Distinct Proximal Humeral Geometry in Chinese Population and Clinical Relevance

Zhang, Qiang MS; Shi, Lewis L. MD; Ravella, Krishna C. BA; Koh, Jason L. MD; Wang, Shaobai PhD; Liu, Cailong MD; Li, Guoan PhD; Wang, Jianhua MD

Journal of Bone & Joint Surgery - American Volume:
doi: 10.2106/JBJS.15.01232
Scientific Articles
Abstract

Background: Replicating humeral anatomy during shoulder arthroplasty is important for good patient outcomes. The proximal humeral geometry of the Chinese population has been rarely reported. We analyzed the geometry of the proximal part of the humerus in Chinese subjects and compared it with that of Western populations and the dimensions of available prostheses.

Methods: Eighty healthy Chinese subjects underwent computed tomography (CT)-arthrography. Three-dimensional (3D) digital humeral and glenoid models were reconstructed, and geometric parameters were measured. Humeral measurements included the radius of curvature, articular surface diameter and thickness, anterior-posterior/superior-inferior (AP/SI) articular surface diameter ratio, articular surface thickness/radius of curvature ratio, surface arc, inclination angle, retroversion angle, and medial and posterior offsets. Glenoid measurements included SI length, AP length, SI radius, and AP radius.

Results: The average radius of curvature (and standard deviation) of the humeral head was 22.1 ± 1.9 mm, the articular surface diameter averaged 42.9 ± 3.6 mm, and the articular surface thickness averaged 16.9 ± 1.5 mm. There was strong linear correlation between the articular surface diameter and thickness (r2 = 0.696, p = 0.001), with a linear regression relationship of thickness = 0.357 × diameter + 1.615. The AP/SI articular surface diameter ratio averaged 0.93 ± 0.03; the articular surface thickness/radius of curvature ratio, 0.77 ± 0.05; the surface arc, 153° ± 5.6°; the inclination angle, 133° ± 3.1°; and the retroversion angle, 22.6° ± 10.2°. The medial and posterior offsets averaged 6.3 ± 0.9 mm and 0.4 ± 0.78 mm, respectively; the SI and AP lengths, 30.15 ± 3.70 mm and 20.35 ± 2.56 mm; and the SI and AP radii, 23.49 ± 2.48 mm and 25.54 ± 3.07 mm. Compared with the Western population, the Chinese cohort had a smaller radius of curvature (p < 0.001), smaller articular surface diameter (p = 0.009), larger articular surface thickness/radius of curvature ratio (p < 0.001), larger surface arc (p < 0.001), smaller inclination angle (p < 0.001), and smaller posterior offset (p < 0.001). Unlike the Western population, the Chinese population had higher glenohumeral conformity in the coronal plane than in the axial plane. Many manufacturers’ shoulder prostheses do not adequately cover the range of humeral head dimensions in our Chinese cohort.

Conclusions: The geometric parameters of the humeri in the Chinese population differ from those in other populations. These differences have clinical relevance with regard to implant design and arthroplasty technique and likely affect clinical outcomes.

Author Information

1Department of Orthopaedic Surgery, Xin Hua Hospital Affiliated to Shanghai Jiao Tong University School of Medicine, Shanghai, China

2University of Chicago Medical Center, Chicago, Illinois

3Department of Orthopaedic Surgery, NorthShore University HealthSystem, Evanston, Illinois

4Massachusetts General Hospital, Boston, Massachusetts

E-mail address for J. Wang: shwangjianhua@gmail.com

Article Outline

Investigators agree that improvement in ranges of motion and function after shoulder arthroplasty is closely related to the surgeons’ ability to restore the patients’ original anatomy with the prosthesis1-4. Even a mild mismatch between native and prosthetic geometry can compromise postoperative shoulder function5,6. Therefore, it is important for prostheses to be able to replicate the native geometry of the proximal part of the humerus.

Geometric measurements of the proximal part of the humerus have been discussed in many studies7-11. During the past 2 decades, investigators have successfully measured proximal humeral geometry in studies of bone specimens9,10. Measurement methodology has advanced from simple determination of humeral head size in 2 dimensions (2D)5 to systematic quantification of humeral morphology in 3 dimensions (3D)12, and from direct measurement of humeral specimens13 to precise manipulation of computer models of the humerus11. As most data published in the Western literature have been on Caucasians, there is a substantial lack of data on humeral geometry in the Chinese population. We are aware of only 1 study in which the humeral geometry of Chinese subjects was measured14, and it lacked several geometric parameters and did not offer comparison with previous studies. Overall, it is unknown whether humeral geometry in Chinese people differs from the humeral geometry in other populations. If there are differences, the prosthetic systems optimized for humeral geometry in Caucasians may not match the humeral anatomy of Chinese patients and can negatively affect postoperative shoulder function.

In this study, we measured the proximal humeral geometry of Chinese subjects and determined glenohumeral conformity with computed tomography (CT)-arthrography and 3D modeling techniques in vivo. We hypothesized that Chinese subjects would have smaller humeral head dimensions and different patterns of glenohumeral conformity compared with other populations.

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Materials and Methods

Subjects

Eighty Chinese subjects, with a mean age (and standard deviation [SD]) of 27.0 ± 6.0 years were recruited. There were 40 women (mean age, 25.5 ± 5.7 years; range, 18 to 43 years) and 40 men (mean age, 28.5 ± 6.0 years; range, 21 to 45 years). Exclusion criteria included rotator cuff tears, shoulder instability, a history of fracture, and osteoarthritis. Potential risks of the study were considered, with previous studies indicating minimal pain or other side effects of arthrography15-17. This study was approved by the hospital ethics committee. The majority of the subjects were health-care professionals, and all provided informed consent.

