Partial Ulnar Head (Eclypse) Replacement

INTRODUCTION

The distal ulnar head and the soft tissues attached to it have been found to be kinematically essential in the coordination of two important movements: forearm pronosupination and wrist circumduction. Furthermore, the ulnar head is also important in maintaining adequate tension of the radioulnar interosseous membrane for a proper radioulnar transfer of loads ( Fig. 31-1 ). When the ulnar head is deformed or absent, forearm motion, grip strength, and lifting capabilities of the hand may become seriously impaired.

Surgical excision of the distal epiphysis of the ulna, a procedure popularized by William Darrach, has been—and perhaps still is—one of the most frequently performed operations in the wrist area. Because of its simplicity and the encouraging results initially published, the intervention gained wide reputation, being indicated to address most symptomatic dysfunctions of the distal radioulnar joint (DRUJ), including complications of radial fractures, radioulnar ligament disruptions, Madelung’s deformity, and rheumatoid arthritis. In recent years, a number of studies have collected enough evidence to establish that the so-called Darrach’s procedure is not as benign an intervention as it was believed to be. Certainly, the head of the ulna is not an irrelevant segment of bone that can be removed without paying a functional penalty.

Aside from a functional loss, excising the distal ulna may also lead to persistent pain at the newly created pseudarthrosis between the radius and the distal stump, the ulnar impingement syndrome or “convergent instability of the distal ulnar stump.” As emphasized by Lees and Scheker, when the patient attempts to lift a weight with the forearm horizontal and in neutral pronosupination, the radius inevitably converges toward the ulnar stump owing to the reaction forces produced by muscles such as the brachialis anterior (BA), the pronator quadratus (PQ), and the abductor pollicis brevis (APB). Protecting the DRUJ against excessive loading are the radial inserted muscles—the brachioradialis (BR) and biceps (B). These latter structures are able to lift up the radius, thus controlling the amount of load that is being exerted at the DRUJ. Unfortunately, this may not be enough, and radioulnar impingement may become painful and seriously affect overall hand function. Indeed, if feasible, reconstructing the DRUJ is likely to be more gratifying for the patient than excising the entire ulnar head.

Not infrequently there are instances in which the ulnar head is only partially destroyed by injury or disease. If only the articular portion of the ulnar head is damaged while the radius maintains a relatively normal articular surface to the ulna, it appears reasonable to replace only the fraction of the ulnar head that is deformed. In the 1980s, Bowers recommended resecting only the portion of ulna covered by cartilage and substituting it with a rolled tendon (i.e., an anchovy). It was the so-called hemiresection-interposition arthroplasty. The early results of the technique were considered satisfactory. Unfortunately, the DRUJ is a load-bearing structure, and the ability of fibrous tissue to prevent the two bones from impinging against each other disappears with time, and the wrist becomes painful again. The Eclypse pyrocarbon implant has been introduced as an improved “anchovy,” which maintains an adequate separation between the two bones throughout the entire range of pronosupination.

The major challenge for any DRUJ implant is to reproduce the complex DRUJ motion without implant failure under the magnitude of forces and torques that are being applied. Most currently available ulnar head prostheses require a complete excision of the ulnar head. By removing the entire ulnar head, however, the efficacy of the physiologic DRUJ stabilizers, namely, the distal radioulnar ligaments, ulnocarpal ligaments, extensor carpi ulnaris (ECU) tendon sheath, and pronator quadratus muscle, is lost. According to most recent studies, these structures play an important role in DRUJ kinematics, and they are able to maintain stable joint rotation in the absence of all other soft tissue stabilizers. Therefore, designing a prosthesis that can replace the articular portion of the ulna without disturbing its physiologic stabilizers appears reasonable. Certainly, a prosthesis without distal connections to the radius and carpus is to be considered nonphysiologic, an equivalent of a humeral head prosthesis without a rotator cuff attachment. The implant is likely to be stable if only the articular portion of the ulnar head is replaced, provided that the stabilizing ligaments can be preserved.

