Hindlimb - Anatomy & Physiology

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 the 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:

1. Tuber Coxae or Coxal Tuberosity forms the palpable point of the hip.

2. 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:

1. The lateroventral part provides the point of insertion for many pelvic muscles.

2. The mediodorsal part articulates 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.

Click here for Ossification centers of the ilium.

Ischium

The Ischium can be divided into three main sections:

1. 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.

2. 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.

3. The medial branch

This forms the caudal section of the pelvic symphysis.

Click here for ossification centers of the ischium.

Pubis

The pubis is an L shaped bone that makes up one of the three bones of the pelvis. It consists of three parts:

1. Body

2. 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.

3. Sagittal symphysial branch

The two pubis fuse at the cranial section of the pubic symphysis. Lying off the ventral surface of the symphysis is the ventral pubic tubercle. The pubis forms 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.

Click here for the 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:

1. 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 intracapsular 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.

2. Femoral Shaft

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

3. 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 gives 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 gastrocnemius. The trochlea is made up of two ridges and a groove that articulates with the patella to form the femeropatellar joint.

Click here for the 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 has 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

The Stifle, Cranial Caudal View - Copyright RVC

A composite, incongruent hinge joint made up of the femerotibial joint and femeropatellar joint.

Femerotibial Joint

Essentially this joint is formed between the femoral condyles and the proximal end of the tibia.
A meniscus exists between each condyle and the tibia to compensate for any incongruency of the articular surfaces. The meniscus is a semilunar fibrocartilage with a thick, convex peripheral border and central thin, concave border. The surface facing the femoral condyles is concave and facing the tibia it is flattened.
As a condylar joint the principal movements are flexion and extension, but due to the presence of the menisci there is a limited amount of rotation.
The fibrous layer of the joint capsule attaches to the margins of the articular surfaces and menisci and so completely encircles the femoral condyles.
The synovial layer of the capsule covers the cruciates and forms a partition between the medial and lateral parts of the joint. These sacs are further seperated by the menisci into a proximal and distal communicating compartments.
The lateral femerotibial joint contains two pouches; one ensheathes the origin of the tendinous origin of the politeal and the other ensheathes the origin of the long digital extensor at the extensor fossa.

Meniscal Ligaments

Cranial tibial ligaments of the menisci - connecting the cranial aspect of the menisci to the medial and lateral cranial intercondyloid area of the tibia.
Caudal tibial ligaments of the menisci - the medial ligament connects the caudal angle of the medial meniscus to the caudal intercondyloid area of the tibia. The lateral ligament connects the caudal angle of the lateral meniscus to the popliteal notch of the tibia.
Femoral ligament of the lateral meniscus - connects the caudal angle of the lateral meniscus to the inside aspect of the medial femoral condyle.
Transverse ligament - connects the cranial angles of the lateral and medial menisci. Found in carnivores and cattle.

Femerotibial ligaments

Lateral and Medial Collateral Ligaments - The lateral connects the lateral epicondyle of the femur to both the lateral condyle of the tibia and the head of the fibula. The medial connects the medial epicondyle of the femur to just distal to the margin of the medial condyle of the tibia. This ligament fuses with the joint capsule and medial meniscus.
Cranial and Caudal Cruciate Ligaments - These ligaments sit in the intercondyloid fossa of the femur inbetween the two synovial sacs. The cranial connects the lateral femoral condyle to the central intercondylar area of the tibia. The caudal connects the medial femoral condyle to the popliteal notch of the tibia.
Oblique Popliteal Ligament - This is made of fibrous strands that are embedded in the joint capsule and run in latero-proximal to medial-distal direction.

Femeropatellar Joint

This joint is formed between the articular surfaces of the patella and femur. The ligaments of this joint can be grouped as the femeropatellar ligaments and the patellar ligament.
Both these groups of ligaments are highly species specific and are discussed on the species pages.

Patella

This is the largest sesamoid bone and lies in the tendinous insertion of the quadriceps.
The articular surface is on the caudal aspect and faces the femur. The free surface faces cranial and is palpable in all species.
The base is at the proximal end and is rough due to muscular attachments.
The apex is at the distal end.

