Mastering External Fixation and Plating of Distal Radius Fractures: A Comprehensive Surgical Guide

INTRODUCTION TO DISTAL RADIUS FRACTURE MANAGEMENT

Distal radius fractures represent one of the most frequently encountered injuries in orthopedic traumatology. While the advent of locked volar plating has revolutionized the management of these fractures, external fixation remains an indispensable technique in the armamentarium of the orthopedic surgeon. External fixation is particularly valuable in the context of severe comminution, highly contaminated open fractures, polytrauma requiring damage-control orthopedics, and cases with profound soft-tissue compromise where immediate internal fixation is contraindicated.

The primary goal of external fixation is to harness the biomechanical principle of ligamentotaxis. By applying longitudinal traction across the radiocarpal joint, the intact volar and dorsal radiocarpal ligaments are tensioned, indirectly reducing the fracture fragments, restoring radial length, and correcting radial inclination. This masterclass delineates the precise surgical techniques for both spanning and nonspanning external fixation, alongside a critical analysis of adjunctive fragment-specific fixation and the biomechanical nuances of volar plating.

SURGICAL ANATOMY AND BIOMECHANICS

The Principle of Ligamentotaxis

Ligamentotaxis utilizes the strong extrinsic ligaments of the wrist—specifically the radioscaphocapitate, long radiolunate, and dorsal radiocarpal ligaments—to pull displaced articular and metaphyseal fragments back into alignment. However, while ligamentotaxis is highly effective at restoring radial length and radial inclination, it is often insufficient for fully restoring volar tilt.

Biomechanics Pearl: Pure longitudinal traction tends to align the carpus with the radial shaft, often leaving the distal articular surface in a neutral or slightly dorsally angulated position. To restore the normal 11 degrees of volar tilt, the external fixator frame must allow for independent palmar translation of the carpus relative to the radial shaft.

Neurovascular and Tendinous Considerations

Safe application of an external fixator requires an intimate understanding of the dorsal and radial anatomy of the forearm and hand:
* Dorsal Radial Sensory Nerve (DRSN): The DRSN exits the deep fascia between the brachioradialis (BR) and the extensor carpi radialis longus (ECRL) in the mid-forearm (approximately 8 to 9 cm proximal to the radial styloid). It branches extensively over the dorsoradial aspect of the wrist and hand. It is the structure most at risk during both proximal and distal pin placement.
* Lateral Antebrachial Cutaneous Nerve (LABCN): Running in close proximity to the cephalic vein, the LABCN provides sensation to the radial aspect of the forearm and must be protected during proximal pin insertion.
* Extensor Tendons: Pins must be placed carefully to avoid transfixing the extensor tendons, particularly the extensor pollicis longus (EPL) and the radial wrist extensors, which can lead to postoperative tethering, loss of motion, or tendon rupture.

PREOPERATIVE PREPARATION AND POSITIONING

Optimal surgical outcomes begin with meticulous preoperative planning and patient positioning.

1. Anesthesia: The procedure is typically performed under a regional brachial plexus block or general anesthesia, depending on patient comorbidities and concurrent injuries.
2. Positioning: The patient is positioned supine with the affected upper extremity extended on a radiolucent hand table.
3. Tourniquet: A well-padded pneumatic tourniquet is applied to the proximal arm. Exsanguination is performed, and the tourniquet is inflated to standard upper extremity pressures (typically 250 mm Hg).
4. Reduction Aids: The fracture is initially reduced manually. Sterile finger traps applied to the index and long fingers, combined with 5 to 10 lbs of counter-traction across the upper arm, can greatly facilitate sustained reduction and simplify frame application.

SURGICAL TECHNIQUE: SPANNING EXTERNAL FIXATION

Spanning external fixation bridges the radiocarpal joint, anchoring in the radial diaphysis proximally and the second metacarpal distally.

