Biomechanics of Ulnar Impaction Syndrome

Ulnar impaction syndrome is characterized by pain and swelling that typically develop in patients with excessive loading across the distal ulna. 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.¹ 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%. Furthermore, these investigators reported that 73% of wrists with tears of the TFCC had either an ulnar-positive or ulnar-neutral variance, indicating that overloading of the ulnar wrist can ultimately lead to injury and degeneration of the TFCC.

The “TFCC,” a term coined by Palmer and Werner in 1981,² is a ligamentous and cartilaginous structure found between the distal ulna and ulnar carpus that, along with the bony architecture in this region, helps maintain the relationship of the distal ulna to the distal radius (Figs. 32-2 and 32-3). Strong volar and dorsal ligaments, termed the “dorsal and palmar radioulnar ligaments,” serve as a capsule surrounding the DRUJ. These ligaments continue onto the horizontal surface of the distal ulna, where they become thickened and serve as limbi for the TFCC. Ultimately, these ligaments go on to attach to the base of the ulnar styloid. Biomechanical studies have revealed a complex interplay between these ligaments and the motion that occurs at the DRUJ. DiTano and coworkers showed that the palmar radioulnar ligament becomes taut in supination, whereas the dorsal radioulnar ligament tightens with pronation (Fig. 32-4).³ This holds importance for different instability patterns that can occur at the DRUJ.

FIGURE 32-2 View from dorsal to palmar of the triangular fibrocartilage complex (TFCC). S, scaphoid; L, lunate; Tq, triquetrum, R, radius; U, ulna; UT, ulnotriquetral ligament; UL, ulnolunate ligament.

(Adapted from Palmer AK. Triangular fibrocartilage complex lesions: a classification. J Hand Surg [Am]. 1989; 14: 595.)

FIGURE 32-3 View looking palmar to dorsal of the volar structures forming part of the TFCC. TC, triquetral capitate ligament; TH, triquetral hamate ligament; LT, lunotriquetral ligament; T, triquetrum; P, pisiform; L, lunate; UL, ulnolunate ligament; UT, ulnotriquetral ligament; UC, ulnocapitate ligament; U, ulna; R, radius; PRU, palmar radioulnar ligament; IOM, interosseous membrane.

(Adapted from Trumble TE: Distal radioulnar joint and triangular fibrocartilage complex. In Trumble TE: Principles of Hand Surgery and Therapy. Philadelphia: WB Saunders, 1999; 129.)

FIGURE 32-4 Axial diagrams of the distal radioulnar joint show that tension in the dorsal and palmar radioulnar ligaments is dependent on forearm rotation. In supination the palmar radioulnar ligament is tight, whereas in pronation the dorsal radioulnar ligament becomes taut.

(Adapted from Bedner MS, Arnoczky SP, Weiland AJ. The microvasculature of the triangular fibrocartilage complex: its clinical significance. J Hand Surg [Am]. 1991; 16: 1103.)

Historical Results of the Procedure

The first ulnar-shortening osteotomy was described by Milch in 1941.⁴ He elected to utilize the procedure on a 17-year-old patient who developed a painful ulnar-positive wrist from a distal radius malunion. Milch’s technique entailed resection of a portion of the ulnar shaft with wire fixation at the osteotomy site. Since this initial description, numerous authors have described various osteotomy types, including transverse,^5,6 oblique (of varying degrees),^6–10 sliding (long oblique),¹¹ and step cut.¹² Several commercially available systems have been developed to facilitate bony contact, compression, and rigid fixation at the osteotomy site.^6,10,11

Attempting to elucidate which osteotomy provides both stability and rapid healing potential, while remaining easy to perform, can be an arduous task. Many authors have reported good results with any of the osteotomy methods just mentioned. In 1995, Wehbé and colleagues reported on their results for ulnar shortening utilizing a transverse osteotomy and the AO small distractor.⁵ In their 24 patients with ulnar impaction syndrome, they had no nonunions and an average time to healing of 9.7 weeks. They did have three delayed unions, but these reportedly healed without incident by 28, 34, and 36 weeks. It should be noted that their criteria for bony healing were quite stringent and if they had used criteria utilized by previous authors their delayed unions would have coalesced by 12, 16, and 20 weeks.

In 2005, Darlis and associates reported their results on 29 patients who underwent a step-cut osteotomy of the ulna for various pathological conditions.¹² Average time to union was 8.3 weeks, and they had no delayed unions or nonunions. Although these authors deem this a simple technique, it does require more cuts than transverse or oblique osteotomies.

