Joel C. Klena, Andrew K. Palmer, and James W. Strickland
DEFINITION
In the past, the gold standard for the treatment of end-stage wrist degeneration and debilitating pain was fusion of the wrist joint. As a salvage procedure, arthrodesis can provide reasonable pain relief and relative preservation of upper extremity function. Unfortunately, fusion of the painful wrist does not guarantee pain relief, nor does it come without functional impairment.7,9,12,17,18
In contrast, total wrist arthroplasty provides an attractive motion- and function-sparing alternative to wrist arthrodesis. Pain relief is achieved, along with preservation of wrist motion and function.2,10,11
Multiple studies have demonstrated that patients consistently prefer motion-sparing procedures over arthrodesis.1,5,8,16
In much the same vein as arthroplasty efforts in the other major joints, early wrist replacement designs were successful in both relieving pain and maintaining function. Unfortunately, early wrist prostheses failed to achieve the long-term survivorship results provided by joint replacements in the shoulder, hip, and knee joints.
Early prosthetic designs suffered from significant biomechanical design flaws. Difficulties arose with implant centering, balance, and fixation.
Significant improvements in implant design have capitalized on modularity, better material considerations, and improved anatomic designs to provide improved longevity.
Current designs strive to achieve the following:
A more anatomic wrist joint than previous wrist designs, either through component design or implant instrumentation
Stable distal fixation by using screw fixation into the carpus while at the same time avoiding the lever arm created by a stem inserted into the third metacarpal
The three most popular wrist designs in the United States today are the Universal 2 (KMI/Integra), the Re-Motion (Small Bone Innovations [SBI]), and the Maestro (Biomet) (FIG 1).
The Universal 2 Total Wrist prosthesis is an improved version of the original wrist of the late Dr. Jay Menon (FIG 1A). A great debt of gratitude is owed to Dr. Menon for popularizing distal screw fixation to the carpus.
The Uni2 design uses a flat carpal cut, screw fixation distally into both the second metacarpal and hamate, and a modular, distally based polyethylene cap that articulates with a proximal cobalt chrome radial component. The improved design attempts to preserve the distal radioulnar joint (DRUJ).
The Uni2 wrist is the prosthesis with which there is the greatest clinical experience to date. The results are encouraging.4
The Re-Motion Total Wrist is essentially the prosthesis marketed initially by Avanta and then SBI with new and improved instrumentation (FIG 1B). It is fundamentally a prosthesis designed to resurface the distal radius.
A concave, cobalt chrome radial component articulates with a convex, distally based, polyethylene cap snapped over a flat carpal plate. The carpal plate is anchored to the carpus with a radial screw that does not penetrate the second metacarpal, and a second screw placed ulnarly. About 15 degrees of “wiggle” or intended motion is built into the snap fit of the polyethylene cap with the carpal plate. No attempt is made to preserve the DRUJ with this implant.
FIG 1 • A. Universal 2 total wrist replacement. B. Re-Motion total wrist replacement. C,D. Maestro (Biomet) wrist replacement.
Many Re-Motion wrist replacements have been performed in conjunction with ulnar head replacement arthroplasty. Preliminary results with the Re-Motion wrist are encouraging.3
The Maestro Wrist is the most recent implant to enter the wrist joint replacement market (FIG 1C,D). It differs significantly in design from the Uni2 and the Re-Motion wrists, having been conceived to resemble successful total hip, knee, and shoulder designs, which use a metal convex component articulating with a concave polyethylene component.
The convex metallic distal component articulates with the proximally based, concave polyethylene body. This UPMWPE body is direct compression molded onto a cobalt chrome (CoCr) alloy radial body with a modular titanium stem. The distal component is composed of a CoCr alloy carpal plate (with or without scaphoid augment) and carpal body and a titanium capitate stem. All components are modular.
Unlike the Uni2 and the Re-Motion wrists, it is not always necessary to attempt fusion of the distal pole of the scaphoid to the surrounding carpus. The Maestro Wrist has a provision to replace the entire scaphoid using a carpal plate incorporating a modular radial augment.
The modular radial stem component is designed to fill the distal radius canal to prevent loosening and provide stability. The instrumentation used to prepare the distal radius is designed to preserve the DRUJ.
The excitement over these three wrist replacement systems has stimulated other investigators to work with companies in producing a total wrist replacement. These other wrist replacement systems are in various stages of design but offer promise for even further advancement of the technology.
ANATOMY
The wrist joint consists of the distal radial articular surface, the distal ulna and triangular fibrocartilage complex, eight carpal bones arranged into proximal and distal rows, and five metacarpal bases.
Four significant articulations exist: the radiocarpal joint, the midcarpal joint, the carpometacarpal joints, and the DRUJ. A combination of interosseous, intrinsic, and extrinsic ligaments provides stabilization (FIG 2).