Distal Pin Insertion (Index Metacarpal)

1. Incision: Make a 2- to 3-cm longitudinal incision over the dorsoradial aspect of the index metacarpal base.
2. Dissection: Utilize blunt dissection with tenotomy scissors to spread the subcutaneous tissues down to the metacarpal periosteum.
   > Surgical Warning: Take extreme care to identify, preserve, and gently reflect the terminal branches of the dorsal radial sensory nerve (DRSN) and the dorsal venous network.
3. Pin Placement: Place a soft-tissue protector (drill sleeve) directly onto the metacarpal bone. Insert two 3-mm self-tapping half-pins.
4. Trajectory: The pins should be inserted at a 30- to 45-degree angle dorsal to the frontal plane of the hand. This trajectory avoids the first dorsal interosseous muscle and the extensor tendons while providing excellent bicortical purchase.
5. Verification: Confirm pin position, spacing, and bicortical length with multiplanar fluoroscopy.

Proximal Pin Insertion (Radial Diaphysis)

1. Incision: Make a 4-cm longitudinal skin incision approximately 8 to 10 cm proximal to the wrist joint, positioned just dorsal to the midline of the radial shaft.
2. Dissection: Proceed with blunt dissection to expose the superficial branches of the LABCN and the DRSN. Remember that the DRSN exits the investing fascia in the mid-forearm between the brachioradialis and the ECRL.
3. Interval Development: Develop the interval between the radial wrist extensors (ECRL and ECRB) to access the bare area of the radial diaphysis.
4. Pin Placement: Insert two 3-mm half-pins, spaced approximately 1.5 cm apart, through a soft-tissue protector.
5. Trajectory: Angle the pins at 30 degrees dorsal to the frontal plane of the forearm. Ensure the pins just perforate the medial cortex of the radius to achieve stable bicortical fixation without endangering the anterior interosseous neurovascular bundle.
6. Verification: Confirm pin placement and depth fluoroscopically.

Frame Assembly and Fracture Reduction

1. Closure: Thoroughly irrigate the pin sites and close the incisions loosely with 4-0 nylon sutures to prevent skin tethering.
2. Frame Application: Apply the selected external fixation frame according to the manufacturer’s specifications.
3. Reduction: For relatively stable fractures, or when utilizing Kirschner wires (K-wires) for augmentation, a simple single-bar frame is usually sufficient. Apply longitudinal traction to achieve ligamentotaxis.
4. Adjusting Volar Tilt: If the fracture remains dorsally angulated, utilize a multi-planar or articulated fixator that allows for independent palmar carpal translation. Translate the distal block palmarly to induce volar tilt of the distal radial articular surface.
5. Final Fluoroscopy: Obtain true posteroanterior (PA), lateral, and 10-degree lateral tilt views to confirm restoration of radial length, inclination, volar tilt, and articular congruity.

SURGICAL TECHNIQUE: NONSPANNING EXTERNAL FIXATION

Nonspanning external fixation is an elegant alternative for minimally comminuted extra-articular fractures or simple articular fractures in patients with excellent bone stock. By avoiding immobilization of the radiocarpal joint, this technique allows for early wrist range of motion.

Indications and Technique

• Patient Selection: Strictly reserved for patients with adequate distal bone stock (typically younger patients) where the distal fragment is large enough to accommodate two pins without compromising the articular surface.
• Proximal Pins: Inserted in the radial diaphysis exactly as described for the spanning technique.
• Distal Pins: Inserted directly into the distal radial fragment.
  • Make a small dorsal radial incision over the distal fragment.
  • Carefully protect the DRSN and extensor tendons.
  • Place a radial-sided pin and a more ulnar-sided pin into the distal fragment, ensuring they are parallel to the articular surface and do not penetrate the radiocarpal or distal radioulnar joints (DRUJ).
• Frame Assembly: Connect the proximal and distal pins with a short bar, reducing the fracture directly rather than relying on ligamentotaxis.

ADJUNCTIVE FIXATION AND FRAGMENT-SPECIFIC PLATING

External fixation alone is often insufficient for complex intra-articular fractures with depressed central articular fragments (die-punch) or displaced volar/dorsal rim fragments.

Kirschner Wire Augmentation

Percutaneous K-wires (1.6 mm or 0.062 inch) can be used to stabilize specific fragments. Radial styloid fragments can be pinned to the intact ulnar shaft of the radius, and dorsal die-punch fragments can be elevated percutaneously and supported with subchondral K-wires.

