Advanced Insights into Distal Radius Fractures: Epidemiology, Classification, Anatomy & Biomechanics

Comprehensive Introduction and Patho-Epidemiology

Global Epidemiology and Demographic Trends

Distal radius fractures represent one of the most ubiquitous orthopedic injuries encountered in clinical practice, accounting for approximately one-sixth of all fractures treated in emergency departments worldwide. The epidemiological profile of these fractures famously follows a bimodal distribution, reflecting two distinct patient populations and mechanisms of injury. In the younger demographic, typically males in their second or third decades of life, these fractures are predominantly the result of high-energy trauma, such as motor vehicle collisions, falls from significant heights, or high-impact athletic endeavors. These high-energy injuries often present with profound articular comminution, significant displacement, and concomitant soft tissue or neurovascular compromises that demand meticulous surgical reconstruction.

Conversely, the second peak in the bimodal distribution occurs in the elderly population, predominantly post-menopausal females, where distal radius fractures act as a hallmark fragility fracture. In this cohort, the mechanism is usually low-energy, most commonly a simple fall onto an outstretched hand (FOOSH) from a standing height. The underlying pathophysiology in these cases is intrinsically linked to osteopenia and osteoporosis, where the structural integrity of the metaphyseal trabecular bone is compromised. As the global population continues to age, the sheer volume of osteoporotic distal radius fractures is projected to rise exponentially, placing a significant burden on healthcare systems and necessitating optimized, cost-effective treatment algorithms.

The socioeconomic impact of distal radius fractures cannot be overstated. Beyond the acute costs of surgical or non-surgical management, these injuries frequently result in prolonged periods of disability, lost wages, and a substantial requirement for physical or occupational therapy. In younger, working-age individuals, a malunited fracture can lead to early-onset post-traumatic osteoarthritis, chronic pain, and permanent functional impairment, drastically altering their career trajectories. In the elderly, a distal radius fracture often heralds a decline in independent living, serving as a sentinel event that precedes more devastating fragility fractures, such as those of the proximal femur.

Understanding these demographic trends is paramount for the orthopedic surgeon, as it directly influences clinical decision-making. A highly comminuted intra-articular fracture in a 25-year-old laborer necessitates a fundamentally different surgical strategy and biologic consideration than an extra-articular, dorsally angulated Colles-type fracture in an 85-year-old sedentary patient. The surgeon must synthesize the patient's physiologic age, functional demands, bone quality, and local injury characteristics to tailor an intervention that maximizes functional recovery while mitigating perioperative risks.

Pathophysiology and Mechanism of Injury

The precise pathoanatomy of a distal radius fracture is dictated by the magnitude, rate, and direction of the applied force, coupled with the position of the wrist at the exact moment of impact. During a classic FOOSH injury, the wrist is typically extended between 40 and 90 degrees. As the axial load is transmitted from the carpus to the distal radius, the volar capsule and ligaments are placed under maximal tension, while the dorsal aspect of the radius experiences severe compressive forces. This biomechanical environment classically results in the failure of the weaker volar tension side followed by the dorsal compression side, producing the characteristic dorsal tilt and metaphyseal comminution seen in Colles fractures.

If the wrist is positioned in flexion during the impact, a less common scenario, the force vectors are reversed. The dorsal ligaments are tensioned, and the volar cortex is subjected to compressive loads, culminating in a Smith fracture, characterized by volar displacement and angulation of the distal fragment. The degree of ulnar or radial deviation at the time of impact further dictates the propagation of the fracture lines. For instance, severe radial deviation combined with an axial load forces the scaphoid to act as a wedge against the radial styloid, frequently resulting in a Chauffeur's fracture (a shear fracture of the radial styloid).

Intra-articular fractures occur when the kinetic energy surpasses the energy-absorbing capacity of the subchondral bone, causing the lunate or scaphoid to impact and split the articular surface of the radius. The lunate facet is particularly vulnerable to these die-punch injuries due to its relatively flat contour and direct articulation with the lunate during axial loading. The resulting articular step-offs and gaps disrupt the delicate tribology of the radiocarpal joint. Even minor articular incongruities (historically defined as greater than 2 millimeters, though modern literature suggests even stricter tolerances) drastically alter contact pressures, accelerating cartilage wear and precipitating post-traumatic arthropathy.