The proximal row of the carpus articulates with the distal radius to form the radiocarpal joint. The distal carpal row articulations with the metacarpal bases form the carpometacarpal joints. Within the distal carpal row, the center of wrist motion is located at the head of the capitate, slightly palmar to the center of the head. This center of rotation may or may not be colinear with the third metacarpal shaft, depending on each patient's anatomy.
Proximally, the center of wrist motion lies ulnar to the radial intramedullary canal. Normal anatomic parameters of the distal radial articular surface include a volar tilt of 11 degrees and a radial inclination of 22 degrees.
The sigmoid notch of the distal radius provides the articulation for the DRUJ. Strong dorsal and palmar radioulnar ligaments provide DRUJ stability.
FIG 2 • Anatomy of the carpus. L, lunate; S, scaphoid; T, triquetrum.
PATHOGENESIS
End-stage wrist degeneration, a common endpoint of multiple pathways, involves loss of joint space and carpal collapse. The primary indication for total wrist arthroplasty is joint destruction secondary to the effects of rheumatoid arthritis.
The classic pattern of deformity and destruction involves the radiocarpal and midcarpal joints and the DRUJ. Attenuation of the extrinsic wrist ligaments destabilizes the carpus, often resulting in an ulnar and volar translation of the wrist (FIG 3).6
Joint replacement is also indicated to manage the pain, deformity, and loss of motion coincident with end-stage arthritis resulting from osteoarthritis, posttraumatic arthritis, or avascular necrosis. Total wrist arthroplasty can provide a salvage option for functional deformities such as scapholunate advanced collapse (SLAC) or irreparable trauma to the distal radius or carpus.
FIG 3 • AP and lateral radiographs showing end-stage rheumatoid wrist arthritis.
NATURAL HISTORY
Irrespective of the pathway taken to end-stage wrist joint destruction, the result is a painful wrist with significant limitation of motion and function.
Instability and misalignment are often present, particularly in the presence of rheumatoid arthritis or functional deformities such as SLAC wrist.
PATIENT HISTORY AND PHYSICAL FINDINGS
Preoperative examination reveals decreased range of motion, decreased grip strength, and difficulties with normal activities. Pain is seen throughout the arc of motion as well as at the endpoint of motion.
In patients with rheumatoid arthritis, the gross alignment of the wrist can be dramatic due to carpal collapse, ulnar translation, or volar subluxation.
The ideal patient for wrist implant arthroplasty is one with significant wrist pain and loss of a functional range of wrist motion with preservation of adequate bone stock, a balanced wrist, and intact tendons.
IMAGING AND OTHER DIAGNOSTIC STUDIES
Standard posteroanterior and lateral wrist radiographs provide sufficient imaging for preoperative planning and templating.
DIFFERENTIAL DIAGNOSIS
Sources of end-stage wrist arthritis
Rheumatoid arthritis
Osteoarthritis
Posttraumatic arthritis
Avascular necrosis
Functional deformities (eg, SLAC wrist)
Trauma to the distal radius and carpus
NONOPERATIVE MANAGEMENT
Nonoperative management consists of activity modification, anti-inflammatory medications, and corticosteroid injections.
Supportive bracing may be a useful adjunct at the expense of decreased motion and function.
Persistent pain and loss of function despite conservative measures can be considered a failure of nonoperative treatment and an indication for arthroplasty.
SURGICAL MANAGEMENT
Absolute contraindications to wrist replacement are ongoing or deep infection and septic arthritis of the wrist.
Patients considered for arthroplasty must be capable of understanding the risks and potential benefits of the procedure and be capable of complying with the postoperative protocol.
Relative contraindications to wrist replacement are unstable and markedly collapsed wrists, lack of adequate wrist motors, and significant bone loss.
If instability, deformity, motor power, or bone loss can be corrected, wrist replacement can be successfully performed.
Previous proximal row carpectomy and even previous arthrodesis are not contraindications to wrist replacement, but one should not expect the same postoperative range of motion of the wrist.
Preoperative Planning
Preoperative radiographs are used for templating.
A determination of size can be made for the radial body and stem, the capitate stem, the carpal plate and body, the scaphoid augment, and the radial and ulnar screws.
A gross estimate of the amount of distal radius to be resected can also be made.
Positioning
The procedure is performed on a hand table using a tourniquet, with either general or regional anesthesia.
Approach
A dorsal incision, slightly radial to midline, is made from 4 cm proximal to the radiocarpal joint to the midpoint of the third metacarpal.
Dissection is carried down to the extensor retinaculum.
The third dorsal compartment is opened and the extensor pollicis longus (EPL) tendon is exposed and mobilized radially.
