the knee joint is a large hinge type of synovial joint allowing flexion and extension of the lower limb the knee joint has three main articular areas the lateral and medial femorotibial articulations between the lateral and the medial Condes of the femur and tibia as well as the intermediate femoropatellar articulation between the Pella and the femur notice that the fibula does not participate in the knee joint okay now the articular surfaces of the knee joint are the medial and lateral femoral condil the patellar surface of the femur between these two condil the articular surface of the patella which is a plateau with an anteroposterior Ridge that fits into the patellar surface known as The trolear Groove and the articular surfaces of medial and lateral condil of the tibia on which the condil of the femur roll because the knee joint articular surfaces are irregularly shaped and in congruent knee joint stability heavily relies on tibiofemoral ligaments and the strength of the surrounding muscles such as the quadriceps now the knee joint is surrounded by a joint capsule which has an external fibrous capsule and an internal synovial membrane superiorly the fibrous capsule attaches to the femur just proximal to the articular margins of the condil posteriorly the fibrous layer encloses the condil and the interc cond fossa and has an opening for the tendon of the popus inferiorly the fibrous layer attaches to the margin of the tibial Plateau except where the tendon of the popus crosses the bone the quadriceps tendon patella and patellar ligament replace the fibrous layer anteriorly and the fibrous capsule is continuous with the medial and lateral margins of these anterior structures then the extensive cobbi membr membrane lines all surfaces bounding the articular cavity not covered by articular cartilage so it can be found attaching to the periphery of the articular cartilage covering both the femoral and tibial condil the posterior surface of the patella and edges of the manisi now the sovial membrane lines the internal surface of the fibrous joint capsule of the knee both medially and laterally however it does not line the fibrous joint capsule centrally in the posterior knee from this view we can see the famous anterior and posterior cruciate ligament and as you can see the sovial membrane actually reflects anteriorly over these anterior surfaces of the cruciate ligaments into the interc cond region instead of going behind them meaning the cruciate ligaments actually lie posterior and outside of the sovial lined articular cavity so they're considered extra articular in addition to lining the posterior surface of the infrapatellar fat pad making this extra articular as well the anterior synovial reflection creates a median infra patellar synovial fold above the patella the synovial membrane of the joint capsule extends underneath the central part of the quadriceps to continue with the sovial lining of the Supra patellar Bersa now the joint capsule is strengthened by six extra capsular external or intrinsic Lig these include the fibular or lateral collateral ligament tibial or medial collateral ligament anterolateral ligament patellar ligament oblique poal ligament and aru poal ligament the patellar ligament the distal part of the quadriceps fous tendon is a thick fibrous band passing from the Apex and adjoining margins of the patella to the tibial tuberosity on its lateral sides it is joined by the medial and lateral patella retinacula which are expansions of the vastus medialis and vastus lateralis respectively which form the joint capsule in the respective areas and help maintain alignment of the patella throughout its movement during knee flexion and extension the collateral ligaments are two strap-like ligaments on the medial and lateral surface of the knee and they contribute to knee stability by limiting Varys and valgus movements of the knee while also contributing to rotational stability the tibial collateral ligament is a flat band that extends from the medial epicondyle of the tibia with its deep fibers firmly attached to the medial meniscus at its midpoint the tibial collateral ligament is a thickened portion of the medial joint capsule and is mirrored by a lateral joint capsule thickening which has garnered recent anatomical interest called the anterolateral ligament the anterolateral ligament of the knee generally inserts on the lateral epicondyle ligament which is a cordlike extracapsular ligament that extends inferiorly from the lateral epicondyle of the femur to the lateral surface of the fibular head then there's the oblique poal ligament which is an expansion of the tendon of the semimembranosus that reinforces the joint capsule posteriorly the ligament arises posterior to the medial tibial cile and passes superolaterally toward the lateral femoral cile blending with the central part of the posterior aspect of the joint capsule and finally the aru poia ligament strengthens The Joint capsule posterolaterally it arises from the posterior aspect of the fibular head and spreads over the posterior surface of the knee joint both the oblique and the aru poal ligament are thought to contribute to posterolateral stability of the knee the knee joint is also strengthened by the intracapsular structures which include the cruciate ligaments and minisi the two cruciate ligaments are located within the fibrous joint capsule so they are intracapsular but lie outside of the synovial lined articular cavity as we said before so are considered extraarticular the anterior cruciate ligament or ACL arises from the anterior interc cond area of the tibia posterior to the attachment of the medial meniscus it extends superiorly posteriorly and laterally to attach to