Furthermore, the mechanism of injury rarely spares the surrounding soft tissue envelope. The energy dissipated during the fracture frequently causes concomitant ligamentous sprains or outright ruptures, particularly of the triangular fibrocartilage complex (TFCC) and the scapholunate interosseous ligament. The periosteum, particularly on the dorsal aspect, is often violently stripped, contributing to fracture hematoma but also compromising the local blood supply essential for secondary bone healing. Recognizing the holistic nature of the trauma—encompassing bone, cartilage, ligaments, and the neurovascular bundles—is critical for achieving comprehensive functional restoration.

Classification Systems and Prognostic Value

The historical landscape of orthopedic surgery is littered with classification systems for distal radius fractures, reflecting the complex and heterogeneous nature of these injuries. Eponyms such as Colles, Smith, Barton, and Chauffeur remain deeply entrenched in the orthopedic vernacular due to their descriptive simplicity and historical significance. However, these eponymous descriptors lack the granularity required to guide modern, fragment-specific surgical fixation or to reliably predict clinical outcomes. Consequently, more sophisticated, anatomically based classification systems have been developed to standardize communication and research.

The AO/OTA classification system is arguably the most comprehensive and widely utilized alphanumeric system in modern traumatology. It categorizes distal radius fractures into three broad types: Type A (extra-articular), Type B (partial articular), and Type C (complete articular). Each type is further subdivided into three groups and subsequent subgroups based on the degree of comminution, the direction of displacement, and the specific articular fragments involved. While the AO/OTA system provides unparalleled descriptive detail, its complexity often limits inter-observer and intra-observer reliability in routine clinical practice, making it more suited for academic research and registry data collection.

The Fernandez classification system offers a more mechanistically driven approach, categorizing fractures based on the primary mechanism of injury: bending (Type I), shearing (Type II), compression (Type III), avulsion (Type IV), and combined high-energy injuries (Type V). This system is highly regarded by orthopedic surgeons because it inherently suggests the necessary method of treatment. For example, a Type I bending fracture may be amenable to closed reduction and casting or simple volar plating, whereas a Type II shear fracture (like a volar Barton's) absolutely mandates surgical buttressing to counteract the deforming shear forces.

Another clinically relevant framework is the Melone classification, which focuses specifically on intra-articular fractures and identifies four foundational components: the radial shaft, the radial styloid, the dorsal medial fragment, and the volar medial fragment. Melone's emphasis on the medial (lunate facet) fragments is crucial, as displacement of these fragments profoundly disrupts the distal radioulnar joint (DRUJ) and the radiocarpal articulation. Ultimately, the true value of any classification system lies not merely in labeling the fracture, but in its ability to dictate the surgical approach, guide the selection of implants, and provide the patient with an accurate prognosis regarding their functional recovery.

Detailed Surgical Anatomy and Biomechanics

Osteology and Articular Geometry

The distal radius is a complex, three-dimensional architectural marvel designed to facilitate multi-planar wrist motion while simultaneously transmitting substantial loads from the hand to the forearm. Osteologically, the distal radius expands from the dense, diaphyseal cortical bone into a broad, cancellous metaphyseal flare. This transition zone is mechanically critical, as the thin cortical shell of the metaphysis is highly susceptible to compressive failure, particularly in the presence of osteoporosis. The volar surface is relatively flat and provides a stable platform for plate fixation, terminating distally at the "watershed line"—a critical surgical landmark representing the most prominent volar margin of the radius, beyond which implants risk impinging on the flexor tendons.

The articular surface of the distal radius is biconcave, articulating with both the scaphoid and the lunate. It is anatomically defined by three critical radiographic parameters: radial inclination (averaging 22 degrees), volar tilt (averaging 11 degrees), and radial height (averaging 11 to 12 millimeters). Restoration of these parameters is the primary objective of surgical intervention, as deviations significantly alter wrist kinematics. The articular surface is divided by a subtle anteroposterior ridge into the scaphoid fossa (which is triangular) and the lunate fossa (which is quadrilateral). The lunate fossa is further bordered medially by the sigmoid notch, a shallow concavity that articulates with the ulnar head to form the DRUJ.

The dorsal aspect of the distal radius is convex and serves as a fulcrum for the extensor tendons. It is characterized by Lister's tubercle, a bony prominence that acts as a biomechanical pulley for the extensor pollicis longus (EPL) tendon, redirecting it toward the thumb. The dorsal cortex is inherently thinner and weaker than the volar cortex, which explains the high propensity for dorsal comminution in extension-type injuries. During surgical reconstruction, the lack of a robust dorsal cortical buttress often necessitates the use of locking plates or structural bone grafts to prevent late fracture collapse and loss of reduction.

