CHAPTER 36 Ulnar Head Implants: Unconstrained

The ulnar head is the keystone for mobility and stability of the ulnar-sided wrist as well as the forearm. It not only is one of the joint partners creating the distal radioulnar joint (DRUJ) but also represents an integral part of the wrist joint. Biomechanically, it represents the only fixed, nonmoving anatomical structure at the wrist level. It, therefore, supplies the bony support around which the radius with the wrist and hand rotates in the DRUJ. Arthrotic destruction of the DRUJ will lead to painful limitation of forearm rotation and reduction of grip strength and therefore compromise hand function. Arthrotic derangement may be the result of intra-articular fractures of the DRUJ either with direct damage of the cartilage of the ulnar head or the sigmoid notch in comminuted fractures or secondary destruction due to intra-articular malunion of the joint line. However, the most common origin consists of the malunited extra-articular distal radius fracture. The dorsal or palmar angulation of the distal radial fragment with loss of the physiological ulnar inclination and shortening of the radius will lead to incongruity of the DRUJ and over time result in arthrotic derangement of this joint. I, therefore, consider the malunited extra-articular distal radius fracture a prearthrotic deformity of the DRUJ.¹

Several salvage procedures have been described to reduce the pain and restore forearm rotation in patients with symptomatic DRUJ destruction, including ulnar head resection^2–4 and the hemi-resection interposition technique.⁵ Partial loss of the ulnar head sacrifices the attachment of the palmar ulnocarpal ligaments and the force transfer from the radius onto the ulnar head. Loss of the ligament attachment will result in a palmar drop of the ulnar-sided wrist with a supination deformity of the hand and a dorsally prominent distal end of the ulna. In a way this is comparable to the well-described caput ulnae deformity in rheumatoid patients. The deformity does not truly represent an “instability of the distal end of the ulna” but an instability of the ulnar-sided wrist. Loss of the bony support of the radius in the DRUJ leads to radioulnar narrowing or impingement during forearm rotation and wrist loading and can radiologically be demonstrated on the transverse loading stress views described by Lees and Scheker (Fig. 36-1).⁶

FIGURE 36-1 A, Posteroanterior radiograph after hemi-resection interposition arthroplasty of the DRUJ. B, Transverse loading view demonstrating radioulnar impingement.

A completely different concept to treat the painfully destroyed DRUJ consisting of fusion of the DRUJ and segment resection proximal to the ulnar head to restore forearm rotation was described by Sauvé and Kapandji in 1936.⁷ With this procedure the supination deformity and the instability at the DRUJ level is prevented as the attachments of the ulnopalmar ligaments and the triangular fibrocartilage complex (TFCC) remain. However, in pronation underloading of the hand the dynamic dorsal stabilizers of the radius and the wrist may not be sufficient to prevent palmar drop of the wrist and hand in relation to the distal end of the ulna, therefore leading again to a dorsally prominent distal ulnar stump. Furthermore, on transverse loading of the hand there is no anatomical structure to prevent the radius to fall onto the distal end of the ulna, resulting in radioulnar impingement (Fig. 36-2).^8,9

FIGURE 36-2 Radioulnar impingement after a Sauvé-Kapandji procedure.

The concept to prevent development of this instability using an ulnar head spacer in rheumatoid patients was first described by Swanson.¹⁰ This is no longer recommended because of the high failure rate of the Silastic spacer material and secondary Silastic-induced synovitis.^11–15

To overcome the secondary “painful instability of the distal ulna,” several stabilizing soft tissue procedures using part of the flexor and/or the extensor carpi ulnaris tendon have been described. None of these procedures was found to reliably restore the stability or reduce symptoms in biomechanical¹⁶ or clinical^17,18 studies. Wide resection of the ulna¹⁹ as well as lengthening procedures after excessive shortening of the ulna²⁰ have been advocated but did not resolve the symptoms in my own or other surgeons’ experience.¹⁷ Considering the biomechanical and clinical shortcomings of the above-described resection procedures, Herbert developed the concept of restoring stability to the DRUJ as well as the wrist joint and the continuity of the ulna by means of an ulnar head prosthesis.

Based on the results of anatomical, radiological, and biomechanical studies of the distal ulna, the ulnar head, and the DRUJ between 1992 and 1994, Timothy Herbert doveloped together with me a two-component modular system for ulnar head replacement in cooperation with Martin-Medizin-Technik (Tuttlingen, Germany). It consists of three sizes of replacement heads and three stem sizes. To restore an adequate length of the ulna after a previous resection arthroplasty, each stem size of the prosthesis is provided with three collar lengths. To avoid the problems associated with cement, particularly in small bones, we decided to use a noncemented stem, allowing osseous integration. Porous-coated titanium was chosen because of its biocompatibility and a modulus of elasticity very similar to that of bone. The head of the prosthesis is composed of ceramic (zirconium oxide) because it was believed to be the most suitable material for articulation with joint cartilage due to its biocompatibility.