In recent years, two apparently similar implants have been developed to substitute for the articular portion of a damaged ulnar head: the First Choice DRUJ System (Ascension Orthopedics, Austin, Texas) and the Eclypse implant (BioProfile, Grenoble, France). The former is a rigid metallic implant that resurfaces the lost portion of ulna. This chapter reviews only the second option.

The Eclypse implant consists of a semicylindrical pyrocarbon spacer, shaped to mimic the joint surface of the distal ulna. The spacer can be implanted without disrupting the insertion of the distal radioulnar ligaments while maintaining an intact ECU sheath. To prevent dislocation of the implant in the extremes of forearm rotation, a titanium stem has been incorporated in the ulna with a distal peg inserted in a cylindrical hole in the center of the spacer. The spacer, however, is free to rotate slightly and translate relative to the stem to allow it to adapt to the changing dimensions of the concavity between the distal ulna and the sigmoid notch. Unlike metal implants, the coefficient of friction of pyrocarbon is extremely low. This makes for a very durable material that can resist large amounts of intrinsic mobility without noticeable wear, as demonstrated by decades of use in the manufacture of cardiac valves.

INDICATIONS AND CONTRAINDICATIONS

The Eclypse implant is particularly indicated in all conditions in which one would consider performing a hemiresection-interposition arthroplasty (Bower’s procedure). These conditions include (1) isolated osteoarthritis of the DRUJ, (2) post-traumatic deformity of the articular surface of the ulnar head with preservation of the sigmoid notch, and (3) ulnar head degeneration secondary to chronic inflammatory disease (e.g., chondrocalcinosis, rheumatoid arthritis), provided there is no major DRUJ instability ( Fig. 31-2 ).

The Eclypse is not indicated for DRUJ instability due to rupture or insufficiency of both the distal radioulnar and ulnocarpal ligaments. If the radioulnar ligaments are disrupted but the ulnocarpal ligaments maintain some level of stability, the implant may be used. Other contraindications are conditions in which the sigmoid is not concave and congruent and when the radius exhibits substantial malalignment. In the latter case, a corrective osteotomy before implantation is recommended. If a noncorrectable radial deformity makes it impossible to bring the implant to articulate with the radius or if the ulnar head has been excised to a level at which no contact can be reestablished between the Eclypse implant and the radial articular surface, this implant should not be used. In the latter cases, a total ulnar head implant or a total DRUJ prosthesis would be indicated.

SURGICAL TECHNIQUE

The intervention is done with the patient supine and under regional anesthesia (axillary block or similar) and with the arm exsanguinated with an above-elbow tourniquet applied. The arm needs to be exposed for later reference.

A dorsoulnar skin incision (Z-shaped, longitudinal, or oblique) centered on the ulnar head is made. Identification and protection of the ulnar branches of the ulnar nerve are obligatory. These branches usually become dorsal at the level of the ulnar styloid process. The subcutaneous tissue is elevated all around the contour of the ulnar head and over the fourth extensor compartment to expose the extensor retinaculum. The fifth extensor compartment is released longitudinally, and an ulnar-based retinacular flap is elevated, taking care not to enter the DRUJ joint. As the flap is raised, the subretinacular space over the DRUJ capsule is uncovered, and the ECU tendon sheath is inspected for its integrity. If the tendon is unstable (subluxable toward the palmar corner of the wrist in supination and ulnar deviation), a reconstruction using a portion of extensor retinaculum is to be considered.

A capsulotomy is designed to expose the ulnocarpal space, the dorsal radioulnar ligament, and the DRUJ, as recommended by this author in a previous publication. Important anatomic landmarks for the capsular incision include the origin and insertions of the proximal fibers of the dorsal radiocarpal (radiotriquetral) ligament and the septum between the fourth and fifth compartments. An ulnar-based capsular flap is developed and detached off the medial edge of the radius. The flap is elevated by sectioning its deep attachment to the peripheral fibers of the dorsal radioulnar ligament. The synovial triangular tissue distal to the fibers of the radioulnar ligament (the so-called ulnocarpal meniscoid) can be excised for better visualization of the ulnocarpal space (see Fig. 31-2 ). The forearm is then fully pronated, and, by adding some dorsal translation force, the head can be almost subluxed without detaching the radioulnar ligaments ( Fig. 31-3 ).