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Patellar Instability
From WikiSM
Contents
Other Names
- Unstable Patella
Background
- This page refers to instability of the Patella within the Trochlear Groove of the Femur
- This is generally referred to as 'patellar instability' (PI)
- Note that Patellar Dislocation is discussed on a separate page
- Although closely related, they are distinct clinical entities
- Important to distinguish from other causes of Patellofemoral Pain
History
Epidemiology
- Incidence
- 29/100,000 per capita risk of dislocation among adolescents (need citation)
- Prevalence
- 2-3% of presentations involving the knee joint include a history of patellar dislocation (need citation)
- 50-60% of first time lateral patellar dislocations occur secondary to a sport related injury (need citation)
- Up to 40% of skeletally immature patients may develop recurrent instability[1]
- Up to 10% of patients may develop contralateral patellar instability[2]
Pathophysiology
- General
- Defined as recurrent dislocations or sensation that the patella is going to dislocation
- Majority of first time dislocations occur with foot planted, tibia externally rotated
- Most patellar dislocations occur in teen years with patellar instability in 20s-30s
Etiology
- Acute traumatic
- For first episode, see Patellar Dislocation
- Episodic/ recurrent instability/ chronic patholaxity
- Most common type, which occurs after an initial dislocation
- Seen in adolescent athletes, more commonly in women
- Alternative patterns described by Chotel in pediatrics[3]
- Congenital dislocation
- Permanent dislocation
- Habitual dislocation in knee flexion
- Habitual dislocation in knee extension
- Syndromic instability
- Refers to neuromuscular, connective tissue, or other disorders
- Examples include: Cerebral Palsy, Ehlers Danlos Syndrome, Marfan Syndome, Down Syndrome
Associated Conditions
Pathoanatomy
- Patella
- Medial Patellofemoral Ligament
- Primary static restraint to lateral instability during first 30° of flexion
- Prevents excessive lateral movement of the patella
- Medial Retinaculum
- Vastus Medialis Obliquus (VMO)
- Most distal portion of the medial quadriceps muscle
- Exerts a medially directed force that helps keep the patella in position
- Trochlear Groove of the Femur
- Variants in trochlear morphology can predispose the patella to maltracking[4]
- Gross subluxation/dislocation
- Can influence recurrent patellar instability
- Tibial Tubercle
- Arises from the lateral aspect of the proximal tibia
- Excessive lateralization increases tibial external rotation, severe genu valgum, or even increased femoral anteversion[5]
- All affect patellar tracking
Risk Factors
- Age 15-19
- Race
- African American
- Caucasian American
- Orthopedic
- History of Patellar Dislocation
- Weak Vastus Medialis Obliquus (VMO)
- Tight lateral structures: Iliotibial Band, Vastus Lateralis
- Anatomic/ Biomechanical
- Trochlear Dysplasia (OR: 18.1)[6]
- Patella alta (OR: 10.4)
- Patellar tilt
- Lateralization of tibial tubercle or increased elevated TT-TG distance (OR: 2.1)
- Lateral femoral condyle hypoplasia
- Miserable Malalignment Syndrome: femoral anteversion, genu valgum, external tibial torsion
- Connective Tissue Disorders
Differential Diagnosis
- Fractures
- Dislocations & Subluxations
- Patellar Dislocation (and subluxation)
- Knee Dislocation
- Proximal Tibiofibular Joint Dislocation
- Muscle and Tendon Injuries
- Ligament Pathology
- Arthropathies
- Bursopathies
- Patellofemoral Pain Syndrome (PFPS)/ Anterior Knee Pain)
- Neuropathies
- Other
- Bakers Cyst (Popliteal Cyst)
- Patellar Contusion
- Pediatric Considerations
- Patellar Apophysitis (Sinding-Larsen-Johnansson Disease)
- Patellar Pole Avulsion Fracture
- Tibial Tubercle Avulsion Fracture
- Tibial Tuberosity Apophysitis (Osgood Schalatters Disease)
- Proximal Tibial Metaphyseal Fracture
- Proximal Tibial Physeal Injury
Clinical Features
- History
- Important to review history of previous patellar dislocations, episodes of patellar instability
- Patient will complain of anterior knee pain
- Physical Exam: Physical Exam Knee
- In acute setting, hemarthrosis is often present
- Tenderness over MPFL, tenderness over medial femoral condyle
