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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
What are degenerative meniscal tears?
Tears that occur as the meniscus weakens with age - probably represents primary OA
26
How are acute meniscal tears and degenerate ones distinguished from each other?
From Hx and examination - Degenerative tears will be Steinmann's -ve Associated symptoms of OA
27
Why is it important to distinguish acute meniscal tears from degenerative ones?
They are treated differently - degenerative tear symptoms will not improve with resection so shouldn't be treated with arthroscopy
28
Tx of meniscal tear
Most - arthroscopic menisectomy In a younger patient with a fresh tear, could consider repair, but these have a 25% failure rate.
29
What % of meniscal tears are not suitable for meniscal repair
90%
30
Why do degenerative meniscal tears not improve with arthroscopy?
They're due to OA in the joint, so removing the meniscus will increase the stress in the already worn and damaged surfaces
31
Role of the ACL
resists anterior subluxation of the tibia
32
Classic mechanism of injury for ACL tear
Turning of the upper body laterally on a planted foot, leading to internal rotation of the tibia
33
Presentation of ACL rupture
"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
Rule of thirds in ACL rupture
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
Tx of ACL rupture
ACL reconstruction NOT repair involves tendon graft passed through tibial and femoral tunnels and secured to bone
36
common locations for tendon graft to be taken for ACL reconstruction
patellar tendon semitendinosis gracilis
37
Role of the PCL
resists posterior subluxation of the tibia
38
Classic mechanism of injury for PCL rupture
Direct blow to anterior tibia with the knee flexed
39
Presentation of PCL rupture
Recurrent hyperextension Instability in descending stairs Popliteal knee pain and bruising
40
Tx of PCL rupture
If isolated - won't require reconstruction If part of multi-ligament injury - PCL reconstruction
41
role of MCL
resists valgus stress
42
presentation of MCL tear
knee laxity pain on valgus stress tenderness over origin or insertion of MCL
43
Tx of MCL tear
hinged knee brace
44
Why is surgery for MCL tears not common
MCL has a good bloody supply and is thin so is always expected to heal
45
What other ligament in the knee is usually damaged with MCL tear
ACL
46
Role of LCL
Resists varus stress
47
What other ligament in the knee is usually damaged with LCL tear
PCL
48
Why is LCL harder to heal than MCL
It is much thicker than MCL
49
What nerve can be damaged with LCL injury and why
Common peroneal nerve The hyperextension and varus giving rise to the injury, and from excessive stretch.
50
Tx of LCL tear
LCL reconstruction with tendon graft
51
Why are complete knee dislocations a surgical emergency
They involve rupture of all 4 knee ligaments, so high chance of neurovascular injury
52
What neurovascular structures are usually damaged in complete knee dislocation
popliteal artery common peroneal nerve +/- leading to compartment syndrome
53
Tx of complete knee dislocations
emergency reduction and external fixation for temporary stabilisation multiple ligament reconstruction rechecking of vascular status
54
When should you suspect osteochondral or chondral injury after knee injury
if there is ongoing pain or effusion after the knee injury
55
Ix for suspected osteochondral knee injury
Xray MRI Arthroscopy
56
Tx of osteochondral knee injury
Depends if the bone is weight-bearing area and how large the fragments are Large - fix with pins Non-weight bearing - remove arthroscopically
57
What does the extensor mechanism of the knee consist of
``` tibial tuberosity patellar tendon patella quadriceps tendon quadriceps muscle ```
58
Causes of patellar tendon or quadriceps tendon rupture
rapid contractile force to the muscles e.g. after lifting heavy weight, after a fall
59
Are patellar tendon ruptures more common in younger or older age groups?
Younger (<40)
60
Are quadriceps tendon ruptures more common in younger or older age groups?
Older (>40)
61
Predisposing factors to extensor mechanism rupture
``` Hx of tendonitis (Quinolone antibiotics) Chronic steroid abuse Diabetes RA Chronic renal failure ```
62
Why should steroid injections for tendonitis of the extensor mechanism be avoided?
High risk of tendon rupture
63
Presentation of extensor mechanism rupture
Unable to straight leg raise Obvious palpable gap in extensor mechanism
64
Ix for suspected extensor mechanism rupture
Xray | USS
65
Tx extensor mechanism rupture
tendon to tendon repair or reattachment of the tendon to the patella
66
Define patellofemoral dysfunction
disorders of the patellofemoral articulation resulting in anterior knee pain
67
In what direction does the patella always dislocate
Laterally

Orthopaedics (16 decks)

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