Measurement of Calcaneal Angles and Its Clinical Significance in Han Chinese Adults in Northwest China


 Objective

We aimed to investigate differences in and trends of normal calcaneal angles among Han Chinese adults from different age groups to establish normal reference ranges of calcaneal angles in these age groups, thereby providing a theoretical basis and morphological reference for the treatment of calcaneal fractures.
Methods

We collected lateral plain radiographs (X-ray) of the normal ankle joints of 6,260 Han Chinese adults who visited the Radiology Department of Shaanxi Provincial People’s Hospital between November 2008 and December 2020 to measure the calcaneal angles, including the Böhler angle (BA), Gissane angle (GA), calcaneal pitch angle (CPA), posterior facet inclination angle (PFIA), and calcaneal-tibial angle (CTA). On this basis, we analyzed the calcaneal angles in different age groups to summarize the characteristics of normal calcaneal angles in Han Chinese adults.
Results

According to the lateral plain radiographs of the normal ankle joints of 6,260 (male: 3,380; female: 2,880) adults (mean age: 46.3 ± 18.2 ), the mean values of the BA, GA, CPA, PFIA, and CTA were 33.17° ± 6.08°, 114.99° ± 8.17°, 25.67° ± 4.72°, 64.35° ± 8.51°, and 91.59° ± 11.57°, respectively. Results of the Pearson correlation analysis suggested negative correlations between age and both BA and PFIA (P < 0.01, respectively) but a lack of correlation between age and the GA, CPA or CTA (P > 0.05, respectively). One-way analysis of variance (ANOVA) and the least significant difference (LSD) test showed that at above the age of 18, there were statistically significant differences both in the BA between different age groups and in the PFIA between different age groups above 41 years old.
Conclusion

In Han Chinese adults, there are significant differences in BA and PFIA between different age groups, with these calcaneal angles exhibiting a trend of decrease with age.

di cult to treat and-if no appropriate reduction or effective xation is conducted to repair the fracturesseverely impair the normal functions of the affected foot [2]. To achieve adequate fracture reduction, the establishment of normal ranges of anatomic parameters as a theoretical basis for calcaneal morphology is necessary. Existing studies on the morphological characteristics of normal calcanea largely focus on the age groups between 20 and 60 y and have a limited sample size [3]. This research gap in developing normal ranges of calcaneal measurements in the population aged above 60 [4], without reliable reference values, exposes this population to an increased risk of a missed or erroneous diagnosis of calcaneal fractures or other related conditions. We therefore enrolled a wider range of age groups in our study to measure normal calcaneal angles in Han Chinese, including the Böhler angle (BA), Gissane angle (GA), calcaneal pitch angle (CPA), posterior facet inclination angle (PFIA), and calcaneal-tibial angle (CTA). Reports suggest individual differences in the BA and GA [3], according to age, race, and sex [5][6][7], as well as ethnicity in China [8,9]. Here, we measured calcaneal angles from X-ray records of different age groups to explore their characteristics and age-related changes and to establish normal reference ranges of calcaneal angles in different age groups as a clinical guide in diagnosing and treating calcaneal conditions.

General information
We assigned lateral plain radiographs of the normal ankle joints of 6,260 adults who visited the Radiology Department of Shaanxi Provincial People's Hospital between November 2008 and December 2020 to 3 age groups aged between 18 and 40, 41 and 60, and ≥ 61 y. We included patients who: (1) were Han Chinese living in Northwest China; (2) had no remarkable deformity or abnormality observed through ankle X-ray imaging; and (3) were aged ≥ 18 y old. We excluded patients with: (1) a con rmed diagnosis of rheumatoid arthritis, ankylosing spondylitis, Kashin-Beck disease, or poliomyelitis; (2) long-term use of hormone therapy; (3) a history of ankle fractures or cancer.
Lateral ankle X-ray lms were originally captured by a trained senior radiologist and evaluated by two residents of the Radiology Department who had received training for the measurement of radiological parameters. We measured calcaneal angles under the supervision of a chief physician of orthopedics and a chief physician of radiology. Additionally, we conducted random sampling at regular intervals to avoid misdiagnosis or repetitive measurement errors. The residents performed measurements separately and we averaged the results.
We used Philips DigitalDiagnost VR, a digital radiography system, for lateral ankle X-ray imaging, with the patient in a lateral recumbent position, the lateral side of the foot against the detector, the sagittal plane parallel to the detector, and the X-ray beam centered at the ankle joint. The X-ray generator was located

Statistical analysis
We used the software SPSS 20.0 for data analysis, with enumeration data expressed in the form of "x±s." We performed the Pearson correlation analysis to examine the correlations between calcaneal angles and age, and the one-way ANOVA to compare calcaneal angles in different age groups. We undertook the least signi cant difference (LSD) test for intergroup pairwise comparison. In determining normal reference ranges of calcaneal angles using the principle of normal distribution, we applied the formula x̅ ± 1.96 × s. We interpreted P<0.05 as indicating a statistically signi cant difference.

General information
We included a total of 6,260 patients (3,380 males and 2,880 females) with a male-to-female ratio of 1.17:1 and a mean age of 46.3 ± 18.2 y (range: 18-93), as we present in Table 1.