Many surgeons today prefer an oblique osteotomy based in large part on a 1993 study by Rayhack and associates.⁶ In that study, 23 transverse osteotomies in which a specialized external compression device was utilized were compared with 17 oblique osteotomies in which a cutting guide designed by the lead author was implemented. Average healing times for the transverse osteotomies was 21 weeks compared with 11 weeks for the group with the oblique osteotomies. Furthermore, one nonunion was noted for the transverse group. Importantly, Rayhack and associates also reported on the biomechanical differences between the two constructs. Cadaveric data revealed no significant difference between the oblique or transverse cuts in regard to anteroposterior or lateral bending strength. The oblique osteotomy was found, however, to be significantly stiffer in torsion.

Several authors utilizing different systems for performing oblique osteotomies have corroborated the excellent results demonstrated by Rayhack and associates. Reporting on 27 patients (30 osteotomies), Chun and Palmer described their results for the oblique osteotomy utilizing a freehand technique.⁷ The wrists were graded both preoperatively and postoperatively with a modified Gartland and Werley system.¹³ Preoperatively, 28 wrists were graded poor and 2 as fair. Postoperatively, 24 wrists were graded excellent with 4 good results, 1 fair result, and 1 poor result. There were no nonunions. Chen and Wolfe also reported good results for the oblique osteotomy utilizing a freehand technique and an AO compression device.⁸ Preoperatively, 14 wrists were graded fair and 4 poor whereas, postoperatively, 13 were graded excellent, 3 good, and 2 fair. They also had no nonunions. Most recently, Mizuseki and colleagues reported their results for 24 oblique osteotomies created by their own device.¹⁰ Healing time averaged 8.1 weeks, and they had no nonunions.

Trumble and colleagues combined arthroscopic repairs of the TFCC with ulnar-shortening osteotomies.¹⁴ Their patients regained 83% of their total range of motion and 81% of their grip strength when compared with the contralateral side. In 19 of 21 patients, pain symptoms improved from complaints of pain even with routine activities to having complete relief of pain with all activities postoperatively. The other two patients had decreased levels of pain after surgery but continued to have occasional discomfort with some heavy activities.

Indications

There are many situations in which the ulnar-shortening osteotomy may be indicated. The most common indication is to eliminate the overloading that occurs in an ulnar impaction syndrome. Other indications include tears of the TFCC that cannot be repaired, previous radial head excision, and associated Essex-Lopresti lesions that result in a ulnar-positive variance (provided the intraosseous membrane instability has been corrected either with a radial head implant or bone-ligament-bone graft), attritional lunotriquetral ligament tears, ulnar nonunions, radial malunions resulting in an ulnar-positive variance, and early post-traumatic distal radioulnar joint (DRUJ) arthritis. Importantly, a shortening osteotomy can also prove beneficial in patients with signs and symptoms of ulnocarpal impaction but radiographs that demonstrate ulnar-neutral or slightly ulnar-negative variance.

Contraindications

The absolute contraindications for the ulnar-shortening osteotomy are minimal. Certainly, an osteotomy should never be performed in an infectious situation in which the hardware could become a nidus and/or the osteotomy site could go onto an infected nonunion. Along this same line, any patient with open wounds that would leave exposed hardware should be evaluated for soft tissue coverage before an osteotomy. The osteotomy should not be performed in isolation for radial malunions that include deformity other than just shortening. Simply shortening the ulna will not restore a congruent sigmoid notch if the deformity present in the distal radius is not also addressed. 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

The typical patient who benefits from an ulnar-shortening osteotomy relates a history of ulnar-sided wrist pain that is exacerbated by pronation/supination activities and forceful grip. On examination many patients will have swelling and tenderness localized to the TFCC and distal ulna (Fig. 32-5). 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. 32-6). Another valuable examination maneuver is the ulnar stress test as described by Nakamura and colleagues.¹⁵ This test is considered positive when pain is elicited by axially loading, flexing, and extending a patient’s pronated and ulnarly deviated wrist. The “fovea test” is performed by asking the patient to flex the wrist. This allows palpation of the FCU, which facilitates locating the fovea of the TFCC—between the flexor carpi ulnaris and ulnar styloid process. Exclusion of other sources of discomfort, such as pisotriquetral arthritis, DRUJ instability or arthritis, or extensor carpi ulnaris tendinitis or hypermobility heightens the suspicion for a pathological process of the TFCC. Plain radiographs, including posteroanterior and lateral views, should be obtained on every patient. Not only do these help determine the amount of shortening that will be required, but they also help determine if there are any other conditions (i.e., lunotriquetral instability/degeneration) that may need to be addressed. Importantly, one must obtain a true posteroanterior view of the wrist with the shoulder abducted to 90 degrees, elbow flexed to 90 degrees, and wrist in neutral rotation. The significance of a true posteroanterior view stems from the fact that rotation at the wrist can increase (pronation) or decrease (supination) ulnar variance. With this in mind, a posteroanterior view of a pronated wrist can be helpful in patients who develop pain during activities that require pronation (i.e., hammering, typing). These patients may not be experiencing symptoms until their ulnar variance becomes positive with pronation.¹⁶ Plain radiographs of the contralateral wrist may be helpful for determining the amount one wants to shorten the ulna. Contralateral views are not as useful, however, when that wrist is also ulnar positive. Magnetic resonance imaging or arthrography may be a reasonable adjunct to the radiographic evaluation when the surgeon suspects an acute tear of the TFCC that possibly can be repaired.

