Introduction

The unstable distal radioulnar joint (DRUJ) may cause considerable disability. Ulnar-sided pain, clunk, prominent ulnar head, and weak grip are only a few of the associated problems. DRUJ arthritis is a consequence of chronic instability. DRUJ instability may be acute or chronic. In the acute setting, reduction followed by bracing or casting is advised unless there is a block to closed reduction. Chronic instability needs treatment to avoid functional loss and arthrosis. While much attention has been paid to the treatment of distal radius fractures, many of the poor outcomes are due to untreated or unrecognized injuries to the DRUJ and its components [1].

Various procedures for stabilizing the DRUJ have been described. Broadly, they may be categorized as: (1) extrinsic radioulnar tether, (2) extensor retinaculum capsulorrhaphy, (3) ulnocarpal sling (2 and 3 are indirect tether techniques) [2], and (4) reconstruction of volar and dorsal radioulnar ligaments [3]. Fulkerson and Watson used a tendon graft looped around the neck of the ulna and threaded through the radius as an extrinsic radioulnar tether [4]. The Herbert sling procedure is an extensor retinaculum capsulorrhaphy that stabilizes the DRUJ by utilizing an ulnar-based flap of extensor retinaculum [5]. A distally based strip of the flexor carpi ulnaris (FCU) tendon was used by Hui and Linscheid to reconstruct the volar ulnocarpal ligament constituting the ulnocarpal sling procedure [6]. This reconstruction also imbricates the dorsal radioulnar ligament upon itself, and the forearm is immobilized until ligament healing. However, an indirect radioulnar link through the carpus is slack and therefore does not restore sufficient DRUJ stability [2].

Since radioulnar stabilization procedures may cause some loss of mobility of the forearm [7], partial or complete resection of the ulnar head has been proposed but may cause a loss of stability, discomfort, or pain. As such, surgical treatment of chronic instability of the DRUJ remains a difficult problem. The ability to stabilize the DRUJ, providing sufficient stability to allow early rehabilitation and range of motion, while also providing flexibility which preserves forearm rotation is the utmost goal. In view of the complex nature of the DRUJ, as well as the diverse array of supporting ligaments, DRUJ stabilization requires a procedure that does not violate the joint-stabilizing structures and does not require a secondary surgery for implant removal.

A direct radioulnar tether does not guide the forearm through normal forearm rotation in addition to the risk of reducing rotation [2]. We hypothesized that using a nylon tape to create an intrinsic radioulnar tether can restore DRUJ stability, while also maintaining a functional range of forearm rotation and improved grip strength. We aimed to highlight this technique as an added treatment option for DRUJ instability and also present functional outcomes after this procedure.

Patients and methods

This prospective study included six cases of isolated DRUJ instability, five chronic, and one acute injury, treated during the period from 2009 until 2014. There were five dorsal and one volar dislocations; Fig. 1. Mean age was 32.1 years while mean follow-up was 37 months. Inclusion criteria included symptomatic instability of the DRUJ, radiographic evidence of DRUJ dissociation, clinical evidence of instability (Fig. 1), and failure of conservative treatment protocol of 6 weeks of splinting followed by local ultrasound and range of motion exercises. Exclusion criteria were DRUJ arthritis or instability due to bony pathology as distal radius malunion or displaced ulnar styloid fracture. All cases were males. Mechanism of injury and demographic data are shown in Table 1. Unstable ulnar head was documented both clinically and radiographically. Instability was clinically detected when the piano-key test and table top test were both positive. The impingement sign was negative in all patients. Radiographically, wrist postero-anterior (PA) and true lateral (LAT) views in zero rotation were used. All radiographs were compared to the contralateral side. When lateral views were equivocal, a clenched-fist PA view of both wrists in forearm pronation was done to assess DRUJ gap. The case with acute injury was reduced under anesthesia but was found highly unstable, and thus was also stabilized using this procedure. Time elapsed between injury and treatment ranged from 1 week to 6 months (average 11.3 weeks).

