Indications

Physicians may consider the APTIS prosthesis for patients who experience pain and weakness at the DRUJ that is not improved by nonoperative treatment. Findings may include instability of the ulnar head and radiographic evidence of dislocation with erosive changes of the distal radioulnar joint. Nonreducible fracture of the ulnar head with loss of cartilage or neck fracture with loss of substance may be followed by primary replacement of the joint with the prosthesis. In past cases, the prosthesis has been used after failed ulnar head resection (e.g., the Darrach procedure) or after failed ulnar head arthroplasty.

Patient Selection

Ideal candidates are those individuals in whom the DRUJ cannot be reconstructed. Other requirements are good bone stock with no history of infection in the area, no systemic disease, and no allergy to nickel. Patients may receive the prosthesis at any time after the skeleton is mature; the timing depends on the individual. In some cases, an individual may sustain a fracture that destroys the DRUJ and it is possible to do an immediate reconstruction. However, because it is not yet available in every institution, a delay may be required to obtain the prosthesis.

Contraindications

Severe osteoporosis, unresolved osteomyelitis, and systemic disease contraindicate the use of the prosthesis. The use of the implant also is contraindicated when bone, musculature, tendons, or adjacent soft tissue is compromised by disease or infection and would not provide adequate support or fixation for the prosthesis. The implant should not be used in patients who have not reached skeletal maturity.

Surgical Technique

The Prosthesis

The DRUJ prosthesis is a semi-constrained ball-and-socket joint comprising a radial component and an ulnar component (Fig. 37-2).

FIGURE 37-2 The components of the prosthesis: the radial plate, the radial plate cover, two screws, the ulnar stem, and the ultra-high-molecular-weight polyethylene (UHMWP) ball.

The radial component (Fig. 37-3) provides the socket for the joint and consists of two parts that are assembled intraoperatively. The main part is shaped in the form of a plate with a hemi-socket on the distal end. The body of the plate, with its five screw holes, is contoured to fit against the distal 6 to 7 cm of the interosseous crest, in the area of the sigmoid notch. The plate is fixed to the radius by two means. The first is a peg that is driven into the distal radius in an ulnoradial direction, whereas the second method of fixing the plate involves the use of five specially designed 3.5-mm cortical screws. The hemi-socket, which is part of the plate, is directed ulnarward and is designed to receive the ultra-high-molecular-weight polyethylene ball (UHMWP) of the ulnar component. The other half of the socket, a cover, is separate from the radial component and is fixed to its counterpart on the plate by means of two screws. This assembly encloses the UHMWP ball. The radial component is available in two sizes, small (size 20) and large (size 30), which fit with the corresponding sizes of the ulnar component.

FIGURE 37-3 The radial component is assembled intraoperatively to provide a socket. It comprises a contoured plate, a cover, and two screws.

A fluted stem and the UHMWP ball (Fig. 37-4) make up the ulnar component. The ball is placed on the distal end of the stem; this combination replaces the articular surface of the ulnar head. The ulnar stems measure 11 cm in interosseous length, and the distal one third is plasma coated to allow bony ingrowth. A gentle flare at its distal end is present to provide better fixation. The stem is also fluted and slightly tapered to provide rotatory stability and ease of insertion, respectively. The most distal end of the stem bears a highly polished peg or pivot that fits into the hole of the UHMWP ball. The stems are provided in two diameters, 4.5 mm and 5.0 mm, and have correspondingly sized UHMWP balls. Each size couples with the small and large radial components, respectively.

FIGURE 37-4 The ulnar component comprises a fluted stem and an ultra-high-molecular-weight polyethylene (UHMWP) ball.

Preoperative graded radiographs are used to determine whether the large or small prosthesis is most likely needed (Fig. 37-5). Digital radiographs can be used if they have accurate measuring capability. The ulna stem size is determined by measuring the narrowest intramedullary diameter of the ulna in its distal 11 cm. A size is chosen that fits this intramedullary diameter best, leaving behind a minimum of 2 mm of cortical bone surrounding the flare of the distal stem. The length of the stem’s extraosseous neck, if one is needed, can also be determined preoperatively with the help of a radiographic measuring template (Fig. 37-6).

FIGURE 37-5 A graded-scale radiograph is mandatory to select the size of the implant, notably the thickness and length of the ulnar stem. Digital radiographs with a means of measure can also be used.

