Knee & Shoulder short answers Flashcards
Describe the coracoacromial arch and the structures that can be found between it and the humeral head.
The coracoarcromial arch consists of the acromion, coracoid process and the coracoacromio ligament. It is superior to the glenohumeral joint and is so strong that if the humeral head is thrust superiorly it will break before the arch does. Between the arch and the humeral head lies the subacromial bursa and the supraspinatus tendon.
List the rotator cuff muscles and discuss their importance
The rotator cuff consists of four muscles; Supraspinatus, Infraspinatus, Teres Minor and subscapularis. Collectively the rotator cuff muscles stabilize the glenohumeral joint by compressing the humeral head against the glenoid cavity
Supraspinatus reinforces the joint capsule superiorly and is the main abductor of the shoulder. It inserts on the superior aspect of the greater tubercle.
Infraspinatus and Teres Minor reinforce the joint capsule posteriorly and aid in external rotation. They insert onto the greater tubercle and the posterior joint capsule.
Subscapularis reinforces the joint capsule anteriorly and aids in internal rotation. It inserts onto the lesser tubercle.
Discuss the causes of impingement syndrome of the shoulder
External impingement syndrome is where the rotator cuff is impinged in a part of the shoulder known as the sub-acromial space. Internal impingement involves other structures within the Glenohumeral joint.
Impingement syndrome is most commonly caused by the acromion impinging on the rotator cuff. This is commonly called external or subacromial impingement. It can be due to arthritis, acromion shape and spurs usually as a part of the normal ageing process.
Impingement can also occur due to repetitive overhead movements such as pitching a baseball wherein the humeral head is repeatedly thrust up into the acromion causing pain and inflammation of the surrounding rotator cuff and bursa.
Describe the bony structures of the knee
The knee consists of three bones, Femur, tibia and patella. The fibula is not a part of the knee joint.
The femur has two condyles, medial and lateral, that make up most of the articular surface of the femur. There are medial and lateral epicondyles superior to these that provide attachments for ligaments and the medial adductor tubercle that provides attachment for adductor magnus. The patella articular surface is found on the anterior of the femur and is two smooth grooves between the condyles. The intercondylar fossa at the posterior of the femur provides passage for important vessels and nerves.
The tibia has two almost flat articular surfaces known as the medial and lateral tibial condyles and are together known as the tibial plateau. Between the condyles are the medial and lateral intercondylar eminences and surrounds that provide attachment for the cruciate ligaments and menisci. The tibial tuberosity is at the anterior of the tibia and provides attachment for the patella tendon.
The patella is a triangle shaped sesamoid bone. The flat base provides attachment for the quadriceps tendon and the pointed apex is the origin of the patellar ligament. The posterior of the patellar is it’s smooth articular surface.
Discuss movements of the knee and the muscles involved
The knee primarily undergoes flexion and extension however there is some gliding and rotation.
Flexion of the knee is facilitated by the hamstring muscles. Biceps femoris laterally, semimembranosus and semitendinosus medially. Gastrocnemius muscles also aid in flexing the knee and ankle as do the Flexors on the medial side of the knee (Sartorius, Gracilis and pes ancerine (gooses foot)) albeit, weakly.
Extending of the knee is facilitated by the quadriceps muscles. Rectus femoris, vastus medialis, vastus intermedius and vastus lateralis.
During the last 20 degrees of knee extension the tibia glides anteriorly on the femurs medial condyle as it is longer.
This prolonged anterior glide on the medial side produces external tibial rotation (the screw home mechanism)
The muscle that locks the knee is the tensor fascia lata and gluteus maximus by way of the Ilio Tibial Tract. They originate on ASIS and insert onto the ITT. The ITT attaches to the lateral condyle of the tibia. It is a hip abductor and steadies the femoral condyles on the tibia.
To unlock the knee the popliteus contracts, rotating the femur laterally 5 degrees on the tibial plateau so flexion can occur. The popliteus originates on the posterior tibia inferior to the condyle and inserts on the lateral femoral condyle, its tendon runs into the knee joint capsule to the posterior lateral meniscus.
Describe the soft tissues that support and protect the knee.
The knee joint is relatively weak and relies on the strength and action of surrounding muscles and their tendons and the ligaments that connect the femur and tibia.
