IMPORTANT POINTS
Ulnar impaction syndrome results from abnormal force distribution across the ulnar carpus.
The increased force across the ulnar carpus leads to painful degenerative changes in the ulnar head, triangular fibrocartilage complex (TFCC), lunate, and triquetrum.
The treatment of this painful condition is to unload the ulnar aspect of the carpus through either a formal ulnar-shortening osteotomy or an arthroscopic or open “wafer” procedure.
PEARLS
A pronated grip view is helpful in patients with neutral or negative ulnar variance but with signs consistent with ulnar impaction syndrome.
The goal of surgical treatment is to obtain neutral to slightly negative ulnar variance.
Resection of more than 4 mm of the distal ulna in a wafer procedure may compromise function and stability of the distal radioulnar joint (DRUJ). In this situation, an ulnar-shortening osteotomy is the recommended procedure.
INTRODUCTION
Ulnar impaction syndrome, also referred to as ulnocarpal abutment, is a degenerative condition of the ulnar side of the wrist resulting from excessive load bearing across the ulnar carpus, triangular fibrocartilage complex (TFCC), and the ulnar head. This excessive loading at the ulnocarpal joint leads to a continuum of pathologic changes including degeneration of the TFCC, chondromalacia of the lunate and ulnar head, and lunotriquetral (LT) ligament disruption. Ulnar impaction syndrome is a common cause of ulnar-sided wrist pain and restricted motion.
The altered loading across the ulnar carpus is usually secondary to either static or dynamic positive ulnar variance. Ulnar variance refers to the relative length of the distal ulnar articular surface relative to the ulnar articular surface of the distal radius ( Fig. 7-1 ). A positive variance indicates that the ulna is longer than the corresponding articular surface of the radius. Static refers to the wrist at rest, and dynamic refers to a stressed or loaded wrist view. The implications of this are that increased ulnocarpal loads can occur with activity even in wrists found to be ulnar neutral or negative on static x-rays. Generally, the radius receives 82% of the load borne through the wrist while the ulna receives 18% of the force. However, Palmer and Werner showed that loads through the distal ulna can change and are directly related to ulnar variance. Increasing ulnar length by 2.5 mm raises ulnar loads to 42%, whereas a decrease in length of 2.5 mm lowers the force seen at the distal ulna to 4.3%. Changing the tilt of the distal radius from normal to 40 degrees of dorsal tilt increases the ulnar load from 21% to 65%.
Of wrists with tears of the TFCC, 73% have either ulnar positive or neutral variance, compared to only 17% of ulnar-negative wrists with perforations of the TFCC, indicating that increased loading and excessive forces across the ulnocarpal joint can ultimately lead to injury and degeneration of the TFCC. Palmer has classified TFCC tears as either Type I (acute tears) or Type II (degenerative tears) ( Table 7-1 ).
| Type I (Acute Traumatic Tears) | Type II (Degenerative Tears) |
|---|---|
| IA Central perforation | IIA Wear of the TFCC |
| IB Ulnar sided tear ± ulnar styloid fracture | IIB Chondromalacia of the lunate or ulna |
| IC Ulnocarpal ligament tear | IIC Perforation of the TFCC with chondromalacia of the lunate |
| ID Radial-sided tear | IID TFCC perforation, lunate chondromalacia, lunotriquetral ligament tear |
| IIE Ulnocarpal arthritis |
Arthroscopic debridement of TFCC tears, which is often successful in alleviating symptoms in ulnar-negative wrists, is often insufficient as an isolated treatment in ulnar-positive wrists. The pain associated with the tear is likely a result of the ulnocarpal impaction. The TFCC tear is simply a result of this chronic impaction. In this scenario, unloading the ulnar side of the wrist by shortening the ulna seems to make empiric sense. Indeed, ulnar shortening in the setting of ulnar positive and even some ulnar neutral wrists with TFCC tears has proved successful in situations in which arthroscopic debridement alone has failed.
History and Physical Examination
The underlying etiology of ulnar impaction syndrome is ulnocarpal overload. Causes of acquired ulnar-positive variance include radial shortening secondary to a distal radius fracture, Essex-Lopresti injury, or acute or chronic physeal injury. The condition also occurs in people with natural ulnar-positive variance. It is interesting that this condition may also occur in the ulnar-neutral and -negative wrist. Excessive compressive load may still be transmitted across the ulnocarpal joint in these situations because, as Palmer has demonstrated, the thickness of the articular disc of the TFCC is inversely proportional to the amount of ulnar variance. Furthermore, ulnar variance changes with functional activity. Friedman and colleagues have confirmed the concept of dynamic ulnar-positive variance, demonstrating that there is a relative increase in ulnar variance that occurs with grip. Activities that require repetitive grip and forearm rotation may therefore predispose the patient to develop ulnar impaction syndrome.
