Knee Joint.pdf

Musculoskeletal System Knee Joint Welcome to this lecture on the knee joint. There should be cause for some celebration perhaps, as in case it has escaped your notice, we have reached a point halfway down the limb! The bad news is that this is a complicated...

Musculoskeletal System Knee Joint Welcome to this lecture on the knee joint. There should be cause for some celebration perhaps, as in case it has escaped your notice, we have reached a point halfway down the limb! The bad news is that this is a complicated joint and there is a lot to say. As a result I have divided this lecture into 4 parts.  Learning Outcomes After this lecture you should be able to: ▪ Describe the bony anatomy of the knee joint, including the shape of the articular surfaces ▪ Know that the femoral and obturator nerves may refer knee pain to the hip and vice-versa ▪ Describe the patello-femoral joint and list its common clinical problems ▪ Define the terms “genu valgum” and “genu varum” ▪ Describe the ligaments of the knee joint and give their functions ▪ Know the position, shape and functions of the menisci, and give an account of their common injuries ▪ Give an account of the movements of the tibiofemoral joints ▪ Describe the capsule and synovium of the joint, and list the bursae associated with it. Know the symptoms and signs of inflammation of these bursae Here are the learning outcomes for this entire lecture.  Musculoskeletal System Knee Joint Part 1: Overview and Knee Dislocation In this first part, we’ll get an overview of the joint and review its instability.  Learning Outcomes After this lecture you should be able to: ▪ Describe the bony anatomy of the knee joint, including the shape of the articular surfaces ▪ Know that the femoral and obturator nerves may refer knee pain to the hip and vice-versa ▪ Describe the patello-femoral joint and list its common clinical problems ▪ Define the terms “genu valgum” and “genu varum” ▪ Describe the ligaments of the knee joint and give their functions ▪ Know the position, shape and functions of the menisci, and give an account of their common injuries ▪ Give an account of the movements of the tibiofemoral joints ▪ Describe the capsule and synovium of the joint, and list the bursae associated with it. Know the symptoms and signs of inflammation of these bursae The learning outcomes for this part of the lecture are that afterwards you should be able to; Describe the bony anatomy of the knee joint, including the shape of the articular surfaces Know that the femoral and obturator nerves may refer knee pain to the hip and vice-versa Describe the patello-femoral joint and list its common clinical problems Define the terms “genu valgum” and “genu varum” The remaining outcomes will be dealt with in subsequent sections of the lecture.  The Knee Joint Overview The knee joint is a surprisingly stable joint considering the bony architecture. There are actually four articulations; the medial and lateral patello-femoral joints, and the medial and lateral tibiofemoral joints. The femoral condyles are large and rounded. The tibial condyles in contrast are almost flat and are hence referred to as ‘plateaus’. This is not an ideal surface on which to base a hinge joint, as the potential for the condyles of the femur to slip off the plateaus are great. All around the joint however, are intracapsular as well as extracapsular ligaments to keep the joint stable.  The Knee Menisci These joint surfaces are also made more stable by the presence of intra-synovial articular discs called menisci. There is a medial meniscus and a lateral meniscus. These are wedge-shaped semi-circular discs which help to deepen the socket for the femoral condyles and hence give added support.  Muscles Crossing the Knee Joint The stability of the joint is also added to by the tone of the muscles of the thigh and leg which cross it. Normal Range of Movements of the Knee o o 30-40 10 o 0-135 The knee joint is a modified synovial hinge joint. It is capable of flexion by 135-140 degrees, but cannot extend beyond the 0 degrees in the normal knee. There are some individuals with hyperextendable knees, but this is due to laxity of ligaments. In the normal knee, hyperextending puts these ligaments at risk of rupture. The hinge is modified as it permits some rotation at the extremes of flexion and extension. In flexion, most of the ligaments are relaxed at hence the joint can be rotated. This involves rotating the tibial plateau on the femoral condyles. Since the menisci are attached to the tibia, the menisci also rotate. The knee typically rotates 10 degrees internally, and 30-40 degrees externally. There is also a medial rotation of the femur on the tibia during the final stages of extension. The tibia is normally on the ground during this action, so it is the femur that moves. We’ll see in the next part of the lecture, that this action is an important one to adjust ligament tension in this phase of standing or walking.  