Distal radius fractures are commonly treated with open reduction and volar plate fixation using a modified Henry approach. This approach goes through the pronator quadratus (PQ). Since the PQ protects the flexor tendons, stabilizes the distal radio ulnar joint, gives blood supply to fractured fragment of the distal radius, and generates up to 21% of the pronation strength,1 some surgeons choose to repair it and some try to preserve it. In some difficult fracture patterns it is sometimes inevitable to detach it or even just difficult to repair it due to friable muscle fascia or bulky plate. Some literature shows that repair or sparing of the PQ does not significantly change functional results after distal radius fracture.2–4 Nonetheless, for protection of the flexor tendon, plate coverage by the PQ can be an argument toward the PQ sparing approach or repair. We conducted this study to determine what was the strength of 3 PQ repair techniques in order to determine which one to use when the PQ needs to be repaired.

MATERIAL AND METHODS

We conducted a study on 9 cadavers and used 18 forearms to form 3 groups of 6 forearms. The specimens were distributed equally in order to have similar age, sex, and dominant hand in each group. Cadavers who had previous history of surgery or fracture of the wrist, neuromuscular disease, or abnormal muscle on dissection were excluded. All forearms were dissected and the PQ was detached on the radial border of the radius, leaving a narrow band of tissue attached to the radius available for further repair. In each group a different repair method was used (shown in Fig. 1). In the first group, 2 separate cross sutures were performed on the fascia of the PQ with Dexon 2.0. In the second group a continuous suture of Dexon 2.0 was performed. Finally, in the third group, 2 suture anchors (Micro Corkscrew FT Arthrex, 2.2 mm×4 mm) were implanted on the radial border of the distal radius where the PQ was detached during the approach and the PQ fascia was reattached to the anchors with modified Krackows sutures. Then, the completely dissected forearm were placed in neutral rotation on a traction simulator (Fig. 2), which applied a distraction load between the 2 bones until there was failure of either the suture, the muscle, or the anchor which was represented by the sudden drop in tension in the muscle (load to failure measurement in Newton). The load required to cause a 5 mm displacement of the repair was also recorded. The type of failure was noted during the loading test by a single observer. Failure was categorized as the following: suture failure (S), muscle tear near the suture (MN) being a suture cut out through the muscle, muscle tear far from the suture (MF) being a tear within muscle fibers without being a suture cut out, and anchor failure (A).

FIGURE 1:

Drawing (1) and picture (2) of each repair technique. Simple sutures (A), continuous sutures (B), suture anchors (C).

FIGURE 2:

Example of a forearm placed in neutral rotation on the custom traction testing machine.

Statistics

Data were analyzed using SPSS version 20 (IBM). Groups’ mean load to failure and load to displacement were compared together with the Kruskal-Wallis test for independent sample. The 3 groups were then compared 2 by 2 with the Mann-Whitney test, to correct for the repeated comparison, the Bonferroni modification was used. Finally, the type of failure was compared between groups with the Fischer exact test for categorical variables.

RESULTS

For the load to failure, the Simple Suture (SS) group could resist 20.7 N, the Continuous Suture (CS) group, 33.3 N, and the Suture Anchors (SA) group 42.5 N (Fig. 3). When comparing the 3 groups there was a statistically significant difference. When comparing each suture method individually to the 2 others, there was a statistically significant difference between the SS and SA groups only (P=0.009 after Bonferroni correction). There was no significant difference between the SA and CS and the CS and SS. For the load to displacement, the strength of the SS, CS, and SA groups, respectively, were of: 20.0, 25.9, and 34.6 N (Fig. 4). Again, there was only a difference between the SS and SA groups with P=0.015. There was no significant difference between the SS and CS, and CS and SA groups. Finally, in the analysis of the mode to failure, in the SS group, there were 4 suture failures and 2 muscle failures near the suture. In the CS group there were 5 muscle failures near the suture and 1 suture failure. Finally in the AS group there were 3 muscle failures far from the suture, 2 muscle failures near the suture, and 1 suture failure.

