BENNETT’S FRACTURE
“Homo habilis”, (KNM - ER 1813), Koobi Fora, Kenya 1.8 million years old. Hunterian
Museum, Glasgow, below stone tools attributed to Homo habilis.
In 1964 Louis Leakey, announced to the world the
discovery of the oldest member of the genus,
“homo”, found at Olduvi Gorge in eastern
Tanzania. The fragmentary skull and mandible
fragments pointed toward an estimated cranial
capacity of around 680 cc, much larger than true
apes, though still very much smaller than modern
humans. Originally thought to be around 600,000
years old the fragments underwent the first
radiometric dating of a truly ancient hominid
fossil using a K/Ar technique. The stunning result
showed that in fact the fragments were 1.75
million years old, but this was not the only surprise. Found alongside the bones in the same
geological stratum was evidence of stone tools suggesting a far more sophisticated level of
intelligence than any previous hominid. Here was the first evidence for tool use in a
hominid. The species was given the name “Homo habilis”, (the “handyman” or
“toolmaker”), surely this was the most ancient “human” ancestor ever discovered. It
seemed to be a true “missing link” between older Australopithecine arboreal ape-like
creatures and the later “Homo erectus” which would eventually evolve into Homo sapiens.
This link was assumed to be in perfect agreement with the theory of the direct step by step
linear and “progressive” descent of the evolution of mankind.
However later and more complete discoveries of hominid fossils has not borne this theory
out, indeed it appears we have really only unearthed the tip of the iceberg with respect to
hominid fossils. Later Homo habilis fossil discoveries, such as the enigmatic 1.8 million
year old KNM-ER 1813 specimen from Kenya, appear to suggest a much more complicated
story. What have in the past been labelled as “habilis” in fact seems to represent a number
of different species altogether and many of these species appear to have coexisted in time
thus destroying the theory of continual linear descent of one species to the next. Instead the
emerging picture seems to be a “bush of many branches” rather than a single trunk of
descent. It now seems that although an intelligent species Homo habilis was not a direct
ancestor of Homo sapiens, rather a side branch that died out. It is interesting to
contemplate that whilst most animals on the planet today have a number, often quite large,
of different species within their parent genus, man is virtually unique in being the only
species of his genus today. Indeed it is thought that at the beginning of Pleistocene period,
better known as the “ice ages”, around 2 million years ago no fewer than four and possibly
more intelligent hominid species coexisted. Homo sapiens for one reason or another is the
sole survivor of the genus homo, today.
Whist in Darwin’s time it seemed perfectly clear that “man” was truly set apart from the
rest of creation, in the 21st century it seems a lot less certain what exactly it is to be
“human”. A number of different criteria have been put forward, first and foremost a large
cranial capacity, yet it is now known that on the whole the Neanderthal species had a
slightly larger one. The upright bipedal gait perhaps… yet many hominid species in the
past have had this. The combination of intelligence combined with the ability of language
probably comes as close to defining what it is to be human as one can get, yet we know
…that Homo habilis had this to some degree by the evidence of their stone tools. A fourth
often overlooked characteristic that may be included is the opposable thumb, the
anatomical arrangement of the first carpo-metacarpal joint that allows the tip of the thumb
to oppose the tips of all the other fingers. Although present in some other primates it is
uniquely developed in Homo sapiens to allow for the critical movements of the pincer grip
without which man could not have achieved the technological capabilities that he has even
with his superior intelligence and language. Even this ability however had been achieved
in other extinct hominid species as much as 1.75 million years ago. It is a profoundly
sobering thought when appreciate now, that but for the quirks of “contingency” we may
well have been sharing our planet with more than one other intelligent species. In this light
it is becomes a little more difficult to think of ourselves as unique and “above” our fellow
creatures. It is to be hoped that this thought may engender more respect for them.
It is extremely important to recognize injury to the carpo-metacarpal joint of our patients,
lest they should lose the full abilities of one of the most unique aspects that separate us
from the rest of our fellow creatures on the Earth today, though not from some others now
long extinct.
BENNETT’S FRACTURE
Introduction
Bennett’s fracture is an intra-articular fracture of the base of the first (thumb) metacarpal.
The anatomy of the human thumb allows for the “prehensile” abilities that were an
essential element in human evolution.
Unless properly recognized and treated, this intra-articular fracture subluxation may result
in an unstable and arthritic joint with significant pain and loss of function.
Note that more complex fractures that involve 3 fragments at the base of the first
metacarpal are sometimes known as Rolando’s fractures.
History
Dr. Edward Hallaran Bennett (1837-1907) was an Irish surgeon.
He first described this fracture in 1882. 1
Mechanism
●
The injury is usually a result of an axial compression force through the first carpometacarpal joint.
A common scenario is the “punch” injury where the thumb is held flexed within the
fist.
●
The metacarpal becomes unstable and will readily dislocate (or sublux) dorsally,
radially and proximally due to the pull of the adductor pollicis and abductor pollicis
longus muscles, (as shown above).
Complications
●
The injury is important to recognize because the first carpo-metacarpal joint (thumb
joint) is critical for the vital “pinch” and “opposition” functions of the thumb. This
injury may therefore severely affect the function of the hand.
●
If the fracture is missed mal-union in the dislocated or subluxed position is likely,
resulting in the rapid onset of symptomatic osteoarthritis in this mobile joint.
●
Unfortunately, even after restoration of articular congruity, some patients may still
develop post traumatic arthritis.
Clinical Features
●
Pain, swelling and tenderness may be seen at the base of the thumb (at the first
metacarpal).
●
Pain can be especially elicited with axial compression on the thumb (but this may
also occur however with a scaphoid fracture or radial styloid fracture).
Investigation
Plain radiography:
Intra-articular fracture of the base of the first metacarpal (Bennett’s fracture)
Standard A-P, lateral and oblique radiographs should be obtained in patients with suspected
fractures or dislocations of the thumb.
More complex injuries, involving Y shaped comminuted fractures of 3 or more fragment
are sometimes referred to as Rolando fractures.
CT scan:
●
CT scan may occasionally be required to further define the exact nature and extent
of more complex injuries.
Management
A thumb spica plaster may be used initially for more minor injuries, however once the
fracture is reduced it is difficult to maintain the reduction due to the constant pull of the
thumb adductors and stiffness readily occurs following prolonged immobilization of this
joint.
Surgical treatment is therefore the best treatment for this injury.
For more minor fractures closed reduction may be tried, with percutaneous pinning,
however the best treatment is early open reduction and internal fixation (ORIF)
especially when:
●
The avulsed fragment of bone involves more than one third of the articular surface.
●
There is more than 1 mm of articular incongruity.
ORIF will:
●
Maintain reduction
●
Enable patients to initiate movement sooner postoperatively, minimizing the
problems of prolonged immobilization.
Following ORIF the hand and thumb are immobilized in a plaster cast for 4-6 weeks.
ORIF is also the usual treatment of a Rolando fracture (although external fixation may be
performed depending on the size of the fragments).
Disposition:
These fractures should be referred to the Orthopaedic unit.
Missed Bennett’s fractures that have developed severe arthritis may require arthrodesis for
relief of symptoms.
References
1.
E. H. Bennett: Fractures of the metacarpal bones. Dublin Journal of Medical
Science, 1882, 73: 72-75.
2.
Ireland D, “Common Hand Injuries in Sport”, Australian Family Physician vol 13
(11) 1984, p. 797-800
Dr J. Hayes
Reviewed May 2013.