Wrist Implant Arthroplasty

Introduction and Epidemiology

The wrist is a highly complex, multi-articulated joint that is frequently subject to end-stage joint degeneration. Historically, the most common etiology for severe pan-carpal arthritis was rheumatoid arthritis (RA). However, with the advent and widespread success of disease-modifying antirheumatic drugs (DMARDs) and advanced biologic therapies, the incidence of severe rheumatoid wrist deformities requiring surgical intervention has steadily and significantly declined. Consequently, osteoarthritis (OA) and post-traumatic arthritis have emerged as the predominant indications for major wrist reconstructive procedures in contemporary orthopedic practice. Common post-traumatic etiologies precipitating pan-carpal degeneration include scaphoid nonunion advanced collapse (SNAC), scapholunate advanced collapse (SLAC), and intra-articular distal radius fractures resulting in severe chondral degradation and secondary incongruity.

For decades, the gold standard for the surgical management of end-stage pan-carpal arthritis has been complete wrist arthrodesis. While total wrist arthrodesis provides highly reliable pain relief, durable stability, and definitive correction of coronal and sagittal deformities, it entirely sacrifices radiocarpal and midcarpal motion. This substantial functional loss is particularly debilitating for patients with bilateral wrist arthritis or polyarticular disease affecting the elbows and shoulders, where compensatory upper extremity kinematics are already severely compromised.

Total wrist arthroplasty (TWA) serves as a motion-preserving alternative to arthrodesis. The primary objective of TWA is to provide excellent pain relief while retaining sufficient motion and grip strength to perform essential activities of daily living (ADLs). Extensive biomechanical studies indicate that the vast majority of ADLs require a functional arc of motion comprising 40 degrees of extension, 40 degrees of flexion, 40 degrees of combined radioulnar deviation, and intact forearm rotation.

The historical trajectory of wrist arthroplasty has been fraught with biomechanical and biomaterial challenges. Early generations of implants, including Swanson silicone spacers and early cemented articulated designs (e.g., Meuli and Volz), demonstrated unacceptably high rates of long-term failure secondary to silicone synovitis, particulate debris-induced osteolysis, implant subsidence, and catastrophic loosening. However, continuous advancements over the past four decades have revolutionized implant design. Modern third- and fourth-generation implants feature critical biomechanical improvements designed to mitigate these historical failure modes, including:
* Distal component fixation primarily within the robust carpus rather than extending deeply into the metacarpal shafts, significantly reducing deleterious lever-arm forces.
* Intercarpal fusion elements designed to provide broad, solid structural support for the distal component.
* Screw augmentation for enhanced initial carpal component fixation.
* Minimal bone resection techniques engineered to preserve the native center of rotation and maintain soft tissue tension.
* Strict preservation of the volar wrist capsule and essential extrinsic ligamentous stabilizers.
* Cementless, porous-coated fixation surfaces to encourage durable osteointegration.
* Broad, semiconstrained ellipsoid articulations that closely mimic native wrist kinematics and permit coupled motion.

Currently, several total wrist implant systems are utilized in modern orthopedic practice, including the Re-Motion (Small Bone Innovations/Stryker), Maestro (Biomet), Universal 2 (Integra LifeSciences), and the Freedom wrist system (Integra LifeSciences). Through improved biomaterials and precise instrumentation, TWA has emerged as a highly viable, evidence-based option for appropriately selected patients.

Surgical Anatomy and Biomechanics

A profound understanding of wrist anatomy and kinematics is paramount for the successful execution of total wrist arthroplasty. The wrist joint complex consists of the distal radial articular surface, the distal ulna, the triangular fibrocartilage complex (TFCC), eight carpal bones arranged in proximal and distal rows, and the bases of the five metacarpals.

Osteology and Articulations

The wrist comprises four major articulations: the radiocarpal joint, the midcarpal joint, the carpometacarpal (CMC) joints, and the distal radioulnar joint (DRUJ). The radiocarpal joint is formed by the articulation of the scaphoid and lunate with the elliptical scaphoid and lunate fossae of the distal radius. The midcarpal joint represents the complex, undulating articulation between the proximal row (scaphoid, lunate, triquetrum) and the distal row (trapezium, trapezoid, capitate, hamate).

In modern TWA, the proximal carpal row is routinely resected to accommodate the implant articulation and decompress the joint. The distal carpal row, specifically the capitate and occasionally the hamate, serves as the foundational bed for the distal component. The capitate is the keystone of the carpal arch and represents the primary site for central peg insertion in current TWA designs.

