Patellar Instability

Author: David Abbasi

Topic updated on 05/05/13 9:52pm

Introduction

Can be classified into following terms
- acute
  - occurs equally by gender
- recurrent
  - occurs more in women
- subluxation
- habitual
Epidemiology
- demographics
  - most commonly occurs in 2nd-3rd decades of life
- risk factors
  - ligamentous laxity (Ehlers-Danlos syndrome)
  - dysplastic vastus medialis oblique (VMO) muscle
  - lateral displacement of patella
  - patella alta
    - causes patella to not articulate with sulcus, losing its constraint effects
  - trochlear dysplasia
  - excessive lateral patellar tilt (measured in extension)
  - lateral femoral condyle hypoplasia
  - increased quadriceps angle (Q angle)
    - average for women 15 degrees
    - average for men 10 degrees
  - previous patellar instability event
  - "miserable malalignment syndrome"
    - a term named for the 3 anatomic characteristics that lead to an increased Q angle
      - femoral anteversion
      - genu valgum
      - external tibial torsion / pronated feet
Mechanism
- usually on noncontact twisting injury with the knee extended and foot externally rotated
- patient will usually reflexively contract quadriceps, reducing patella back into trochlear groove
  - osteochondral fractures occur most often as the patella relocates

Anatomy

Passive stability
- medial patellofemoral ligament (MPFL)
  - femoral insertion origin is between medial epicondyle and adductor tubercle
    - is usual site of avulsion of MPFL
  - is primary restraint in first 20 degrees of knee flexion
- patellar-femoral bony structures account for stability in deeper knee flexion
Dynamic stability
- provided by vastus medialis (attaches to MPFL)

Presentation

Symptoms
- anterior knee pain
Physical exam
- large hemarthrosis
  - absence of swelling supports ligamentous laxity and habitual dislocation mechanism
- medial sided tenderness (over MPFL)
- increase in passive patellar translation
  - measured in quadrants of translation (midline of patella is considered "0"), and also should be compared to contralateral side
  - normal motion is <2 quadrants of patellar translation
    - lateral translation of medial border of patella to lateral edge of trochlear groove is considered "2" quadrants and is considered abnormal amount of translation
- patellar apprehension
- increased Q angle
- J sign
  - excessive lateral translation in extension which "pops" into groove as the patella engages the trochlea early in flexion
  - associated with patella alta

Imaging

Radiographs
- rule out fracture or loose body
  - medial patellar facet (most common)
  - lateral femoral condyle
- AP views
  - best to evaluate overall lower extremity alignment and version
- lateral views
  - best to assess for trochlear dysplasia
  - evaluate for patellar height (patella alta vs baja)
    - Blumentsaat's line should extend to inferior pole of the patella at 30 degrees of knee flexion
    - Insall-Salvati method
      - normal between 0.8 and 1.2
    - Blackburne-Peel method
      - normal between 0.5 and 1.0
    - Caton Deschamps method
      - normal between 0.6 and 1.3
    - Plateau-patella angle
      - normal between 20 and 30 degrees
- axial views
  - best assess for lateral patellar tilt
  - lateral patellofemoral angle
MRI
- help further rule out suspected loose bodies
  - osteochondral lesion and/or bone bruising
  - medial patellar facet (most common)
  - lateral femoral condyle
- tear of MPFL
  - tear usually at medial femoral epicondyle

