Predicting the stability of Colles fractures after treatment determines the treatment approach. Orthopedic surgeons will try their best to pursue a good quality of closed reduction after a fracture occurs. However, when Colles fractures occur, many of them had already been decided whether they were suitable for conservative treatment. In this study, patients were followed prospectively for fracture displacement within 4 weeks, and 3 variables that might predict fracture redisplacement after Colles fracture reduction and splint fixation were obtained. These three variables correspond to three questions: (1) whether the patient's volar cortex can achieve good alignment after reduction; (2) whether the patient's dorsal cortical fracture is comminuted; and (3) whether the patient's radial displacement before reduction Significantly. We hope that these questions can provide a reference for clinical orthopaedic physicians in deciding whether to perform closed reduction and splinting in patients with Colles fractures.
First, the factor most strongly associated with fracture displacement after splinting was volar cortical alignment. Dhillon used digital photography to compare the thickness of the volar and dorsal cortices of the adult cadaveric radius in a dissection experiment and showed that the volar cortex was statistically significantly thicker than the dorsal cortex[10], thus suggesting that the supporting effect of the volar cortex on the distal radius is similar to the "calcar" of the femoral neck. According to Wolff's law, repetitive loads on the bone cause adaptive responses that allow the bone to better cope with these loads. In the case of the radius, most of these loads may come from muscle strength, and the volar cortex is responsible for maintaining the stress of the musculoskeletal system[11, 12]. The stabilization acts as a support rod like an angle iron pulley system. In a prospective multicenter study of 387 nonoperatively treated distal radius fractures, Wadsten found that 96% (53/55) of volar comminuted distal radius fractures were displaced, with no volar comminuted fracture displacement rates reduced to 72% (84/117), and after multivariate regression analysis, volar comminution was the strongest predictor of displacement[13]. Phillips concluded in the closed reduction and cast immobilization of patients with distal radius fractures in the emergency department that if the volar cortex recovered or maintained integrity during the operation, only 38% required further surgery, and vice versa if the volar dislocation or did not recover, then 65% required surgery, which suggested that anatomical reduction of the volar cortex became an important factor for the patient to avoid further surgery[14]. In our study, univariate and multivariate regression analysis and LASSO dimensionality reduction showed that the anatomical alignment of the volar cortex had a statistically significant difference between groups, and was positively correlated with non-displacement. The more anatomically aligned the cortex was, the more the effect of the "radial calcar" was exerted, and the more stable the fracture healing process was. When the volar cortex was anatomically aligned, the displacement rate was only 10.45%, and when the volar cortex was not anatomically aligned, the displacement rate was as high as 80.00%. The nomogram also indicated that volar cortical malalignment was sufficient as an independent risk factor for fracture displacement. Phillips believed that anatomical alignment of the volar cortex can effectively prevent axial compression of the fracture end, and restoration of the volar cortical hinge was a necessary step to allow external fixation to function under the "three-point index" condition and if the volar cortex did not recover, the rate of surgery was 7.5 times higher[14]. Combined with the mechanism of action of splint external fixation[15], we believe that good anatomical alignment of the volar cortex may play four important roles in the treatment of Colles fractures with splint external fixation: (1) The volar cortex can resist axial compressive stress and thus avoid short fractures; (2) The contact mechanism of the volar cortex enhances the meshing force of the fracture end; (3) The volar cortex provides the fulcrum of the fracture lever force to avoid slippage of the distal end of the fracture; (4) The volar cortex and the splint produce restricted and stable physiological stress which may help promote fracture healing.
Dorsal comminution is common in Colles fractures, and in this study, dorsal comminution was also one of the risk factors for predicting fracture redisplacement after splinting. Wichlas concluded that fractures without dorsal comminution had the best palmar inclination and "three-point index" values after manual reduction and cast external fixation, while dorsal comminuted fractures had equally ideal effects after reduction compared with fractures without dorsal comminuted[4]. He believes that this may be because the fixation force of the external fixation plaster provides reliable support on the dorsal side. However, in a prospective multicenter study by Wadsten, 73% (106/145) of dorsally comminuted distal radius fractures were later displaced, compared with 16% of non-dorsal comminuted fractures (13/81) displacement occurred later[13]. What’s more, another meta-analysis also concluded that dorsal comminution was an independent risk factor for poor prognosis after conservative treatment[16]. In our study, 49.06% of the fractures with dorsal comminuted were redisplaced, and only 11.36% of the fractures without dorsal comminuted were redisplaced. Dorsal comminution was statistically significant in both multivariate regression analysis and LASSO dimensionality reduction. The lack of dorsal cortical support after fracture reduction does not provide sufficient mechanical stability, which is why dorsal comminution has been identified as one of the instability criteria in many studies. For the type of dorsal comminuted fracture, in the treatment principle of early functional exercise, muscle contraction force acts on the fracture end, which not only produces axial compressive stress, but also shear stress of the bone fragment to the dorsal side. As discussed above, the splint external fixation system mainly provides elastic fixation against the vertical axis of the radius and lacks effective axial traction. The fixation force of the splint without a compression pad is relatively uniform, and it is difficult to effectively resist the tendency of displacement of the dorsal comminuted fracture. When the position of the pressure pad under the splint is not good or the loose splint cannot be adjusted in time, the effect force generated by the splint cannot offset the tendency of axial displacement of the fracture, and the fracture is more likely to be displaced.
There are few studies on the correlation between radial displacement before reduction and displacement after conservative treatment of Colles fractures. In this study, radial displacement before reduction was significantly correlated with displacement after fracture splinting, and the correlation coefficient and nomogram score were second only to volar cortical malalignment, which was one of the main risk factors for fracture displacement. We think this may be related to 2 factors. First of all, orthopaedic surgeons generally pay more attention to volar and dorsal reduction, because the main stress direction of Colles fracture is from volar to dorsal[17], so it is easier to ignore radial displacement during reduction. Secondly, splinting is a fixation that encourages early mobilization, and its fixation does not encourage crossing the distal carpal bone. Therefore, the stress of muscles such as the abductor pollicis longus and extensor pollicis brevis may cause further radial displacement of the distal end of the fracture fragment[18]. When the displacement reaches a certain level and cannot be corrected, three-dimensional fracture reduction will be lost. Therefore, we believe that the greater the degree of radial displacement of Colles fractures before reduction, the more severe the injury and the easier to ignore the reduction of the radial displacement direction is the basis of its displacement. The contractile activity of soft tissues such as the muscles of the affected limb provides adverse stress for its displacement tendency[19]. The fixation mechanism of the splint cannot counteract the pulling force of the muscles on the distal fragment, resulting in displacement of the fracture after fixation.