We shall continue our look at the human skeleton with the next installment of the Skeletal Series blog posts with a consideration of the leg elements. Previously covered was the hip and we shall now cover the femur (upper leg), patella (kneecap) and the tibia and fibula (the two lower leg elements). The evolution of the leg mirrors that of the arm, from ancient fins to rod bearing segments, and as per the arm the leg contains a single upper bone with two lower bones making up the limb ending in the quite unique foot or Pes (White & Folkens 2005: 255).
The femur is the human body’s longest and sturdiest bone that helps to take the whole weight of the body during ambulation (Schwartz 2007: 151). The tibia is the larger of the lower leg bones and it is easier to tell it apart from its slimmer lateral partner, the long and angular fibula. The patella is the body’s largest sesamoid bone, safely ensconced in its muscle pouch in the anterior portion of the knee. The human knee is particularly interesting as it ‘locks’ when stood straight up and unlocks with the aid of the popliteus muscle by laterally rotating the distal femur, which helps critically stabilise the knee.
During excavation of the supine skeleton in-situ, the lower limb bones tend to survive well because of their structural design and bone density. In extended burials, and dependent on burial and soil conditions, the lower limb bones are often well-preserved and relatively easy to distinguish from the rest of the body. As always, care must be taken when excavating the soil on top of and around the lower body. The fibula can often be found fragmented or broken due to its lateral positioning and the effect of the weight of the soil and associated tibia lying close to it (Larsen 1997). Even in cremated or burned skeletal tissue samples, particular features and landmarks of the lower limb long bones can easily be identified, and sometimes even sided as larger fragments can sustain slightly higher temperatures and minimal warping (White & Folkens 2005).
Leg Anatomy and Elements
The lower limb in the modern human is an interestingly adapted limb to bipedal walking, and as such it has changed anatomically from our nearest cousins (the great apes) to cope with our locomotion (Jurmain et al. 2011). In this section we’ll cover the basic gross anatomy of each bone with a more in-depth look at the knee component after. As mentioned elsewhere (and on this blog here) long bone growth is typically through the distal metaphysis (distal border of the diaphysis of the limb) and its epiphysis through the growth plate.
The femur, as stated, is the longest limb bone with several distinctive bony elements. It is a fairly distinct bone with a high level of robusticity and dense, compact bone due to it being the main supporting limb doing ambulation. The head of the femur fits into the acetabulum of the hip bone (ilium, ischium and pubis bones). Unlike the humerus and the glenoid cavity joint, it has a direct ligament attachment between femoral bone and acetabulum, the ligamentum teres, which fits it snugly from the fovea capitis depression on the femoral head into the hip joint, helping to stabilise the joint (White & Folkens 2005: 255). It is also heavily walled with muscles, from the trunk of the torso down to the knee, with the gluteal (lateral-posterior), adductors (medial), quadriceps (anterior) and hamstring (posterior) muscle groups acting on the bone at various points (Gosling et al. 2008).
The main osteological features found on the femur include the greater and lesser trochanter’s, which are found in the proximal half of the femur, just below the femoral neck. The greater and lesser trochanter’s act as muscle attachment sites for the gluteal muscles, amongst others, and sometimes a third trochanter can been seen just distal of the lesser (White & Folkens 2005). Directly posterior, and running down the length of the shaft of the femur, is the linea aspera, one of the main attachment points for a variety of muscles, including the vastus and adductor muscle groups.
At the proximal femoral end the linea aspera collects the spiral, pectineal and gluteal lines (White & Folkens 2005: 257). The lateral and medial condyles mark the distal articular surface with the tibia bone of the lower limb. Alongside the medial edge of the medial epicondyle (just above the medial condyle) lies the adductor tubercle, the insertion point for the adductor magnus muscle (Gosling et al. 2008: 260). The femur can be easily sided as the trochanters are medial and posteriorly positioned, with the linea aspera running directly posteriorly and the adductor tubercle located medially on the medial epicondlye. The mid-section shaft of the femur is tear shaped, with the round body in the anterior position and the top of the ‘tear’ pointing posteriorly.
The patella is the human skeletal systems largest sesamoid bone, and can be found in the anterior muscular pouch on the knee joint, anchored by the quadriceps tendon and patellar tendon on the distal anterior femoral surface (see diagram below). It does not attach or articulated directly with any other bone. The patella functions to ‘protect the intricate muscles and ligaments inside the knee joint, to increase area of contact between the patellar ligament and the femur, and to lengthen the lever arm of the quadricep muscles’ (White & Folkens 2005: 270). The apex of the patella is the most distal point of the bone, and the smooth posterior articular facet rides the ligaments and muscles located anteriorly of the distal femur.
The tibia is a distinctly shaped bone with an proximal medial and lateral condyles, medial and laterally intracondylar eminence’s (set posteriorly on the superior surface), an anterior proximal tibial tuberosity, the curved ‘tri-blade’ of the body (anterior, medial and posterior crests, with the medial malleolus marking the distal extremity of the bone (White & Folkens 2005: 273-79). The landmarks on the tibia represent muscle origin and insertion points, such as the soleal line on the posterior aspect of the proximal tibia, which represents the soleus muscle origin. The tibia is connected to the laterally positioned fibula with a strong interosseus membrane connecting the two throughout the length of the fibula, with articulations at the proximal and distal segments of the tibia (Gosling et al. 2008: 277). Distally, the tibia articulates with the talus, the first tarsal bone of the foot. To easily side the tibia, the malleolus is located on the medial distal aspect of the tibia, and the tibial tuberosity represents the anterior facing proximal end of the bone.
The fibula is the thinner of the two lower legs bones, and does not bare any substantial weight (White & Folkens 2005). It’s primarily importance is providing the lateral border of the ankle joint, with which it articulates with the calcaenous bone. The head of the fibula, located superiorly, can be easily complicated with the distal malleolar articular surface, and to add to the woes of identification, the body of the fibula, without the proximal or distal segments, is nearly impossible to identify because of its irregularity. The interosseous crest is located medially, and serves as the attachment for the interosseus membrane which spans between the length of the tibia and fibula. To side an intact fibula quickly, use the posterior facing malleolar fossa, which can be found on the distal articular surface of the fibula. The fibula has also been used as marker of sex (Sacragi & Ikeda 1995) and although this method is rarely used, it could be useful in a forensic or archaeological context where the skeletal remains may be limited.
- Although not mentioned here, please take the time to get associated with the fleshy articular pads between the femur and tibia (be aware as this is a fleshed photo).
Gosling, J. A., Harris, P. F., Humpherson, J. R., Whitmore I., & Willan P. L. T. 2008. Human Anatomy Color Atlas and Text Book. Philadelphia: Mosby Elsevier.
Hawks, J. 2011. Femur: major landmarks and how to side it. From www.johnhawks.net. Accessed 2012.
Jurmain, R. Kilgore, L. & Trevathan, W. 2011. Essentials of Physical Anthropology International Edition. London: Wadworth.
Larsen, C. 1997. Bioarchaeology: Interpreting Behaviour From The Human Skeleton. Cambridge: Cambridge University Press.
Roberts, C. & Manchester, K. 2010. The Archaeology of Disease Third Edition. Stroud: The History Press.
Sacragi, A & Ikeda, T. 1995. Sex Identification From The Distal Fibula. International Journal of Osteoarchaeology. 5: 139-143. (access required).
Schwartz, J. H. 2007. Skeleton Keys: An Introduction to Human Skeletal Morphology. New York: Oxford University Press.
White, T. & Folkens, P. 2005. The Human Bone Manual. London: Elsevier Academic Press.