The Hamann-Todd osteologic collection at the Cleveland Museum of Natural History consists of nearly 3000 disarticulated human skeletons gathered approximately at the beginning of the 20th century from the unclaimed dead of the Cleveland city morgue. We obtained 200 adult skeletons from this collection for this study. To select a study sample representing the normal human population, we diversified the sample in terms of race, age, and gender and excluded femora that were anatomically abnormal. Specifically, the initial sample was divided equally among genders and available races (50 white males, 50 white females, 50 black males, and 50 black females being selected at random from the collection’s sample of each subpopulation) and femora from individuals older than 18 years were included, excluding femora not fully mature at the time of death. Additionally, we excluded individual femora that on gross visual inspection appeared anatomically abnormal, ie, those affected by disease, such as arthritis, osteonecrosis, or other deformity. This yielded a total of 375 femora available for study (Table ).
Sample selection and demographics
Each of the specimens was digitally photographed in two standardized positions, termed AP and lateral. For the AP photographs, we first placed each pair of femora in a supine position on a flat laboratory bench with anterior surfaces directed toward the ceiling and femoral shafts parallel to one another. In this position, specimens rested distally on the convex surfaces of the medial and lateral condyles and proximally on the greater trochanter. The femoral neck then was made parallel to the superior surface of the laboratory bench by either rotating the femoral shaft internally and supporting the lateral condyle if the neck axis was anteverted or rotating the femoral shaft externally and supporting the medial condyle if the neck axis was retroverted. Parallelism between the femoral neck and laboratory bench was determined through visual inspection. The investigator taking the photographs (PAT) used square cards, approximately 1 mm in thickness, to increasingly support the medial or lateral condyle until the axis of the neck appeared parallel to the laboratory bench surface. By taking a photograph from directly overhead (camera lens parallel to the laboratory bench and femoral neck axis as confirmed by a level), we obtained accurate AP pictures; any potential distortion resulting from neck version was eliminated by making all components of the setup parallel. For the lateral photographs, we again placed each pair of femurs on the flat laboratory bench surface with anterior surfaces facing up. The femora then were abducted until the femoral necks were parallel with the plane produced by the edge of the laboratory bench. Parallelism again was determined through visual inspection. The investigator taking the photographs (PAT) increasingly abducted the femoral shafts until the axis of the neck appeared parallel to the laboratory bench edge from overhead. Additionally, each femur was checked to ensure the medial and lateral condyles rested on the surface of the laboratory bench distally, allowing the table surface to represent the transcondylar axis. By taking pictures with the lens of the camera parallel to the edge of the laboratory bench (as confirmed using a T-square ruler) and even with its surface (as confirmed through the camera’s view finder), we obtained accurate lateral images. Any distortion produced by the angle of inclination was eliminated by making the neck axis and camera parallel.
Using ImageJ software (nih.gov), we obtained 12 raw measurements from each specimen, six from each of the two views. These measurements were used to define three parameters of the head-neck relationship (translation, rotation, concavity) and two parameters of the neck-shaft relationship (neck version, angle of inclination).
The first parameter of the head-neck relationship examined was head-neck translation. Although the femoral head often is pictured as centered on the axis of the femoral neck, this may not represent normal anatomy. Rather than being perfectly aligned on the neck axis, it is possible normal individuals regularly have minor shifts or translations of the head on the neck in the plane perpendicular to the neck’s axis in AP and/or superior-inferior vectors. To quantify these potential translational movements, four offset measurements were obtained based on descriptions by Ito et al. [10
] and Siebenrock et al. [24
]: anterior (AOS) and posterior (POS) offsets were acquired from the lateral photographs (Fig. ); superior (SOS) and inferior (IOS) offsets were acquired from the AP photographs (Fig. ). Each of these measurements was defined as the minimum distances between two lines drawn parallel to the femoral neck axis on each of the four cardinal surfaces. The femoral neck axis was produced by drawing a straight line that by visual inspection was equidistant from the anterior/posterior or superior/inferior borders of the femoral neck along the neck’s length. The two lines parallel to this axis, needed for the measurements of translation, then were drawn and visually positioned. The first line was drawn tangential to the convexity of the femoral head and the second tangential to the concavity of the femoral neck. The distance between these parallel lines represented the perpendicular distance separating these two contours on a single cardinal surface. We then used these four raw offset measurements to calculate two offset ratios: AOS/POS and SOS/IOS. Femurs with AOS/POS ratios equal to 1 would be offset equally anteriorly and posteriorly and thus have minimal translation in this vector. Similarly, femurs with SOS/IOS ratios equal to 1 would be offset equally superiorly and inferiorly, having minimal translation in this vector. However, femurs with AOS/POS and/or SOS/IOS ratios greater than 1 would be translated more anteriorly and/or superiorly, respectively, whereas femurs with AOS/POS and/or SOS/IOS ratios less than 1 would be translated more posteriorly and/or inferiorly, respectively. These two ratios thus defined translational movements of the femoral head on the neck in both major axes.
Fig. 1 The AOS was defined as the perpendicular distance (ab) between Lines A and B. Line A was drawn parallel to the neck axis and tangential to the convexity of the femoral head; Line B was drawn parallel to the neck axis and tangential to the concavity of (more ...)
