Osteology Of The Distal Femur, Patella, Tibia And Fibula

Question 1

The femoral shaft

Answer 1

The shaft of the femur descends from the trochanters with a slight medial angulation; this brings the knees closer to the body’s centre of gravity, increasing the stability of the body.

On the posterior surface of the femoral shaft, there is a roughened ridge of bone called the linea aspera

Proximally, the medial border of the linea aspera becomes the pectineal line and the lateral border becomes the gluteal tuberosity, where the gluteus maximus muscle inserts.

Distally, the linea aspera widens and forms the floor of the popliteal fossa, and the medial and lateral borders form the medial and lateral supracondylar lines.

The medial supracondylar line ends at the adductor tubercle, where the adductor magnus muscle inserts. The lateral supracondylar line ends at the lateral femoral condyle.

Question 2

Distal femur

Answer 2

The distal femur is characterised by the presence of the medial and lateral condyles, which articulate with the tibia and patella to form the knee joint

The medial femoral condyle is larger than the lateral femoral condyle; it bears more weight in the standing position because the centre of mass of the body passes medial to the knee joint.

The trochlear (patellofemoral) groove lies on the anterior surface of the distal femur - this articulates with the patella.

The inferior and posterior surfaces of the femoral condyles articulate with the menisci of the knee and the tibia. The more prominent lateral femoral condyle helps prevent lateral displacement of the patella during patellar tracking

People with a flatter lateral femoral condole are more likely to experience patellar instability

The medial and lateral epicondyles are bony elevations above the non-articular areas of the condyles

The medial epicondyle is the larger of the two. The medial and lateral collateral ligaments of the knee originate from their respective epicondyles.

The intercondylar fossa is a depression found on the posterior surface of the femur, between the two condyles

The anterior cruciate ligament (ACL) attaches to the medial aspect of the lateral femoral condyle and the posterior cruciate ligament (PCL) to the lateral aspect of the medial femoral condyle

Question 3

Patella

Answer 3

The patella is located at the anterior aspect of the knee joint, within the trochlear (patellofemoral) groove of the femur.

Its superior aspect is attached to the quadriceps tendon, and its inferior aspect to the patellar ligament

The patella is classified as a sesamoid type bone due to its position within the quadriceps tendon and is the largest sesamoid bone in the body.

It has a triangular shape, with anterior and posterior surfaces

The apex of the patella is situated inferiorly and is connected to the tibial tuberosity by the patella ligament.

The base forms the superior aspect of the bone and provides the insertion area for the quadriceps tendon.

The posterior surface of the patella articulates with the femur, and is marked by two facets:

Question 4

Tibia

Answer 4

The tibia is the main bone of the leg, forming what is more commonly known non- medically as the ‘shinbone’

It has expansions at its proximal and distal ends where it articulates at the knee and ankle joints respectively. The tibia is the second largest bone in the body and is a key weight-bearing structure.

The proximal tibia is widened by the medial and lateral condyles, which aid in weight-bearing

The condyles form a flat surface, known as the tibial plateau, The tibial plateau articulates with the femoral condyles to form the major articulation of the knee joint.

The head of the fibula articulates with the proximal tibia at the proximal tibiofibular joint. It does not form part of the knee joint.

Question 5

The intercondylar area

Answer 5

The intercondylar area is located between the tibial condyles; in the centre of the intercondylar area is the intercondylar eminence

On either side of the intercondylar eminence are the medial and lateral intercondylar tubercles.

The intercondylar eminence is the main site of attachment for the anterior cruciate ligament and the menisci of the knee joint

The intercondylar tubercles of the tibia articulate with the intercondylar fossa of the femur. The posterior cruciate ligament attaches to the posterior edge of the intercondylar area.

Question 6

Shaft of the tibia

Answer 6

The shaft of the tibia is prism-shaped, with three borders: anterior, posterior and lateral

Question 7

Fibula

Answer 7

The fibula is located in the lateral aspect of the leg. Its main function is to act as an attachment for muscles, rather than bearing weight.

It has three main articulations:
-Proximal tibiofibular joint – articulates with the lateral condyle of the tibia.

Question 8

Functional anatomy of the knee

Answer 8

The knee joint is a hinge-type synovial joint, which mainly allows for flexion and extension with a small degree of medial and lateral rotation. It is formed by articulations between the patella, femur and tibia.

Question 9

Articulating surfaces

Answer 9

The knee joint consists of two articulations:

Question 10

Neurovasculature

And

Stability

Answer 10

The blood supply to the knee joint is through the genicular anastomoses around the knee, which are supplied by the genicular branches of the femoral and popliteal arteries

Their clinical relevance is that if the popliteal artery is gradually occluded by atheroma, the genicular anastomoses can dilate to maintain the blood supply to the leg.

