Managing Disorders of the Equine Hind Limb

Anatomy

Muscles of the Hip 1

Muscle	Origin	Insertion	Action	Nerve
Pectineus	Pubis	Femur	Adduct the limb & flex the hip	Obturator
Ilipsoas
Psoas Major	Ventral surface of lumbar vertebrae	Lesser trochanter of femur	Flex hip & externally rotate thigh	Ventral branches of thoracic & lumbar nerves & femoral nerves
Iliacus	Ventral surface of wing of the ilium
Gracilis	Pubic symphysis	Med tibia	Adduct limb	Obturator
Adductor	Pubic symphysis	Caudal surface of femur	Adduct limb	Obturator

Muscles of the hip 2

Muscle	Origin	Insertion	Action	Nerve
Internal Obturator	Pelvic Floor	Trochanteric fossa of femur	Lateral rotation of femur	Ischiatic
Gemelli	Ischium	Trochanteric fossa of femur	Lateral rotation of femur	Ischiatic
External Obturator	Ventral surface of pubis and ischium	Trochanteric fossa of femur	Adduct thigh	Ischiatic
Quadratus femoris	Ischium	Caudal surface of femur	Extend hip & adduct thigh	Obturator
Deep gluteal	Body of ilium	On or near greater trochanter	Extension Abduction	Gluteal

Muscles of the hip and stifle

Muscle	Origin	Insertion	Action	Nerve
Superficial Gluteal	Dorsal to hip joint	Third Trochanter	Abduct hip	Gluteal
Tensor fascia latae	Tuber coxae	Lateral femoral fascia	Hip flexion & stifle extension via tension of lat femoral fascia	Gluteal
Biceps femoris	Ischiatic tuberosity (Tuber Ischii)	Greater Trochanter	Extend hip Abduct hip	Gluteal
Semitendinosus	Ischiatic tuberosity	Tibia and calcaneal tub.	Extend hip Flex stifle Extend tarsus	Ischiatic
Semimembranosus	Ischiatic tuberosity	Femur and tibia	Extend hip Flex or  extend stifle	Ischiatic

hip and stifle 2 

Muscle	Origin	Insertion	Action	Nerve
Middle Gluteal	Wing of ilium	Greater trochanter of femur	Extension and abduction	Gluteal
Rectus femoris	Ilium (cranioventral iliac spine)	Patella and patella tuberosity	Flexion of hip Extension of stifle	Femoral
Vastus lateralis	Proximal femur		Extends the stifle
Vastus medialis
Vastus intermedius

Muscles of the Stifle, hock and pes 

Muscle	Origin	Insertion	Action	Nerve
Gastrocnemius	Distocaudal surface of the femur	Calcaneal tuberosity	Extend tarsus Flex stifle	Tibial
Long digital extensor	Extensor fossa of femur	Extensor processes of digital phalanges	Flex hip Extend stifle	Peroneal
Soleus	Head of fibula	Tendon and lateral head of gastrocnemius	Extend tarsus	Tibial
Lateral digital extensor	Fibula	Lateral aspect of digit	Extend digits Flex tarsus	Peroneal
Deep digital flexor	Tibia and fibula	Distal Phalanx	Extend tarsus Flex digits	Tibial
Superficial digital flexor	Caudal distal femur, deep to gastrocnemius	Calcaneal tuberosity Middle phalanx	Flex stifle Extend tarsus Flex digits	Tibial

Pelvic Limb Stay Apparatus

Function

The horse uses its pelvic limb stay apparatus to support the weight of the caudal end of its body while using a minimal amount of muscular activity. The pelvic stay apparatus is more significant than that in the pelvic limb. When employed by one pelvic limb, the stay apparatus allows the other pelvic limb to be placed in a "resting" position with just the tip of the hoof touching the ground. Although the stay apparatus reduces the amount of energy required to remain standing, the amount of muscular effort is not reduced. This explains why you see horses switching their weight from one hind limb to another.

How does the stay apparatus function?

The pelvic limb stay apparatus has three essential elements. The first element, the stifle joint locking mechanism, allows the weight of the caudal body to rest, essentially, on the locked joint. The second element, the reciprocal mechanism, ensures that the stifle and hock joints will move in unison, and the leg will move in a smooth, coordinated manner. The first and second elements work together. The third element involves other ligaments/tendons in the distal limb.