Neurovasculature of the Knee Joint (not for inclusion in the lecture presentation) The capsule of the knee joint is supplied by four nerves. These are the femoral nerve and obturator nerve, anteriorly and medially, and the tibial and common fibular nerves posteriorly and laterally. You don’t need to worry about the detail however. The only key thing to remember is that the femoral and obturator nerves also supplied the hip joint. Pain is often referred from one joint to another. This is quite bizarre! It is like the brain is saying “OK – I’ve picked up pain signals from the femoral nerve, so what could that mean? It looks up the manual and the first thing the manual says is it carries signals from the hip, so it gives the patient an awareness of a pain in the hip, not knowing that the femoral nerve also supplies the knee. It’s very telling about the guesswork in our brain’s processing. Maybe it knows that it could be both and just tosses a coin every time. The blood supply is from an anastomosis from the popliteal artery and descending branches from the hip and thigh, together with recurring branches from below. You don’t need to know any of the detail here. The term genu is directly from the Latin for knee, hence these are the genicular arteries. Again, all you need to appreciate is the branches for a rich anastomosis. Please Note: This material is not examinable and is given for interest only (although you should be aware that the femoral and obturator nerves supply both hip and knee joints, and hence pain can be referred from one to the other).  Retinaculae of the Knee Joint Lateral Medial retinaculum retinaculum Lateral collateral Infrapatellar fat pad ligament (capsule absent) Medial Patellar collateral tendon ligament The joint is remarkable in many ways, not least because this synovial joint does not have a capsule anteriorly. The synovium is therefore free to move under the quadriceps muscle at the front of the joint. In addition, there are many gaps in the capsule, that allow the synovium to form bursae outside the joint capsule. There are said to be at least 12 bursae around the joint.. We’ll have a chance to discuss some of those in part 4 of this lecture. Like most hinge joints in the body, the knee is supported by collateral ligaments. These are the lateral (or fibular) collateral ligament and the medial (or tibial) collateral ligament. The patellar tendon acts like a ligament supporting the front of the joint and is often referred to as the ligamentum patellae. There is a pad of fat behind the patellar tendon, and this prevents the synovium from escaping from the joint anteriorly. However, this is aided even more by expansions of the tendons of the vasti muscles crossing downwards over the joint. These are the medial and lateral retinaculae. These keep both the synovium and fat pad in check.  Capsule of the Knee Joint Oblique popliteal ligament Arcuate ligament At the back of the joint the capsule is strong, and it is supported by the oblique popliteal and arcuate ligaments. The capsule is taut in full extension but relaxed during flexion. As we will see later, there are a multitude of ligaments that support the joint, but we’ll discuss them in the part 3 of the lecture.  Knee Dislocation Due to all of the ligaments and tendons, the knee is amazingly stable despite its bony instability. Of course the reason the joint lacks a good bony support is because it is designed to permit a huge range of movement. A joint is only as stable as it can be against the forces placed upon it. If the force is extreme, then the joint will dislocate. Since the extensor apparatus is very stable and strong in front, the femur tends to dislocate backwards. However, it requires a major traumatic event however for this to happen. The classification of a knee dislocation is based on the direction of displacement of the tibia, not the femur. Hence what we see here is an anterior dislocation. These are the most common type and are usually caused by hyperextension of the knee. This can occur in motor vehicle accidents, falling from a height or via heavy contact in sporting activity. They are however, very rare. Please Note: This material is not examinable and is given for interest only.  