Fractures of the distal part of the radius are commonly associated with a fracture of the ulnar styloid base, but the influence of the ulnar fracture on the outcome of treatment is unclear. These large ulnar styloid fractures include at least part of the origin of the triangular fibrocartilage complex and may represent an alternative to an intrasubstance tear of the triangular fibrocartilage complex in the setting of a displaced fracture of the distal part of the radius. There are few data available to clarify the debate between those who believe that a fracture of the ulnar styloid base contributes to the potential for decreased forearm rotation, arthritis, pain, and chronic instability of the distal radioulnar joint1-4 and those who do not5,6. Some authors have suggested that characteristics such as the size and displacement of the ulnar styloid fracture fragment may predict instability of the distal radioulnar joint3,7-10.
Using data from a prospective study of open reduction and plate fixation of fractures of the distal part of the radius, we retrospectively compared matched cohorts of patients with and without an untreated fracture of the ulnar styloid base to test the null hypothesis that an ulnar styloid fracture does not affect wrist function and arm-specific health status. In a second analysis, we tested the null hypothesis that there is no difference in wrist function and health status between patients with =2 mm of displacement of a fracture of the ulnar styloid base and patients with a less displaced fracture.
The patients included in this investigation represent a subset of patients from a large prospective cohort study that was performed for another purpose. Between 2001 and 2004, 420 patients were enrolled in a prospective multicenter cohort study of open reduction and plate-and-screw fixation of fractures of the distal part of the radius. Inclusion criteria were an age of eighteen years or older, open reduction and internal plate-and-screw fixation performed within ten days after the injury, and no prior open reduction and internal fixation. Exclusion criteria included general or local conditions that adversely affect bone physiology, such as tumor, hyperparathyroidism, and osteogenesis imperfecta; multiple traumatic injuries (an Injury Severity Score of >1611); coenrollment in another study; and a history of drug or alcohol abuse.
After excluding forty-one patients with inadequate preoperative radiographs and three patients with bilateral fracture, we considered 376 patients for inclusion in the current study. On the basis of clinical experience with the repair of ulnar styloid fractures in the setting of Galeazzi and distal radial fractures combined with our understanding of the anatomy of the origin of the triangular fibrocartilage complex, we made the otherwise arbitrary decision to consider any fracture involving =75% of the total height of the ulnar styloid process as a fracture of the ulnar styloid base. Thus, the fractures were all large enough to qualify for rigid fixation. The ulnar styloid fracture fragments were measured on posteroanterior and lateral digital radiographs with use of a calibrated measurement tool (eFilm; Merge Healthcare, Milwaukee, Wisconsin). Ulnar-sided fractures were classified as (1) absent (150 patients), (2) involving the tip of the styloid (thirty-two patients), (3) involving the base of the styloid (169 patients), (4) involving the ulnar neck (twenty-three patients), and (5) involving the ulnar diaphysis (two patients). Fractures at several levels (e.g., the ulnar neck and styloid or the ulnar neck and head) were classified according to the most proximal element of the fracture. Fractures that involved <75% of the height of the ulnar styloid were relatively uncommon and readily distinguished from larger fractures.
There were 242 women and 134 men with an average age of fifty-five years (range, eighteen to eighty-three years). The left wrist was involved in 205 patients and was on the dominant side in nineteen (9%) of them. The right arm was involved in 171 patients and was on the dominant side in 163 (95%) of them. The initial injury was a result of a fall from standing height in 236 patients; was a higher-energy injury such as one sustained in a fall from a height, a motor-vehicle collision, or a fall during sports in 103 patients; and had an unknown cause in thirty-seven.
Patients with an ulnar neck fracture were significantly more likely to be female and older (Table I). There were no other significant differences in demographic and injury-related factors among the patients with no ulnar fracture, those with a fracture of the ulnar styloid base, those with a fracture of the ulnar styloid tip, and those with a fracture of the ulnar neck.