FIGURE 32-5 Patients with overloading of the distal ulna or a pathological process of the TFCC will often have tenderness and/or swelling in an area just distal to the ulnar styloid.

FIGURE 32-6 The ulnar impaction maneuver is performed by ulnarly deviating the wrist (A) and translating the carpus in volar and dorsal directions (B). This maneuver is positive when pain is elicited.

The required and optional equipment needed for the ulnar-shortening osteotomy is minimal. The procedure, as it will be described here, does require an ulnar-shortening system from Trimed (Valencia, CA). Other equipment required for this procedure includes a radiolucent lateral armboard, a fluoroscopy machine, a wire driver and drill, a lobster claw reduction forceps, a set of baby Hohmann retractors, and a sagittal saw and saw blade (0.4 mm thick; 25 mm long). Occasionally in the revision cases it is helpful to have the 3.5-mm AO Small Fragment Set (Synthes, Paoli, PA).

The patient is placed in the supine position with a pneumatic tourniquet as high as possible on the arm. The arm in its entirety should rest comfortably on a radiolucent hand table.

After exsanguination of the arm and inflation of 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. The incision is continued between the interval separating the extensor carpi ulnaris and the flexor carpi ulnaris. The periosteum of the ulna is then incised and both muscles are reflected using an elevator and baby Hohmann retractors. Care must be taken to avoid injury to the ulnar artery and nerve, which lie just radial to the flexor carpi ulnaris. 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. 32-7). 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, it is necessary to utilize plate benders to contour the plate to account for variations in ulnar shape. Plates can also be bent to overcompensate for the normal curvature of the ulna. This will help prevent gapping at the osteotomy site at the time compression is applied.

FIGURE 32-7 Intraoperative photograph demonstrating the 15-cm incision and volar plate placement. Most often the volar surface is the broadest and flattest for plate application. Baby Hohmann retractors protect the underlying soft tissues.

The position of the lag screw depends 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 will be distal to the osteotomy site. With dorsally set plates in the right arm the lag screw will be proximal to the osteotomy. The opposite is true for left-sided plates in which for volar plates the lag screw will be proximal and for dorsal plates the screw starts distally. 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 the cutting guides.

The plate is provisionally secured to the ulna with the help of the ulnar plate clamp. Using the 2.3-mm drill bit, 3.2-mm diameter self-tapping screws are used to fix 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 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 applied. Two 0.062-inch Kirschner wires (K-wires) are placed in the slots of the guide that are away from the lag screw hole (Fig. 32-8). 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.

FIGURE 32-8 A, The plate is initially secured with three screws on the same side as the lag screw. On the other side, a screw is inserted into the slot at the point farthest from the lag screw. Similar to the slot screw, two 0.062-inch K-wires are inserted in separate slots at a point farthest from the lag screw. B, Close-up view of the K-wires being inserted at a point farthest from the lag screw. Inserting the K-wires and slot screw away from the lag screw will allow for in-line compression after the osteotomy is completed.

Correlating to measurements made from preoperative radiographs for ulnar variance, a cutting guide is selected for the intended amount of resection (2 to 5 mm). Marked “A” and “B,” these cutting guides are designed with pegs that can only be inserted so that the osteotomy cuts are made perpendicular to the path of the planned lag screw. Guide A is placed first. This guide defines the width of the osteotomy and is marked as either A-2, 3, 4, or 5 mm (Fig. 32-9). Five millimeters is usually the maximum correction required, but it can be more in certain trauma situations. After placing baby Hohmann retractors around the ulna to protect the adjacent soft tissues, the osteotomy is completed. Use of saline irrigation is recommend to cool the saw blade and prevent thermal injury. Guide A is then replaced with the finish cutting guide B. Once the sequential osteotomies have been completed the bone wafer is detached from its soft tissue attachments and excised (Fig. 32-10). Of paramount importance for the procedure is to keep the plate firmly fixed to the ulna to ensure parallel osteotomy cuts. Therefore, screws should be checked during the osteotomy and retightened as necessary to prevent plate slippage.

FIGURE 32-9 “A” and “B” guides for completing the osteotomies. Note that the A guides are available for 2-, 3-, 4-, or 5-mm resections.

FIGURE 32-10 A, Application of guide A, which will determine the amount of ulnar shortening. Note the guide slides directly into the side of the plate. B, Completion of the first osteotomy through guide A. C, Completion of the second osteotomy through guide B and wafer removal.

