Presentation on theme: "CT Evaluation of Patellofemoral Pain Campbell, SC, Monu, JUV, Seo, GS University of Rochester, Rochester, NY Strong Memorial Hospital."— Presentation transcript:
CT Evaluation of Patellofemoral Pain Campbell, SC, Monu, JUV, Seo, GS University of Rochester, Rochester, NY Strong Memorial Hospital
Before we begin… Before we can begin a discussion of the CT evaluation of patellofemoral pain, the normal, basic, axial anatomy of the knee must be reviewed.
Before we begin… Lets review the necessary anatomy… Medial Patellar Facet Lateral Patellar Facet Femoral trochlea Lateral Femoral Condyle Medial Femoral Condyle
Now we can discuss pathology… Medial Patellar Facet Lateral Patellar Facet Femoral trochlea Lateral Femoral Condyle Medial Femoral Condyle
There are many causes of anterior knee pain… Chondromalacia patella Plica syndrome Meniscal Pathology Patellar bursitis Patellar tumors Jumpers Knee Sindig-Johansson- Larsen's disease Bipartite patella Patellar subluxation or instability Many of these pathologies are best evaluated on plain film or MRI, however…
Chondromalacia patella Plica syndrome Meniscal Pathology Patellar bursitis Patellar tumors Jumpers Knee Sindig-Johansson- Larsen's disease Bipartite patella Patellar subluxation or instability CT is uniquely suited to evaluate for patellar subluxation and instability. There are many causes of anterior knee pain…
Plain Film Views Traditionally, plain film views were used to evaluate the patello- femoral joint. They have the dis- advantage of only evaluating the knee at a fixed degree of flexion and not reliably displaying the knee joint at less than 30 degrees of flexion. Degrees of flexion in some traditional plain film views: Merchant45 Laurin20 Sunrise115 Merchant view of the knee
CT has the advantage of: Allowing a true axial view of the patellofemoral joint. Ease of patient positioning. Ability to reliably image the patellofemoral joint in multiple degrees of flexion.
So well use CT to evaluate the patellofemoral joint. Q. But what are we looking for? A. Patellar Instability.
What is patellar instability? Also known as… Malalignment Subluxation Recurrent dislocation Patellar tracking abnormality In a nutshell, any abnormal biomechanical relationship between the patella and the femoral trochlea. But before we can define abnormal, we have to talk about whats normal.
The Normal Patellofemoral Relationship The patella may be slightly lateral to the apex of the femoral trochlea at full knee extension. The patella reduces medially with increasing flexion of the knee joint. Contraction of the quadriceps applies lateralizing force to the patella but will not cause significant subluxation in a normal knee. This lateralizing force decreases with increasing knee flexion.
Q. Why does quadriceps contraction apply a lateralizing force to the patella? A. The Q angle.
The Q Angle The patella is subjected to forces of the rectus femoris and the vastus medialis, lateralis and intermedius when these muscles contract. The net force of these muscles pulls along a line from the center of the patella to the anterior superior iliac spine.
The Q Angle The patella is attached to the tibial tubercle by the patellar tendon. The tibial tubercle lies laterally to the vector of the contracted quadriceps muscle force. With contraction, this pulls the patella laterally. With flexion of the knee, the tibia derotates bringing the tubercle more medial, and the Q angle decreases, bringing the force of the quadriceps in line with the tubercle and exerting a reducing force on the patella. Q
So now that we know what to expect from the normal knee, how do we use CT to evaluate the symptomatic knee?
CT Positioning Place the patient in a lateral decubitus position. Place a spacer between the knees and ankles to create an alignment similar to a relaxed stance.
CT Positioning Scan through the patellar apices at 0, 20, 30, 40 and 50 degrees of flexion. At each degree of flexion, have the patient contract his or her quadriceps muscles.
