Patellofemoral instability has many potential causes and risk factors. One of the most significant risk factors for recurrent patella dislocations is trochlear dysplasia. The trochlea is the groove on the front of the femur within which the patella (kneecap) glides. Dysplasia refers to when the groove is not formed normally. The amount of dysplasia exists along a spectrum from the groove just being shallow towards a large bump. The patella is most susceptible to dislocation before it engages in the trochlear groove. Normally this engagement occurs around 20-30 degrees of knee flexion. Within that early flexion range the MPFL (and other soft tissue stabilizers) prevents the patella from dislocating. Patients with dysplasia have later engagement of the patella and in the most severe cases the patella actually has to go over or around a bony bump before it can engage in the groove.
Many patients who experience patella dislocations may have trochlear dysplasia. Some studies have identified trochlear dysplasia in over 85% of patients who have experienced a patella dislocation. Those with more severe dysplasia may notice that their kneecap moves awkwardly when they bend their knee. This can present as the knee not feeling ‘right’ and not trusting the knee. Sometimes the kneecap seems to ‘jump’.
A thorough physical exam is important to determine the mobility of the patella, the rotational parameters of the leg and knee, and for other special tests such as the “J-sign”. X-rays, particularly the lateral x-ray is the classic way to diagnose and classify the degree of dysplasia. An MRI scan and/or CT scan is also useful to view the complex anatomy of the femoral trochlea.
Trochlear Dysplasia: Solid line indicating where the new groove will lie.
The trochleoplasty procedure is designed to create a more normal groove for the patella to articulate within. An incision is made over the front of the knee and the kneecap is moved out of the way. I then use special instruments to elevate a thin flap of cartilage and bone from your current trochlea. Using special chisels and burs, I then remove extra bone to create a new groove. The flap of cartilage is then pushed back into the newly created groove and secured with special absorbable anchors. Once the new trochlear groove is established I then reconstruct the MPFL to balance the patella tracking. Sometimes other procedures are also indicated at the same time as the trochleoplasty and MPFL reconstruction; this can include cartilage restoration and tibial tubercle osteotomy. The procedure takes approximately 2 hours and is performed on an outpatient basis (you go home same day).
Patients are weight bearing as tolerated in a knee brace and use crutches for 2-4 weeks. I encourage full range of motion of the knee immediately to prevent stiffness, including the utilization of a continuous passive motion machine (CPM). No direct pressure should be placed on the kneecap, including kneeling, for the first 6 months. Return to impact activities and running can start as soon as 3-4 months after surgery.
Dr. Daniel Elkin is a leading Orthopedic Surgeon performing Patella Stabilization Surgery in the Willamette Valley. He is one of only a few surgeons in Oregon performing trochleoplasty surgery on a regular basis. He specializes in complex knee reconstruction and knee arthroscopy and is conveniently located in Salem, Oregon