Fig. 1
figure 1

a Preoperative photo showing dimple due to volar dislocation of ulnar head and dorso-radial fullness. b PA and LAT x-rays documenting the volar ulnar head dislocation

Full size image
Table 1 Demographic data for all patients
Full size table

Surgical technique

Under general anesthesia, a direct approach to distal radius and ulna was used. Under C-arm control and with the forearm in supination (dorsal dislocated cases) or pronation (volar dislocation case) and manually compressing the two bones, two 2.0-mm Kirschner wires were drilled across the DRUJ, starting at the ulna and spaced 1 cm apart. One at a time, each wire was removed and its track drilled using a 2.5-mm drill bit, opening volar to the first compartment extensor tendons (Fig. 2). The tunnels were widened using a 3.2-mm drill bit (Fig. 2). Using the cannula of a 14-gauge spinal needle as a shuttle for a leading thread, nylon tape (polyamide 66–white woven non-absorbable tape; 6 mm × 70 cm [W277]—manufactured by Johnson & Johnson Intl., Ethicon, Somerville, NJ, USA) was folded (Fig. 3a) was passed across the radius then DRUJ, within the ulna and back again over a bone bridge (Fig. 3b). The folded tape was passed again across the DRUJ and out through the radius (Fig. 3c). The forearm was placed in a neutral rotation and the DRUJ was compressed to obliterate any gapping. The tape was tied over a bone bridge over the radius (Fig. 3d). To avoid knot slippage, we secured the knot after the first throw using a no. 0 prolene suture (Fig. 3d). A second throw of the nylon tape was then taken and the tape was cut. The course of the nylon tape and position of the knot over the radius is shown in Fig. 4. The position of the ulnar head within the sigmoid notch was checked under C-arm control. Range of forearm rotation was checked after knot tying before the final closure.

Fig. 2
figure 2

a Radial approach seen with 2.5-mm drill bit and Kirschner wire exiting through the radius. b C-arm image showing first wire starting at ulna, across DRUJ and through the radius. c C-arm image showing both the drill bit and second Kirschner wire passing from ulna to radius

Full size image
Fig. 3
figure 3

a Distal ulna exposed showing nylon tape across distal tunnel and Kirschner wire still within proximal tunnel. b Nylon tape passed across both tunnels; ulnar loop seen. c: Nylon tape pulled fully and loop rested against ulnar head (arrow). d From radial approach, final knot tied and cut (arrow), secured by prolene suture

Full size image
Fig. 4
figure 4

The course of the nylon tape and position of the knot over the radius

Full size image

Postoperative protocol

All patients were placed in an above elbow plaster of Paris splint for protection during the first 2 weeks. At week 2, stitches were removed, followed by splint removal and change to a below elbow cast for another 2 weeks. Physical rehabilitation consisting of warm packs, local ultrasound, exercises to restore forearm rotation, and range of motion exercises to restore wrist flexion and extension were started at 4 weeks, thrice weekly and continued until satisfactory rotation was established. A removable wrist brace was worn during the day and was removed during exercises.

Postoperative follow-up

Patients were examined weekly for the first 2 weeks, when sutures were removed. Plain radiographs (wrist PA and true lateral views) were used to check postoperative alignment (Fig. 5). Radiographs were taken immediately after the operation, every month for the first 6 months, then at 9 months, 1 year, and at the final follow-up. Functional outcomes were assessed using the patient-rated wrist evaluation score (PRWES) as well as flexion/extension, forearm rotation, and grip strength. Pain was assessed using the 10-cm horizontal visual analog score (VAS) for pain as well as the pain subscore of the PRWES.

Fig. 5
figure 5

Postoperative PA and lateral radiographs showing reduced ulnar head; no gapping and minimal dorsal alignment after reduction of volar dislocation

Full size image

Results

Postoperative wrist pain gradually subsided. Five patients reported improved grip strength. Forearm rotation was satisfactory in four cases and with mild painful limitation in two. Grip strength and functional score showed the most improvement. No foreign body reactions were reported until the final follow-up. Patient satisfaction was 83.3 %. Dissatisfaction occurred due to intolerance to the knot over the radius and limitation of forearm rotation. Mean VAS improved from 7.8 to 3.1 while mean PRWES improved from 77 to 24.1 points; Table 2. Wrist flexion improved from a mean of 39.1° preoperatively to 67.5° at final follow-up. Similarly, wrist extension improved from a mean of 46.6° preoperatively to 70.8° at final follow-up. Mean preoperative forearm supination was 38.3° preoperatively and improved to 52.5°, while pronation improved from 45° to 50.8° at final follow-up; Table 3. Radiographic evaluation showed no gapping in the PA view. The lateral view in zero rotation showed maintenance of reduction in four cases. Minimal dorsal displacement was detected in two cases, within 3 mm (Fig. 5). However, these patients showed acceptable forearm rotation and had no pain. Radiographs showed tunnel widening in one patient (case 5). Two patients reported pain related to the surgical sites, which gradually improved over 3 months. All patients returned to their previous work and activity. We report no re-operation.