Understanding the vascular anatomy of the distal radius is also paramount, particularly when considering surgical approaches and fracture healing. The primary blood supply to the distal metaphysis is derived from the anterior interosseous artery, the radial artery, and their terminal anastomotic networks. The volar capsular attachments carry vital intra-osseous vascular channels. Aggressive soft tissue stripping, particularly of the volar radiocarpal ligaments and the pronator quadratus, can compromise this delicate vascular network, increasing the risk of delayed union, nonunion, or avascular necrosis of specific articular fragments.

Ligamentous Anatomy and Carpal Stability

The stability of the radiocarpal joint is not derived from its bony architecture, which is inherently shallow, but rather from a robust and intricate network of extrinsic and intrinsic ligaments. The extrinsic ligaments bridge the radius and ulna to the carpus, while the intrinsic ligaments connect the individual carpal bones. The volar extrinsic ligaments are significantly thicker and mechanically stronger than their dorsal counterparts, serving as the primary stabilizers of the wrist against the natural tendency of the carpus to translate ulnarly and volarly along the sloped articular surface of the radius.

Among the volar radiocarpal ligaments, the Radioscaphocapitate (RSC) ligament is considered the strongest and most critical in preventing dorsal translation of the carpus following a distal radius fracture. Originating from the radial styloid, the RSC courses obliquely across the waist of the scaphoid to insert on the body of the capitate. It acts as a vital sling that supports the proximal carpal row. In the setting of a distal radius fracture, preservation or repair of the RSC is paramount; failure to restore its tension can lead to devastating carpal instability, specifically dorsal intercalated segment instability (DISI) or ulnar translocation of the carpus.

Other notable volar ligaments include the Long Radiolunate (LRL) and Short Radiolunate (SRL) ligaments. The LRL originates from the volar rim of the scaphoid fossa and inserts on the lunate, providing critical stability to the radiolunate articulation and preventing ulnar translation. The SRL originates from the volar margin of the lunate fossa and inserts directly onto the volar horn of the lunate. Interestingly, the Radioscapholunate (RSL) ligament, historically known as the Ligament of Testut, is not a true mechanical stabilizer. Rather, it is a neurovascular conduit that tethers the proximal pole of the scaphoid and lunate to the radius, carrying crucial vascular supply from the anterior interosseous system.

The dorsal radiocarpal ligaments, while thinner, play an essential role in preventing volar translation of the carpus during wrist flexion. The primary dorsal stabilizer is the dorsal radiocarpal ligament, which originates from the dorsal rim of the radius and courses ulnarly to insert on the triquetrum. During surgical approaches to the dorsal wrist, meticulous elevation and subsequent meticulous repair of the dorsal retinaculum and capsular ligaments are required to prevent iatrogenic carpal instability and to ensure a smooth gliding surface for the extensor tendons, thereby preventing postoperative adhesions and tendon ruptures.

Biomechanics and Load Transmission

The biomechanics of the human wrist involve a highly sophisticated transmission of forces across a multi-link kinematic chain. In a healthy wrist with neutral ulnar variance (where the articular surfaces of the distal radius and distal ulna are perfectly level), the axial load generated during gripping or weight-bearing is distributed unevenly but predictably. Landmark biomechanical studies by Palmer and Werner demonstrated that the distal radius absorbs approximately 80% of the axial load, while the ulna absorbs the remaining 20% through the triangular fibrocartilage complex (TFCC).

This delicate balance of load transmission is exquisitely sensitive to alterations in ulnar variance, which frequently occur following malunion of a distal radius fracture. If a distal radius fracture heals with radial shortening, it effectively creates a state of ulnar positive variance. Palmer and Werner's research revealed that an increase in ulnar positive variance by merely 2.5 millimeters drastically alters the kinematics of the wrist, increasing the load transmitted across the ulnocarpal joint from 20% to approximately 42%. This massive shift in force transmission strongly predisposes the patient to ulnocarpal impaction syndrome, characterized by accelerated wear of the TFCC, chondromalacia of the lunate and ulnar head, and debilitating ulnar-sided wrist pain.