Sixteen (7%) of the 226 fractures of the distal part of the ulna were treated with open reduction and internal fixation; the sixteen included nine ulnar styloid fractures, five ulnar neck and styloid fractures, and two diaphyseal ulnar fractures. The decision to perform the open reduction and internal fixation depended on the preference of the surgeon or the center and did not correspond with injury characteristics or radiographic appearance. Patients who received surgical treatment for the ulnar fracture were excluded from this study.
Matched Cohorts: Patients with an Untreated Fracture of the Ulnar Styloid Base Compared with Patients with No Ulnar Fracture
Of the 310 patients with an untreated fracture of the ulnar styloid base or no ulnar fracture, 241 (78%) had a six-month evaluation, 226 (73%) had a one-year evaluation, and 227 (73%) had a two-year evaluation.
A case-control study design was used. From the group of patients with at least twelve months of follow-up, two cohorts of seventy-six patients—one with an untreated fracture of the ulnar styloid base and the other with no ulnar fracture—were matched on the basis of (1) sex, (2) age within ten-year groups, (3) mechanism of injury (a fall from a standing height compared with a higher-energy injury mechanism), and (4) fracture type according to the AO classification (A, B, or C)12 with use of a frequency matching technique. There were no significant differences between these two matched cohorts with respect to the injured side, whether the injury was on the dominant side, Fernandez classification13, open injury, work before the accident, medical illness, concomitant injury, smoking history, interval between injury and surgery, operative approach, primary carpal tunnel release, supplemental stabilization (Kirschner wire or lag screw), or use of bone graft (Table II).
Six patients had complications, including loss of reduction in two (one in each cohort), loosening of a screw requiring a second operation to remove the screw in two (one in each cohort), a superficial infection requiring a reoperation for irrigation and débridement in one (in the cohort without an ulnar fracture), and a rupture of the extensor pollicis longus tendon in one (in the cohort with an ulnar styloid fracture).
Minimal Displacement Compared with Greater Displacement of Fractures of the Ulnar Styloid Base
In a separate analysis, we considered the complete cohort of 160 patients with an untreated fracture of the ulnar styloid base, not just those in the matched pairs. Of these 160 patients, 132 with at least six months of follow-up were analyzed. Seventy-eight of the 132 patients had a fracture that was seen to be displaced <2 mm on the injury radiographs and fifty-four had a fracture with =2 mm of displacement. Sixty-four patients (82%) with a minimally displaced fracture and forty-nine (91%) with a more displaced fracture were evaluated at one year, and sixty-six (85%) and forty-three (80%), respectively, were evaluated at two years. Our evaluation of displacement was based on these patients.
Of the patients with <2 mm of displacement of the fracture of the ulnar styloid base, fifty-five were women and twenty-three were men. The average age was fifty-seven years (range, twenty to eighty-three years). The original injury was a result of a fall from a standing height (a low-energy injury) in forty patients, was a higher-energy injury in fifteen, and had an unknown cause in twenty-three. None of the fractures were associated with a wound or an ipsilateral upper-limb injury.
Of the patients with =2 mm of displacement of the ulnar styloid fracture, twenty-six were women and twenty-eight were men. The average age was fifty-three years (range, twenty-one to seventy-nine years). The original injury was the result of a fall from a standing height in twenty-three patients, was a higher-energy injury in nineteen, and had an unknown cause in twelve. All fractures were closed, and none of the patients had an injury in the ipsilateral limb.
There were no significant differences between these two cohorts with respect to the baseline characteristics.
Clinical Evaluation
Each patient was evaluated according to the system of Gartland and Werley14 at six, twelve, and twenty-four months after the surgery. Patients also completed the Disabilities of the Arm, Shoulder and Hand (DASH)15 and Short Form-36 (SF-36)16 questionnaires and rated their pain both at rest and in motion on a 10-point visual analogue scale at each follow-up point.