Adult Treatment

Nonoperative
- NSAIDS, activity modification, and physical therapy
  - indications
    - mainstay of treatment for first time patellar dislocator
      - without any loose bodies or intraarticular damage
    - habitual dislocator
  - techniques
    - short-term immobilization for comfort followed by 6 weeks of controlled motion
    - emphasis on strengthening
      - closed chain short arc quadriceps exercises
      - VMO strengthening
      - core strengthening of hip abductors, gluteals, and abdominals
    - patellar stabilizing sleeve or "J" brace
    - consider knee aspiration for tense effusion
      - positive fat globules indicates fracture
Operative
- arthroscopic debridement vs ORIF
  - indications
    - displaced osteochondral fractures or loose bodies
    - chronic patellofemoral instability
  - techniques
    - arthroscopic vs open
- MPFL repair
  - indications
    - acute first time dislocation
  - techniques
    - direct repair when surgery can be done within first few days
      - no clinical studies support this over nonoperative treatment
- MPFL reconstruction with autograft vs allograft
  - indications
    - recurrent instability
  - techniques
    - gracilis or semitendinosus commonly used (stronger than native MPFL)
    - femoral orgin can be reliably found radiographically (Schottle point)
- Fulkerson osteotomy (anterior and medial tibial tubercle transfer)
  - indications
    - increased Q angle with lateralized tibial tubercle
  - techniques
    - anteromedialized displacement of osteotomy and fixation
- tibial tubercle distalization
  - indications
    - patella alta
  - techniques
    - distal displacement of osteotomy and fixation
- lateral release
  - indications
    - only indicated if there is a lateral tilt
  - technique
    - arthroscopic
- trochleoplasty
  - indications
    - if trochlear dysplasia present
  - techniques
    - arthroscopic deepening procedure
- osteochondral defect repair
  - indications
    - large osteochondral loose body
  - techniques
    - primary repair vs allograft depending on size

Pediatric Treatment

Same principles as adults in general but
- must preserve the physis
  - do not do tibial tubercle osteotomy (will harm growth plate of proximal tibia)

Complications

Recurrent dislocation
- redislocation rates of 15-44% have directed interest more towards surgical treatment
Medial patellar dislocation and medial patellofemoral arthritis
- almost exclusively iatrogenic as a result of prior patellar stabilization surgery

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Qbank (7 Questions)

TAG

(OBQ11.188) Which of the following best describes the radiographic landmarks on a lateral radiograph for locating the femoral attachment of the medial patellofemoral ligament (MPFL) during reconstruction? Topic

Review Topic

1. The intersection of a line extended from the middle of the shaft and Blumensaat's line
2. Anterior to a line extended from the middle of the shaft and Blumensaat's line
3. Posterior to a line extended from the posterior cortex of the shaft and distal to Blumensaat's line
4. Anterior to a line extended from the posterior cortex of the shaft and distal to Blumensaat's line
5. Anterior to a line extended from the posterior cortex of the shaft and proximal to Blumensaat's line

PREFERRED RESPONSE ▶

DISCUSSION: Correct positioning of a graft for MPFL reconstruction requires accurate placement of the femoral attachment site which is anterior to a line extended from the posterior cortex and just proximal to the posterior extension of Blumensaat's line. Intra-operative fluoroscopy can be used to accurately identify this position.

Schottle et al have described the radiographic landmark to be 1 mm anterior to the posterior cortex extension line, 2.5 mm distal to the posterior origin of the medial femoral condyle, and proximal to the level of the posterior point of the Blumensaat line.

Redfern et al evaluate this radiographic point and found it to be within 4mm of the true attachment on anatomic dissection.

This is demonstrated in Illustration A: the star shows the correct location anterior to the posterior cortical extension line (solid black line), proximal to Blumensaat's (red) line, and between the posterior origin of the medial femoral condyle and the posterior aspect of Blumensaat's line (perpendicular dashed lines).

Illustrations: A

REFERENCES:

1. Schöttle PB, Schmeling A, Rosenstiel N, Weiler A. Radiographic landmarks for femoral tunnel placement in medial patellofemoral ligament reconstruction. Am J Sports Med. 2007 May;35(5):801-4. PMID:17267773 (Link to Abstract)

2. Redfern J, Kamath G, Burks R. Anatomical confirmation of the use of radiographic landmarks in medial patellofemoral ligament reconstruction. Am J Sports Med. 2010 Feb;38(2):293-7. PMID:19822768 (Link to Abstract)

Question Authors:

Patrick McCulloch MD, John Badylak MD, Ben Taylor MD,

Please Rate Educational Value!