Conversely, surgical over-lengthening of the radius or excessive resection of the distal ulna creates an ulnar negative variance. While this decreases the load on the ulnar side of the wrist, it disproportionately increases the stress across the radiocarpal joint, potentially accelerating radiocarpal osteoarthritis. Furthermore, alterations in the volar tilt profoundly impact biomechanics. A loss of the normal 11 degrees of volar tilt, resulting in dorsal angulation, shifts the contact stresses of the radiocarpal joint dorsally. This not only limits wrist flexion but also drastically reduces the mechanical advantage of the extrinsic finger flexors, leading to a measurable decrease in grip strength.

The distal radioulnar joint (DRUJ) is intrinsically linked to the biomechanics of the distal radius. The DRUJ relies on the precise congruency of the sigmoid notch and the ulnar head to allow for smooth pronation and supination. Any residual translation, rotation, or shortening of the distal radius alters the tension on the dorsal and volar radioulnar ligaments of the TFCC. A malunion of the radius can cause the ulnar head to impinge against the sigmoid notch, leading to severe restrictions in forearm rotation, chronic DRUJ instability, and early arthrosis. Therefore, restoring the anatomic dimensions of the radius is not merely about radiocarpal mechanics, but is equally vital for preserving the complex function of the forearm axis.

Exhaustive Indications and Contraindications

Operative vs Non-Operative Decision Making

The decision to pursue operative intervention versus non-operative management for a distal radius fracture is one of the most nuanced exercises in orthopedic traumatology. Non-operative management, typically consisting of closed reduction and cast immobilization, is generally reserved for stable, extra-articular fractures with minimal displacement, or for low-demand, elderly patients whose medical comorbidities preclude safe surgical intervention. The goal of non-operative treatment is to maintain an acceptable radiographic alignment while prioritizing early functional rehabilitation to prevent stiffness.

Operative intervention is strongly indicated for fractures that are inherently unstable and cannot be maintained in an acceptable position within a cast. The classic radiographic criteria for instability, originally described by Lafontaine, include initial dorsal angulation greater than 20 degrees, dorsal comminution, intra-articular extension, associated ulnar fractures, and patient age over 60 years. Modern indications for surgery also focus heavily on the prevention of post-traumatic arthritis and the restoration of grip strength. Absolute radiographic indications for surgery typically include radial shortening greater than 3 to 5 millimeters, dorsal tilt exceeding 10 degrees past neutral, and intra-articular step-off or gap greater than 2 millimeters.

Patient-specific factors are equally critical in the decision-making process. A young, high-demand manual laborer or an elite athlete will have a much lower threshold for surgical fixation to ensure anatomical restoration and rapid return to function. Conversely, an 85-year-old patient with severe dementia and low functional demands may be best served with a period of brief immobilization followed by early motion, even in the presence of a malaligned fracture, as the risks of surgery and anesthesia may outweigh the functional benefits. The surgeon must engage in shared decision-making, clearly articulating the risks of malunion (e.g., weakness, visible deformity, future arthritis) versus the risks of surgery (e.g., nerve injury, tendon rupture, infection).

Furthermore, the presence of concomitant injuries heavily skews the algorithm toward surgical stabilization. A distal radius fracture associated with an acute compartment syndrome, an open fracture with soft tissue compromise, or a concomitant scaphoid fracture (a "floating carpus") represents an absolute indication for immediate operative intervention. Similarly, an acute, progressive median neuropathy (acute carpal tunnel syndrome) in the setting of a displaced fracture necessitates urgent reduction and fixation, often combined with a formal carpal tunnel release.

Absolute and Relative Contraindications

While surgical fixation is highly effective, it is not universally appropriate. Absolute contraindications to the internal fixation of distal radius fractures are relatively rare but must be strictly respected. Active, untreated local or systemic infection is an absolute contraindication to the placement of orthopedic hardware. In such scenarios, if the fracture is highly unstable, management must pivot to external fixation or temporary splinting until the infectious process is eradicated. Additionally, patients who are medically unstable—such as those in multi-system organ failure or those with severe, unoptimized cardiopulmonary disease who cannot tolerate anesthesia—should not undergo elective or semi-elective internal fixation.

