In vivo baseline measurements of hip joint range of motion in suspensory and nonsuspensory anthropoids

Abstract

Hominoids and atelines are known to use suspensory behaviors and are assumed to possess greater hip joint mobility than nonsuspensory monkeys, particularly for range of abduction. This assumption has greatly influenced how extant and fossil primate hip joint morphology has been interpreted, despite the fact that there are no data available on hip mobility in hominoids or Ateles. This study uses in vivo measurements to test the hypothesis that suspensory anthropoids have significantly greater ranges of hip joint mobility than nonsuspensory anthropoids. Passive hip joint mobility was measured on a large sample of anesthetized captive anthropoids (nonhuman hominids = 43, hylobatids = 6, cercopithecids = 43, Ateles = 6, and Cebus = 6). Angular and linear data were collected using goniometers and tape measures. Range of motion (ROM) data were analyzed for significant differences by locomotor group using ANOVA and phylogenetic regression. The data demonstrate that suspensory anthropoids are capable of significantly greater hip abduction and external rotation. Degree of flexion and internal rotation were not larger in the suspensory primates, indicating that suspension is not associated with a global increase in hip mobility. Future work should consider the role of external rotation in abduction ability, how the physical position of the distal limb segments are influenced by differences in ROM proximally, as well as focus on bony and soft tissue differences that enable or restrict abduction and external rotation at the anthropoid hip joint.

Keywords: external rotation; hip abduction; orthogrady; passive joint mobility; primates.

Figure 1

Adduction, abduction, internal rotation and external rotation were measured from the “horizontal” posture, which was defined as when the femur was 90° (perpendicular) to the examination table. Adduction and abduction were measured relative to the horizontal surface of the examination table for accuracy but the angles were then adjusted to the midline (indicated in grey). Although best illustrated from a caudal view (shown above), adduction and abduction were measured cranially between the abdomen and thigh.

Figure 2

Mean and interquartile ranges are indicated by the boxplots. All angles shown, except adduction, are significantly different between locomotor groups (p<0.05). Note that smaller values for flexion reflect a higher range of motion (see Figure 1). Dark dots indicate suspensory data points and light dots indicate non-suspensory data points.

Figure 3

Ranges of flexion-extension, adduction-abduction, and internal-external rotation are shown. Mean and interquartile ranges are indicated by the boxplots. Dark dots indicate suspensory data points and light dots indicate non-suspensory data points.

Figure 4

Examples of passive positions of abduction for (a) Pongo pygmaeus, (b) Gorilla gorilla, and (c) Macaca mulatta. The patella is indicated by blue arrows to highlight the external rotation that accompanies abduction in suspensory species. Note the lateral knee orientation (externally rotated thigh) in Pongo and Gorilla and the anterior orientation (non-rotated thigh) in Macaca.