FIGURE 3:

Load to failure for each group.

FIGURE 4:

Load to displacement for each group.

DISCUSSION AND CONCLUSION

This cadaveric study shows that a repair with suture anchors is stronger than simple cross sutures. There is no difference when comparing simple to continuous sutures and continuous suture to suture anchors for pure tensile loading. This result may be counterintuitive, but it probably reflects a lack of statistical power because there is a clear trend toward a linear increase in strength between the 3 groups. We used a cutoff diastasis of 5 mm to quantify the load to displacement because we believe it may clinically affect the quality of the repair. However, there is no available published data to support this at the moment. In that way again, there is only a difference between suture anchors and simple suture, with simple suture and continuous suture being equivalent. It seems that the failure site of the simple suture technique is the suture itself on the radial border of the fixation where there is minimal soft tissue available for reattachment. We can emphasize that this kind of reattachment can be even more difficult in the presence of an orthopedic implant, which was not the case and can be a limitation of this study. For the continuous suture method, the failure site seemed to be on the ulnar side of the repair in the PQ muscle. We can hypothesize that it can be caused by suture cutting through muscle or strangulating it by the continuous pattern. Finally, for the suture anchors, the most frequent site of failure was in the muscle, mostly far from the suture showing that the repair is probably stronger than the PQ itself. There was no suture anchor pull out showing again that it is the strongest mean of repair. This study is of course limited by the fact that it is a cadaveric study and bone and tissue resistance to repair could be different in vivo and dynamic with time and healing. We also acknowledge that the direction of the distraction was linear and not rotational as pronation is. However, the PQ muscle fibers are perpendicular to the bone which was the direction of the force applied to our cadaveric model. Even if we did not reproduce a rotational motion like pronation, the direction of the strain was the same as the contraction of the fibers. As noted by Mulders et al4 in a systematic review on repair of the PQ, it is difficult to conclude if clinical results after PQ repair are reliable because no study has shown the relation between the quality or durability of the repair and the functional outcome of a patient. Moreover, it is difficult to estimate what is the force needed by the repair to withstand physiological load of the PQ especially after surgery when the patient is immobilized for a short period. For this reason, it would be interesting to correlate this study in vivo and to measure the durability of the repair with an imaging tool after physiological loading in real life situation. It could then lead to new conclusion as if the PQ really need to be repaired after distal radius volar plate fixation and what repair technique is to be preferred. However, as shown by our study, if the PQ has to be repaired, simple cross and continuous sutures are probably insufficient means of repair from a biomechanical standpoint. The use and cost of suture anchors can then be debatable when no clinical evidence supports the need to repair the PQ for biomechanical outcome. If PQ repair is deemed necessary for soft tissue coverage or for biological aid in fracture healing, suture anchor is the strongest repair choice. This conclusion must be weighed against the fact that no in vivo tensile strength value sustained by the PQ is known in the literature and that SS could be sufficient to hold the repaired PQ while the wrist is immobilized post operatively.

ACKNOWLEDGMENTS

The authors thanks Denis Bisson and Claudia Beaulieu, prosectors in charge of the anatomy laboratory, for their valuable contribution. The author also thanks Dr Karina Lebel for her help in reviewing the statistical methodology for this project.

REFERENCES 1. McConkey MO, Schwab TD, Travlos A, et al. Quantification of pronator quadratus contribution to isometric pronation torque of the forearm. J Hand Surg Am. 2009;34:1612–1617. 2. Tosti R, Ilyas AM. Prospective evaluation of pronator quadratus repair following volar plate fixation of distal radius fractures. J Hand Surg Am. 2013;38:1678–1684. 3. Hershman SH, Immerman I, Bechtel C, et al. The effects of pronator quadratus repair on outcomes after volar plating of distal radius fractures. J Orthop Trauma. 2013;27:130–133. 4. Mulders MAM, Walenkamp MMJ, Bos FJME, et al. Repair of the pronator quadratus after volar plate fixation in distal radius fractures: a systematic review. Strategies Trauma Limb Reconstr. 2017;12:181–188.