Intercondylar Groove

The femur is the longest bone of the human body. It consists of a rounded proximal head that articulates with the acetabulum at the hip, a nearly cylindrical shaft, and a distal metaphysis that forms two large rounded condyles that articulate with the tibia.

From: Forensic Science and Medicine

Forensic Medicine of the Lower Extremity: Human Identification and Trauma Analysis of the Thigh, Leg, and Foot

Edited by: J. Rich, D. E. Dean, and R. H. Powers © The Humana Press Inc., Totowa, NJ

Fig. 1. Anterior femur: (A) Anterior view of the entire femur; (B) The distal articular surface shows how the patellar surface blends into the medial and lateral tibial surfaces.

Because of its relationship with the osteology of the knee, the distal portion of the femur will be the focus of this section. This distal portion is widely expanded to provide a large surface for the transmission of body weight to the top of the tibia. It is made up of two large condyles that are partially covered by articular cartilage. These two condyles are separated posteriorly by the intercondylar notch but are united anteriorly, where they provide an articular surface for the patella.

2.1.1. Articular Surfaces

The patellar and the tibial surfaces are the two major divisions of the distal articular surface. The patellar surface is concave from side to side and has a groove along its long axis. It is higher on the lateral side and is separated from the tibial surfaces by two relatively indistinct grooves. The tibial surface is further divided into medial and lateral parts. Anteriorly the tibial surfaces are continuous with the patellar surface, but posteriorly they are separated by the intercondylar notch or fossa (Figs. 1, 2). Normally, all of these articular surfaces are covered with a thick layer of cartilage that protects the underlying bone.

2.1.2. Condyles

The femoral condyles are convex from side to side and front to back, and both project posteriorly past the plane of the posterior shaft of the femur. The medial femoral

condyle is larger and rounder than the lateral condyle and projects downward and medially to such an extent that the lower surface of the lower end of the bone appears to be practically horizontal when seen from the side (Fig. 3). The lateral femoral condyle is less prominent but is longer from front to back. It is wide and steeply sloped medially to laterally, where it creates a large weight-bearing surface against the interspinous eminence

Medial

Medial

Groove for popliteusx Lateral epicondyle

Fig. 3. The epicondyles of the femur: lateral and medial views.

Groove for popliteusx Lateral epicondyle

Fig. 3. The epicondyles of the femur: lateral and medial views.

of the lateral tibial plateau. The lateral femoral condyle is comparatively narrow posteriorly, where it is not in weight-bearing apposition with the tibia.

2.1.3. Epicondyles

Immediately superior to the femoral condyles are the epicondyles and their tubercles, which provide attachments for many muscles, tendons, and capsular ligaments (Fig. 4). Some of these attachment sites are well defined on the bone, but others are much more subtle. The attachment site of the tibial collateral ligament on the medial femoral epicondyle is a distinct raised area immediately anterior and inferior

Medial

Adductor tendon & vastus medialis

/ Posterior oblique ligament

/ Posterior oblique ligament

Fibular collateral ligament I "Cheek" of femur

Tendon of popliteus

Fig. 4. Attachment sites for soft tissues. Just above the articular surfaces, the distal femur has numerous sites of attachment for periarticular soft tissues (10,11).

Fibular collateral ligament I "Cheek" of femur

Tendon of popliteus

Fig. 4. Attachment sites for soft tissues. Just above the articular surfaces, the distal femur has numerous sites of attachment for periarticular soft tissues (10,11).

to the adductor tubercle, which in turn is the attachment site for the adductor tendon as well as for the vastus medialis obliquus muscle. Just inferior to the medial epi-condyle is the attachment site for the mid third of the medial capsular ligament; slightly posterior to this is the insertion site of the posterior oblique ligament and capsular arm of the semimembranosus (Fig. 5).

The lateral epicondyle provides attachment sites for the fibular collateral ligament, the tendon of the popliteus muscle, fibers of the iliotibial tract, and the lateral capsular ligament. Just superior and posterior to the epicondyle is the most distal extent of the linea aspera. This raised area of bone provides attachment sites for the iliotibial tract, the vastus lateralis, and the short head of the biceps. Between the lateral epicondyle and the linea aspera is the attachment site for the lateral head of the gastrocnemius.

Fig. 5. The capsular expanse of the semimembranosus covers the entire posteromedial corner of the knee joint (illustration by the author, reproduced with permission from ref. 1; Hughston Sports Medicine Foundation, Inc., Columbus, Georgia).