Ligamentous Stabilizers

Wrist stability is governed by a complex array of intrinsic (interosseous) and extrinsic ligaments. Extrinsic ligaments connect the radius or ulna to the carpus, while intrinsic ligaments originate and insert entirely within the carpus.
* Volar Extrinsic Ligaments: These are robust, thick structures that provide the primary restraint to carpal subluxation. Key structures include the radioscaphocapitate (RSC) ligament, the long radiolunate (LRL) ligament, and the short radiolunate (SRL) ligament. Preservation of the volar capsule and these volar radiocarpal ligaments during TWA is critical; their violation inevitably leads to volar instability and dorsal subluxation of the implant.
* Dorsal Extrinsic Ligaments: The dorsal radiocarpal (DRC) ligament and the dorsal intercarpal (DIC) ligament form a V-shaped stabilizing complex. The standard surgical approach for TWA necessitates capsulotomy through the dorsal capsule; meticulous, tensioned repair of this layer is required to restore dorsal stability and prevent postoperative dislocation.

Wrist Biomechanics and Implant Kinematics

The native center of rotation of the wrist is located within the proximal pole of the capitate. Recreating this center of rotation in all three planes is the primary biomechanical goal of TWA. If the joint line is elevated (distalized) or depressed (proximalized), the moment arms of the extrinsic flexor and extensor tendons are fundamentally altered. This leads to joint imbalance, limited range of motion, and accelerated implant wear due to eccentric loading.

Native wrist motion does not occur in pure orthogonal planes. Instead, functional motion predominantly follows the "dart thrower's motion" (DTM) path, coupling radial extension with ulnar flexion. Modern semiconstrained ellipsoid implants are designed to permit this coupled motion while providing sufficient constraint to prevent dislocation. Load transfer across the native wrist is distributed approximately 80% through the radius and 20% through the ulna via the TFCC. TWA alters this load distribution, concentrating compressive and shear forces across the radial and carpal implant interfaces. Therefore, achieving rigid initial press-fit fixation and subsequent biologic osteointegration of the components is essential to prevent subsidence. Historically, the distal component has been the most vulnerable to aseptic loosening due to the substantial shear forces exerted during grip and lifting.

Indications and Contraindications

Patient selection is the single most critical determinant of long-term success and survivorship in total wrist arthroplasty. TWA is not a universal solution for wrist arthritis; it is a highly specific, salvage-level procedure tailored for patients who require motion preservation but place low mechanical demands on the joint.

Ideal candidates are typically older, low-demand individuals with end-stage pan-carpal arthritis. Patients with polyarticular rheumatoid arthritis are classic candidates, as preservation of wrist motion facilitates essential personal hygiene and the use of assistive ambulatory devices (e.g., platform walkers). Bilateral wrist arthritis is a strong indication for TWA on at least one side to prevent the severe functional limitations associated with bilateral arthrodesis.

Conversely, TWA is strictly contraindicated in high-demand patients, heavy manual laborers, and individuals who require the use of impact tools or assistive devices that place axial loads through the palm (e.g., standard canes or crutches). In these populations, the shear forces placed across the implant will inevitably lead to early catastrophic failure, osteolysis, and loosening. Total wrist arthrodesis remains the definitive procedure of choice for young, active, or high-demand patients.

Operative vs Non-Operative Management Table

Pre Operative Planning and Patient Positioning

Thorough preoperative planning is essential to anticipate bone stock deficiencies, select appropriate implant sizing, and determine the requirement for concomitant procedures (e.g., DRUJ arthroplasty, Darrach procedure, Sauvé-Kapandji procedure, or extensor tendon transfers).

Imaging and Templating

Standard preoperative imaging includes high-quality posteroanterior (PA), lateral, and oblique radiographs of the affected wrist. The PA view is utilized to assess the coronal alignment of the carpus relative to the radius and to evaluate the bone stock of the distal radius, capitate, and third metacarpal. The lateral view is critical for assessing sagittal alignment, volar subluxation of the carpus, and the presence of a dorsal intercalated segment instability (DISI) or volar intercalated segment instability (VISI) deformity.

In cases of significant post-traumatic deformity, previous hardware, or severe rheumatoid osteopenia, a computed tomography (CT) scan without contrast is highly recommended. CT provides a three-dimensional assessment of the intramedullary canals of the radius and third metacarpal, ensuring that the stems of the components can be accommodated without iatrogenic fracture or cortical perforation.

Digital templating is performed to estimate the size of the radial and carpal components. The surgeon must ensure that the radial component will rest securely on the cortical rim of the distal radius without excessive dorsal, volar, or radial overhang, which could impinge on extensor tendons or soft tissues. The carpal component template must align the center of rotation of the implant with the anatomic center of rotation (the proximal pole of the native capitate).

Patient Positioning and Setup

The patient is positioned supine on the operating table with the operative extremity extended on a radiolucent hand table. A well-padded pneumatic tourniquet is applied to the proximal arm. Prophylactic intravenous antibiotics are administered prior to tourniquet inflation. The arm is prepped and draped in a standard sterile fashion. Intraoperative fluoroscopy (C-arm) is positioned either parallel or perpendicular to the hand table, ensuring unimpeded orthogonal views of the wrist can be obtained throughout the procedure without compromising the sterile field.

