The Hindlimbs
Anatomy
Appendicular Skelton:
(Fig. 1) Moving up from the foot of the horse is the hoof wall. Just as in the forelimb, the hoof wall is joined by the short pastern bone and pastern joint at the upper end. Next, is the long pastern bone joined with the fetlock joint. The fetlock joint is connected to the cannon bone. The cannon bone is then joined to the tarsal joints or the hock. Above the hock is the tibia and fibula. These two bones join the femur at the stifle joint. The upper bone of the hindlimb, femur, is attached to the pelvis by ball-and-socket joint.
The stifle joint has a patella or knee-cap much like the human knee. The femur, tibia and patella join together with the help of various ligaments and modified structures at the ends of the both the femur and tibia. The hindfoot is made mostly of the hock which has six bones. These six bones are arranged in two rows. The metatarsus is again called the cannon. The phalanges is the forefoot (Siegal 1996).
Figure 1. Anatomy of the Hindlimb. The figure shows a side view of the anatomical features of the hindlimb. Permission from www.spequine.com.
Musculature:
Extension of the hip moving the hindlimb rearward is controlled by the semitendinosus, semimembranosus and biceps femoris. These three muscles also help to flex the stifle, along with a small but powerful muscle, the soleus, located behind the tibia. The gluteal muscles and the tensor fascia latae run from the hip to the femur. They work to pull the rear limb forward and flex the hip. The lateral digital extensor and long digital extensor flex the hock and extend the digits. Three tendons, superficial, deep digital flexors and suspensory ligament, provide the support for the lower leg and help to maintain the proper angles necessary for function.
General:
The thighs and gaskins (between the stifle and hock) should be well-muscled to provide the strength necessary for locomotion. The hocks should be wide and flat and the pasterns should be shorter and less sloping than the pasterns in the forelimbs. As seen with the forelimbs, a properly set stance is important for proper and efficient function.
Motion
The hindlimb also can be considered to be a pendulum in motion. The hip joint-time curve (Fig. 1) and cranio-cuadal (Fig. 2) movement on the distal metatarsus during one complete stride are similar. The rotation point in the hindlimb is considered the acetabulum. The maximal protraction in the hindlimb occurs after the maximal protraction in the forelimb. This is almost a 10 percent time difference. The hindlimb reaches its’ maximal protraction just before ground contact. The role of pelvic rotation in hindlimb motion during the stance and the swing phase differs between the sagittal plane and the transverse plane. During one complete stride the pelvic angle in the sagittal plane remains parallel with the horizon while that of the transverse plane changes considerably (Back et al. 1995b).
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| Figure 1. Angle Time Diagram of Hip. Data taken from horses (n=24) at a trot. Adapted from (Back et al. 1995b.) | Figure 2. Cuadal-Cranio Movement. Shows the comparison of distal metatursus relative to proximal femur. Data taken from horses (n=24) at a trot. Adaptedf rom (Back et al. 1995b.) |
The hindlimbs propel the horse forward. Therefore, most of the work is carried out by the joints; the hock joint and stifle. Hindlimbs generate energy and do positive work during the stance phase. Most of this energy is generated in the hip. As speed increases the work done by the hindlimb is consistent (Dutto et al. 2006).