The so-called "cheek" of the femur (1) provides an attachment site for the synovial membrane and separates both medial and lateral epicondylar areas of bone from the articular surfaces.

2.1.4. Intercondylar Notch

The intercondylar notch separates the medial and lateral femoral condyles and is the attachment site for the cruciate ligaments, the ligaments of Wrisberg and Humphrey, and the frenulum of the patellar fat pad (Figs. 1, 6-8). A large portion of the notch is rough and pitted by vascular foramina, but it is relatively smooth where it provides attachment for ligaments. To accommodate the ligaments, the notch is widened posteriorly where it is not in apposition with the tibia. In the most posterior superior portion, the notch connects to the intercondylar line, a distinct ridge of bone that provides attachments for the oblique popliteal ligament and the posterior portion of the arcuate ligament (Fig. 9).

2.1.5. Popliteal Surface

A large portion of the posterior distal femur is described as the popliteal surface. It is the floor of the upper part of the popliteal fossa of the knee and is covered by fat,

Fig. 6. Sagittal sections of the femur expose medial and lateral sides of the intercondylar notch and show the attachment sites for the cruciate ligaments as well as the ligaments of Humphrey and Wrisberg (12). The frenulum of the infrapatellar fat pad, shown in Fig. 8, also inserts in the notch but the bony landmarks are ambiguous and variable (1).

Fig. 6. Sagittal sections of the femur expose medial and lateral sides of the intercondylar notch and show the attachment sites for the cruciate ligaments as well as the ligaments of Humphrey and Wrisberg (12). The frenulum of the infrapatellar fat pad, shown in Fig. 8, also inserts in the notch but the bony landmarks are ambiguous and variable (1).

which separates it from the popliteal artery. It is a relatively flat, slightly concave surface that is deeply pitted with vascular foramina. Lateral to this is a raised area of bone where the plantaris, the lateral head of the gastrocnemius, and the arcuate ligament attach. At the most medial edge of the popliteal surface, the bone expands to provide an attachment site for the medial head of the gastrocnemius, the adductor aponeurosis, and the semimembranosus retinaculum (Figs. 2, 9,10).

2.2. Tibia

The tibia is the larger of the two bones of the lower leg and, except for the femur, is the longest bone of the skeleton. The proximal end is flattened and expanded to provide a large surface for bearing body weight transmitted through the lower end of the femur. The shaft is prismoid in section, especially in the proximal third. The distal end is smaller than the proximal end, and there is a stout process—the medial malleolus— at the end. The proximal end forms a large portion of the knee joint.

Fig. 7. The intercondylar notch is widened posteriorly to accommodate the proximal attachments of the posterior cruciate, the anterior cruciate, and the ligament of Wrisberg. (illustration by the author, reproduced with permission from ref. 1; Hughston Sports Medicine Foundation, Inc., Columbus, Georgia).

Fig. 7. The intercondylar notch is widened posteriorly to accommodate the proximal attachments of the posterior cruciate, the anterior cruciate, and the ligament of Wrisberg. (illustration by the author, reproduced with permission from ref. 1; Hughston Sports Medicine Foundation, Inc., Columbus, Georgia).

2.2.1. Articular Surfaces

The uppermost portion of the tibia is expanded, especially in the transverse axis, into two prominent condyles. The articular surface of the larger medial condyle is concave and essentially ovoid. It is flattened where it comes in contact with the medial meniscus, and the imprint of the medial meniscus can frequently be seen on the bone. The articular surface of the lateral tibial condyle is more circular in outline and likewise bears a flattened imprint of the corresponding lateral meniscus (Fig. 11). Both articular surfaces are normally covered with thick cartilage, and they rise sharply in the center of the joint to form their respective sides of the intercondylar eminence.

As the anterior articular margins of the two articular surfaces recede from each other, the middle of the tibial plateau broadens into a fairly flat, smooth area that is devoid of cartilage. The infrapatellar fat pad covers this portion and separates it from

Fig. 8. Suprapatellar plica. The suprapatellar plica is a fold of the normal synovium surrounding the knee. It originates superolaterally over the supracondylar fat pad. It is tethered superiorly by the articularis genu. When healthy and smooth, it glides over the medial articular surface and inserts distally into the infrapatellar fat pad (illustration by the author, reproduced with permission from ref. 1; Hughston Sports Medicine Foundation, Inc., Columbus, Georgia).