Patients with ulnar impaction syndrome often present with ulnar-sided wrist pain, localized swelling, and occasionally limitation of motion. On examination many patients will have swelling and tenderness localized to the TFCC and distal ulna ( Fig. 7-2 ). Pain is exacerbated by ulnar deviation during power grip combined with pronation and supination. The ulnar impaction maneuver, performed by moving the distal ulna in a volar and dorsal direction with the wrist in ulnar deviation, can help elicit pain that stems from the TFCC and ulnar impaction ( Fig. 7-3 ). Nakamura’s ulnar stress test is performed by ulnarly deviating the pronated wrist while axially loading, flexing, and extending the wrist. The differential diagnosis of ulnar-sided wrist pain is large. However, the physician must rule out other causes of pain such as pisotriquetral arthritis, distal radioulnar joint (DRUJ) instability or arthritis, or extensor carpi ulnaris (ECU) tendonitis. These conditions can coexist, and fluoroscopic-guided lidocaine injections (with or without corticosteroids) can be very helpful in pinpointing primary pain generators.
Imaging Studies
Plain radiographs, including posteroanterior (PA) and lateral views, should be obtained on every patient. Contralateral wrist views may be helpful for preoperatively determining the amount of shortening necessary in acquired (i.e., traumatic) ulnar-positive cases. One must obtain a true PA of the wrist with the shoulder abducted to 90 degrees, elbow flexed to 90 degrees, and the wrist in neutral rotation ( Fig. 7-4 ). The significance of a true PA view stems from the fact that rotation at the wrist can increase (pronation) or decrease (supination) ulnar variance. With this in mind, a PA view of a pronated wrist can be helpful in patients who develop pain during activities that require pronation or ulnar deviation (i.e., hammering, typing). These patients may not be experiencing symptoms until their ulnar variance becomes positive with pronation. Minami and colleagues reported using an additional “pronated grip” x-ray. For the pronated grip view, the shoulder is adducted to the patient’s side and slightly externally rotated. With the forearm pronated, the patient makes a strong, full fist. Patients who are ulnar neutral or ulnar negative with signs and symptoms consistent with ulnar impaction syndrome should have pronated grip view. Tomaino found an average 2-mm increase in ulnar variance with the pronated grip view.
With advanced ulnar impaction syndrome, degenerative changes may be seen on the ulnar aspect of the proximal lunate articular surface (or radial aspect of the proximal triquetrum) and on the “kissing” area of the ulnar head on x-ray. Magnetic resonance imaging (MRI), although not routinely required, may show focal signal abnormality in the ulnar aspect of the lunate, the radial aspect of the triquetrum, and the radial aspect of the ulnar head. Arthrogram and MR arthrogram do not add significantly to the treatment plan because the diagnosis of ulnar abutment is not based on a tissue tear.
Treatment
Conservative therapy, consisting of activity modification, anti-inflammatory medications, and wrist splinting should be tried for 3 to 6 months before proceeding to surgical treatment. Steroid injections into the ulnocarpal articulation may also provide temporary relief. Avoidance of repetitive loading activities, particularly those requiring ulnar deviation, may ease symptoms.
Many effective surgical procedures have been described for when these conservative steps are no longer successful. These options focus on unloading the ulnar aspect of the wrist. The most common procedures include ulnar shortening osteotomy, “wafer” resection of the distal ulna, and arthroscopic wafer procedures. Diagnostic arthroscopy is performed at the time of ulnar shortening to stage the severity of ulnar impaction.
Ulnar-Shortening Osteotomy
Indications
Ulnar-shortening osteotomy is considered the gold standard for treatment of ulnar impaction syndrome. The goals of the shortening procedure are to relieve pain by unloading the ulnacarpal joint and prevent arthritis by reestablishing a neutral or slightly negative ulnar variance. The procedure is indicated in patients with positive ulnar variance and symptoms of ulnar impaction syndrome. The procedure may also be indicated in patients with ulnar-neutral or ulnar-negative variance who have symptoms of ulnar impaction syndrome and signs of impaction on a pronated grip view or MRI.
