Glossary
Trochlea (trochlear groove)
Quick answer
The trochlea is the V-shaped groove at the front of the lower femur in which the kneecap slides. A deep, well-formed groove keeps the kneecap on track, while a shallow one can let it slip sideways, explains Dr. Pablo Gelber, knee surgeon at Aman Hospital in Doha, Qatar.
What it is
Between the two femoral condyles, at the front of the knee, the femur forms a groove lined with cartilage. As the knee bends, the back of the kneecap fits into this groove and is guided along it. The outer side of the groove is usually higher, acting as a wall that resists the natural tendency of the kneecap to drift outwards.
Why it matters for patients
Some people are born with a shallow or flat groove, called trochlear dysplasia. It is one of the main reasons the kneecap dislocates, often in teenagers and young adults, and it raises the chance of the kneecap coming out again. The cartilage of the trochlea can also be worn or damaged, contributing to front knee pain, grinding and patellofemoral arthritis.
When dysplasia is significant, a surgeon takes it into account when planning treatment for an unstable kneecap. Most patients are treated with ligament reconstruction or realignment; reshaping the groove itself (trochleoplasty) is reserved for selected severe cases.
How it is examined
A lateral X-ray and MRI show the depth and shape of the groove. CT or MRI measurements also help a surgeon judge how the kneecap lines up with it.
Frequently asked questions
Can a shallow trochlea be fixed with exercise?
Exercise cannot change the bony shape, but strengthening the hip and thigh muscles often improves control of the kneecap and reduces symptoms.
Does everyone with a shallow groove dislocate their kneecap?
No. Many people with mild dysplasia never have a problem. It is one risk factor that a surgeon weighs alongside ligament laxity, alignment and kneecap height.
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