The radial wrist extensors are also exposed and mobilized radially.
The first compartment tendons are mobilized from the distal radius and protected.
The tendons of the fourth and fifth compartments are mobilized ulnarly, without opening their respective compartments.
With the extensor tendons mobilized and retracted radially and ulnarly, the capsule is opened longitudinally and reflected radially and ulnarly, exposing the distal radius and entire carpus to the base of the third metacarpal.
TECHNIQUES
MAESTRO PROSTHESIS
The senior author's personal experience is primarily with the Maestro prosthesis, and thus the technique of the Maestro total wrist arthroplasty is presented here.
Although approved for implantation with cement, most wrists are implanted without cement fixation.
Cement is usually preferred in cases of significant absent bone stock and in revision situations.
Carpal Preparation
Position the carpal resection guide to allow resection of 2 to 3 mm of the capitate head. It is held in position with two 0.062-inch Kirschner wires (TECH FIG 1A,B).
Place the first wire into the capitate neck and the second into the metaphysis of the third metacarpal, ensuring that the guide is parallel to the third metacarpal axis.
TECH FIG 1 • A,B. Carpal resection guide in place. Kirschner wires in the capitate head and third metacarpal metaphysis. C. Insertion of the radial resection guide. D. Scoring of the distal radius resection reference line. E,F.Proximal carpal resection. (A,C–E: Courtesy of Biomet, Warsaw, IN.)
With proper placement, the ulnar guide wing will lie close to the triquetrum–hamate articulation and the radial wing will bisect the scaphoid at its distal third.
Loosen the thumbscrew on the carpal resection guide to allow insertion of the radial resection guide boom (TECH FIG 1C).
With the wrist in neutral, score the radius through the cutting slot in the guide to provide a reference for the distal radial resection (TECH FIG 1D).
Remove the radius resection guide and use the carpal resection guide handle to stabilize the carpal guide during carpal resection.
Cut the scaphoid, capitate head, hamate edge, and triquetrum at a 90-degree angle to the axis of the forearm–jig (TECH FIG 1E,F).
As an alternative, the scaphoid can be completely removed and a carpal plate incorporating a scaphoid augment used.
Capitate Reaming and Selection of Carpal Plate
After removing the carpal resection guide and Kirschner wires, remove the proximal carpus.
Place a guidewire into the capitate at the apex of the resection, directly into the center of the capitate (TECH FIG 2A). This may or may not coincide with the center of the third metacarpal. Attention is focused on the capitate and not the capitate–third metacarpal relation.
Ream the capitate (TECH FIG 2B).
The depth of reaming can be verified under fluoroscopy. A direct indication of the trial stem size is indicated by depth marks on the reamer.
Provisionally determine the trial carpal plate by the curvature and width of the remaining proximal carpal surface. The plate should lie flush with the hamate and proximal capitate surfaces.
Three separate scaphoid augments are available (TECH FIG 2C).
Assemble the plate and stem and insert them into the reamed capitate and onto the resected carpal surface. (TECH FIG 2D).
With adequate plate fitting, alignment is such that a radial screw will easily be inserted into the second metacarpal and an ulnar screw inserted into the hamate.
Radius Resection
Insert a 0.062-inch Kirschner wire directly into the center of the medullary canal of the radius (TECH FIG 3A).
The correct insertion point is in the lower corner of the dorsal-ulnar quadrant of the radius articular surface (TECH FIG 3B). This corresponds to a point near the center of the radius and immediately below the groove of the tubercle of Lister. Correct wire placement is confirmed under fluoroscopy.
TECH FIG 2 • A,B. Capitate reaming over the previously placed guidewire. C. Scaphoid augments. D. Insertion of the trial carpal plate and stem. (A: Courtesy of Biomet, Warsaw, IN.)
TECH FIG 3 • Radial guidewire insertion. A. Kirschner wire insertion. B. Cross-sectional view demonstrating correct entry point to be in line with the radius canal. C,D. Placement of the radial resection guide. E. Chisel guide insertion. F,G. Radial broach insertion. (A–C,E,F: Courtesy of Biomet, Warsaw, IN.)
The perfectly placed Kirschner wire is overdrilled with the cannulated drill bit to a minimum depth of 40 mm.
Remove the Kirschner wire and successively ream the radius by hand until the reamer chatters on the intramedullary canal.
The final reamer is left in the canal and the radius resection guide boom and guide are attached (TECH FIG 3C,D).
Align the proximal portion of the guide over the score mark made on the dorsal cortex and secure it with Kirschner wires.
After removing the reamer and guide boom from the medullary canal, cut the radius.
The saw cut should follow exactly the contour of the resection guide and should not enter the DRUJ, thus maintaining its normal anatomy.
