Flashcards in Session 9 Deck (56)
Describe the bony surface involved in the knee joint
The knee is the articulation between the medial and lateral condyles of the femur and the tibia and the patellar surface of the femur and articular surface of the patellar.
The mismatched shape of the bony surfaces means that the joint is relatively weak and its stability relies on muscles and ligaments.
There is also a proximal tibiofibular joint - there is little movement here.
Out of the two femoral condyles, the medial takes more weight so it has developed to be larger.
Describe the flat-ish surface of the Tibia
Known as the tibial plateau.
Medial surface is slightly concave, lateral surface is slightly convex - BUT SOMETIMES HARD TO TELL. The two surfaces are separated by an intercondylar eminence 'elevated ridge'.
The femoral condyles rest on top of the tibial surface BuT this is not very stable due to mismatch of shapes.
What are the Menisci and what do they do?
They are crescentric plates of Fibrocartilage and deepen the surface of articulation, act as shock absorbers.
They are very hard to repair once damaged -common sporting injury.
Thicker at edges - wedge-shaped - taper to thin unattached edges in the interior of the joint.
Considered as intracapsular structures inside the knee joint.
What is the Medial Meniscus?
Attached anteriorly and posteriorly to the intercondylar areas of the tibia anterior to the attachment of the cruciate ligaments.
Laterally it is firmly attached to the tibial collateral ligament; this attachment means that damage to the tibial collateral ligament is almost invariably associated with tearing of the medial meniscus.
What is the Lateral Meniscus?
Almost circular, smaller and more movable than the medial meniscus.
It is connected to the posterior cruciate ligament by the posterior meniscofemoral ligament.
How are the Menisci connected together anteriorly?
By transverse ligament of the knee - slender fibrous band which cross the anterior intercondylar area and tethers the Menisci to each other during knee movements.
Describe the stabilising effect of muscles on the knee joint
Most important is Quadriceps femoris
Especially inferior fibres of Vastus Medialis (prevents patella sliding laterally) and Vastus Lateralis + Iliotibial tract (medially)
Describe the intracapsular ligaments
The cruciate ligsments criss cross within the joint capsule of the ligament but outside the synovial cavity.
They maintain contact with the femoral tibial articular surfaces during flexion of the knee.
The chiasm ( crossing) of the cruciate ligsments serves as the pivot for rotators movements of the knee.
Describe the Anterior Cruciate Ligament
The weaker of the two, arises from the anterior intercondylar area of the tibia, just posterior to the attachment of the medial meniscus. Attaches to the proximal part of the medial side of the lateral condyle of the femur.
Relatively poor blood supply (so healing is more difficult).
Limits posterior rolling (turning and travelling) of the femoral condyles on the tibial plateau, converting it to spin (turning in place).
Also prevents posterior displacement of the femur on the tibia and hyperextension of the knee joint.
When the joint is flexed at a right angle, the tibia cannot be pulled an trophy (like pulling out a drawer) because it is held by the ACL.
Describe the Posterior Cruciate Ligament
The stronger of the two cruciate ligaments, arises from the posterior intercondylar area of the tibia and attaches to the anterior part of the lateral surface of the medial condyle of the femur - passing superiorly and anteriorly on the medial side of the ACL to do do.
The PCL limits anterior rolling of the femur on the tibial plateau during extension, converting it to spin.
Also prevents anterior displacement of the femur on the tibia or posterior displacement of the tibia on the femurs and hyperflexion of the knee joint.
In the weight-bearing flexed knee, the PCL is the main stabilising factor for the femur e.g. When walking downhill.
What is PAMs APpLes?
Regarding cruciate ligaments:
Posterior passes Anteriof inserts Medially
Anterior passes Posterior inserts Laterally
What are the Collateral Ligaments?
Taut when the knee is fully extending, contributing to stability while standing. As flexion proceeds they become increasingly slack, permitting and limiting (serving as check ligaments) rotation at the knee - prevent excessive medial of lateral displacement of the joint.
Medial (Tibial) and Lateral (Fibular)
Describe the TCL and FCL
Tibial Collateral Ligament: weak, flattened
Fibular Collateral Ligament: strong cord-like
TCL: extends from medial epicondyle of femur to medial condyle and superior part of the medial surface of the tibia.
FCL: extends from the lateral epicondyle to the lateral surface of her Fibular head (also reinforced by Ilio-tibial tract). The tendon of the biceps femoris is split into parts by the FCL.
What is clinically important to know about the collateral ligaments?
The tendon of the popliteus passes deep to the FCL separating it from the lateral meniscus.
At its midpoint, deep (middle) fibres of the TCL are firmly attached to the medial meniscus.
What are the other extra-capsular ligaments of the knee joint, apart from the collateral ligaments?
Patellar ligament: distal part of the quadriceps femoris tendon passing from the apex and adjoining margins of the patella to the tibial tuberosity. It is an anterior ligament.
Oblique popliteal ligament: recurrent expansion (thickening) of the tendon of the semimembranosus that reinforces the joint capsule posteriorly as it spans the intercondylar fossa.
Arcuate popliteal ligament also strengthens the joint posterolaterally. Both popliteal ligaments are thought to contribute to posterolateral stability of the knee.
What happens when the knee is locked in extension?
When the knee is fully extended with the foot on the ground, the knee passively "locks" because of medial rotation of the femoral condyles on tibial plateau (femur rotated internally over Tibia).
This makes the lower limb a solid column and more adapted for weight bearing. The thigh and leg muscles can relax briefly without making the joint too unstable.
