Percutaneous Pinning for Proximal Humerus Fractures: An Intraoperative Masterclass

Introduction and Epidemiology

Proximal humerus fractures represent a significant portion of all appendicular skeletal injuries, accounting for approximately 5% to 6% of all adult fractures. They exhibit a classic bimodal distribution: high-energy trauma in younger demographics and low-energy fragility falls in the elderly osteoporotic population. As the global population ages, the incidence of these fractures continues to rise, presenting an escalating challenge for orthopedic surgeons.

Proximal humerus fractures are defined as those involving the proximal portion of the humerus, inherently affecting the glenohumeral joint mechanics and shoulder girdle stability. Fracture lines predictably divide the proximal humerus into specific parts defined by anatomic structures that arise from early centers of ossification. These “parts” were first described by Codman and subsequently led to the development of the Neer classification, which remains the most commonly utilized taxonomic system in contemporary orthopedic practice. The parts refer to the head of the humerus (articular segment), the greater tuberosity, the lesser tuberosity, and the humeral shaft.

Proximal humerus fractures are classified as two-, three-, or four-part fractures according to the Neer classification. Displacement of a “part” is classically defined as greater than 1 cm of translation or greater than 45 degrees of angulation. Importantly, displacement itself is not necessarily an absolute indication for surgery but rather a criterion for classification. The type of fracture, degree of displacement, the likelihood of osteonecrosis, and comprehensive patient considerations (physiologic age, functional demands, medical comorbidities) all factor heavily into surgical decision-making.

Percutaneous pinning, or closed reduction and percutaneous pinning (CRPP), offers a minimally invasive alternative to open reduction and internal fixation (ORIF) or arthroplasty. By preserving the fracture hematoma and avoiding extensive soft tissue stripping, CRPP minimizes the iatrogenic disruption of the tenuous vascular supply to the humeral head, thereby theoretically reducing the risk of osteonecrosis in appropriately selected fracture patterns.

Surgical Anatomy and Biomechanics

A profound understanding of proximal humeral anatomy is mandatory for executing percutaneous pinning, as the surgeon must rely on tactile feedback, fluoroscopic imaging, and precise knowledge of neurovascular safe zones.

Osteology and Centers of Ossification

The proximal humerus arises from four distinct centers of ossification: the humeral head, the greater tuberosity, the lesser tuberosity, and the shaft. These developmental boundaries dictate the predictable fracture lines seen in clinical practice.

The greater tuberosity is positioned laterally and has three distinct facets for the insertion of the rotator cuff musculature: the superior facet for the supraspinatus, the middle facet for the infraspinatus, and the inferior facet for the teres minor. The lesser tuberosity is located anteriorly and serves as the primary insertion site for the subscapularis muscle.

Between these two tuberosities lies the intertubercular (bicipital) groove. The rotator interval is the anatomic space located between the upper border of the subscapularis and the anterior border of the supraspinatus. The long head of the biceps tendon lies in a shallow groove on the anterior proximal humerus and enters the glenohumeral joint at the rotator interval. The proximal 3 cm of the long head of the biceps tendon lies deep to the interval tissue intra-articularly. Importantly, the fracture line separating the greater and lesser tuberosities lies just posterior to the biceps groove.

Muscular Attachments and Deforming Forces

Fracture displacement is primarily driven by the unopposed pull of the attached musculature. Understanding these deforming forces is critical for achieving and maintaining closed reduction prior to percutaneous fixation.

• Greater Tuberosity: Pulled superiorly and posteriorly by the supraspinatus and infraspinatus/teres minor, respectively.
• Lesser Tuberosity: Pulled medially by the subscapularis.
• Humeral Shaft: Pulled medially and proximally by the pectoralis major, latissimus dorsi, and teres major. The pectoralis major muscle inserts on the proximal shaft of the humerus lateral to the long head of the biceps tendon, while the latissimus dorsi muscle inserts onto the proximal shaft medial to the biceps groove.
• Articular Segment (Humeral Head): Often remains neutral or is driven into varus/valgus depending on the integrity of the medial calcar hinge and the force vector of the injury.

Vascular Anatomy and Osteonecrosis Risk

The vascular supply to the proximal humerus is a critical determinant of fracture healing and the risk of avascular necrosis (AVN).

The anterior humeral circumflex artery (AHCA) courses laterally along the inferior border of the subscapularis. The anterolateral branch (often referred to as the arcuate artery) of the anterior humeral circumflex artery travels superiorly along the lateral aspect of the biceps groove and enters the humeral head at the proximal-most aspect of the groove. Historically, classical anatomical studies suggested this vessel provided about 85% of the blood supply to the humeral head.

However, more recent quantitative perfusion studies have demonstrated that the posterior humeral circumflex artery (PHCA) gives off several small branches that run adjacent to the inferior capsule of the shoulder, providing a substantial, robust, and often dominant blood supply to the humeral head, especially in the setting of fracture where the AHCA is frequently disrupted.

Preservation of the medial hinge (calcar) is paramount, as disruption of the medial periosteum significantly increases the risk of ischemia. Hertel's criteria for predicting ischemia include a metaphyseal head extension (calcar length) of less than 8 mm, disruption of the medial hinge, and a basicervical fracture pattern.

Indications and Contraindications

Patient selection is the most critical factor in the success of percutaneous pinning for proximal humerus fractures. The technique demands adequate bone stock to allow for pin purchase and a fracture pattern amenable to closed reduction.

Ideal candidates are those with two-part surgical neck fractures, select three-part fractures, and valgus-impacted four-part fractures where the articular segment is not laterally translated. Valgus impacted fractures often have an intact medial periosteal hinge, which facilitates closed reduction and portends a lower risk of osteonecrosis.