Radiographic Evaluation
The alignment of the distal part of the radius was measured on posteroanterior and lateral radiographs with use of commercial software (eFilm). Ulnar inclination, palmar tilt, ulnar variance, and articular congruity were measured with use of the standardized techniques described by Kreder et al.17. Because the radiographs were digital and unscaled, it was not possible to measure ulnar variance and articular step-off in millimeters. Instead, we used a new technique for measuring ulnar variance and articular step-off in reference to the measured length of the capitate. We have investigated this technique and found it to be reliable, but our work has not yet been published. The length of the capitate was measured on posteroanterior radiographs with use of the guidelines described by Nattrass et al.18. Ulnar variance was reported as positive or negative with the interval expressed as a ratio to the length of the capitate. Radiographic signs of osteoarthritis were rated, with use of the system of Knirk and Jupiter, as grade 0 (no arthritis), grade 1 (slight joint-space narrowing), grade 2 (marked joint-space narrowing with osteophyte formation), or grade 3 (bone on bone with osteophyte and cyst formation)19.
Statistical Analysis
Patients with an untreated fracture of the ulnar styloid base were compared with those with no ulnar fracture to evaluate differences in wrist function and health status at six, twelve, and twenty-four months after the surgery. The likelihood ratio test was used to test the null hypothesis that there would be no difference in wrist function and health status between the two cohorts. Twenty-two parameters (each motion and radiographic measurement, grip strength, pain at rest, pain in motion, Gartland and Werley score, SF-36 mental and physical component scores, DASH score, arthritis grade, return-to-work status, and complications within two years) were assessed at each time interval (six months, one year, and two years) and regressed on two indicator variables (ulnar fracture and follow-up time) and one interaction term (ulnar fracture and time). The interaction term was included to determine whether a potential ulnar fracture effect was time-dependent. For each outcome, the repeated measurements of each patient were pooled and analyzed together in one overall linear regression model. This approach allows the assessment of an overall effect of an untreated fracture of the ulnar styloid base and of time on the outcome while considering all available data and avoiding multiple analyses at each follow-up point. In addition, it allowed us to quantify the effect of one factor (such as ulnar fracture) at each moment of follow-up within the same model.
The likelihood ratio test was used to study the overall effect of an ulnar styloid fracture on each of the twenty-two separate outcome parameters: the maximum likelihood estimate of the full regression model (including ulnar fracture, time, and the interaction term) was compared with that of a null regression model (time only) to determine whether adding the ulnar fracture variable would significantly improve the model. A significant value of this test reflects a significant difference in outcome due to the presence of an ulnar styloid fracture. In a similar fashion, the full regression model was compared with a model without the "time" variable to determine the overall time effect on outcome. Significance was adjusted for multiple testing with use of a Bonferroni correction. A p value of <0.003 (0.05/22) was considered to be significant. We then used the same full regression model to determine the effect size and timing (six, twelve, and twenty-four months) using the Wald test.
A post hoc power analysis was performed with use of repeated-measures analysis of variance as a model for our approach. It was determined that a sample size of seventy-six patients per group provided >99% power to detect a minimum difference of 10 points in the DASH score with a known standard deviation of 13. Forty-two patients per group would have been sufficient for 90% power.
In a second analysis, a similar approach was used to determine any differences in wrist function and health status between patients with an ulnar styloid fracture that was displaced <2 mm and those with greater initial fracture displacement.
The descriptive analysis of the entire database was performed with use of the Fisher exact test and the Kruskal-Wallis test. Baseline group comparison of the matched cohorts was performed with use of the Fisher exact and two-sample Wilcoxon rank-sum (Mann-Whitney) tests.
Source of Funding
Financial support for this study was received from the AO Clinical Investigation and Documentation in Dübendorf, Switzerland.
Matched Cohorts: Fracture of the Ulnar Styloid Base Compared with No Ulnar Fracture
Effect of Time on Outcome
Patients with an untreated fracture of the ulnar styloid base and patients with no ulnar fracture both had significant improvement in the arc of wrist flexion and extension, wrist flexion, wrist extension, the arc of forearm rotation, pronation, supination, the arc of radioulnar deviation, radial deviation, ulnar deviation, grip strength, and the DASH and Gartland and Werley scores between six months and one year.
