- Discussion:
- see
anatomy and
biomechanics of the patella;
-
patient characteristics:
- patellar subluxation or dislocation may occur during childhood but is more frequently seen in adolescence;
- in some cases, dislocation occurs in knees w/ patellofemoral dysplasia, but this may be less common than previously thought;
- may occur equally in males and females and often occurs from high level sports;
- ref:
Characteristics of patients with primary acute lateral patellar dislocation and their recovery within the first 6 months of injury.
-
pathophysiology:
- w/ acute traumatic dislocation, at least one medial structure must fail;
- most often the
medial patellofemoral ligament fails off of its femoral attachment, but in some cases it fails off of the patellar attachment;
- alternatively, there may be a fracture at the medial chondro-osseous junction;
- normally the knee is reduced in flexion due to the medializing effect of the lateral trochlear facet;
- as the knee is extended, however, the patella may subluxate or dislocate if static and dynamic restrainst are deficient;
-
associated injuries:
-
osteochondral fracture of the lateral femoral condyle and/or
patella;
- most common sequelae of lateral patellar instability is damage to articular surface of patella, resulting in
chondromalacia patella.
-
pediatric patellar avulsion fractures
-
diff dx:
- subluxation of the patella needs to be distinguished from
malalignment of patella:
-
medial synovial plica:
-
multipartite patella
-
chondromalacia
-
jumper's knee:
-
patellar ligament rupture
-
Sindig-Larsen-Johanssen disease;
- quadriceps contracture:
- patients show habitual patellar dislocation in flexion;
-
risk factors:
-
patella alta (most important)
- generalized ligamentous laxity (perhaps more common with atraumatic instability);
- genu valgum
-
increased femoral anteversion w/ compensatory external tibial torsion;
- ref:
Internal torsion of the distal femur as a cause of habitual dislocation of the patella: a case report and a review of causes of patellar dislocation.
- increased
Q angle
- loss of dynamic stability:
- contribution of distal oblique portion of vastus medialis muscle is critical;
- loss of static stability:
- hypoplastic lateral condyle:
- flat lateral femoral condyle will permit patella to sublux laterally;
- tear of
medial patellofemoral ligament:
-
natural history:
- need to distinguish between traumatic and atraumatic dislocation;
- how and when did the patella reduce;
- references:
-
The natural history of recurrent dislocation of the patella. Long-term results of conservative and operative treatment.
-
Acute patellar dislocations. The natural history. x
-
Patella alta and patella infera. Their etiological role in patellar dislocation, chondromalacia, and apophysitis of the tibial tubercle.
-
Recurrent dislocations and subluxations of the patella.
-
Patella alta and recurrent dislocation of the patella.
-
Recurrent dislocation of the patella. Relation of treatment to OA.
-
Acute patellar dislocation in children: incidence and associated osteochondral fractures.
-
Habitual dislocation of the patella in flexion.
-
Epidemiology and Natural History of Acute Patellar Dislocation.
- Examination of Patellofemoral Joint:
- Radiographic Features: (see:
radiographic evaluation of the knee:)
-
lateral view
- look for
patella alta and/or
patellar osteochondral fracture;
-
axilla view and
merchant technique: (looking for trochlear dysplasia)
- if patella is well centered in groove at 30 deg of flexion, tracking is normal;
- w/ h/o previous patellar dislocation, look for concomitant medial patellar facet fractures;
- because increased flexion results in reduction of subluxated patella, x-rays be obtained w/ in 20 and 45 degrees of flexion;
- note that in children, there will always be an apparent osseous patellofemoral dysplasia, but the cartilaginous border is thicker
than seen in adults;
- references:
-
Radiological measurements in patellofemoral disorders. A review.
-
Radiographic analysis of patellar tilt.
-
Radiology of postnatal skeletal development. X. Patella and tibial tuberosity.
- CT scan:
- CT scanning should be reserved for those difficult cases in which plain radiographs are indeterminate;
- may reveal occult osteochondral fractures;
- may reproduce patellofemoral relationships including normal alignment, lateral patellar tilt, and patellar
subluxation;
- CT images are taken thru the first 45 deg of knee flexion;
- taken at 0 deg, 15 deg, 30 deg, and 45 deg of flexion;
- use the posterior condyles as a reference line for determining tilt;
- Non Operative Treatment:
- acute dislocation:
- if patient presents w/ the patella unreduced, then reduction is effected by flexing the hip and then applying medial stress
while gradually extending the knee;
- first episode of traumatic lateral patellar dislocation or subluxation is treated non operatively unless there is a loose
fracture fragment in the joint;
- a period of immobilizaiton may be needed to allow medial restraints to heal;
- unfortunately, upto 50% of pts will have recurrent episodes of patellofemoral instability, and, in this group,
surgical correction is indicated;
- w/ patellar subluxation, treatment involves
quadriceps strengthening exercises;
- patellar knee sleeves may be of some use, however, prospective studies have failed to demonstate their effectiveness;
-
First-time Traumatic Patellar Dislocation: A Systematic Review.
- Surgical Treatment:
- in child, patellar subluxation or dislocation often requires arthroscopy;
- if osteochondral lesions are encountered, then reduction and pinning is indicated;
- factors which disfavor soft tissue procedures:
- generalized hyper-elasticity
- patellofemoral dysplasia
- increased
Q angle (lateralized tibial tubercle)
- treatment options:
- soft tissue procedures:
-
medial patello-femoral ligament repair:
-
lateral retinacular release:
- indicated only in individuals demonstrating tightness of lateral retinaculum.
- patella tilt test indicates tightness of lateral retinaculum.
- especially poor results are noted when a lateral retinacular release is performed in patients w/ multidirectional patellar instability;
- ref:
Arthroscopically Assisted Medial Reefing Without Routine Lateral Release for Patellar Instability.
- osseous realignment:
-
distal realignment procedures
Preliminary experience with a method of quadricepsplasty in recurrent subluxation of the patella.
Proximal and distal reconstruction of the extensor mechanism for patellar subluxation.
Treatment of acute patellar dislocation.
Surgical treatment of recurrent dislocation of the patella.
Magnetic Resonance Imaging of Patellofemoral Kinematics with Weight-Bearing.
