The Knee Flashcards
What are the three articulations of the knee joint?
Two femorotibial articulations (b/w lateral and medial femoral and tibial condyles)
One femoropatellar articulation
What is the most important muscle in stabilising the knee joint?
Quadriceps femoris
What is the most stable position of the knee and why?
Erect, extended position - all articular surfaces congruent, collateral ligaments taut
Name the 5 extracapsular ligaments of the knee.
- Patellar ligament
- Fibular/lateral collateral ligament
- Tibial/media collateral ligament
- Oblique popliteal
- Arcuate popliteal
Which is stronger - the LCL or the MCL?
LCL is stronger than the MCL
Describe the relationship of the collateral ligaments to their menisci.
LCL - separated from lat meniscus by popliteal tendon
MCL - deep fibres firmly attached to medial meniscus (consider that when MCL is injured, meniscus also often injured)
What is the ‘unhappy triad’ and how is is sustained?
Three different injuries often sustained at one time due to the relationship of the different structures to each other.
MCL, ACL, medial meniscus
Injury most often sustained when either: (1) blow to lateral side of extended knee or (2) excessive lateral twisting of flexed knee
What are the intra-articular ligaments of the knee?
Cruciate ligaments - ACL and PCL
Medial and lateral meniscus
Which is stronger - ACL or PCL?
PCL is stronger than ACL
What is the main stabilising factor for femur in weight-bearing flexed knee?
PCL - prevents anterior displacement of femur on tibia. Therefore, one q on hx that can be asked, “Are you still able to walk downhill?”
Describe the location of the ACL.
*Always think ANTERIOR IN RELATION TO ATTACHMENT TO TIBIA
Arises from the anterior intercondylar area of tibia, attaches to posterior part of lateral condyle of femur
What is the function of the ACL?
Prevents posterior displacement of femur on tibia and hyperextension of knee joint
Describe the location of the PCL.
*Always think POSTERIOR IN RELATION TO ATTACHMENT TO TIBIA
Arises from the posterior intercondylar area of tibia; attaches to anterior part of medial condyle of femur
Describe the structure and function of the menisci.
Fibrocartilaginous cresecents that acts as shock absorbers and facilitates lubrication - thicker at external margins.
Lateral meniscus more circular in shape and anchored to popliteus tendon.
Medial meniscus more C-shaped and anchored to MCL.
Name three clinical features of a knee ligamentous tear.
- Swelling - appearing almost immediately after injury (worse with partial tears)
- Tenderness acutely over torn ligament; pain worse and more sharply defined when tear is partial
- Joint laxity
How are isolated complete tears of the LCL managed?
Rare.
Conservative management as for MCL - long cast-brace worn for 6 weeks and graded exercises encouraged thereafter.
How are isolated tears of the ACL managed?
Non-professionals: conservative management with long cast-brace worn (2-4,6 weeks) and movement/muscle-strengthening exercises encouraged thereafter
Professionals: early operative reconstruction
Name four sources for ACL reconstruction.
- Hamstring (semintendinosus +/- gracilis)
- Middle 1/3 patellar tendon
- Allograft (e.g. cadaver)
- LARS (ligament augmentation and reconstruction) surgery -synthetic ligament
How are isolated tears of the PCL managed?
Conservatively - most patients end up with little or no loss of function; chronic instability while walking up stair may warrant late reconstruction
Name four indications for operation in patient with chronic knee instability.
- Recurrent locking, with MRI or arthroscopic confirmation of a meniscal tear
- Intolerable symptoms of giving way
- Suboptimal function in a sportsperson or others with similarly emanding occupations
- Ligament injuries in adolescents (the long-term effects of chronic instability in this group are more marked)
How do you grade severity of knee ligament ‘sprains’?
Grade 1 - no laxity
Grade 2 - partial rupture; laxity
Grade 3 - complete rupture: no end-point
Describe the classification of knee dislocations.
Anterior: occurs from hyperextension of knee; often PCL & ACL both torn; either MCL or LCL or both will usually be injured
Posterior: ACL and PCL tears
Lateral
Medial
Rotary: usually posterolateral
How are MCL sprains treated?
Grade 1 and 2: RICE, functional rehabilitation - active exercises encouraged/crutches and weight-bearing as tolerated
Grade 3: brace (short-hinged or long-cast?)
Describe the popliteal artery injuries that can be sustained in anterior vs posterior knee dislocations.
Anterior dislocations - intimal tear or intra luminal thrombus
Posterior dislocations - avulsion or complete disruption of artery
Name two other injuries that are associated with knee ligamentous injuries.
Popliteal artery injury
Common peroneal nerve injury
Describe mechanism of injury associated with common peroneal nerve injury.
Associated with varus force and LCL injury
Describe the anterior and posterior drawer tests.
Demonstrate ACL and PCL respectively.