Conversely, severe osteopenia or osteoporosis is a relative to absolute contraindication, as the pins will lack sufficient cortical purchase, leading to inevitable construct failure, pin migration, and loss of reduction. Head-splitting fractures, severe comminution, and fractures that cannot be anatomically reduced via closed maneuvers must be managed with alternative techniques.

Pre Operative Planning and Patient Positioning

Thorough preoperative planning mitigates intraoperative complications and ensures efficient execution of the percutaneous technique.

Radiographic Evaluation

Standard trauma series radiographs of the shoulder are mandatory, including a true anteroposterior (Grashey) view, a scapular Y view, and an axillary lateral view. The axillary view is non-negotiable, as it provides definitive assessment of glenohumeral dislocation and anterior-posterior tuberosity displacement.

A non-contrast Computed Tomography (CT) scan with 3D reconstruction is highly recommended for all complex proximal humerus fractures. CT imaging delineates articular surface involvement, the exact degree of tuberosity displacement, the presence of a head-split component, and the integrity of the medial calcar.

Operating Room Setup and Positioning

The patient is typically positioned in the beach chair position, with the backrest elevated to approximately 45 to 60 degrees. The patient must be shifted laterally so that the affected shoulder extends completely off the edge of the operating table, allowing for unobstructed posterior extension and fluoroscopic access.

A radiolucent arm board or a specialized limb positioner (e.g., Spider arm) can be utilized to assist with reduction maneuvers. The C-arm fluoroscopy unit is usually brought in from the superior aspect (head of the bed) or from the contralateral side, depending on the specific OR setup and anesthesia team positioning. The surgeon must verify that perfect AP and axillary views can be obtained prior to prepping and draping.

Detailed Surgical Approach and Technique

The success of CRPP relies entirely on the surgeon's ability to achieve an anatomic or near-anatomic closed reduction and to place implants within designated neurovascular safe zones.

Closed Reduction Maneuvers

Reduction is typically achieved through a combination of longitudinal traction, manipulation of the arm into flexion or extension, and varus/valgus alignment.
- For a standard varus-displaced surgical neck fracture, the shaft is often adducted and pulled proximally by the pectoralis major. Reduction involves longitudinal traction, gentle abduction, and anterior translation of the shaft to align it with the head.
- For a valgus-impacted fracture, lateral traction is applied to disengage the tuberosities, followed by elevation of the humeral head using a blunt elevator introduced percutaneously or via a heavy threaded Schanz pin utilized as a joystick.

If the greater tuberosity is displaced, a 2.5 mm or 3.0 mm terminally threaded pin can be inserted percutaneously into the tuberosity fragment to serve as a joystick, pulling it inferiorly and anteriorly into its anatomic bed.

Pin Placement and Safe Zones

Once reduction is achieved and verified on orthogonal fluoroscopic views, fixation is initiated. Terminally threaded pins (typically 2.5 mm to 3.0 mm) are preferred over smooth K-wires to maximize purchase in the cancellous bone of the humeral head and to resist backing out.

Lateral Ascending Pins (Shaft to Head):
The lateral pins provide the primary stability against varus collapse. The entry point is on the lateral cortex of the humeral shaft.
Neurovascular Safe Zone: The axillary nerve courses horizontally around the surgical neck, approximately 5 to 7 cm distal to the lateral edge of the acromion. To avoid the axillary nerve, the entry point for the lateral pins must be either significantly distal to this zone (at the level of the deltoid tuberosity) or carefully placed through a mini-open incision spreading down to bone. Pins are directed from distal-lateral to proximal-medial, aiming for the subchondral bone of the inferior and central humeral head. Typically, two or three lateral pins are utilized.

Anterior Descending Pins (Greater Tuberosity to Shaft):
To neutralize the superior pull of the rotator cuff and stabilize the greater tuberosity, anterior descending pins are placed. The entry point is the anterior aspect of the greater tuberosity.
Neurovascular Safe Zone: The cephalic vein and the long head of the biceps tendon must be avoided. The pins are directed from proximal-anterior to distal-posterior, engaging the medial cortex of the humeral shaft.

Construct Biomechanics

The final construct should resemble a multi-planar scaffolding. The crossing of the lateral ascending pins and the anterior descending pins creates a biomechanically stable construct that resists both varus/valgus bending and torsional forces. The pins are cut beneath the skin to reduce infection risk, though some surgeons prefer leaving them prominent for easier removal in the clinic, provided the patient is compliant with pin site care.

Complications and Management

While CRPP minimizes soft tissue trauma, it is not without significant risks. The complication profile differs distinctly from that of ORIF.

Pin migration is the most frequently encountered complication, occurring in up to 10% to 20% of cases, particularly in patients with undiagnosed osteopenia. Migration can be superficial (backing out through the skin) or deep (advancing into the glenohumeral joint or mediastinum). Deep migration requires immediate surgical retrieval.

Superficial pin site infections are relatively common if pins are left proud, usually resolving with oral antibiotics and early pin removal. Deep intra-articular infections are rare but devastating, necessitating formal irrigation and debridement.

Axillary nerve injury can occur during placement of the lateral pins. This is largely preventable by adhering to strict safe zones and utilizing drill sleeves that protect the soft tissues during pin insertion.

Post Operative Rehabilitation Protocols

The postoperative rehabilitation following CRPP requires a delicate balance between protecting the tenuous percutaneous fixation and preventing debilitating shoulder stiffness (adhesive capsulitis).

**Phase I: Immobilization (Weeks 0-4

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