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CT-Arthrography and Model Reconstruction

Shoulder arthrography was performed using a 20-gauge needle via an anterior approach, and an injection of 3 to 8 mL of iohexol 70% (300 mg/mL; Omnipaque, GE Healthcare) was given (Fig. 1-A). Iohexol creates a distinct boundary between the cartilage of the humeral head and the glenoid cavity on CT (Fig. 1-B). CT was performed with a 256-slice scanner (Brilliance iCT; Philips Healthcare) with the arm in external rotation. Only 1 arm of each patient was studied (70 left arms and 10 right arms). The scanning range spanned from the top of the acromioclavicular joint to the proximal radioulnar joint to include the entire humerus.

Additional 1-mm-thick axial images were reconstructed, and images were processed by segmentation in order to obtain a 3D surface model in MATLAB software (version 2012b; MathWorks). The segmentation was performed in a Boolean difference subtraction fashion. First, the entire humeral bone, glenoid bone, cartilage, and iohexol volume were segmented as whole parts. The iohexol was then segmented and subtracted from the whole volume segmentation on the basis of its high density (gray scale). Next, the humeral bone was segmented and separated from the cartilage on the basis of its relatively high density (Fig. 1-C). The bone surface model with cartilage was accurately reconstructed with the above steps (Fig. 1-D). The model of the glenoid was reconstructed similarly. The segmentation work was performed on CT images magnified 5-fold. Our method follows the gold standard of reconstruction using CT images based on a semi-automated measurement method for which interobserver and intraobserver reliabilities have been established15,18.

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Parameter Measurement

Solid modeling software (Rhinoceros; Robert McNeel & Associates) was employed to measure the geometric parameters of the humeral surface model (Fig. 2). These parameters, which represent the dimensions and the shapes of the humeral head as well as the orientation and location of the articular surface relative to the proximal humeral shaft axis or the transepicondylar axis, included the radius of curvature of the humeral head, diameter of the articular surface, thickness of the articular surface, anterior-posterior/superior-inferior (AP/SI) articular surface diameter ratio, articular surface thickness/radius of curvature ratio, surface arc, inclination angle, retroversion angle, medial offset, and posterior offset (Figs. 3 and 4).

The orientations of the glenoid cavity were determined using the method described by Iannotti et al.19. Four points were marked on the glenoid cavity (Fig. 5-A): superior (H), inferior (H′), anterior (L), and posterior (L′). Then the maximum superior-inferior (SI) length (H to H′) and anterior-posterior (AP) length (L to L′) of the glenoid cavity were measured. The SI radius of the glenoid cavity was measured as the radius of the circle best fitting the arc of the glenoid cavity in the vertical direction (Fig. 5-B). The AP radius of the glenoid cavity was measured as the radius of the circle best fitting the arc of the glenoid cavity in the horizontal direction.

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Data Process and Statistical Analysis

The means and SDs as well as the 10th and 90th percentiles (80% range) of the geometric parameters were calculated9. Bar graphs were plotted to show the distributions of the parameters. The relationship between the diameter and thickness of the articular surface was determined with Spearman correlation analysis. If a strong correlation was found, linear regression analysis was used to determine the equation of the regression line. The relationship between the humeral head size and the subjects’ height was also determined with Spearman correlation analysis. An independent-samples t test was applied to determine the differences in geometric measurements. The results of this study were compared with those in a Western population cohort derived by combining several series from the published literature5,7,9-12,19-21. The sample sizes, means, and SDs from the individual studies were tabulated to calculate the total sample size, mean, and SD for the combined cohort. Significance was set as p < 0.05. Statistical analysis was performed using SPSS software (version 13.0; SPSS).

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Results

Dimensions of Humeral Head

In our cohort, the humeral head radius of curvature averaged 22.1 ± 1.9 mm; the articular surface thickness, 16.9 ± 1.5 mm (80% range, 14.8 to 18.8 mm); and the articular surface diameter, 42.9 ± 3.6 mm (80% range, 38.9 to 48.1 mm) (Table I, Fig. 6). There was a strong correlation between the articular surface diameter and thickness (r2 = 0.696, p = 0.001), with a linear regression relationship (Fig. 7) of: thickness = 0.357 × diameter + 1.615.

There was a strong correlation between the height of the subject and the humeral head radius of curvature (r2 = 0.712, p < 0.001), articular surface thickness (r2 = 0.407, p < 0.001), and articular surface diameter (r2 = 0.699, p < 0.001).

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Shape of Humeral Head

The AP/SI articular surface diameter ratio averaged 0.93 ± 0.03 (80% range, 0.88 to 0.96, Table I); the articular surface thickness/radius of curvature ratio, 0.77 ± 0.05 (80% range, 0.71 to 0.82); and the surface arc angle, 153° ± 5.6° (80% range, 146.6° to 159.6°).

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Orientation and Offsets of the Articular Surface

On average, the inclination angle, or head-shaft angle, was 133° ± 3.1°; the retroversion angle was 22.6° ± 10.2° (80% range, 7.9° to 35.4°) (Fig. 8); the medial offset was 6.3 ± 0.9 mm; and the posterior offset was 0.4 ± 0.78 mm (Fig. 9).

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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.

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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).

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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.

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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.

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Discussion

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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