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Related Videos

MPFL reconstruction for patella dislocation

Sports - Educational Presentation - Patellar Instability

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TAG

(OBQ10.188) A 27-year-old football player sustains an acute lateral patellar dislocation. Which of the following is the most likely site of injury seen on MRI? Topic

Review Topic

1. Soft-tissue patellar-sided avulsion of medial patellofemoral ligament
2. Soft-tissue femoral-sided avulsion of medial patellofemoral ligament
3. Midsubstance medial patellofemoral ligament rupture
4. Bony femoral avulsion of medial patellofemoral ligament
5. Bony patellar avulsion of medial patellofemoral ligament

PREFERRED RESPONSE ▶

DISCUSSION: The most common site of medial patellofemoral ligament (MPFL) injury is a soft-tissue avulsion injury of the ligament off the femur. Both midsubtance and patellar-sided soft tissue avulsions are more common than bony avulsions. Bony avulsion off the patella can occur as well, and according to the referenced study by Torisuka et al, the MPFL remains attached to the medial patellar fragment and excellent clinical and radiographic results can occur with open reduction and fixation with suture anchors. The reported study by Nomura et al reported that MRI is >80% sensitive and >80% specific (regarding location) for detecting MPFL injuries as well as their location. In addition, they noted a 96% MPFL injury rate with patellar dislocation.

REFERENCES:

1. Toritsuka Y, Horibe S, Hiro-Oka A, Mitsuoka T, Nakamura N. Medial marginal fracture of the patella following patellar dislocation. Knee. 2007 Dec;14(6):429-33. PMID:17884512 (Link to Abstract)

2. Nomura E, Horiuchi Y, Inoue M. Correlation of MR imaging findings and open exploration of medial patellofemoral ligament injuries in acute patellar dislocations. Knee. 2002 May;9(2):139-43. PMID:11950578 (Link to Abstract)

Question Authors:

Ben Taylor MD, Patrick McCulloch MD, John Badylak MD,

Please Rate Educational Value!

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Average 4.0 of 6 Ratings

TAG

(OBQ08.49) A high school softball player has chronic activity-related anterior knee pain without a history of instability. Which radiographic measurement is used to indicate when a lateral retinacular release may be helpful? Topic

Review Topic

1. Congruence angle
2. Q angle
3. Sulcus angle
4. Lateral patello-femoral angle
5. Patellar height index

PREFERRED RESPONSE ▶

DISCUSSION: The lateral patello-femoral angle is the angle formed by lateral patellar facet and a line drawn across most prominent aspects of anterior portion of the trochlea on a CT scan or Sunrise view radiograph. If there is a negative patellar tilt on this measurement, the patient may benefit from a lateral release for pain relief. Lateral release is not used for instability. The sulcus angle refers to the depth of the trochlea; the congruence angle measures the relationship of the center of the patella to the center of the trochlea. These are used to assess malalignment and instability.

Illustrations: A

REFERENCES:

2. Nha KW, Papannagari R, Gill TJ et al. In vivo patellar tracking: clinical motions and patellofemoral indices. J Orthop Res. 2008 Aug;26(8):1067-74. PMID:18327809 (Link to Abstract)

3. Grelsamer RP, Weinstein CH, Gould J, Dubey A. Patellar tilt: the physical examination correlates with MR imaging. Knee. 2008 Jan;15(1):3-8. Epub 2007 Nov 26. Review. PMID:18023186 (Link to Abstract)

Question Authors:

Patrick McCulloch MD, Guillem Lomas MD, Derek Moore,

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TAG

(OBQ07.30) An athlete sustains a traumatic patellar dislocation. The MRI shows a hemarthrosis with a floating osteochondral fragment. Which of the following is the most likely site of origin for the loose fragment? Topic

Review Topic

1. The lateral patellar facet
2. The medial patellar facet
3. The odd patellar facet
4. The medial trochlea
5. The central trochlea

PREFERRED RESPONSE ▶

DISCUSSION: Lateral patellar dislocations are by far the most common. The medial facet of the patella will impact on the lateral trochlear ridge. Either of these would be acceptable answers, but lateral trochlea is not listed. Even without an osteochondral fracture, an MRI of an acute patellar dislocation will generally show bone bruises in these two locations.

