The purpose of this study was not only to obtain the parameters for a single proximal humerus but also to use simple geometric parameters to describe the proximal humerus shape in the entire population of North China region based on measurements of multiple samples. Our results are expected to facilitate the increase in perceptions of the proximal humeral morphology among surgeons, assist with the design of shoulder prostheses and proximal humeral fixation instruments, and improve the clinical outcome of trauma and other disease of the proximal humerus.
Previously reported humeral parameters were mostly obtained from the cadaver specimens or X-ray based 2-dimensinal measurements. Several CT-dependent studies have been published as well in recent years. CT could eliminate the errors brought from posture and tube projection angles and CT could be easily acquired, stored and applied to reconstruct 3D models. Most studies based on CT measurements are from Western sources. This study, aimed to precisely establish the anatomical parameters dataset of the proximal humerus in a Northern Chinese population, differs from previous studies in population selection and measured parameters.
The morphometric parameters of each anatomical structure of the humeral head were measured in detail in this study. AAHH, RCHH, DHH and THH in cHHP and tHHP were used to describe the morphology of the humeral head; MO and PO were used to describe the relative position of the humeral head to the proximal humeral shaft; IA, AANS and RCNS were used to describe the morphology of metaphysis; superior, Inferior, anterior and CAHAN were used to describe the morphology of anatomical neck; HGT, HLT, VIG, LIG, DIG, CAIG,UAGT and LAGT were used to describe the morphology of proximal anterolateral region of the humerus. The morphology of the proximal humerus was converted into above parameters, and thus, the morphology characteristics of patient’s humerus could be communicated among doctors and researchers without pictures or other visual ways.
A total of 25 proximal humeral parameters were measured, 12 parameters were significantly larger in males than females (P < 0.05). There were apparently different physiological structures between the sexes, nearly all the differences in parameters between men and women were related to the size of proximal humeral anatomical landmarks such as the RCHH, HGT or VIG, rather than the parameters such as the IA, AANS or CAHAN; nevertheless, no difference was observed in RCNS and humeral head offset, either medially or posteriorly. These results suggests that the female humerus is not a simple scaled-down version of male humerus; therefore, sex differences should be considered when designing medical devices. In present study, left and right side of humerus showed strong symmetry. The contralateral humerus can serve as a reliable reference for injury side during the treatment.
The geometric parameters of intertubercular groove have not been paid much attention in previous studies. The long head of the bicep tendon passes through the intertubercular groove and covered by the transverse humeral ligament. The influence of anatomical and morphological variations of the intertubercular groove could be responsible for shoulder disorders such as subluxations, tears and tendinitis of biceps tendon. In addition to measuring the length, depth and concave angle of intertubercular groove, this study measured the volume of the intertubercular groove by mask filling simulation. This parameter that may better reflect the containment function of the intertubercular groove for more exploration of the correlation between the morphological variations and the long head of the bicep tendon disorders in the future.
We focused on the geometry of the lateral to the greater tuberosity of the humerus where the proximal humerus plate placement was often performed. Poor fit of plate placement could cause pain, limited mobility, screw loosening and even plate fracture. Parameters we measured could optimize the plate design, in order to increase the plate fitting and decrease mobility of unstable fracture segments for better surgical results.
Correlation analysis showed no correlation with age for all proximal humeral morphometric parameters. Proximal humeral morphology may not be susceptible to aging or daily use. Complex interrelationship exists among the dimensional parameters of the humeral head, suggested that the morphology of the humeral head existed mutually synergistic developmental mechanisms.
In previous studies, the humerus was usually simplified as a sphere, making measurement of the parameters convenient [8]. We described the humeral head morphology by using two orthogonal, osculating circles and measured the parameters of the humeral head in both two circles which could present the morphology in cHHP and tHHP plane of humeral head, for more accurate measurement results. Parameters measured from the same humeral head in sagittal versus coronal planes were compared using paired t tests. Statistically significant differences were observed in curvature (average curvature on coronal humeral head plane—average curvature on transversal humeral head plane = 1.55 mm, P < 0.001), diameter (average diameter on coronal humeral head plane—average diameter on transversal humeral head plane = 3.06 mm, P < 0.001) and thickness (average thickness on coronal humeral head plane—average thickness on transversal humeral head plane = 1.03 mm, P < 0.001) of the same humeral head in coronal humeral head plane and transversal humeral head plane, suggesting that humeral head could not be well fitted as a sphere. However, the three-dimensional analysis using CT scans neglected the thickness of the articular cartilage, and the present findings might have underestimated the parameters of humeral head.
We obtained several findings by comparing humeral head morphology data for cohorts of different local populations. East Asian cohorts have smaller humeral head sizes compared with Western cohorts. In the coronal plane of the humeral head, Eastern cohorts have smaller curvature and diameter of the humeral head compared with Western cohorts. However, the arc and thickness of the humeral head are greater in East Asians, indicating that there was more articular surface coverage of the humeral head on the coronal plane in East Asian cohorts. By analyzing the degree of dispersion of the two groups, larger standard deviations of all differential parameters were found in Western cohorts. This finding may indicate that a smaller range of prosthesis size was required in East Asian cohorts. Our data can be used as the humerus morphological parameters of the yellow race to provide a reference for subsequent research as well.
The shoulder prosthesis is a component that needs to be implanted and used for the long-term. Improving design accuracy and simulating the real situation are important to reduce unnecessary load and wear [20]. Having a digital understanding of proximal humeral morphology plays a role in diagnosing and classifying disease, designing prosthesis and instrument, enhancing surgical precision and guiding patient recovery.