33.1 Introduction

Arthritic destruction of the distal radioulnar joint (DRUJ) is frequently associated with painful limitation of forearm rotation and a reduction of grip strength. Multiple pathologies may cause the arthritic degeneration of the joint including chronic instability of the DRUJ, rheumatoid, or primary osteoarthritis and Madelung’s deformity. Primary osteoarthritis is rare. Posttraumatic arthritis is common especially following distal radius fractures, that is, both malunited extra-articular distal radius fractures and intra-articular fractures involving the sigmoid notch or the ulnar head.

Traditional treatment options for symptomatic degeneration of the DRUJ have included resection of the ulnar head, hemiresection +/– interposition arthroplasties, and the Sauvé-Kapandji procedure. All these procedures can restore forearm rotation and often give satisfactory clinical results. But some patients have persisting or new pain and functional impairment following these procedures. This is typically due to painful instability of the forearm bones especially under loading. The loss of the ulnar support of the wrist may lead to a carpal supination deformity. The loss of the bony support for the radius may lead to painful radioulnar impingement with the distal radius abutting the distal end of the ulna under transverse loading called the “ulnar impingement syndrome.” ¹ This can be shown with stress radiographs as proposed by Lees and Scheker ² (Fig. 33.1).

To treat this secondary forearm instability, Timothy Herbert reported reconstruction of the original DRUJ using a silicone ulnar head spacer. The concept included the realignment of the radius relative to the ulna using the spacer and an ulnar-based local soft tissue flap to stabilize the forearm complex. The initial results were good but did not last due to failure of the silicone with loading. ³ Based on this experience, Schoonhoven and Herbert developed a more biocompatible and lasting ulnar head replacement, called the ulna head prosthesis (UHP).

The primary goal of the new technique was to relieve pain and restore stability and function in patients with painful instability of the forearm following previous resection arthroplasties of the DRUJ. The reported biomechanical ⁴ and clinical studies ^{5 , 6 , 7 , 8} have demonstrated good restoration of DRUJ stability and improved clinical outcomes which are maintained into the long-term. This has led to increasing use of the UHP as the primary operation to treat patients with painful arthritis of the DRUJ.

33.2 Herbert Ulnar Head Prosthesis

Following anatomical and radiological investigations assessing the diameter of the intramedullary canal of the distal ulna, the diameter and shape of the ulnar head, and the geometry of the DRUJ, an interchangeable, modular ulnar head prosthesis was developed. The anatomical shape of the stem of the prosthesis is designed to achieve primary fit-press stability within the intramedullary canal of the ulna. The titanium coating of the stem allows for osseointegration for long-term stability. There are three different stem designs. The standard stem with a collar length of 2 mm was developed for primary reconstruction of the distal radioulnar joint. The stem with a collar length of 4 mm allows for accurate length reconstruction following mild previous resection of the distal ulna, whereas the revision stem with a collar length of 17 mm allows reconstruction following larger previous resections.

Due to its elasticity and biocompatibility, zirconium ceramic was chosen as the material for the head of the prosthesis. It is also available in three sizes, and all stems and heads are interchangeable (Fig. 33.2).

33.3 Operative Technique

The operative technique depends in part upon how much distal ulna is remaining and the local soft tissue structures/damage. Principally, it consists of bony and soft tissue elements.

The bone cut is primarily determined by preoperative templating. If the ulnar head is still in place it is removed by cutting the distal ulna at the predetermined level. It is better to start cutting the distal ulna too long as it can easily be cut further proximal. The sigmoid notch of the radius is inspected and any osteophytes are removed or steps within the joint line are smoothed with a burr. Using the appropriate rasps (standard or revision), the intramedullary canal of the ulna is prepared and the trial stem is inserted into the ulna. A trial head is used and intraoperative fluoroscopy is performed to check the correct stem size and fit within the intramedullary canal of the ulna. The trial head is chosen based upon the size of the excised ulnar head or if already excised by preoperative templating against the opposite side. The trial head needs to be matched against the sigmoid notch of the distal radius. The correct alignment of the head within the sigmoid notch of the radius and the correct length of the implant aims to achieve an ulna-minus variance of 2 mm to avoid ulnar impaction syndrome. This is the time to make adjustments prior to insertion of the definitive implant.

Stabilization of the restored DRUJ following ulnar head replacement is achieved using an ulnar-based local soft tissue flap consisting of the joint capsule, the extensor retinaculum, the sixth extensor compartment with the extensor carpi ulnaris tendon, and the triangular fibrocartilaginous complex (TFCC).

Following a longitudinal incision over the dorsal aspect of the DRUJ, the fifth extensor compartment is identified, opened longitudinally, and the extensor digiti minimi tendon is mobilized and retracted radially. A soft tissue flap is incised through the floor of the fifth extensor compartment and the dorsal capsule of the joint overlying the DRUJ. This flap is extended proximally about 3 cm to expose the neck of the distal ulna (Fig. 33.3). It is then raised ulnarly in one layer and extended distally along the dorsal radioulnar ligament. Following osteotomy of the ulna, the ulnar head or its remains are excised. We recommend that any deficiencies of the floor of the sixth extensor compartment or the TFCC should be repaired. At this stage, two or three holes are drilled through the dorsal rim of the sigmoid notch using a small drill or K-wire (0.8 mm). Nonabsorbable (2–0) sutures are inserted through these drill holes to allow fixation of the ulnar flap following insertion of the prosthesis. The definitive implant is inserted and the ulnar-based soft tissue flap is sutured to the dorsal radioulnar ligament and the dorsal rim of the sigmoid notch (Fig. 33.4). Prior to the final reattachment, the forearm rotation and stability of the DRUJ are checked to estimate the correct tension of the flap. This dorsal reattachment may be further supported with a longitudinal suture of the ulnar remains of the extensor retinaculum of the fifth extensor compartment onto the dorsal part of the flap using 3–0 absorbable suture material, leaving the extensor digiti minimi tendon subcutaneously. We recommend inserting a drain into the wound, although there is no evidence to establish its use and the skin is closed. A sterile dressing and a long arm plaster are applied, with the elbow in about 70 degrees of flexion, supination of about 30 degrees, and the wrist in 20 degrees of extension to minimize tension on the ulnar-based soft tissue flap.

This approach and the operative technique have been published previously. ^{9 , 10 , 11}

Postoperative immobilization depends on the quality of soft tissues and the stability that has been achieved with the procedure and varies from 2 to 4 weeks of immobilization in the above elbow plaster followed by 2 to 4 weeks of immobilization in an ulnar gutter splint. Unrestricted movement is allowed between 6 and 8 weeks and unrestricted use and loading 12 weeks following the procedure.