Introduction
Patella is the flat kneecap located at the front of the knee joint. Congenital dislocation of the patella (CDP) is a rare orthopedic condition in which there is a permanent displacement of the kneecap from its normal position, and it cannot be reduced back to its original position manually. The symptoms usually occur after birth and are sometimes diagnosed later in childhood. Management of this condition often involves surgical intervention. This article will discuss congenital dislocation of the patella, its causes, symptoms, and treatment in detail.
What Are the Anatomical Considerations for CDP?
Patella, also known as the kneecap, is the most prominent sesamoid bone in the human body. It is a triangular-shaped bone in front of the knee joint in the groove on the top of the thigh bone. It helps in protecting the anterior part of the knee joint, facilitates the extension of the knee joint, and allows for smoother movement of the knee during extension and flexion. The two-round prominence at the end of the thigh bone is the lateral and medial femoral condyle.
What Happens During the Dislocation of the Patella?
The congenital patella dislocation either presents as a fixed or obligatory kneecap dislocation.
-
Fixed dislocation is a pathological condition when the kneecap remains permanently fixed to the lateral aspect of the femoral condyle. This type is often associated with other syndromes. They cannot be reduced manually and always requires surgical intervention. It may occur on one or both sides.
-
The obligatory dislocation of the patella is the intermittent displacement of the kneecap out of its place completely with each flexion and extension movement of the knee joint. This type of dislocation often occurs isolated, and it is well tolerated.
What Causes Congenital Dislocation of the Patella?
The embryonic development of the lower limb usually begins in the fourth week of gestation. The internal rotation of the myotome during embryonic development is responsible for the formation and orientation of the extensor mechanism of the knee joint (a complex structure that involves quadriceps muscle, tendon, and patella). Failure of the internal rotation of the myotome or non-rotation results in congenital dislocation of the patella.
The fixed dislocation of the patella is often associated with other syndromes, such as the following.
-
Arthrogryposis (a congenital condition affecting joints causing tightening or shortening of the joint).
-
Larson syndrome (a rare genetic disorder affecting the development of bones in the body).
-
Diastrophic dysplasia (a genetic condition affecting the development of bones and cartilage).
-
Downs syndrome (a genetic disorder that occurs due to the presence of an extra set of chromosomes).
-
Nail-patella syndrome (a syndrome that is associated with abnormalities of the knee, hipbone, nails, and elbow).
-
Ellis Van Creveld syndrome (a rare genetic condition that generally affects bone growth).
What Are the Symptoms of Congenital Dislocation of the Patella?
The severity of the symptoms differs for each individual. The common signs and symptoms of congenital patella dislocation involve the following.
-
Severe limping.
-
Inability of the affected child to fully straighten or extend the knee. Loss of range of motion of knee during both active and passive motion.
-
Genu Valgum also known as knock knees, that involves inward rotation of the legs with the ankle apart and gives an appearance as if the knees are touching one another.
-
Various foot deformities.
-
Abnormal external rotation of the affected child's shinbone gives a pigeon-toed appearance.
-
Palpable kneecap on the lateral aspect of the knee.
How Is Congenital Dislocation of the Patella Diagnosed?
The clinician performs a detailed history and physical examination of the affected child. The radiographic investigation of the affected child is an effective way to diagnose this condition. However, radiographic methods such as X-rays are recommended between the ages of three to five since the ossification of the kneecap is completed after three years of age.
-
An anteroposterior view of the kneecap help in visualizing the size and position of the kneecap and other associated pathological conditions.
-
An axial view of the kneecap helps assess the size, position, shape, and intercondylar groove.
-
In children whose patellar ossification is not completed, an echography may be performed to visualize the cartilaginous part of the kneecap and the surrounding structures. It also helps assess the position of the kneecap in relation to the thigh bone.
-
Other imaging studies, such as Magnetic resonance imaging (MRI), may be performed to evaluate the joint structure and the associated systems and are also used during preoperative preparation.
How Is Congenital Dislocation of the Patella Treated?
Early diagnosis and management of the condition are essential to prevent further complications of kneecap dislocation. The most effective management method is surgical intervention. Corrective surgery involves surgical realignment of the extensor mechanism of the knee joint. Various surgical techniques are available for this condition, but the most recommended method is Stanisavljevic.
-
The patient is given general anesthesia to make the patient sleep and not feel any pain during the procedure.
-
An incision is made five centimeters below the greater trochanter, a large bony eminence on the thigh bone. The incision is extended distally, creating a curved incision at the base of the kneecap.
-
The dislocated kneecap is surgically released from the lateral femoral condyle and reduced and placed into the shallow groove of the femoral condyle.
-
Surgical displacement of the kneecap is performed, and the quadriceps muscles are released and placed in their original position.
-
The fascia lata that surrounds the muscle of the thighs is preserved during kneecap displacement and is used to fill the gap in the lateral portion of the thigh.
-
Post-operatively, casting is applied to hold the surgically corrected kneecap for two to three weeks after surgery.
-
The patients are referred for physical therapy to improve the knee joints' active and passive range of motion once the casting is removed.
Conclusion
Congenital dislocation of the patella (CDP) is a rare orthopedic condition present from birth. The condition is characterized by the permanent dislocation of the kneecap from its normal position in the lateral aspect of the femoral condyle. They occur either as an isolated identity or in association with other syndromes. The diagnosis of the condition is made through physical examination based on the patient's clinical findings. Imaging studies are performed to evaluate the dislocated kneecap. Effectively managing this condition is the surgical correction of the dislocated kneecap. Neglected and delayed diagnosis may result in knee arthritis; hence, early diagnosis and immediate surgical treatment of the affected child are essential.