The Patello-Femoral Joints Let’s now consider the patello-femoral part of the joint. The patella is a triangular shaped sesamoid bone and has a base above and an apex below. The quadriceps tendon attaches to the base and the patellar tendon attaches to the apex. It forms an articulation between both of the femoral condyles. The fact that the patella is able to articulate at the knee joint is remarkable in itself. The patella is merely a sesamoid bone within the tendon of the quadriceps muscle. It is only able to do so by the absence of the anterior part of the capsule. Although the posterior surface of the patella becomes incorporated into the knee joint, it only articulates with the femoral condyles, and does not articulate at all with the tibia. It hence forms the medial and lateral patello-femoral joints. The Patello-Femoral Articular Surfaces M L There is an articular surface of the patella for each condyle with a vertical ridge in between, clearly signaling that there are two separate articulations. The lateral femoral condyle projects more anteriorly than the medial one and is hence larger. The lateral articular surface on the patella is also larger to match.  The Sunrise View This discrepancy between medial and lateral articular surfaces is obvious to see on a sunrise view X-ray of the knee. This is the view commonly used to visualize the patellofemoral joints.  Function of the Patella It might seem obvious why the patella exists. It clearly protects the quadriceps tendon from excessive friction at the joint. However, it is also to make the mechanics of the knee more efficient. This model of the joint with and without a ‘patella’ make the point clearly. Extension of the knee is much more difficult without a suitable fulcrum around which quadriceps can act as a lever.  Patello-Femoral Dislocation Most dislocations of the knee joint are lateral dislocations of the patella. These are often caused by sudden medial rotation of the femur, such as in twisting of the joint. In the normal knee, the patella is pulled upwards by the quadriceps muscle via its tendon. The direction of pull is along the mechanical axis of the femur. This is exactly the direction of the fibres of the rectus femoris muscle. However, the vastus intermedius and vastus lateralis pull the patella laterally, with the vastus intermedius tending to pull along the anatomical axis of the femur, and vastus lateralis even further laterally. The resultant pull from these two strong muscles tends to cause the patella to deviate from its intended course and could potentially cause dislocation. The potential dislocation is prevented by two factors. Firstly, the lateral condyle of the femur is elevated (projects further forwards) to prevent this displacement. Secondly, the fibres of vastus medialis insert into the lower border of the patella and are orientated almost horizontally at this point. This serves to correct the lateral pull of the others. In patients with a wasting of the vastus medialis (e.g.; after prolonged bed rest), or a congenital under-developed lateral epicondyle, there is a tendency for the patella to dislocate laterally.  Signs of Patello-Femoral Dislocation (not for inclusion in the lecture presentation) Not only is it obvious by the patients state of pain and discomfort that the patella has dislocated, but the physical signs are blatantly obvious. Here we can an example where the left patella has dislocated laterally. Medial dislocation is possible, but very rare. Please Note: This material is not examinable and is given for interest only.  Q-Angle (not for inclusion in the lecture presentation) Because the femur is angled, the quadriceps muscle pulls along the mechanical axis rather than the anatomical one. This creates an angle across the knee joint, known as the quadriceps angle (or Q-angle). This angle is measured by a one line drawn from the anterior superior iliac spine and centre of the patella, and another from the tibial tuberosity to the centre of the patella. The angle of intersection of the two lines is the Q-angle. The angle can be measured by a simple protractor. Since females have wider hips, the femur is angled more, and hence the Q-angle is greater in women than it is in men. This equates to about 17 degrees in women and 14 degrees in men. However, this Q-angle can also be affected by some pathologies. Excessively wide hips will increase this angle, as will abnormally placed knees (e.g.; genu valgum or tibial torsion). An increase in the Q-angle is sometimes associated with increased femoral anteversion or femoral torsion. A high Q angle places enormous strain on the patella and can lead to such individuals being prone to patellar dislocation. Sometimes though, the cause of an abnormal Q-angle is due to a mal-positioned patella (e.g.; a high riding patella or a displaced patella). Please Note: This material is not examinable and is given for interest only.  