The erect, extended position of the joint is most stable as the articular surfaces are congruent, the primary ligaments (cruciate and collateral) are taut and the many tendons around the joint provide a splinting effect.
The fibrous layer of the joint capsule has a few thickened parts that make up intrinsic ligaments but mostly it is thin and incomplete in some areas.
The fibrous layer has an opening posterior to the lateral tibial condyle where the Tendon of popliteus passes out of the joint capsule to attach to the tibia.
The quadriceps tendon, Patella and patella ligament replace the fibrous layer anteriorly, that is to say the fibrous layer is continuous with the lateral and medial margins of these structures.
The synovial membrane covers all surfaces that aren’t articular. It lines the fibrous layer laterally and medially but becomes detached from it centrally. From the posterior aspect of the joint the synovial membrane reflects anteriorly into the intercondylar region covering the cruciate ligament and infrapatellar fat pad so they are excluded from the articular cavity. This creates the median infrapatellar synovial fold.
Superior to the patella the knee joint cavity extends deep to the vastus intermedius as the supra patella bursa.
Prepatellar bursa between patella and skin, results in “housemaid’s knee” when inflamed. It allows movement of the skin over the underlying patella.
Deep infrapatella bursa between the upper part of the tibia and the patellar ligament. It allows for movement of the patellar ligament over the tibia.
Superficial infrapatella bursa between the patellar ligament and skin.
There are five extracapsular ligaments of the knee (also called intrinsic or capsular to help differentiate between the internal ligaments). The patellar ligament, fibular collateral, tibial collateral, oblique popliteal and arcuate popliteal ligaments.
The patella ligament joins the distal margins of the patella to the tibial tuberosity. The medial and lateral portions of the quadriceps tendon form the patella retinacula which make up the joint capsule on either side of the patella and help maintain patella alignment.
The fibular collateral (A) ligament or lateral collateral is not connected to the lateral meniscus (M) as popliteus (B) passes deep to it.
The tibial collateral ligament or Medial collateral is firmly attached to the medial meniscus. The TCL is weaker than the FCL and more often damaged. As a result, the TCL and medial meniscus are commonly torn during sports.
Oblique popliteal and arcuate popliteal both reinforce the joint capsule posteriorly.
The intra articular ligaments of the knee consist of the cruciate ligaments and menisci. The tendon of popliteus is also intra articular during part of its course.
The cruciate ligaments criss cross each other. During medial rotation they wind around each other limiting movement to about 10 degrees. During lateral rotation they become unwound so that nearly 60 degrees of lateral rotation is allowed when the knee is flexed at 90 degrees.
The anterior cruciate ligament is the weaker one. It arises from the anterior intercondylar area of the tibia. It limits posterior rolling of the femur on the tibia and hyperextension of the knee joint. When the joint is flexed 90 degrees the tibia cannot be pulled anteriorly because the ACL holds it back. guides the screw home mechanism associated with knee extension
The posterior cruciate ligament is the stronger one. It arises from the posterior intercondylar area of the tibia. The PCL limits anterior rolling of the femur on the tibia and hyperflexion. The PCL is the main stabiliser for the femur when flexed and weight bearing i.e. walking downhill.
The menisci are fibrous cartilaginous discs between the tibia and femoral articular surfaces. They are thicker laterally and thin medially. They are firmly attached to the intercondylar area of the tibia and externally to the fibrous capsule. The coronary ligament joins the menisci posteriorly and the transverse ligament anteriorly.
Briefly describe two soft tissue injuries that can occur around the knee.
Collateral ligament injury
The medial (or tibial) collateral ligament is more easily damaged than the Lateral (fibula) collateral ligament. The LCL is not attached to the lateral meniscus as the popliteal ligament passes deep to it.
The MCL is attached to the medial meniscus and as a result the MCL and medial meniscus are commonly torn during sports.
The cause of collateral ligament injuries is most often a blow to the lateral side of the leg that cause the medial ligament to stretch and tear and as such the medial meniscus. For example, a hockey puck hitting the knee.
Bursitis is when the bursa fills with excessive fluid and causes pressure in the surrounding tissues. It can be caused by overuse injuries, repetitive movement, trauma and excessive pressure or infection Pre-patella bursitis is most common in people who spend time kneeling (often called housemaid’s knee, carpet layer’s knee).
