A bony prominence is an anatomical area where a bone lies very close to the surface of the skin, offering minimal natural padding from muscle and fat. The term usually refers to sites at risk for tissue damage when external pressure is applied for an extended period. Understanding these locations is important because they are where pressure injuries, commonly known as bedsores, most frequently develop, especially in individuals with limited mobility. The lack of soft tissue makes these areas highly susceptible to injury from sustained force.
Defining Bony Prominences
A bony prominence represents a point of high pressure concentration when the body contacts a firm surface. In these areas, the skeletal structure is covered by a relatively thin layer of muscle, fat, and skin. This differs significantly from parts of the body that have thick, protective padding, such as the buttocks or thighs, which naturally distribute weight over a wider area. The thin tissue layer means external force is directly transmitted to the underlying bone, compressing the soft tissue in between.
Key Anatomical Locations
The locations of high-risk bony prominences vary depending on the body position. When a person is lying on their back, the most common sites for injury are the sacrum (tailbone area) and the heels. Other areas at risk include the shoulder blades, elbows, and the occiput (back of the head).
For individuals lying on their side, the pressure shifts to different points. The greater trochanter, the prominence on the side of the hip, and the ankles, specifically the medial and lateral malleoli, become vulnerable. When a person is seated, pressure is concentrated primarily on the ischial tuberosities (sit bones) and the sacrum.
How Pressure Causes Tissue Damage
Tissue damage begins when sustained external pressure exceeds the normal pressure inside the body’s smallest blood vessels, the capillaries. External forces greater than this range compress the vessels, restricting blood flow. This mechanical blockage of blood supply to the soft tissue is called ischemia. Without a consistent supply of blood, the tissue is deprived of the oxygen and nutrients it needs to survive, leading to cell death and tissue breakdown.
The resulting injury, known as a pressure injury, often presents as a small surface wound. However, the damage frequently forms a cone shape with a much wider area of unseen tissue destruction beneath the skin. Because underlying muscle and fat tissue are more sensitive to ischemia than the skin, deep tissue damage can occur before obvious signs appear on the surface. Shearing forces, which occur when skin remains stationary while underlying tissue shifts, can also stretch and tear blood vessels, accelerating the injury process.
Strategies for Protection
Protecting bony prominences requires a proactive approach focused on reducing and redistributing pressure. The most direct strategy involves regular repositioning, or turning a person to relieve pressure on specific areas. For those confined to a bed, this should follow a structured schedule, with turning intervals adjusted based on individual skin tolerance.
Specialized equipment is an important preventive measure. Pressure-redistributing support surfaces, such as high-specification foam or alternating air mattresses and cushions, help spread body weight over a larger area. Specific practices include using a 30-degree lateral turn when lying on the side to prevent direct hip pressure, and heel elevation to entirely lift the heels off the bed surface.
Routine skin assessments are necessary to check for early signs of damage, such as persistent redness or discoloration, which indicates possible tissue injury and requires immediate action. Maintaining good skin health through cleansing, moisturizing, and managing moisture from incontinence also reduces the risk of breakdown.