Knee Angles (not for inclusion in the lecture presentation) genu varum genu valgum (bow leg) (knock-knee) A patient with a genu valgum will have an increased Q angle, and this puts enormous stress on the medial collateral ligament. It also puts an increased pressure on the cartilage and bone on the lateral side of the joint. Colloquially, a genu valgum is known as knock-knee. The opposite to a genu valgum is a genu varum. This is also known as a bow-leg, and it will cause a stretch the lateral collateral ligaments and put excessive strain on the medial side of the joint. This can lead to tearing of the cartilaginous disc (meniscus) and condyles of tibia and femur on that side. One reason for the development of these conditions is weakness of the ligaments on the appropriate side. The lack of support allows the joint to bend to the side. Please Note: This material is not examinable and is given for interest only.  Musculoskeletal System Knee Joint Part 2: Tibiofemoral Joints Welcome to this second part of the lecture on the knee joint. In this part we will look at the joints between the femoral and tibial condyles.  Learning Outcomes After this lecture you should be able to: ▪ Describe the bony anatomy of the knee joint, including the shape of the articular surfaces ▪ Know that the femoral and obturator nerves may refer knee pain to the hip and vice-versa ▪ Describe the patello-femoral joint and list its common clinical problems ▪ Define the terms “genu valgum” and “genu varum” ▪ Know the position, shape and functions of the menisci, and give an account of their common injuries ▪ Give an account of the movements of the tibiofemoral joints ▪ Describe the ligaments of the knee joint and give their functions ▪ Describe the capsule and synovium of the joint, and list the bursae associated with it. Know the symptoms and signs of inflammation of these bursae The learning outcomes for this part of the lecture are that afterwards you should be able to Know the position, shape and functions of the menisci, and give an account of their common injuries Give an account of the movements of the tibiofemoral joints The remaining outcomes will be dealt with in subsequent parts of the lecture.  Tibiofemoral Joints There are two joints here – a medial one and a lateral one. On each side the tibial condyle articulates with the femoral condyle. Remember, the tibial condyles are misnamed as they are flat. A condyle means a knuckle-shape, which is certainly true for the femoral condyles, but the tibial ones are flat. They are therefore also referred to as tibial plateaus.  The Menisci Posterior horns Transverse genicular ligament Anterior horns The incongruence of the articular surfaces of the knee joint is compensated for by the presence of articular fibro-cartilaginous pads over each tibial condyle - the menisci. These menisci are wedge- shaped pads, which have anterior and posterior horns attached to the sides of the tibial intercondylar eminence. They are composed of bands of longitudinally arranged collagen fibres which run between the two horns. They are thicker around the periphery, and thinner medially. Indeed they have a medial margin which does not cover all of the articular surface of the condyle. The medial meniscus is C-shaped, whilst the lateral meniscus is O-shaped. They are attached to the margins of the tibial condyles by a coronary ligament. This runs all the way around the inferior margin of each meniscus. In addition, the medial meniscus is anchored to the deep part of the medial collateral ligament. The lateral meniscus has no similar attachment to its collateral ligament is hence is freer to move. The two anterior horns are attached to each other by the transverse genicular ligament. Between these two horns there is the attachment of the anterior cruciate ligament. Similarly, between the two posterior horns there is the attachment of the posterior cruciate ligament.  Functions of the Menisci The menisci clearly act to make the joint more congruous. They serve to deepen the concavity of the tibial condyles and help to wedge the femoral condyles in place during movement of the joint. They also act as shock-absorbers and help to evenly distribute the load of body weight on the joint. As the menisci become compressed they lose some of the synovial fluid contained within them. This aids lubrication of the joint by acting like wet sponges. As the synovial fluid moves in and out of the menisci during walking, it helps in the lubrication of the joint.  Tears of the Menisci Tears of the menisci are common as they are subject to large forces placed upon them. There are many different types of tear, and these can be along the longitudinal axis, horizontal axis or radial axis. There are a multitude of other classifications of these tears which are beyond the scope of this lecture.  Red Zones of the Menisci The menisci are intra-synovial and so are bathed in synovial fluid, from which they receive their nutrients, but the most peripheral part of the meniscus is also able to receive a blood supply, as it lies close to (indeed attaches to) the capsule. There is termed the red zone. A torn meniscus without access to blood directly will not heal quickly or effectively. Torn menisci are therefore often repaired or removed surgically. Sometimes pain at the joint line or abnormal clicks in the joint are some of the indications of meniscal damage.  