Fracture

What is a fracture?

Fracture is the medical term used to describe a break in a bone. When a bone breaks, the muscles and blood vessels around the broken bone are usually damaged as well. Most fractures are caused by trauma to the body as a result of high-impact force or stress. A pathologic fracture is a special term to describe a bone-breaking as a result of disease in the bone. Usually, very little force is required to cause a pathologic fracture because the diseased bone is weaker than normal bone. Bone diseases that can lead to pathologic fractures include osteoporosis (or bone thinning), cancer and/or infections in the bone, and certain medications.

Bone fractures and osteoporosis

Osteoporosis is a disease that commonly affects older adults. It results in thin, delicate bones that break more easily than normal, healthy bones. Osteoporosis is more common in older men and women, especially in women who are in menopause. Fractures associated with osteoporosis typically involve the vertebrae (spine), femur (hip), lower radius (wrist), or upper humerus (shoulder).

Cancer in a bone

Cancer cells found in a bone are divided into two categories: primary bone tumours (a tumour that started in the bone) and metastasis (cancers that have started in another location and spread to the bone). In older adults, metastasis to the bone is much more common than a primary bone tumour. The types of tumours that commonly spread to bone include invasive ductal carcinoma of the breast, adenocarcinoma and squamous cell carcinoma of the lung, clear cell renal cell carcinoma of the kidney, adenocarcinoma of the prostate, and papillary thyroid carcinoma. In contrast, primary bone tumours such as osteosarcoma are more common in children and young adults. Lymphoma, a type of cancer that starts from the cells in the immune system, can be seen in the bones of both children and adults.

Types of bone fractures

  •  Simple fracture: A broken bone where the overlying skin is unaffected.
  • Compound fracture: A broken bone with damage to the surrounding muscle and overlying skin.
  • Comminuted fracture: A bone that has broken into many pieces.
  • Displaced bone fracture: A fracture where the broken ends of the bone no longer line up.
  • Stress fracture: Small fractures that happen as a result of repeated force to a bone. Stress fractures are common in athletes.  For example, runners may get stress fractures in their lower legs and feet from the repeated force of the foot hitting the ground.
  • Greenstick fracture: A type of fracture that occurs in the softer bones of children and babies. The break doesn’t go through the bone completely.
  • Pathologic fracture: A type of fracture that occurs in a previously diseased bone.

How do pathologists make this diagnosis?

Most fractures are diagnosed based on examining X-ray imaging alone. However, a pathologist can be involved in making this diagnosis if surgery is performed to remove part of the broken bone. For example, a severe hip fracture is commonly treated with hip replacement surgery (hemiarthroplasty). The fractured bone is removed by the surgeon and examined by a pathologist under a microscope, who looks carefully at the architecture of the bone and the healing process of the fracture. When pathologists examine bone under the microscope, they are looking for conditions that may have weakened the bone and led to the fracture. Most importantly, they are looking for diseases like cancer in the bone, which require urgent treatment.

What does a bone fracture look like under the microscope?

The appearance of a fracture under the microscope depends on the time that has passed since the fracture occurred, the cause of the fracture, and the age of the patient. Pathologists usually examine representative sections, which means that some, but not all, of the tissue sample, will be examined under the microscope.

Early microscopic features include blood and acute inflammatory cells around the fracture. The broken pieces of bone typically die by a process called necrosis. Some pathologists describe dead, or necrotic, bone as non-viable. In contrast, living bone is called viable. The dead bone and blood may form a mass called a soft tissue callus, or procallus. The callus acts as a glue that holds the bone together while it heals. These early changes are seen immediately after the fracture occurs and disappear after approximately seven days.

Bones

Fracture

Late microscopic features include the development of a bony callus that is made of new bone and cartilage. The new bone in the bony callus is less organized and not as strong as normal, healthy bone. The repair process is complete when the bony callus is replaced by well-organized new bone.

When examining the bone sample under the microscope, your pathologist will also look for conditions that may have led to the fracture. Specifically, your pathologist will carefully examine the bone to look for any evidence of infection, cancer, osteopenia (weak bones), or osteoporosis. Finally, your pathologist will look for trilineage hematopoiesis, which is the normal process for creating new blood cells inside the bone.

by Zuzanna Gorski MD and Bibianna Purgina MD FRCPC (reviewed July 28, 2021)
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