Dislocation of Patella

• Largest sesamoid bone• Thick articular cartilage

proximally• Articular surface

divided into medial and lateral facets by a longitudinal ridge

• Distal pole nonarticular• The patella lies within

the fascia lata and the fibers of the quadriceps tendon

Extraosseous and Intraosseous vascular systems The primary blood supply to the patella is from a dorsal

arterial ring derived from branches of the geniculate anastomotic system around the knee

The arterial ring is made up of a central superior geniculate vessel; medial, lateral superior, and lateral inferior geniculate vessels; and an inferior recurrent tibial vessel

The primary intraosseous blood supply of the patella enters the bone by vessels through the middle of the anterior portion of the body of the patella and through the distal pole vessels

Arterial Blood Supply

The patellar retinaculum derives from the deep investing fascia lata in combination with the aponeurotic fibers from the vastus medialis and vastus lateralis

The retinaculum inserts directly into the proximal tibia Contributions from the lateral aspect of the vastus

lateralis, iliotibial tract, and patellofemoral ligaments of the joint capsule help to complete the retinaculum

The patella tendon originates at the apex of the patella and inserts into the tibial tubercle

The patella retinaculum and the iliotibial track fibers blend into the patella tendon at the insertion on the anterior portion of the proximal tibia.

Anatomy of soft tissue

PATELLA CAN BE DISPLACED UPWARDS-PATELLA ALTA

DOWN WARDS-PATELLA INFERA LATERAL MEDIAL LATERAL COMMON, ALL OTHES RARE

LATERAL DISLOCATION IS THE MOST LIABLE TO RECURRENT DISLOCATION/HABITUAL DISLOCATION.

MORE COMMON IN FEMALES Q ANGLE-MALES 8-10 FEMALES 15 FACTORS THAT INCREASE Q ANGLE CAUSE

RECURRENT PATELLAR DISLOCATION

The Q(quadriceps) angle is measured from the anterior superior iliac spine through the patella and to the tibial tubercle

Q angle

Subluxation or dislocation of the patellofemoral joint most commonly occurs secondary to a rotational or twisting injury with simultaneous contraction of the quadriceps.

Less commonly glancing blows to the knee can cause dislocation of the patella

Mechanism of Injury

Increased Q angle (laterally inserted patellar tendon, excessive tibial external rotation or genu valgum, femoral anteversion or internal rotation)

Patella alta Insufficient lateral trochlea or shallow

patellofemoral groove Vastus medialis atrophy Insufficient medial patellofemoral ligament Genu recurvatum or patellar hypermobility

Predisposing abnormalities

Severe pain, deformity of the anterior knee and flexed position is characteristic of an acutely dislocated patella

Palpation will reveal the abnormal position of the patella

Patellofempral crepitus is palpable Wasting of quadriceps and vastus medialis Frequently patella reduces spontaneous When the patella is reduced by the knee being

straightened manually by an observer, usually a loud pop or crack is noted with significant improvement in pain

Signs and Symptoms

Examination of the reduced patellar dislocation reveals a large effusion and medial patellar tenderness

Occasionally a defect in the medial retinaculum can be palpated

Flexion is limited due to the medial soft tissue injury and the presence of the large effusion

Usually tenderness + in the area of the superior medial pole of the patella

Palpation of the undersurface of the patella and the lateral femoral condylar edge are helpful in identifying an acute osteochondral fracture

In the presence of a loose articular piece > mechanical locking symptoms

With a recurrent patellar dislocation or subluxation, the swelling and pain are usually less than those of the first injury

Anteroposterior, tunnel, lateral and axial patellofemoral views (most commonly the technique of Merchant)

Bilateral views

Radiographic Evaluation

Tunnel views – evaluating loose bodies that can come to lie in the femoral notch

Anteroposterior views – evaluation of patellar shape, partition and evidence of fracture

Lateral view – determination of patellar height, fractures and patellofemoral arthritic changes

Axial views (sunrise view) – evaluating intraarticular fractures, trochlear position of the patella, patellofemoral arthritis and avulsion injury of the medial patellofemoral ligament

Evaluation of patellar height for recognition of patella alta or infera is routinely performed on a lateral view

Insall and Salvati A ratio is measured between the length of the

patella and that of the patellar tendon On average the ratio of LT/LP is 1.02 with a

standard deviation of 0.13 A ratio of 0.80 or less > patella infera, >1.20

patella alta

Conservative management should be used when possible and includes maintenance of quadriceps strength, functional retraining and control of swelling and pain

Surgical techniques should be used for chronic patellar problems only after conservative treatment has failed over a significant time period usually 4 to 6 months

Methods of Treatment

Closed reduction can be performed Extensor mechanism integrity evaluated Quality of reduction assessed Intraarticular fragments looked for

Asymmetrically subluxed or tilted patella or evidence of an intraarticular fragment are indications for operative treatment with repair of the medial patellofemoral ligament, lateral release and removal or internal fixation of the osteochondral fragment

Acute Dislocation

Non Operative treatment includes casting in extension for 6 weeks and early range of motion exercises with functional rehabilitation

LATERAL RETINACULAR RELEASE PROXIMAL EXTENSOR REALIGNEMENT DISTAL EXTENSOR REALIGNMENT PROXIMAL AND DISTAL REALIGNEMENT PATELLECTOMY WITH EXTENSOR

REALIGNEMENT DURING ALL SURGICAL PROCEDURES

THOROUGH LOOK OF ARTICULAR SURFACE NECCESARY

Surgical repair involves EUA followed by a thorough evaluation of the articular surfaces to rule out a chondral or osteochondral fracture

Small patellar fragments should be debrided Large fragments or those that involve the

femoral weight-bearing surface should be reduced and fixed using biodegradable implants

Repair of the medial patellofemoral ligament and torn retinaculum

Overtensioning may cause medial subluxation of the patella

Indications for a lateral release involve preexisting tilt, increased Q angle and lateral patellar subluxation

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