86 Dislocated Ulnar Head Prosthesis
86.1 Patient History Leading to the Specific Problem
This 78-year-old patient presented with pain on his left wrist, localized to the ulnar side with limited pronation/supination and inability to lift weight. He retired from his job 13 years ago, but he was an avid wood worker, to which he devoted at least 8 hours of the day. Since his last surgery, he was unable to do any work with his left hand.
He was initially seen somewhere else because of severe pain in the left wrist. Weight bearing was most painful while holding the shoulder abducted, the elbow flexed at 90 degrees, and the forearm in neutral position.
Physical examination found no piano key sign, but pain with compression of the radius and ulna in the distal forearm, which had a grinding sensation while pronating and supinating the forearm.
Radiography found arthritis of the distal radioulnar joint (DRUJ), and after conservative therapy was exhausted, the patient opted for surgical intervention.
The ulnar head was excised, and a bipolar no constraint prosthesis was placed, including resurfacing of the sigmoid notch. In short period of time, the prosthesis was unstable, and three attempts were made to stabilize the implant, including brachioradialis wrap.
After the third procedure, the patient sought a second opinion. He consulted us because of his inability to use the hand, with feeling of instability, pain, and limitation on pronation and supination.
86.2 Anatomic Description of the Patient’s Current Status
The patient was in obvious discomfort during our examination. Clinically, the ulnar part of the implant was prominent and the patient had pain with the most minimal contact in the area of the ulnar head.
Supination was more restricted than pronation, and both were painful. His pronation was measured at 30 degrees and supination at 5 degrees. The range of motion was limited mechanically as well as by pain, and he was unable to lift weight.
Initial radiographs in our clinic showed dislocation of the prosthesis (▶Fig. 86.1). The ulnar head component was dorsal, and the radial part was palmarly displaced. The sigmoid notch part of the implant was in good position. The reason of the radius being palmarly displaced is because there is no support for the radius as the triangular fibrocartilage (TFC) cannot be sutured to the metal head of the implant.
86.3 Recommended Solution to the Problem
The DRUJ is an intrinsically unstable joint due to the difference in arcs of the sigmoid notch and the seat of the ulnar head. Stabilization of this joint depends on the dynamic and static stabilizers. The radioulnar ligaments are responsible for the static stability of the DRUJ. The pronator is the main dynamic stabilizer of the DRUJ. The deep head of the pronator is particularly important in compressing the DRUJ through the radius’s arc of motion about the ulna. The static stabilizers have been excised or defunctionalized during the course of the prosthesis placement, similar to a Darrach procedure. Some implants have holes distally for reinsertion of the TFC; it is unlikely that the TFC ligaments can be connected to metal, ceramic, or any other material and stay there.
The DRUJ can be saved when there is instability, but cartilage is present. Ligament reconstruction of the TFC can solve the problem by creating a new dorsal, palmar, or both ligaments following the direction of the damaged ligament(s). With this technique, the origin and insertion of the ligament is maintained and allows the original ligament to adhere to the grafted tendon that are placed on top of the TFC, restoring the function of the mechanoreceptors. This technique does not require wide opening of the DRUJ and only a 3-mm capsulotomy is required to find the fovea and the most distal part of the sigmoid notch, either dorsal, palmar, or both (▶Fig. 86.2). With this technique, the tendon inside the joint is nourished by the synovial fluid and the interosseous part is in cancellous bone from where the tendon gets its nourishment. When there is instability of the DRUJ, treatment should not be delayed.
Fig. 86.1 (a, b) Radiograph of the first visit to our office showing a subluxated nonconstraint implant of the left forearm in this 78-year-old man.
If there is limited area of arthritis, as in the cases of posttraumatic arthritis, an ulnar shortening can change the contact between the radius and the ulna (▶Fig. 86.3). It makes the joint more congruent and distributes the forces evenly. Where the most proximal border of the seat of the ulna was pressing on limited area of the sigmoid notch, with the ulna shortening as shown in the picture, there is more evenly applied pressure and the pain settles. This technique has helped 57% of patients to achieve excellent to good results. An added benefit of ulnar shortening is that it helps tighten the TFC as well as decompressing the ulnar side of the carpus. If there is instability after ulnar shortening, ligament reconstruction could be added to the shortening. But when the cartilage is totally gone, the only solution is a joint replacement.