The nerve supply, according to Hilton’s law, is by the nerves which supply the muscles which cross the joint. These are the femoral, tibial and common peroneal (common fibular) nerves.

The knee joint is inherently unstable. To improve stability, the tibial articular surface is deepened by the menisci and the joint is supported by the joint capsule, ligaments and the surrounding musculature.

Question 11

Menisci

Answer 11

The medial and lateral menisci are fibrocartilaginous structures in the knee that serve two functions:

Question 12

Ligaments

And cruciate ligaments

Answer 12

The major ligaments in the knee joint can be divided into:

Question 13

Ligaments that strengthen the capsule

Answer 13

The joint capsule surrounds the sides and posterior aspect of the knee joint but is deficient anteriorly.

This deficiency allows the synovial membrane to extend up beneath the patella, forming the suprapatellar bursa.

The capsule is strengthened laterally and medially by the inferior fibres of the vastus lateralis and medialis muscles respectively.

It is strengthened posteriorly by the oblique popliteal ligament - this is a continuation of some of the fibres from semimembranosus tendon in a superolateral direction from its main insertion on the medial tibial condyle, posteriorly across the back of the knee, to the lateral femoral condyle.

Question 14

Extracapsular ligaments

Answer 14

The patellar ligament is a continuation of the quadriceps femoris tendon distal to the patella.
It inserts onto the tibial tuberosity

The medial and lateral collateral ligaments are strap-like ligaments.

They act to stabilise the hinge motion of the knee, preventing excessive medial or lateral angulation of the tibia on the femur.

Medial (tibial) collateral ligament (MCL).
This is a wide flat ligament, found on the medial side of the joint. Proximally, it attaches to the medial epicondyle of the femur, distally it attaches to the medial condyle of the tibia. It is also adherent to the medial meniscus.

The MCL resists valgus (lateral) angulation of the tibia on the femur (Note: remember vaLgus = Lateral).

Lateral (fibular) collateral ligament (LCL).
This is thinner and rounder than the medial collateral ligament. It attaches proximally to the lateral epicondyle of the femur; distally it attaches to a depression on the lateral surface of the fibular head.

The lateral collateral ligament is reinforced by the iliotibial tract. It resists varus (medial) angulation of the tibia on the femur.

Although the medial collateral ligament is broad, it is weaker than the lateral (fibular) collateral ligament. (However it works together with accurate ligament and popliteal tendon so is overall stronger)

Excessive lateral displacement of the tibia may cause the medial collateral ligament to tear, and this in turn often results in tearing of the medial meniscus.

Question 15

Bursae

Answer 15

A bursa is a small sac lined by synovial membrane, containing a thin layer of synovial fluid.

It provides a cushion between the bones and tendons/muscles surrounding a joint.

This helps to reduce friction between the bones and soft tissues and allows free movement.

Bursae are filled with synovial fluid and are found in association with most of the major joints of the body. They can either be communicating or non-communicating with the joint cavity.

Suprapatellar bursa – This is an extension of the synovial cavity of the knee, located between the quadriceps femoris muscle and the femur.

Question 16

Movements

Answer 16

The knee joint permits four movements

Question 17

The anterior compartment of the thigh

Answer 17

The musculature of the thigh can be split into three compartments; anterior, medial and posterior.

Each compartment has a distinct innervation and function.

The muscles in the anterior compartment of the thigh are mostly innervated by the femoral nerve (L2-L4), and as a general rule, act to extend the leg at the knee joint.

The arterial supply of this compartment is via the branches of the femoral artery: the lateral and medial femoral circumflex arteries and the profunda femoris branch.

The muscles in the anterior thigh are the pectineus, sartorius and quadriceps femoris. The iliopsoas muscle insertion is also in the anterior compartment of the thigh

Question 18

Illiopsoas

Answer 18

The iliopsoas is composed of two muscles, the psoas major and the iliacus.

They have separate origins and muscle bellies and a separate innervation, but share a common insertion and common function, hence why they are commonly referred to as iliopsoas.

The psoas major originates from the transverse processes of the T12-L5 vertebrae and the lateral margins of the intervertebral discs between them.

The iliacus originates from the iliac fossa of the pelvis. They insert together onto the lesser trochanter of the femur

Actions: The iliopsoas flexes the lower limb at the hip joint and assists in lateral rotation of the femur at the hip joint.

Innervation: The psoas major is innervated by anterior rami of L1-3; the iliacus is innervated by the femoral nerve.

Question 19

Quadriceps femoris

Answer 19

The quadriceps femoris consists of four individual muscles which have a common tendon of insertion; these are the rectus femoris, vastus medialis, vastus lateralis and vastus intermedius.

