Age-Related Variations in Volar Cortical Angle of the Distal Radius

Abstract

Background: The ideal volar locking plate for the treatment of distal radius fracture should anatomically fit the volar surface of the distal radius. The purpose of this study was to measure the volar cortical angle (VCA) of uninjured adult distal radii to determine how well the VCA matches that of modern volar locking plates and whether variations in the VCA are related to demographic factors. Methods: A retrospective radiographic analysis of 273 uninjured adult distal radii was performed. Patients were stratified into age quintiles: less than 27 years, 27 to 43 years, 44 to 51 years, 52 to 64 years, and 65 years or older. The VCA was measured on lateral wrist radiographs, and patient demographics, including age and sex, were collected. Multivariable linear regression analyses were performed to determine the relationship between VCA and demographic factors. Results: The VCA ranged from 23.2° to 42.6°, with a mean of 32.2° (SD = 3.79). Mean VCA was 32.8 (SD = 4.17) in the youngest cohort (<27 years) and 30.4 (SD = 3.63) in the oldest cohort (>65 years). Mean VCA decreased with age, approximately 0.04° per year after adjusting for sex. Men had a 1.6° greater VCA than women after adjusting for age. Conclusion: Mean VCA was greater than the VCA of modern volar locking plates. The VCA decreased with age in both men and women, and men had a greater VCA than women. Such differences must be taken into account to avoid malreduction, tendon irritation, or intra-articular screw placement using current volar plate designs.

Introduction

Distal radius fractures are the most common fracture encountered by orthopedic surgeons, accounting for 18% of all adult fractures.^1,2 Over the past 2 decades, there has been a trend toward operative management of distal radius fractures.^3,4 Open reduction and internal fixation (ORIF) with volar locked plates has emerged as an attractive option as it allows for a direct anatomic reduction and provides sufficient biomechanical stability for early wrist mobilization.^5-7 Functional outcomes after distal radius fixation are closely related to the restoration of the anatomy with attention to volar tilt, ulnar variance, and congruity of the articular surface.⁸ Restoration of volar tilt is achieved with an anatomic reduction of the volar subchondral bone, which can be facilitated through utilization of precontoured distal radius plates.

The commonly used commercial volar distal radius plates are designed with fixed angles that range from 18 to 30° to fit the palmar surface of the distal radius.⁹ These plates have a variable fit to the volar cortical angle (VCA), the angle between the palmar surface of the distal radius and the shaft of the radius.¹⁰ A prior distal radius radiographic study found the mean VCA of uninjured distal radii to be 37°, far greater than the VCA found on commercial plates.¹¹ Studies that examined cadaveric distal radii have shown that the precontoured angle of modern volar plates does not anatomically match the VCA of human cadavers⁹ and that the VCA varies between individuals.¹²

The purpose of this study was to measure the VCA of uninjured adult distal radii and determine whether the VCA predictably varies with patient demographics such as age and sex. Prior studies have failed to show a predictable association with age. Predictable variations in VCA may allow for improved volar plate designs to better match the normal distal radial anatomy and aid in achieving an anatomic reduction while preventing tendon irritation or intra-articular screw placement.

Materials and Methods

We queried our institution’s clinical data warehouse for patients undergoing routine radiography of the wrist for wrist pain from 2005 to 2015. Patients presenting with wrist pain (International Classification of Diseases, Ninth Revision [ICD-9] code 719.43) and undergoing standard anteroposterior/lateral/oblique wrist radiography (Current Procedural Terminology [CPT] code 73110) were identified. All patients were being investigated for wrist pain pathology other than fracture. Patients were excluded if there was evidence of a prior distal radius fracture, carpal bone fracture, or inadequate lateral radiographs of the wrist as defined by the scaphopisocapitate relationship.¹³ Of the 938 patients identified, we excluded 665, leaving 273 patients for this study. We excluded 553 for a lack of adequate lateral radiographs, 91 for evidence of a prior distal radius fracture, and 21 for evidence of a prior carpal bone fracture.