Relative contraindications require a careful balancing of risks and benefits. Severe osteopenia or osteoporosis is a significant relative contraindication for traditional non-locking plates, as the screws will inevitably fail to achieve adequate purchase in the metaphyseal bone. However, the advent of fixed-angle volar locking plates has largely mitigated this issue, allowing for stable fixation even in poor bone stock. Another relative contraindication is the presence of a highly contaminated open wound; in these cases, staged management with initial debridement, external fixation, and delayed internal fixation once the soft tissue envelope has recovered is the prudent course of action.

Severe baseline cognitive impairment or psychiatric non-compliance is a critical relative contraindication. Post-operative success relies heavily on the patient's ability to adhere to weight-bearing restrictions and participate actively in rehabilitation protocols. A patient who cannot comprehend instructions may prematurely load the wrist, leading to catastrophic hardware failure or loss of reduction. In such populations, more robust fixation constructs, prolonged casting, or accepting a non-operative malunion may be the safest alternatives.

Finally, the condition of the local soft tissue envelope dictates surgical timing and feasibility. Massive fracture blisters, severe edema, or compromised skin integrity over the planned surgical incision site are strong relative contraindications to immediate open reduction and internal fixation (ORIF). Operating through compromised skin drastically increases the risk of deep surgical site infections and wound dehiscence. The surgeon must exercise patience, utilizing temporary splinting, elevation, and closed reduction until the soft tissues declare themselves amenable to surgical incision, indicated by the return of skin wrinkles and the resolution of fracture blisters.

Indications and Contraindications Table

Pre-Operative Planning, Templating, and Patient Positioning

Advanced Imaging and 3D Templating

The foundation of a successful surgical outcome begins long before the first incision, rooted in meticulous pre-operative planning and advanced imaging. Standard orthogonal radiographs—comprising posteroanterior (PA), true lateral, and oblique views—are the initial standard of care. The PA view allows for the assessment of radial height, radial inclination, and ulnar variance, while the true lateral view is critical for evaluating volar tilt and the alignment of the carpus with the longitudinal axis of the radius. Oblique views are particularly useful for delineating radial styloid fractures and assessing the integrity of the DRUJ.

However, in the presence of intra-articular extension or severe comminution, plain radiographs often underestimate the complexity of the fracture pattern. In these scenarios, a high-resolution computed tomography (CT) scan is absolutely paramount. CT imaging provides a multi-planar reconstruction of the articular surface, allowing the surgeon to identify hidden die-punch fragments, assess the degree of central articular depression, and evaluate the integrity of the volar and dorsal cortices. The axial cuts are especially crucial for assessing the sigmoid notch and determining if a separate dorsal or volar ulnar corner fragment exists, which may require specialized fragment-specific fixation.

Modern orthopedic practice increasingly utilizes 3D templating software to map out the surgical strategy. By importing the patient's CT data, the surgeon can virtually reduce the fracture fragments and trial various implant sizes and configurations. This digital pre-operative run-through allows for the precise selection of plate width, length, and screw trajectory, minimizing intra-operative trial and error. Templating is particularly vital when dealing with complex, multi-fragmentary Melone type IV fractures, ensuring that every critical articular fragment is captured by a locking screw or a dedicated buttress pin.

Furthermore, templating aids in anticipating the need for adjunctive procedures. If the CT scan reveals a massive metaphyseal void following virtual reduction, the surgeon can pre-operatively plan for the harvesting of autologous iliac crest bone graft or the utilization of osteoinductive allografts/synthetics. Anticipating these needs ensures that the patient is consented appropriately, the necessary equipment is available in the operating theater, and the surgical time is optimized, thereby reducing the duration of tourniquet inflation and anesthesia.

Patient Optimization and Anesthesia

Patient optimization prior to surgery is a multidisciplinary effort, particularly in the elderly demographic where comorbidities are prevalent. While distal radius fractures are rarely life-threatening, the stress of surgery and anesthesia can exacerbate underlying cardiovascular or pulmonary conditions. A thorough pre-operative medical evaluation is required, focusing on optimizing glycemic control in diabetics, managing hypertension, and addressing any anticoagulation protocols. For patients on chronic blood thinners, a coordinated plan to bridge or hold these medications must be established to minimize intra-operative bleeding and post-operative hematoma formation without placing the patient at undue thromboembolic risk.

The choice of anesthesia is a critical component of the surgical plan and is typically determined through a collaborative discussion between the surgeon, the anesthesiologist, and the patient. Regional anesthesia, specifically a supraclavicular or axillary brachial plexus block, has become the gold standard for distal radius fracture surgery. Regional blocks provide profound intra-operative muscle relaxation, which greatly facilitates fracture reduction, while simultaneously offering excellent post-operative analgesia, significantly reducing the need for systemic opioids.