They form the main bulk of the thigh, and collectively are one of the most powerful muscles in the body.

The muscles that form quadriceps femoris unite proximal to the knee joint and insert onto the base of the patella via the quadriceps tendon.

The patella is attached to the tibia by the patella ligament. The quadriceps femoris is the main extensor of the knee.

Question 20

Vastus Lateralis

Answer 20

Vastus lateralis originates from the greater trochanter and the lateral lip of the linea aspera and inserts via the quadriceps tendon into the base of the patella

Actions: Vastus lateralis extends the knee joint and stabilises the patella.

Innervation: Femoral nerve.

Question 21

Vastus intermedius

Answer 21

Vastus intermedius originates from the anterior and lateral surfaces of the femoral shaft and inserts into the base of the patella via the quadriceps tendon

Actions: Vastus intermedius extends the knee joint and stabilises the patella.

Innervation: Femoral nerve.

Question 22

Vastus Medialis

Answer 22

Vastus medialis originates from the intertrochanteric line of the femur and the medial lip of the linea aspera.

It inserts into the base and medial aspect of the patella via the quadriceps tendon.

The inferior fibres are orientated horizontally and are known as the vastus medialis obliquus (VMO; or obliquus genus).

Actions: Vastus medialis extends the knee joint and stabilises the patellar. Contraction of the VMO resists lateral displacement of the patella.

Innervation: Femoral nerve.

Question 23

Rectus Femoris

Answer 23

Rectus (Latin = straight) femoris originates as two tendons: the anterior (or straight) tendon arises from the anterior inferior iliac spine of the pelvis; the posterior (or reflected) tendon arises from a groove above the rim of the acetabulum.

The two promptly unite and the common muscle belly runs straight down the leg, inserting onto the base of the patella via the quadriceps tendon

Actions: Rectus femoris is the only muscle of the quadriceps to cross both the hip and knee joints. It flexes the thigh at the hip joint and extends the leg at the knee joint.

Innervation: Femoral nerve.

Question 24

Sartorius

Answer 24

The sartorius is the longest muscle in the body. It is long and thin, running across the thigh in an inferomedial direction.

The sartorius is positioned more superficially than the other muscles in the thigh.

Sartorius originates from the anterior superior iliac spine and attaches to the medial aspect of the proximal tibia as part of the pes anserinus (along with gracilis and semitendinosus).

Actions: Sartorius flexes, abducts and externally (laterally) rotates the thigh at the hip joint. It also flexes and internally (medially) rotates the tibia at the knee joint. easily recalled as a sailor dancing the hornpipe.

Innervation: Femoral nerve.

Question 25

Pectineus

Answer 25

The pectineus muscle is a flat muscle that forms the base of the femoral triangle.

It sometimes has a dual innervation, and therefore can be considered a transitional muscle between the anterior thigh and medial thigh compartments.

Attachments: Pectineus originates from the pectineal line on the anterior surface of the superior pubic ramus and inserts on the pectineal line on the posterior surface of the femur, just inferior to the lesser trochanter.

Actions: Pectineus adducts and flexes the thigh at the hip joint.

Innervation: Femoral nerve. Pectineus may also receive a branch from the obturator nerve.

Question 26

The medial compartment of the thigh

Answer 26

The muscles in the medial compartment of the thigh are collectively known as the hip adductors. There are five muscles in this group: gracilis, obturator externus, adductor brevis, adductor longus and adductor magnus

All of the medial thigh muscles are innervated by the obturator nerve, which arises from the lumbar plexus (anterior divisions of L2, 3 and 4). The arterial supply of the medial thigh is via the obturator artery.

Question 27

Adductor Magnus

Answer 27

The adductor magnus is the largest muscle in the medial compartment of the thigh. It lies posteriorly to the other muscles.

Functionally, the muscle can be divided into two parts; the adductor component, and the hamstring component

The adductor component originates from the inferior ramus of the pubis and the ischium and inserts onto the linea aspera of the femur.

The hamstring component originates from the ischial tuberosity and inserts onto the adductor tubercle and medial supracondylar line of the femur

The insertions of the two components are separated by the adductor hiatus

Actions: The adductor and hamstring components both adduct the thigh. The adductor component also flexes the thigh, with the hamstring component extending the thigh.

Innervation: The adductor component is innervated by the obturator nerve (L2-L4), the hamstring component is innervated by the tibial component of the sciatic nerve (L4-S3).

Question 28

Adductor longus

Answer 28

The adductor longus is a large, flat muscle. It partially overlies the adductor brevis and adductor magnus.

Adductor longus forms the medial border of the femoral triangle. It originates from the body of the pubis, and expands into a fan shape, attaching broadly to the middle third of the linea aspera of the femur

Actions: Adductor longus adducts the thigh.

