Anatomical Predictors of Fracture Instability

Fracture instability may be defined as an inability to resist displacement after an anatomical reduction. The standard radiographic parameters of the distal radius include a radial inclination of 23 degrees (range 13 to 30 degrees), a radial length of 12 mm (range 8 to 18 mm), and an average volar tilt of 12 degrees (1 to 21 degrees).^2–5 There are difficulties in reliably predicting fracture instability based on radiographs alone. Algorithms have been developed to gauge the risk of redisplacement of a fracture after reduction, but to no avail. Two separate scoring systems have been devised to calculate this risk based on the initial injury films. In a prospective study of 80 patients, both scoring systems were found to underestimate the degree of fracture instability and to have a poor correlation with the predicted and the actual instability.⁶

In a now classic article, Lafontaine and colleagues⁷ identified numerous risk factors that were associated with redisplacement of a distal radius fracture despite an initial satisfactory reduction. These included the presence of dorsal tilt greater than 20 degrees, comminution, intra-articular involvement, an associated fracture of the ulna, and age older than 60 years. If three or more of these factors were present, there was a high likelihood of fracture collapse. Altissimi and coworkers⁸ noted that the severity of the initial radial shortening alone seemed to be a reliable indicator of late instability.

Advanced age influences fracture instability because of the associated osteopenia. In patients older than 60 years, Leone and coworkers⁹ found that the degree of radial shortening, volar tilt, the amount of dorsal comminution, and advanced age were predictive of early or late failure. An unexpected finding was that one third of undisplaced fractures occurred in patients older than 65 years. Abbaszadegan and colleagues¹⁰ determined that age was the only statistically significant predictor of secondary displacement. After obtaining an acceptable initial closed reduction, patients who were older than 60 years had four times the risk for 4-week failure over patients younger than 60 years. The risk for displacement increased as age increased.

One can surmise from these observations that there is a higher likelihood of secondary fracture collapse in elderly patients even with less initial displacement. In this age group, Dicpinigaitis and associates¹¹ found that fracture site settling may occur for up to 6 months. Because of the risk of late collapse, adjuvant internal fixation with locking plates should be considered in elderly and osteopenic patients.

Greater force is necessary to fracture the radius in younger patients because of their higher bone density, which can result in more comminution and a higher risk of subsequent fracture collapse.¹² In young patients, lesser degrees of fracture site displacement can be tolerated, so adjuvant external or internal fixation should be considered. Trumble and coworkers^13,14 recommend internal fixation if there is more than 2 mm of radial shortening and more than 15 degrees of dorsal tilt after a closed reduction, if there is comminution of more than two cortices, or if there is a displaced intra-articular component.

Anatomical Predictors of Osteoarthritis

Articular congruity is paramount in the development of post-traumatic osteoarthritis. In a classic article, Knirk and Jupiter¹⁵ retrospectively reviewed 43 intra-articular fractures in 40 young adults (mean age 27.6 years) that were treated at Massachusetts General Hospital, with a mean follow-up of 6.7 years. Because most of the fractures (38 of 43) were treated with older, nonrigid fixation methods that were popular at that time, including cast or pins and plaster, there was a high incidence of residual intra-articular incongruity. Knirk and Jupiter¹⁵ noted that radiographic evidence of arthritis was present in 8 of 8 of the fractures in which articular incongruity was 2 mm or more, in contrast to only 2 of 19 of the fractures that healed with a congruous joint. Osteoarthritis was found in 22 of 24 of the patients who had any step-off whatsoever.¹⁵

In their study of 59 patients, Altissimi and coworkers¹⁶ found a 31% incidence of osteoarthritis when there was 2 mm or more of articular step-off at the 3.5-year follow-up. Catalano and colleagues¹⁷ studied 21 patients younger than 45 years old who had undergone internal fixation of displaced intra-articular fractures. At an average of 7.1 years, osteoarthrosis of the radiocarpal joint was radiographically apparent in 16 wrists (76%). A strong association was found between the development of osteoarthrosis of the radiocarpal joint and residual displacement of articular fragments at the time of bony union (P < .01). The authors revisited 16 of these patients at 15 years. Arthrosis was present in 13 of 16 of the wrists, and there was an additional 67% reduction of the joint space.¹⁸ Even 1 mm of intra-articular congruence has been associated with the development of arthrosis.¹⁹

The predictive value of these studies is that articular incongruity after a distal radius fracture is the most significant factor in the development of radiocarpal osteoarthritis. Articular displacement that is identified on the initial injury films warrants a more aggressive surgical approach.

Predictors of Residual Impairment