Session 4: Disorders of the Knee Flashcards
What is this?
A femoral shaft fracture of the left femur.
Mechanism of fracture from femoral shaft fracture in previously healthy children and adults.
High-velocity trauma like falls from a heigh and road traffic collosions.
In young children think of child-abuse as well.
Mechanism of fracture of femoral shaft fracture in elderly patients.
Since they be osteoporotic, have bone lesions, bone metastases their femur can be more prone to fracture.
This means that a low-velocity injury can cause a fracture like falling over from a standing position.
How do patients clinically present with a femoral shaft fracture?
Proximal fragment often abducted + flexed.
Distal fragment usually adducted into a varus deformity + extended.
The patient will have a tense swollen thigh and pain.
What is particularly important to consider in a patient with a femoral shaft fracture?
There will be a large amount of blood loss which can be up to 1000-1500 ml meaning the patient can develop hypovolaemic shock.
Treatment of femoral shaft fracture.
Treated with surgical fixation.
Why is the proximal part of the femur abducted and flexed in femoral shaft fracture?
The pull of gluteus medius and minimus on the greater trochanter will abduct the proximal femur. The iliopsoas will flex it.
Why is the distal part of the femur adducted and extended in a femoral shaft fracture?
Adductor magnus and gracilis adduct the distal femur.
Gastrocnemius will extend the distal femur.
What is this?
A distal femoral fracture
Mechanism of injury in distal femoral fracture of young patients.
In elderly.
High-energy sporting injury.
In elderly commonly associated with osteoporosis and fall from standing.
Important structure to consider in distal femoral fracture.
The popliteal artery and careful assessment of the neurovascular status of the limb before and after.
What is this?
Tibial plateau fracture.
What are tibial plateau fractures?
Which kinds are there?
Which is the most common?
Fracture affecting the articulating surface of the tibia within the knee joint. They can be unicondylar meaning they affect on condyle but also bycondylar meaning they will affect both tibial condyles.
Lateral tibial condyle fracture is most common.
Tibial plateau fractures can also be associated with menisci tear and ACL injuries.
Mechanism of injury in tibial plateau fracture.
High-energy injuries where the usual mechanism is axial loading with varus or valgus angulation meaning there is an abnormal medial or lateral flexion load of the knee.
Common complication of tibial plateau fracture.
Post-traumatic osteoarthritis since the articular cartilage is always damaged.
What is this?
Patellar fracture
Mechanism of injury of patellar fracture.
Most commonly occur in patients aged 20-50 years.
Direct impact injury onto the patella.
Eccentric contraction of the quadriceps.
How will the patient clinically present with a patellar fracture?
Often a palpable defect in the patella and a haemarthrosis.
Unable to perform a straight leg raise meaning lifting the leg off the bed by flexing at the hip and keeping the knee extended.
Being unable to perform a straight leg raise is not always a problem in patellar fracture.
How come sometimes it is a problem, and sometimes it is not?
It depends on if the patella has been displaced distally to the insertion of the quadriceps tendon.
If it has quadriceps muscles won’t be able to extend the knee.
Treatment of displaced patellar fracture.
Treament of non-displaced patellar fracture.
Displaced: surgical fixation and reduction.
Non-displaced: protected while healing takes it natural course by the use of splinting and using crutches.
What is subluxation?
Partial displacement.
In what direction is it most common for the patella to dislocate?
Why?
Laterally due to the Q-angle between the line of pull of the quadriceps tendon and the patellar ligament.
VMO keeps the patella from dislocating laterally however. VMO stabilise the patella within the trochlear grove.
What is this?
Lateral dislocation of the patella.
Common mechanism of injury of patellar dislocation + age group.
Trauma like twisting injury in slight flexion.
Usually athletic-teenagers internally rotating their femur on a planted foot whilst flexing the knee.
Predisposing factors of patellar dislocation.
Generalised ligamentous laxity
Weakness of the quadriceps muscles and VMO of vastus medialis.
Shallow trochlear groove with a flat lateral lip
Long patellar ligament
Previous dislocations
Treatment of patellar dislocation.
Extending the knee manually reducing the patella
Immobilisation during healing.
Physiotherapy to strenghten VMO
What is the most common type of knee injury?
Meniscal tears
Mechanism of injury of meniscal tears.
Sudden twisting motion of a weight-bearing knee in a high degree flexion
Clinical presentation of meniscal tear.
Intermittent pain and joint line tenderness. Restricted motion due to pain or swelling.
Knee clicking, catching and locking. Sensation of giving way.
