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Orthopaedics > Knee > Flashcards

Knee Flashcards

1
Q

what condition predisposes to medial compartment knee OA

A

genu varum

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2
Q

what condition predisposes to lateral compartment knee OA

A

genu valgus

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3
Q

What procedure may younger patients with medial compartment OA benefit from rather than TKR?

A

Osteotomy - shifts the load to the lateral compartment
or
UKR

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4
Q

What are the 3 types of knee replacement

A
  1. TKR - replacement of all 3 compartments
  2. Unicompartmental knee replacement
  3. Patellofemoral replacement
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5
Q

Disadvantages of UKR for isolated compartment OA

A

Higher failure rates than TKR

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6
Q

materials used in TKR

A

Femoral component - cobalt chrome, stainless steel

Tibial component - cobalt chrome, stainless steel, titanium

High density polyethylene bearing surface

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7
Q

What happens to the ACL and PCL in TKR

A

The ACL is usually excised

The PCL can be left, but is usually sacrificed in most designs

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8
Q

What happens to the collateral ligaments in TKR

A

Any tight ligaments need to be lengthened or released for a symmetrical balance as unequal tension of the collateral ligaments leads to stress and eventual loosening.

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9
Q

What is there a higher chance of with TKR compared to THR

A

unexplained pain

?complexity and reliance on soft tissue tension

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10
Q

Why do the menisci have limited healing potential

A

Only a blood supply on the outer third - the rest is avascular

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11
Q

Role of the knee menisci

A

Distribute load from convex femoral condyles to relatively flat tibial articular surfaces

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12
Q

Compare the fixing of the medial and lateral menisci

A

Medial is more fixed whereas lateral is more mobile

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13
Q

Why are tears more common in the medial menisci

A

Because it is more fixed, so is under a greater amount of shear stress

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14
Q

Classic mechanism of injury for meniscal tear

A

Twisting force on a loaded knee e.g. football, squatting

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15
Q

What % of ACL ruptures also have a meniscal tear

A

25%

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16
Q

Presentation of meniscal tear

A

localised pain to medial (majority) or lateral joint line

Steinmann’s test +ve - pain on tibial rotation localising to affected compartment

effusion develops day after injury

catching sensation or knee ‘locking’ - difficulty straightening the knee

instability - if a loose fragment is caught in the knee when walking

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17
Q

define true knee ‘locking’

A

a mechanical block to full extension caused by a torn meniscus flipping over and becoming stuck in the joint line

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18
Q

define ‘pseudo-locking’

A

not a sign of meniscal injury - temporary difficulty in straightening the joint which will either resolve spontaneously or there is a ‘trick manoeuvre’ which relieves the issue

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19
Q

Ix for suspected meniscal tear

A

MRI

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20
Q

Patterns of meniscal tear

A

Parrot beak tear

Longitudinal tear

Radial tear

Bucket handle tear

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21
Q

Describe a radial meniscal tear

A

Extends radially from the free edge of the meniscus

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22
Q

Describe a longitudinal meniscal tear

A

Tear is parallel to the circumference of the meniscus

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23
Q

Describe a parrot beak tear

A

Type of oblique tear - the tear gap has a curved V shape

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24
Q

Describe a bucket handle tear

A

A large longitudinal tear is able to flip out of its normal position and displace anteriorly or into the intercondylar notch where the knee locks and is unable to fully extend due to mechanical obstruction from the trapped meniscal fragment

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25
Q

What are degenerative meniscal tears?

A

Tears that occur as the meniscus weakens with age - probably represents primary OA

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26
Q

How are acute meniscal tears and degenerate ones distinguished from each other?

A

From Hx and examination -
Degenerative tears will be Steinmann’s -ve
Associated symptoms of OA

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27
Q

Why is it important to distinguish acute meniscal tears from degenerative ones?

A

They are treated differently - degenerative tear symptoms will not improve with resection so shouldn’t be treated with arthroscopy

28
Q

Tx of meniscal tear

A

Most - arthroscopic menisectomy

In a younger patient with a fresh tear, could consider repair, but these have a 25% failure rate.

29
Q

What % of meniscal tears are not suitable for meniscal repair

A

90%

30
Q

Why do degenerative meniscal tears not improve with arthroscopy?