Nomura looked at 39 consecutive arthroscopies after lateral dislocation and 95% had patellar chondral defects. They also reported that the medial facet of the patella is the most commonly injured site of the patella.

REFERENCES:

2. Nomura E, Inoue M, Kurimura M. Chondral and osteochondral injuries associated with acute patellar dislocation. Arthroscopy 2003; 19: 717-21. PMID:12966379 (Link to Abstract)

Question Authors:

Patrick McCulloch MD, Derek Moore, Ben Taylor MD,

Please Rate Educational Value!

4.0

Average 4.0 of 8 Ratings

TAG

(OBQ07.112) Which of the following is associated with the highest risk of recurrent patellar instability following a traumatic lateral patellar dislocation? Topic

Review Topic

1. Younger age
2. Increased Q-angle
3. Male gender
4. Previous patellar instability event
5. Amount of lateral patellar tilt

PREFERRED RESPONSE ▶

DISCUSSION: Females (not males) have a higher incidence of patellofemoral instability due to their increased Q-angle. The Q-angle or quadriceps angle is the angle formed by the intersection of a line from the ASIS to the patella and from the patella to the tibial tubercle as demonstrated in Illustration A. Normal Q-angle in males is 14 degrees and in females is 18 degrees. A higher angle means that there is a larger lateral vector force on the patella, which predisposes to lateral patellar instability. While an increased Q-angle increases the chance for dislocation, a previous history of dislocation is the strongest predictor.

Fithian et al prospectively followed 189 patients for 2-5 years and found that the risk was highest among females 10 to 17 years old and those with previous instability episodes. Patients with a prior history had 7 times higher odds of subsequent instability episodes during follow-up than first time dislocators.

Illustrations: A

REFERENCES:

1. Fithian DC, Paxton EW, Stone ML, Silva P, Davis DK, Elias DA, White LM. Epidemiology and natural history of acute patellar dislocation. AJSM 2004;32:1114-1121 PMID:15262631 (Link to Abstract)

2. Garrick JG (ed): Orthopaedic Knowledge Update: Sports Medicine 3. American Academy of Orthopaedic Surgery, Rosemont, IL, 2004, pp213-221

Question Authors:

Patrick McCulloch MD, Derek Moore, Ben Taylor MD,

Please Rate Educational Value!

4.0

Average 4.0 of 9 Ratings

TAG

(OBQ04.46) All of the following are predisposing factors for lateral patellar dislocation in a native knee EXCEPT? Topic

Review Topic

1. Excess femoral internal rotation
2. Excess external tibial rotation
3. Lateral femoral condylar hypoplasia
4. Increased Q-angle
5. Insufficiency of the vastus lateralis

PREFERRED RESPONSE ▶

DISCUSSION: Predisposing factors to lateral patellar dislocation include: excess femoral internal rotation, external rotation of the tibia, lateral femoral condyle hypoplasia, insufficiency of the VMO, an increased Q angle, a tight lateral retinaculum, patella alta, patella tilt, generalized ligamentous laxity, and patellofemoral dysplasia. The common theme throughout this list of predisposing features is an inequality in forces acting medially and laterally on the patella, with resultant higher rates of lateral patellar dislocation.

Dejour et al examined CT scans on 134 patients treated for patellar instability. They identified 4 common factors the unstable symptomatic knees: 1. Trochlear dysplasia (85%), 2. Quadriceps dysplasia (83%), 3. Patella alta (24%), 4. Tibial tuberosity-trochlear groove, pathological when greater than or equal to 20 mm (56%).

