The distal radius palmar cortical angle in adolescent versus adult populations

Abstract

Purpose:

Volar distal radius plates are pre-contoured to aid restoration of anatomy during open reduction internal fixation of distal radius fractures. Incorrectly contoured plates can result in malreduction, leading to malunion, pain, and loss of function. The purpose of this study was to investigate whether adolescent distal radius anatomy on the palmar cortical surface differs from that in adults, in order to determine whether adult plates are suitable for use in adolescents.

Methods:

Lateral wrist radiographs were used to measure the distal radius palmar cortical angle (PCA) in adolescent age groups (12–13, 14–15, and 16–17 years old) and compared to a skeletally mature control group (30–50 years old). Two assessors measured 423 PCAs twice.

Results:

There was a statistically significant (p = <0.05) difference in the PCA of the control group compared to each adolescent group. The mean PCA for both males and females decreased as age increased (increasing curvature of the volar distal radius with age). The mean PCA (male/female) was 164.38°/163.00° in ages 12–13, 162.14°/160.92° in ages 14–15, 157.52°/158.18° in ages 16–17, and 149.65°/154.03° in the control group aged 30–50 years. Agreement between assessors was high with an Interclass correlation coefficient (ICC) of 0.97.

Conclusion:

There is a statistically significant and potentially clinically important difference in the curvature of the distal radius volar cortex between adolescents and adults. This difference persists even in the 16–17 age group. As the PCA curvature is significantly greater in adults compared to adolescents, plates pre-contoured for adults may lead to malreduction of distal radius fractures into flexion in adolescent patients.

Introduction

Distal radius fractures are common injuries affecting all age groups. ¹ In adults, locking plates are often used during open reduction internal fixation. The plates are pre-contoured to aid restoration of anatomy ² and provide stable fixation allowing early mobilization. They are often used as a reduction template and incorrectly contoured plates may result in malreduction, leading to malunion, pain, and loss of function. ^{3 –6}

Although several studies have been undertaken looking at the distal radius anatomy of adults, little data are available regarding adolescents. Adolescent patients presenting with distal radius fractures are often treated with a closed reduction and cast but on occasion, open reduction and internal fixation is indicated. The authors have noticed that the use of plates designed for adults in this situation can lead to malreduction into flexion or prominence of the plate volarly.

A literature search revealed that the palmar cortical angle (PCA) was a recognized method for quantifying the anatomy of the distal radius on plain radiographs. ⁷ The purpose of this study is to investigate whether adolescent distal radius anatomy on the palmar (volar) cortical surface differs from that in adults, in order to determine whether adult plates are suitable for use in adolescent patients. The authors hypothesize that adolescent patients will have less curvature on the palmar aspect of the distal radius, that is, a greater PCA.

Methods

Normal lateral wrist radiographs were retrospectively collected using the imaging archive system of a South Australian public hospital. Radiographs were collected for patients in four age groups for comparison: 12–13 years, 14–15 years, 16–17 years, and a control group aged 30–50 years. Radiographs were collected separately for male and female patient groups. Radiographs were collected in reverse chronological order until a sufficient number for each group had been included.

Inclusion criteria for a satisfactory wrist radiograph were a true lateral radiograph with no bony pathology visible. Radiographs were excluded if they were of poor quality, if bony pathology was present or if the osseous anatomy appeared grossly abnormal. Wrist radiographs were deemed to be a true lateral if the palmar cortex of the pisiform bone intersected approximately the central third of the interval between the anterior cortex of the distal pole of the scaphoid and the capitate.

Two assessors both twice measured the PCA of included lateral wrist radiographs. The PCA was defined at the angle made by the intersection of two lines—(A) along the volar aspect of the radial shaft and (B) along the volar tilted portion of the distal radius (Figure 1). ⁷ A higher PCA corresponds to lesser curve on the volar aspect of the distal radius. As well as PCA, other patient data collected included age and gender.

Figure 1.

Method used to measure the PCA on lateral wrist radiographs. PCA: palmar cortical angle.

Statistical analysis was performed using SAS 9.4 (SAS Institute Inc., Cary, North Carolina, USA). A linear regression was performed to investigate the relationship of the PCA versus age and gender. A p value was considered statistically significant if <0.05.

Results

The PCA was measured on 423 radiographs with 50 to 54 lateral radiographs included for each age group and each gender. The mean PCA for both males and females decreased as age increased (increasing curvature of the volar distal radius with age). The mean PCA (male/female) was 164.38°/163.00° in ages 12–13, 162.14°/160.92° in ages 14–15, 157.52°/158.18° in ages 16–17, and 149.65°/154.03° in the control group aged 30–50 years (Figure 2). Table 1 shows the mean PCA, standard error, and 95% confidence interval, and these are represented in Figures 3 and 4. Assumptions of a linear regression were upheld. There was a statistically significant difference in mean measurement across the four age categories (global p value <0.0001, χ ² = 43.51, df = 3). All pairwise comparisons across age (where gender was constant) were significant.