Meniscal Tears Medial collateral ligament The lateral meniscus is freer to move than the medial one, and hence is less likely to be torn as it can adapt to excessive forces placed upon it. The medial meniscus is attached to the deep part of the medial collateral ligament, and hence is less able to escape from any undue stress. The most common injury is a longitudinal tear along the length of the meniscus and is called a ‘bucket-handle’ tear because it leaves a medial segment which is no longer tethered and is free to flip over like a bucket-handle. This may cause an interference with the articulations, and the knee may not fully extend. There are many other classifications of meniscal tears, but this is one of the most problematic as the loose segment may interfere with movement of the joint.  Tibio-Femoral Joint L L A P P A M M This is a view of the articular surfaces of the right tibia and right femur. The joint has been fully flexed and then the bones turned edge on. Hence the anterior side of the tibia is to the left, and the anterior side of the femur is on the right. The lateral articular surfaces of both bones is shown in orange. Remember, the most anterior part of the femoral condyle is reserved for the articulation with the patella. During walking, when body weight is loaded onto the joint, the knee is in extension, and when the other limb takes the body load, the joint can be flexed again. To move from flexion to extension there is a combination of gliding and rolling of the femoral condyles over the tibial plateaus. The femoral interaction starts from its posterior side and glides and rolls forwards. The medial articular surfaces are shown in green. You can see that there is asymmetry between the medial to lateral sides. The medial femoral condyle is larger and more curved than the lateral. When the two condyles interact with the tibia, the femoral condylar surface moves anteriorly, but the lateral one will use up its articular surface quicker than the medial one. Hence, the medial side can continue in extension until its surface is used up. This causes a medial rotation of the femur on the tibia in the final 15 degrees of extension. This rotation causes a tightening of all of the ligaments of the joint, and therefore puts the joint into a ‘close- packed’ position. In such a position, there is little freedom of movement, and the joint becomes a solid stable entity. The joint is then said to be ‘locked’.  Popliteus Muscle Arcuate ligament If the joint is locked in full extension, it needs to be rotated in the opposite direction in order to be unlocked. Hence the role of the popliteus muscle is to laterally rotate the femur. This muscle arises from the triangular area in the back of the tibia, just proximal to the soleal line, and inserts onto the lateral femoral epicondyle. It attaches inside the capsule of the knee joint and does this by piercing the posterior aspect of the capsule. There is a thickening of the capsule at its point of entry called the arcuate ligament. In fact, there is a complex of ligaments on the posterolateral aspect of the knee (known as the posterolateral complex), of which the arcuate ligament is part. Popliteus is supplied by the tibial nerve.  Musculoskeletal System Knee Joint Part 3: Ligaments of the Knee Joint The stability of the knee joint is largely dependent on its ligaments, and part 3 of this lecture will focus on the principal ones that support the joint.  Learning Outcomes After this lecture you should be able to: ▪ Describe the bony anatomy of the knee joint, including the shape of the articular surfaces ▪ Know that the femoral and obturator nerves may refer knee pain to the hip and vice-versa ▪ Describe the patello-femoral joint and list its common clinical problems ▪ Define the terms “genu valgum” and “genu varum” ▪ Know the position, shape and functions of the menisci, and give an account of their common injuries ▪ Give an account of the movements of the tibiofemoral joints ▪ Describe the ligaments of the knee joint and give their functions ▪ Describe the capsule and synovium of the joint, and list the bursae associated with it. Know the symptoms and signs of inflammation of these bursae There is a single outcome for this part of the lecture which that afterwards you should be able to : Describe the ligaments of the knee joint and give their functions The final outcome will be dealt with in part 4.  