Dimensions of Glenoid Cavity and Glenohumeral Conformity
The values for the glenoid cavity (Table I) averaged 23.49 ± 2.48 mm (80% range, 20.14 to 26.94 mm) for the SI radius, 25.54 ± 3.07 mm (80% range, 22.00 to 29.56 mm) for the AP radius, 30.15 ± 3.70 mm (80% range, 25.88 to 35.77 mm) for the SI length, and 20.35 ± 2.56 mm (80% range, 17.59 to 24.38 mm) for the AP length. The mismatch between the radius of curvature and the SI radius averaged 1.45 ± 1.40 mm, with a ratio between those parameters of 0.94 ± 0.05. The mismatch between the radius of curvature and the AP radius was 3.50 ± 3.01 mm, and the ratio between those parameters was 0.87 ± 0.10.
Differences According to Sex
In our cohort, the dimensions of the humeral head differed significantly between men and women (Table II). Compared with men, women had a significantly smaller mean radius of curvature (20.6 versus 23.5 mm, p < 0.001), articular surface thickness (16 versus 17.9 mm, p < 0.001), and articular surface diameter (40.1 versus 45.6 mm, p < 0.001); a significantly larger posterior offset (0.60 versus 0.20 mm, p = 0.019); and a significantly smaller SI radius (22.07 versus 24.97 mm, p < 0.001), SI length (27.09 versus 33.43 mm, p < 0.001), and AP length (18.34 versus 22.51 mm, p < 0.001).
Comparison with Other Populations (Tables III, IV, and V)
The average humeral head radius of curvature in our study (22.1 mm) was similar to that in a Chinese cohort reported on by Zhang et al.14 (22.3 mm, p = 0.42) but significantly smaller than that in a Western cohort derived by combining the cohorts in the studies by Pearl and Volk5, Boileau and Walch7, Robertson et al.11, Hertel et al.9, and DeLude et al.12 (23.6 mm, p < 0.001). The articular surface thickness in our Chinese subjects (16.9 mm) was similar to that in the Chinese subjects in the study by Zhang et al.14 (16.7 mm, p = 0.363) and the Western subjects (16.9 mm, p = 0.937).
The articular surface diameter in the Western subjects, which was reported by only Boileau and Walch7 and Hertel et al.9, was significantly larger than that in our Chinese subjects (44.2 versus 42.9 mm, p = 0.009). The articular surface thickness/radius of curvature ratio, available from the studies by Pearl and Volk5 and Hertel et al.9, was significantly lower than our result (0.71 versus 0.77, p < 0.001). The surface arc in our subjects was significantly larger than that reported by Hertel et al.9 (153° versus 145°, p < 0.001).
The inclination angle and retroversion angle were reported in most of the studies. The inclination angle in our cohort was similar to that in the Chinese subjects reported on by Zhang et al.14 (133° versus 132°, p = 0.486; Table IV) but different from that in the Western cohort (136°, p < 0.001). The retroversion angle was similar among the 3 cohorts (22.6° in our study compared with 21.1° in the study by Zhang et al.14 and 24.5° in the combined Western cohort5,7,9-12,20; p = 0.340 and 0.187, respectively). The medial offset in our cohort was significantly larger than that in the previous Chinese cohort14 (6.3 versus 5.0 mm, p < 0.001) but similar to that in the Western cohort (6.6 mm, p = 0.125). The posterior offset in our study (0.40 mm) was significantly lower than that in the previous Chinese14 (3.5 mm) and Western7,9,11,12 (1.6 mm) cohorts (p < 0.001).
The SI radius in the Western cohort reported by Zumstein et al.21 was significantly larger than that in our Chinese cohort (28.2 versus 23.49 mm, p < 0.001; Table V), whereas the AP radius was similar between these 2 cohorts. Our Chinese cohort has a significantly smaller SI length (30.15 versus 39 mm, p < 0.001) and AP length (20.35 versus 29 mm, p < 0.001) than the Western cohort reported on by Iannotti et al.19.
Comparison of Chinese Humeral Head Dimensions with Current Prostheses
We compared articular surface thickness and diameter in our cohort with the dimensions of some of the historical and currently available shoulder implants (Fig. 10). The regression line of this study cohort and 95% confidence ellipse are included in the graph. The prosthetic systems that were added included Smith & Nephew Cofield 2, Stryker ReUnion TSA, Tornier Aequalis, DePuy Global Advantage, and Zimmer Anatomical. In general, the available prostheses did not cover the lower range of humeral head diameter in our cohort. The smallest available diameter of the Stryker, DePuy, and Zimmer prostheses was 40 mm, whereas 45% of our female subjects had an articular surface diameter of <40 mm; no male subjects had an articular surface diameter of <40 mm. The smallest diameters of the Smith & Nephew and Tornier prostheses were 36 and 37 mm, respectively.
The head thickness of the Smith & Nephew Cofield 2 prostheses available for a given diameter was too large for the Chinese cohort. The Stryker ReUnion system has at least 3 head-thickness options at each diameter; except for lacking lower-diameter options, it covered our cohort relatively well. The Tornier Aequalis and Zimmer Anatomical prostheses closely mimic the slope of the graph; neither implant offers more than 1 thickness option except at higher diameters. The DePuy Global Advantage offers 3 thickness options at each diameter, but available diameters are in 4-mm increments and the corresponding thickness does not increase with increases in the diameter of the head.