Tarsal Joint/Hock

A composite joint between the tibia, fibula, tarsal bones and metatarsals which has four levels of articulation. The joint capsules' fibrous layer extends from the distal crus to the proximal metatarsal and thus covers the whole tarsus. The synovial layer forms four synovial sacs for each level of articulation. The points of articulations are: Tarsocrural Joint, Proximal Intertarsal Joint, Distal Intertarsal Joint and the Tarsometatarsal Joint. The intratarsal joints are very closely apposed and so allow very little movement. Tarsocrural Joint

A cochlear joint formed by the articulation of the trochlea of the talus and the distal end of the tibia. And the articulation between the calcaneous and the distal end of the fibula or lateral malleolus (cows).
It has a large joint capsule that communicates with the proximal intertarsal joint. It has two plantar pouches that extends proximally above the medial and lateral malleoli. It also has a dorsal pouch that continues under the medial tendon of the cranial tibial muscle.

Proximal Intertarsal Joint

Proximally the talus and calcaneus articulate and distally the central and forth tarsal bone articulate.
The extent of direction of movement is species variable.
A rigid joint formed by the central tarsal bone and the small tarsal bones distally.

Tarsometatarsal Joint

This is the articulation between the distal tarsal bones and the metatarsal bones.

Ligaments of the Tarsus

Long lateral collateral ligament connects the lateral malleolus to the proximal part of the lateral metatarsal bones. Along it's course it attaches to the lateral tarsal bones.
Short lateral collateral ligament connects the lateral malleoulus to the calcaneus and the talus and lies deep to the long lateral collateral ligament.
Long medial collateral ligament connects the medial malleolus to the proximal part of the medial metatarsal bones. Along it's course it attaches to the medial tarsal bones.
Short medial collateral ligament connects the medial malleolus to the calcaneus and the talus and is deep to the long ligament.
Dorsal tarsal ligament is a triangular sheath, which is spread between the medial part of the talus, the central and 3rd tarsal bones and the 3rd and 4th metatarsal bones.
Long plantar ligament is a strong ligament connecting the calcaneus to the central and 4th tarsal bones and the proximal part of the 3rd and 4th metatarsal bones.
Numerous short ligaments bridge the joint spaces in the intratarsal joints.
Strong fascia help keep tendons in place and are partially fused to the joint capsule. The most important are the proximal extensor retinaculum, which holds down the tendon of the long digital extensor and the cranial tibial muscles, and the distal extensor retinaculum, which holds the tendon of the long digital extensor in place.

Muscles of the Hindlimb

Girdle Musculature

These muscles arise from the ventral aspect of the lumbar vertebrae and will insert on either the pelvis or femur. They are also known as the sublumbar muscles.
Their main function is to:
- Stabilise the vertebral column and pelvis during locomotion.
- Control dorsiflexion and ventriflexion of the spine.
The Psoas Minor
- Function: flexion of the vertebral column during the stance phase. Stabilisation of the vertebral column.
- Origin: 2nd-3rd caudal thoracic vertebrae on their ventral aspect and the 4th/5th cranial lumbar vertebrae
- Insertion: via a strong tendon to the psoas tubercle of the femoral shaft.
The Iliopsoas - the strongest muscle of the girdle
- Function: Flexion of the hip and outward rotation of the stifle. ie. draws hindlimb forward
- In all animals, except carnivores where they are fused, the muscle can be divided into two distinct parts.
- The Greater Psoas - the lumbar portion.
  - Origin: last thoracic vertebrae and ribs and the bodies and transverse processes of the lumbar vertebrae.
  - Insertion: Incorporates with iliac muscle and inserts on the lesser trochanter.
  - It is positioned dorsally to the psoas minor and ventral to the quadrate lumbar muscle.
- The iliac muscle
  - Origin: wing and shaft of ilium
  - Insertion: via the common iliopsoas tendon to the lesser trochanter of the femur.
  - The muscle passes through the muscular lacuna; an opening between the os coxae laterally and caudally, the rectus abdominus medially and the iliac fascia cranially.
The quadrate lumbar muscle
- Function: stabilisation of the lumbar vertebral column
- Origin: Ventral aspect of the transverse processes of the lumbar vertebrae and the proximal ends of the ribs
- Insertion: Ventral aspect of the wings of the ilium and sacrum.

Rump Muscles

The rump muscles main function is to extend the hip and some also extend the stifle and tarsus. They can be grouped into four distinct groups; the gluteals, the hamstrings, the medial muscles of the thigh and the inner pelvic muscles.

