Hindlimb - Anatomy & Physiology

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Common structures of the Proximal Hindlimb and Pelvis

Ilium

• The ilium makes up the craniodorsal part of the hip bone.
• It extends in a cranio-dorsal direction from the hip joint to the articulation with sacrum.
• It is made from a cranial wing and a caudal body.

Ilial Wing

• The margin of the wing is known as the iliac crest. Along the crest are two very important anatomical landmarks:
  • Tuber Coxae or Coxal Tuberosity forms the palpable point of the hip.
  • Sacral Tuber is the thickened mediodorsal angle of the ilial wing.
• The lateral surface of the wing provides a point of attachment for the gluteal muscles.
• The medial surface has two distinct parts:
  • The lateroventral part provides the point of insertion for many pelvic muscles.
  • The mediodorsal part articulate with the sacrum forming the sacroiliac joint
• The caudodorsal border of the wing is very concave and along its surface exists the greater sciatic notch. This is where the sciatic nerve runs over the ilium.

Ilial Body

• The only anatomical feature of note is the psoas tubercle on the ventral border. This provides attachment for the psoas muscle.

Ossification Centers of the Ilium

Ischium

The Ischium can be divided into three main sections:

• The body
  • Is part of the acetabulum
  • The dorsal border is continuous with that of the ilium forming the ischiatic spine; this tapers towards the lesser sciatic notch.
• The caudal plate
  • Extends cranially into the symphysial and acetabular branches, which form the caudal borders of the obturator foramen.
  • The caudal section is thickened forming the ischial tuberosity. This is a visible landmark in most animals.
  • The medial caudal borders meet in a concave fashion forming a broad and deep notch called the ischial arch.
• The medial branch
  • This forms the caudal section of the pelvic symphysis

Ossification Centers of the Ischium

Pubis

• The pubis is a L shaped bone that makes up one of the three bones of the pelvis.
• It consists of three parts:
  • Body
  • Transerse acetabular branch - the cranial edge of which is the pectin of pubis and forms the iliopubic emminence, to which some of the abdominal muscles attach.
  • Sagittal symphysial branch
• The two pubis fuse at the cranial section of the pubic symphysis. Lying of the ventral surface of the symphysis is the ventral pubic tubercle.
• The pubis form more than half the obturator foramen. This is an opening in the pelvic floor that allows the obturator nerve to pass through it; the foramen is closed by musculature and soft tissue.

Ossification Centers of the Pubis

Femur

The femur is the strongest of the long bones and provides the origin and attachment for many muscles and tendons. This means that it is charcacteristically modelled for each species. Despite this it can be divided into three basic parts: The Femoral Head

• The head is offset from the main shaft of the femur, points in a medial direction and articulates with the acetabulum.
• It has a hemispherical articular surface with an associated notch, fovea capitis, which provides attachment for the intracasular ligament.
• Lateral to the head is the greater trochanter. This process provides attachment to the gluteal muscles.
• The trochantic fossa seperates the greater trochanter and the neck of the femur. It provides a site of insertion for the deep hip muscles.
• The lesser trochanter is a smaller process on the medial side that provides a site of attachment for the iliopsoas.

Femoral Shaft

• The caudal surface is roughened proximally and is framed by the medial and lateral lips
• These lips extend distally end enclose the popliteal surface. They also provide attachment for the adductor muscles.

Distal Extremity

• This consists of the medial and lateral condyles caudally and a trochlea cranially.
• The condyles articulate with the tibia and menisci to form the femorotibial joint.
• The intercondylar fossa lies between the condyles and is seperated from the polpiteal surface by the intercondylar line.
• Both condyles are roughened on their abaxial surfaces providing attachment for the collateral ligaments of the stifle joint.
• The extensor fossa is one of a pair of depressions on the lateral condyle. It is the more cranial of the two and forms an attachment point for the long digital extensor and third perineal muscle. The caudal depression givens origin to the popliteal.
• On the caudal aspect of each condyle are facets for the articulation with the fabellae. These are sesamoid bones that are embedded in the tendinous insertion of the gastrocneumius.
• The trochlea is made up of two ridges and a groove that articulate with the patella to form the femeropatellar joint.

Ossification Centers of the Femur

Joints of the Proximal Hindlimb

Sacroiliac Joint

• This is a synovial joint that is formed by the articulations between the auricular surfaces of the ilial wing and the sacrum.
• It had a joint capsule that tightly surrounds the joint and is strengthened by the ventral sacroiliac ligaments.
• The sacroiliac ligaments are:
  • Interosseous sacroiliac ligaments - these lie between the iliac tuberosity and the dorsal aspect of the sacral wing.
  • Dorsal Sacroiliac ligaments - this is made up of two branches. The short branch connects the sacral tuber to either the mammilary processes (carnivores and pigs)or to the spinous processes (ruminants and horses) of the sacrum. The long branch connects the sacral tuber to the lateral aspect of the sacrum.
• The sacrotuberous ligament is highly variable among species.

