Reconstruction FRCS > Alignment in TKR > Flashcards

Alignment in TKR Flashcards

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1
Q

Describe the normal anatomical alignment of the femur and tibia?

A
  • Femur is in 5-7o of Valgus
  • tibia is in in 2-3 o of varus
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2
Q

What are the technical goals of TKR?

A
  1. Restore mechanical alignment
  2. Restore joint line
  3. Balance ligaments
  4. maintain normal q angle - maintain patella-femoral tracking
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3
Q

Can you draw the mechanical and anatomical axis of the limb?

A
  • Tibial anatomical axis - a line that bisects intramedullary canal
  • tibial mechanical- centre of prox tibia to centre of the ankle
  • Femoral mechanical thru centre of femoral head to intercondylar notch
  • anatomical line bisects the medullary canal of the femur
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4
Q

How is femoral alignment achieved?

A
  • The difference between the anatomcial and mechanical axis ( 5-7 degrees)
  • perpendicular to mechanical axis
  • jig measures 6 degrees from femoral guide ( antomical axis)
  • Will vary if tall <5o or short >7o
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5
Q

How is tibial alignment achieved?

A
  • Usually mechanically and anatomical axis of tbia coincide so can usually cut the proximal tibia perpendicular to the anatomical axis
  • if there is a tibia defomrity the tibial cut must be made perpendicular to the mechanical axis and an extra medullary guide is used
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6
Q

How is patellofemoral alignment achieved in TKR?

A
  • Aim to preserve patella tracking
  • abnormal patellar tracking is the most common complication of TKR
  • aim to avoid increasing the q angle by not
    • ​IR of femoral prosthesis
    • Medialisation of femoral components
    • IR of the tibial prosthesis
    • placing the patellar prosthesis lateral on the patella
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7
Q

What axis are use to ensure good femoral prosthesis placememt to avoid increasing the q angle?

A
  • Transepicondylar axis
    • line running from medial to lateral epicondyles
    • the axis is parallel to the cut tibial surface
    • a post femoral cut parallel to the epicondylar axis will create the appropriate rectangular flexion gap
  • Posterior condylar axis
    • line running across tips of the 2 posterior condyles
    • this is 3 degrees of IR from the transepicondlyar axis , the femoral prosthesis should be ER by 3 degrees from this axis to produce a rectangular flexion gap
    • *****if the lateral condyle is hypoplastic use the posterior condyle axis -> IR of the femoral component***
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8
Q

What is the Q angle?

Why is increasing this in TKR a problem?

A
  • the angle between the axis of the extensor mechanism ( ASIS to patella) and axis of patella tendon ( centre of patella to tibial tuberosity)
  • increase Q angle-> increase in lateral subluxation forces over patella relative to trochlear groove
  • -> pain and mechanical symptoms , accelerated wear and dislocation
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9
Q

What happens if the femoral component is placed in Internal rotation?

A
  • you bring the trochlear groove and patella medially
  • Increase Q angle to the tibial tuberosity
  • also make the medial component tight in flexion
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10
Q

What happens if the femoral component is medialised?

A
  • Bring the trochlear groove to a more medial position
  • so bring the patella medial
  • increasing the q angle
  • so you want the femoral component to be slightly lateral
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11
Q

What is the preferred rotation of the tibia?

A
  • Neutral
  • best way to ahieve this is to centre over medial third of tibial tubercle
  • this will leave a portion of the posteromedial tibia uncovered and some overhang of the prothesis over the tibia on the posterolateral tibia
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12
Q

What happens if the tibial component is IR and medialised?

A
  • IR=> external rotation of the tibial tuberosity -> increase Q angle
  • medialisation will also increase Q angle
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13
Q

What position of the patella prothesis wll increase the q angle?

A
  • lateralisation of the patella
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14
Q

What is the preferred position of the patella prostheis?

A
  • Centred over patella or medialised
  • to decrease the q angle
  • remove lateral osteophytes
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15
Q

What are the complications of patella non resurfacing cf resurfacing?

A
  • Increased risk of anterior knee pain
  • increased risk of secondary resurfacing
  • no increased risk of revision surgery
  • no increased risk of extension tendon complications
  • no diff inpt satisfaction
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16
Q

How is joint line preserved in TKR?