Innervation: Obturator nerve (L2-L4).

Question 29

Adductor Brevis

Answer 29

The adductor brevis is a short muscle, lying proximal and deep to the adductor longus.

Adductor brevis is situated between the anterior and posterior divisions of the obturator nerve so can be used as an anatomical landmark to identify these branches

Adductor brevis originates from the body of pubis and the inferior pubic ramus. It attaches to the linea aspera on the posterior surface of the femur, proximal to the adductor longus.

Actions: Adductor brevis adducts the thigh.

Innervation: Obturator nerve (L2-L4)

Question 30

Gracillis

Answer 30

The gracilis is the most superficial and medial of the muscles in the medial compartment of the thigh. It crosses both the hip and the knee joints.

Gracilis originates from the inferior pubic ramus and the body of the pubis.

Descending almost vertically down the medial thigh, it inserts onto the medial surface of the proximal tibia, between the tendons of the sartorius (anteriorly) and the semitendinosus (posteriorly) as part of the pes anserinus

Actions: Gracilis adducts the thigh at the hip and flexes the leg at the knee.

Innervation: Obturator nerve (L2-L4).

Question 31

Obturator externus

Answer 31

Obturator externus is sometimes classed as a member of the ‘deep muscles of the gluteal region’ and sometimes as part of the ‘medial compartment of the thigh’.

Obturator externus originates from external surface of the obturator membrane and from the adjacent bone. It passes posterior to the neck of the femur, inserting onto the posterior aspect of the greater trochanter.

Actions: Adduction and lateral (external) rotation of the thigh.

Innervation: Obturator nerve (L2-L4).

Question 32

The femoral triangle

Answer 32

The femoral triangle is an anatomical region of the proximal anterior thigh.

Many large neurovascular structures pass through this area.

The femoral triangle has three borders:

Question 33

The femoral canal

Answer 33

The femoral canal is an anatomical compartment, located within the femoral triangle.

It is the smallest and most medial part of the femoral sheath and is approximately 1.3cm long.

The femoral canal has four borders and an opening:

Question 34

The adductor canal

Answer 34

The adductor canal (subsartorial canal) is a narrow conical tunnel located in the thigh.

It is 15cm long, extending from the apex of the femoral triangle to the adductor hiatus of the adductor magnus. The canal serves as a passageway for structures passing between the anterior thigh and posterior leg.

The adductor canal is bordered by the following muscular structures:

Question 35

Femoral nerve

Answer 35

The femoral nerve is one of the major peripheral nerves of the lower limb.

It is formed in the lumbar plexus from the posterior divisions of the L2, L3 and L4 roots.

The femoral nerve descends from the lumbar plexus in the abdomen, passing through the fibres of the psoas major muscle.

It exits the psoas major at the inferior part of its lateral border, passing behind the fascia iliaca (fascia overlying the iliacus muscle) to approximately the mid-point of the inguinal ligament (halfway between the anterior superior iliac spine and the pubic tubercle.

It then passes behind the inguinal ligament to enter the thigh, and splits into an anterior and posterior division approximately 4cm below the inguinal ligament.

The femoral nerve passes through the femoral triangle lateral to the femoral vessels (enclosed within the femoral sheath) and gives off articular branches to the hip and knee joints.

The terminal cutaneous branch of the femoral nerve is the saphenous nerve which continues, with the femoral artery and vein, through the adductor canal

The femoral nerve innervates the anterior thigh muscles that flex the hip joint (pectineus, iliacus, sartorius) and extend the knee (quadriceps femoris: rectus femoris, vastus lateralis, vastus medialis and vastus intermedius).

The first cutaneous branches to arise from the femoral nerve are the anterior cutaneous branches; these arise in the femoral triangle and supply the skin on the anteromedial thigh.

The terminal cutaneous branch of the femoral nerve is the saphenous nerve which supplies the skin on the medial side of the leg and the foot sometimes as far as the base of the great toe

Question 36

Obturator nerve

Answer 36

The obturator nerve is formed by the anterior divisions of the second, third and fourth lumbar nerves in the lumbar plexus.

It descends through the fibres of the psoas major muscle and emerges from its medial border, running posteriorly to the common iliac arteries and laterally along the pelvic wall to the obturator foramen.

It then enters the thigh through the obturator canal and splits into anterior and posterior divisions.

The anterior division of the obturator nerve descends anterior to adductor brevis, and posterior to adductor longus and pectineus. It gives off branches to the adductor longus, adductor brevis and gracilis muscles.

In rare cases it also gives off a branch to the pectineus muscle. It then pierces the fascia lata to become the cutaneous branch of the obturator nerve and supply the skin over the middle part of the medial thigh.

