Osteology: Leg

The femur is the proximal bone of the hindlimb.  It is the largest bone in the human body.  The femur articulates proximally with the acetabulum of the os coxa to form the hip joint.  Distally, the femur articulates with the tibial condyles to form the knee joint.

The proximal femur is dominated by its massive, nearly spherical head.  The articular surface of the femoral head is disrupted by the fovea capitis, an excavated depression in the otherwise smooth surface.  The head is connected to the rest of the femur by its neck. Two roughed trochanters on the proximal femur provide important muscle attachment sites.  The greater trochanter projects superiorly from the dorsal surface of the proximal tibia.  The gluteus medius and gluteus minimus muscles take origin here and serve as critical hip stabilizers during walking.  Further distally, several major hip flexors take origin from the lesser trochanter.  The two trochanters are united by an intertrochanteric crest on the dorsal surface of the proximal femur and an intertrochanteric line on the ventral surface.

The femoral shaft is roughly cylindrical in cross-section.  The shaft expands medially-laterally as it approaches the distal end.  The ventral aspect of the femoral shaft has few diagnostic features.  The dorsal aspect of the femur bears the linea aspera, which is the insertion point for several hip adductors and a major origin site for several knee extensors.  The linea aspera is a double ridge, with medial and lateral margins running the full length of the femoral shaft.  These lines

The distal femur bears two large articular condyles which rest on the corresponding condyles of the tibial plateau.  The broader lateral condyle is separated from the narrower, more curved (in distal view), medial condyle by a broad depression known as the intercondylar fossa.  The medial condyle projects further distally such that the shaft tilts laterally when the condyles are set upon a flat surface  (e.g. the tibial plateau).  The two condyles merge ventrally as the patellar surface, an articular facet for the patella.  The medial epicondyle and lateral epicondyle sit just proximal to the condyles, where they provide attachment sites for the collateral knee ligaments.  The lateral epicondyle is separated from the lateral condyle by the popliteal groove.

Siding the Femur

For proximal femora, the head faces superiorly and medially.  The fovea capatis is offset inferiorly and dorsally.  The greater trochanter points superiorly and the lesser trochanter is dorsal.  For shaft fragments, the linea aspera is dorsal, and the shaft widens medially-laterally on the dorsal end.  For distal femora, the condyles form a horseshoe shape in distal view, and the horseshoe opens dorsally.  The asymmetries between the condyles discussed above are useful for distinguishing medial from lateral.  The patellar surface is ventral.  The popliteal groove is on the lateral side.

Sex Determination using the Femur

The size of the femur, especially the diameter of the femoral head, is tightly correlated with body mass.  Thus, because males and females differ in average body mass (a condition known as sexual dimorphism), the diameter of the femoral head alone is a fairly good predictor of sex.  Stewart (1979) used 50 male and 50 female skeletons of known sex to show that 93% of skeletons in his sample could be correctly assigned to sex using femoral head diameter alone (see Figure).

 The patella is the largest sesamoid bone in the human body.  It is imbedded in the tendon of the biceps femoris muscle. The patella rides along the patellar surface on the ventral surface of the distal femur during knee extension and flexion.  Viewed from the ventral aspect, the patella is shaped like a clam, with a distally pointed apex and a rounded base. The dorsal surface is a large articular surface with a medial articular facet and a lateral articular facet for the patellar surface of the femur.  The apex is also visible from the dorsal aspect. From this view it can be seen that the apex is nonarticular.

Siding the Patella

The base of the patella is proximal, while the apex points distally.  The lateral articular facet is larger than the medial facet.

The tibia is the medial bone of the lower leg.  As the only lower leg bone which articulates with the femur, it bears nearly all of the weight of the body that is transmitted through the lower leg.  The proximal tibia is a broad plateau upon which the femoral condyles rest, forming the knee joint. The sharp ventral margin of the tibial shaft is easily palpated in the living person; this is the familiar shin bone.  The shaft tapers distally, then expands slightly to form the articular surface for the talus at the ankle joint.  The tibia articulates with the fibula both proximally and distally.

