Updated: 4/7/2019

TKA Patellofemoral Alignment

Topic
Review Topic
0
0
Questions
17
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0
Evidence
19
0
0
Videos
2
Techniques
3
https://upload.orthobullets.com/topic/5017/images/Femoral Implant Rotation Illustration small_moved.jpg
Introduction
  • Abnormal patellar tracking is the most common complication of TKA.
    • the most important variable in proper patellar tracking is preservation of a normal Q angle.
  • Abnormal Q angle 
    • an increase in the Q angle will lead to
      • an increased lateral subluxation forces on the patella relative to the trochlear groove
      • possible pain, mechanical symptoms, accelerated wear, and even dislocation.
    • it is critical to avoid techniques that lead to increase Q angle. Common errors include 
      • internal rotation of the femoral prosthesis
      • medialization of the femoral component
      • internal rotation or medialization of the tibial prosthesis 
      • placing the patellar prosthesis lateral on the patella 
Anatomy
  • Q Angle
    • the Q angle is defined as angle between
      • axis of extensor mechanism (ASIS to center of patella)
      • axis of patellar tendon (center of patella to tibial tuberosity)
Imaging
  • CT scan
    • malrotation of components is best diagnosed with CT scan of the knee 
Femoral Prosthesis
  • There are three reference axis that one may use:
    1. anteroposterior axis
      • defined as a line running from the center of the trochlear groove to the top of the intercondylar notch
      • a line perpendicular to this defines the neutral rotational axis
    2. transepicondylar axis
      • defined as a line running from the medial and lateral epicondyles
      • the epicondylar axis is parallel to the cut tibial surface
      • A posterior femoral cut parallel to the epicondylar axis will create the appropriate rectangular flexion gap
    3. posterior condylar axis
      • defined as a line running across the tips of the two posterior condyles
      • this line is in ~ 3 degrees of internal rotation from the transepicondylar axis, the femoral prosthesis should be externally rotated 3 degrees from this axis to produce a rectangular flexion gap q
      • if the lateral femoral condyle is hypoplastic, use of the posterior condylar axis may lead to internal rotation of the femoral component q q
      • WARNING: the average posterior condylar twist angle is 3º but the range is  1-10º. Therefore vary angle of femoral rotation based on variances in femoral anatomy.
      • Therefore vary angle of femoral rotation
        Based on variances in femoral anatomy.
  • Internal Rotation of Femoral Prosthesis will Increase Q angle
    • by internally rotating the femoral prosthesis, you are effectively bringing the groove and the patella medially. This will increase the Q angle to the tibial tubercle
    • will also make the medial compartment tight in flexion with subsequent TKA stiffness
  • Medialization of the Femoral Prosthesis will Increase Q angle
    • a medialized femoral prosthesis will bring the trochlear groove to a more medial position, and thus bring the patella medial with it, thus increasing the Q angle
    • therefore, you want the femoral component to be slighly lateral if anything
Tibial Prosthesis
  • The preferred rotation of the tibial component is neutral, with no internal or external rotation.
    • the best way to obtain this is to have the tibial component centered over the medial third of the tibial tubercle
    • this may leave a portion of the posteromedial tibia uncovered and some overhang of the prosthesis over the tibia on the posterolateral tibia.
  • Internal Rotation of Tibial Prosthesis will increase Q angle
    • internal rotation of the tibial component effectively results in relative external rotation of the tibial tubercle and an increase in the Q angle
  • Medialization of tibia will increase Q angle
Patellar Prosthesis
  • The preferred position of the patellar prosthesis is to be either centered over the patella or medialized   
    • medializing the patellar component is one strategy to decrease the Q angle. 
    • results in uncoverage of lateral facet. Consider removing to lessen risk of lateral facet syndrome.
    • another alternative is use of an oval shaped patella with the apex medialized.
  • Lateralization of the patellar prosthesis will increase the Q angle and increase maltracking
  • Intraoperative lateral subluxation of the patella
    • if patella laterally subluxes intraoperatively during trialing, deflate tourniquet and recheck before performing a lateral release
  • Indications for resurfacing
    • absolute
      • inflammatory arthritis
      • patella maltracking
      • patellofemoral arthritis as the main indication for TKA
  • Options for resurfacing during TKA
    • always resurface
    • never resurface
      • option to perform patelloplasty
        • excision of marginal osteophytes, reshaping of patella
    • selective resurfacing
  • Patella resurfacing vs. Non-resurfacing
    • less anterior knee pain with resurfacing
    • less revision rates  with resurfacing  
    • inferior results with secondary resurfacing
    • increase complications (fx, tendon injury, etc.) with resurfacing
    • similar patient satisfaction rates
    • trochlear design important:  “patellar friendly”
      • thinner anterior flange
      • anatomic trochlear groove
 