Figure 2.

Mean PCA measurements (degrees) in males and females for each age group. PCA: palmar cortical angle.

Table 1.

Mean palmar cortical angles (degrees) and 95% CI.

Age category (years)	PCA (degrees)	Lower 95% CL	Upper 95% CL
12–13	163.69	162.98	164.40
14–15	161.52	160.80	162.24
16–17	157.85	157.14	158.57
30–50	151.92	151.19	152.66

PCA: palmar cortical angle; CL: confidence interval.

Figure 3.

Mean PCA, 95% confidence interval, and PCA data range in females by age group. PCA: palmar cortical angle.

Figure 4.

Mean PCA, 95% confidence interval, and PCA data range in males by age group. PCA: palmar cortical angle.

When examining the relationship between PCA and gender for the four age groups, it was found that males had a higher PCA in age groups 12–13 and 14–15, whereas females had a higher PCA in age groups 16–17 and 30–50 years. Mean PCA was statistically significantly different in the 12–13 age group (females with a lower PCA) and control group (30–50-year age group; males with a lower PCA).

Agreement between assessors was high with an interclass correlation coefficient of 0.97.

Discussion

The morphometric data collected during this study examined the influence of age and gender on the distal radius PCA and found both to have a statistically significant influence. The results demonstrate that as age increases, the PCA decreases, meaning that as adolescents mature, the distal radius volar surface increases in curvature. The significant difference in PCA between adolescents and adults means that pre-contoured plates designed for adult wrists may not be suitable for use in adolescent patients and their use may result in malreduction leading to malunion. Although incorrectly contoured locking plates are less likely to lead to malreduction than compression plates, some surgeons use pre-contoured plates as a reduction template when fixing difficult or comminuted fractures, and these fractures are at risk of being fixed in flexion in adolescent patients. In addition, if locking plates prominent on the volar surface as the contouring does not match the distal radius, there is an increased risk of flexor pollicis longus tendon irritation and rupture. Several studies have demonstrated the detrimental effect distal radius malunion has on range of movement, function, and pain. ^{3 –6} Other methods of internal fixation may be more appropriate in adolescent patients including non-contoured plates or k-wires.

The angles of the adult distal radius PCA were comparable to the findings from a study by Gasse et al. that examined 74 cadaveric distal radii and found a PCA of 155° on the lateral column and 145° on the medial column of the distal radius. ⁸ Gender data were not available.

This study also demonstrated a statistically significant difference in the PCA between males and females in the youngest (12–13 years) and oldest age groups (30–50 years) tested, but in different directions. The trend line demonstrates that in the 12–13-year-old group, females have a significantly lower PCA (more curved distal radius) compared to males. This difference becomes less in the 14–15-year-old group, and in the 16–17-year-old group males instead have a lower PCA with the difference becoming statistically significant in the 30–50-year-old group. This indicates that although adolescent males initially have less curvature of the distal radius, their anatomy changes at a greater rate compared to females as age increases. The eventual result is adult males with a statistically and clinically significant greater curvature of the distal radius compared to females. Evans et al. ⁹ similarly found a statistically significant difference in the PCA between adult males and females, with males having an angle of 146.4° and females 148.5°.

A previous study by Oppermann et al. also examined the influence of gender on adult distal radius anatomy. ¹⁰ The study used 49 three-dimensional (3-D) cast models of human cadaveric radii, and similarly found the PCA of females to be statistically significantly greater on the lateral aspect of the radius; however, no difference was found when looking at the medial column.

This study had several limitations. The data were gathered retrospectively so despite clear criteria to ensure true lateral wrist radiographs, consistency was difficult to ensure. Rotational difference in the radiographs may have led to variation in the angles measured. In addition, previous 3-D studies have demonstrated that the PCA slightly differs between the medial and intermediate columns of the radius ¹¹ ; however, this study using two-dimensional lateral radiographs only allowed for the measurement of a single PCA.

This study only assessed the difference between adult and adolescent wrists with respect to the PCA despite other factors, including radial inclination, tilt and width, being factors in plate design. These features may also differ, and further investigation into the morphology of the adolescent wrist would be warranted if an adolescent-specific plate were to be designed.

Although this study demonstrated a significant difference in the PCA in adults compared to adolescents, whether fracture malreduction in adolescents to the position of an adult wrist leads to pain or loss of function was not assessed.

Conclusions

There is a statistically significant and potentially clinically important difference in the curvature of the distal radius volar cortex between adolescents and adults. This difference was greatest in the youngest age group and although it lessened with increasing age, persisted even in the 16–17 age group. As the curvature of the distal radius is significantly greater in adults compared to adolescents, plates pre-contoured for adults may lead to malreduction of distal radius fractures into flexion in adolescent patients. Whether this leads to any functional deficit requires investigation.