Fig. 8. Suprapatellar plica. The suprapatellar plica is a fold of the normal synovium surrounding the knee. It originates superolaterally over the supracondylar fat pad. It is tethered superiorly by the articularis genu. When healthy and smooth, it glides over the medial articular surface and inserts distally into the infrapatellar fat pad (illustration by the author, reproduced with permission from ref. 1; Hughston Sports Medicine Foundation, Inc., Columbus, Georgia).

the patellar ligament. The medial and lateral menisci insert between this smooth, flat area and the articular surfaces just posterior to this fat pad. The area of attachment for the anterior cruciate ligament fits between the meniscal attachments and the intercondylar spines or eminences. Immediately posterior to the intercondylar eminences are attachment sites for the posterior horns of the medial and lateral menisci. Behind these, the posterior intercondylar area slopes sharply downward into a fovea and provides an attachment site for the lower end of the posterior cruciate ligament. The posterior intercondylar area ends in a ridge to which the posterior capsular structures are attached (Figs. 10, 11).

SemimembrarH

femoral condy._

Medial head ol gastrocnemius retinaculum

Adductor apoi

Medial

SemimembrarH

Medial head ol gastrocnemius retinaculum

Adductor apoi

Lateral head of gastrocnemius

Arcuate ligament

Lateral femoral condyle

Plantaris

Fig. 9. The posterior portion of the distal femur consists of a central popliteal surface with attachments for periarticular structures across almost the entire distal expanse. These periarticular structures are shown in Figs. 5, 9, 10, 16, 17).

Lateral head of gastrocnemius

Arcuate ligament

Lateral femoral condyle

Plantaris

Fig. 9. The posterior portion of the distal femur consists of a central popliteal surface with attachments for periarticular structures across almost the entire distal expanse. These periarticular structures are shown in Figs. 5, 9, 10, 16, 17).

2.2.2. Tibial Tuberosity

A large tuberosity that is divided into a lower roughened region and a smooth upper region is present on the anterior surface of the proximal tibial shaft. The patella ligament inserts on the lower region. The upper surface of this tuberosity is tilted backward relative to the long axis of the shaft, but the inferior surface projects forward in a triangular protuberance (Fig. 12).

2.2.3. Condyles

On the lateral side of the tuberosity, the tibia first forms a ridge that provides attachment sites for the lateral capsule and fibers from the iliotibial tract (Figs. 12, 13). The strongest, direct attachment for the iliotibial tract, however, is on the lateral tibial tubercle. A prominent ridge just posterior to the tubercle provides an attachment site for the lateral capsular ligaments. The lateral tibial condyle is somewhat flattened below and articulates with the head of the fibula posteriorly. The fibular facet is directed downward and laterally to match the articular surface of the head of the fibula. The posterior edge of the fibular facet is on the posterolateral portion of the proximal tibia, just below the posterolateral tibial plateau. The most posterior third of the lateral condyle has an acute posterior slope just medial to the plateau (Figs. 12, 14, 15).

The medial tibial condyle projects much farther posteriorly than does the lateral condyle, and the entire nonarticular surface provides an extensive attachment site for the tendon and retinaculum of the semimembranosus. The superior posteromedial edge of this condyle has a distinct groove for the direct arm of the semimembranosus, and the tibial attachment for the posterior oblique ligament and the mid third of the medial

Fig. 10. Proximal surface of the tibia with associated soft tissues: superior view (illustration by the author, reproduced with permission from ref. 1; Hughston Sports Medicine Foundation, Inc., Columbus, Georgia).

capsular ligament is just above this groove. The most medial portion of the medial tibial condyle is raised to create a smooth projection that secures a bursa over which the tibial collateral ligament glides. This ligament produces a distinct ridge that extends down the medial shaft of the tibia. As the distal condyle blends into the shaft, it drops off sharply and angles anteriorly to produce the medial surface of the tibial tuberosity and provide an attachment site for the tendons of the sartorius, gracilis and semitendinosus (Figs. 14, 16-18).

2.2.4. Posterior Surface

The proximal tibia expands posteriorly and angles obliquely from the medial to lateral direction. Distally it ends abruptly as the shaft drops off to form a deep depression to accommodate the bulk of the popliteus muscle. Medial and posterior to the fibular facet, the tendon of the popliteus produces a distinct groove on the bone. The posterior border of the tibial plateau ends in a sharp ridge medial to this popliteal groove, and the posterior popliteal ligament inserts in the area inferior to the ridge.

