Patellofemoral malalignment has been often misunderstood and poorly diagnosed in the medical community. The term patellofemoral refers to the joint where the patella (kneecap) sits on the femur (thighbone). Physical therapist will often get referrals from physicians of “anterior knee pain”, “patellofemoral syndrome” or “patellofemoral pain”, but this is not a diagnosis but a symptom. It is important to understand the underlying problem that is causing the patient’s knee pain in order to know the best way to treat.
When an individual dislocates the patella, it is important to understand and determine if this is a chronic problem or an acute problem. If chronic, how long has it been going on and the symptoms that follow the injury. A physical exam of both knees is critical as well as getting appropriate x-rays. At the Shelbourne Knee Center, where all we treat are knee problems, our office sees more patellofemoral problems than the average orthopedic surgeon does in a year. This is because patellar dislocations and patellar subluxations are relatively rare. About 1/10 of major knee injuries that come through the Shelbourne Knee Center are patellofemoral dislocations. If an orthopedist does not see more than one per year, it becomes difficult to identify best practice patterns for treatment. Most x-ray technicians do not have the proper equipment necessary to take a Merchants View of the patellofemoral joint, which is most sensitive to the alignment of the patella to the femur. This view allows the physician to see both patellae and how they sit relative to the femur, and to determine joint space changes as well as how the patellae sit relative to the trochlear groove (a deep depression in the femur where the patella rests). Most x-ray technician take a sunrise view, which puts the knee in a more flexed (bent) position making it impossible to know the relationship between the patella and the femur. The merchants view allows the quadriceps muscle to relax and the knee is only flexed to 45°. It is also important to have x-rays of both knees and not just the injured so that a comparison can be made from injured knee to normal knee. The lateral view is also valuable and should be taken with the knee flexed 60° so that the length of the patellar tendon can be measured from the inferior pole of the patella to the tibial tubercle. The measurements should be compared to normative values of patients who have had no history of patellar dislocations. The normal patellar tendon length of women is 45 mm and 50 mm for men. From the lateral view, the height of the patella can be measured by measuring the distance from the inferior tip of the patella chondral surface to the level of Blumensaat’s line.
The last view is a lateral quad-active view. This view allows for evaluation of the height of the patella in relation to the trochlear groove: inferior tip of the patella chondral surface to the superior edge of the trochlea as seen below.
The physical exam of the knee should start with range of motion measurements (ROM), quad tone, and check for effusion in the knee joint. Then the patient should sit on the side of the table and evaluate the following:
- J-Sign: the movement of the patella as the patient actively extends the knee to determine if the patella moves out of the trochlea laterally at full extension.
- Patella Height: position of the patellae in relation to where they are pointed towards the examiner (waist, chest, or over the shoulders)
- Patella tilt: by placing thumbs on the lateral aspect of the patella and moving the patella medially and gently lifting the medial aspect of the patella, the examiner can observe increased laxity of the medial retinaculum, and compare this motion to the opposite knee.
The last component is getting an MRI scan to evaluate the integrity of the medial retinaculum as well as chondral defects (damage to the articular cartilage that lines the patella) in the patella femoral joint.
Based on the subjective history, physical exam findings, x-rays and MRI results, a proper evidence-based treatment plan can be determined. The type/level of activity of the patient and age of the patient should be part of the consideration when developing a treatment plan. The Shelbourne Knee Center has an effective treatment algorithm for patellar dislocations or malalignment, which is backed by research.