 

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Technique Guides (3)
Questions (17)

(OBQ13.105) Which of the following intra-operative errors most commonly leads to patellar maltracking during a total knee arthroplasty? Review Topic

QID: 4740
1

Using the gap balancing technique instead of measured resection technique

1%

(24/4249)

2

Internal rotation of the femoral component

90%

(3816/4249)

3

External rotation of the tibial component

6%

(234/4249)

4

Lateralization of the femoral prosthesis

2%

(105/4249)

5

Overresection of the patella

1%

(46/4249)

ML 1

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PREFERRED RESPONSE 2

(OBQ12.187) Which of the following intra-operative steps would put a patient at risk for lateral patellar maltracking during total knee arthroplasty (TKA)? Review Topic

QID: 4547
1

External rotation of the femoral component

8%

(338/4161)

2

Medial placement of the patellar component

4%

(167/4161)

3

Internal rotation of the tibial component

79%

(3307/4161)

4

Lateral translation of the femoral component

4%

(147/4161)

5

Superior placement of the patellar component

4%

(160/4161)

ML 2

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PREFERRED RESPONSE 3

(OBQ10.181) Internal rotation of the femoral component in primary total knee arthroplasty may lead to which of the following? Review Topic

QID: 3274
1

A net lateral patellar tilt and increased lateral subluxation

94%

(3873/4126)

2

A decreased Q angle

3%

(134/4126)

3

Patella baja

0%

(13/4126)

4

A loose medial compartment and tight lateral compartment

2%

(88/4126)

5

Balanced medial and lateral flexion gaps

0%

(15/4126)

ML 1

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PREFERRED RESPONSE 1
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(OBQ09.89) Following a left total knee arthroplasty, all of the following can cause the condition seen in Figure A EXCEPT: Review Topic

QID: 2902
FIGURES:
1

Internal rotation of the femoral prosthesis

3%

(77/2708)

2

Internal rotation of the tibial prosthesis

5%

(126/2708)

3

Lateralization of the femoral prosthesis

79%

(2148/2708)

4

Medialization of the tibial prosthesis

8%

(209/2708)

5

Lateralization of the patellar prosthesis

5%

(138/2708)

ML 2

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PREFERRED RESPONSE 3

(OBQ09.242) A 66-year-old woman with genu valgum osteoarthritis undergoes total knee replacement. What technical error could lead to post-operative lateral patellar instability? Review Topic

QID: 3055
1

External rotation of the tibial component

2%

(65/3119)

2

External rotation of the femoral component

5%

(158/3119)

3

Internal rotation of the femoral component

91%

(2824/3119)

4

Lateralization of the femoral component

1%

(26/3119)

5

Medialization of the patellar component

1%

(40/3119)

ML 1

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PREFERRED RESPONSE 3
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(OBQ08.185) A standard total knee is performed on a 56 year-old female using spinal anesthesia and a tourniquet. After cementation of all the components, the patella is noted to sublux laterally during range of motion. The alignment and rotation of the femoral, tibial, and patellar components all appear perfect. The surgeon should now: Review Topic

QID: 571
1

Perform a lateral release

9%

(242/2654)

2

Revise tibial component into more external rotation

0%

(12/2654)

3

Revise the femoral component into more external rotation

1%

(14/2654)

