Compleat medical study material

PHYLOGENY

320 million years ago with subsequent development the femur rotated internally and the fibula receded distally away from the lateral femoral condyle. The osseous patella appeared last (approximately 65 million years ago)


EMBRYOLOGY

The basic outline of the knee is present in its entirety by the tenth week of gestation .The essential changes actually occur an even shorter period (3 to 4 weeks ).
Streeters staging system outline 23 horizons from the single cell to the end of the embryonic period ( when the nutrient vessel pentrates the humerus ) at approximately 7 weeks gestation The limb bud appears in horizon 13(28 days ) as a mesodermal condensation.By horizon 16(33days),the femur and the tibia and fibula begin to appear.At horizon 20(41 days the fibrous capsule appears. At horizon 22 (45 days ) the patella is present along with the cruciates collaterals, and menisci.
By 9 to 10 weeks of age the menisci separate from the articular surfaces and have developed attachments to the capsule The epiphyses are Visible by 36 weeks gestation The times of appearance and closure of the epiphyses are Summarized in table.The female epiphyses appear sooner than their male counterparts and close off earlier only the distal femoral and proximal tibial plates are present at birth The patella and proximal fibula appear next (approximately 3 to 4 years of age ) followed by the tibial tuberosity at age 7 to 15 years The patella can have many configuarations;(bi-partite) is located superolaterally,is occasionally bilateral ,should not be confused with a fracture fragment .

BONE STRUCTURE

The Knee is a diarthrodial, tricompartmental joint consisting of a medial and lateral tibiofemoral and anterior patellofemoral articulation The medical femoal condyle is longer and larger than the lateral femoral condyle and has a larger circumference The width of the medical condyle at the level of the tibiofemoral articulation is slightly smaller than the lateral condyle The two condyles diverge at angle of 28 degrees from each other.
The lateral femoral condyle has notch between the anterior one third and the posterior two-thirds of the circumference This notch separates the patellofemoral articulation from the tibiofemoral and clearly distinguishes the lateral condyle from the medial on a true lateral protection.The over valgus of the knee is explained by the anteroposterior projection of the distal femur with the medial condyle extending distal to the lateral The tibial plateau consists of two condyles The medial condyle is concave and wider from anterior to posterior than the lateral condyle is flat or convex.The medial condyle projects farther posterior and anterior than the lateral condyle on the true lateral view The tibial tubercle lies between the two condyles,usually in the midline although sometimes it may be slightly externally rotated towards the lateral side.The patellofemoral articulation includes the femoral sulcus and the posterior surface of the patella The distal margin of the sulcus can be identified by the notch on the lateral femoral condyle Medially the separation points is not as apparent The sulcus angle is 137 degress with a variation of 8 degress The entire sulcus is slightly internally rotated with respect to the femoral shaft This is partially caused by the higher prominence of the lateral condyle.The patellar surface can be divided into seven facets three located medially three laterally and one above the medial facets The medial facets are usually smaller than the lateral and more convex than concave The median ridge of the patella is located in the center of the femoral sulcus. Some what lateral to the midline but is almost never medial. In earlier species the fibula articulates with the femur with development the fibula recedes distally and articulates only with the tibia The proximal tibiofibular joint lies posterior to the metaphyusis of the tibia and distal to the knee joint .

LIGAMENTS

There are four major ligamentous structures in the knee the medial and the lateral collateral ligaments and the anterior and posterior cruciate ligaments the collateral ligaments are extra-articular whereas the two cruciate ligaments are intra-articular but extrasynovial.

The Collateral Ligaments

The medial collateral ligaments originates from the medial femoral condyle at the adductor tubercle and descends distally and fans out as it inserts into the medial tibial metaphysis It appears sail like and consists of two layers the superficial layer follows the course outlined above.The deep layer originates from the femoral condyle slightly below the adductor tubercle and then proceeds distally to attach to the medial meniscus on its superior aspect The ligament continues from the inferior aspect of the meniscus distally to blend into the superficial ligament along the medial tibilal metaphysic.
The lateral collateral ligament originates from the lateral femoral condyle slightly posterior to its mid portion and descends to the fibula on its mid posterior to its mid portion and desends to the fibula on its posterior aspect The ligament is a thin structure almost strawlike in appearance

