Does the pronator-sparing approach improve functional outcome, compared to a standard volar approach, in volar plating of distal radius fractures? A prospective, randomized controlled trial

In this randomized clinical trial for patients with DRFs, we compared clinical outcomes of treatment with volar locking plate fixation performed with either an SVA or a PqSA. We found that the SVA group showed significantly favourable PRWE and DASH scores, compared to the PqSA group, at 6 months after surgery. These scores were defined a priori as primary and secondary outcome parameters. At all other included time points, the PRWE, DASH, and MMWS values were not significantly different between the two study groups.

Since the volar approach has evolved into the standard surgical approach for treating DRFs, it has remained controversial as to whether the PQ muscle should be repaired [8, 10, 11, 31,32,33,34] and whether it should be spared from the start [13,14,15]. Proponents of the PQ repair and sparing approaches have argued that the muscle could protect the flexor tendons by covering the hardware, that pronation strength would be restored, and that distal radio-ulnar joint stability would be maintained and augmented [32,33,34]. On the other hand, opponents have claimed that tight closure of the muscle might lead to pain [11] and even to ischaemic contracture, which could result in limited forearm rotation [31].

Previous studies that compared PQ repair to non-repair did not find any differences in clinical outcome at 6 and 12 months postoperatively [8,9,10,11]. On the other hand, Tosti and Ilias demonstrated that patients displayed better grip strength and wrist flexion after PQ repair in early (at 6 weeks) postoperative clinical assessments [10]. A recent systematic review and meta-analysis by Shi and Ren included six studies that represented a total of 203 patients who received pronator repair and 180 patients who lacked pronator repair. They revealed that the two groups showed no significant differences in the DASH score or in pronation and grip strength [35].

A minimally invasive plate osteosynthesis combined with a pronator-sparing approach was first described by Sen and Harvey in 2008 [13]. Later, Dos Remedios et al. and Cannon et al. described the pronator-sparing approach combined with a standard FCR approach [14, 15]. The rationale behind introducing this approach was that, according to the authors, it required less soft tissue stripping, caused less flexor tendon stiffness postoperatively, and carried a lower risk of surgery-related complications compared to the standard approach. Those authors also suggested that potential benefits could include better pronation and grip strength, better stability of the distal radio-ulnar joint, and less scarring, which would result in a better range of motion. Based on these potential advantages, we hypothesized that a PqSA would yield better clinical outcomes than the SVA without PQ sparing.

Our results did not support our hypothesis. The two study groups showed no significant difference in the MMWS at any evaluated time point. The MMWS is a physician-based scoring system that evaluates pain, active wrist extension and flexion, and wrist grip strength (expressed as percentages of analogous measurements in the contralateral wrist) in addition to the ability to return to regular work and activities [22]. We found no differences in grip strength or range of motion between the two study groups. Therefore, we concluded that the PqSA did not influence the functional parameters of the wrist after a DRF. Fan et al. first compared the pronator-sparing and pronator-repair approaches in a comparable patient cohort [36]. They included patients with AO/OTA type A2 to C3 fractures who had a mean age of 42.5 years. They found that the pronator-sparing group had better grip strength, a greater range of motion in forearm rotation, and less wrist pain than the pronator-repair group at 1, 2, and 6 weeks postoperatively. However, consistent with our results, they found no significant differences in later assessments performed at 3 and 12 months. Another study by Itoh et al. that compared pronator sparing and pronator release and repair showed similar results [37]. In 65 patients with AO/OTA type C2 and C3 fractures, they assessed range of motion for wrist flexion and extension, forearm rotation, percentage of grip strength compared to the contralateral uninjured wrist, and pain at six different time points. Their results showed no significant differences in any functional parameters, except that the pronator-sparing group reported significantly lower pain scores at 2, 3, and 4 months postoperatively.

In this study, the PRWE was the primary patient-reported outcome measure. Originally described by MacDermid et al. in 1998 [18], the PRWE is a reliable tool for quantifying pain and disability after DRFs, and it was found to be the most sensitive outcome instrument for patients treated for DRFs [19]. We found that the PRWE revealed a significantly better score in the PqSA group at 6 months, but no significant difference was observed at any other time point. At 6 months, the absolute mean difference in the PRWE was 6.6 points, which was at the lower end of the previously published MCID (6–14 points) for the PRWE [27, 28, 30, 38]. While statistically different, the difference is most likely not clinically meaningful. At 6 months, we also found a significant difference (mean: 7 points) in the DASH scores between the two study groups which favoured the PqSA group. This value was below the previously published MCID (10–13.5 points) for the DASH score [30, 38]. Previous comparative studies showed that the sparing approach resulted in better clinical outcomes. For example, Fan et al. showed significantly better DASH values in the pronator-sparing group after 6 weeks, but only minimal, insignificant differences after 3 and 12 months [36]. They reported DASH scores of 26.3 in the repair group and 18.4 in the pronator-sparing group, which were below the values we measured at 8 weeks. However, similar to our results, the 8-point difference between their two groups was below the published MCID for the DASH score [30, 38]. That study did not include an evaluation at 6 months postoperatively. Itoh et al. also found significantly lower QuickDASH scores in the pronator-sparing group after 1 and 2 months [37]. Moreover, the difference was within the range of the published MCID (8–19 points) for the QuickDASH score [28, 30]. Nevertheless, they also failed to detect significant differences in the assessed clinical outcome parameters at a later postoperative time point.

This study had some limitations. As opposed to previous studies [36, 37], we did not assess clinical outcome parameters or patient-rated outcome measures in the early postoperative period. Therefore, we could not determine whether the PqSA was associated with favourable results at early time points, as shown in previous studies. Previous studies showed that the superficial head of the pronator quadratus muscle is the prime mover of forearm pronation [39]. Therefore, it would have been useful to measure the pronation torque in addition to the collected parameters. That measurement might have demonstrated a positive effect of the PqSA. Indeed, Armangil et al. previously demonstrated that inhibiting PQ function led to an 18.5% reduction in pronation strength [40]. A similar result was found by McConkey et al. [7], who used lidocaine to paralyse the PQ of healthy subjects and found that pronation torque was reduced by 21%. In contrast, studies by Ahsan and Yao [41] and Huh et al. [42] reported that a pronator muscle detachment had no effect on grip strength or pronation. Another study limitation was that our study included multiple surgeons and two different plate systems, which might have influenced the study results.

In conclusion, this randomized comparative clinical trial failed to demonstrate clinically relevant differences in outcomes between the PqSA and SVA for volar plate osteosynthesis in patients with DRFs.

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