Fig. 11. Proximal surface of the tibia: superior view.

A deep fovea in the central part of the posterior proximal tibia marks the lower site of attachment for the posterior cruciate ligament. A distinct osseous ridge extends from just below the posterolateral tibial plateau and runs obliquely toward the medial border of the tibial shaft, the bony origin of the soleus muscle (Figs. 7, 11, 14, 18).

2.3. Fibula

The fibula, the lateral bone of the leg, is more slender than the tibia. It does not share in the transmission of body weight but functions primarily as an anchor for the muscles of the lower leg. The shaft, which has a variable shape that is molded by the muscles to which it gives attachment, ends distally as the lateral malleolus.

The head of the fibula is the only portion that contributes to the structure of the knee joint. The shape of the head is extremely variable, and all its diameters are expanded in relation to the shaft. Its upper surface contains an articular facet that joins onto the inferior lateral tibial condyle, but the exact location of the articulation with the tibia is not constant. The styloid process projects upwards from the lateral part of the superior surface of the head and is the site of attachment for the arcuate ligament. Anterior to this is a small depression that marks the attachment of the fibular collateral ligament. Short, strong ligaments totally surround the tibiofibular articular surfaces and create what is an almost immovable "plane joint" between the two bones. The tendon of the combined long and short heads of the biceps femoris inserts on the anterior surface of the head of the fibula (Fig. 15).

Fig. 12. Proximal tibia: anterior and lateral views.

2.4. Patella

The patella is a large sesamoid bone within the quadriceps femoris tendon that articulates with the patellar surface of the distal femur. The anterior surface is flattened, with just a slight convex curve. The surface is perforated with many nutrient foramina and is marked with numerous rough, longitudinal striae. The inferior half is roughly triangular and the superior border is rounded. The medial and lateral borders are relatively

Fig. 13. Anterior and lateral views of the proximal tibia showing soft tissue attachment sites.

thin but provide substantial areas for musculotendinous attachments. The superolateral border is the site of attachment of the vastus lateralis tendon, where a distinct notch often is present or even an accessory ossification center.

An articular surface covers most of the posterior patella and molds to fit smoothly against the femur. It made up of a large medial and lateral facet; a central ridge; and a single, small, medial facet that is sometimes referred to as the "odd" facet (2). The lateral facet is the largest and deepest of the three facets.

Just inferior to the articular surface is an area known as the apex. The inferior border of the apex is roughened and provides attachment for the patellar ligament. Its superior surface is covered by the infrapatellar fat pad and an extension of synovium termed the ligamentum mucosum or frenulum (Fig. 19).

2.5. Fabella

Fabella, a term derived from the Latin word for "little bean," is a sesamoid bone buried in the lateral head of the gastrocnemius muscle near the musculotendinous junction. The fabella is approximately 13.5 mm long and 3.5 mm wide on average but can be as large as 22 mm x 14 mm (3-5). Data on the occurrence of a fabella vary greatly; the reported frequency ranges from 9.8 to 22% in the normal population and up to 35% in

Groove for semimembranosus

/ Posterior fovea

Groove for semimembranosus

/ Posterior fovea

Fig. 14. Bony topography of the posterior and medial proximal tibia.

Medial

Fig. 14. Bony topography of the posterior and medial proximal tibia.

patients with clinically significant osteoarthritis of the knee (3,4,6). Among individuals who have a fabella, it is bilateral in 71 to 85% (6,7).

The anterior surface of the fabella is covered with cartilage and forms an articulation with the posterior surface of the lateral femoral condyle. The fabella articulates with only a portion of the lateral femoral condyle when the knee is in extension, and the concave curve of the fabella touches only a small arc of the condyle. This limited contact area produces a fabella articular surface that curves very gently in both a superior-inferior and a medial-lateral direction. The overall shape of the fabella is variable, but the curve of the

Fig. 15. The fibula: (A) Anterior view of the entire fibula; (B) Lateral view of the fibula and its relation to the tibia.

anterior articular surface is very consistent and its most distinguishing feature. This curve distinguishes a fabella from a toe sesamoid. Where the toe sesamoid forms a joint with the first metatarsal, the curve is opposite that of the fabella-femur articulation (8) (Fig. 20).

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