The Cruciate Ligaments
The Cruciate ligaments are located in the central portion of the knee they are covered by a synovial shealth that separates them from the intra-articular space and prevents synovial fluid from contacting the cruciate ligament surfaces .The anterior cruciate ligament consists of two bundles It originates from the lateral femoral condyle and proceeds distally to the anterior medial tibial plateau with a spiral rotation The anteromedial bundle is not as structurally significant as the posterolateral The origin on the femoral condyle is oval and is almost horizontal when the knee is flexed to 90 degrees This origin shifts to vertical when the knee is in full extension The tibial insertion is oval and slightly medial to midline on the anterior surface of the plateau The posterior cruciate ligament does not have any distinct bundles.It orginates from the medial femoral condyle and inserts on the posterior surfaces of the tibial plateau in the midline (fig.1-17 and 1-18) its origin on the medial femoral condyle is also oval and is 90 degrees offset from the anterior cruciate ligament origin.That is the posterior cruciate ligament origin is horizontal with the knee in full extension and becomes vertical with 90 degrees of flexion of the knee

Other Ligaments
There are several lesser ligaments in the knee.
MENISCI
There are two menisci in the knee: medical and lateral. The embryologic data indicate that the menisci develop during the fetal period and initially appear to be C-shaped. There is no distinct data to indicate that the discoid lateral meniscus is an embryologic aberrancy. The lateral meniscus is slightly more circular than the medial .The menisci are attached on the superior and inferior surfaces to the capsule. The coronary ligaments are circular and proceed horizontally from anterior to posterior around the periphery of the meniscus.The lateral meniscus has a defect in the attachment at the mid portion where the popliteus tendon passes through from posteroinferior to anterosuperior to attach to the lateral femoral condyle. The tendon proceeds beneath the lateral collateral ligament and attaches just anterior to it on the condyle. It is debatable whether the tendon has any attachment to the lateral meniscus.There are synovial pillars anterior and posterior to the defect that enforce the capsular attachment to the lateral meniscus that may greater motion anterior to posterior than the medial meniscus, which has a stronger attachment to the capsule and less excursion.

PLICAE
Plicae are infoldings of the lining of the knee they are not necessarily present in every knee and do not represent pathologic entities unless there is associated inflammation about the base. There are three synovial plicae
1.The supra patellar plica is circular in appearance and almost closes off the supra patellar pouch when it is present The medial plica extends from the medial capsule at the level of the superior margin of the femoral condyle and traverses the medial joint space across to the patellar fat pad in the midlinle .The ligamentum mucosum ( the third plica ) originates from the roof of the intercondylar notch and crosses to the patellar fat pad; this structure is important because it may be confused with the anterior cruciate ligament during the course of an arthroscopy and .The lateral recess of the knee also has a fold in that mimics a plica but has not formerly been considered one.

MUSCLES

The musculature of the knee can be divided into four major areas the quadriceps the medical hamstrings the lateral hamstrings and the posterior gastroc –soleus complex .The quadriceps group forms the extensor mechanism of the knee The intermedius muscle is wrapped about the anterior femoral shaft and is the deepest muscle of the group. The vastus medialis and lateralis are on either side of the intermedius and superior to it .The rectus femoris the most superficial inserts directly into the quadriceps tendon.
The medial hamstrings include the gracilis the semi-membranosus and the semi-tendinosus. All have origins on the pelvis and insert on the medial side of the tibial metaphysis. They cause flexion and internal rotation. The lateral hamstrings include the two heads of the biceps femoris ( one from the pelvis and the other from the femoral shaft ).This group leads to flexion and slight external rotation,but does not at all equal the force exerted by the medial group.
The remaining posterior muscle is the gastrocnemius solecus complex The two heads of the gastrocnemius originate from the posterior aspect of the femoral condyles. They also contribute somewhat to flexion. The plantaris muscle originated from the posterior aspect of the lateral femoral condyle and inserts into the medial side of the calcaneus .The popliteus has its origin on the posterior tibial metaphysic and inserts into the lateral side of the lateral femoral condyle. Both of these smaller muscles may contribute slightly to flexion. The popliteus is also thought to cause rotation of the femoral condyle.

