Reduction of Patellar Dislocation 

Updated: Apr 05, 2019
Author: Moira Davenport, MD; Chief Editor: Erik D Schraga, MD 

Overview

Background

Patellar dislocations are common, particularly in adolescent females and athletes. Patients usually present with an inability to extend an obviously deformed knee. A sizable effusion may also be seen. This injury may be due to direct trauma to the patella or to a valgus stress combined with flexion and external rotation.[1]

The reported incidence of patellar dislocation is 5.8 per 100,000, but it may be as high as 29 per 100,000 in the adolescent population.[2]  There are several varieties of patellar dislocation, as follows:

  • Lateral - The most common type of patellar dislocation
  • Horizontal - A rare occurrence, in which the patella has rotated on its horizontal axis with the articular surfaces facing either proximally or distally
  • Vertical - Also a very uncommon event, in which the patella rotates around its vertical axis with impaction of one of the lateral surfaces in the intercondylar notch of the femur
  • Intercondylar - Any type of dislocation in which the patella remains in its anatomic position and may be rotated around its vertical or horizontal axis

Several anatomic factors, including a lateralized tibial tubercle,[3]  the tibial tuberosity–trochlear groove distance,[3, 4]  the tibial tuberosity–posterior cruciate ligament distance,[5] the shape and dimensions of the patella,[6, 7]  and the width of the patellar tendon,[7] may increase the likelihood of lateral patellar dislocation.

Reduction of a lateral dislocation of the patella is a simple and safe procedure. Otherwise, an orthopedist should be consulted for these more uncommon types of dislocations.

Indications

Nonsurgical reduction can be attempted on any lateral or medial dislocation of the patella. An immediate attempt at reduction should be made on any dislocation associated with vascular compromise of the distal extremity, though this is exceedingly uncommon in the setting of an isolated lateral patellar dislocation and should prompt further examination into possible concurrent injuries.

Some surgeons have advocated surgical rather than nonsurgical intervention to treat patellar dislocation, out of concern for possible recurrence. A Cochrane review by Smith et al found that although there was some evidence appearing to favor surgical management of primary patellar dislocation, the quality of the currently available evidence was too poor to allow any firm conclusions to be made.[8]

In a systematic review that included 2134 primary acute patellar dislocations (2086 patients) treated either conservatively or surgically, Longo et al found that whereas surgical treatment was associated with a significantly lower rate of recurrence and better results in the short-to-medium term, the results of the two approaches were not significantly different in the long term.[9]

Contraindications

A patellar dislocation associated with a fracture of the proximal tibia or distal femur should not be reduced in this manner. Osteochondral fractures may occur in the setting of patellar dislocation. Caution should be used in evaluating for a fracture, either by exam or by radiographs, prior to attempting reduction. Any superior, intercondylar, or horizontal dislocation should be examined by an orthopedic surgeon. Any dislocation with suspected locked osteophyte should be examined by an orthopedic surgeon. Arthroscopic reducation of a locked patellar dislocation has been described.[10]

 

Periprocedural Care

Patient Education and Consent

Explain the procedure, risks, and benefits to the patient. Lateral or medial reduction is a safe and technically simple procedure. Obtain informed consent for the reduction (and the procedural sedation if necessary). To optimize successful rehabilitation, educate the patient regarding aftercare.

Equipment

No equipment is needed for the reduction.

A knee immobilizer, crutches, or both are needed for aftercare.

Patient Preparation

Anesthesia

Anesthesia is usually not required for this procedure, though some patients have significant anxiety and pain. Procedural sedation should be used as needed to maximize the patient's comfort during the reduction.

Positioning

Place the patient supine or with the legs hanging off the side of a gurney (see the image below).

Positioning for lateral patellar reduction. Positioning for lateral patellar reduction.
 

Technique

Approach Considerations

Obtain prereduction and postreduction radiographs to rule out any osteochondral fractures, if such lesions are suspected on the basis of mechanism of injury or findings from physical examination.

Computed tomography (CT) can detect small bony fragments that result from patellar dislocation. These fragments often are not seen on standard radiographs. CT should be considered in first-time dislocation patients and in dislocations that result from significant forces.[11]

Magnetic resonance imaging (MRI) may be considered in patients with acute traumatic patellar dislocations to help determine the nature of any osteochondral and soft-tissue injury.[12] It may be useful for evaluating the anatomic sequelae of the dislocation, assessing the risk of recurrence, and determining whether conservative or surgical management is warranted in the acute setting.

The literature reports controversy regarding which patients should undergo operative repair of primary dislocations. Most patients do well with a short course of immobilization followed by physical therapy.[13, 14]

Medial patellofemoral ligament injury typically results from patellar dislocation[15] ; thus, follow-up with an orthopedic surgeon is recommended for all patients with patellar dislocations.[16, 17, 18, 19, 20]

Patellar Reduction

Stand on the lateral side of the leg on which the patellar reduction is to be done. (See the video below.) Slightly flex the injured leg at the hip to decrease tension on the quadriceps muscles. Extend the knee while applying gentle anteromedially directed force on the lateral patellar edge to lift the patella over the femoral condyle. For a medial dislocation, use the same technique, but stand medial to the dislocation and apply an anterolateral force.

Conducting patellar reduction.

When reduction is complete, apply a knee immobilizer so that the knee is in full extension.

Arrange a follow-up appointment for the patient with an orthopedic surgeon. Some patients with complete dislocation may require surgery to prevent recurrence.

Complications

Osteochondral fractures are a very uncommon complication of reduction of a patellar dislocation. Related complications of the dislocation itself may include recurrent dislocations, degenerative arthritis, or osteochondral fractures.