FIGURE 37-6 An ulnar stem template used with graded-scale radiographs determines stem diameter and length. Lengths vary from standard to 4 cm extended.

Incision Placement and Dissection

The forearm is placed in full pronation and a 9- to 10-cm hockey stick incision is made above the dorsal lateral aspect of the distal ulna, turning radially just distal to the head of the ulna (Fig. 37-7). Dissection can then either follow the interval between the extensor digiti quinti minimi and extensor carpi ulnaris or the interval between the flexor and extensor carpi ulnaris for added protection of the dorsal sensory branch of the ulnar nerve. If the patient has had surgery in the area, the old incision may be incorporated into the exposure. Taking care to protect the dorsal sensory branch of the ulnar nerve, the incision is then carefully deepened. A fascial/retinacular flap can be created to later provide a barrier between the prosthesis and tendons (Fig. 37-8). The extensor carpi ulnaris tendon sheath is then released from the ulnar head to the insertion of the extensor carpi ulnaris. When approaching the ulna between the extensor carpi ulnaris and the extensor digiti quinti, the extensor digiti quinti is elevated from the ulna and interosseous membrane. The extensor mass is also elevated to expose the interosseous crest of the radius.

FIGURE 37-7 A hockey-stick incision is placed on the dorsum of the hand between the extensor carpi ulnaris and the extensor digiti quinti minimi.

FIGURE 37-8 A dorsal fascial flap is elevated to interpose between the prosthesis and the extensor tendons.

If present, the head of the ulna is then excised at a level just proximal to the head (Fig. 37-9). The radial attachment of the TFC, if found intact, is left undisturbed. If left in situ, this structure can provide a buffering barrier between the prosthesis and the carpus. Excising the ulnar head eases exposure of the radius by allowing the ulnar shaft to be retracted volarward.

FIGURE 37-9 The head of the ulna is removed just proximal to the distal radioulnar joint, which allows the ulna to be displaced volarly.

Any osteophytes found in the DRUJ are now excised. The dissection then follows dorsally over the ulna, exposing the dorsal surface of the interosseous membrane. The interosseous membrane is elevated 8 to 9 cm from the distal radius along its interosseous crest.

The trial radial plate is then placed over the interosseous surface of the radius. The distal end of the trial plate should be in the area of the sigmoid notch, with the volar edge of the body of the plate aligned with the volar edge of the radius (Fig. 37-10). In cases with radial deformity or a prominent volar lip, a bur can be used to contour the radius for better trial positioning. A minimum of 3 mm is required to separate the distal end of the trial plate and the radiocarpal joint. This space is needed to prevent carpal impingement during ulnar deviation. Proximal positioning is limited by radial width because the radial plate peg is designed to remain within the radius. The volar-facing edge of the trial plate should be on the same plane as the volar surface of the radius. Positioning of the trial plate should also ensure that the plate is not tilted dorsalward or volarward.

FIGURE 37-10 The trial radial plate is positioned on the radius. Contouring of the radius, if necessary, can be performed with a bur.

Temporary fixation of the trial plate can be accomplished by using 0.045-inch Kirschner wires (K-wires). Both posteroanterior and lateral positioning is confirmed with an image intensifier (Fig. 37-11). After position confirmation, a 2.5-mm drill bit with the provided guide is used to drill a transverse hole through the sliding guide hole of the trial plate (Fig. 37-12). A depth gauge is used to measure the length of the screws and a 3.5-mm tap is used. None of the screws should more than pierce the outer cortex to prevent possible radial nerve irritation. The oval hole allows for final positioning adjustments, if necessary.

FIGURE 37-11 With an image intensifier, the position of the trial radial plate is evaluated in posteroanterior and lateral views, with carpal clearance and lateral alignment confirmed, respectively.

FIGURE 37-12 Once the surgeon is satisfied with the position of the trial radial plate, a 3.5-mm screw is placed in the oval hole. The oval or sliding hole allows final positioning adjustments.

Positioning of the trial plate is again checked and adjustments made if needed. Once the final position is confirmed, the distal K-wire is removed and, using power, the radial peg drill bit is passed through the center distal guide hole of the trial plate. This creates a hole that will accommodate the radial peg portion of the prosthesis (Fig. 37-13).

FIGURE 37-13 A dedicated drill bit is used to drill for the radial peg. A stopping plate prevents penetration through the radius.