REFERENCES:

1. Halbrecht JL, Jackson DW: Acute Dislocation of the patella, in Fox, JM Delpizzo W (eds): The patellofemoral joint. 1993, p 123.

2. Dejour H, Walch G, Nove-Josserand L, Guier C. Factors of patellar instability: an anatomic radiographic study. Knee Surg Sports Traumatol Arthrosc. 1994;2(1):19-26. PMID:7584171 (Link to Abstract)

Question Authors:

Patrick McCulloch MD, Derek Moore, John Badylak MD,

Please Rate Educational Value!

3.0

Average 3.0 of 12 Ratings

Cases

	MPFL rupture, patella instability, lateral meniscus tear (C1059) Sports - - Patellar Instability HPI - Patient underwent a RIGHT tibial tubercle transfer, VMO quadricepsplasty, and la... Would you treat this patient with PT or early surgery?	9/21/2011 80 responses
	Medial patellofemoral ligament rupture (C1221) Sports - Treatment Consult - Patellar Instability HPI - 22 y/o male s/p traumatic patellofemoral dislocation 9 months ago. Failed conse... What would you do for this patient to correct patellofemoral instability?	6/14/2012 167 responses

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Videos

	MPFL reconstruction for patella dislocation Sports - Educational Presentation - Patellar Instability Demonstration of hamstring autograft reconstruction of the medial patellofemoral...	4/21/2013 112 views 4
	MPFL Reconstruction with Free Soft Tissue Graft - Dr. Mark Miller Sports - Surgical Techniques - Patellar Instability This video demonstrates a MPFL Reconstruction using a Free Soft-Tissue Graft per...	10/11/2012 269 views 4
	Fulkerson Osteotomy - Dr. Mark Miller Sports - Surgical Techniques - Patellar Instability This video demonstrates a Fulkerson osteotomy.	9/25/2012 440 views 5
	Medial Patello Femoral Ligament Reconstruction Sports - Techniques - Patellar Instability Medial Patello Femoral Ligament Reconstruction for Acute Patella dislocation / m...	1/16/2012 118 views 5
	Dynamic J Sign in patellofemoral joint instability Sports - Physical Exam - Patellar Instability The VDO shows the "Dynamic J Sign" of left knee. This sign represents patellofem...	1/16/2012 45 views 0
	True Patellar "J Sign" Sports - Physical Exam - Patellar Instability This is an example of the patellar "J Sign". The patella subluxes laterally in a...	1/15/2012 1430 views 4
	"Reverse" J sign of patellofemoral instability Sports - Physical Exam - Patellar Instability Clinical video showing "reverse" J sign with chronic patellofemoral instability....	12/4/2011 89 views 0

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Groups

ABOS II: Patellar Instability

General - Oral Boards Review

7/29/2011

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Evidence & References Show References

Level of Evidence 4 (Case Series)

Toritsuka Y, Horibe S, Hiro-Oka A, Mitsuoka T, Nakamura N. Medial marginal fracture of the patella following patellar dislocation. Knee. 2007 Dec;14(6):429-33. PMID:17884512 (Link to Abstract)

Level of Evidence 5 and Other Journal Articles (includes Case Reports, Expert Opinions, Personal Observations, and Biomechanic Studies)

Wijdicks CA, Griffith CJ, LaPrade RF, Johansen S, Sunderland A, Arendt EA, Engebretsen L. Radiographic identification of the primary medial knee structures. J Bone Joint Surg Am. 2009 Mar 1;91(3):521-9. PMID:19255211 (Link to Abstract)
Schöttle PB, Schmeling A, Rosenstiel N, Weiler A. Radiographic landmarks for femoral tunnel placement in medial patellofemoral ligament reconstruction. Am J Sports Med. 2007 May;35(5):801-4. Epub 2007 Jan 31. PMID:17267773 (Link to Abstract)
Nomura E, Horiuchi Y, Inoue M. Correlation of MR imaging findings and open exploration of medial patellofemoral ligament injuries in acute patellar dislocations. Knee. 2002 May;9(2):139-43. PMID:11950578 (Link to Abstract)