Coxafemoral/Hip Joint

• This is a spheroidal joint formed by the femoral head and the acetabulum.
• The acetabulum
  • Formed by all three pelvic bones and an additional small acetabular bone in carnivores that is present in carnivores.
  • The craniolateral part is made by the ilium, the caudolateral part by the ischium and the medial part by the pubis.
  • The cavity of the acetabulum consists of a peripheral articular lunate surface and the non-articular acetabular fossa in it's centre.
  • The lunate surface is crescent shaped and has on its medial aspect the acetabular notch.
  • Cattle also have a cranioventral notch present.
  • The acetabular lip is a band of fibrocartilage that lies on the acetabular rim, thus deepening the acetabulum.
• The joint capsule is large and attaches to the acetabular lip.
• The ligament of the femoral head connects the fovea in the head, by running through the acetabular notch, to the acetabular fossa. It is covered by a synovial membrane and for the majority is intracapsular.
• The acessory ligament of the femur is only present in the horse. It originates from the straight muscle of the abdomen and passes through the acetabular notch to finally attach in the fovea of the femoral head.
• The transverse acetabular ligament crosses the acetabular notch and ensures that the other two ligaments remain in their notch.

Common Structures of the Distal Hindlimb

Tibia

The tibia is one of the major weight bearing bones of the hind limb and is involved in both the stifle and hock. The tibia can be divided into three distinct sections:

Proximal Extremity

• It is three sided and has two condyles which are seperated by the popliteal notch on its caudal aspect.
• The condyles have an articular surface which articulates with its corresponding femoral condyle or the distal surface of the meniscus.
• In between these articular surfaces lies the intercondylar eminence. The central intercondylar area divides this into a higher medial part and a lower lateral part.
• Cranial and caudal to the eminence are depressions where ligaments attach.
• The lateral side of the condyle has an articular facet for the articulation with the fibula.
• The extensor groove is a large notch on the craniolateral aspect which allows passage of the long digital extensor muscle.

Tibial Shaft

• It is craniocaudally compressed.
• The tibial tuberosity/tibial crest projects cranially from the proximal part of the shaft and is an important palpable landmark.
• The cranial border of the tibia is an extension of the crest distally. It divides the cranial aspect of the shaft in two. The medial aspect is subcutaneous and the lateral aspect is covered in muscles.

Distal Extremity

• This carries the cochlea which has two grooves divided by a ridge.
• This central ridge is directed sagittally in most species.
• The cochlea articulates with the trochlear ridges of the talus.
• The medial malleolus lies on the medial side of the cochlea and is a bony protuberence.
• The lateral aspect of the cochlea is highly variable in domestic species.

Ossification Centers of the Tibia

Fibula

The fibula lies laterally to the tibia and proximally doesn't interact with the stifle joint. The fibula consists of a proximal head, a neck, a shaft and a distal extremity/lateral malleoulus. During evolution the fibula has been reduced in size and so also in relative strength and function. The amount of reduction is highly variable in domestic species.

Tarsal bones

The tarsus/hock is made up of two bones that lie between the crus and metatarsals. The proximal row is made of the talus and calcaneous and articulate with the tibia forming the tarsocrural joint. The distal row is made up of the central, 1st, 2nd, 3rd and 4th tarsal bones. The pattern of these bones is highly variable amongst domestic species. But in general they articulate with proximal row forming the tarsocrural joint and with the metatarsal bones forming the tarsometatarsal joint.

Talus

• The largest bone of the tarsus and is the medial bone of the proximal row.
• It can be divided into three distinct areas; the compact body, the trochlea and the head.
• The trochlea has prominent sagittal ridges dorsoproximally that articulate with the sagittal grooves and intermediate ridge of the distal end of the tibia.
• The cylindrical head is a smaller distal trochlea that articulates with the central tarsal bone. The plantar and lateral sides articulate with the calcaneous.

Calcaneus

• It lies laterally and plantar to the talus.
• It articulates medially and dorsally to the talus and distally towards the 4th tarsal bone.
• It has a proximal plantar projection called the calcaneal tuberosity, it is this that forms the palpable point of the hock. It acts as a lever for muscles involved in hock extension.
• The susentaculum tali lies on the medial aspect of the distal portion of the calcaneus. It supports the deep digital flexor tendon and overlaps the talus on its plantar side.

Distal Row of Tarsal Bones

• These are highly variable amongst species but are discussed on their relevant pages.

Joints of the Distal Hindlimb

• Stifle Joint
• Patella
• Tarsal Joint/Hock

Muscles of the Hindlimb

• Girdle Musculature
• Rump Muscles
• Muscles of the Stifle

Vasculature of the Hindlimb

• Arteries of the Hindlimb
• Veins of the Hindlimb
• Lymphatics of the Hindlimb

Species Specifics

• Canine Hindlimb
• Equine Hindlimb
• Bovine Hindlimb