To unlock the knee, the popliteus contracts, rotating the femur laterally about 5 degrees on the tibial plateau so that flexion of the knee can occur.
Describe the blood supply to the knee joint
10 vessels that form the peri-articular genicular anastomoses around the knee: the genicular branches of the femoral, popliteal and anterior and posterior recurrent branches of the anterior tibial recurrent and circumflex Fibular arteries.
The middle genicular branches of the popliteal artery penetrate the fibrous layer of the joint capsule and supply the cruciate ligaments, synovial membrane and peripheral margins of the Menisci.
Describe the innervation of the knee joint
Reflecting Hilton's law, the muscles supplying the muscles crossing (acting on) the knee joint also supply the joint --> articular branches from the femoral, tibial and common Fibular serves supply its anterior, posterior and lateral aspects respectively.
However the obturator and saphenous (cutaneous) nerves supply articular branches to its medial aspect.
What does knee joint stability depend on?
Depends almost entirely on its associated ligaments and surrounding muscles.
If a force is applied against the knee when the foot cannot move, ligament injuries are likely to occur.
Ligament injuries refers to damage of the collaterals, cruciates and Menisci. Sometimes all 3.
How would you test the collateral ligaments?
The TCLs and FCL are tightly stretched when the leg is extended, normally preventing disruption of the sides of the knee joint.
Damage of the collateral ligaments can be assessed by attempting to either medially rotate or laterally rotate the tibia on the femur (rotation of the knee) against resistance. Pain on attempted medial rotation indicates damage to the TCL and pain on attempted lateral rotation indicates damage to the FCL.
What is the Unhappy Triad of Knee Injuries?
Firm attachment of the TCL to medial meniscus is clinically significant because tearing of this ligament frequently results in concomitant testing of the medial meniscus.
Injury is frequently caused by a blow to the lateral side of the extended knee or excessive lateral twisting of the flexed knee that disrupts the TCL and concomitantly tears and/or detaches the medial meniscus from the joint capsule.
This is a common injury in basketball, football and volleyball - athletes who twist their flexed knees laterally while running.
The ACL (arises just posterior to the attachment of the medial meniscus, pivot for rotator movements of the knee and is taut during flexion) may also tear subsequent to the rupture of the TCL, creating an unhappy triad.
How may the ACL be damaged and how could you test the ACL for damage?
Can be damaged in hyperextension of the knee joint and severe force directed anteriorly against the femur with knee semiflexed (e.g. A cross-body block in football).
ACL rupture is a common injury in skiing accidents - the free tibia slides anteriorly under the fixed femur known as the anterior drawer sign. You test the ACL pulling the tibia forwards on the femoral condyles.
The ACL may tear away from the femur of tibia; however tears commonly occur in the mid portion of the ligament.
How may the PCL be damaged and how could you test the PCL for damage?
Although the PCL is stronger, it can be damaged by falling onto the tibial tuberosity when the knee is flexed (e.g. When knocked to the floor in basketball).
PCL ruptures usually occur in connection with tibial or Fibular collateral ligament tears. They can also occur in head-on collisions when seat belts are not worn and the proximal end of the tibia strikes on the dashboard.
PCL ruptures allow the free tibia to slide posteriorly under the fixed femur - tibia is pushed back against the femur - known as the posterior drawer sign. To test the PCL, push the tibia posteriorly in the femoral condyles.
Why is the Lateral Meniscus not normally injured when the PCL is injured?
It is relatively mobile and PCL is not attached to it.
Pain on lateral rotation of the tibia on the femur indicates injury of the lateral meniscus.
How are Menisci usually injured?
Menisci are usually injured in conjunction with TCL or ACL injuries.
Pain on medial rotation of the tibia on the femur indicates injury of the medial meniscus.
Peripheral meniscal tears can often be repaired or they may heal on their own because of the generous blood supply to this area.
If the tears do not heal or cannot be repaired, the meniscus is removed (e.g. By arthroscopic surgery). Knee joints from which a meniscus has been removed suffer no loss of mobility; however the knee may be less stable and the tibial plateau often undergoes inflammatory reactions.
What is Suprapatellar Bursitis?
An infection caused by bacteria entering the Suprapatellar bursa from the torn skin (due to abrasions or penetrating wounds).
The infection may spread to the cavity of the knee joint, causing localised redness and enlarged popliteal and inguinal lymph nodes.
Suprapatellar bursa is an extension of the synovial cavity of the knee between the quadriceps femoris and the femur.
What is Prepatellar Bursitis?
Friction between the skin and patella however the bursa may also be injured by compressive forces resulting from a direct blow or from falling on the flexed knee.
If the inflammation is chronic, the bursa becomes distended with fluid and forms a swelling ANTERIOR to the knee - "Housemaid's Knee"
The prepatellar bursa lies between the apex of the patellar and the skin.
What is Subcutaneous (superficial) Infrapatellar Bursitis?
Caused by excessive friction between the skin and the tibial tuberosity; the Oedeoma occurs over the PROXIMAL end of tibia "Clergyman's Knee" (roofers and floor tillers).
Superficial Infrapatellar bursa is found between the tibial tuberosity and skin.
What is Deep Infrapatellar Bursitis?
Results in oedema between the patellar ligament and the tibia, superior to the tibial tuberosity.
The inflammation is usually caused by overuse and subsequent friction between the patellar tendon and the structures posterior to it, the Infrapatellar fat pad and tibia.
Enlargement of the deep Infrapatellar bursa obliterates the dimples normally occurring on either side of the patellar ligament when the leg is extended.
Bursa lies between the patellar tendon and the tibia.