Following the development of the prosthesis a three-phase clinical study design was developed. Initially, three patients with painful instability of the wrist and forearm after resection arthroplasty were treated in 1995 with promising early results.²¹ The second phase consisted of a prospective multicenter study limited to another 20 patients. Because of the excellent mid-term results of these patients,²² the prosthesis was released to other surgeons. The third phase consisted of the evaluation of the long-term results, and all patients with a follow-up of more than 5 years are currently under review.

Indications

Before further outlining the indications for the ulnar head prosthesis, it is important to emphasize that no implant will ever function as well as the original ulnar head. Therefore, ulnar head excision is only justified if the joint surface of the DRUJ is irreversibly destroyed. In any other pathological process of the DRUJ every attempt must be made to restore the DRUJ and therefore prevent the possible development of arthrotic joint destruction.

Originally the procedure was developed to solve the unsolvable and to overcome the problems associated with painful instability of the wrist and forearm after previous resection arthroplasties of the DRUJ. Increasing experience with this procedure and the lasting excellent results over the past 12 years have led us to extend the indication to other pathological processes. As clinical experience demonstrated that stability of the forearm can be restored with this prosthesis, the indications were extended to primarily use the ulnar head replacement in patients with painful osteoarthritis of the DRUJ.

Post-traumatic Osteoarthrosis of the DRUJ

Distal forearm fractures are the most common cause of problems at the DRUJ. Arthroplasty should be considered only if forearm rotation remains painful after the corrective osteotomy or if there is evidence of irreversible joint damage of the DRUJ at the time of the osteotomy. Anatomical alignment of the radius and the ulna is a prerequisite for ulnar head replacement. Any significant radial deformity represents a contraindication for this procedure. In particular, any malunion of the radial or ulnar shaft must be corrected either before or at the time of ulnar head replacement. Mild deformities of the radial metaphysis (10 degrees of dorsal angulation) may be accepted but any more significant or a palmar malangulation of the radial metaphysis requires correction to allow reconstruction of the DRUJ with the ulnar head prosthesis. In patients with significant painful arthrosis of both the radiocarpal and distal radioulnar joints, partial (i.e., radioscapholunate) or complete fusion of the radiocarpal joint and ulnar head replacement may be performed at the same time.

Other Indications

In acute trauma, primary ulnar head replacement may be considered in cases with irreducible, comminuted fractures of the ulnar head requiring ulnar head excision.

Primary osteoarthrosis of the DRUJ is a rare condition but represents an ideal indication for ulnar head replacement because there is no additional DRUJ pathological process that must be addressed at the time of surgery. It frequently affects middle-aged active patients who expect normal performance of the wrist and hand in their professional and private life (Fig. 36-3). The same applies for patients with a giant cell tumor of the ulnar head requiring ulnar head resection.

FIGURE 36-3 A, Radiograph of a 55-year-old patient with painful arthrosis of the DRUJ. B, Radiograph 46 months after primary ulnar head replacement.

The DRUJ is frequently affected in patients with rheumatoid arthritis. I consider ulnar head replacement only in the younger and active rheumatoid patient with the arthrotic or ankylotic type of rheumatoid arthritis, minimal other joint involvement, a stable DRUJ, and a sufficient antirheumatoid medication. Hemi-resection arthroplasty of the DRUJ still represents the best treatment option for the majority of rheumatoid patients because either the insufficient stabilizing soft tissues or the osteoporosis will not allow prosthetic ulnar head replacement, and the patients’ reduced activity level will most probably not lead to symptoms arising from any instability after this procedure.

Another major indication for ulnar head replacement is as a revision procedure in patients with painful instability of the wrist and forearm after previous resection arthroplasties (hemi-resection or complete resection of the ulnar head) or a Sauvé-Kapandji procedure. The long-term experience with this difficult group of patients has proved that reconstruction of the DRUJ using the ulnar head prosthesis is an effective method to cure the problem. However, revision surgery is often difficult and less predictable than when the operation is carried out as a primary procedure. In patients with painful instability after a Sauvé-Kapandji procedure two options for reconstruction are available. Resection of the fusion mass and insertion of the prosthesis is recommended if either the fusion has not healed completely or the original fusion has been performed in an ulnar-positive variance situation leading to additional symptoms of ulna impaction syndrome. In all other cases a spherical head, designed by Fernandez and colleagues,²³ may be used to articulate within the previously fused ulnar head after reaming of a socket into the proximal fusion mass.

Age of the patient as such does not affect my decision for the procedure. In particular, young and active patients with a high demand on the performance of their hand and wrist will most likely develop a symptomatic instability after one of the salvage procedures and therefore benefit from primary reconstruction of the DRUJ using the ulnar head prosthesis. Older patients in their retirement frequently have the same expectations for their private and sport activities. Salvage procedures should therefore be reserved for patients with low functional demands, in whom instability is unlikely to become symptomatic.

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