Collateral Ligaments Like most hinge joints, the knee is supported by collateral ligaments. There is a strap-like medial collateral ligament, also referred to as the tibial collateral ligament. It has two bands, a superficial and a deep part. The superficial part arises from the medial epicondyle of the femur and inserts distally onto the proximal shaft of the tibia. The deep part also runs between these two attachments, but in addition is anchored to the medial meniscus. The lateral collateral or fibular collateral ligament is thinner and more of a cord-like structure. It is attached proximally to the lateral epicondyle and distally to the head of the fibula.  Collateral Ligaments Function The collateral ligaments prevent sideways movement of the joint and prevent against varus or valgus angulation of the tibia. These ligaments are taut on full extension of the joint, and relaxed during flexion. It is in extension remember that body load is applied to the joint, and that is when it needs most support.  Collateral Support of the Knee Joint It is not only collateral ligaments that give support and stability at the sides of the joint. On the medial side of the joint anteriorly there is the medial patellar retinaculum from the vastus medialis muscle. That supports the anteromedial side. Behind the medial collateral ligament there are the tendons of the pes anserinus muscles. There is also the medial head of the gastrocnemius muscle of the calf that we have yet to discuss. On the lateral side, there is the lateral patellar retinaculum from vastus lateralis which supports the anterolateral side. Behind that is attachment of the iliotibial tract onto the tibia. Posteriorly, either side of the fibular collateral ligament are the biceps femoris attachment onto the head of the fibula, and deep to it is the tendon of popliteus. Hence, there is a lot of support either side of the joint.  Valgus Stress Test (not for inclusion in the lecture presentation) When standing and moving, the muscles have an important role in aiding the stability. Whilst sitting, there is little support as both the muscles and the collateral ligaments are relaxed. Hence to test the ligaments and other supporting structures, it is necessary to have the knee extended. One can then apply the valgus stress test to stretch the medial supporting tissues, including the medial collateral ligament. The knee or thigh is pushed inwards, whilst the foot is pulled outwards. Any laxity in the support will result in a valgus bend to the leg. Please Note: This material is not examinable and is given for interest only.  Varus Stress Test (not for inclusion in the lecture presentation) Next, by supporting the knee on the inside, and pushing the leg inward, the lateral collateral ligament is tested. Any excessive varus movement of the distal limb would indicate that the lateral support tissue was compromised, and the lateral collateral ligament was possibly torn. Please Note: This material is not examinable and is given for interest only.  Cruciate Ligaments The cruciate ligaments are named because they cross each other. A crux is Latin for cross. The anterior cruciate ligament arises from the anterior intercondylar ridge of the tibia, and inserts onto the medial surface of the lateral condyle of the femur posteriorly. The posterior cruciate ligament arises from the posterior intercondylar ridge of the tibia, and inserts onto the lateral surface of the medial condyle of the femur anteriorly. But that’s so much easier to visualise than it is to say or remember by listing the attachments! I recommend just staring at this image for a little while.  Anterior Cruciate Ligament The key action of these ligaments is to prevents forwards and backwards displacement of the femur on the tibia. The anterior cruciate will prevent anterior displacement on the tibia. If the tibia is fixed on the ground, then the movements are transferred to the femur, and the ligament then prevents the femur from being displaced backwards. The anterior cruciate ligament is subject to great stress during full extension of the limb, since it is taut on full extension. It is tightened even more by the locking mechanism of the knee. On the animation on the right, we can see the effects of a torn anterior cruciate ligament. The tibia has an excessive displacement anteriorly.  Posterior Cruciate Ligament The posterior cruciate ligament performs the opposite action to the anterior one. It is about three times the thickness of the anterior one, and only part of it is taut in extension. The remaining part is taut in flexion – the only ligament to do so. It prevents excessive forward movement of the femur. This is a particular risk when flexing the knee. Whilst walking or running forwards, our knees are partially flexed as we begin to transfer body weight onto our limb. At this moment that are two structures helping to keep the femur from slipping forwards. First is the posterior cruciate ligament. Perhaps this is the reason the ligament is so thick and strong. The second is the tightness in the extensor mechanism. Quadriceps femoris is contracting to resist the tendency to flex the joint, and ultimately to bring it into extension. Hence the patellar tendon is stretched firmly across the front of the joint.  