Table 2 Preoperative and final PRWE score
Full size table
Table 3 Wrist and forearm range of motion for the patient cohort
Full size table

Discussion

Although isolated DRUJ dislocation is uncommon [8], unrecognized or untreated injuries to the DRUJ may lead to poor outcomes; thus, chronic instability requires DRUJ stabilization to avoid onset of arthritis. Treatment protocols are continuously evolving. Various tether techniques previously described involved the use of autologous tendon re-routing with added donor-site morbidity. We present here a group of patients treated using nylon tape to create a trans-osseous sling across the DRUJ, which restored stability, allowed forearm rotation, and required no removal.

The radius rotates around a fixed ulna with a wide radius of curvature of the radial sigmoid notch. Being shallow in relation to the ulnar head, this allows volar and dorsal translation of the ulnar head during rotation. This translation amounts to 2.8 mm dorsal and 5.4 mm volar in pronation-supination, respectively [9]. In the current technique, the tunnels were drilled to 3.2 mm, which allowed easy introduction of the folded nylon tape and ensured maintained dorsal-volar ulnar translation. Since motion of the radius about the ulnar head is a combination of rolling and sliding, not simple rolling [10], this allows the radius to move even when a tether is placed between the radius and ulna.

A 3.2-mm bony tunnel is technically sound, based on the fact that a tunnel greater than 3.5 mm in diameter would exceed one third of the distal ulna width (anterior-to-posterior) and may predispose to fracture [11]. Creating narrower bone tunnels would make passing the tape difficult and may further block rotation due to tight fit of the tape in the tunnels.

In addition to the radioulnar ligaments and the triangular fibro-cartilage complex (TFCC), the interosseous membrane (IOM) was found to play an important role in supporting the DRUJ [12]. Watanabe and co-workers reported the role of the distal IOM in supporting the DRUJ and found ruptured distal IOM in cases of dorsal dislocation. They also found that the distal IOM acts to constrain movement of the radius during forearm rotation, thus preventing dislocation of the radius from the DRUJ [12]. The study by Watanabe showed that the middle and proximal portions of the IOM were less important [12]. Further, the secondary stabilizers of the DRUJ including the IOM, ulnocarpal ligaments, and extensor carpi ulnaris subsheath provide sufficient stability to prevent instability following healing [13]. As such, creating a sling to restore and maintain the relative relation of the distal radius and ulna may allow healing of the IOM and secondary stabilizers in acute cases or may replace the radioulnar tether originally provided by the distal IOM.

A connection between distal radius and distal ulna maintains congruency of the DRUJ. When examining the relative role of the deep and superficial distal radioulnar ligaments in conferring longitudinal stability to the DRUJ, Shen and co-workers [14] found significantly more proximal migration of the radius when the deep ligament was sectioned. This indicates the important role of the volar and dorsal radioulnar ligaments in resisting longitudinal migration [12]. Similarly, creating a sling between the distal radius and ulna, passing across the radius through two bony tunnels and held over a bony bridge, can help resist or reduce proximal migration and aid in avoiding radioulnar gapping.

In addition to the static stabilizers, dynamic stabilizers also play a role. The deep head of the pronator quadratus is a prime stabilizer of the DRUJ. Viscoelastic forces within the deep head compress the ulnar head within the sigmoid notch during forearm rotation [12]. In view of this fact, we used the nylon tape to seat the ulnar head within the sigmoid notch. Over-tightening was avoided as it was thought to result in reduced forearm rotation. Manual compression helped avoid DRUJ gapping and nylon tape was manually tightened, checking for distal ulnar motion. We aimed at leaving minimal dorsal-volar ulnar motion and forearm rotation at the time of final knot tying.

The technique described by Adams and Berger is an anatomical reconstruction. Although the results are satisfactory, the technique is technically demanding, and the need to wrap the tendon around the neck of the ulna necessitates a considerable length of the tendon graft [11]. Moreover, to keep the ulnar head seated in the sigmoid notch, considerable tension needs to be applied to the tendon as it is wrapped around ulna neck. In the current technique, the nylon tape has no slack and the tunnels are straight, allowing easy manual tensioning.