The proximal tibia is a broad plateau which bears a medial condyle and a lateral condyle which correspond with their respective femoral condyles.  The lateral condyle is more rounded than the more elongate oval of the medial condyle.  The condyles are separated from one another by the medial intercondylar tubercule and the lateral intercondylar tubercule.  Two depressions for the attachment of the cruciate ligaments of the knee are located just anterior and posterior to these tubercules.  The proximal fibular articular facet is perched just below the lateral condyle on the dorsal aspect of the proximal tibia.  The ventral side of the proximal tibia bears the tibial tuberosity, the large and blunt insertion site for the tendon of quadriceps femoris, a major knee extensor.

The shaft of the tibia has a very distinctive, nearly triangular cross section.  The apices of this triangle correspond with the medial margin, interosseous margin, and the anterior margin of the tibia.  The flat shaft surface between the medial margin and the anterior margin is not covered by any muscles in the living person and is easily palpated.  The shaft surface between the interosseos margin and the anterior margin is also flat and relatively featureless.  The shaft surface between the interosseous and medial margins of the tibia is more convex than the other surfaces along its proximal end.  Proximally, the surface is marked by the soleal line for the insertion of the popliteus muscle and the origin for the soleus muscle.  A large, distally oriented nutrient foramen is usually visible just distal to the soleal line.

The distal end of the tibia bears a large and expanded articular surface for the talus.  The medial malleolus projects distally from the medial aspect of the distal tibia.  The medial malleolus forms the palpable medial bony bulge at the ankle joint. The malleolar groove, located on the dorsal surface adjacent to the medial malleolus, provides the path traversed by tendons of the tibialis posterior and flexor digitorum longus muscles.  These muscles are ankle dorsiflexors.  The fibular notch on the lateral side of the distal fibula is the distal articular surface for the fibula.  This articular surface is not as smooth as many other articular surfaces.

Siding the Tibia

For proximal tibiae, the asymmetries between the condyles discussed above are useful for distinguishing medial from lateral. The tibial tuberosity is ventral, while the proximal fibular facet is located on the dorsal-lateral corner of the proximal tibia.

For shaft fragments, the soleal line and the nutrient foramen are dorsal.  The soleal line slants from lateral to medial as it plunges distally. The shaft tapers from proximal to distal.  The anterior margin is the sharpest and best defined of the tibial margins.  The interosseous margin is lateral, and is offset dorsally.

For distal tibiae, the medial malleolus is medial, and the fibular notch is lateral.  The malleolar groove is dorsal. The laterally oriented talar articular surface of the medial malleolus has a lobe which projects more distally than the rest of the articular surface.  This lobe is on the ventral side.

The fibula is the long, thin, lateral bone of the lower leg.  The fibula does not articulate with the femur, so it bears very little weight.  It articulates proximally and distally with the tibia and forms the lateral bony prominence that is palpable at the ankle, where it articulates with the talus.  The fibula is the attachment site for several important muscles which act on the foot and ankle.

The proximal fibula has a bulbous head with a superiorly projecting apex on the lateral side.  The head bears a proximal fibular articular surface which faces medially, towards its articulation with the corresponding articular facet on the tibia.

The fibular shaft is extremely variable in cross section.  The very sharp and pronounced anterior margin traverses the ventral surface of the shaft.  The medially located interosseous margin is more rounded than the anterior margin.  The posterior margin runs the length of the dorsal shaft surface. There is frequently a posteriorly located nutrient foramen which dives distally into the bone.

The distal end of the fibula also has an expanded surface bearing the talar articular surface.  Just posterior to this surface is the maleolar fossa, which serves at the attachment point for several ankle ligaments.

Siding the Fibula

For proximal fibulae, the articular surface for the tibia faces ventral-medially.  For distal fibulae, the lateral malleolus is lateral, and the talar articular surface faces medially.  Fibular shaft fragments can be quite difficult to side without comparative material.