Patellar Conditions Flashcards
Patellar dislocation - Definition/Description
Clinically relevant anatomy
Clinical presentation
A patellar dislocation occurs by a lateral shift of the patella, leaving the trochlea groove of the femoral condyle. This mostly occurs as a disruption of the medial patellofemoral ligament.
The patellofemoral joint makes part of the knee joint. The articular surfaces consist of the patella and the trochlear surface of the femoral condyles.
The articular cartilage on the medial facet is thicker than on the lateral facet, with the lateral facet bigger than the medial It has an anterior projection on the lateral femoral condyle, lateral to the patellar groove. This prevents lateral dislocation of the patella.
The patellofemoral articulation depends on the function of the quadriceps as it increases the angle of pull of the patellar tendon, improving the mechanical advantage of the quadriceps in knee extension.
The suspension and movement of the patella is provided by passive and active stabilizers:
Passive stabilizers: Tensor fascia lata, patellar ligament, knee capsule, patellofemoral ligament (medial and lateral), meniscopatellar ligament (medial and lateral)
Active: Quadriceps, patellar ligament, retinaculum
The medial patellofemoral ligament is the primary stabiliser (53-67%) against lateral displacement/dislocation of the patella.
It is situated deep to the vastus lateralis muscle, ranging from the posterior aspect of the medial femoral condyle to the superiomedial part of the patella, vastus medialis and quadriceps tendon
One of the common findings related to acute, primary, traumatic patellar dislocations is hemarthrosis of the knee, caused by rupture of the medial restraints of the patella. Medial swelling will also be prominent.Patellar dislocations often reduce spontaneously when the knee are extended.
Main complaints from the patient will include:
Pain
Instability of the knee
Locking of the knee after the trauma
Patella alta
Patella alta or high-riding patella refers to an abnormally high patella in relation to the femur. The patella sits high on the femur where the groove is very shallow. Here, the sides of the femoral groove provide only a small barrier to keep the high-riding patella in place. This condition has been associated clinically with patellofemoral dysfunction and is considered a predisposing factor for the development of patellofemoral pain (PFP). Patella alta is also characterized as instability of the patella
Patella alta can occur as the result of a sports injury, though, it’s largely majority of the time it is a congenital/developmental condition that is unrelated to trauma. Its pathophysiology is not completely clear, but it is hypothesized that one of the causes of patella alta, are abnormally long patellar tendons
Patella alta is a positional fault defined most simply as the superior displacement of the patella within the trochlear groove of the femur. Patella alta has been shown to be associated with chondromalacia on the articular surface of the patella and pain. Patella alta has also been implicated in patellar osteoarthritis. The prevalence of patella alta in individuals with patellar osteoarthritis was 6 times that of individuals with normal patellar articular cartilage. Additionally, both Leung et al (1996) and Kannus (1992) reported that subjects with anterior knee pain demonstrated a significantly more superior patellar position in the affected knee relative to healthy, control knees.
A common symptom of patellar injury and dislocation is acute pain after direct contact or sudden change of direction. With sudden changes in direction, the femur medially rotates over the ground-stabilized tibia. Under these conditions, athletes commonly feel the knee giving way, which is the result of quadriceps inhibition from pain, a physiologic protective mechanism. Rapid swelling, intense knee pain, and difficulty with any knee flexion usually occur. Other dysfunctions with similar presentations and mechanism of injury are meniscal and ligamentous injuries, particularly injuries of the anterior cruciate ligament
The patient sits on the edge of the examination table with the feet on the ground. The knees are bent at 90 degrees, and the thigh is horizontally positioned. The vertical position of the patella height is best observed from lateral. In Patella Alta it can be seen that the partially tilted patella protrudes above the level of the thigh. This is more remarkable In a unilateral Patella alta. A patella alta may be noticed during inspection thanks to a so-called Camel hump patella The knee has two striking bulges: one is the tibial tuberosity, the other one is the patella. The space distal to the patella and proximal to the fat body of Hoffa is characterized by a notch.