- Special Tests
- Special tests may be deferred in the acute setting
- Consider evaluating for ligamentous laxity using the Beighton Score[7]
- Patellar Apprehension Test: Apply medial and lateral pressure to the patella testing for apprehension
- Patellar J Sign: Evaluate path of patella during flexion and extension
- Patellar Grind Test: Apply pressure to patella with knee in extension, patient contracts quadriceps
- Patellar Glide Test: Passively glide patella medially and laterally
Evaluation
- Standard Radiographs Knee
- Ideally, standard AP and lateral weight bearing views, as well as sunrise view
- May not be possible in setting of acute dislocation
- Plain radiography
- Help identify fractures of the patella, avulsion fractures, loose bodies and sometimes large cartilage defects
- PA radiographs at 45 degrees flexion may aid in assessment of the coronal alignment of the tibiofemoral joint
- Lateral views and Sunrise or Merchant views
- Provide information to trochlear morphology, patellar height and patellar tilt
- Lateral patellar Tilt ((Laurin’s angle))
- Assessed by the lateral patellofemoral angle on sunrise or merchant view
- Angle is measured between a line along the subchondral bone of the lateral trochlear facet and posterior femoral condyles
- Normal: angle greater than 11° that opens laterally
- Abnormal angles: parallel or open medially
- Patellar height
- Can be measured by both direct and indirect methods
- The Insall-Salvati Ratio: ratio measuring the length of the patella ligament, patellar length
- A normal ratio is 1.0; a ratio of 1.2 suggests patella alta and 0.8 patella baja
- Caton-Deschamps Index (CDI): distance between the distal point of the patellar articular surface and the anterior superior margin of the tibia, divided by the patellar articular surface length
- A normal ratio is 1.0; a ratio of less than 0.6 suggests patella baja and a ratio of 1.3 suggests patella alta
- Blackburne-Peel method (BP): ratio of the height of the lower pole of the articular surface above a tibial plateau line to the articular surface length of the patella
- Normal between 0.54- 1.06; A ratio of less than 0.54 is considered to be patella alta
- Technique described by Blumensaat uses the roof of the intercondylar notch as a reference line and is one of the most commonly used direct methods for the assessment of patellar height
- True lateral radiographs and sunrise views can help identify other risk factors
- The trochlear findings were elucidated by Dejour and Le Coultre and were subsequently revised to create the trochlear dysplasia classification system [8]
- Crossing sign: occurs when the trochlear groove lies in the same plane as the anterior border of the lateral condyle, which represents a flattened trochlear groove
- Double contour sign: occurs when the anterior border of the lateral condyle lies anterior to the anterior border of the medial condyle, which represents a convex trochlear groove or hypoplastic medial condyle
- Supratrochlear spur can arise from the proximal aspect of the trochlea and can also indicate a risk factor
CT
- Computed tomographic (CT)
- Can more accurately characterize the morphology of the trochlea
- Assess femoral and tibial torsion
- Tibial tubercle to trochlear groove (TT-TG) distance
- Assesses relative rotation of femur to tibia
- The TT-GG distance is between two perpendicular lines; one from the posterior cortex to the tibial tubercle and one from the posterior cortex to the trochlear groove
- Average 8-10 mm in pediatric and adult patients; a TT-TG distance of greater than 20 is highly associated with patellar instability.
MRI
- Common Findings[9]
- Bruising pattern of lateral femoral condyle, medial patella
- Disruption of the MPFL (at the medial femoral epicondyle insertion)
- Articular cartilage injuries if present
Classification
Parikh Classification of Patellar Instability
- Type I: first patellofemoral dislocation with (A) or without (B) osteochondral fracture[10]
- Type II: recurrent subluxation (A) or dislocation (B)
- Type III: dislocatable patella by the examiner or patient which is either passive (A) or habitual in flexion/extension (B).
- Type IV: dislocated patella that is either reducible (A) or irreducible (B).