The Gluteals

They lie over the lateral and caudal aspect of the pelvic wall and extend between the thigh and ilium. Superficial Gluteal Muscle

This muscle shows great species variance and will be explained on their respective homepages.
Function - Extension of the hip, also retraction of the limb and supports outward rotation.

Gluteofemoral Muscle

This muscle only exists in the cat.
Function - Retraction and abduction of the limb and hip extension
Origin - 2nd-4th caudal vertebrae
Insertion - Lateral aspect of patella and fascia lata via an aponeurosis
Location - Between the superficial gluteal muscle and biceps muscle of the thigh.

Middle Gluteal Muscle

This muscle also shows great species variance. Though all species have a superficial and deep portion that are seperated by a tendinous sheet. Both tendons on their site of insertion are protected by a synovial bursa.
Function - most powerful extensor of the hip, also abducts and retracts the limb.

Piriform Muscle

This is fused to the middle gluteal muscle except in carnivores.
Function - Extensor of hip and abducter of the limb.
Origin - last sacral vertebrae and sacrotuberous ligament.
Insertion - just distal to the greater trochanter on the lateral aspect of the femur.
Location - caudal and medial to the middle gluteal and is covered by the superficial gluteal.

Deep Gluteal Muscle

Function - abduction of the limb.
Origin - lateral aspect of the ilial shaft
Insertion - via a short tendon to the greater trochanter.

Tensor Muscle of the Fascia Lata

This muscle shows great species variance.
Function - flexion of the hip and extension of the stifle.

The Hamstrings

These muscles cover the caudal aspect of the thigh and are multi-articular. They originate near the ischium and extend to the tibia and have some tendinous components that will make up the common calcanean tendon.

Biceps Muscle of the thigh

The largest and most lateral of the muscles, it is superficial and covered only by fascia and skin.
It consists of cranial part arising from the sacrum and sacrotuberous ligament and a small caudal part arising from the ischium.
The muscle is composed of multiple parts and has different points of insertion in different species.
Function - Extension and abduction of the limb. The cranial part extends the hip and stifle, though the caudal part extends the hip but flexes the stifle. It also causes tarsal extension.
See species pages as is very species specific.

Abductor muscle of the thigh

Only present in carnivores
Function - abduction of the limb
Origin - sacrotuberous ligament
Insertion - crural fascia

Semitendinous

Function - extends the hip, stifle and tarsus when the foot makes contact with the ground, therefore propulsing the animal. On a non-weightbearing leg it flexes the stifle and rotates the leg back and out.
Origin - the ischial tuberosity (pelvic head)
Insertion - cranial margin of the tibia and a tendinous insertion on the calcaneal tuberosity.

Semimembranous

The most medial of the hamstrings.
Function - Extension of the hip and stifle in a weightbearing stance. On a non-weightbearing limb it adducts and retracts the limb.
Origin - can be from either just the pelvic head or from the pelvic head and vertebral head. This is dependent on species.
Insertion - onto the medial condyle of the femur and the medial condyle of the tibia.

Medial Muscles of the Thigh

This muscle groups main functions are to adduct the limb and to prevent unwanted abduction. They lie between the pelvic floor and the medial aspect of the femur.

Sartorius

Function - flexion of the hip, advancement and abduction of the limb. It can also extend the hip via its attachments to the crural fascia and stifle fascia.
Origin - Coxal tuberosity; ilial shaft or tendon of psoas minor
Insertion - Deep fascia of the leg
Location - superficially on the craniomedial border of the thigh as a strap like muscle.

Gracilis

Function - adductor of the limb, extends the stifle.
Origin - from an aponeurosis of the pelvic symphysis, the insertional tendons of the straight muscle of the abdomen. A tendinous plate is formed between the two aponeurosi of the gracilis' on which the adductor muscles originate.
Insertion - An aponeurotic insertion with the crural fascia that attaches to the tibial crest.
Location - broad muscular sheet on the caudal aspect of the medial part of the thigh.

Pectineal Muscle

Function - flexor of the hip, adductor and supinator of the limb.
Origin - iliopubic eminence of pelvic floor
Insertion - medial border of the femur
Location - a fusiform muscle extending between the pecten of the pubis, the pelvic floor and the femur.

Adductor Muscles

Function - adduction of the limb, can also retract the limb
Origin - the tendinous plate of the gracilis muscles.
Insertion - medial aspect of the femur, fascia and ligaments of the medial aspect of the stifle.

