In human anatomy, the third trochanter is a bony projection occasionally present on the proximal
femur
The femur (; ), or thigh bone, is the proximal bone of the hindlimb in tetrapod vertebrates. The head of the femur articulates with the acetabulum in the pelvic bone forming the hip joint, while the distal part of the femur articulates wit ...
near the superior border of the
gluteal tuberosity
The gluteal tuberosity is the lateral one of the three upward prolongations of the linea aspera of the femur, extending to the base of the greater trochanter. It serves as the principal insertion site for the gluteus maximus muscle.
Structure ...
. When present, it is oblong, rounded, or conical in shape and sometimes continuous with the gluteal ridge. It generally occurs bilaterally without significant side to side
dimorphism
Dimorphism or dimorphic may refer to:
Science
* Dimorphic root systems, plant roots with two distinctive forms for two separate functions
* Sexual dimorphism, a phenotypic difference between males and females of the same species
* Nuclear dimorph ...
.
A structure of minor importance in humans, the incidence of the third trochanter varies from 17 to 72% between ethnic groups and it is frequently reported as more common in females than in males. Structures analogous to the third trochanter are present in other mammals, including some primates.
It is called the third trochanter in reference to the
greater and
lesser trochanters that are always present on the femur.
Function
Its function is to provide an attachment for the ascending tendon of the
gluteus maximus muscle
The gluteal muscles, often called glutes are a group of three muscles which make up the gluteal region commonly known as the buttocks: the gluteus maximus, gluteus medius and gluteus minimus. The three muscles originate from the ilium and sacru ...
. It may function as (1) a reinforcement mechanism for the proximal femoral
diaphysis in response to increased ground reaction force and (2) to increase the attachment surface area for the gluteal musculature and thereby providing greater efficiency of contracture. Mechanical load from the gluteus maximus may, on the other hand, affect the morphology of the proximal femur, similar to how
quadriceps
The quadriceps femoris muscle (, also called the quadriceps extensor, quadriceps or quads) is a large muscle group that includes the four prevailing muscles on the front of the thigh. It is the sole extensor muscle of the knee, forming a large ...
determines the size and shape of the
tibial tuberosity, and thereby the shape of the third trochanter.
However, no certain conclusions regarding the biomechaniccal role of the third trochanter can be made.
Anthropology
The third trochanter is associated with short, robust femora,
and is frequently present and well developed in
Neanderthal
Neanderthals (, also ''Homo neanderthalensis'' and erroneously ''Homo sapiens neanderthalensis''), also written as Neandertals, are an extinct species or subspecies of archaic humans who lived in Eurasia until about 40,000 years ago. While ...
s (that were shorter and more robust than
anatomically modern humans
Early modern human (EMH) or anatomically modern human (AMH) are terms used to distinguish ''Homo sapiens'' (the only extant Hominina species) that are anatomically consistent with the range of phenotypes seen in contemporary humans from extin ...
) but generally absent in
higher primates
The simians, anthropoids, or higher primates are an infraorder (Simiiformes ) of primates containing all animals traditionally called monkeys and apes. More precisely, they consist of the parvorders New World monkeys (Platyrrhini) and Catarrhi ...
.
Studying fossils of ''
Ardipithecus ramidus'' (a
Chimpanzee-human last common ancestor candidate), noted that in this species—as well as in ''
Proconsul
A proconsul was an official of ancient Rome who acted on behalf of a consul. A proconsul was typically a former consul. The term is also used in recent history for officials with delegated authority.
In the Roman Republic, military command, or ' ...
'', ''
Nacholapithecus'', and ''
Dryopithecus
''Dryopithecus'' is a genus of extinct great apes from the middle–late Miocene boundary of Europe 12.5 to 11.1 million years ago (mya). Since its discovery in 1856, the genus has been subject to taxonomic turmoil, with numerous new species b ...
'' (
Miocene
The Miocene ( ) is the first geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and means "less recent" ...
primates)—
homologs to the third trochanter and the
hypotrochanteric fossa are present while both traits are absent in extant apes. They concluded that the
hominid
The Hominidae (), whose members are known as the great apes or hominids (), are a taxonomic family of primates that includes eight extant species in four genera: '' Pongo'' (the Bornean, Sumatran and Tapanuli orangutan); ''Gorilla'' (the e ...
morphotype
In biology, polymorphism is the occurrence of two or more clearly different morphs or forms, also referred to as alternative ''phenotypes'', in the population of a species. To be classified as such, morphs must occupy the same habitat at the s ...
is
primitive
Primitive may refer to:
Mathematics
* Primitive element (field theory)
* Primitive element (finite field)
* Primitive cell (crystallography)
* Primitive notion, axiomatic systems
* Primitive polynomial (disambiguation), one of two concepts
* Pr ...
and the femoral shape of apes is
derived contrary to what was previously thought.
See also
*
Fourth trochanter
Notes
References
*
*
*
{{Authority control
Bones of the lower limb
Femur