Detailed Surgical Approach and Technique

The surgical execution of a total wrist arthroplasty demands meticulous soft tissue handling, precise bone resection, and rigorous attention to implant alignment. Deviations in technique can lead to rapid implant failure or severe instability.

Dorsal Surgical Approach

A longitudinal dorsal incision is made, centered precisely over Lister's tubercle, extending approximately 5 cm proximal and 5 cm distal to the radiocarpal joint. Full-thickness fasciocutaneous flaps are elevated, taking care to identify and protect the dorsal sensory branches of the radial and ulnar nerves.

The extensor retinaculum is exposed. The third extensor compartment is opened, and the extensor pollicis longus (EPL) tendon is mobilized and transposed radially. The retinaculum is then elevated as a radially based or ulnarly based flap, exposing the second compartment (extensor carpi radialis longus and brevis) and the fourth compartment (extensor digitorum communis and extensor indicis proprius). These tendons are retracted to expose the underlying dorsal wrist capsule. A thorough tenosynovectomy is performed if rheumatoid pannus is present.

Capsulotomy and Joint Exposure

A robust capsulotomy is essential for subsequent closure and joint stability. A distally based, rectangular capsular flap is typically elevated from the distal radius, reflecting the dorsal radiocarpal and dorsal intercarpal ligaments distally to expose the radiocarpal and midcarpal joints. Meticulous preservation of the volar capsule is mandatory; the volar ligaments must remain completely intact to prevent volar instability and support the implant against subsidence.

Bone Resection

The proximal carpal row (scaphoid, lunate, and triquetrum) is excised. This can be facilitated by using a threaded Steinmann pin as a joystick in each bone, combined with sharp dissection and a rongeur. Extreme care is taken not to violate the volar capsule during the excision of the lunate and scaphoid.

Attention is then directed to the distal radius. Using the system-specific cutting guide, an oscillating saw is used to resect the articular surface of the distal radius. The cut is typically made perpendicular to the long axis of the radius in both the coronal and sagittal planes. The amount of bone resected should be minimal—only enough to provide a flat, bleeding cancellous bed for the radial component. If the DRUJ is severely arthritic, a concurrent Darrach resection or Sauvé-Kapandji procedure may be performed; otherwise, the sigmoid notch is preserved.

The distal carpal row is prepared next. The proximal pole of the capitate is resected to create a flat surface. Depending on the specific implant system, the articular surfaces between the capitate, hamate, and trapezoid may be decorticated to promote intercarpal fusion, which provides a rigid, unified foundation for the distal component.

Canal Preparation and Trialing

The intramedullary canal of the radius is sequentially broached to accommodate the radial stem. The broach must be aligned with the anatomic axis of the radius to prevent coronal or sagittal malalignment. Similarly, the central peg of the carpal component is prepared by drilling or broaching into the capitate and, if required by the design, down into the intramedullary canal of the third metacarpal.

Trial components are inserted. A trial reduction is performed, and the wrist is taken through a full range of motion under fluoroscopic guidance. The surgeon must critically assess for:
1. Impingement: Ensure the carpal component does not impinge on the radius during maximum extension or radial/ulnar deviation.
2. Stability: The joint should not subluxate volarly or dorsally during motion.
3. Tension: The soft tissues should be appropriately tensioned. If the joint is excessively tight, further bone resection may be necessary. If it is too loose, a thicker polyethylene bearing or a larger component may be required to restore the joint line.

Final Implantation and Closure

Once optimal sizing and balance are confirmed, the trial components are removed. Copious pulsatile irrigation is performed to remove bone debris. The definitive implants are inserted. Modern systems primarily utilize cementless, porous-coated stems for biologic fixation, relying on a press-fit technique. If bone stock is severely compromised (e.g., severe RA with cystic changes), polymethylmethacrylate (PMMA) bone cement may be utilized for immediate fixation.

The polyethylene bearing is engaged. A final fluoroscopic check confirms component seating, alignment, and absence of fracture. The dorsal capsule is meticulously repaired using heavy non-absorbable sutures. A robust capsular closure is critical to prevent postoperative dislocation. The extensor retinaculum is repaired over the EDC tendons to prevent bowstringing, leaving the EPL transposed in the subcutaneous tissue. The skin is closed in layers, and a bulky, well-padded short-arm splint is applied with the wrist in neutral alignment.

Complications and Management

Despite significant advancements in implant design, total wrist arthroplasty remains a technically demanding procedure with a distinct complication profile. The surgeon must be prepared to identify and manage both early and late complications.

