Our study indicated that traumatic intramuscular rupture in the superficial head of the pronator quadratus after distal radius fracture may affect outcomes after DRF surgery via a volar approach. There was intramuscular rupture of the PQ in 27 patients (49%), and PQ was intact in 28 (51%) patients. This finding supports our alternative hypothesis that the rupture of the pronator quadratus muscle in addition to the L-shaped incision from surgery, which increases the risk of muscle denervation and scarring, can affect functional outcomes.
The literature on the integrity of the PQ muscle in DRF surgery is scarce. In their demographic data, Sonntag et al reported 75% intact PQ muscles prior to DRF surgery, while in 16,7% of 72 patients PQ muscles were not intact, but further analysis was not conducted on this matter17. In our study, we found an intact PQ muscle in 51% of the patients, demonstrating the importance of reporting this variable when discussing whether the PQ should be repaired after volar plating.
Our results are comparable to those of Zwigart et al who assessed pronator quadratus repair integrity following volar plate fixation for distal radius fractures18. In their 3-month follow-up study of 24 patients, they noted an intact PQ in 46% of patients. They reported no significant difference in ROM or grip strength between the intact and not intact groups. In their study, patients with a less severe PQ injury tended to have better grip strength, but the difference was not statistically significant. In our study, we did find a statistically significant difference in grip strength in favor of the intact group.
An anatomic study conducted by Sakamoto et al underlines important information on the innervation patterns of the anterior interosseous nerve to each head of the PQ muscle19. The branches innervating the superficial head run on the radius in a medial to lateral direction, and they advocate surgeries for distal radius fractures to be conducted on the more lateral forearm. We speculate that laceration and frying of the PQ muscle from the initial trauma, prior to surgical distal and radial detachment, may also potentially cause denervation of the muscle, thus affecting the outcome.
PQ muscle function after distal radius fracture may depend on many factors, including initial trauma, positioning and type of volar plate, muscle healing, retraction of an unrepaired muscle and durability of the repair in a repaired muscle. Fang et al found that the PQ muscle was replaced by scar tissue with nonintact muscle fibers in 103 patients on plate removal2. PQ muscle fibers were observed in 23 patients, although the muscle fibers were loose, thin, and decreased in number. Additionally, the remaining muscle fibers had different degrees of adhesion to the volar plates, radial carpal flexor muscles and interosseous membrane. They found no difference in outcome between the patients with healed PQ muscle and those without healed PQ muscle. In contrast to our study, Fang et al only included patients with an intact PQ muscle before release, indicating that scarring and fibrosis are not reserved for a ruptured PQ prior to surgery.
Some authors claim that patients experience an early effect of PQ repair. In a retrospective study of 63 patients, Pathak et al reported improved pain relief and ROM at 4 weeks, and improved grip strength at 3 months in the repair group20. We could not confirm these early findings in our study. Others speculate that a too tight repair can compromise PQ function. Hershman et al conducted a prospective study of 112 patients whose forearm ROM was the primary outcome and reported poorer radial wrist deviation in the PQ repair group21. This finding contrast with our findings, as we found no differences in ROM.
In a meta-analysis including five RCTs and six retrospective case-control studies, Lu et al did not find any functional benefit of PQ repair after volar plate fixation of DRF22. A subgroup analysis, however, revealed different effects on pronation strength in patients with different AO fracture types. Type B DRFs favored PQ repair and non-AO type B fractures favored no PQ repair. Only one study in the review provided grip strength data in comparison with the uninjured side, while the other studies only provided actual measured values in kilograms. In our study we found lower mean grip strength in the group with a severed PQ muscle. The difference was 17%, which is lower than the proposed MCID of 19.5%. This indicates that patients who present with a ruptured PQ after DRF have weaker grip strength. However, when individual results were compared to the opposite wrist, the two groups in our study recovered the same. We therefore suggest that grip strength data should be provided in comparison with the uninjured side when using grip strength as an outcome in treatment group comparisons. Other recent reviews and meta-analyses have concluded that PQ repair does not improve PROMs, ROM or grip strength1,23,24, which is in line with our findings.
Finally, the protective effect of PQ repair on flexor tendon irritation, flexor tendon rupture or symptomatic implant removal is not obvious, as adhesions and flexor pollicis longus rupture still occur after repair2,25.
Our findings suggest that patients with a ruptured pronator quadratus after DRF who undergo additional surgical release of the muscle via volar plating, have lower Quick Dash score and EQ-5D index scores after 1 year than patients with an intact PQ prior to surgical release. The difference in the QuickDASH may, however, be of minor clinical relevance as it is lower than the proposed MCID. Our findings may indicate that PQ rupture might be a confounding factor in studies comparing PQ repair or not.
The present study has several limitations. We did not assess the integrity of the PQ muscle using ultrasound or MRI throughout the healing period. Thus, we are not able to describe the failure rate of the repair or retraction of the unrepaired muscles in relation to clinical outcomes. Next, the decision to repair the PQ was not randomized, and we did not perform pronation or supination strength testing.
The present study also has strengths. First, a high follow up rate of 98%, and also the study population was quite homogenous, as patients with intraarticular fractures and younger patients were excluded from the original RCT.
In the present study, patients with an intramuscular rupture of the PQ muscle prior to volar plating in distal radius fracture surgery had an inferior clinical outcome compared to patients with an intact PQ. The differences were, however, less than those considered clinically relevant, and thus of uncertain clinical relevance to the individual patient. We encourage further larger randomized clinical trials to establish the clinical benefit of PQ repair and suggest that PQ integrity be reported.