Effect of an Untreated Fracture of the Ulnar Styloid Base on Outcome
According to the likelihood ratio test, a fracture of the ulnar styloid base had no significant effect on the overall outcome. However, when compared with the patients with no ulnar fracture, the patients with an untreated fracture of the ulnar styloid base had a trend toward less grip strength at six months (71% [of that on the contralateral side] compared with 79%; mean difference, -8% [95% confidence interval = -15.3% to -0.6%]; p = 0.03) and less flexion (54° compared with 59°; mean difference, -5° [95% confidence interval = -11.7° to -0.8°]; p = 0.02) and ulnar deviation (32° compared with 36°; mean difference, -4° [95% confidence interval = -7° to -0.1°]; p = 0.05) at twenty-four months (Table III).
Radiographic Evaluation
There were no significant differences between the groups with regard to the volar angulation, radial inclination, or ulnar variance of the distal radial fracture at any follow-up interval (Table IV). At one year, an intra-articular step-off was seen in six patients with an untreated fracture of the ulnar styloid base and in three patients with no ulnar fracture (p = 0.49).
Displacement of the Fracture of the Ulnar Styloid Base
There were no significant differences between the patients with <2 mm of displacement of the unrepaired fracture of the ulnar styloid base and those with =2 mm of displacement with regard to any outcome measure at six, twelve, or twenty-four months after the surgery (Table V).
In our study of patients in whom an unstable fracture of the distal part of the radius had been treated with open reduction and internal fixation, we were unable to demonstrate any differences between the outcomes for the patients who had an untreated fracture of the ulnar styloid base and those for the patients with no ulnar fracture. However, it must be emphasized that we did not assess the stability of the distal radioulnar joint either clinically or radiographically and we can offer only circumstantial evidence that there were no differences in instability between the patients with and those without a fracture of the ulnar styloid base.
Fracture of the base of the ulnar styloid has been identified by several authors as a potential cause of inferior outcomes in patients with a fracture of the distal part of the radius1,3,7-10. One of the issues has been the stability of the distal radioulnar joint since the triangular fibrocartilage complex originates from the base of the styloid and repair of a styloid base fracture can restore stability of the distal radioulnar joint20. May et al.7 focused on the issue of instability of the distal radioulnar joint, which they diagnosed in fourteen of 166 patients with a distal radial fracture. Eleven of the fourteen patients with instability had a fracture of the ulnar styloid base. They concluded that fractures at the base of the ulnar styloid and ulnar styloid fractures with substantial displacement (defined as >2 mm) are risk factors for the development of instability of the distal radioulnar joint.
Like other authors, we evaluated wrist function and overall outcome (i.e., DASH scores) rather than instability of the distal radioulnar joint specifically, in part because instability of the distal radioulnar joint was not specifically assessed in the prospective cohort study from which these patients were drawn and in part because instability of the distal radioulnar joint is difficult to define and measure. In a study of 272 patients with a fracture of the distal part of the radius, Stoffelen et al. reported that all thirteen patients with instability of the distal radioulnar joint had a fracture of the base of the ulnar styloid3. They noted that patients with a fracture of the ulnar styloid base had worse outcomes than patients with no ulnar styloid fracture. Ruch et al. found that, among patients with a displaced fracture of the ulnar styloid base, those treated with the forearm in fixed supination had slightly better outcomes than those treated with tension-band wiring of the fracture of the ulnar styloid base10. In a clinical trial in which the fracture of the distal part of the radius was treated with cast immobilization and the ulnar fracture was randomized to be treated with repair (of the triangular fibrocartilage complex or a large ulnar styloid fracture) or to be not treated, there was no difference in outcome21.