Study These Flashcards
A
  • goal to restore joint line that is the same thickness as the bone and cartilage that was removed
  • this preserves ligament tension
  • elevating the joint line >8mm ->
    • Mid flexion instability
    • patellofemoral tracking problems
    • patella Baja
  • Lowering joint line
    • Lack of full extension
    • flexion instability
17
Q

What is the goal in varus deformity of the knee?

Study These Flashcards
A
  • release tight medial structures
  • tighten the lax lateral ligaments
18
Q

Describe the intraop release in a varus knee?

Study These Flashcards
A

tight medial ( concave), loose lateral ( convex side)

  1. Osteophytes, meniscus and capsule
  2. **Deep MCL and capsule **
  3. Posteriomedial corner
    • semimembranosus and capsule
  4. Superifical MCL
    • ​​can find it as it blends into pes anserine complex
    • cannot completely release-> valgus instability so only perform subperiosteal elevation
    • if tight in extension = release post oblique portion
    • if tight in flexion= release anterior portion
  5. ​PCL- rarely released
19
Q

How are the lateral structures tightened in varus knee deformity?

Study These Flashcards
A
  • use a prothesis that is the size to fill up the gap and make the stretched lateral ligaments taut
20
Q

What is the goal in valgus knee deformity

Study These Flashcards
A
  • Tight lateral components ( concave), Loose Medial (convex)
  • Release lateral components correct valgus
  • tighten loose medial components
21
Q

What is the order of lateral release to the knee?

Study These Flashcards
A
  1. Osteophytes, meniscus, capsule
  2. Lateral capsule
  3. Iliotibial band- tight in extension
    • z plasty or release of Gerdy’s tubercle
  4. popliteus- tight in flexion
    • release ant part of insertion
  5. LCL
    • some release before iliotbial band/popliteus
    • if do release consider constrained prothesis
22
Q

How is flexion/ contraction deformity released?

Study These Flashcards
A
  • Concave side is posterior- needs to be release
  1. Osteophytes
  2. Posterior capsule
  3. Gastronemius muscles ( medial to lateral)
  • all releases are preformed with knee at 90 degrees of flexion
    • allows popliteal artery to fall posteriorly to decrease risk of injury
    • NB not to tx by more tibial resection-> change joint line -> patella alta
23
Q

What is the complication of releases?

Study These Flashcards
A
  • Peroneal nerve palsy
    • correction of valgus and flexion deformity has highest risk of injury
24
Q

What is the tx of a pt with peroneal n palsy post op?

Study These Flashcards
A
  • Immediately release dressing
  • Flex knee
  • watch for 3 months to see if function returns
  • if function doesn’t return, consider nerve conduction studies or operative exploration to access for damage
25
What is the goal of gap ( sagittal ) balancing in TKR?
* Goal is to obtain a gap that is equal in flexion and extension * this will ensure the tibial insert is stable throughout the arc of motion * if **asymmetric tightness= adjust femur** * _distal femur= affect extension gap_ * _posterior femur= affect flexion gap_ * **​if symmetrical tightness** (extension+ flexion)**= adjust tibia** * **​tibia cuts affect flexion and extension**
26
What do you do if tight in flexion and tight in extension?
* didn't cut enough tibia so * Cut more tibia
27
What do you do if balanced in flexion but tight in extension?
* didn't take enough off distal femur or didn't release enough post capsule so 1. **Release post capsule** 2. **cut more distal femur**
28
What do you do if loose in flexion and tight in extension?
* _distal femur too long_ 1. **resect more distal femur or use thinner distal augmentation wedge** 2. **upsize femoral component**
29
What do you do if tight in flexion and balanced in extension?
* _not enough removed from post femur/ PCL scarred, too tight_ 1. **decrease size of femoral component** 2. **recess and release PCL** 3. **resect post slope in tibia** 4. **resect more posterior femoral condyle** 5. **release posterior capsule**
30
What do you do if loose flexion and balanced in extension?
* resected too much off posteror femur 1. **increase size of femoral component** ( ap only) 2. **Posteriorize femoral component** ( use augment post femur)
31
What do you do if tight in flexion and loose extension?
* too much distal femur removed and too little posterior 1. **Downsize femur** 2. **use thicker tibial insert until balanced**
32
What do you do if loose in flexion and loose in extension?
* cut too much tibia 1. use thicker tibia PE 2. use thicker tibial metal insert
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