SUMMARY The morphology of muscle attachment sites, or entheses, has long been assumed to directly reflect in vivo muscle activity. The purpose of this study is to examine whether variations in muscle activity that are within normal physiological limits are reflected in variations in external attachment site morphology. This study tests the hypothesis that increased muscle activity (magnitude, number and frequency of loading cycles) results in the hypertrophy of muscle attachment sites. The attachment sites of six limb muscles and one muscle of mastication (control) in mature female sheep were measured and compared in exercised (weighted treadmill running for 1 h per day for 90 days) and sedentary control animals. Attachment site surface morphology was assessed by quantifying the size (3D surface area) and complexity (fractal dimension parallel and perpendicular to soft tissue attachment) of the surfaces. The results of this study demonstrate no effect of the exercise treatment used in this experiment on any measure of enthesis morphology. Potential explanations for the lack of exercise response include the mature age of the animals, inappropriate stimulus type for inducing morphological change, or failure to surpass a hypothetical threshold of load for inducing morphological change. However, further tests also demonstrate no relationship between muscle size and either attachment site size or complexity in sedentary control animals. The results of this study indicate that the attachment site morphological parameters measured in this study do not reflect muscle size or activity. In spite of decades of assumption otherwise, there appears to be no direct causal relationship between muscle size or activity and attachment site morphology, and reconstructions of behavior based on these features should be viewed with caution.

The ability to mentally manipulate objects in three dimensions is essential to the practice of many clinical medical specialties. The relationship between this type of visual-spatial ability and performance in preclinical courses such as medical gross anatomy is poorly understood. This study determined if visual-spatial ability is associated with performance on practical examinations, and if students' visual-spatial ability improves during medical gross anatomy. Three hundred and fifty-two first-year medical students completed the Mental Rotations Test (MRT) before the gross anatomy course and 255 at its completion in 2008 and 2009. Hypotheses were tested using logistic regression analysis and Student's t-test. Compared with students in the lowest quartile of the MRT, students who scored in the highest quartile of the MRT were 2.2 [95% confidence interval (CI) 1.2 and 3.8] and 2.1 (95% CI 1.2 and 3.5) times more likely to score greater than 90% on practical examinations and on both practical and written examinations, respectively. MRT scores for males and females increased significantly (P < 0.0001). Measurement of students' pre-existing visual-spatial ability is predictive of performance in medical gross anatomy, and early intervention may be useful for students with low visual-spatial ability on entry to medical school. Participation in medical gross anatomy increases students' visual-spatial ability, although the mechanism for this phenomenon is unknown.

Radiological images show anatomical structures in multiple planes and may be effective for teaching anatomical spatial relationships, something that students often find difficult to master. This study tests the hypotheses that (1) the use of cadaveric computed tomography (CT) scans in the anatomy laboratory is positively associated with performance in the gross anatomy course and (2) dissection of the CT-scanned cadaver is positively associated with performance on this course. One hundred and seventy-nine first-year medical students enrolled in gross anatomy at Boston University School of Medicine were provided with CT scans of four cadavers, and students were given the opportunity to choose whether or not to use these images. The hypotheses were tested using logistic regression analysis adjusting for student demographic characteristics. Students who used the CT scans were more likely to score greater than 90% as an average practical examination score (odds ratio OR 3.6; 95% CI 1.4, 9.2), final course grade (OR 2.6; 95% CI 1.01, 6.8), and on spatial anatomy examination questions (OR 2.4; 95% CI 1.03, 5.6) than were students who did not use the CT scans. There were no differences in performance between students who dissected the scanned cadavers and those who dissected a different cadaver. These results demonstrate that the use of CT scans in medical gross anatomy is predictive of performance in the course and on questions requiring knowledge of anatomical spatial relationships, but it is not necessary to scan the actual cadaver dissected by each student.

Superior and anterior hyoid movements are important events in pharyngeal deglutition. This cross-sectional study uses a cadaver model to document the structural properties of the muscles underlying these movements in an effort to understand how their morphology influences function. Measurements to determine physiological cross-sectional areas (PCSAs) of swallowing muscles were taken from hemisected head and neck formalin-fixed cadaver specimens (n = 13). Coordinates of muscle attachment sites and PCSAs were used to calculate î and ĵ unit force vectors, where î and ĵ represent anterior-posterior and superior-inferior directions, respectively. The suprahyoid muscle subsamples were grouped for analysis as follows: digastric (DG), geniohyoid (GH), mylohyoid (MH), and stylohyoid (SH). The ANOVA with Tukey HSD post hoc analysis of unit force vectors showed the following results: GH (−0.44 ± 0.15 cm2) >MH (−0.02 ± 0.21 cm2), DG (−0.05 ± 0.11 cm2), SH (0.14 ± 0.04 cm2), with negative values representing the anterior direction (p < 0.01); and MH (0.91 ± 0.28 cm2) >DG (0.29 ± 0.14 cm2), SH (0.22 ± 0.08 cm2), GH (12 ± 0.08 cm2), with positive values representing the superior direction (p < 0.01). The morphology of the suprahyoid muscles suggests that based on structural properties, the geniohyoid has the most potential to displace the hyoid in the anterior direction and the mylohyoid has the most potential to displace the hyoid in the superior direction. These data in complement with physiological findings may provide greater insight into these movements for those developing novel treatments for dysphagia.