A biomechanical research using a joint stimulator showed that repair of the wrist capsule restores normal kinematics better than a radioulnar ligament reconstruction [15]. Christopher and co-workers believe there is an opportunity to consider extrinsic soft tissue stabilization techniques, reporting good to excellent outcomes in a series of 14 patients using the Herbert sling technique (extensor retinaculum capsulorraphy) [15]. Similarly, we report satisfactory results using the current technique.

Injuries around distal radioulnar joint may be associated with distal radius fractures or fractures of the ulnar styloid [8]. In this case series, only cases of isolated DRUJ dissociation were included. This accounts for the low number of cases in this study. However, most literature reports were on limited numbers of patients. Sénéchaud et al. report a series of ten cases, while Tsai and Stilwell [16] report treating five cases. Similarly, Purisa et al. treated five cases [17].

Ellanti and Grieve reported that DRUJ dislocation resulted from fall on the out-stretched hand or, rarely, a blow to the ulnar aspect of the wrist which may be dorsal or volar [18]. This coincided with our findings (Table 1).

Fulkerson and Watson described an extrinsic radioulnar tether by using a FCU tendon graft looped around the neck of the ulna and threaded through the radius for the management of anterior dislocation of distal ulna [4]. Recently, this technique has also been used for traumatic DRUJ instability [17]. The technique presented here is an intrinsic tether, which creates a loop within the ulna, reducing the relative motion between the tape and the ulna, aimed at reducing foreign body reaction. Further, we avoided the need to harvest a tendon graft. However, case no. 5 underwent accelerated physical rehabilitation and showed tunnel widening on follow-up x-rays.

Previous techniques described the use of tendon autografts. For fixation, the ends were sutured to each other or the graft was fixed inside the tunnel using biodegradable interference screws or to bone using suture anchors [11]. No fixation implants were used in the current technique. We relied on tying the nylon tape, thus allowing tensioning of the tape to allow seating of the ulna head within the sigmoid notch, while also maintaining minimal translation.

Purisa and co-workers, using the Fulkerson-Watson reconstruction technique, treated five cases of isolated chronic DRUJ instability. MRI of three patients revealed tear of the TFCC at its attachment. All five patients were treated using this technique, which the authors reported as being easier than intra-articular techniques and had restored DRUJ stability satisfactorily [17]. Apparently, stabilizing the DRUJ may allow TFCC tears detached from the base of the ulnar styloid process to heal. In a biomechanical evaluation of DRUJ reconstructions, the authors found direct and indirect tether techniques as non-anatomic and do not restore normal biomechanics or joint stability [19]. Even though the current technique is a direct tether, we believe it can restore joint stability. In fact it may become extra stiff and this was a concern during knot tying.

Nylon tape has been used to reconstruct the acromioclavicular and coracoclavicular ligaments with low complication rates [20]. To our knowledge, this is the first report on use of nylon tape to stabilize the DRUJ. We report no complications after mean follow-up of 37 months.

Some authors advocated 6 weeks of immobilization in a cast followed by 2 months of wrist immobilization as motion and strength are recovered [2]. We avoided long periods of immobilization and used immobilization for only 4 weeks, 2 weeks of which were in a below elbow cast. The aims were to avoid undue wrist pain, swelling, and stiffness and to begin range of motion and muscle strengthening. We found this rehabilitation protocol satisfactory. We agree with Adams and Lawler that postoperative rehabilitation should not be aggressive and better extended over a 4–6 month period. One of our cases underwent an expedited physical rehabilitation protocol and developed tunnel widening appreciated on follow-up x-rays.

Limitations of this study include the small number of cases and absence of comparison with another treatment modality. Larger patient cohort is needed and thus we shall continue to recruit patients in order to report results on a larger patient group.

Conclusion

This procedure represents a direct tether across the joint, passing strictly within bone, thus avoiding soft tissue violation. Re-operation was not required since no hardware removal was needed and the implant was well tolerated. DRUJ stability was immediately attained. Forearm rotation was maintained and improved with physical rehabilitation. With improved forearm function and wrist grip strength, this simple procedure may be considered a new treatment option.