Several issues complicate interpretation of these data. First, it is not clear how to define and objectively measure instability of the distal radioulnar joint, and in many studies the authors used indirect measures such as wrist function and overall outcome1-10. Second, there are many other factors—with treatment of the distal radial fracture itself being a prominent one—that may not have been adequately accounted for in prior analyses. Third, it is reasonable to assume that distal radial fractures with substantial displacement must result in some failure of the triangular fibrocartilage complex if the ulna is not also fractured. This supposition is supported by the observation, by Lindau et al.22, of injuries to the triangular fibrocartilage complex in nearly 80% of patients with a distal radial fracture who had been evaluated arthroscopically as well as the observation, by Richards et al.23, that injury to the triangular fibrocartilage complex was associated with greater shortening and dorsal angulation of the radius at the time of injury. Fracture of the ulnar styloid base is probably an alternative to intrasubstance failure of the triangular fibrocartilage complex, and both injuries are potential sources of instability of the distal radioulnar joint and of diminished outcome, although this hypothesis has not been formally evaluated to our knowledge. Indeed, the issue of how large the ulnar styloid fracture must be in order to spare the triangular fibrocartilage complex remains speculative, and our cutoff of 75% of the total ulnar styloid height was based on clinical experience and knowledge of the anatomy but was otherwise arbitrary.
The strengths of our study include relatively consistent treatment methods (open reduction and plate-and-screw fixation of all distal radial fractures, with volar plate fixation of the majority) and prospective collection of functional, health status, and complication data. However, there are several important shortcomings. First and foremost, instability of the distal radioulnar joint was not specifically and formally evaluated with either clinical examination or stress radiographs, and our primary study focus did not address instability of the distal radioulnar joint; rather, we assessed wrist motion, function, and health status as well as the absence of documented symptoms, complications, and treatments specific to radioulnar joint instability at two years postoperatively. It is notable that there was little improvement in any measure of function or health status after the six-month postoperative evaluation. Another weakness of our study is that there were no guidelines for internal fixation of large ulnar styloid fractures in the prospective cohort study. We interpreted our data according to our impression that internal fixation of the ulnar styloid was based on preconceived notions about indications for internal fixation of ulnar fractures and did not reflect specific differences in preoperative or intraoperative instability of the distal radioulnar joint; however, there may have been some selection bias in that nine patients had open reduction and internal fixation of a fracture of the ulnar styloid base. Additional study weaknesses include its retrospective nature (it was planned after the data had been collected prospectively) and the unvalidated techniques used to measure ulnar variance on uncalibrated digital radiographs and to measure displacement of the ulnar styloid fracture. Finally, it must be emphasized that we compared patients with and without fractures of the ulnar styloid base without addressing the more difficult-to-quantify issues of instability of the distal radioulnar joint or the degree of injury to the triangular fibrocartilage complex.
Despite the shortcomings of this study, our data suggest that patients with a fracture of the base of the ulnar styloid (displaced or not) can expect to regain wrist function and a health status that are similar to those of patients with no ulnar styloid fracture, at least when the distal radial fracture was treated with open reduction and plate-and-screw fixation. The differences that approached significance were small, were probably clinically irrelevant, and were inconsistent over time. This suggests that anatomic reduction and internal plate fixation of the distal part of the radius mitigates or lessens the value of operative treatment of a fracture of the ulnar styloid base. The indications for internal fixation of the ulnar styloid after open reduction and internal fixation of the distal part of the radius remain unclear.
Since open reduction and volar plate fixation of the distal part of the radius (as was used in the majority of the patients in this series) restores the volar metaphyseal cortex, it may result in radiographic alignment of the distal radial fragments that is better and more reliable than that provided by external fixation, with which the volar cortex often remains in bayonet apposition24,25. Although instability of the distal radioulnar joint was not specifically assessed in this study, our finding that outcomes were not affected by a fracture of the ulnar styloid base might be explained by the improved inherent stability of the distal radioulnar joint that resulted from the improved restoration of distal radial anatomy, which may provide a greater measure of congruity with and capture of the ulnar head in the sigmoid notch of the radius. It also might be explained by the presumed intact interosseous ligament of the forearm. 