Textbooks

Review of Orthopaedics, 6th Edition, Mark D. Miller MD, Stephen R. Thompson MBBS MEd FRCSC, Jennifer Hart MPAS PA-C ATC, an imprint of Elsevier, Philadelphia, Copyright 2012
AAOS Comprehensive Orthopaedic Review, Jay R. Leiberman. Published by American Academy of Orthopaedic Surgeons, Rosemont IL. Copyright 2009
Orthopaedic Knowledge Update 10, John M Flyn. Published by American Academy of Orthopaedic Surgeons, Rosemont IL. Copyright 2011
Hoppenfeld SP. Surgical Exposures in Orthopaedics: The Anatomic Approach. Lipponcott, Williams, and Wilkins, Philadelphia, PA, Copyright 2009
Orthopaedic In-training Examination (OITE) Questions 2004-2012, American Academy of Orthopaedic Surgeons, Rosemont IL. Copyright 2004-2012
Self-Assessment Examination (SAE) Questions 2004-2012, American Academy of Orthopaedic Surgeons, Rosemont IL. Copyright 2004-2012

Undefined

Schöttle PB, Schmeling A, Rosenstiel N, Weiler A. Radiographic landmarks for femoral tunnel placement in medial patellofemoral ligament reconstruction. Am J Sports Med. 2007 May;35(5):801-4. PMID:17267773 (Link to Abstract)
Redfern J, Kamath G, Burks R. Anatomical confirmation of the use of radiographic landmarks in medial patellofemoral ligament reconstruction. Am J Sports Med. 2010 Feb;38(2):293-7. PMID:19822768 (Link to Abstract)
Orthopaedic Knowledge Update: Sports Medicine 3. Garreck JG (editor) American Academy of Orthopaedic Surgeons. Rosemont, IL. Copyright 2004.
Nha KW, Papannagari R, Gill TJ et al. In vivo patellar tracking: clinical motions and patellofemoral indices. J Orthop Res. 2008 Aug;26(8):1067-74. PMID:18327809 (Link to Abstract)
Grelsamer RP, Weinstein CH, Gould J, Dubey A. Patellar tilt: the physical examination correlates with MR imaging. Knee. 2008 Jan;15(1):3-8. Epub 2007 Nov 26. Review. PMID:18023186 (Link to Abstract)
Garrick(ed) Orthopaedic Knowledge Updat: Sports Medicine 3. American Academy of Orthopaedic Surgeons. Rosemont IL. Copyright 2004
Nomura E, Inoue M, Kurimura M. Chondral and osteochondral injuries associated with acute patellar dislocation. Arthroscopy 2003; 19: 717-21. PMID:12966379 (Link to Abstract)
Fithian DC, Paxton EW, Stone ML, Silva P, Davis DK, Elias DA, White LM. Epidemiology and natural history of acute patellar dislocation. AJSM 2004;32:1114-1121 PMID:15262631 (Link to Abstract)
Garrick JG (ed): Orthopaedic Knowledge Update: Sports Medicine 3. American Academy of Orthopaedic Surgery, Rosemont, IL, 2004, pp213-221
Halbrecht JL, Jackson DW: Acute Dislocation of the patella, in Fox, JM Delpizzo W (eds): The patellofemoral joint. 1993, p 123.
Dejour H, Walch G, Nove-Josserand L, Guier C. Factors of patellar instability: an anatomic radiographic study. Knee Surg Sports Traumatol Arthrosc. 1994;2(1):19-26. PMID:7584171 (Link to Abstract)

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Patellar Instability

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