Inner Pelvic Muscles

This set of muscles are a rather mixed group of small muscles lying close to the hip joint. They lie between the pelvis and trochantic fossa of the femur.

Internal Obturator

Only exists in carnivores and horses.
Function - extension of the hip and rotation of the femur laterally.
Origin and insertion - are both dependent on species involved.

External Obturator

Function - supinator of the femur and adductor of the limb
Origin - the ventral pelvic surface close to the obturator foramen
Insertion - trochantic fossa

Gemellus

Function - rotation of the limb laterally
Origin - ischiatic spine
Insertion - unites partially with the internal obturator and so inserts on the trochantic fossa.

Quadrate Muscle

Function - extension of the hip and retraction of the limb
Origin - ventral aspect of ischium
Insertion - trochantic fossa

Articular muscle of the hip joint

Only in carnivores and horses
Function - causes tension of the joint capsule and thus helps prevent damage to the peri-articular structures.
Origin - Hip joint capsule

Muscles of the Stifle

Many of the muscles of the hip (see Girdle Musculature and Rump Muscles) act on the stifle by inserting on structures involved with the stifle or are distal to it. There are only really two muscles that act solely on the stifle; the quadriceps and the popliteal.

Quadriceps

This muscle forms the main muscle bulk on the cranial aspect of the thigh but is covered by the tensor muscle of the fascia lata, the sartorius and the medial femoral fascia.
The quadriceps are the main extensors of the stifle and the straight muscle also flexes the hip.
The muscle consists of four parts that have seperate points of origin but have a common single tendon, the patella tendon that inserts onto the patella and tibial tuberosity.
The four parts are:
- Lateral Vastus - On the craniolateral side of the femur originating from the lateral aspect of the proximal femur.
- Medial Vastus - on the craniomedial side of the femur originating from the medial aspect of the proxial femur.
- Intermediate Vastus - on the cranial surface of the femur it is totally covered by the other quadriceps muscles and is the weakest muscle of the quadriceps.
- Straight muscle/Rectus femoris - originates from the ilial shaft cranial to the acetabulum and runs down to the patella tendon between the two bellies of the lateral and medial vastus.

Popliteal

Function - flexor of the stifle and pronator of the leg.
Origin - a tendinous origin from the lateral condyle of the femur.
Insertion -a broad tendon on the medial and caudal surface of the proximal tibia.
Location - On the caudal aspect of the stifle and runs under the lateral collateral ligament before it inserts.

Vasculature of the Hindlimb

Innervation of the Hindlimb

The nerves that supply the hindlimb arise from the lumbosacral plexus that lies on the medial wall of the pelvis. These nerves are:

Femoral Nerve

Origin - cranial part of the lumbosacral plexus, L4 and L5. (Sometimes L3 and L6)
Motor innervation - Quadriceps and iliopsoas muscle.
Sensory innervation - the medial aspect of the limb.
Route - through the iliopsoas.

Obturator Nerve

Origin - middle part of the lumbosacral plexus, L5 and L6.
Motor innervation - adductor muscles; external obturator, adductor and gracilis.
Sensory innervation - none
Route - through the iliopsoas, medial to the ilial shaft and then through the obturator foramen.

Gluteal Nerves

Origin - L6, L7 and S1
Motor innervation - gluteal muscles, tensor fascia lata, biceps femoris and semitendinosus.
Sensory innervation - none
Route - direct to the gluteals.

Sciatic Nerve

Origin - L6, L7, S1 and S2.
Motor innervation - biceps femoris, semintendinosus, semimembranosus.
Sensory innervation - the nerve divides into the tibial and fibula nerves where cutaneous fibres run.
Route - the largest nerve in the body. It leaves the pelvis at the greater sciatic notch and curves in a ventral caudal direction around the hip joint. It runs distocaudally over the femur between the biceps femoris medially and the adductor, semimembranosus and semitendinosus muscles medially. It then divides into the tibial and fibular nerves.

Tibial Nerve

Origin - the sciatic nerve.
Motor innervation - extensors of the hock, flexors of the digits, popliteal muscle.
Sensory innervation - caudal aspect of the limb below the stifle.
Route - it runs caudal to the stifle joint into the muscle.

Fibular (Peroneal Nerve)

Origin - the sciatic nerve.
Motor innervation - flexors of the hock, extensors of the digits.
Sensory innervation - cranial and lateral aspect of the limb.
Route - caudal to the stifle.

Species Specifics