Management
Prognosis
Nonoperative
- Indications
- Majority of cases
- Absence of loose bodies or osteochondral fragments, other soft tissue injuries
- NSAIDS
- Physical Therapy
- Emphasis: Quadriceps/ VMO Strengthening, core and hip strengthening
- Kinesiology Taping
- Knee Immobilizer
- May be indicated early in acute setting
- Patellar Brace
- Patellar stabilizing sleeve or "J" brace
Operative
- Indications
- Failure of conservative management
- Associated osteochondral fragment (≥ 5 mm)
- Associated osseous avulsion of the MPFL
- Associated meniscus tear
- Techniques
- Medial patellofemoral ligament reconstruction
- MPFL reconstruction with autograft vs allograft
- Trochleoplasty
- Tibial tubercle osteotomy
- Arthroscopic debridement (removal of loose body) vs Repair
- Fulkerson-type osteotomy (anterior and medial tibial tubercle transfer)
- Tibial tubercle distalization
- Lateral release
Rehab and Return to Play
Rehabilitation
- Needs to be updated
Return to Play
- Full recovery time to return to sport ranges from 3-8 months
- Depends on any procedures performed
- Return to sport following Menetrey guidelines[11]
- Full recovery of knee motion
- Recovery of strength
- Absence of a knee effusion, pain
- Competence with sport specific exercises
- Strongly consider
- Patellar Stabilizing Brace up to 1 year
- Kinesiology Taping]
Complications
- Patellofemoral Osteoarthritis
- Up to 20% of cases at 20 years following initial dislocation[2]
- Patella Fracture
- Can occur as a surgical complication
- Recurrent instability
- Failure of surgical fixation
- Inability to return to sport
- Quadriceps weakness
- Pediatric specific complications
- Physeal arrest
See Also
- Internal
- External
- Sports Medicine Review Knee Pain: https://www.sportsmedreview.com/by-joint/knee/
References
- ↑ Lewallen LW, McIntosh AL, Dahm DL. Predictors of recurrent instability after acute patellofemoral dislocation in pediatric and adolescent patients. Am J Sports Med. 2013;41(3):575–81.
- ↑ 2.0 2.1 Sanders TL, Pareek A, Hewett TE, Stuart MJ, Dahm DL, Krych AJ. High rate of recurrent patellar dislocation in skeletally immature patients: a long-term population-based study. Knee Surg Sports Traumatol Arthrosc. 2017
- ↑ Chotel F, Berard J, Raux S. Patellar instability in children and adolescents. Orthop Traumatol Surg Res. 2014;100(1 Suppl):S125–37.
- ↑ Weber-Spickschen TS, Spang J, Kohn L, Imhoff AB, Schottle PB. The relationship between trochlear dysplasia and medial patellofemoral ligament rupture location after patellar dislocation: An MRI evaluation. Knee. 2011;18:185–8
- ↑ Steensen RN, Bentley JC, Trinh TQ, Backes JR, Wiltfong RE. The prevalence and combined prevalences of anatomic factors associated with recurrent patellar dislocation: A magnetic resonance imaging study. Am J Sports Med. 2015;43:921–7.
- ↑ Christensen TC, Sanders TL, Pareek A, Mohan R, Dahm DL, Krych AJ. Risk factors and time to recurrent ipsilateral and contralateral patellar dislocations. Am J Sports Med. 2017;45(9):2105–10.
- ↑ Beighton P, Solomon L, Soskolne CL. Articular mobility in an African population. Ann Rheum Dis. 1973 Sep;32(5):413-8
- ↑ Dejour D, Le Coultre B. Osteotomies in patello-femoral instabilities. Sports Med Arthrosc. 2007 Mar;15(1):39-46
- ↑ Elias DA, White LM, Fithian DC. Acute lateral patellar dislocation at MR imaging: injury patterns of medial patellar soft-tissue restraints and osteochondral injuries of the inferomedial patella. Radiology. 2002 Dec;225(3):736-43.
- ↑ Parikh SN, Lykissas MG. Classification of lateral patellar instability in children and adolescents. Orthop Clin North Am. 2016;47(1):145–52.
- ↑ Menetrey J, Putman S, Gard S. Return to sport after patellar dislocation or following surgery for patellofemoral instability. Knee Surg Sports Traumatol Arthrosc. 2014;22(10):2320–6.
Created by:
John Kiel on 15 March 2021 18:40:10
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Last edited:
4 October 2022 15:55:42
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