Disorders of the Knee

Question 1

How do femoral shaft fractures usually occur in children and young adults?

Answer 1

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

Question 2

How do femoral shaft fractures usually occur in the elderly?

Answer 2

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.

Question 3

How does the limb present in femoral shaft fractures?

Answer 3

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.

Question 4

Blood loss in femoral shaft fractures?

Answer 4

The blood loss in closed femoral
shaft fractures is 1000-1500 mL and the patient may develop hypovolaemic
shock (see CVS unit). The blood loss in open femoral fractures may be double
this amount.

Question 5

How are femoral shaft fractures fixed?

Answer 5

Surgical fixation
Traction splint

Question 6

What is a tibial plateau fracture?

Answer 6

A fracture affecting the articulating surface of the tibia within the knee joint

Question 7

How does a tibial plateau fracture usually occur?

Answer 7

Axial (top to bottom) loading with varus or valgus angulation (an abnormal
medial or lateral flexion load) of the knee.

Question 8

How are tibial plateau fractures classified?

Answer 8

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

Question 9

Complications of tibial plateau fractures?

Answer 9

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.
Tibial plateau fractures can also be associated with meniscal tears and anterior
cruciate ligament (ACL) injuries.

Question 10

How are patella fractures caused?

Answer 10

Direct impact injury (e.g. knee against
dashboard) or by eccentric contraction of the quadriceps (the muscle is contracting but the joint is extending).

Question 11

Examination of patella fracture?

Answer 11

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).

Question 12

Further examination of patella fracture?

Answer 12

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 (see image).

Question 13

Treatment of patella fractures?

Answer 13

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.

Question 14

How can X-rays be viewed incorrectly and suggest a patellar fracture?

Answer 14

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 15

What is patella dislocation?

Answer 15

Patella dislocation refers to the patella being completely displaced out of its normal alignment. Subluxation is partial displacement.

Question 16

Which way does the patella usually dislocate and why?

Answer 16

Due to the ‘Q angle’
between the line of pull of the quadriceps tendon and the patellar ligament, the most
common direction for the patella to dislocate is laterally.

Question 17

How is the patella stabilised?

Answer 17

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.

Question 18

What is the most common cause of patella dislocation?

Answer 18

Trauma, often a twisting injury in slight flexion or a direct
blow to the knee.

Question 19

What is age group is a patella dislocation most common in, and why?

Answer 19

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).

Question 20

What are the factors that can predispose to a patellar dislocation?

Answer 20

• Generalised ligamentous laxity
• Weakness of the quadriceps muscles, especially the VMO
• Shallow trochlear (patellofemoral) groove with a flat lateral lip
• Long patellar ligament
• Previous dislocations

Question 21

How is a patella dislocation treated?

Answer 21

The treatment involves extending the knee then manually reducing the patella.
Immobilisation is used whilst healing takes place, and this is followed by physiotherapy
to strengthen the VMO.

Question 22

How do meniscal injuries usually occur?

Answer 22

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

Question 23

What will a patient with a meniscal tear complain of?

Answer 23

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.

Question 24

What will a meniscal tear look like on examination?

Answer 24

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.

Question 25

How are meniscal tears treated?

Answer 25

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 26

How to collateral ligament injuries usually occur?

Answer 26

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.

Question 27

Which collateral ligament is more likely to be injured?

Answer 27

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

Question 28

What will a patient with a collateral ligament injury complain of?

Answer 28

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.

Question 29

What is the unhappy triad ('blown knee')?

Answer 29

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 30

How does an anterior cruciate ligament injury usually occur?

Answer 30

It 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.

Question 31

What will a patient with an ACL tear complain of?

Answer 31

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’.

Question 32

What is anterolateral rotatory instability?

Answer 32

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 asudden ‘slip’ when the knee is flexed to 20-40˚. This is characterized by a sudden sensation of the knee ‘giving way’

Question 33

How is an ACL injury treated?

Answer 33

Some patients, particularly those with low functional demands on their knee, can function well with a ruptured ACL by using their musculature to stabilise the joint. Sportsman and very active people will often need surgical reconstruction.

Question 34

How does a posterior cruciate ligament injury usually occur?

Answer 34

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.

Question 35

How are PCL tears usually treated?

Answer 35

PCL injuries respond well to conservative management with bracing and rehabilitation.

Question 36

What are the tests for cruciate ligament injuries?

Answer 36

Anterior and posterior cruciate ligament injuries can be detected using the anterior and posterior drawer tests respectively. Lachman’s test can also be used to detect ACL injuries.

Question 37

What is dislocation of the knee joint?

Answer 37

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.

Question 38

What artery is usually injured and why?

Answer 38

The popliteal artery can tether proximally where it enters the popliteal fossa, and distally where it exits. 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.

Question 39

What must be checked after reduction of the knee joint?

Answer 39

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

Question 40

What are the three types of swelling around the knee?

