Recurrent dislocation of the patella is not a common entity. It may be congenital, developmental, or post-traumatic.
In contrast, recurrent subluxation of the patella is quite common. It is more common in females.
Causes of Recurrent Dislocation of Patella
In children with diseases that cause ligamentous laxity (e.g. osteogenesis imperfecta, arachnodactyly, or the Ehlers-Danlos syndrome), lateral dislocation of the patella is more common.
Lateral Soft Tissue Contracture
Taut lateral patellar retinaculum and patellofemoral ligament contracted and hypertrophied vastus lateralis and tight iliotibial tract may contribute to dislocation of the patella.
Atrophy, weakness, or a high oblique insertion of the vastus medialis is a factor in most patients. The vastus medialis is a dynamic medial stabilizer of the patella.
Malalignment of the Lower Limb
Lateral tibiofibular torsion and genu valgum will displace the insertion of the patellar ligament laterally and cause valgus position of the quadriceps mechanism.
Q angle is the angle formed between the patellar tendon with a vertical line extended distally from the center of the inferior pole of the patella. Its value can provide a guide to the rotatory-angular forces.
This is a high riding patella. In this, the normal buttressing effect of the lateral femoral condyle, which serves to check the tendency to lateral patellar displacement, will be lost.
A traumatic lateral dislocation inadequately treated will result in stretching and weakening of the medial capsule of the knee and insufficiency of the vastus medialis, predisposing to recurrent lateral subluxation.
Presentation of Recurrent Lateral Dislocation and Subluxation
The typical patient is a teenage girl who becomes physically active in exercises or sports. The presenting complaint is a pain in the knee in around or behind the patella, especially on flexion.
There may be symptoms of giving a way of knee and a swelling might be present in the knee. Locking and popping of the knee may also be present.
The dislocation is precipitated by a sudden contraction of the quadriceps muscle when the tibia is in lateral rotation and the knee is in extension or slight flexion.
A dislocated patella is obvious on examination but the patient of recurrent dislocation is usually seen between the episodes.
In these patients apprehension test is quite confirmatory.
While attempting to displace the patella laterally with the knee flexed 30 degrees and the quadriceps relaxed, exert laterally directed pressure with both thumbs pressing on the medial side of the patella.
The patient becomes fearful and uncomfortable when the patella reaches the point of maximum displacement and will resist and seize the examiner’s hand and straighten her knee to replace the patella in its relatively normal position.
This is referred to as Fairbank’s apprehension test.
With knee extended, the sense of apprehension is not elicited. This happens because the patella moves readily on the flat condylar and supracondylar surface of the femur and not across the highest point of the lateral condyle.
Another finding that may be noted during the examination is a limited excursion of the patella medially with the knee in extension. The lateral soft tissue might be taut.
Tenderness may be elicited on compression of the patella and palpation over the medial retinaculum.
Knee deformities like genu valgum and lateral torsional deformity of the tibia are usually present.
The patellar tendon may insert laterally with an abnormal increase of the Q angle.
In case of high riding patella, the tendon may be elongated with a high-riding patella. Hamstring spasm and knee swelling may be present
In between the episodes, x-rays may entirely be normal. Patella alta [high riding patella] and osteochondral fractures should be looked for.
CT scanning should be done in the cases where plain radiographs are indeterminate. It may show may reveal occult osteochondral fractures and may reproduce patellofemoral relationships.
MRI may show bone bruises in the medial aspect of the patella and the lateral aspect of the lateral femoral condyle.
Treatment of Recurrent Dislocation of Patella
The treatment of patellofemoral joint subluxation depends on the following factors.
- Degree of lateral displacement of the patella
- Mechanism or type of subluxation or dislocation-whether it is due to
- Malalignment of the quadriceps mechanism with contracture of the lateral patellar retinaculum and iliotibial band.
- Muscle imbalance between a weak and high oblique vastus medialis and a hypertrophied, low, and transverse vastus lateralis
- Extreme ligamentous hyperlaxity
- Trauma resulting weakening of the vastus medialis.
- Malposition of the patella
- Angular or rotational deformity of the knee and leg
- Presence or absence of bony hypoplasia of the lateral femoral condyle.
- Presence or absence of chondromalacia of the patella.
- Psychological aspects
A rough guide to the management of this condition is as follow
Congenital Dislocation of the Patella
- Marked soft-tissue contracture of the lateral side of the knee
- Malalignment and contracture of the quadriceps mechanism
- Secondary developmental structural changes
- Shallow femoral sulcus
- Hypoplasia of the patella.
- Surgical replacement of the patella in the femoral sulcus by
- Release and lengthening of all lateral contracted soft-tissue structures
- Tautening of the medial capsule and retinaculum
- Distal and lateral advancement of the vastus medialis
- Tenodesis of the semitendinosus to the patella
- Shortening of the patellar tendon by distal-medial transfer.
Chronic Developmental Subluxation or Dislocation of Patella
These are associated with
- Severe ligamentous hyeprlaxity
- Genu valgum
- Hypoplasia of the lateral femoral condyle.
- Patella alta may be present
- Contracture and malalignment of the vastus lateralis
- High insertion and hypoplasia of the vastus medialis.
- Surgical relocation of the patella
- Realignment of the quadriceps muscle
- Tenodesis of the semitendinosus tendon to the patella if Patella Alta is there.
Post-Traumatic Recurrent Lateral Subluxation or Dislocation
The great majority of acute patellar dislocations are lateral. Occasionally, however, they may be medial, intra-articular, or superior.
Acute dislocations associated with osteochondral fracture require surgical treatment. The fragment is removed or reattached along with soft tissue repair.
Nonoperative management is followed if examination of the aspirated blood from the knee does not show fat droplets and there is no evidence of osteochondral fracture.
In doubt, the diagnostic arthroscopic examination may be conducted
- Immobilization of the knee in an above-knee cylinder cast for three to four weeks
- Rehabilitation exercises for the quadriceps and hamstrings after that.
Recurrent post-traumatic dislocations require surgical intervention.
Recurrent post-traumatic subluxations an initial period of conservative management should always be tried. If it fails, operative treatment is indicated
- Release of the lateral patellar retinaculum and vastus lateralis
- Tautening of the medial capsule and medial patellar retinaculum
- Distal lateral transfer of the vastus medialis.
Patellar Subluxation with Lateral Pressure Syndrome
The initial treatment should be nonsurgical, particularly when the associated chondromalacia is not severe. The nonoperative treatment includes
- Exercises restore the motor strength of the quadriceps femoris, and especially vastus medialis.
The exercises should be isometric. Isotonic exercises should not be performed, as they markedly increase the patello-femoral load.
- Hamstrings exercise
- Descending and climbing stairs, bicycle riding, contact sports, and other strenuous physical activities are curtailed.
- Analgesics and anti-inflammatory drugs
Operative measures are carried out when conservative management fails to relieve.