The posterior division descends through the obturator externus muscle, which it supplies, before passing posterior to adductor brevis but anterior to adductor magnus. It supplies both adductor brevis (which is supplied by the anterior and posterior divisions) and the adductor component of adductor magnus (Note: the hamstring component is supplied by the tibial nerve).

Question 37

Arteries of the thigh and gluteal region

Answer 37

The main artery of the lower limb is the femoral artery.

The common femoral artery is a continuation of the external iliac artery (which itself is a terminal branch of the common iliac artery).

The external iliac artery becomes known as the common femoral artery when it crosses under the inguinal ligament and enters the femoral triangle.

In the femoral triangle, the profunda femoris (or deep femoral) artery branches from the posterolateral aspect of the common femoral artery.

It travels posteriorly and distally, giving off three types of branch:

Question 38

Other Arteries of the Thigh

Answer 38

In addition to the femoral artery, there are other arteries that supply the lower limb.

The medial compartment of the thigh is supplied by the obturator artery, which arises from the internal iliac artery in the pelvic region.

It enters the medial compartment of the thigh via the obturator canal. The gluteal region is largely supplied by the superior and inferior gluteal arteries.

These arteries also arise from the internal iliac artery, entering the gluteal region via the greater sciatic foramen.

The superior gluteal artery leaves the greater sciatic foramen above the piriformis muscle and the inferior gluteal artery leaves below the muscle.

In addition to the gluteal muscles, the inferior gluteal artery also contributes towards the blood supply of the posterior thigh

Question 39

Deep Veins of the thigh and gluteal region

Answer 39

Once the popliteal vein has entered the thigh via the adductor hiatus, it becomes known as the femoral vein.

The femoral vein ascends in the adductor (subsartorial canal), accompanying the femoral artery.

The profunda femoris vein (deep vein of the thigh) follows the course of the profunda femoris artery.

Via perforating veins, it drains blood from the thigh muscles. It drains into the distal section of the femoral vein.

The (common) femoral vein leaves the thigh by passing deep to the inguinal ligament, medial to the femoral artery, at which point it becomes known as the external iliac vein.

The gluteal region is drained by inferior and superior gluteal veins, which follow the course of the superior and inferior gluteal arteries. These empty into the internal iliac vein.

Similarly, the obturator vein follows the course of the obturator artery and drains the medial compartment of the thigh. It enters the pelvis through the obturator foramen, along with the obturator artery and nerve, and terminates by draining into the internal iliac vein.

Question 40

Superficial veins of the lower limb

Answer 40

The superficial veins of the lower limb run in the subcutaneous tissue.

There are two major superficial veins – the great (long) saphenous vein, and the small (short) saphenous vein.

The great (long) saphenous vein is formed by the dorsal venous arch of the foot, and the dorsal vein of the great toe.

It passes anteriorly to the medial malleolus at the ankle and ascends the medial side of the leg, medial to and then posterior to the medial aspect of the tibia.

It passes a hands breadth posterior to the medial border of the patella at the knee and then ascends in the medial aspect of the thigh to pierce the saphenous opening of the fascia lata, 1-3 cm distal to the inguinal ligament.

The great saphenous vein drains into the femoral vein at the saphenofemoral junction in the femoral triangle.

The small (short) saphenous vein is formed by the dorsal venous arch of the foot, and the dorsal vein of the little toe.

It passes posterior to the lateral malleolus, along the lateral border of the Achilles (calcaneal) tendon.

It then ascends the posterior leg and passes between the two heads of the gastrocnemius muscle to drain into the popliteal vein at the saphenopopliteal junction in the popliteal fossa.

Question 41

Lymphatics

Answer 41

The lymphatic system drains tissue fluid, plasma proteins and other cellular debris into the bloodstream and is also involved in immune defence.

Once this collection of substances enters the lymphatic vessels it becomes known as lymph; lymph is subsequently filtered by lymph nodes and directed into the venous system.

The lymphatic vessels of the lower limb can be divided into superficial and deep vessels.

Their distribution is similar to that of the veins of the lower limb.
The superficial lymphatic vessels can be divided into:

Question 42

Femoral shaft fractures

Answer 42

Femoral shaft injuries in previously-healthy children and young adults are usually the result of high-velocity trauma e.g. falls from a height, or road traffic collisions.

In young children, non-accidental injury (child abuse) should also be considered.

In the elderly with osteoporotic bones, or in patients with bone metastases or other bone lesions (e.g. bone cysts), femoral shaft fractures can occur following a low- velocity injury, such as falling over from the standing position.

The musculature acts as a deforming force after a femoral shaft fracture. The proximal fragment is often abducted due to the pull of gluteus medius and minimus on the greater trochanter and flexed due to the action of iliopsoas on the lesser trochanter.