Answer 40

1. Bony e.g. Osgood-Schlatter’s disease (see below) 2. Soft tissue - Localised e.g. an enlarged popliteal lymph node; a popliteal artery aneurysm o Generalised e.g. lymphoedema of the lower limb * Fluid - Inside the joint = effusion - Outside the joint = soft tissue haematoma

Question 41

What is a knee effusion?

Answer 41

An effusion is an accumulation of fluid inside the knee joint; it is never normal.

Question 42

How are effusions classified?

Answer 42

Effusions can be acute (defined as < 6 hours after injury e.g. after cruciate ligament rupture) or delayed (> 6 hours after injury)

Question 43

What causes delayed swelling of the knee?

Answer 43

Delayed swelling of the knee (e.g. the day after injury) is usually due to reactive synovitis. Inflammation of the synovium, in response to injury, leads to the production of an increased volume of synovial fluid.

Question 44

How can knee effusions be divided?

Answer 44

1. Haemarthrosis (blood in the joint). Diagnostically, a haemarthrosis is an ACL rupture until proven otherwise. 2. Lipo-haemarthrosis (blood and fat in the joint). A lipo-haemarthrosis is a fracture until proven otherwise as the fat has usually released from the bone marrow.

Question 45

What is the pre-patellar bursa?

Answer 45

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.

Question 46

How does a patient with pre-patella bursitis present?

Answer 46

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.

Question 47

Popular name for pre-patellar bursitis?

Answer 47

Housemaid's knee

Question 48

Popular name for infra patellar bursitis?

Answer 48

Clergyman's knee

Question 49

What is supra patellar bursitis?

Answer 49

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

Question 50

How does suprapateller bursitis differ to others?

Answer 50

Rather than being a sign of localized irritation, "suprapatellar bursitis" is more usually a sign of significant pathology in the knee joint.

Question 51

What are the causes of a knee effusion?

Answer 51

- Osteoarthritis - Rheumatoid arthritis - Infection (septic arthritis; see below) - Gout and pseudogout - Repetitive microtrauma to the joint (as a result of running on soft or uneven surfaces).

Question 52

How does semimebranosus bursitis occur?

Answer 52

Fluid is the semimembranosus bursa is an indirect consequence of swelling within the knee joint. 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.

Question 53

Popular name for semimembranosus bursitis?

Answer 53

Popliteal cyst or Baker's cyst

Question 54

What is Osgood-Schlatter's disease (OSD)?

Answer 54

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

Question 55

Who is Osgood-Schlatter's disease (OSD) most common in?

Answer 55

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.

Question 56

What do patients with OSD complain of?

Answer 56

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

Question 57

How is OSD treated?

Answer 57

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 58

Typical symptoms of knee osteoarthritis?

Answer 58

Knee pain, stiffness and swelling

Question 59

What is common in the knee joint with osteoarthritis?

Answer 59

Deformity at the knee joint is common with osteoarthritis. For example, the patient may develop a varus deformity (deviation of the distal component toward the midline; see image below), a valgus deformity (deviation away from the midline) or a fixed flexion deformity (in which the knee cannot be fully extended)

Question 60

How can osteoarthritis of the knee be classified?

Answer 60

The arthritis can be uni-, bi-, or tri- compartmental (affecting one, two or all three of the medial femorotibial, lateral femorotibial and patellofemoral compartments).

Question 61

What is septic arthritis of the knee?

Answer 61

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.

Question 62

What pathogens are associated with septic arthritis of the knee?

Answer 62

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

Question 63

What are the risk factors for septic arthritis of the knee?

Answer 63

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

Question 64

Why are prosthetic joint at risk of developing septic arthritis?

Answer 64

Prosthetic joints (joint replacements) are particularly at risk, either due to intra- operative contamination (60-80% of cases), or to haematogenous spread from a distant infective focus (e.g. during dental surgery). 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 [see Infection unit]. Polymethacrylate cement used in the joint replacement also inhibits white blood cell and complement function, thereby increasing the risk of infection.

Question 65

Why does bacterial invasion cause septic arthritis?

Answer 65

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.

Question 66

What is the symptom triad for septic arthritis?

Answer 66

- Fever (40-60% of cases) - Pain (75%) - Reduced range of motion The symptoms may evolve over a few days to a few weeks. The fever is usually low grade with rigors present in only 20% of cases.

Question 67

What will you see upon examination of septic arthritis of the knee?

Answer 67

The joint should be examined for erythema (redness), swelling (90% have an obvious effusion), warmth, tenderness, and limitation of active and passive range of motion. Conversely, the physical findings are usually minimal in infection of a prosthetic joint, and swelling is only slight. The most distinctive finding is a draining sinus (tract between the site of infection and surface of the overlying skin), which originates from the underlying infected joint.

Question 68

How to treat septic arthritis of the knee?

Answer 68

Aspiration of the joint should be carried out immediately and the aspirate should be sent for urgent microscopy, culture and sensitivities.