A

They’re due to OA in the joint, so removing the meniscus will increase the stress in the already worn and damaged surfaces

31
Q

Role of the ACL

A

resists anterior subluxation of the tibia

32
Q

Classic mechanism of injury for ACL tear

A

Turning of the upper body laterally on a planted foot, leading to internal rotation of the tibia

33
Q

Presentation of ACL rupture

A

“pop” is heard

haemarthrosis develops within a hour of injury

rotatory instability

Anterior drawer test +ve and Lachmans test +ve - excessive anterior translation of the tibia

34
Q

Rule of thirds in ACL rupture

A

1/3 can compensate and able to function well

1/3 can avoid instability by avoiding high impact sports

1/3 do poorly with frequent giving way in normal activities

35
Q

Tx of ACL rupture

A

ACL reconstruction NOT repair

involves tendon graft passed through tibial and femoral tunnels and secured to bone

36
Q

common locations for tendon graft to be taken for ACL reconstruction

A

patellar tendon
semitendinosis
gracilis

37
Q

Role of the PCL

A

resists posterior subluxation of the tibia

38
Q

Classic mechanism of injury for PCL rupture

A

Direct blow to anterior tibia with the knee flexed

39
Q

Presentation of PCL rupture

A

Recurrent hyperextension

Instability in descending stairs

Popliteal knee pain and bruising

40
Q

Tx of PCL rupture

A

If isolated - won’t require reconstruction

If part of multi-ligament injury - PCL reconstruction

41
Q

role of MCL

A

resists valgus stress

42
Q

presentation of MCL tear

A

knee laxity
pain on valgus stress
tenderness over origin or insertion of MCL

43
Q

Tx of MCL tear

A

hinged knee brace

44
Q

Why is surgery for MCL tears not common

A

MCL has a good bloody supply and is thin so is always expected to heal

45
Q

What other ligament in the knee is usually damaged with MCL tear

A

ACL

46
Q

Role of LCL

A

Resists varus stress

47
Q

What other ligament in the knee is usually damaged with LCL tear

A

PCL

48
Q

Why is LCL harder to heal than MCL

A

It is much thicker than MCL

49
Q

What nerve can be damaged with LCL injury and why

A

Common peroneal nerve

The hyperextension and varus giving rise to the injury, and from excessive stretch.

50
Q

Tx of LCL tear

A

LCL reconstruction with tendon graft

51
Q

Why are complete knee dislocations a surgical emergency

A

They involve rupture of all 4 knee ligaments, so high chance of neurovascular injury

52
Q

What neurovascular structures are usually damaged in complete knee dislocation

A

popliteal artery
common peroneal nerve

+/- leading to compartment syndrome

53
Q

Tx of complete knee dislocations

A

emergency reduction and external fixation for temporary stabilisation

multiple ligament reconstruction

rechecking of vascular status

54
Q

When should you suspect osteochondral or chondral injury after knee injury

A

if there is ongoing pain or effusion after the knee injury

55
Q

Ix for suspected osteochondral knee injury

A

Xray
MRI
Arthroscopy

56
Q

Tx of osteochondral knee injury

A

Depends if the bone is weight-bearing area and how large the fragments are

Large - fix with pins
Non-weight bearing - remove arthroscopically

57
Q

What does the extensor mechanism of the knee consist of

A 
tibial tuberosity 
patellar tendon 
patella 
quadriceps tendon 
quadriceps muscle
58
Q

Causes of patellar tendon or quadriceps tendon rupture

A

rapid contractile force to the muscles e.g. after lifting heavy weight, after a fall

59
Q

Are patellar tendon ruptures more common in younger or older age groups?

A

Younger (<40)

60
Q

Are quadriceps tendon ruptures more common in younger or older age groups?

A

Older (>40)

61
Q

Predisposing factors to extensor mechanism rupture

A 
Hx of tendonitis (Quinolone antibiotics) 
Chronic steroid abuse 
Diabetes 
RA 
Chronic renal failure
62
Q

Why should steroid injections for tendonitis of the extensor mechanism be avoided?

A

High risk of tendon rupture

63
Q

Presentation of extensor mechanism rupture

A

Unable to straight leg raise

Obvious palpable gap in extensor mechanism

64
Q

Ix for suspected extensor mechanism rupture

A

Xray

USS

65
Q

Tx extensor mechanism rupture

A

tendon to tendon repair or reattachment of the tendon to the patella

66
Q

Define patellofemoral dysfunction

A

disorders of the patellofemoral articulation resulting in anterior knee pain

67
Q

In what direction does the patella always dislocate

A

Laterally

Orthopaedics (16 decks)

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