Patient demographics at the time of the radiography were collected. The VCA was measured on lateral radiographs and were recorded in degrees (to the nearest 0.1°) using General Electric Picture Archiving and Communication Systems Centricity software. To measure the VCA, a straight line was drawn along the volar surface of the shaft of the distal radius. A second line was drawn parallel to the volar cortex of the distal radius (volar cortical line). The angle between these 2 lines was measured (Figure 1). Three observers including 1 orthopedic surgery resident and 2 orthopedic surgery research personnel made the measurements (RG, PH, EB) who were trained by senior faculty (RS, SM). Interrater variability showed strong agreement between reviewers (κ = 0.84). All 3 observers were unaware of patient age and sex at the time of measurements.

Figure 1.

Method of measuring volar cortical angle on lateral wrist radiographs with a (a) straight line drawn along the volar surface of the shaft of the distal radius and (b) a parallel line drawn to the volar cortex of the distal radius (volar cortical line).

Statistical Analysis

A study of 32 cases per subgroup would have 80% power to detect a difference of 2° assuming a standard deviation of 4.0. Based on our power analysis, patients were divided into age quintiles to meet the minimum sample size: less than 27 years, 27 to 43 years, 44 to 51 years, 52 to 64 years, and older than 65 years. Variables were tested for normality using the Shapiro-Wilk test. T-tests were used to assess whether VCA varied between blacks and whites. The other races were not analyzed due to small numbers. Multivariable linear regression analyses were performed to determine the relationship between distal radius VCA, adjusting for age and sex because we thought these variables may be predictive of VCA. We also conducted multivariable linear regression analysis adjusting for age, sex, and an interaction term between age and sex to assess whether the VCA effect varied between men and women.

All tests were 2-sided, and the a priori type I error rate, α, was set at 0.05. Values of P < .05 were considered statistically significant. This study was approved by the local institutional review board with a waiver of consent.

Results

Table 1 lists patient demographics of the 273 patients included in this study. Age ranged from 18 to 94, with a mean of 48.3 (SD = 19.4). Eighty-six (31.5%) were men, and 187 (68.5%) were women. The VCA ranged from 23.2° to 42.6°, with a mean of 32.2° (SD = 3.79; Figure 2). The VCA was normally distributed (Shapiro-Wilk P > .05). Table 2 lists the VCA as stratified by age quintiles. Mean VCA was 32.8 (SD = 4.17) in the youngest cohort (age <27 years) and 30.4 (SD = 3.63) in the oldest cohort (age ≥65 years) (P = 0015). The VCA did not vary between African Americans and whites (P = .724).

Table 1.

Demographic and Clinical Characteristics of Study Participants.

Age, y	48.28 (range = 18-94, SD = 19.44)
Male sex (%)	86 (31.5)
Race/Ethnicity (%)
Asian	8 (2.9)
African American	58 (21.2)
Hispanic	5 (1.8)
White	180 (65.9)
Not available	22 (8.1)
Laterality (% right)	129 (47.3)

Figure 2.

Histogram of VCA with frequencies.

Note. VCA = volar cortical angle.

Table 2.

Quantitative Measures of Distal Radius Measurements Stratified by Age Quintiles.

	Quintile 1 (n = 54)	Quintile 2 (n = 53)	Quintile 3 (n = 62)	Quintile 4 (n = 46)	Quintile 5 (n = 58)
	Age <27 years	27-43 years	44-51 years	52-64 years	Age ≥65 years
Mean age (SD)
All	22.46 (2.38)	34.66 (5.09)	48.39 (2.17)	57.07 (4.50)	76.48 (8.03)
Males	22.05 (2.14)	34.38 (5.07)	48.38 (2.43)	56 (4.42)	76.25 (8.81)
Females	22.69 (2.51)	34.84 (5.18)	48.39 (2.11)	57.41 (4.53)	76.61 (7.71)
Mean volar cortical angle (SD)
All	32.82 (4.17)	33.05 (3.61)	34.01 (2.59)	32.15 (3.68)	30.38 (3.63)
Males	33.68 (4.67)	34.0 (4.21)	35.15 (2.20)	34.03 (2.89)	31.84 (3.85)
Females	32.35 (3.86)	32.42 (3.07)	33.64 (2.62)	31.56 (3.73)	29.61 (3.30)