the posterior part of the medial side of the lateral cile of the femur the ACL serves to prevent anterior translation of the tibia in relation to the femur and and it also helps prevent hyperextension and excessive internal rotation of the knee the posterior cruciate ligament or PCL is stronger than its brother the ACL and it arises from the posterior interc cond area of the tibia it then passes superiorly and anteriorly on the medial side of the ACL to attach to the anterior part of the lateral surface of the medial condil of the femur the PCL prevents posterior translation of the tibia in relation to the femur and helps to prevent hyperflexion of the knee and now for the T minisi of the knee joint which are small c-shaped discs found within the synovial cavity that are considered intraarticular the minisi have thick external margins which become thinner As you move medially and unattached edges in the interior of the joint the minisi are made of fibrocartilage and are placed on the articular surface of the tibia and function to allow for joint congruency load distribution and Joint stability of the knee first the medial meniscus is c-shaped and broader posteriorly than anteriorly its anterior end is attached to the anterior interc cond area of the tibia and its posterior end is attached to the posterior interc cond area the medial meniscus also firmly adheres to the Deep surface of the tibial collateral ligament speaking of which the lateral meniscus is nearly circular smaller and more freely movable than the medial meniscus the lateral meniscus also has an intimate relationship with the tendon of the popius whose medial part of the tendon attaches to the posterior horn of the lateral meniscus its anterior end is attached to the anterior interc cond area of the tibia and its posterior end and is attached to the posterior interc cond area finally the anterior edges of the minisi are joined by the transverse ligament of the knee now although we'd love to spare you the details there are also about 12 bur around the knee which are fluid-filled structures that help reduce friction between muscles tendons and skin during movement the most important ones are the subcutaneous prepatellar Bersa and infrapatellar Bersa which are located between the anterior patella and the skin and the skin and tibial tuberosity respectively and the Deep infra patella Bursa which is located between the anterior surface of the tibia and the patellar ligament next are the four bers that communicate with the synovial cavity of the knee joint these are the Supra patellar Bersa located between the anterior surface of the lower part of the femur and deep surface of the quadriceps Fus the PO Bersa between the tendon of popus and the lateral cile of the tibia the Anin Bersa which is deep to the tendonous distal attachments of the Sartorius gracilis and semitendinosis and finally the gastrus bers which are deep to the proximal attachments of the medial and lateral gastrus head tendons the two main movements of the knee joint are flexion primarily produced by the hamstrings and extension which is primarily produced by the quadriceps Fus when standing with feet fixed on the ground the knee passively locks due to medial rotation of the femoral Condes as they rest on the tibial Plateau allowing us to stand for long periods without fatiguing our quadriceps when the popus muscle contracts it laterally rotates the femur helping us unlock our knee so flexion can occur which is also crucial for initiating our gate more minor movements of the knee are medial rotation primarily done by the semitendinosis and semimembranosus as well as lateral rotation primarily done by the biceps Fus when it comes to muscles that contribute to the stability of the knee these include the quadriceps femoris Sartorius popius gracilis biceps Fus semitendinosis and semimembranosus switching now to neurovascular supply the arteries supplying the knee joint are the vessels that form the periarticular genicular anastomosis around the knee the five genicular branches of the poal artery include the superior lateral Superior medial inferior lateral inferior medial and middle genicular arteries the descending genicular branch of the femoral artery the descending branch of the lateral circumflex femoral artery two recurrent branches of the anterior tibial artery and the circum Flex fibular branch of the posterior tibial artery and going back to Hilton's law the nerves supplying the muscles crossing the knee joint also Supply The Joint these include the articular branches from the femoral tibial and common fibular nerves as well as the sainis nerve although we really are kneee in this fascinating topic perhaps it's time to have a small break and try to recognize some of the structure of the knee joint all right as a quick kneecap sorry quick recap the knee joint is a hinge type of synovial joint between the femur tibia and patella and a joint capsule also formed by a fibrous and synovial layer The Joint has six extra capsular ligaments the patellar ligament the tibial and fibular collateral ligament the anterolateral ligament the oblique poal ligament and the aru poal ligament it also has intraarticular structures including the anterior cruciate ligament posterior cruciate ligament and the medial and lateral minisi the important bers around the knee are the subcutaneous prepatellar and infrapatellar bers and the four bers that communicate with the synovial cavity of the knee joint the Supra patellar Bersa the popus Bersa the anserine Bersa and finally the gastrus Bersa knee joint movements include flexion extension medial rotation and lateral rotation helping current and future clinicians Focus learn retain and Thrive learn more