Place the appropriate radius intramedullary guide into the canal and insert the chisel guide until flush with the resected surface (TECH FIG 3E).
Insert the chisel into each side of the guide in sequence and gently tap it until fully seated.
After removing the chisel and guide, remove the chiseled bone from the distal radius. Reinsert the intermedullary guide, and over this, broach the distal radius to the templated size desired (TECH FIG 3F,G).
Trial of Carpal and Radial Components
Insert the previously assembled trial components for the carpal and the radial stem–body assembly (TECH FIG 4A).
With the wrist in full flexion, a standard-size carpal head is snap fit to the carpal plate (TECH FIG 4B).
The wrist is distracted and extended for reduction (TECH FIG 4C). About 2 to 3 mm of joint separation with distraction indicates appropriate tension. The carpal head may be adjusted to a +2 or +4 size until tension is appropriate. Satisfactory radial and ulnar deviation should be demonstrated.
Excessive tissue tension can be remedied with additional radial resection. Distal ulnar impingement can be addressed with a Darrach-type resection of the distal ulna.
Remove the trial components; if the proper tension has been achieved, perform final irrigation.
Carpal Body Insertion and Fixation
Assemble the carpal implant and inject bone cement, if indicated, into the capitate. Insert the stem of the assembled prosthesis into the capitate and impact it.
Insert a single 0.062-inch Kirschner wire into the ulnar screw hole using the drill guide. Verify under fluoroscopy that the wire is directed centrally into the central portion of the hamate.
Insert a second Kirschner wire through the radial screw hole and verify that it is through the trapezoid into the intermedullary canal of the second metacarpal.
Overdrill both Kirschner wires with the cannulated drill bit (TECH FIG 5). Screw depth can be measured directly from the score marks on the drill bit.
Place the appropriate-size screws and verify placement fluoroscopically if needed.
Radial Body Insertion and Fixation
Assemble the radial stem to the radial body. If indicated, inject bone cement into the radius, and impact the stem until fully seated.
Reduce the wrist components and take final radiographs (see Fig 1C).
Closure
Close the wrist capsule and dorsal retinaculum with nonabsorbable sutures.
If the distal ulna was resected, the capsular closure should include a secure closure of the DRUJ.
The placement of a drain before closure is at the surgeon's preference.
Close the skin and place a sterile bulky dressing and palmar splint.
TECH FIG 4 • A. Trial component placement. B. Carpal head attached to carpal plate. C. Reduction of trial components. (Courtesy of Biomet, Warsaw, IN.)
TECH FIG 5 • Drilling for ulnar screw placement. The first screw is placed into the central portion of the hamate. (Courtesy of Biomet, Warsaw, IN.)
POSTOPERATIVE CARE
Early finger motion is begun as allowed by the bulky postoperative bandage. Any drains placed are removed within 24 hours.
The splint is removed at the 1-week follow-up visit and a cast or splint is placed for an additional 1 to 3 weeks.
Splint removal with gentle active motion several times daily is permitted at 2 weeks after surgery.
If a distal ulna resection was performed, the forearm is splinted in neutral rotation for at least 3 weeks before starting forearm rotation exercises.
More vigorous active and passive range of motion is begun at 4 weeks postoperatively.
OUTCOMES
The results of a prospective study evaluating the use of the Universal 2 total wrist replacement in rheumatoid patients showed that this wrist provides good early outcomes in this cohort of patients if severe preoperative wrist laxity is not present.4
The authors reported significant improvement in range of motion and an improvement in the DASH score (Disabilities of the Arm, Shoulder and Hand) of 14 points at 1 year and 24 points at 2 years.
Three prostheses were unstable and required further treatment.
FIG 4 • Postoperative range of motion. A. Flexion. B. Extension. C. Radial deviation. D. Ulnar deviation.
Early results of the Maestro wrist replacement have been encouraging. A recent series of 14 patients with a minimum follow-up of 24 months (average 28 months) revealed that all patients had satisfactory pain relief postoperatively.
Motion (FIG 4) improved from an average of 28 degrees flexion and 27 degrees extension before surgery to 41 and 43 degrees, respectively, postoperatively. Radial and ulnar deviation averaged 19 and 23 degrees, respectively.
No significant complications were noted.15
COMPLICATIONS
Short-term complications include early postoperative wound concerns, superficial infections, and deep infections.
The most significant long-term complication encountered is implant loosening. Loosening is not an immediate indication for revision but does necessitate close clinical and radiographic monitoring for progression.
Implant instability may result from poor component placement, implant loosening, ligamentous instability, or component wear. Each case must be dealt with individually after determining the cause of such instability.
Periprosthetic fracture is also an infrequently seen complication. Two options are available for salvage of loose or fractured prostheses: component revision or wrist arthrodesis.13,14
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