Aseptic Loosening and Subsidence

Aseptic loosening is the most common long-term complication and the primary reason for revision surgery. It most frequently affects the distal (carpal) component. The etiology is multifactorial, including stress shielding, particulate wear debris (polyethylene disease) leading to macrophage-induced osteolysis, and excessive shear forces due to patient non-compliance with lifting restrictions. Radiographically, loosening presents as progressive radiolucent lines, component subsidence, or a change in component alignment. Management of symptomatic loosening typically requires revision arthroplasty if adequate bone stock remains, or conversion to a total wrist arthrodesis utilizing a robust dorsal spanning plate and structural bone grafting (e.g., iliac crest autograft).

Instability and Dislocation

Dislocation or subluxation usually occurs early in the postoperative period. It is frequently the result of soft tissue imbalance, specifically failure of the dorsal capsular repair, or coronal/sagittal malalignment of the components. Volar dislocation may occur if the volar extrinsic ligaments were iatrogenically injured during proximal row resection. Management of acute dislocation involves prompt closed reduction and prolonged immobilization. Recurrent instability necessitates surgical exploration, capsular reconstruction, and potentially revision of malpositioned components to restore appropriate soft tissue tension.

Periprosthetic Fracture

Intraoperative fractures can occur during broaching or press-fit stem insertion, particularly in the osteopenic radius or third metacarpal. These must be recognized intraoperatively and managed with cerclage wiring or conversion to a cemented, longer-stemmed implant. Postoperative periprosthetic fractures resulting from trauma are managed based on fracture location and component stability, often requiring open reduction and internal fixation (ORIF) with specialized periprosthetic plating systems.

Summary of Complications

Post Operative Rehabilitation Protocols

The postoperative rehabilitation protocol is a delicate balance between protecting the soft tissue repair and initiating early motion to prevent arthrofibrosis. Patient compliance with lifelong restrictions is mandatory for implant survivorship.

Phase I: Immediate Postoperative (0 - 2 Weeks)

The wrist is immobilized in a bulky, rigid short-arm splint or cast applied in the operating room. The wrist is positioned in neutral to slight extension to relieve tension on the dorsal capsular repair. The patient is instructed to keep the extremity elevated to minimize edema. Immediate active range of motion of the digits, thumb, elbow, and shoulder is encouraged to prevent stiffness and reduce swelling. No active or passive wrist motion is permitted during this phase to allow the dorsal capsular repair to heal.

Phase II: Early Motion (2 - 6 Weeks)

At the two-week postoperative mark, the surgical dressings and sutures are removed. The patient is transitioned to a custom-molded thermoplastic wrist orthosis. Under the strict guidance of a certified hand therapist, gentle active and active-assisted range of motion of the wrist (flexion, extension, radial/ulnar deviation) is initiated. The orthosis is worn at all times except during therapy sessions and hygiene. Forceful gripping, weight-bearing through the hand, and passive stretching are strictly prohibited to protect the implant interfaces while biologic osteointegration occurs.

Phase III: Strengthening and Transition (6 - 12 Weeks)

Radiographs are obtained at 6 weeks to confirm component position and absence of early subsidence. If clinical and radiographic progression is satisfactory, the orthosis is gradually weaned for light ADLs but retained for sleep and higher-risk activities. Gentle isometric strengthening may begin, but aggressive strengthening is avoided. The focus remains on maximizing functional range of motion, particularly the dart thrower's arc, rather than maximizing grip strength.

Long-Term Maintenance

By 12 weeks, patients are typically discharged from formal therapy. However, the surgeon must explicitly counsel the patient regarding lifelong activity modifications. To ensure the durability of the arthroplasty, patients are permanently restricted from lifting objects greater than 10 to 15 pounds with the operative extremity. Repetitive impact activities (e.g., hammering, golf, tennis) and axial loading (e.g., pushing up from a chair using the palm) must be avoided indefinitely to prevent accelerated wear and catastrophic loosening.

Summary of Key Literature and Guidelines

The evolution of total wrist arthroplasty is well-documented in the orthopedic literature. While early generations of implants yielded disappointing long-term results, data regarding third- and fourth-generation implants demonstrate significant improvements in survivorship and patient-reported outcomes.

Registry data, particularly from the Scandinavian registries (e.g., Boeckstyns et al.), have demonstrated that modern TWA implants yield a 5-year survivorship exceeding 90%. However, survivorship tends to decline to approximately 70-80% at 10 to 15 years, primarily due to distal component loosening. Comparative studies between TWA and total wrist arthrodesis consistently show that while arthrodesis provides superior grip strength and durability, TWA offers significantly higher patient satisfaction scores in cohorts requiring bilateral intervention or suffering from polyarticular disease. Current clinical guidelines emphasize that rigorous patient selection, precise surgical technique focusing on soft-tissue balance, and strict adherence to postoperative weight-bearing restrictions are the most critical factors in achieving successful, long-term outcomes in wrist implant arthroplasty.