The distal segment is adducted into a varus deformity due to the action of the adductor muscles (adductor magnus, gracilis) and extended due to the pull of gastrocnemius on the posterior femur.

The patient will have a tense swollen thigh. The blood loss in closed femoral shaft fractures is 1000-1500ml and the patient may develop hypovolaemic shock

The blood loss in open femoral fractures could be double this

Femoral shaft fractures are treated with surgical fixation

Question 43

Distal femoral fractures

Answer 43

In younger patients, the usual mechanism is a high-energy sporting injury and there is often significant displacement of the fracture fragments.
In the elderly, this type of fracture is usually seen in association with osteoporotic bone; the usual mechanism in the elderly is a fall from standing.

The popliteal artery may become involved if there is significant displacement of the fracture and careful assessment of the neurovascular status of the limb before, and after, reduction of the fracture is essential.

Question 44

Tibial plateau fractures

Answer 44

Tibial plateau fractures also tend to be high-energy injuries. The usual mechanism is axial (‘top to bottom’) loading with varus or valgus angulation (an abnormal medial or lateral flexion load) of the knee.

These are fractures affecting the articulating surface of the tibia within the knee joint.

They can be unicondylar (affecting one condyle) or bicondylar (affecting both tibial condyles). Fractures affecting the lateral tibial condyle are the most common.

The articular cartilage is always damaged, and despite careful approximation of the fracture fragments, most patients will develop a degree of post-traumatic osteoarthritis in the affected joint.

Question 45

Patellar fractures

Answer 45

Patellar fractures account for 1% of all skeletal injuries. They are either caused by a direct impact injury (e.g. knee against dashboard) or by eccentric contraction of the quadriceps (avulsion fracture).

Most occur in patients aged 20-50 years. The patella is the largest sesamoid bone in the body and its most important blood supply is via the inferior pole.

On examination, there is often a palpable defect in the patella and a haemarthrosis (blood in the joint).

If the extensor mechanism is disrupted (i.e. the fracture completely splits the patella distal to the insertion of the quadriceps tendon), the patient will be unable to perform a straight leg raise i.e. to lift the leg off the bed by flexing at the hip and keeping the knee extended.

Displaced patellar fractures require reduction and surgical fixation

Undisplaced patellar fractures can be protected whilst healing takes place through splinting and using crutches, and do not usually require surgical fixation.

Note: In 8% of the population the patella is bipartite (in two parts) and this can be mistaken for a patella fracture on an X-ray. A bipartite patella develops because there is failure of union of a secondary ossification centre with the main body of the patella. It is a normal anatomical variant.

Question 46

Patella dislocation

Answer 46

Patella dislocation refers to the patella being completely displaced out of its normal alignment.

The patella is usually held in the correct position by contraction of the inferior, almost horizontal, fibres of vastus medialis, the vastus medialis obliquus (VMO).

The specific role of the VMO is to stabilise the patella within the trochlear groove and to control tracking of the patella when the knee is flexed and extended.

The most common cause is trauma, often a twisting injury in slight flexion or a direct blow to the knee. The age group most commonly affected are athletic teenagers and the usual mechanism is internal rotation of the femur on a planted foot whilst flexing the knee (e.g. in a sudden change of direction during sports).

There are a variety of factors that can predispose to patellar dislocation, including:

Question 47

Meniscal injuries

Answer 47

Meniscal injuries (meniscal tears) are probably the most common type of knee injury.

They typically occur during a sudden twisting motion of a weight-bearing knee in a high degree of flexion.

The patient usually describes intermittent pain, localised to the joint line, alongside reports of the knee clicking, catching, locking (inability to fully extend the knee due to an intra-articular foreign body) or a sensation of giving way.

Swelling occurs as a delayed symptom due a reactive effusion or not at all, as the menisci are largely avascular (except at their periphery).

Acute haemarthrosis is therefore rare and if present, indicates a tear in the peripheral vascular aspect of the meniscus or an associated injury to the anterior cruciate ligament.

A chronic effusion (increased synovial fluid) can occur due to synovitis (inflammation of the synovial membrane).

On examination, the patient usually has joint line tenderness and restricted motion due to pain or swelling.

A mechanical block to motion or locking can occur with a displaced tear due to loose meniscal fragments becoming trapped between the articular surfaces.

Acute traumatic meniscal tears are usually treated surgically by either meniscectomy or meniscal repair.

However, there is increasing evidence that meniscal tears that result from a chronic degenerative process within the knee have a similar prognosis with conservative management as with surgery.

Hence, conservative management is increasingly being recommended for these.

