Last Updated on October 30, 2023
Why should a fracture occur and what are types of forces that cause the fracture to occur?
A fracture is a break in continuity of the bone. Bone is a very strong tissue that is composed of minerals, which provide rigidity, and collagen, which provides tensile strength.
A fracture is caused by a force acting on the bone which is more than it can sustain.
When bone is subjected to an excessive stress, it will fail. Under normal circumstances, a bone withstands many activities that vary in stress. But when the force exceeds the strength of the bone, it breaks.
There are many extrinsic factors that are important in causing the injury. These are the magnitude, duration, and direction of the force acting on the bone and the rate at which this force is applied.
A bone is subjected to various kinds of forces in our day to day life. Some try to compress it, some bend while others rotate. Depending on their action, the forces on bone could be classified as compression, tension, and shear forces.
Compressive Forces or Compression
A compressive force acts along the long axis of a bone so as to compress the bone material [see image below]. Compressive forces result in impacted fractures or compression fractures. A force of compression causes metaphyseal impaction fractures, crushing injury to epiphysis, the collapse of vertebrae etc.
For compressive force to result in fracture, one end of a bone must be in a fixed position while the other end is forced toward the fixed end. An example is a man jumping on the ground from a height on his feet and getting a compression fracture of the vertebra as a result.
A force that pulls apart both the axial ends is an example of tensile force. For tensile force to result in fracture, one end of a bone must be in a fixed position while the other end is forced away from the fixed end.
This will create a separation or avulsion fracture.
Common areas for this to occur include the tibial tuberosity, greater trochanter, and olecranon.
This kind of force will be a force that tries to twist the bone along its long axis. This usually is a result of one end of a bone being placed in a fixed position while the other end of the bone is forced to rotate. Torsional forces generally result in short or long spiral fractures.
Shearing forces are unaligned forces pushing one part of a body in one direction, and another part the body in the opposite direction.
A shearing force will produce a fracture parallel to the direction of the applied force. Bone is weakest under shear stress making fractures of this nature common even with minimal trauma. The following image is an example of shear forces on bone.
These are a major classification of types of forces that a bone has to withstand. But actually, a bone has to resist the combination of these forces. For example, a bone may undergo a force called bending force, [ imagine bending a stick]. It would amount to compressive forces on one surface and tensile forces on other leading to two kinds of forces acting simultaneously.
A force may have a direct impact on the bone or may produce a fracture indirectly.
Patterns of Fractures Depending on the Force
Directly Applied Forces
It is an application of a small force to a localized area of bone. It generally produces a transverse fracture. In such cases most of the energy is absorbed by the bone and damage to soft tissue damage is minimal.
When a large force is applied to a larger area of bone, it will cause comminution or a transverse fracture, with extensive soft tissue damage.
These injuries are typical of missile injuries such as a gunshot wound. These cause extensive comminution and soft tissue damage in high-velocity impacts and moderate damage in low-velocity impacts.
Indirectly Applied Forces
Indirect force is one which is away from the fracture site. This kind of force produces fracture by an indirect mechanism.
Traction or tension fracture
A muscle that forcibly contracts and pulls away a piece of bone attached to its musculotendinous unit (i.e., avulsion ) will produce a traction fracture.
A force causing bending of the bone such that one side is under compression and the other under tension will cause fracture which is transverse. The side under tension fractures first.
A combination of horizontal and vertical stresses will cause fracture at 45 degrees to the long axis of the bone.
Excessive axial loads will cause fractures of cancellous bone [impaction fractures] or longitudinal fracture of the cortical bone.
It is a dictum in orthopedics that no two fractures are alike. Every fracture behaves differently from other. In the same part fractured, there could be different types of treatment depending on many factors other than fracture geometry.
Treatment of fractures takes various things into consideration -age of the patient, fracture pattern, type of bone fractured, part of the bone fractured, any other associated injury any chronic problem and sometimes your expectation the treatment. We discuss it one by one.
Patient age is an important consideration in the treatment of a fracture. Most of the pediatric fractures can be treated by nonoperative methods. There are many few indications for use of surgical treatment for children as compared to an adult.
An undisplaced fracture at any age would require just a plaster application (there are exceptions to this statement though).
A displaced fracture would always require closed or open reduction (open reduction is a term used to treat the fractures by surgically opening the fracture fragments.
Area of the bone fractured
Metaphyseal fractures (Fractures near to bone ends) are more amenable to closed reduction & splintage than shaft fractures in case of long bones. Intra-articular fractures (fractures in which break also occurs at the end of the bone that takes part information of joint) require strict anatomical reduction when compared to nonarticular fractures.
Type of bone fractured
This is a very important consideration because biomechanics of each bone & joint are different, there tend to occur different kind forces on fractured fragments in different bones.
Accordingly, the primary & surgical treatment varies.
The pressure of large wound along with fracture is an indication for wound cleaning, debridement (removal of dead tissue) and fixation.
Associated multiple fractures in other bones is also an indication for surgery. The aim is to stabilize all the bones so that patient can be made mobile.
Chronic problems if any also make an important factor in kind of treatment that can be given to the patient.
Choice of patient
This too has an important bearing on treatment. Some people would accept plaster application for a long time but will not take the risk to undergo surgery.
All said and done, the basis of both nonoperative, operative treatment is same.
To align the fractured fragments into anatomically acceptable position and hold it there till union between fractured fragments occurs.
This simple principle is the guiding factor in all complex modes of treatment.
These are main factors which form the basis of treatment in case of fractures. A physician would always choose from one of the available choices and thus there could be variations in treatment from one doctor to another.