The Knee Flashcards
What is a plica?
During embryonic development, the knee is divided into 3 separate compartments by membranes. These are resorbed and the knee becomes a single chamber. If they are incompletely absorbed, various degrees of tissue remain and are called synovial plicae. The mediopatellar plica is the most frequently cited cause of plica syndrome. It lies on the medial wall of the joint, originating suprapatellarly and coursing obliquely down to insert on the infrapatellar pad.
Describe the symptoms of an irritated plica.
The exact symptoms will be determinedby the location. THe most common symptom is pain on the medial side of the knee. It can cause discomfort with prolonged sitting (moviegoer’s sign”
Describe patella-trochlear groove contact as the knee moves from full extension to full flexion.
During the initial 20 degrees of knee flexion there is no contact between the patella and femur. From 20-45 degrees the distal third of the patella makes contact with the uppermost part of femoral condyles (initial contact between lateral patellar facet and lateral femoral condyle). From 45-90 degrees the middle third contacts the femur. At 90 degrees, the proximal potion of the patella makes contact. At full flexion, the odd facets of the patella make contact.
What is patella baja?
A low position of the patella, possibly caused by adhesions following disruption of the infrapatellar bursa. This disruption may occur during harvesting of the central third of the patella tendon for reconstruction of the ACL, or other surgery in this area
Describe the “lateral blow-out” sign of the knee.
The anterior lateral portion is thin. When swelling is present in the knee, this area bulges out, especially when the knee is flexed.
Discuss the role of the posterior oblique ligament?
It is the predominant ligamentous structure on the posterior medial corner of the knee. Attaches to the adductor tubercle of the femur and distal to tibia and posterior joint capsule, and moves laterally and proximal to lateral gastroc insertion. The main role of the ligament is to control anterior medial rotary instability and resists valgus loads when the knee moves into full extension. When an athlete makes a side step cut, the POL helps keep the pivot leg from opening in valgus. May act in synergy with the semimembranosus. Prevents excessive tibial ER and femoral IR. Considered part of the MCL complex, along with superficial and deep portions of the MCL.
What important function does the arcuate complex provide?
Similar to the POL. The arcuate complex is the posterior one third of lateral supporting structures including the LCL, arcuate ligament (y shaped from the fibular head moving proximal), and the extension of the popliteus. It helps to control IR of the femur or ER of the tibia
How does the anatomic arrangement of the ACL dictate its function?
IR of the tibia causes the ACL to tighten. The anteromedial bundle is more taut in flexion, the posterolateral band is more taut in extension. This allows the ACl to control the pivot shift through the complete knee ROM.
What is the function of the PCL?
IR of the tibia causes the ACL to tighten. It resists posterior movement of the tibia on the femur. Has 3 bundles. The posteromedial bundle is most taut in full extension.
What is the function of the IT band?
Inserts at Gerdy’s tubercle. It changes its function from extensor to flexor as the knee approaches 30 degrees flexion (inversion of muscle action). A portion of the iliotibial tract has attachments into the linea aspera to prevent the pivot-shift
How does the ITB affect the pivot-shift test of the knee?
As the knee flexes, the ITB shifts posteriorly. Normally the ACL and middle LCL prevent the shift, but in their absence the ITB allows the tibia to move posteriorly
Describe anatomic reasons for patellar instability.
A high Q angle predisposes the lateral subluxation of the patella. A loose retinaculum, patella alta, and a weak or dysplastic VMO can cause subluxation.
Describe how patella alta can lead to patellar tendinitis.
When a person decelerates, the knee is flexed and the patella should be in the trochlear groove. If patella alta is present, the patella may not be in the groove and inc stress on the patellar tendon.
Describe the arterial blood vessels of the knee.
Branches of the popliteal artery split and form a genicular anastamosis composed of the superior medial and lateral genicular arteries and the inferior medial and lateral genicular arteries. These combine to give the ACL a plentiful blood supply such that a tear leads to hemarthrosis. The middle genicular artery supplies the PCL.
Do the cruciate ligaments really cross?
Yes and they twist during knee flexion, extension, and IR
Describe the alignment of the femur and tibia during WB?
The WB line is normally slightly toward the medial knee, such that the knee is opened laterally. If this aligment is altered, tibial varum (angle greater than 170 degrees) or tibial valgum (angle less than 170*) can occur.
Are there differences between female and male knee joint anatomy and biomechanics?
No, but females tend to have a wider pelvis, greater femoral anteversion, more frequent coxa varus, and more tibial torsion (greater Q angle)
What is the normal amount of tibial torsion and how is it measured?
Measured by having the patient sit with the knee flexed to 90 degrees over the edge of a table. Visualize a line between the malleoli and look down at the top of the knee. The normal angle is 12 to 15 degrees of ER.
Which meniscus is most commonly injured and why?
medial meniscus. It is adhered to the MCL, greater WB through the medial compartment leads to more degeneration with age.
What is the Q-angle?
Measured by extending a line through the center of the patella to the ASIS and the center of the patella through the tibial tubercle. The normal value is 13 to 18 degrees. (Men tend to have less of an angle). Increases in the q angle are associated with femoral anteversion, tibial ER, genu valgum, subtalar hyperpronation
What anatomic structures encourage lateral tracking of the patella?
dysplastic patella, patella alta, or a shallow intercondylar groove can contribute to lateral tracking of the patella
How is chondromalacia classified (very general)?
There are 4 types based on arthroscopic appearance.
How is PF pain classified?
Several ways (merchant, Holmes and clancy, Wilk). Wilk described it as instability, tension (overload of muscle), friction, and compression of the joint.
What is lateral pressure syndrome?
Caused by a tight lateral retinaculum that pulls and tilts the patella laterally, increasing pressure on its lateral facet. Tx includes stretching the lateral retinaculum, medial glides and tilts, and stretching of the distal IT band. Quad strengthening or patellar taping may also be used.
Define bipartite patella?
An intact ossification center usually at the superolateral pole. Radiographs may be mistaken for a fracture.
What are the names of the “diseases” affecting the patella tendon?
Patella tendon: Osgood-Schlatter disease is apophysitis of the tibial tubercle
Quad tendon: Sinding-Larsen_Johansson disease is apophysitis of the distal pole of the patella
Can a leg length discrepancy contribute to PF pain?
The lengthened leg may cause subtalar pronation, genu valgus, walking with a partially flexed knee.