Question 48

Collateral ligament injury

Answer 48

Injuries to the collateral ligaments of the knee are a common sporting injury, particularly in direct
contact sports such as football. They usually result from acute varus or valgus angulation of the knee

The medial and lateral collateral ligaments normally control the lateral movement of the knee joint and brace it against unusual varus or valgus deformation.

Together, the collateral ligaments also work with the posterior cruciate ligament (PCL) to prevent excessive posterior motion of the tibia on the femur.
Varus = medial angulation of the distal segment
Valgus = lateral angulation of the distal segment (Remember vaLgus = Lateral)

In acute valgus strain, the medial collateral ligament (MCL) is at risk and in varus strain the lateral collateral ligament (LCL) is at risk.

The MCL is injured more commonly than the LCL, but a torn LCL has a higher change of causing knee instability.

This is because the medial tibial plateau forms a deeper and more stable socket for the femoral condyle than the lateral tibial plateau.

Hence, an intact LCL plays a more critical role in maintaining the stability of the knee Immediately after the injury, the patient will experience pain and swelling of the knee

As the initial pain and stiffness subside, the knee joint may feel unstable and the patient may complain of it giving way or not supporting their body weight.

The unhappy triad (or ‘blown knee’) is an injury to the anterior cruciate ligament, medial collateral ligament and medial meniscus.

This results from a strong force applied to the lateral aspect of the knee. The medial meniscus is firmly adherent to the medial collateral ligament, which is why it is also injured.

Question 49

Anterior cruciate ligament injury

Answer 49

Anterior and posterior cruciate ligament injury Cruciate ligament injuries are very common. The anterior cruciate ligament (ACL) is weaker than the posterior cruciate ligament (PCL) and is more commonly injured.

The anterior cruciate ligament (ACL) is usually torn as a result of a quick deceleration, hyperextension or rotational injury e.g. following a sudden change of direction during sport.

It is usually a non-contact injury i.e. no other players are involved.

The ACL can also be torn by the application of a large force to the back of the knee with the joint partly flexed. The patient typically reports feeling a popping sensation in their knee with immediate swelling.

When the swelling has subsided, the patient experiences instability of the knee as the tibia slides anteriorly under the femur.

Patients tend to describe this as the knee ‘giving way’.

When the ACL is ruptured, the tibia can slide anteriorly under the femur.

As the intact ACL passes inferiorly from posterolateral to anteromedial within the knee, it also plays a role in controlling the rotational stability of the knee by preventing medial (internal) rotation of the tibia when the knee is extended.

If the ACL is torn, rotation of the tibia occurs with the PCL as the centrally-located axis; the medial tibial condyle rotates internally and the lateral tibial condyle subluxes anteriorly.

Spontaneous reduction of the lateral tibial condyle then occurs with a sudden ‘slip’ when the knee is flexed to

Question 50

Posterior cruciate ligament injury

Answer 50

The most common mechanism of posterior cruciate ligament (PCL) injury is a ‘dashboard injury’; the knee is flexed and a large force is applied to the upper tibia, displacing it posteriorly.

This is seen in road traffic collisions when the proximal leg collides with the dashboard.

The PCL can also be torn during football when the player falls on a flexed knee with their ankle plantarflexed.

The tibia hits the ground first and is displaced posteriorly, avulsing the PCL.

A tackle with the knee flexed can also cause this injury. Finally, a severe hyperextension injury can also avulse the PCL from its insertion on the posterior aspect of the intercondylar area.

After a PCL tear, the tibia can be displaced posteriorly on the femur. PCL injuries respond well to conservative management with bracing and rehabilitation.

Anterior and posterior cruciate ligament injuries can be detected using the anterior and posterior drawer tests respectively

Lachman

Question 51

Dislocation of the knee joint

Answer 51

Dislocation of the knee joint is an uncommon injury and always results from high energy trauma.

To dislocate the knee joint, at least three of the four ligaments (MCL, LCL, ACL and PCL) must be ruptured.

An associated arterial injury is very common because the popliteal artery is tethered proximally when it enters the popliteal fossa at the adductor hiatus and distally where it exits the popliteal fossa by passing under the tendinous arch of the soleus muscle.

As the popliteal artery is so immobile, if the knee joint dislocates, there is a high risk of it being injured.

It may tear resulting in an obvious haematoma or it may be crushed or suffer a traction injury (with endothelial damage leading to subsequent thrombotic occlusion.

After reduction of the knee joint, it is therefore essential to fully assess the vascularity of the leg e.g. with Magnetic Resonance Angiography (MRA).

Question 52

Swelling around the knee

Answer 52

Swellings around the knee can be:

Question 53

Bursitis of the knee

Answer 53

Bursitis is inflammation of a bursa.