4

Revise the patellar component to a more medial position on the native patella

1%

(39/2654)

5

Reevaluate patellar tracking after deflation of the tourniquet

88%

(2339/2654)

ML 1

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PREFERRED RESPONSE 5

(SAE07HK.43) Which of the following aids in correction of patellar tracking after total knee arthroplasty (TKA)? Review Topic

QID: 6003
1

Internal rotation of the femoral component

2%

(2/120)

2

Internal rotation of the tibial component

5%

(6/120)

3

Increasing size of the tibial component

1%

(1/120)

4

Medialization of the patellar component

90%

(108/120)

5

Joint line elevation

2%

(3/120)

ML 1

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PREFERRED RESPONSE 4

(OBQ07.137) The posterior condylar axis may be used to determine the rotation of the femoral component in total knee arthroplasty. Which of the following describes the normal relation of the posterior condylar axis? Review Topic

QID: 798
1

Parallel to the transepicondylar axis

4%

(117/3204)

2

Perpendicular to the anteroposterior axis (Whiteside's line)

3%

(109/3204)

3

3 degrees externally rotated to the transepicondylar axis

33%

(1045/3204)

4

3 degrees internally rotated to the transepicondylar axis

57%

(1841/3204)

5

7 degrees externally rotated to the transepicondylar axis

2%

(78/3204)

ML 4

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PREFERRED RESPONSE 4

(OBQ06.162) Failure to identify a hypoplastic lateral condyle in a valgus knee will result in which of the following errors if a posterior condylar referencing guide is used for total knee arthroplasty? Review Topic

QID: 348
1

External rotation of the femoral component

10%

(243/2503)

2

External rotation of the tibial component

1%

(30/2503)

3

Internal rotation of the femoral component

87%

(2168/2503)

4

Internal rotation of the tibial component

2%

(39/2503)

5

Internal rotation of the tibial and femoral components

0%

(10/2503)

ML 1

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PREFERRED RESPONSE 3

(OBQ05.242) Internal rotation of the femoral component during total knee arthroplasty can result in which of the following? Review Topic

QID: 1128
1

Increased need for lateral release

90%

(1798/1993)

2

Decreased post-operative pain

0%

(4/1993)

3

Increased polyethylene thickness

1%

(15/1993)

4

Decreased post-operative Q angle

8%

(150/1993)

5

Elevation of the native joint line

1%

(20/1993)

ML 1

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PREFERRED RESPONSE 1

(OBQ05.45) Malrotation of total knee components leading to patellar tracking problems is best diagnosed by what radiographic modality? Review Topic

QID: 81
1

3-joint standing x-rays

5%

(123/2487)

2

dynamic examination under anesthesia with fluoroscopy

10%

(243/2487)

3

CT scan of the knee

77%

(1925/2487)

4

45 degree flexed PA x-rays of the knee

7%

(175/2487)

5

magnetic resonance arthrogram of the knee

0%

(6/2487)

ML 2

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PREFERRED RESPONSE 3

(OBQ04.15) Which of the following factors MOST places the knee at risk of patellar maltracking in total knee arthroplasty? Review Topic

QID: 126
1

Thickness of patellar resection

1%

(16/1362)

2

Cruciate retaining component

0%

(4/1362)

3

Medial placement of patellar component

9%

(119/1362)

4

Preoperative patellar tilt

9%

(121/1362)

5

Lateral placement of patellar component

80%

(1095/1362)

ML 2

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PREFERRED RESPONSE 5

(OBQ04.155) Which of the following intra-operative techniques during total knee arthroplasty (TKA) decreases the need for lateral retinacular release? Review Topic

QID: 1260
1

Internal rotation of femoral component

4%

(81/2125)

2

External rotation of femoral component

87%

(1848/2125)

3

Internal rotation of tibial component

3%

(63/2125)

4

Lateralization of patellar component

5%

(102/2125)

5

Insertion of a posterior cruciate retaining device

1%

(28/2125)

ML 1

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PREFERRED RESPONSE 2
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