Trochlear Dysplasia

Chronic knee pain, feeling of instability, feeling like the knee gives out... The go to guys to check would be meniscus, LCL, MCL, ACL, and PCL. But when everything clears, what next? A young, athletic person with no perceivable injury should not have these symptoms. With x-ray and MRI diagnostics, further anatomical structures can be analyzed beyond standard testing. One possible explanation for these symptoms may be trochlear dysplasia.

Femoral trochlear dysplasia is characterized by an abnormal shape of the trochlea at the distal end of the femur. The femoral trochlea loses its normal concave anatomy to become flat and sometimes convex with highly asymmetrical facets. Normally, the trochlear groove is concave and has a higher ridge on the lateral side. This helps to allow the patella to slide easily through the groove at the distal end of the femur, guided by it's bony constraints. Once the patella is engaged in this groove it is extremely difficult to dislocate (1)

Normal Knee Anatomy

When the groove becomes flattened, shallow, or convex, the patella becomes unstable, relying on the medial patellofemoral ligament and the quadriceps to hold the patella in place (1). In Trochlear Dysplasia the trochlea does not adequately contain the patella until the knee is in deep flexion. This leaves the patella vulnerable to dislocation early in the knee flexion arc, which is the position in which the foot strikes the ground when running (4). This gives patients a sensation of instability and buckling of the legs in daily and sports activities. Trochlear dysplasia also causes knee pain during flexion activities such as walking up or down stairs or running (2).

Because the severity of trochlear dysplasia can vary from minor to severe, treatment options are varied. They can include a reconstruction of the medial patellofemoral ligament, a tibial tubercle osteotomy, a trochleoplasty, where the distal aspect of the femur is cut and reshaped to create more of a normal groove, a distal femoral osteotomy, and other associated treatments. A thorough workup is necessary to determine the best course of action for each patient (1). 

More conservative treatment methods for may include physiotherapy with a focus on quadriceps strengthening, proprioceptive training, and stabilizing the knee. A hinged knee brace with patellar alignment guides may also be useful for milder cases, providing additional support and stability.

References:
1) http://drrobertlaprademd.com/trochlea-dysplasia
2) http://www.orpha.net/consor/cgi-bin/OC_Exp.php?lng=EN&Expert=1863
3) http://www.bjj.boneandjoint.org.uk/content/88-B/10/1331.long
4) http://www.kneesurgeon.com.au/patella-trochlear-dysplasia.html