Contraindications
DRUJ arthritis is the primary contraindication to the procedure. Ulnar shortening may worsen symptoms of DRUJ arthritis by making the sigmoid notch more incongruous. In this situation, consideration should be given to the Sauve-Kapandji procedure, distal ulna resection (Darrach), or ulnar head replacement. Additionally, ulna shortening alone will not alleviate symptoms of DRUJ instability, although it can be used in conjunction with a DRUJ stabilizing procedure if both instability and ulna impaction are present. The osteotomy should not be performed in isolation for radial malunions that include deformity other than just shortening. In this situation, corrective osteotomy of the distal radius is the appropriate procedure (although occasionally both radial and ulna osteotomies are necessary). Finally, the shortening should not be performed alone in Essex-Lopresti situations where the radial head has been previously excised. In this instance, continued shortening of the radius would be expected unless the osteotomy was performed in conjunction with a radial head replacement.
Surgical Technique
According to Lauder and colleagues the required and optional equipment needed for the ulnar-shortening osteotomy is minimal. The procedure, as described here, uses the TriMed, Inc. (Valencia, CA) ulnar-shortening system, although other shortening systems are available. Additionally, many freehand shortening techniques have been described. Other equipment required for this procedure include a radiolucent lateral arm board, a fluoroscopy machine, a wire driver and drill, a lobster claw reduction forceps, a set of baby Homan retractors, and a sagittal saw and saw blade (0.4-mm thick, 25-mm long). Occasionally, in revision cases it is helpful to have a Small Fragment Set with a 3.5 LCD plate available.
The patient should be in the supine position with a pneumatic tourniquet placed as high as possible onto the arm. The arm in its entirety should rest comfortably on a radiolucent hand table.
After exsanguinating the arm and inflating the tourniquet, a skin incision is made along the subcutaneous border of the ulna. This incision should begin 1 to 2 cm proximal to the ulnar styloid and continue proximally for 15 cm. Incisions at or distal to the ulnar styloid must be made carefully to avoid injury to the dorsal sensory branch of the ulnar nerve, although the incision typically does not extend this far distally. The incision is continued between the interval separating the ECU and the flexor carpi ulnaris (FCU). The periosteum of the ulna is then incised and the FCU and ECU are reflected using an elevator and baby Homan retractors. Care must be taken to avoid injury to the ulnar artery and nerve, which lie just radial to the FCU. A substantial portion of each muscle must be reflected to adequately visualize the osteotomy.
Whenever possible the plate should be applied to the volar surface of the ulna ( Fig. 7-5 ). Not only is there more soft tissue padding, but this side also tends to be the flattest surface of the ulna, allowing for the best plate to bone contact. If the volar surface is not practical, then the surgeon should choose the flattest side that is still amenable to adequate soft tissue coverage. Occasionally, plate benders may be necessary to contour the plate to account for variations in ulna shape. Plates can also be bent to compensate for the normal curvature of the ulna. This will help prevent gapping at the osteotomy site at the time compression is applied.
The position of the lag screw is dependent on both the arm being operated on and the location of the plate. For a right arm osteotomy and a volarly placed plate the lag screw hole must be distal to the osteotomy site. With a dorsally set plate the lag screw must be proximal to the osteotomy. The opposite is true for left-sided plates. Regardless of the orientation of the plate or which ulna is being osteotomized, it is critical that the two small holes on the side of the plate be easily accessible for mounting of the cutting guides.
The plate is provisionally secured to the ulna with the help of the Ulnar Plate Clamp™. Following drilling with the 2.3-mm bit, 3.2-mm diameter self-tapping screws are used to secure the plate to the ulna on the same side as the lag screw. When dealing with brittle bone, the 2.3-mm drill holes can be tapped to precut screw threads. A fourth screw is placed in the slotted (sliding) screw hole to affix the plate both proximal and distal to the planned osteotomy site. This screw should be placed at the end of the slot farthest from the lag screw. This allows for compression after the osteotomy is completed. At this point the combination Pin/Drill Guide™ is used to properly place two 0.62″ K-wires (Kirschner wires) in the slots away from the lag screw hole ( Fig. 7-6 ). The shorter (50-mm) K-wire is placed first followed by the longer (100-mm) wire. The differing K-wire lengths and the guide ensure the pins will remain parallel during insertion. The Pin/Drill Guide™ is now removed.
