Patellar instability
Understanding this condition
The patella (kneecap) is the bone at the front of the knee, nestled in the trochlear groove of the femur (a channel-shaped groove). When this engagement is defective — a too-flat trochlea, a too-high patella, a misaligned axis — the patella can slip out of its track, which is called patellar dislocation.
Patellar instability refers to the repeated tendency of the patella to shift or dislocate. It can occur after an initial trauma or exist on a particular morphology (often congenital).
Symptoms
The first episode is typically a dislocation: the patella comes out of its groove, most often when pivoting on the weight-bearing leg. The knee locks, is very painful, and the patella sometimes returns to its position spontaneously (reduction).
Subsequently, apprehension dominates: fear that the patella will "jump out" again, a sensation of instability with certain movements (stairs, squatting, sport). Anterior knee pain and intermittent swelling may develop.
How can it progress?
Repeated dislocations progressively damage the cartilage of the patella and trochlea, predisposing to early patellofemoral osteoarthritis. Each episode may detach cartilaginous or bony fragments.
Chronic instability also leads to a loss of confidence in the knee and a significant functional impact, especially in young and athletic patients.
Treatment options
After a first episode: immobilisation then physiotherapy to strengthen the quadriceps (particularly the vastus medialis) and stabilise the patella. This may be sufficient.
In cases of recurrence or significant anatomical abnormalities, a stabilisation procedure is proposed. Several techniques exist (medial patellofemoral ligament reconstruction, tibial tubercle transfer, trochleoplasty), chosen according to the abnormalities present. A specialist consultation and precise imaging workup are essential to plan the procedure.