Patellofemoral dysplasia is a birth defect that affects the kneecap joint with the femur, in the knee. When significant, it predisposes to pain syndrome and recurrent dislocations and may require surgery.

Definition

Patellofemoral dysplasia is a developmental abnormality affecting one or both knee (bilateral dysplasia). It relates more specifically to the patellofemoral joint, between the femur and the patella, more commonly called the kneecap.

This joint plays a major role in extending and flexing the leg. The kneecap is a small, flat bone, roughly triangular in shape, located in front of the knee, attached to the quadriceps and tibia by tendons. When the knee is flexed, it slides into a groove in the femur called the trochlea.

In people with patellofemoral dysplasia, there is a morphological abnormality in the shape of the patella or trochlea, the latter may be more or less flat, or even bulging. When the knee is bent, the patella does not engage properly in the trochlea and tends to come out of its housing, like a rope coming out of its pulley: this is called a dislocation. knee. 

Dysplasia is a predisposing factor for patellar pain syndrome and recurrent dislocations. Patellar instability is itself a risk factor for a form of osteoarthritis of the knee (gonarthrosis) corresponding to the wear and tear of the cartilage at the level of this joint and scientifically designated under the term patellofemoral chondropathy.

Causes

Patellofemoral dysplasia is a congenital condition whose causes are poorly understood. There are, however, familial forms of bilateral dysplasia which suggest genetic determinism.

Diagnostic

The questioning of the patient and the clinical examination guide the diagnosis. The doctor documents the painful episodes (patellar pain on the external facet most often) and instability. He listens to knee crunches (sign of the plane) and tests his knee mobility, muscle strength and joint function.

Dysplasia is characterized by medical imaging.

A lateral x-ray is the standard examination for detecting dysplasia of the trochlea. The external eccentricity of the patella is observed at 30 ° of flexion. If abnormalities are detected, a CT scan (to measure the eccentricity of the patella) or an MRI (to specify the position of the patella and assess the cartilaginous lesions) may be requested. These examinations make it possible to refine the diagnosis, in particular within the framework of a preoperative assessment.

The people concerned

Patella instability is a relatively common multifactorial pathology in adolescents and adults. Dysplasia is an essential factor in its genesis, but its incidence remains difficult to assess.

pain

Patellar pain syndrome associated with dysplasia is manifested by dull, mechanical pain, which occurs when the knee is strained, especially when going down stairs or walking on sloping ground. Resting pains are also characteristic: we speak of “cinema sign” because they occur after a long sitting position (more rarely lying down), or when standing up.

These pains may be accompanied by joint swelling.

Biomechanical problems and dislocations

Moderate dysplasia can cause a feeling of “knee sagging”. Sometimes “pseudo-blockages” appear when the knee flexes. They are due to the poor engagement of the patella in the trochlea and generally disappear after the second attempt.

The luxations occur when the ball joint “derails” and slides outward. The dislocation is sometimes incomplete, with a patella that comes back in place spontaneously: we speak of subluxation. When complete, locking the knee in flexion is accompanied by severe pain and a leg lengthening maneuver must be performed by the patient himself or by an outside person to put the patella back in place and reduce dislocation.

Severe dysplasias cause recurrent dislocations.

Patellofemoral osteoarthritis (chondropathy)

Patellofemoral dysplasias can cause osteoarthritis of the knee (gonarthrosis), due to cartilage damage caused by dislocation or, in moderate and well-tolerated dysplasia, to wear and tear due to abnormal friction during joint function.

Medical treatment

When moderate dysplasia combined with other factors is expressed by painful patellar syndrome and instability without dislocations, or by femoro-patellar osteoarthritis, medical treatment, not specific for dysplasia, may suffice.

• Attitude to Pain: A sore knee should be put to rest. Applying an ice pack can be helpful in reducing inflammation or pain.
• Rehabilitation: Physiotherapy sessions are the main part of the treatment. Muscle rebalancing may indeed be enough to significantly improve instability and reduce pain.
• The exercise program is mainly based on stretching the various tendons and muscles of the knee (hamstrings and quadriceps) and on muscle strengthening exercises.
• Osteoarthritis: The treatment combines strategies intended to limit stress on the joint (weight loss, orthopedic insoles, etc.) with rehabilitation. Analgesic and anti-inflammatory drugs are used in the treatment of osteoarthritis attacks. Different complementary approaches intended primarily to protect the cartilage can be tried.

Surgical treatment

The specific treatment of patellofemoral dysplasia is surgical. It is offered in the event of failure of rehabilitation and recurrent dislocations, and requires a short hospital stay.

This à la carte treatment may include several “à la carte” actions depending on the anatomical abnormalities and lesions observed:

• Refocusing the patella

The surgical intervention can allow to recenter the patella thanks to techniques acting in particular on the insertion of the tendon on the tibia (transposition of the TTA, or anterior tibial tuberosity), or on the ligament which connects the external edge of the tibia. patella to the femur (external patellar fin).

• Trochléoplasty

This intervention aims to correct the anomalies of the femoral trochlea either by hollowing it out or by raising its outer edge.

Complications from surgery are rare, and support recovery is immediate, with or without a removable knee brace. Rehabilitation is necessary.

Surgery for severe patellofemoral dysplasia is one way to prevent osteoarthritis of the joint. In elderly subjects who have not benefited from it, deterioration of the cartilage may be an indication for the fitting of a patellofemoral prosthesis or a total knee prosthesis.

Dysplasia in itself is congenital and cannot be prevented. On the other hand, the fight against overweight and a well-conducted sports practice, avoiding inappropriate stress on the knee while allowing balanced bodybuilding, help prevent the appearance of a pain syndrome or instability of the kneecap.