General anesthesia is generally reserved for patients who have contraindications to regional blocks, such as localized infection at the injection site, pre-existing severe peripheral neuropathies, or extreme patient anxiety. In some cases, a combined approach is utilized, where a regional block is placed for post-operative pain control, and a light general anesthetic or deep intravenous sedation is administered to ensure patient comfort and immobility during the procedure. The use of a pneumatic tourniquet is standard practice to provide a bloodless surgical field, and the regional block helps mitigate the severe ischemic pain associated with prolonged tourniquet inflation.

In the immediate pre-operative holding area, the surgical site must be meticulously marked, and a formal "time-out" is conducted to verify the patient's identity, the correct operative extremity, and the planned procedure. Prophylactic intravenous antibiotics, typically a first-generation cephalosporin (or appropriate alternatives for allergic patients), must be administered within one hour prior to the surgical incision to minimize the risk of surgical site infection. This rigorous pre-operative checklist ensures a safe and highly coordinated transition into the operating theater.

Operative Setup and Positioning

Proper patient positioning and operating room setup are critical for maximizing surgical efficiency and ensuring unimpeded fluoroscopic access. The patient is typically positioned supine on a standard operating table. The operative extremity is extended onto a radiolucent hand table. It is imperative that the hand table is completely radiolucent and free of metallic supports beneath the wrist, as these will obscure the fluoroscopic images critical for assessing articular reduction and hardware placement.

The positioning of the fluoroscopy unit (C-arm) must be coordinated before the patient is prepped and draped. The C-arm is usually brought in from the foot of the bed or parallel to the hand table, allowing the surgeon to easily rotate the machine between PA and lateral projections without breaking the sterile field. The monitor should be placed directly across from the surgeon, ensuring an ergonomic line of sight. Establishing a smooth workflow with the radiology technician prior to the incision saves valuable tourniquet time and minimizes frustration during the critical phases of fracture reduction.

A well-padded pneumatic tourniquet is applied to the proximal brachium. The arm is exsanguinated using an Esmarch bandage, and the tourniquet is typically inflated to 250 mmHg or 100 mmHg above the patient's systolic blood pressure. The surgeon must be acutely aware of the tourniquet time, aiming to complete the procedure within 90 to 120 minutes to prevent ischemic injury to the peripheral nerves and musculature. If the surgery extends beyond this window, the tourniquet must be deflated for a period of reperfusion before re-inflation.

The surgical prep involves a meticulous scrub of the entire hand, wrist, and forearm, extending up to the level of the tourniquet. The draping must allow for full, unrestricted manipulation of the elbow, forearm, and wrist. The ability to freely pronate and supinate the forearm, as well as flex and extend the wrist, is absolutely essential for achieving anatomical reduction, assessing DRUJ stability, and obtaining true orthogonal fluoroscopic views. Any restriction in the draping can compromise the surgeon's ability to execute these critical maneuvers.

Step-by-Step Surgical Approach and Fixation Technique

The Modified Henry Approach (Volar)

The volar approach to the distal radius, specifically the modified Henry approach, has become the undisputed workhorse in modern orthopedic trauma surgery. This approach exploits the internervous and intermuscular plane between the flexor carpi radialis (FCR), innervated by the median nerve, and the radial artery. The patient's arm is supinated, and a longitudinal incision is made directly over the course of the FCR tendon, typically extending 8 to 10 centimeters proximally from the distal wrist crease. The incision can be gently curved or zig-zagged across the wrist crease to prevent scar contracture.

Upon incising the skin and subcutaneous tissues, the superficial fascia of the FCR is identified and longitudinally incised. The FCR tendon is meticulously retracted ulnarly, which serves to protect the underlying median nerve and the palmar cutaneous branch. The deep fascial sheath forming the floor of the FCR tendon is then incised, granting access to the deep volar compartment. The radial artery must be identified and carefully protected radially; its delicate venae comitantes are prone to bleeding if roughly handled. Retractors are placed to maintain this interval, exposing the underlying flexor pollicis longus (FPL) tendon and the pronator quadratus (PQ) muscle.

The PQ muscle is the final soft tissue barrier to the volar surface of the distal radius.