Haemarthrosis is uncommon.
Why is haemarthrosis uncommon in meniscal tear?
What should you consider if there is haemarthrosis?
Because the menisci is largerly avascular.
This means that haemarthrosis would indicate a tear in the peripheral vascular aspect of the meniscus or an associtaed injury to the anterior cruciate ligament.
Treatment of acute meniscal tear.
Treatment of meniscal tear with suspected chronic degenerative process.
Treated surgically by either meniscectomy or meniscal repair.
If the meniscal tear instead is because of chronic degenerative process within the knee conservative management will have the same prognosis as with surgery.
Why might a locked knee be a presenting sign of a torn meniscus?
Shredded cartilage from the meniscal tear can end up in the articulating surface locking the knee.
Mechanism of collateral ligament injury.
Common sporting injury resulting from acute varus of valgus angulation of the knee.
Which collateral ligament is more likely to tear?
Why?
Medial collateral ligament is more likely to tear because it is less mobile and more rigid.
A torn LCL however has a higher chance of causing knee instability because the medial tibial plateau forms a deeper and more stable socket for the femoral condyla than the lateral tibial plateau does.
Clinical presentation of collateral ligament injury.
Pain + swelling. Unstability of the knee joint giving way and not being able to support body weight.
What is the unhappy triad?
Mechanism of injury.
Injury of ACL, medial collateral ligament and medial meniscus.
Strong force applied to the lateral aspect of the knee.
Why is the medial meniscus also injured in the unhappy triad?
Because the medial firmly is adhering to the medial collateral ligament.
What injury is most common, ACL injury or PCL?
ACL since it is weaker.
Mechanism of injury of ACL injury.
Quick deceleration, hyperextension or rotational injury following a sudden change of direction during sports.
Usually non-contact injury.
Clinical presentation of torn ACL.
Acute: popping sensation in knee with immediate swelling
When swelling goes down patient will experience instability of the knee as the tibia slide anteriorly under the femur.
Knee giving way.
Anterolateral rotatory instability.
Treatment of torn ACL.
In patients with low functional demands on their knee treat conservatively because they can function well with a ruptured ACL by using musculature to stabilise the joint.
Sportsmen and active people will often need surgical reconstruction.
Mechanism of injury of torn PCL.
Dashboard injury meaning knee is flexed and a large force is applied to the upper tibia displacing it posteriorly. Common in road traffic collisions.
Can be torn during football when player falls on a flexed knee with their ankle plantarflexed.
Tackles
Treatment of PCL tear.
Respond well to conservative treatment with bracing and rehabilitation.
How can you test for ACL and PCL injuries?
How can you test for specifically ACL injury?
ACL + PCL use anterior and posterior drawer tests.
ACL use Lachman’s test
What is this?
Dislocation of the knee joint
Mechanism of injury of dislocated knee joint.
High energy trauma.
This is a very uncommon injury.
What will be the status of the ligaments in a dislocated knee joint?
Three of the four ligaments (MCL, ACL, PCL and LCL) must be ruptured.
Associated injuries more than ligamental tear in dislocation of knee joint.
Arterial injury. Popliteal artery is prone to injury in knee joint dislocation. This can lead to complete tear of it or endothelial damage leading to thrombotic occlusions (Virchow’s triad).
This means that it is essential to fully assess the vascularity of the leg with MRI.
Causes of swelling around the knee.
Bony swelling in Osgood-Schlatter’s disease.
Soft tissue swelling like enlarged popliteal lymph node or popliteal artery aneurysm. Also lymphoedema of lower limb.
Fluid like effusion or soft tissue haematoma.
What is a knee effusion?
Accumulation of fluid inside the knee joint.
Haemarthrosis is a knee effusion due to blood.
Common cause of acute knee effusion.
Common cause of delayed knee effusion.
ACL rupture.
Reactive synovitis (inflammation of the synovium -> increased volume of synovial fluid)
Acute knee effusions can be divided into two categories. Which?
Haemarthrosis which is blood in the joint. Diagnostically haemarthrosis is an ACL tear until proven otherwise.
Lipo-haemarthrosis which is both 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.
How can you distinguish between a haemarthrosis and a lipo-haemarthrosis?
Fat is less dense than blood so it will appear darker on an x-ray.
Most commonly inflamed bursae of the knee.
Prepatellar bursa
Infrapatellar bursa
Pes anserinus bursa
What is housemaid’s knee?
Pre-patellar bursitis
Mechanism of injury of pre-patellar bursitis.