The peg of the bone compression clamp is inserted into the side of the plate. The cannulated portion of the clamp is then used as a drill guide to place a third 0.062-inch K-wire low on the bone between the slotted hole and the two parallel K-wires previously inserted. The position of this third wire creates compression forces perpendicular to the osteotomy. The screw in the slotted hole is then loosened to allow compression at the osteotomy using the bone compression clamp (Fig. 32-11). Once compression has been achieved, the slot screw should be retightened. At this time radiographs should be obtained to determine if the ulnar variance has been corrected to neutral or slightly negative. It is important to check that plate contact has not changed due to a changing radius of curvature of the ulna from shortening. If this does occur, the plate may need to be bent a second time to afford better conformity and plate contact.

FIGURE 32-11 A, Graphic depiction of the bone compression clamp in position and compressing the osteotomy as the plate slides on the slot screw and K-wires. B, Intraoperative photograph showing the compression clamp in place before compressing the osteotomy. C, Intraoperative photograph demonstrating compression at the osteotomy site while a lag screw is being inserted.

To insert the lag screw the pin/drill guide can be reapplied or the surgeon can choose to drill the hole freehand. A 3.2-mm drill bit is used first for the near cortex (Fig. 32-12). This is followed by the 2.3-mm drill bit, which is sent through the far cortex. The lag screw should be tapped to guarantee good purchase of the screw threads. A lag screw of appropriate length (normally 18 to 20 mm) is inserted. The final two screws adjacent to the slotted hole are inserted, followed by removal of the drill guide, compression clamp, and three K-wires. Final radiographs should be obtained to ensure proper screw lengths (Fig. 32-13).

FIGURE 32-12 Graphic depiction of the hole preparation for the lag screw. Note the compression across the osteotomy site with the bone compression clamp. The slotted screw has been loosened, allowing the plate to slide proximally.

FIGURE 32-13 A, Preoperative radiographs show ulnar-positive variance in a patient with a long-standing history of ulnar-sided wrist pain. Postoperative anteroposterior (B) and lateral (C) views illustrating a healed osteotomy and ulnar-negative variance.

The wound is then irrigated and the tourniquet released to check for active bleeding. Wound margins can be injected with bupivicaine and epinephrine for both hemostasis and postoperative analgesia. A drain is placed, and the fascial interval between the flexor carpi ulnaris and extensor carpi ulnaris is closed to avoid muscle herniations. The subcutaneous and skin layers are closed separately with interrupted sutures. A long arm, well-padded splint is then applied.

Patients are seen at 2 weeks for their first postoperative visit when sutures are removed. Compliant patients are fitted with a removable long arm splint fabricated by one of our hand therapists. This allows for removal during showers and commencement of elbow flexion and extension exercises. Noncompliant patients are placed into a long arm cast. At 6 weeks, radiographs are obtained and gentle wrist range of motion exercises are started if there are early signs of bony consolidation. If there are more signs of bony union at 9 weeks, then the patients are instructed to begin gentle strengthening exercises.

Complications

In a properly performed osteotomy the complications are minimal. The most commonly reported adverse outcome is hardware prominence and tenderness.^8,10,12 In our series of 17 osteotomies we found that four patients ultimately required plate removal owing to ongoing problems with hardware prominence. Other possible complications include infection, delayed union, nonunion, and nerve palsies. In our patients we did not experience any of these situations. The risk of delayed or nonunions can be minimized by avoiding thermal injury during the osteotomy and ensuring good apposition and compression when securing the plate. Nerve palsies can be avoided by the careful placement of retractors during the osteotomy and plate placement. Furthermore, when incisions are made distal to the ulnar styloid, extreme care should be taken to identify and protect the dorsal sensory branch of the ulnar nerve as it courses from volar to dorsal.

Results

Seventeen patients were followed for a minimum of 12 months after undergoing shortening osteotomies with the Trimed system. Overall, the results were quite good, comparing favorably with other studies utilizing similar systems. Preoperative and postoperative range of motion, grip strength, pain, and Disabilities of the Arm, Shoulder, and Hand (DASH) scores are tallied in Table 32-1. Bony union, defined as bridging of the trabecular bone and cortical margin blurring, was achieved at an average of 7.41 weeks. The average shortening was 4.12 mm.

Summary

The ulnar-shortening osteotomy has become the gold standard for alleviating symptoms that stem from the overloading of the ulnar wrist that occurs with ulnar-positive variance. Although the technique can be technically demanding, especially when freehand cuts are made, the complications are few. Certainly, any number of systems and techniques can be utilized to create the osteotomy. Probably more important than the advantages or disadvantages of any technique is the surgeon’s comfort level with his or her particular approach. Regardless of the technique utilized, the goal with any shortening is to obtain an ulnar-neutral or slightly ulnar-negative variance with good apposition and compression at the osteotomy site.