Clinical DRUJ instability does not influence the long-term functional outcome of conservatively treated distal radius fractures

During the research visit DRUJ instability of both the injured and non-injured wrist was tested by an experienced trauma surgeon not involved in the initial treatment and unaware of the injured side. Static instability was tested using the stress test [8, 11, 12]. The test was considered positive if there was more anterioposterior movement, in any direction, of the ulna relative to the stabilized radius in the injured wrist compared to the uninjured wrist. Dynamic instability was tested using the clunk test [13]. The test was considered positive if a “clunk” was palpable for either the patient or examiner, during pronosupination of the lower arm with the wrist held between the examinator’s thumb and index finger.

Further physical examination of both wrists consisted of measurement of range of motion and grip- and pinch strength for both the injured and non-injured wrist. Range of motion was measured using a goniometer. Grip and pinch strength were based on the mean value of three successive measurements using a Jamar^® Hydraulic Hand Dynamometer and a Jamar^® Hydraulic Pinch Gauge, respectively. Maximum range of motion of the injured wrist was expressed in degrees and as a percentage of the non-injured wrist.

Conventional trauma radiographs in lateral and anterioposterior view were evaluated by one observer (MW) to determine the fracture classification according to the Comprehensive Classification of Fractures [14]. CT scans of both wrists were obtained and evaluated for radiocarpal arthritic changes according to the classification of Knirk and Jupiter and for union of the ulnar styloid, if a fracture was previously present [15]. The CT scans were made at 3-mm intervals using an Aquilion One (Toshiba Medical Systems). Axial sections of the wrist were obtained with the arm outstretched position above the head in prone position to minimize the exposure to radiation.

Participants scored pain on a visual analog scale five times for the posttraumatic wrist, indicating perceived pain (1) in rest, (2) with 10 kg loadbearing with the elbow extended and (3) with 10 kg loadbearing with the elbow 90° flexed, (4) during pronosupination without loadbearing and (5) during pronosupination with 10 kg of loadbearing. Furthermore, the Disabilities of the Arm, Shoulder and Hand (DASH) score, Modified Mayo Wrist Score (MMWS) and Gartland and Werley score were filled out by the participants [16‐18].

Baseline characteristics and outcome scores of the clinically DRUJ stable and unstable groups were compared. The static DRUJ unstable group was compared to the stable group, as was the dynamic DRUJ unstable group. Continuous data were compared between groups by the independent samples t test, categorical data by the Pearson’s Chi-square test. Analyses were performed using SPSS version 20 (SPSS Inc, Chicago IL). p values below 0.05 were considered statistically significant.

In patients with an unstable DRUJ flexion and extension averaged 81° (range 58°–102°) and 89° (range 58°–110°), respectively. Radial deviation averaged 25° (range 5°–40°) and ulnar deviation averaged 40° (range 25°–58°). The average pronation and supination measured 84° (range 60°–100°) and 89° (range 75°–110°), respectively. In patients with a stable DRUJ of the injured wrist flexion averaged 68° (range 35°–92°) and extension 85° (range 55°–105°). Radial deviation averaged 24° (range 6°–40°) and ulnar deviation averaged 40° (range 21°–65°). The average pronation and supination measured 87° (range 68°–109°) and 92° (range 60°–118°), respectively. Function expressed as percentage of the uninjured arm is shown in Table 2. Flexion was found to be statistical significantly better in the DRUJ unstable group. Further results did not differ between patients with and without DRUJ instability.

In patients with an unstable DRUJ the grip and pinch strength averaged 98 % (range 59–115 %) and 101 % (range 51–133 %), respectively, indexing the uninjured for the injured wrist. In patients with a stable DRUJ, the grip and pinch strength averaged 93 % (range 63–132 %) and 95 % (range 50–161 %), respectively, indexing the uninjured for the injured wrist. No differences in strength were found between the groups (Table 2).

Ten of the DRUJ unstable patients revealed only static DRUJ instability, of which two suffered from wrist pain in rest and seven patients showed both static and dynamic instability, of which one suffered from wrist pain in rest. Two patients suffered from pain prior to the trauma, in the injured wrist.

In the DRUJ unstable group, three patients indicated pain in the injured wrist in rest with a mean of 5.3 (range 0–50). The mean outcome for pain, with 10 kg loadbearing with the elbow extended, with 10 kg loadbearing with the elbow 90° flexed, during pronosupination without loadbearing and during pronosupination with 10 kg of loadbearing on the VAS was 11.8 (range 0–70), 10.6 (range 0–60), 0.0 (range 0–0) and 11.2 (range 0–70), respectively. Mean DASH score was 10 (range 0–28). One patient did not fulfill the DASH. The MMWS was excellent or good in 16 and poor in one patient. The Gartland and Werley ratings were excellent in 5 patients, good outcome in 9 patients and fair in 3 patients.