Fig. 2 The SOS was defined as the perpendicular distance (ef) between Lines E and F. Line E was drawn parallel to the neck axis and tangential to the convexity of the femoral head; Line F was drawn parallel to the neck axis and tangential to the concavity of (more ...)
The second parameter of the head-neck relationship examined was head-neck rotation. Although common depictions of the femoral head-neck junction place the physeal scar perpendicular to the axis of the femoral neck, this may not represent normal anatomy. Rather, it is possible even in normal individuals that a certain amount of rotation of this scar (and therefore the femoral head) is present. To quantify these potential rotational movements, two original measurements, termed physeal angles, were devised, one from each of the two available views. The AP physeal angle was defined as the superior-lateral angle made between the intersection of the femoral neck axis, as defined previously, and a line representing the physeal scar in the AP pictures (Fig. ), whereas the lateral physeal angle was similarly defined as the anterior-lateral angle made between these same lines in the orthogonal, lateral view (Fig. ). The line representing the physeal scar also was produced by visual inspection and ignored any encroachment of the scar onto the femoral neck. Femoral heads with AP and/or lateral physeal angles equal to 90° would not be rotated with respect to the neck axis. However, femoral heads with AP and/or lateral physeal angles greater than 90° would be adducted and/or retroverted, respectively, whereas femoral heads with AP and/or lateral physeal angles less than 90° would be abducted and/or anteverted, respectively. These two angles thus defined rotations movements of the head on the neck in both major axes.
The anteroposterior physeal angle was defined as the acute, superior-lateral angle between Lines DE and EF. Line DE represented the physis; Line EF represented the neck axis.
The lateral physeal angle was defined as the acute, anterior-lateral angle between Lines AB and BC. Line AB represented the physis; Line BC represented the neck axis.
The third and final parameter of the head-neck relationship examined was head-neck junction concavity. Although an idealized femoral head is nearly spherical even as it meets the femoral neck, normal sphericity at the head-neck junction may differ from this idealized conception and among individuals. To quantify sphericity of the head as it joins the neck, four measures of the concavity of this junction, expanded from the description by Nötzli et al. [19
], were determined, two (alpha and beta angles) from the lateral view (Fig. ) and two (gamma and delta angles) from the AP view (Fig. ). The alpha angle defined the extent of the concavity at the anterior head-neck junction. It was produced by the intersection of two lines. The first was the femoral neck axis. The second was a line formed by connecting two points on the femoral head; Point B was the center of the femoral head as found by ImageJ after visually inscribing a perfect circle around an ideally spherical femoral head and Point A was the point where the anterior cortical surface of the head-neck junction first exited the same perfect circle. The beta, gamma, and delta angles were similarly used to define the concavities of the posterior, superior, and inferior head-neck junctions, respectively. Smaller angles represented concave head-neck junctions and therefore nearly spherical femoral heads. Progressively larger angles represented junctions with increasingly less concavity, ranging from mild flattening of the junction to severe extension of the junction beyond the limits of a spherical head. These four angles thus defined the extent of concavity of the head-neck junction in four cardinal locations.
Fig. 5 The alpha angle was defined as the acute angle between Lines AB and BD. Line AB was formed by connecting Point B (the center of the femoral head) with Point A (the point where the cortical surface of the head-neck junction first exited a perfect circle (more ...)
Fig. 6 The gamma angle was defined as the acute angle between Lines EF and FH. Line EF was formed by connecting Point F (the center of the femoral head) with Point E (the point where the cortical surface of the head-neck junction first exited a perfect circle (more ...)
The first parameter of the neck-shaft relationship examined was neck version (Fig. ). This angle was measured from an accurate lateral view, the femoral shafts being abducted allowing the neck axis to be parallel with the camera. It was created by the intersection of the neck axis and transcondylar plane (plane of the laboratory bench) and defined the degree to which the neck was above or below the plane created by the condyles. Angles superior to this plane were arbitrarily positive and angles below it negative.
The neck version was defined as the acute angle between Lines AB and BC. Line AB represented the neck axis; Line BC represented the transcondylar axis produced by the superior surface of the laboratory bench.
The second parameter of the neck-shaft relationship examined was angle of inclination (Fig. ). This angle was measured from an accurate AP view, the femoral neck axes being parallel to the camera’s lens. It was created by the intersection of the anatomic axes of the femoral neck and shaft and thus defined the position of the neck relative to the shaft in the accurate AP view. Similar to the method for defining the femoral neck axis, the axis of the proximal shaft was produced by visual inspection and drawn such that it would be equidistant from the medial and lateral cortical surfaces of the shaft along its length.
The angle of inclination was defined as the acute angle between Lines AB and BC. Line AB represented the neck axis; Line BC represented the femoral shaft.
Ranges, means, and standard deviations were determined for each of the measurements made for the population as a whole and for the various subpopulations based on gender and age (younger or older than 50 years at the time of death). We used paired Student’s t tests to establish the significance of any noted differences and post hoc power analysis, which revealed a power greater than 0.90 for all examined differences, was used to confirm the adequacy of the sample size. Pearson’s coefficients were calculated to examine correlations between variables.