35.1 Introduction

The radioulnar joint is a bicondylar joint made up of the proximal (PRUJ) and distal radioulnar joints (DRUJ). ¹ When lifting an object by flexing the elbow with the forearm in neutral rotation, the force is transferred from the ulnar insertion of the brachialis muscle up to the head of the ulna, the sigmoid notch, and eventually the hand.

When the DRUJ is damaged or unstable, weight lifting can be difficult or even painful. ² Typically, patients with DRUJ conditions experience ulnar-sided wrist pain, exacerbated by lifting objects. ^{3 , 4}

Different surgical strategies have been proposed to treat these problems. The majority of these aims at removing the ulnar head, partially ⁵ or totally. ⁶ The success of these arthroplasties relies on the integrity of the capsule and ligament that maintain the joint congruency. However, they fail to maintain the key anatomical structures necessary for force transfer from the hand to the forearm. Arthrodesis of the DRUJ together with the interruption of the diaphysis (i.e., Sauvé-Kapandji procedure) results in the same uncoupling of the two forearm bones and can lead to loss of function. ⁷ Another approach is the replacement of the ulnar head with ⁸ or without ligament reinsertion. ⁹ Finally, interposition arthroplasty with Achilles tendon has been proposed to avoid the painful impingement of the distal ulnar stump with the radius. ¹⁰ Importantly, the function of the DRUJ remains often limited after this procedure and may be associated with pain, residual symptomatic instability, or stiffness, particularly under load. ¹¹

All these operations may result in limited functional recovery, mainly due to residual instability of the ulnar head replacement or the impingement of the ulnar stump with the radius, especially in active patients. In some cases, patients experience a painful snap during forearm rotation that further limits function.

35.2 The Implant and Technique

The semiconstrained DRUJ prosthesis (Aptis Medical) was first proposed in 2001 ¹² as a total joint arthroplasty able to replace not only the two joint components of the DRUJ, but also the function of the triangular fibrocartilage complex (TFCC). ¹³

The prosthesis is completely modular. The radial component is a plate adapted to the anatomical shape of the ulnar aspect of the radius and terminates distally with a hemisocket to receive the ball. It is available in three sizes; it has a peg on the radial side and it is coated with a titanium plasma spray to enhance osteointegration. The plate is secured to the radius by three to five screws depending on the size of the plate. Recently, locking implants have been developed, further improving the quality of the radial fixation. The ulnar stem is also coated with titanium plasma spray and has a distal pin for the ultra-high molecular weight polyethylene ball. The stem is available in different sizes and neck length to allow for loss of the distal ulna at previous operations.

The size of the implant can be planned on posteroanterior and lateral radiographs. The approach is dorsal through an 8-cm long skin incision along the ulnar border of the distal ulna with a 3-cm oblique extension over the wrist. In most cases, scars from previous surgery dictate the skin incision, but it should be as close to the ulnar border of the forearm as possible for an easy positioning and fixation of the plate on the ulnar margin of the radius. The dorsal branch of the ulnar nerve must be identified and carefully protected throughout the whole operation. The extensor retinaculum is then exposed and partially incised at the level of the second dorsal compartment to harvest an ulnar-based flap. At the level of the DRUJ the dorsal capsule is also included in the flap. The extensor carpi ulnaris (ECU) compartment is then incised and the tendon completely freed up to its distal insertion. At this point, the ulnar head, if still present, is removed and the interosseous membrane is cut for 8 to 9 cm to allow for a better mobilization of the ulnar stump and exposure of the sigmoid notch. It is recommended to resect the volar margin of the radius to place the radial plate trial at 90 degrees to the coronal plane and not tilted dorsally. The distal end of the plate should be at least 3 mm below the lunate fossa. The plate is temporarily fixed with K-wires and screws and its position is checked with a fluoroscope. The plate should not overlap the dorsal cortex of the radius to reduce the risk of extensor tendon irritation. The definitive plate is then placed and secured with screws. The most proximal screw should be monocortical to prevent stress fractures.

The forearm is rotated into maximal pronation and a guide used to resect the ulna to the planned length. A 2.4-mm guide is placed in the medullary canal and progressive reamers (4.0–6.0 mm) are inserted up to the 11-cm mark until a tight fit is ensured. The distal part of the ulna is finally prepared with the medullary finish reamer of the corresponding size. At this point, the stem is introduced with a plastic impactor until the coated part is flush with the bone. The distal end of the ulnar peg should be proximal to the distal end of the radial plate. The ball and the closing cover are then placed and secured. The retinaculum flap is passed under the ECU tendon and sutured in its original position over the second dorsal compartment. The wound is closed in layers and a short arm splint is applied to protect the soft tissues.

Hand therapy is started within 1 to 2 days with finger mobilization, active wrist movement, and gentle forearm rotation. After 4 weeks, full rotation of the forearm is allowed and weight-bearing exercises are started 6 weeks after surgery. Full load is allowed after 3 months.

35.3 Indications and Contraindications

The Aptis semiconstrained implant can in theory be used for all cases of pain and instability of the DRUJ. ⁴ The main indications are adults with symptomatic rheumatoid, degenerative or posttraumatic arthritis of the DRUJ, and after previous surgery. ¹³

In our experience most patients had had one or more previous surgical interventions for different DRUJ problems, in particular, partial or total ulnar head excision with instability with the proximal stump impinging with the radius (Fig. 35.1a–c). ¹⁴ We have also used the Aptis implant for ulnar head or ulnar stump instability following wrist fusion (Fig. 35.2a–d) and for salvage of painful, unstable ulnar head replacements (Fig. 35.3a–f).

Contraindications are known metal allergy (cobalt-chrome, nickel), an immature skeleton, active infection, or an ulnar stump of less than 11 cm.