In the DRUJ stable group, three patients indicated pain in the injured wrist in rest with a mean of 4.7 (range 0–80). Average outcome for pain with 10 kg loadbearing with the elbow extended, with 10 kg loadbearing with the elbow 90° flexed, during pronosupination without loadbearing and during pronosupination with 10 kg of loadbearing on the VAS was 9.3 (range 0–60), 7.7 (range 0–90), 3.0 (range 0–60) and 8.9 (range 0–80), respectively. Mean DASH score was 7.9 (range 0–68). The MMWS ratings were excellent or good in 25 patients, satisfactory in 5 and poor in 2 patients. The Gartland and Werley ratings were excellent and good outcome in 25 patients and satisfactory or poor in 7 patients.

There were no significant differences between DRUJ stable and instable groups in terms patient reported outcomes (Table 2). Comparing patients with static or dynamic DRUJ instability separately to stable DRUJ patients, no statistical significant differences were found (data not shown).

In the present study, only a significant better flexion of the wrist was found in the DRUJ unstable patients. No further differences in function or strength were found, comparing patients with a stable DRUJ to patients with an unstable DRUJ. Since flexion and extension of the wrist primarily concern the radiocarpal joint and not so much the DRUJ, finding a difference was not anticipated for this motion. The greater range of flexion in the DRUJ unstable group may be spurious given the relatively small number of patients and the absence of other plausible explanations. However, the expected difference in pronosupination, a movement mainly involving the DRUJ, was not found. A reason for this may be the influence of muscle dependent stabilizers of the DRUJ, such as the extensor carpi ulnaris tendon, the pronator quadratus muscle and the radioulnar interosseous membrane [19‐21]. During pronosupination the muscles tighten resulting in a more stable DRUJ, independent of ligamentous stabilization. These muscle-tension dependent stabilizers may also be the reason for absence of difference in grip- and pinch strength; a finding corresponding with the results of Lindau et al. [22]. Since muscle relaxation is warranted during the clinical tests, the DRUJ is no longer supported resulting in a positive testing result.

Distal radial ulnar joint instability results from malfunctioning of joint stabilizing structures. These stabilizers are, among others, ligamentous and therefore invisible on conventional radiographs and computed tomography (CT) without contrast. Secondary signs may be visualized using these radiological techniques. Since the triangular fibrocartilage complex (TFCC) attaches to the ulnar styloid process (USP), non-union of the USP may indicate loss of TFCC as a stabilizing factor. Static and dynamic DRUJ instability was found in 33 and 17 %, respectively, of the patients in the current study. No difference was found in the number of ulnar styloid non-unions in DRUJ unstable patients compared to DRUJ stable patients. This implies that the TFCC is not the only stabilizing structure and that non-union of the ulnar styloid has no influence on DRUJ stability, which corresponds with literature [9, 10, 23‐26].

According to Stoffelen et al., DRUJ instability may cause ongoing wrist pain [27]. Lindau et al. found no statistical difference in pain comparing lax DRUJ patients with DRUJ stable patients [22]. Similarly, in this study we found no statistically significant difference in pain between patients with or without clinical DRUJ instability. The absent difference in pain scores may be due to the long follow-up of this (4 years) and Lindau’s study (6 years), compared to the follow-up of 1 year in the study of Stoffelen et al. Still these conclusions should be interpreted with caution since ongoing pain after distal radius fractures can be caused by several factors which are not all evaluated in this and other studies [22, 28‐30].

Arthritic changes of the DRUJ after chronic instability have been described [31]. For this reason, it is remarkable that no arthritic changes in the DRUJ were found, despite symptomatic wrists in some patients. These results may be caused by the fact that symptoms were not attributed to a specific wrist region, e.g., the DRUJ region or follow-up as too short to develop DRUJ arthritic changes. Furthermore most distal radius fractures did not involve the DRUJ and may therefore not result in cartilage damage, a finding that may be seen in a posttraumatic incongruent DRUJ.

The shortcomings of this study include the small number of patients analyzed, due to the loss of follow-up of many patients and refusal to participate of many others. However, no differences in age or fracture type was found comparing participant with no participants so the participants may be assumed to be representative for the whole group although we were not informed about residual complaints in non-participants. Another study limitation is that, although widely used, the reliability and accuracy of the tests for determination of clinical DRUJ instability is uncertain. [8, 13, 27, 32] This may be due to the subjective qualification of “more laxity compared to the non-injured wrist” when using the stress test. Since the tests were done only once, by one investigator we were not able to establish inter- and intra-observer variation. In the absence of other clinical tests, the stress test and clunk test were used to mimic daily clinical practice and enable comparison of the results with published literature.

Furthermore, no information was available on the presence of DRUJ instability before the distal radius fracture. This aspect is hard to evaluate in any study since this pre-trauma information is generally lacking. Mikic [33] showed an increasing percentage of TFCC tears during lifespan, suggesting that degenerative DRUJ instability may have been present in some of the patients.