The bursae of the knee that are most commonly inflamed are the prepatellar bursa, infrapatellar bursa, pes anserinus bursa (deep to the common insertion of the sartorius, gracilis and semitendinosus tendons), and the suprapatellar bursa.

Question 54

Pre-patellar bursitis

Answer 54

The pre-patellar bursa is a superficial bursa with a thin synovial lining, located between the skin and the patella.

It is does not communicate with the joint space and usually contains a minimal amount of fluid.

Inflammation of this bursa, however, results in a marked increase of fluid within the space.

The patient usually presents with knee pain and swelling. There may be some erythema overlying the inflamed bursa.

The patient finds it difficult to walk due to the pain and will not be able to kneel on the affected side.

There is usually a history of repetitive trauma to the bursa such as may occur during scrubbing the floor, hence the term ‘Ho

Question 55

Infrapatellar bursitis

Answer 55

The infrapatellar bursa essentially consists of two bursae, one of which sits superficially between the patella tendon (below the kneecap) and the skin

The second referred to as the deep infrapatellar bursa is sandwiched between the patella tendon and tibia bone (shin).

Bursitis most commonly affects the superficial infrapatellar bursa.

Infrapatellar bursitis usually occurs due to repeated microtrauma caused by activities involving kneeling.

The popular name clerg

Question 56

Suprapatella bursitis

Answer 56

The suprapatellar bursa is an extension of the synovial cavity of the knee joint.

A knee effusion therefore often presents with swelling in the suprapatellar pouch (the suprapatellar bursa extends superiorly from beneath the patella under the quadriceps muscle).

Hence, rather than being a sign of localized irritation, “suprapatellar bursitis” is more usually a sign of significant pathology in the knee joint.

Causes of a knee effusion include

Question 57

Semimembranosus bursitis

Answer 57

Like suprapatellar bursitis, fluid is the semimembranosus bursa is an indirect consequence of swelling within the knee joint.

The semimembranosus bursa is located beneath the deep fascia of the popliteal fossa in the interval between the semimembranosus muscle and the medial head of the gastrocnemius muscle.

It is attached to the posterior capsule of the knee joint and may communicate with it by a small opening.

If the knee joint is inflamed and there is an effusion, the fluid can force its way through this narrow communication into the semimembranosus bursa.

The resulting swelling in the popliteal fossa is known as semimembranosus bursitis or more commonly as a popliteal cyst or Baker

Question 58

Osgood - schlatter’s disease (OSD)

Answer 58

OSD is inflammation of the apophysis (site of insertion) of the patellar ligament into the tibial tuberosity.

OSD most commonly occurs in teenagers who play sport (running and jumping) and causes localised pain and swelling. It is bilateral in 20-30% of cases.

Patients complain of intense knee pain during running, jumping, squatting, ascending and descending stairs and during kneeling.

OSD usually resolves with rest and ice.

The pain and swelling resolve at the age of skeletal maturity when the apophysis (which has a separate ossification centre) fuses. However, the bony prominence usually remains permanently.

Question 59

OA of the knee

Answer 59

The typical symptoms of knee osteoarthritis are knee pain, stiffness and swelling. The pain may follow a pattern, for example:

Question 60

Septic arthritis of the knee

Answer 60

Septic arthritis is the invasion of the joint space by micro-organisms, usually bacteria (but occasionally viruses, mycobacteria and fungi).

It differs from reactive arthritis, which is a sterile inflammatory process that can result from an extra-articular infection e.g. gastroenteritis.

The knee is the most common joint affected by septic arthritis (50% of cases), followed by the hip (20%), shoulder, ankle and wrists.

The most common pathogen is Staphylococcus aureus. Other pathogens include Staph. epidermidis, Neisseria gonorrhoeae (in sexually active individuals), Strep. pneumoniae.

Risk factors include the extremes of age, diabetes mellitus, rheumatoid arthritis, immunosuppression and intravenous drug abuse.

Prosthetic joints (joint replacements) are particularly at risk, either due to intra- operative contamination (60-80% of cases)

The patient may become symptomatic months or even years after the initial operation.

Delayed wound healing is a major risk factor for prosthetic joint infection.

The biofilm produced by Staph. epidermidis protects this pathogen from the host’s defences and from antibiotics

Polymethacrylate cement used in the joint replacement also inhibits white blood cell and complement function, thereby increasing the risk of infection
.
The major consequence of bacterial invasion is damage to articular cartilage, either due to the organism’s pathologic properties (e.g. proteases secreted by Staph. aureus) or to the host’s immune response.
Neutrophils stimulate synthesis of cytokines and other inflammatory products, resulting in the hydrolysis of collagen and proteoglycans.

Patients with septic arthritis typically present with the symptom triad of: