to anticipate challenges and tailor post-operative care. Obtain informed consent, detailing potential complications.
4. Anesthesia and OR Setup: Discuss anesthetic plan (general anesthesia often with regional block), C-arm availability and positioning, and potential need for a traction table or specific arm positioners.
5. Antibiotic Prophylaxis: Administer pre-operative intravenous antibiotics per institutional protocol.

Patient Positioning

The patient is typically placed in a supine position on a radiolucent operating table.
* Table Elevation: Elevate the upper portion of the table to approximately 60 degrees. This "beach chair" or semi-Fowler position allows for easier access to the shoulder, improved visualization for the surgeon, and facilitates fluoroscopic imaging in both AP and lateral planes.
* Shoulder Placement: Position the patient so that the shoulder of the affected limb lies over the edge of the table. This allows for free manipulation of the arm, including traction, rotation, and abduction/adduction, which are critical for fracture reduction.
* Alternative Table: Alternatively, use a specialized radiolucent table or a standard operating table with a shoulder attachment that allows for complete radiographic visualization of the shoulder and humerus in both anterior-posterior and lateral planes without repositioning the patient or the C-arm.
* C-arm Positioning: The C-arm must be positioned to allow for clear AP and lateral views of the proximal humerus and fracture site. This usually means positioning the C-arm from the opposite side of the table or carefully adjusting its arc to obtain true lateral views.
* Arm Preparation: The entire affected arm, from the hand to the shoulder, should be prepared and draped in a sterile fashion, allowing for sterile manipulation throughout the procedure. The arm should be freely movable.
* Axillary Roll: A small roll placed beneath the ipsilateral axilla can help prevent brachial plexus compression and improve stability.
* Head Position: The head should be supported and secured to prevent inadvertent movement during surgery.

Fig. 1-78: Patient in a semi-Fowler (beach chair) position with the shoulder at the edge of the table, facilitating access and fluoroscopic imaging.

Detailed Surgical Approach / Technique

The minimally invasive anterolateral approach prioritizes direct access to the proximal humerus entry point while minimizing soft tissue disruption. This section outlines the step-by-step technique for intramedullary nail insertion.

Incision and Initial Dissection

1. Skin Incision: A longitudinal skin incision, typically 3-5 cm in length, is made over the anterolateral aspect of the proximal humerus. The incision should be centered over the anticipated nail entry point, which is typically just lateral to the articular surface of the humeral head and just medial to the greater tuberosity.
2. Subcutaneous Dissection: Dissect through the subcutaneous tissues to expose the underlying deltoid muscle fascia. Meticulous hemostasis is maintained.
3. Deltoid Splitting: The deltoid muscle fibers are carefully split longitudinally. It is crucial to limit the split to avoid damage to the axillary nerve, which typically crosses the surgical neck 5-7 cm distal to the acromion. A split of 3-4 cm is generally safe. Retractors are used cautiously to avoid excessive stretch on the deltoid and underlying nerves.
4. Exposure of Rotator Cuff and Entry Point: After splitting the deltoid, the subdeltoid bursa is encountered and incised. This exposes the underlying rotator cuff tendons, primarily the supraspinatus. The entry point for an intramedullary nail is determined radiographically, typically just lateral to the articular surface of the humeral head and just medial to the greater tuberosity. This optimal entry point aims to minimize damage to the rotator cuff insertion (especially supraspinatus) and preserve articular cartilage.
   • As seen in the anatomical representations, the entry point is carefully selected to avoid the critical articular surface and vital structures.
     
   • The proposed entry point is often located in a small bare area or through the rotator cuff footprint.
     
   • Anterior-posterior view illustrating the common entry point, slightly lateral to the apex of the humeral head.
     
   • Lateral view showing the entry point alignment with the medullary canal.
     
   • Fig. 1-50 (composite): Illustrating the typical entry point for antegrade humeral intramedullary nailing, just lateral to the articular surface of the humeral head and medial to the greater tuberosity.

Entry Portal Creation and Medullary Preparation

1. Pilot Hole: Using a sharp awl or a small drill bit, a pilot hole is created at the determined entry point. This must be aligned with the humeral shaft's medullary canal. Fluoroscopic guidance (AP and lateral views) is essential to confirm correct trajectory.
2. Guidewire Insertion: A guidewire is carefully advanced down the humeral shaft, past the fracture site. Fluoroscopy confirms its central position within the canal and beyond the fracture.
3. Reaming (Optional but common): If a reamed nail is planned, sequential reaming is performed over the guidewire. Reaming helps to enlarge the medullary canal, allowing for a larger diameter nail, which can increase construct stability and cortical contact. Careful attention is paid to reaming incrementally and avoiding cortical perforation, especially at the fracture site. The reamer should pass the fracture site without difficulty.

Fracture Reduction

Achieving anatomical reduction of the fracture is critical before nail insertion.
* Traction and Manipulation: Gentle longitudinal traction is applied to the arm. This can be combined with rotation, adduction/abduction, and flexion/extension maneuvers.
* Indirect Reduction Techniques:
* Percutaneous Joysticks: Kirschner wires can be inserted percutaneously into major fragments and used as "joysticks" to manipulate and align them.
* External Rotation: For proximal fragments in valgus, external rotation of the arm can aid in reduction.
* Closed Reduction with Fluoroscopy: The primary goal is to achieve reduction under fluoroscopic guidance, minimizing further soft tissue disruption.
* Limited Open Reduction: If closed reduction is unsuccessful, a small, separate percutaneous incision may be required to insert a reduction clamp or instrument to aid in fragment alignment. This should be as minimally invasive as possible.

Nail Insertion and Locking

1. Nail Insertion: The chosen intramedullary nail is carefully advanced over the guidewire, past the fracture site, until its proximal end is flush with the entry portal. The nail is gently rotated as it advances to navigate the humeral curvature. Fluoroscopy confirms the position of the nail in both planes.
2. Proximal Locking: Once the nail is optimally seated, proximal interlocking screws are inserted. Modern humeral nails typically have multiple proximal locking options (e.g., in different planes, divergent angles) to enhance stability in the metaphyseal bone. A targeting guide is generally used, and fluoroscopy confirms screw length and position. It is critical to ensure proper purchase in the proximal fragment, avoiding articular penetration.
3. Distal Locking: Distal interlocking screws are then inserted. This can be achieved with a targeting jig or via freehand technique using fluoroscopic guidance. Distal locking screws are essential to prevent rotation and shortening. For mid-shaft fractures, two distal screws are usually preferred for stability.

Final Assessment and Closure

1. Fluoroscopic Confirmation: After all screws are inserted, obtain final AP and lateral fluoroscopic images to confirm fracture reduction, nail position, and screw lengths and positions. Ensure no articular penetration and adequate fixation.
2. Wound Irrigation and Hemostasis: Thoroughly irrigate the wound to remove any bone debris. Achieve meticulous hemostasis.
3. Rotator Cuff Repair (If necessary): If the entry portal significantly disrupted the rotator cuff (e.g., supraspinatus), a repair should be performed using absorbable sutures.
4. Deltoid Repair: The split deltoid muscle fibers are reapproximated with absorbable sutures.
5. Layered Closure: The subcutaneous tissue is closed, followed by skin closure using sutures, staples, or adhesive strips. A sterile dressing is applied.

Complications & Management

Despite its advantages, the minimally invasive anterolateral approach to the proximal humerus and intramedullary nailing are associated with potential complications. Awareness and proactive management are essential for optimal patient outcomes.

Table 2: Common Complications, Incidence, and Salvage Strategies

General Considerations for Complication Management

• Prevention: Many complications are preventable through meticulous pre-operative planning, careful surgical technique, appropriate implant selection, and vigilant post-operative monitoring.
• Early Recognition: Prompt recognition of complications through clinical examination, imaging, and laboratory tests is crucial for effective management.
• Patient Education: Patients should be counseled on potential complications and the importance of adhering to rehabilitation protocols.
• Multidisciplinary Approach: Management of complex complications may require a multidisciplinary approach involving pain specialists, infectious disease specialists, and rehabilitation physicians.

Post-Operative Rehabilitation Protocols

Post-operative rehabilitation following minimally invasive proximal humerus approach for IMN is crucial for restoring function, preventing stiffness, and ensuring optimal recovery. Protocols are tailored to the individual patient, fracture stability, bone quality, and quality of fixation.

Phase 1: Immobilization and Early Protected Motion (Weeks 0-6)

Goals:
* Control pain and swelling.
* Protect the healing fracture and surgical repair (deltoid, rotator cuff).
* Prevent shoulder stiffness while allowing for early motion of adjacent joints.

Activities:
* Immobilization: The arm is typically immobilized in a sling or shoulder immobilizer. The duration varies but is generally 2-4 weeks, or longer for unstable fractures or poor fixation.
* Pain Management: Pharmacological intervention (NSAIDs, opioids, muscle relaxants) and cryotherapy.
* Elbow, Wrist, Hand ROM: Active range of motion (AROM) exercises for the elbow, wrist, and hand are encouraged immediately to prevent stiffness and promote circulation.
* Pendulum Exercises: Gentle pendulum exercises for the shoulder can be initiated, typically around 1-2 weeks post-op, or once stable and pain allows. These are passive, gravity-assisted movements.
* Gentle Passive Range of Motion (PROM) for Shoulder (Physiotherapist-guided): For stable fractures with secure fixation, PROM (flexion, abduction, external/internal rotation) may begin cautiously at 2-4 weeks, guided by a physical therapist, keeping the elbow flexed to minimize stress on the healing deltoid. External rotation should be limited to prevent excessive stress on the subscapularis and anterior capsule if rotator cuff was violated.
* Scapular Mobility: Gentle scapular retraction and protraction exercises.
* Weight Bearing: Non-weight bearing on the affected arm. No lifting objects heavier than a coffee cup.

Phase 2: Active Assisted and Active Motion (Weeks 6-12)

Goals:
* Gradually increase active shoulder range of motion.
* Initiate isometric strengthening.
* Reduce sling dependence.

Activities:
* Discontinuation of Sling: The sling is typically discontinued as tolerated, usually around 6 weeks, or once clinical and radiographic signs of healing are evident.
* Active Assisted Range of Motion (AAROM): Progress from PROM to AAROM, using the unaffected arm or a pulley system to assist motion.
* Active Range of Motion (AROM): Begin active shoulder flexion, abduction, and rotation exercises as pain and healing allow. Avoid painful arcs of motion.
* Isometric Strengthening: Initiate gentle isometric exercises for the rotator cuff (internal/external rotation) and deltoid, with the arm in neutral rotation and abduction. Gradually increase resistance as tolerated.
* Light Functional Activities: Begin light activities of daily living, avoiding heavy lifting or sudden movements.

Phase 3: Progressive Strengthening and Return to Function (Weeks 12+)

Goals:
* Restore full strength and endurance.
* Improve proprioception and neuromuscular control.
* Facilitate return to sport or demanding occupational activities.

Activities:
* Progressive Resistance Exercises: Advance to resistance band exercises and light weight training for all shoulder musculature (deltoid, rotator cuff, scapular stabilizers). Gradually increase weight and repetitions.
* Proprioceptive Training: Incorporate exercises that challenge balance and coordination, such as medicine ball throws or perturbation training.
* Functional and Sport-Specific Training: For athletes or individuals with demanding occupations, specific drills mimicking their activities are introduced.
* Endurance Training: Continue with cardiovascular conditioning.
* Implant Removal Consideration: For younger, active patients, implant removal may be considered typically 12-18 months post-op, once the fracture is fully healed, to address any residual shoulder impingement or pain related to the hardware. This is individualized.
* Full Return to Activities: Gradual return to full activities and sports, typically 4-6 months post-surgery, depending on fracture healing, strength, and range of motion.

Key Principles:
* Individualization: Protocols must be tailored to the patient, fracture type, and fixation stability.
* Pain as a Guide: Activities should not cause excessive pain.
* Gradual Progression: Avoid aggressive advancements that could jeopardize healing or fixation.
* Communication: Close collaboration between the surgeon, physical therapist, and patient is paramount.
* Protection of Deltoid and Rotator Cuff: Special attention to protecting the healing deltoid and any potentially compromised rotator cuff tissue throughout the rehabilitation process.

Summary of Key Literature / Guidelines

The role of intramedullary nailing (IMN) via a minimally invasive proximal approach for humeral fractures has been extensively studied, with a growing body of evidence supporting its efficacy and specific indications.

• Humeral Shaft Fractures: For diaphyseal humeral fractures, IMN has consistently demonstrated high union rates (typically >90%) and favorable functional outcomes. Compared to plating, IMN is often associated with shorter operative times, smaller incisions, and potentially reduced blood loss. However, IMN has historically been linked to higher rates of shoulder pain and stiffness, often attributed to rotator cuff irritation or proud nails at the entry site. Modern nail designs and careful surgical technique aim to mitigate these issues. Several studies and meta-analyses have concluded that both plating and nailing are effective for humeral shaft fractures, with the choice often depending on fracture morphology, surgeon preference, and patient factors (e.g., polytrauma where IMN may offer a less invasive option). For segmental fractures or those with bone loss, IMN provides excellent stability.
• Proximal Humeral Fractures with Diaphyseal Extension: While plating (especially locking plates) remains the gold standard for many complex proximal humeral fractures, IMN can be a viable option for specific patterns, particularly Neer 2-part surgical neck fractures, or more complex patterns with significant diaphyseal extension where the proximal fragment is sufficiently robust for nail purchase. The advantage of IMN here is its load-sharing nature and potentially less soft tissue stripping compared to extensive plating approaches. However, the risk of articular penetration, rotator cuff impingement, and limited rotational control for highly comminuted proximal fragments must be considered.
• Pathologic Fractures: IMN is widely recognized as the preferred method for stabilizing pathologic humeral fractures due to metastatic disease. It provides immediate pain relief, robust stability, and facilitates early functional recovery and adjuvant therapies (radiation). The minimally invasive approach is particularly advantageous in this often-frail patient population.
• Nonunions: For aseptic nonunions of the humeral shaft, IMN, often combined with reaming and bone grafting, has proven highly successful. The reaming process itself can provide biological stimulus, and the nail offers strong mechanical stabilization.
• Comparison with Open Reduction and Internal Fixation (ORIF) with Plates: While IMN offers advantages of load sharing and less invasive soft tissue dissection, plating provides better control of alignment, especially in highly comminuted metaphyseal-diaphyseal junction fractures, and allows for direct visualization of the fracture site. A systematic review by Heineman et al. (2018) highlighted similar union rates between IMN and plating for humeral shaft fractures but noted a higher incidence of shoulder pain with antegrade IMN and elbow pain with retrograde IMN. The anterolateral approach for antegrade nailing aims to minimize the shoulder morbidity associated with the traditional direct superior entry.
• Technique Evolution: The evolution of IMN designs, including multiple proximal locking options and specific curvatures, coupled with the refinement of minimally invasive approaches, has broadened the indications and improved outcomes. The emphasis on precise entry point selection lateral to the articular cartilage and careful deltoid-splitting techniques are key advancements.
• Future Directions: Advancements in navigated surgery and intraoperative imaging may further enhance the precision and safety of minimally invasive IMN techniques, particularly in challenging fracture patterns or revision cases. The balance between maintaining minimal invasiveness and achieving optimal biomechanical reduction and fixation will continue to drive research and development in this area.

In conclusion, the minimally invasive anterolateral approach for proximal humeral IMN offers a valuable tool in the orthopedic surgeon's armamentarium, particularly for humeral shaft fractures, pathologic fractures, and select proximal humeral patterns. Its successful application hinges on a profound understanding of surgical anatomy, meticulous pre-operative planning, precise execution, and a structured post-operative rehabilitation protocol.

Clinical & Radiographic Imaging