Cruciate Ligament Injury When the limb is extended, all ligaments are taut, including part of the posterior cruciate. If there is then a sudden additional medial twisting action of the body when the foot is planted on the ground, the ligaments are subject to injury. This may occur for example in a contact sport such as rugby, or football. The anterior cruciate ligament is more delicate than the posterior one, since it is thinner. It is therefore much more prone to injury. Both cruciate ligaments are highly vascular, and if ruptured may leak blood inside the joint capsule, causing a haematoma. This may result in swelling, discoloration of the joint, and pain.  The Lachman’s Test (not for inclusion in the lecture presentation) The cruciate ligaments may be tested using the Lachman’s test. The patient has the knee bent to about 30 degrees, and the hamstrings are therefore relaxed. Anterior displacement of the tibia suggests anterior cruciate injury, and posterior displacement, posterior cruciate injury. Please Note: This material is not examinable and is given for interest only.  The Unhappy Triad (not for inclusion in the lecture presentation) The anterior cruciate ligament is not the only structure at risk of a twisting of the body upon full extension. The collateral ligaments are also at risk. They are all equally at risk is there is a valgus or varus bending in full extension. Such injuries are common in many contact sports. Either there is a rugby or football tackle that fixes the foot firmly on the ground, and the momentum of the trunk then twists and tears the ligaments. An alternative or additional threat is posed by a sideways tackle that forces the joint into valgus as shown in the illustration. This is likely to tear both the anterior cruciate and medial collateral ligament. Because the medial collateral ligament is attached to the medial meniscus, this also results in a tearing of that structure as well. Hence, three structures are torn together, giving rise to the ‘unhappy triad’ (of O’Donaghue). O’Donaghue first described this common association of injuries back in the 1950s. Please Note: This material is not examinable and is given for interest only.  Musculoskeletal System Knee Joint Part 4: Bursae of the Knee So this is the final part of the lecture on the knee joint. In this section we will consider the bursae in and around the joint.  Learning Outcomes After this lecture you should be able to: ▪ Describe the bony anatomy of the knee joint, including the shape of the articular surfaces ▪ Know that the femoral and obturator nerves may refer knee pain to the hip and vice-versa ▪ Describe the patello-femoral joint and list its common clinical problems ▪ Define the terms “genu valgum” and “genu varum” ▪ Know the position, shape and functions of the menisci, and give an account of their common injuries ▪ Give an account of the movements of the tibiofemoral joints ▪ Describe the ligaments of the knee joint and give their functions ▪ Describe the capsule and synovium of the joint, and list the bursae associated with it. Know the symptoms and signs of inflammation of these bursae The single learning outcome is that afterwards you should be able to: Describe the capsule and synovium of the joint, and list the bursae associated with it. Know the symptoms and signs of inflammation of these bursae.  Synovium of the Knee Joint Inside the capsule of the knee joint, lies the popliteus tendon and the cruciate ligaments. It is important to stress that although these structures lie inside the joint capsule, they lie outside the synovial membrane. In other words, they are intra-capsular but extra-synovial. For the cruciate ligaments, this occurs because the synovial membrane loops around them from behind. The importance of this is that the cruciate ligaments are therefore able to get access to a blood supply. If they rupture, they bleed causing a haematoma within the capsule. This may cause pain and interfere with movements.  Infrapatellar Fat Pad Infrapatellar fat pad The other structure to lie outside the synovium is the infrapatellar fat- pad. This exists anteriorly behind the patellar tendon. The synovium sits on top of this, and its presence prevents the synovial membrane from dropping down at this point.  Infrapatellar Fat Pad Attachments The fat pad is held in place by anchoring both to the patella (black arrows on the dissection image), and to the intercondylar region with an infrapatellar and alar folds (white arrow).  