Knee flexed at 90 degrees, foot immobilised, hamstrings released
If able to sublux tibia anteriorly, then ACL may be torn
If able to sublux tibia posterior, then PCL may be torn
Describe the Lachmann test
Demonstrates torn ACL
Knee flexed at 15-20 degrees
Cup one hand around femur with thumb on anterior thigh – the other hand should be cupped around proximal tibia, thumb anteriorly. Pull tibia anteriorly – positive if laxity felt – make sure you comment on end-point! (soft vs hard)
If difficult, can place your knee under thigh to provide more support – instead of cupping, one hand can push down on femur while the other is cupped around proximal tibia (as above)
Similar to anterior drawer test but more reliable due to less muscular stabilisation
What is the pivot shift sign?
Demonstrates torn ACL
Start with knee in extension - Internally rotate foot, slowly flex knee while palpating/applying a valgus force
Normally knee will flex smoothly. If incompetent ACL, tibia will sublux anteriorly on femur at start of maneuver. During flexion, the tibia will reduce and externally rotate about the femur (the ‘pivot’).
Describe the collateral ligament stress test. (2)
- With knee in full extension, apply valgus force to test MCL, apply varus force to test LCL
- Repeat tests with knee in 20 degree flexion to relax joint capsule
Results - if opening only in 20 degrees of flexion - due to MCL damage only
If opening in 20 degrees of flexion AND full extension - due to MCL, cruciate and joint capsule damage
List 5 clinical features of meniscal tears.
- Immediate pain, difficulty weight-bearing, instability and clicking
- Increased pain with squatting and/or twisting
- Effusion (haemarthrosis) with insidious onset (24-48h)
- Joint line tenderness medially or laterally
- Locking of knee (if portion of meniscus mechanically obstructing extension)
What investigations would you order if you suspect a meniscal tear?
MRI or arthroscopy
BUT ANY KNEE INJURY = X-RAY
How are meniscal tears managed? (3)
- RICE, ROM and strengthening, NSAIDs for pain relief (or panadol if NSAIDs contra-indicated)
- Surgical repair only reserved for younger patients with vertical longitudinal tear within vascularised outer 1/3 of meniscus (‘red-red’ zone)
- If damage is in avascular area –> partial meniscectomy –> but causes long-term OA so only performed when patient suffers joint locking or meniscal pain that is refractory to conservative management –> potential for mensical autografts in these patients
Which meniscus is more commonly torn and why? (2)
Medial
- Different shape (Medial = C-shaped, lateral = shorter incomplete circle)
- Because medical meniscus attached to MCL. Lateral meniscus pulled out of way of compression between femur and tibia by popliteus.
Describe the blood supply of the menisci.
Only outer third supplied - superior and inferior branches of medial and lateral geniculate arteries
Describe the motor and sensory changes that occur when the common peroneal nerve is injured (which can occur in knee injuries).
- Motor - common peroneal nerve supplies peroneus longus, brevis, short head of biceps femoris - therefore injury results in foot drop (dorsiflexion of foot is compromised)
- Sensory - loss of sensation to dorsal surface of foot + anterolateral leg
What is a bucket handle meniscus tear and how does it occur?
Vertical or oblique tear in posterior horn running toward the anterior horn –> loose section remaining attached anteriorly and posteriorly –> potential for locking
Twisting force on knee when it is partially flexed
What is the Apley grind test?
Test used to evaluate for meniscal tear.
Patient lays prone on examination table/ with knee flexed to 90 degrees. Tibia is pushed down into knee joint while being rotated. If maneouvre produces pain (also click/pop) = positive Apley test
What is a Segond fracture?
Avulsion fracture of the knee which involves lateral aspect of tibial plateau, frequently associated with ACL tear
What investigations would you consider if a knee dislocation is suspected? (3)
- X-rays: AP, lateral, skyline
- ABI (abnormal <0.9)
- Arteriogram if abnormal vascular exam (such as abnormal pedal pulses)
How is a dislocated knee managed? (4)
- Urgent closed reduction
- Assessment of peroneal nerve, tibial artery (which comes from the popliteal artery) and ligamentous injuries
- Repair of associated injuries; also may need decompressive fasciotomy especially if vascular repair undertaken
- Knee immobilisation - 6-8 weeks
List 3 indications for a TKR (primary vs secondary)
- Relief of pain associated with arthritis of the knee in patients who have failed non-operative treatments - should be main indication!
- Correction of a deformity
- Restoration of function
List 3 contra-indications for a total knee replacement.
- Active infection in the knee or anywhere in the body
- A non-functioning extensor mechanism
- Poor extremity circulation of vascularity
TKR: what if a patient is on antibiotics?
Patients with resolved infections should be off antibiotics at least 48 hours prior to surgery
Remember, active infection = contraindication
What are the three most commonly used X-rays viewed of the knee?
- Standing AP view
- Lateral view - used to assess patellofemoral joint and the position of the patella
- Tangential patellar view - ‘sunrise’ ‘skyline’ or Merchant
What are the risks of a TKR? (general vs specific)
General
- infection
- anaesthetic and intraoperative events
- thromboembolism
Specific
- nerve and arterial injuries
- periprosthetic fractures
- aseptic failure
