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 with ...
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
T ...
. 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.
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 trochanter
The lesser trochanter is a conical posteromedial bony projection of the femoral shaft. it serves as the principal insertion site of the iliopsoas muscle.
Structure
The lesser trochanter is a conical posteromedial projection of the shaft of the fe ...
s 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 sacr ...
. It may function as (1) a reinforcement mechanism for the proximal femoral
diaphysis
The diaphysis is the main or midsection (shaft) of a long bone. It is made up of cortical bone and usually contains bone marrow and adipose tissue (fat).
It is a middle tubular part composed of compact bone which surrounds a central marrow cavit ...
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
The tuberosity of the tibia or tibial tuberosity or tibial tubercle is an elevation on the proximal, anterior aspect of the tibia, just below where the anterior surfaces of the lateral and medial tibial condyles end.
Structure
The tuberosity o ...
, 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 th ...
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.
Studying fossils of ''
Ardipithecus ramidus
''Ardipithecus ramidus'' is a species of australopithecine from the Afar region of Early Pliocene Ethiopia 4.4 million years ago (mya). ''A. ramidus'', unlike modern hominids, has adaptations for both walking on two legs ( bipedality) and life i ...
'' (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
''Nacholapithecus kerioi'' was an ape that lived 14-15 million years ago during the Middle Miocene. Fossils have been found in the Nachola formation in northern Kenya. The only member of the genus ''Nacholapithecus'', it is thought to be a key g ...
'', 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 recen ...
primates)—
homologs
A couple of homologous chromosomes, or homologs, are a set of one maternal and one paternal chromosome that pair up with each other inside a cell during fertilization. Homologs have the same genes in the same loci where they provide points alon ...
to the third trochanter and the
hypotrochanteric fossa are present while both traits are absent in extant apes. They concluded that the
hominid 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 and the femoral shape of apes is
derived
Derive may refer to:
* Derive (computer algebra system), a commercial system made by Texas Instruments
* ''Dérive'' (magazine), an Austrian science magazine on urbanism
*Dérive, a psychogeographical concept
See also
*
*Derivation (disambiguatio ...
contrary to what was previously thought.
See also
*
Fourth trochanter
The fourth trochanter is a shared characteristic common to archosaurs. It is a knob-like feature on the posterior-medial side of the middle of the femur shaft that serves as a muscle attachment, mainly for the '' musculus caudofemoralis longus'' ...
Notes
References
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{{Authority control
Bones of the lower limb
Femur