Adequacy of the final position of the trial component is then confirmed (Fig. 37-14). Once satisfied, the trial component is removed and replaced with the radial plate component. Care should be taken to avoid interposition of soft tissue between the plate and the bone. A plastic impactor is provided to protect the face of the plate while using a mallet, if needed, for the radial peg’s insertion (Fig. 37-15). Next, the 3.5-mm screw that was used in the trial plate’s oval hole will be applied to the radial plate’s oval hole. Up to four additional 3.5-mm screws can be used to complete fixation.

FIGURE 37-14 Image intensifier posteroanterior and lateral views are required before accepting final position of the plate.

FIGURE 37-15 The permanent plate replaces the trial plate.

It is prudent to keep the most distal screw short to prevent it from potentially impinging against the transverse peg. For this purpose, an 18-mm screw is recommended for use in all cases. Once all screws have been inserted, their length is verified before approaching the ulna (Fig. 37-16).

FIGURE 37-16 Radial plate fixation is confirmed noting screw length; avoiding excessive length will prevent radial nerve irritation.

Resection of the Distal Ulna

With the forearm fully pronated, a specially designed measuring device is inserted along the ulna and into the hemi-socket of the radial component. The device employs correspondingly sized, removable balls (black for small and blue for large) and enables the surgeon to assess the exact amount of ulnar shaft to be resected. Ulnar resection should be performed through good bone stock. With the measuring device in place, the proximal edge of the metal lip below the ball indicates the appropriate resection level for a standard-length ulnar stem (Fig. 37-17). Once assembled, 1 mm of tolerance should be evident between the ball and the base of the ulnar stem. An extended stem with a suitably lengthened extraosseous neck can then be used when too much bone has been lost due to injury or previous surgery (Fig. 37-18).

FIGURE 37-17 A measuring device marked in increments is placed in the radial plate socket to determine the proper length of the ulna before the final resection is made.

FIGURE 37-18 As an example, the measuring device is placed next to a 4-cm extended ulnar stem. Note the polished extraosseous portion of the stem.

For cases with additional ulnar loss (e.g., after trauma or after Darrach or Sauvé-Kapandji procedures), the measuring device is marked in 1-cm increments. This allows the selection of an appropriate length of extended stem (see Fig. 37-18). If the ulnar length falls between marks, it will be resected to the next closest proximal mark. This length should be determined preoperatively using the template.

After the appropriate length of the distal ulna has been resected, a 0.062-inch guidewire is inserted into its medullary canal to act as a centralizing guide. Travel of the guidewire should be confirmed with an image intensifier. A cannulated drill bit (either small or large) is then inserted over the guidewire and the medullary canal drilled to a marked length of 11 cm (Fig. 37-19).

FIGURE 37-19 A cannulated drill bit following a guidewire is introduced 11 cm inside the ulna.

Next, the medullary reamer of corresponding size (20 or 30) is inserted into the canal and drilled down until its shoulder comes into contact with the distal end of the ulnar shaft (Fig. 37-20). This completes preparation of the ulnar shaft.

FIGURE 37-20 A reamer is introduced into the ulna until its shoulder reaches the distal end.

The medullary canal and surrounding soft tissue is profusely and thoroughly irrigated using gravity irrigation. Next, the ulnar stem component is introduced. A plastic impactor is used to protect the polished distal peg of the ulnar stem (Fig. 37-21). If all procedures have been followed, the standard-length stem should be impacted flush with the distal end of the ulna shaft. When an extended stem is indicated, it is impacted until the plasma coating is within the ulna. In cases in which more ulna is resected than intended, care should be taken not to overinsert the selected stem. Leaving a portion of the plasma coating proud of the distal ulna is an option. When in its final position, the distal end of the stem should be no more proximal than the distal end of the radial plate.

FIGURE 37-21 The ulnar stem is introduced into the ulna, and a plastic impactor is used to protect the stem when using a mallet.

The ulnar component is completed by placing the UHMWP ball over the distal peg of the ulnar stem. This combination replaces the function of the ulna head. The ball and stem are then positioned within the hemi-socket of the radial component, effectively replacing the two articular surfaces of the DRUJ (Fig. 37-22).

FIGURE 37-22 The UHMWP ball is placed on the ulnar stem and into the radial socket.

