DIAPHYSIS: FUNCTIONS, COMPOSITION AND DIAPHYSEAL FRACTURES - ANATOMY AND PHYSIOLOGY - 2025

The diaphysis is the central part of the long bones. It is responsible for supporting the weight of the body as columns and, at the same time, increasing the power of the muscles by working as a lever. Not all bones have diaphyses, only long bones. The bone structures where it is found are located mainly in the extremities.

Thus, the bones of the body that have diaphysis are: in the upper extremities, the humerus, the radius, the ulna (formerly known as the ulna), the metacarpals and the phalanges; and in the lower extremities the bones with diaphysis are the femur, tibia, fibula (formerly known as fibula), metatarsals and phalanges.

In addition to those mentioned previously, the ribs and clavicles are also long bones with diaphysis although they are not found in the extremities. All bones with diaphysis are known as long bones and in addition to the central part (diaphysis) they have two additional parts.

These two parts are the epiphyses, located at the ends of the bone; and the metaphyses, which are located at the junction of the diaphysis and the epiphysis. Each of these sections of the bone has specific functions for the proper functioning of the skeleton.

The rest of the bones in the body do not have a diaphysis. They are classified as flat bones, and their structure and function are different from those of long bones.

Composition of the diaphysis

In general, long bones are made up of two well differentiated parts: the cortex or cortical bone, and the bone marrow.

The cortex represents the exterior of the bone and is covered by the periosteum, while the marrow occupies the interior of the bone, with blood and lymphatic vessels running inside.

Cortical bone

The cortex is made up of dense bone, laminar in structure, very hard and with a certain torsion that allows it to withstand the great stresses to which the diaphysis is usually subjected.

The cortex is organized like a tube, which allows the bone to be very strong but at the same time light. However, it is not a hollow tube but with a very important tissue inside: the bone marrow.

On the outside, the diaphysis of long bones is covered by a thin layer of richly innervated fibrous tissue known as the “periosteum”, which is responsible for sensitivity and at the same time functions as an anchor point for muscle and tendon insertions.

Bone marrow

The bone marrow is a soft tissue made up of hematopoietic cells (producers of red blood cells) during childhood. Later they are made up mainly of fatty tissue.

The bone marrow functions as a shock absorber, absorbing the forces that are generated towards the interior of the diaphysis.

Features

The diaphyses have two main functions:

1- This structure is capable of supporting the weight of the human body as a «pylon or column», especially the diaphysis of the femur and the diaphysis of the tibia; The shaft of the humerus and the shaft of the ulna (radius) can also do this, although to a lesser extent and for a limited time.

2- It serves as an anchor point to the muscles (through the tendons) and certain ligaments, allowing the force generated by the muscular system not only to be transmitted to the bones, but to be amplified by acting as levers.

Since there is more than one muscle taking insertion in the diaphysis of the bones, these have specialized structures that allow to increase the insertion surface, (for example, the rough line in the diaphysis of the femur). These structures form grooves and valleys in the shaft where the tendons of the muscles individually insert.

In general, the muscles are inserted into two consecutive bones, passing in most cases over a joint (union between two specific bones). Then, depending on the fixed point that the muscle contraction takes, there will be one movement or another in the limb.

Diaphyseal fractures

Diaphyseal fractures are the most common in long bones. They usually occur due to a direct impact, where the force is applied perpendicular to the long axis of the bone.

According to their characteristics, diaphyseal fractures can be classified into simple (when the diaphysis is fractured in a single point), complex (when the fracture occurs in two or more points) and comminuted (when the diaphysis is fractured in multiple fragments).

Furthermore, fractures can be transverse (the fracture line has a direction perpendicular to the long axis of the bone), oblique (the fracture line between 30 and 60º in relation to the long axis of the bone) and spiral (they form a spiral around the diaphysis).

Depending on the type of fracture, the type of treatment for it is decided. They have two basic options: orthopedic treatment and surgical treatment.

Orthopedic treatment

Orthopedic treatment (conservative or non-invasive) is one that consists of immobilizing the limb where the diaphyseal fracture occurs using an orthopedic element.

Gypsum or synthetic casts are usually used, although immobilization devices such as skeletal traction can also be used.

The goal of this treatment is to keep the ends of the fracture in contact in order to allow the scar tissue to form a callus that will eventually fuse the two ends.

Orthopedic treatment is usually reserved for simple and transverse fractures, although this is not a sine qua non condition.

On the other hand, this is the treatment of choice as long as there is no contraindication in children, since surgical procedures can damage the growth plate and compromise the final length of the limb.

In cases of diaphyseal fractures of the long bones of the hands and feet -metacarpals and metatarsals-, the treatment of choice is usually orthopedic (immobilization) although in certain cases it is necessary to require surgery.

Surgical treatment

The surgical treatment of diaphyseal fractures consists of performing surgery. Through an incision in the skin, access is made to the muscular planes, which are separated to gain access to the fracture site.

Once in the area, different synthetic materials can be used, such as cortical plates with cortical screws, which are ideal for the diaphyses of unloaded bones such as the humerus, ulna, radius and fibula.

Endomedullary nails (blocked or not with cortical screws) can also be used, these are ideal for treating load bearing bones such as the femur and tibia.

Regardless of the osteosynthesis material chosen, the procedure is performed by the orthopedic surgeon under general anesthesia. The objective is to keep all the fracture fragments joined together by the nail or the plate, something that would not be possible in certain cases with orthopedic treatment.

In cases of diaphyseal metacarpal and metatarsal fractures, special wires or screws are usually used as synthetic material, although these procedures are reserved for very complex fractures that would not be possible to resolve with orthopedic treatment.

In general, this treatment is reserved for spiral, comminuted or complex fractures, as long as there is no contraindication.

References

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