Dorsal Fragment-Specific Plating

For fractures with displaced dorsal lunate facet fragments or severe dorsal comminution that cannot be reduced via ligamentotaxis, a limited dorsal approach is warranted. A low-profile, fragment-specific dorsal plate works exceptionally well to buttress these fragments. Currently, most dorsal plating is performed using a fragment-specific technique, often in conjunction with external fixation or volar plating, to minimize the risk of extensor tendon irritation historically associated with bulky dorsal plates.

VOLAR PLATE FIXATION: BIOMECHANICS AND PITFALLS

While external fixation is a critical tool, the popularity of locked volar distal radial plate fixation continues to dominate the management of most displaced distal radius fractures, prompting the rapid evolution of new devices.

Biomechanical Superiority

Capo et al. conclusively demonstrated the biomechanical superiority of volar plating over both dorsal plating and radioulnar dual-column plating. The volar cortex of the distal radius is typically less comminuted than the dorsal cortex, providing a stable buttress. Locked screws act as fixed-angle devices, supporting the articular surface even in osteoporotic bone, negating the need for intact opposite cortex support.

Clinical Outcomes and Complications

Several clinical studies have reported superior early functional results with volar plating compared to dorsal plating, external fixation, and percutaneous pinning. However, volar plating is not without significant risks. A complication rate of approximately 15% has been reported in the literature.

Clinical Pitfall - Tendon Rupture: The most devastating complication of volar plating is flexor or extensor tendon rupture. Flexor pollicis longus (FPL) rupture can occur due to prominent plate placement distal to the watershed line. Extensor tendon rupture occurs when screws are too long and penetrate the dorsal cortex.

• Intra-articular Penetration: Screw penetration into the radiocarpal joint is a major risk. Knight et al. reported screw penetration of the radiocarpal joint in 11 of 40 patients evaluated with postoperative CT scans. Meticulous fluoroscopic evaluation, including the dorsal horizon view, is mandatory to confirm extra-articular screw placement.
• Implant Profile: The design of the plate significantly impacts outcomes. Soong et al. reported that a low-profile volar plate produced zero tendon ruptures in a cohort of 95 patients. Precise volar plate placement on the metaphyseal area of the distal radius—strictly proximal to the watershed line—is paramount to lessen the problems of flexor tendon irritation, tenosynovitis, and eventual rupture.

POSTOPERATIVE PROTOCOL AND REHABILITATION

The success of external fixation relies heavily on rigorous postoperative care and early rehabilitation.

1. Pin Site Care: Pin tract infections are the most common complication of external fixation. Patients must be instructed on daily pin site care, typically using a mixture of normal saline and chlorhexidine or hydrogen peroxide, followed by the application of sterile gauze to prevent skin tethering.
2. Mobilization: Immediate active range of motion of the fingers, thumb, elbow, and shoulder is mandatory to prevent stiffness and complex regional pain syndrome (CRPS).
3. Edema Control: Strict elevation of the limb above the level of the heart is required for the first 48 to 72 hours.
4. Frame Removal: For spanning external fixators, the frame is typically removed in the clinic at 6 to 8 weeks postoperatively, once radiographic evidence of bridging callus is observed. Following removal, patients are transitioned to a removable volar splint and commence formal physical therapy focusing on wrist range of motion and progressive strengthening.

COMPLICATIONS AND AVOIDANCE

• Over-distraction: Excessive traction during spanning external fixation can lead to delayed union, nonunion, and severe stiffness of the fingers due to tethering of the extrinsic flexors and extensors. The radiocarpal joint space on the PA radiograph should never exceed the thickness of the uninjured contralateral wrist (typically 2-3 mm).
• Neurologic Injury: Iatrogenic injury to the DRSN during pin placement can result in debilitating neuromas. Always use blunt dissection down to the bone and utilize soft-tissue protectors during drilling and pin insertion.
• Complex Regional Pain Syndrome (CRPS): Prophylactic administration of Vitamin C (500 mg daily for 50 days) has been suggested in some literature to reduce the incidence of CRPS following distal radius fractures, though its efficacy remains debated. Early finger mobilization is the most proven preventative measure.

By adhering to these strict anatomical principles, biomechanical concepts, and meticulous surgical techniques, the orthopedic surgeon can effectively utilize external fixation to achieve optimal functional and radiographic outcomes in the management of complex distal radius fractures.