To better replicate the proximal humeral anatomy with a prosthesis, it is important to have a 3D understanding of normal humeral morphology. This knowledge can affect prosthetic design, sizing, and positioning. Fischer et al. showed that displacement of the center of rotation by 20% of its radius alters the lever arm of the rotator cuff by 20%22. An inability to replicate native anatomy can lead to eccentric loading at the periphery of the glenoid, increasing glenoid wear and glenoid loosening5.
There is evidence that Asian populations have significantly different osseous anatomy compared with Western populations23,24. These differences are not only in sizes but also in orientations and alignments of bone and cartilage. The proximal humeral anatomy in the Chinese population has not been studied extensively and has not been compared with data on Western populations.
Previous investigators have used cadavers, radiographs, conventional CT, or direct measurements to study the extramedullary and intramedullary morphology of the proximal part of the humerus in Western populations5,7,9,10,12,15. In the current study, we measured the geometric parameters of the proximal part of the humerus in vivo in Chinese subjects by using CT-arthrography, with which iohexol injection can identify the location and thickness of cartilage. To our knowledge, this is the first study in which this method was utilized to image the entire humeral head volume including cartilage.
Humeral head dimension has been reported to be highly correlated with subjects’ height and sex25,26. In our cohort, the subjects’ height was significantly correlated with the radius of curvature, articular surface thickness, and articular surface diameter. As in previous studies, our male subjects had larger humeral head and glenoid dimensions (radius of curvature, articular surface thickness, articular surface diameter, SI radius, SI length, and AP length), but there were no statistically significant differences between the sexes with respect to the shape/orientation parameters of the humeral head (articular surface thickness/radius of curvature ratio, surface arc, inclination angle, retroversion angle, and medial offset).
While the humeral head dimensions calculated in our study were similar to those reported by Zhang et al. in their Chinese cohort14, several measurements differed significantly from those in the combined Western cohort. In the coronal plane, the radius of curvature and diameter of the articular surface in our Chinese cohort were significantly smaller; therefore, the surface arc was significantly larger than the surface arc in the only other study in which that measurement was reported9. In the sagittal plane, the contour of the articular surface was oval with an AP/SI articular surface diameter ratio of 0.93, slightly larger than that in the Western cohort19. Current state-of-the-art techniques are still using a spherical prosthetic head to replicate a slightly oval articular surface, and this can potentially limit shoulder function postoperatively3,6. Further study should focus on designing an oval prosthetic head for both Chinese and Western patients by combining the data from both our and previous studies5,7,9-12,14,20.
The pattern of glenohumeral conformity in our Chinese cohort was opposite that in the Western population studied by Zumstein et al., who described a more curved cartilaginous glenoid cavity in the transverse plane than in the coronal plane21—i.e., the AP radius was smaller than the SI radius in their Western population, and the AP radius was larger than the SI radius in our Chinese cohort. However, the sample size in the study by Zumstein et al. was only 9. The ratios between the humeral head radius of curvature and the glenoid AP radius and SI radius show that, in the Chinese cohort, glenohumeral conformity was higher in the coronal plane than in the axial plane. More studies and large sample sizes are needed to verify these findings among different populations. Such differences in the Chinese population would have a substantial impact on prosthetic design for Chinese patients.
When compared with the combined Western cohort, our Chinese cohort had a significantly smaller inclination angle. A mismatch between the inclination angles of the prosthesis and the native humerus would lead to either a superior shift in the center of rotation or overcutting of the surgical humeral neck.
The retroversion angle in our cohort was similar to that reported by Zhang et al.14 and in the combined Western cohort. Edelson studied humeral head retroversion of dry bone specimens from various ethnic groups and found that it was larger (more retroverted) in northern Chinese people than in white and black Americans27. However, the difference in the results may be due to differences in methodology among studies3. A retroversion angle calculated by defining the transepicondylar axis as the distal reference axis may differ from one determined by using the trochlear axis as the distal reference axis, as there is already a natural angle (3° to 8°) between these 2 axes28. Surgeons should attempt to properly restore patients’ original retroversion angle during shoulder arthroplasty, as poor restoration of this angle may increase shoulder instability after surgery29.
The medial offset in our Chinese cohort was similar to values reported in the Western studies. The posterior offset in our study was significantly smaller than the value reported in the combined Western cohort. Only 1 study (by DeLude et al.) demonstrated posterior offset that was smaller than ours, and it used dry bone specimens and a sample size of only 2812.
Our study had several limitations, including comparisons with other studies that employed different methodology. When multiple cohorts are combined, variability in the methods used in the individual studies could lessen significance. Our technique of 3D CT of the entire humerus with arthrography of the glenohumeral joints of healthy adult volunteers is unique and addresses some concerns with previous methods3. The study sample of 80 is moderate in size, but given the in vivo nature of the study it compares favorably with the sample sizes in most other studies. Additional studies of larger samples of different populations, all employing the same methodology, can further clarify ethnic differences in proximal humeral anatomy.
In summary, the proximal humeral anatomy of Chinese subjects is significantly different from the published data in Western populations. The Chinese subjects had a significantly smaller proximal humeral radius of curvature and diameter of the articular surface as well as a different shape of the humeral head compared with Western populations. They also had higher glenohumeral conformity in the coronal plane than in the axial plane. Many shoulder prosthesis systems do not match Chinese humeral head dimensions well. These data could have important relevance with regard to prosthetic designs and surgical implantation techniques.
Investigation performed at the Xin Hua Hospital Affiliated to Shanghai Jiao Tong University School of Medicine, Shanghai, China
Disclosure: Funding from the National Natural Science Foundation of China (81171706) and Shanghai Municipal Natural Science Foundation (11ZR1427400) supported this research. The Disclosure of Potential Conflicts of Interest forms are provided with the online version of the article.
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