VASCULATURE
The femoral artery divides into a deep and a superficial branch.The deep branch terminated in the upper thigh. The superficial branch continues distally into the adductor canal and spirals around the posterior aspect of the medial femoral condyle There are seven major vessels that form the blood supply to the knee the superolateral superomedial, inferolateral, inferomedial, and middle geniculates take origin from the popliteal artery and proceeds distally. The recurrent anterior tibial originates from the anterior tibial and proceeds proximally to the knee Of the five geniculate that take origin directly from the popliteal artery the superolateral geniculates originates most superiorly followed by the superomedial. The middle geniculate originates at the level of the joint line and supplies the anterior cruciate ligament .The inferolateral extends anteriorly along the lateral joint line, and the inferomedial is located 2 cm distal to the medial joint line along the metaphysic of the tibia Several of the vital structures within the knee joint have a tenuous blood supply that can easily be compromised. The patella is surrounded by a circular plexus of vessels .The majority of the blood supply is distally based coming through the fat pad Thus a transverse fracture of the patella may cut off the proximal blood and lead to avascular necrosis. The anterior cruciate supply comes from the femoral side through the overlying synovium from the middle geniculate injury to the synovial shealth can lead to loss of the ligaments intergrity even without any significant me chanical injury to the ligament’s itself. The circulation to the posterior cruciate is entirely different ,coming from the surrounding capsule and synovium with a much broader base. Thus, vascular injury to the posterior cruciate is extremely rare The menisci are not nourished through the synovial flund that surrounds them; rather the vessels along the joint line derived from the inferolateral and inferomedial geniculates penetrate from the periphery to the inner edges This explains why meniscal tears in the inner third of the body heal very poorly, if at all. The blood supply to the distal femur and proximal tibia is less well under stood and appears to depend upon the vasculature established for the original nourishment of the epiphyseal plated even after they are closed.

INNERVATION

The muscles about the knee are innervated by the nerve roots from L2 through S2.
The femoral nerve supplies the quadriceps group and the sartorius The sciatic nerve contains two major division the tibial and peroneal The tibial nerve supplies the large majority of the posterior and medial muscles about the knee. This group includes the long head of the biceps,semitendinosus, plantaris, popliteus gastrocnemius and soleus. The single muscle innervated in the thigh by the peroneal nerve is the short head of the biceps femoris The dermatomes of the lower extremities begin with L2 and extend to S2 they tend to spiral around the lower leg. The anterior cutaneous innervation begins medially from the obturator nerve and proceeds laterally to the femoral nerve and then to the lateral sural femoral cutaneous. Just distal to this area the saphenous nerve and the lateral sural curaneous complete the anterior pattern. The posterior cutaneous innervation is a continuation of the anteromedial and anterolateral coverage with the posterior femoral cutaneous covering the midline

KNEE JOINT

The knee joint is formed by the condyles of femur and tibia, and posterior articular surface of the patella. It is a compound and complex synovial joint. Three primitive joint cavites –femoro-patellar and medial and lateral condylar .Condylar articulations are primitively separated from each other by a sagittally oriented intercondylar septum which is subsequently divided by an intercondylar foramen into a short anterior segment and a long posterior segment. Functionally ,the knee joint is a condylar and modified hinge –joint. It is a modified hinge-joint because of two reasons:
(a) transverse axis of movement is not fixed and moves forward during extension and translates backward in flexion;
(b) along with extension and flexion there is a conjunct rotation of femour on tibia ( and vice versa ) around a more or less vertical axis .
Condyles of femur – Both medial and lateral condyles of femur bulge backwards are separated from each other intercondylar notch. Anterior surface of both condyles form a patellat articular Surface, which is saddle shaped and concave from side to side but convex from above downwards.Patellar surface of the femour articulates with the posterior articular surfaces of the patella. Patellar surface extends much higher over the lateral femoral condyle of the articular surface of both femoral condyles is known as the tibial surface, which articulates with the upper surface of the respective tibial condyles and their menisci The patellar surface of femour, however extends to the undersurface of the medial femoral condyle in semilunar impression close to the intercondylar notch ; the most medial articular facet of patella comes in contact with this impression of femur during full flexion of knee joint. Viewed in lateral profile tibial articular surface of each femoral condyle accommodates the arcs of numerous circles with different radii. When the centres of all circles are joined a curved line is formed which is known as the evolute of the profile. The transverse axis of the knee joint changes from moment to moment during extension and flexion along the evolute. The lateral condyle of femur is more massive than the medial condyle because most of the body weight is transmitted from the hip to knee joints through the lateral condyle. However the medial condyle bulges more medially.Summit of the medial convexity of the medial femoral condyle is known as the medial epicondyle which gives attachment to the upper end of tibial collateral ligament Maximum convexity lateral surface of lateral femoral condyle lateral epicondyle which provides the upper attachment to the fibular collateral ligament. The lateral wall of the intercondylar notch of the femur receives the upper attachments of the anterior cruciate ligament in the postero-superior part The medial wall of the upper end of the posterior cruciate ligament in the anteo-inferior part .the anterior part of intercondylar notch gives attachment to the apex of infrapatellar synovial fold; upper margin of the notch provides attachment to the capsular ligament and oblique popliteal ligament of knee joint on close inspection, a subsidiary notch is lateral part of lower margin of the intercondylar notch it lodges the anterior surface stretched anterior cruciate ligament at the end of the extension of knee joint.
In anatomical position lower surfaces of both femoral condyles assume a horizontal position and articulate with the corresponding condyles of the tibia and their menisci therefore in adults the long axes of femur and tibia meet each other forming an angle of about 170o, which is open laterally.