Bursae of the Knee Joint Medial view There are bursae all around the knee, protecting the tendons where they lie close to bone. One bursa in front of the joint, the prepatellar bursa, protects skin. Four of the bursae are in continuity with the joint. These are the suprapatellar bursa in front, the semimembranosus and gastrocnemius bursae behind, and the popliteus bursa laterally.  Bursae of the Knee Lateral view This is a lateral view and shows the popliteus bursa. In this illustration, the semimembranosus and gastrocnemius bursae are combined This is a common finding.  Popliteus Bursa The popliteus bursa protects the tendon of popliteus as it winds laterally under the fibular collateral ligament to reach the lateral epicondyle of the femur. The gastrocnemius bursa sits under the medial head of the gastrocnemius tendon and as we have just heard, often merges with the one under the semimembranosus. Although this is a lateral view, actually the gastrocnemius and semimembranosus bursae are posteromedial. Enlargement of these bursae due to inflammation, will hence cause a swelling at this location at the back of the joint.  Popliteal (Baker’s) Cyst Another cause of a swelling at the back of the knee is a popliteal cyst. This may be an enlarged semimembranosus bursa, but any swollen bursa in the popliteal region is termed a popliteal or Baker’s cyst, named after Dr William Baker who first described them. It may be a newly created bursa in which the synovium has managed to escape from the joint capsule. Baker’s cysts may occur following any knee inflammation, but most commonly are associated with an inflammatory reaction in the late stages of osteoarthritis of the knee.  Anserine Bursa On the medial side of the joint, there is the anserine bursa. This does not communicate with the joint cavity. This lies between the pes anserinus tendon insertions and the tibial attachment of the medial collateral ligament. This is the most common bursa to be affected by running. Anserine bursitis is usually caused by constant friction or an external blow to the area. It is common in athletes that have excessive rotation and valgus stress at the knee. The symptoms may be confused with an injury to the medial collateral ligament.  Suprapatellar Bursitis (not for inclusion in the lecture presentation) Of the anterior bursae, the suprapatellar bursa is the most significant. The top of that bursa lies a whole hands-breadth above the level of the patella and indeed needs to be held there by a small muscle, the articularis genu. That is a slip of muscle from the vastus intermedius. This bursa is really the upward extension of the synovial cavity of the joint, hence any joint inflammation may lead to fluid accumulation here. These lead to bulges appearing behind the vastus medialis and lateralis muscles. Please Note: This material is not examinable and is given for interest only.  Pre-Patellar Bursitis (not for inclusion in the lecture presentation) The prepatellar bursa is situated between the patella and skin. Historically it has been called carpet layer's or housemaid's knee. Prepatellar bursitis is a common problem in athletes who suffer repeated knee trauma, such as falling on the knee or getting hit on the patella. The condition is usually easy to evaluate because of the large amount of fluid it contains. Please Note: This material is not examinable and is given for interest only.  Infrapatellar Bursitis (not for inclusion in the lecture presentation) There are two bursae that lie either side of the patellar tendon. Since the patellar tendon is inferior to the patella, these are called the superficial and deep infrapatellar bursae. They are less prone to injury than the prepatellar one, but the mechanism of action is the same. Any prolonged or repetitive stress on the bursae may cause them to become inflamed, leading to a well-defined, isolated swelling at their location. Historically, these were often seen in priests and those answering the call to prayer, and hence clinically the condition was referred to as ‘clergyman’s knee’. These days, the church provides cushions for everyone, so this term is no longer appropriate, but nevertheless persists. Please Note: This material is not examinable and is given for interest only.  Treatment for Bursitis (not for inclusion in the lecture presentation) Treatment for all bursitis is the same. The excess fluid is removed by aspiration and non-steroidal anti-inflammatory agents are used to treat the inflammation. It is important though to identify the cause of the inflammation in order that it doesn’t recur. Please Note: This material is not examinable and is given for interest only.  Musculoskeletal System Knee Joint And so that ends this lecture on the knee joint. In the next lecture, we will move downwards to discuss the anatomy of the leg.