Repetitive trauma to the bursa which can occur when scrubbing floor etc.
Can also occur in fall onto knee or blunt trauma to knee.
Clinical presentation of pre-patellar bursitis.
Knee pain and swelling.
Erythema overlying the inflamed bursa.
Patient will find it difficult to walk due to the pain and will not be able to kneel on the affected side.
What is Clergyman’s knee?
Infrapatellar bursitis.
Mechanism of injury of infrapatellar bursitis.
Repeated microtrauma caused by activities involving kneeling however this is in a more upright position than in prepatellar bursitis.
What is suprapatellar bursitis a sign of?
Sign of significant pathology in the knee joint as the suprapatellar bursa is an extension of the synovial cavitiy of the knee joint.
This means that a knee effusion often present with swelling in the suprapatellar pouch.
Common causes of knee effusion.
Torn ACL
Fracture
Osteoarthritis
RA
Infection like septic arthritis
Gout + pseudogout
Repetitive microtrauma to the joint
What is this?
Baker’s cyst
What is Baker’s cyst?
Also called popliteal cyst or semimembranous bursitis.
What causes Baker’s cyst?
Knee effusion can cause semimembranous bursitis as there is a small opening between the knee joint and the semimembranous bursa.
Fluid can force its way through this narrow communication into the semimembranous bursa.
What is Osgood-Schlatter’s disease (OSD)?
When is it most common?
Inflammation of the apophysis (site of insertion) of the patellar ligament into the tibial tuberosity.
Most common in teenagers.
At the age of skeletal maturity when the apophysis fuses this resolves itself.
However there will be a bony prominence which usually remains permanently.
Clinical presentation of OSD.
Intense knee pain during running, jumping, squatting, ascending and descending stairs and during kneeling.
It is usually resolved with rest and ice.
Signs and symptoms of Osteoarthritis of the knee.
Knee pain which comes and goes precipitated by activities such as bending, kneeling, squatting and climbing stairs.
Stiffness after prolonged inactivity or rest (getting out of bed in the morning).
Swelling
Crepitus
Varus deformity can develop
Valgus deformity
Fixed flexion deformity (no full extension)
Risk factors of OA of knee joint.
Age
Female sex
Previous trauma to joint (think tibial plateau fracture)
Obesity
Family history
RA
Gout
SA
Haemophilia with haemarthrosis
Treatment of OA of knee joint.
Treatment ladder.
Vastus medialis rehab to reduce instability.
Analgesia
Weight loss
Surgery
Signs of OA on x-ray.
LOSS
Loss of joint space
Osteophytes
Subchondral cysts
Subchondral sclerosis (increased bone formation around joint)
What is septic arthritis?
How does it differ from reactive arthritis?
Invasion of the joint space by micro-organisms (usually bacteria, but can be viruses, mycobacteria and fungi).
Reactive arthritis is a sterile inflammatory process that can result from an extra-articular infection like gastroenteritis.
Most common pathogen of septic arthritis.
Other causative organism.
S. aureus
Others such a Staph. epidermidis, Neiserria gonorrhoeae, Streptococcus viridans, Strep. pneumoniae, Group B Streptococci.
Risk factors of septic arthritis.
Diabetes mellitus
Extremes of age
RA
Immunosuppression
IV drug abuse
Common cause of septic arthritis (or highly increased risk factor).
Prosthetic joint. Either due to intra-operative contamination during the operation contamination has occured.
Or haematogenous spread from a distance infective focus like during dental surgery like Strep. viridans.
Biofilm produced by Staph. epidermidis protects this pathogen from the host’s defences and from antibiotics.
The patient may become symptomatic months or even years after the initial operation.
Major consequence of SA due to bacterial invasion.
Damage to articular cartilage either due to the organism’s pathological properties or due to the host’s immune response.
Neutrophils stimulate synthesis of cytokines and other inflammatory products resulting in hydrolysis of collagen and proteoglycans (breakdown of cartilage)
Signs and symptoms of SA.
Usually a triad of symptoms:
Fever, pain and reduced range of motion.
Also:
Erythema, swelling, warmth, tenderness and limitation of active and passive range of motion.
How do clinical presentation differ in SA of a prosthetic joint and a normal joint?
SA in prosthetic joint usually has minimal physical findings and swelling is only slight. Most distinctive presentation in prosthetic is a draining sinus which originates from the underlying infected joint.
Treatment of SA.
Aspiration of the joint should be carried out immediately and the aspirate should be sent for urgent microscopy, culture and sensitivities.
Then treat the causative organism.