Results Of Measurement Of Calcaneal Angles
We observed a signi cant negative correlation between the BA and age (r = − 0.286, P < 0.001) (Tables 2  and 3). Additionally, the BA in different age groups showed statistically signi cant differences (all P < 0.05), demonstrating the age-related reduction of the BA (Table 4). Similarly, we observed a signi cant negative correlation between the PFIA and age (P < 0.01), the angle reducing with age (Tables 2 and 3). The LSD test results revealed that the PFIA reduced gradually with increasing age after 41 y, and the differences were statistically signi cant (P < 0.01) (Tables 3 and 4). GA, CPA, and CTA were not signi cantly correlated with age (P > 0.05) ( Table 2), and the differences in these calcaneal angles between different age groups lacked statistical signi cance (P > 0.05) ( Table 4). No age-related changes were observed in these angles.

Discussion
Our results showed that in Han Chinese adults in Northwest China, the BA and the PFIA were 33.17° ± 6.08° and 64.35° ± 8.51°, respectively, which differed from the previously reported measured values of the Mongols and the Uyghurs, indicating a degree of ethnic differences. The BA and GA of the Indian population are reported to differ signi cantly from those of populations from other countries, consistent with our ndings. In this study, we found that the PFIA was signi cantly negatively correlated with age, gradually decreasing with age after 41 y, (P < 0.01), due possibly to a high degree of pressure on the posterior calcaneal articular facet (PCAF) and a reduction in calcaneal height caused by age-related degeneration of the calcaneal articular facets or osteoporosis. The reported negative correlation between the BA and age in adults [1] supports our study results demonstrating a signi cant negative correlation between BA with age among those aged 18 to 93 y with normal calcanea (P < 0.01). With calcaneal tuberosity providing the attachment site for the calcaneal tendon, its upper margin is generally thought to be gradually elevated by hyperostosis with age, increased activities, or overuse, resulting in narrowing of the BA. On this basis, our study results suggested that the heights of the posterior calcaneal margin and PCAF changed with age.
The measurement of the BA and GA has been widely applied in clinical practice [14,15], such as evaluation, reduction, and prognosis assessment of calcaneal fractures. A single BA reference range for all age groups may lead to inappropriate treatment for older patients. Changes in normal calcaneal angles are generally classi ed clinically as either traumatic or non-traumatic changes, including pes cavus, pes planus, and so on. Where changes in the BA and GA are observable on the lateral calcaneus Xray lm-and are thus considered signi cant clinical indicators to assessing the severity and prognosis of calcaneal fractures-changes are considered traumatic [16,17],. In the case of arch collapse due to a lack of support for the hindfoot caused by an intra-articular calcaneal displacement fracture, the BA and CPA reduce, the CTA increases [1], the PCAF is compressed, and the GA becomes larger; moreover, the PFIA decreases and, with the displacement of bone fragments toward the anterosuperior direction, the calcaneal tendon becomes slack. To ensure effective GA and PFIA restoration, surgical treatment must emphasize proper reduction of the PCAF and the bone fragments. Considering that a reduced BA can result in intra-articular stress changes, it is crucial to restore calcaneal height and intra-articular stress distribution and optimize the prognosis by improving the BA intraoperatively [18]. GA restoration is also bene cial to the anastomosis of the articular surface of the subtalar joint [19][20][21]. Preoperative and postoperative BA are reportedly strongly correlated with the severity of injury related to intra-articular calcaneal displacement fractures, and with functional recovery, respectively [22]. The BA and GA are two signi cant indicators useful in the evaluation of calcaneal fracture reduction [16,17]. Based on the results of our study, we propose that the PFIA can also guide the intraoperative reduction of the PCAF; we also suggest that calcaneal tuberosity is another noteworthy indicator for the evaluation of calcaneal fracture reduction. In most cases, comparison between the affected foot and the healthy foot based on adequate radiographic measurement before surgery facilitates the clinical evaluation of calcaneal fractures, and surgical treatment plans are determined after a comprehensive analysis of calcaneal angles, length, width, and height. However, the within-subject comparison design is meaningless in cases where the patient's healthy foot has a history of deformity, old fractures, or cancer in the preoperative or intraoperative setting. Since calcaneal angles can vary with different patterns across a lifetime, the establishment of normal reference ranges of calcaneal angles through the measurement of normal calcanea in different age groups is necessary. The use of these reference ranges will bene t the analysis of the anatomical changes following a calcaneal fracture, assist in the comprehensive preoperative radiographic measurement of calcaneal angles to evaluate fracture severity, enhance the development of an appropriate surgical treatment plan, provide guidance for intraoperative reduction and prognosis assessment, and improve the postoperative treatment of calcaneal fractures [23]. In addition, the availability to hospitals and governments of the normal reference ranges of calcaneal angles in Han Chinese adults in Northwest China, determined after extensive measurement, will be of enormous bene t in setting up a database of calcaneal angles covering all age groups; the availability of these normal reference ranges to designers may facilitate the creation of suitable fracture-speci c plates for different age groups.
This study has some limitations in that it covers only the population in Northwest China. To gain a deeper understanding of calcaneal development in China's general population, future studies will bene t from a larger sample size, covering more areas and ethnic groups in China based on patient data analysis at a greater number of hospitals. In addition, as the anatomical and morphological structures of the calcaneus are highly complex, X-ray images should be interpreted in combination with computed tomography (CT) ndings. Non-random sampling may also have introduced an unforeseeable bias to the present study. Despite these limitations, our study has revealed clear evidence for age-related changes of the PFIA. Methods of measurement of calcaneal angles