How do we analyze the images? Select the image containing the patellar apex for each knee at each degree of flexion with and without quadriceps contraction. Assess four aspects of alignment: Depth of the femoral trochlea Angle of the femoral trochlea Degree of patellar displacement Degree of patellar angulation
Femoral Trochlear Depth 1.Draw a line parallel to the femoral condyles 2.Draw a line at the deepest point of the femoral trochlea, parallel to the first line. 3.Draw a third line at the highest point of the lateral trochlea and measure between the second and third lines. This is the femoral trochlear depth (FTD). FTD
Femoral Trochlear Depth 1.Draw a line parallel to the femoral condyles. 2.Draw a second line parallel to the first at the deepest point of the femoral trochlea. 3.Draw a third line parallel to the highest points of the medial and lateral aspects of the trochlea. 4.Measure between the second and third lines at the trochlear apex. This is the femoral trochlear depth (FTD). Alternatively…
Femoral Trochlear Angle 1.Draw two intersecting lines along the medial and lateral facets of the femoral trochlea. 2.This is the femoral trochlear angle (FTA, also known as the sulcus angle). FTA
Patellar Displacement 1.Bisect the angle of the femoral trochlea. 2.Draw a line from the apex of the femoral trochlea through the apex of the patella. 3.The angle between these two lines is the congruence angle (CA). 4.If the patellar apex is medial to the trochlear apex the CA is negative. If its lateral, the CA is positive. - + CA
Patellar Displacement 1.Draw a line parallel to the femoral condyles. 2.At 90 degrees to the first line draw one line intersecting the patellar apex. 3.Then draw a line bisecting the trochlear apex. 4.The difference between the second and third lines is the measurement of patellar subluxation. If negative, the patella is medial; if positive, the patella is lateral to the femoral trochlea. Alternatively…
Patellar Angulation 1.Draw a line parallel to the posterior femoral condyles. 2.Draw a second line parallel to the first at the patellar apex. 3.The angle between the lateral patellar facet and this second line is the patellar tilt angle (PTA). + -
Patellar Angulation If the reference line is drawn along the anterior femoral condyles, the resulting angle is called the lateral patello- femoral angle (LPFA) + - Alternatively…
Patellar Angulation 1.Draw a line parallel to the posterior femoral condyles. 2.Draw a second line along the axis of the patella. 3.The resulting angle is the patellar inclination. Alternatively…
Normal Values Several studies have been performed to determine normal values in asymptomatic knees and results show a wide range with patellar displacement and patellar tilt being the most specific and sensitive indicators of patellar malalignment. There is no agreement on what constitutes normal anatomy of the patellofemoral joint. G.R. Scuderi
Evaluating the Measurements: Femoral Trochlear Depth Femoral Trochlear Depth> 5 mm Remember, the femoral trochlear depth will decrease with increasing flexion.
Evaluating the Measurements: Femoral Trochlear Angle Femoral Trochlear Angle<130 degrees The femoral trochlear angle or sulcus angle will normally decrease with increasing flexion. Some studies have indicated a normal trochlear angle as high as 156 degrees.
Evaluating the Measurements: Patellar Displacement Congruence Angle<0 degrees or Patellar Subluxation>0 mm The patella may be slightly lateral at full extension of the knee, but in the normal knee this will resolve by 20 degrees of flexion. Quadriceps contraction will exacerbate patellar lateralization, particularly at lesser degrees of knee flexion. The bottom line: The apex of the patella should align with or be medial to the apex of the femoral trochlea.
Evaluating the Measurements: Patellar Angulation Patellar Tilt Angle>8 degrees The normal patellar tilt angle should open laterally. If the lines drawing the tilt angle are parallel or open medially, the patella is tilted and abnormally aligned. Quadriceps contraction will exacerbate patellar tilt, particularly at lower degrees of knee flexion.
Evaluating the Measurements: The femoral trochlear angle and femoral trochlear depth will decrease with increasing flexion in the normal knee. The patellar displacement and patellar angulation will remain relatively constant throughout flexion in the normal knee but may increase with quadriceps contraction and decrease with progressive knee flexion. The type of patellar malalignment (i.e. displacement vs. angulation) may also change with quadriceps contraction.
Evaluating the Measurements: While a patient may only have only one abnormal measurement, the shape of the trochlea (including the angle and depth) and the location of the patella (including subluxation and tilt) are interelated and many patients will have more than one abnormality.
What if you cant make a measurement? If there isnt a femoral trochlea to measure at the level of the patellar apex, the rest of the measurements are meaningless. This may indicate patella alta and should be correlated with a lateral plain film.
Now for some examples… Shallow femoral trochlear angle Note: a shallow femoral trochlear angle does not necessarily mean an abnormal femoral trochlear depth. 131 deg.
Now for some examples… Shallow femoral trochlear depth While an abnormal femoral trochlear depth and angle often go together, they may be isolated findings. 4mm
Now for some examples… A subluxed patella. The patella may be subluxed in isolation without tilt. +
Now for some examples… Abnormal patellar tilt. The patella is not lateralized. 6
Now for some examples… Abnormal patellar displacement and patellar tilt.
Significance of the Measurements There are no absolute radiographic measurements that indicate surgical correction. Each individual measurement should be considered as only one aspect of the patients potential problem. Many other factors, including ligamentous, cartilaginous and muscular components may be missed by this technique. Even meticulous radiographic evaluation is no substitute for a thorough history and careful physical exam.
Significance of the Measurements Each measurement has an associated cause or underlying anatomic abnormality. Shallow femoral trochlear depth and angle may indicate trochlear dysplasia or sequelae of previous dislocation as well as predisposition to recurrent patellar dislocation. An abnormal patellar tilt and angulation may indicate a tight lateral retinaculum, deficient medial ligamentous support, or malposition of the distal extensor mechanism (the tibial tubercle).
Significance of the Measurements Identification of the anatomic abnormality allows the orthopedist to select the appropriate treatment for the patient. Options for treatment of include rest, physical rehabilitation, NSAIDs or surgical intervention (lateral release, proximal or distal realignment, medial retinaculum repair, osteotomy or patellectomy).
Significance of the Measurements This patient with abnormal patellar subluxation benefited from distal realignment (osteotomy and tubercle transfer).
Conclusions Patellar instability is an important cause of anterior knee pain. Patellar instability can be easily and dynamically studied by CT. Measurements taken by CT of the patellofemoral joint can be used to identify the anatomic abnormalities contributing to patellar instability and help determine the patients therapeutic options.
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