Mean VCA decreased with age, approximately 0.04° per year after adjusting for sex (P < .05, 95% confidence interval [CI] = −0.063 to −0.019) (Figure 3). Multivariate analysis adjusting for age and sex shows that the age effect is similar in men and women (P = .724). Multivariate analyses including the interaction term between age and sex showed that the decrease in VCA was not statistically significantly different between men and women (P = .302). Men have on average a 1.6° greater VCA than women even after adjusting for age (P < .05, 95% CI = 0.68-2.52).

Figure 3.

Plot of volar cortical angle versus age.

Discussion

Our study validates prior studies that the VCA of our population does not anatomically match the VCA of current volar plate designs.^9,12,14 With a mean VCA of 32.2° in our cohort, the angles of current plates (18°-30°) would appropriately anatomically fit less than 16% of our population. As precontoured plates are often used as a template for reduction, current volar plate designs may not adequately reconstruct the distal radius and undercorrect the volar tilt.

Anatomic reduction remains the goal of internal fixation. Multiple studies have demonstrated the importance of restoring the normal anatomy of the distal radius with regard to functional outcome and preservation of the normal biomechanics of the wrist.^15-18 Changes in the volar tilt have been shown to lead to a shift in contact points for load transfer and a significant increase in the axial load supported by the ulna and ulnocarpal joint.^15,17,19 The poor contact between modern volar plating systems and the distal radius volar cortex could explain why current volar locking plate designs may not optimally obtain and maintain an anatomic reduction.²⁰ While one solution to the lack of adequate VCA could be to manually contour the plate intraoperatively to match the VCA of the uninjured contralateral wrist, future plate designs may benefit from modifying the prefixed volar angle.

Our study further demonstrates for the first time that VCA varies with demographic factors, specifically age. Because the fit of the plate to the distal radius may be implicated as a cause of tendon irritation or intra-articular screw placement, awareness of such variations may allow for increased vigilance in patients with VCA that does not match that of current volar plate designs. Our results show that VCA decreases with age and men have on average a larger VCA, suggesting that current plates may fit the volar cortex of elderly female patients better than younger male patients. Human bone is known to show morphological changes with age.^21-23 One possibility to explain the decrease in VCA with age is due to distal radius remodeling secondary to chronic micro-trauma from repetitive load by normal activities of daily life.²⁴ Certain occupational work could predispose the wrist to constant micro-damage that increases exponentially with age.²⁵ Age-dependent changes may also play a role in patients with osteopenia or osteoporosis. The Wolfe law where bone changes as a result of stress placed on the bone itself might be a factor of decreasing loading characteristics as we age. Future studies comparing VCA with bone mineral densities measured by dual X-ray absorptiometry are required to support this hypothesis.

This study does have limitations. First, the radial and intermediate columns of the distal radius have been shown to have variations in VCA.¹⁴ Cross-sectional imaging with computed tomography (CT) or magnetic resonance imaging (MRI) would be required to adequately assess the variation of VCA across the volar surface of the distal radius. While CT and MRI data sets are available at our institution, the total number of “normal” wrists undergoing CT or MRI scans were too few to proceed forward with data collection from cross-sectional imaging. Second, a longitudinal cohort study following patient radiographs for several years would be necessary to definitely conclude the decrease in VCA is an age effect rather than a cohort effect. Finally, we were unable to obtain adequate data on occupation and hand dominance, as these factors could also play a role in variations in VCA. The radiographs utilized in this study may in fact be “abnormal” as patients had imaging for investigation of wrist pain and may be a potential cause of the findings. As with all retrospective analyses, our data set is bias upon either the patient correctly recalling any prior injuries or the correct documentation of such.

Our study demonstrates that an anatomic reduction with ORIF may be made more difficult using current plate designs. As there are significant variations in VCA based on age and sex, surgeons need to be aware that current plates may not be anatomic and future plate designs should take such factors into account to prevent tendon irritation, malreduction, or intra-articular screw penetration.