Finally, the cover is positioned over the radial socket and secured with the two screws provided (Fig. 37-23). This encapsulates the UHMWP ball, which recreates the stabilizing effects of an intact TFC and completes the prosthesis.

FIGURE 37-23 The radial plate cover is secured in place, and assembly is completed.

An image intensifier is once again used to confirm adequacy of the overall position of the completed prosthesis (Fig. 37-24). The forearm is moved through a full range of pronation/supination, ensuring free movement. If full motion is not evident, check for any contact of the ulna with the radial plate. If necessary, the ulna can be trimmed to allow full motion. It may also be necessary to release more of the interosseous membrane if it is causing restriction of motion.

FIGURE 37-24 Final posteroanterior and lateral views before closure.

The fascial/retinacular flap is now used to cover the prosthesis and create a barrier for the tendons (Fig. 37-25). The tourniquet is released, complete hemostasis is secured, and the wound is closed in a layered fashion. The skin is closed with interrupted sutures. It is recommended that a prophylactic antibiotic be used for approximately 5 days.

FIGURE 37-25 The fascial flap is positioned between the extensor tendons and the implant.

A bulky soft tissue dressing is applied with the forearm in neutral position. Immediate limited motion can begin according to patient tolerance. The dressing remains in position for 2 weeks, at which time the sutures are removed and full range of motion exercises are encouraged. Therapy is initiated, if necessary, with active range of motion. Without the possibility of dislocation, patients can both move through a full range of motion and bear weight (Fig. 37-26).

FIGURE 37-26 Radiograph of a patient demonstrating lifting against gravity after placement of the prosthesis.

Complications

In two known cases, infection resulted in the removal of the prosthesis. In one case, antibiotic beads were placed at the site and a new prosthesis was applied 6 months later. Motor vehicle accidents caused the ulnar stems to break in two cases. In both cases, the stems were replaced and the patients regained function and continue unremarkably. In two cases, heterotopic bone led to a restriction in motion. Both cases were treated with excision through irrigation and immediate range of motion. No recurrence has been evident. Osteophyte formation and tendinitis have been seen when a fascial flap has not been placed between the extensor carpi ulnaris and the prosthesis.

Results

The need for a device to completely replace function of the DRUJ became evident as patient after patient entered the clinic after multiple DRUJ reconstruction and salvage procedures. These patients were at a loss after experiencing an average of 5.5 surgical procedures in an attempt to relieve their pain and instability. Some of the patients with unreconstructable DRUJs had undergone nearly all the described soft tissue, resection, stabilization, and implant arthroplasties combined, none of which provided long-term stability and pain relief. The device described in this chapter was developed as an answer for these patients. It is the only device that replaces the function of three parts of the DRUJ. By replacing the function of the ulnar head, the sigmoid notch, and the TFC, all factors in the joint that could cause instability and pain are eliminated. Preoperatively and postoperatively, the patients were asked to demonstrate not only range of motion but also function, including grip strength and weight-bearing ability. To our knowledge, no current published studies using any other technique test for a patient’s functional ability to bear weight or even measure grip strength (Fig. 37-27). All patients receiving the total DRUJ demonstrated acceptable range of motion (Fig. 37-28) and, more importantly, increased pain-free functional abilities. This improvement included increased grip strength and weight bearing. The goal is not only to relieve pain but also to allow persons with a previously destroyed DRUJ to become once again a functional asset to themselves and society.

FIGURE 37-27 Various patients demonstrate the ability to bear weight.

FIGURE 37-28 Various patients demonstrate range of motion, pronation, and supination.

If all else, including soft tissue techniques and ulnar shortening, fails, rather than a partial replacement (i.e., replacement of the ulnar head), a total DRUJ replacement like the one presented here is necessary because it will reproduce the function of the sigmoid notch, the ulnar head, and the TFC. We have had experience with over 200 patients who had deranged distal radioulnar joints as a consequence of trauma, congenital abnormality, degenerative arthritis, inflammatory arthritis, and, most frequently, after ulnar head resection had been performed and failed. It has been shown that excision of the head of the ulna leads to impingement and pain with supination and lifting.¹⁰ The majority of these patients have had between 2 and 14 procedures on the DRUJ, from partial excision of the DRUJ to wide excision of the ulna, passing through all the techniques of soft tissue stabilization available. Once the total replacement has taken place, the patient has been able to stop taking prescription pain medications and return to a productive life. More than 10 centers have had experience with this device with similar results to ours.