Condyles of tibia- The upper articular surfaces of both medial and lateral condyles of tibia are concave but much shallower than the corresponding condyles of femur However the tibial concavity is somewhat deepened by the medial and lateral menisci which occupy the peripheral two-thirds of both condyle. The articular surface of the medial condyle is ovoid and that of the lateral condyle is circular in outline; medial condylar surface is longer antero-posteriorly than its lateral counter part The posterior margin of articular surface of lateral condyle is grooved for the tendon of popliteus. Intercondylar area intervenes between the articular surfaces of both condyles this area is wide in front and behind but constricted in the middle which is occupied by the intercondylar eminence presenting medial and lateral tubercles. The anterior part of the intercondylar area gives attachment from before backwards to anterior horn of the lateral meniscus.The posterior part of the area provides attachment to the following from before backwards posterior horn of the lateral meniscus posterior horn of the medial meniscus lower attachment of the posterior cruciate ligament The posterior surface of the medial condyle of tibia presents an extra-capsular transverse groove for the attachment of semimembranosus. Postero-laterally the lateral condyle presents an articular facet for articulation with the head of fibula forming a plane synovial superior tibio-fibula joint Anterior surface of the lateral condyle presents a triangular flattend area for the attachment of the ilio-tibial tract. Anterior surface of both condyles is triangular with the apex directed below and formed by the upper part of the tubercle of tibia ,where ligamentum patellae is attached medial and lateral patellar retinacula are attached to the respective margins of the triangle

Articular surface of patella- Posterior surface of the patella is mostly articular except close to the apex where ligamentum patellae is attached the articular surface comes in contact with the patellar surface femur. The articular surface is primarily divided into a large lateral and small medial area by a vertical ridge which fits into the corresponding groove of the patellar surface of femur the medial area present medially a narrow strip separated by a vertical ridge lateral and medial areas further therefore altogether seven facets are present on the articular surface
During extension of knee the patella moves upward and laterally due to obliquity of the shaft of femur The natural tendency of lateral displacement of patella is prevented by two factors ( bony and muscular) (a) Raised lateral margin of the patellar articular surface of femur (b) Insertion of vastus medialis along the medial margin of patella extends more below than the corresponding insertion of Vastus laterlis to its lateral margin Contraction of vastus medialis from the medial side therefore ,prevents lateral displacements of patella.
(c) Clinically the Q- angle is represented by the intersection of a line drawn from the anterior superior iliac spine to the centre of patella and another line extending upward from the tibial tuberosity through the centre of patella when the angles is greater than 150 the quadriceps pull increases the forces for lateral displacement of patella
Functions of the patella-
1. Patella protects the knee joint from the front but it is not essential for the movements of the joint
2. It hinders the beginning of extendion from extreme flexion because it is sandwiched between the advancing condyles of femur and tibia.
3. Patella however facilitates the end of extension by keeping the ligamentum patellae away from the transverse axis of the joint and increases the momentum of the quadriceps pull

Cruciate ligaments( see figs 25.7,25.9,25.10) – The anterior and posterior cruciate ligaments are intra-capsular but extra synovial they cross like the letter X hence called cruciate They are named as anterior and posterior according to their tibial attachements both ligaments are taut at the extremes of flexion and extension of the joint The cruciate ligaments are developed from the posterior part of primitive intercondylar

Anterior cruciate ligament-
Attachment: Below it is attached to the anterior part of intercondylar area of tibia in between the anterior horns of medial and lateral menisci. Above it is attached to the posterior part of medial surface of lateral condyle of femur it is oblique in direction and extends upward backward and laterally
Measurements – Length , 38 mm
Width, 11 mm
Functions-
(a) It binds the bones together;
(b) It is stretched during extensions and therefore prevents hyper –extension( fig 25.15-a)
(c) It prevents forward displacement of tibial condyles
(d) Since it is taut during extension it forms a vertical axis around which femur rotates on tibia during extension or flexion of knee joint In standing the anterior cruciate ligaments lodges in a subsidiary notch in the lateral part of intercondylar notch of femur.












Anterior cruciate ligament-

Attachment : Below it is attached to the anterior part of intercondylar area of tibia in between the anterior horns of medial and lateral menisci. Above it



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