Trabecular pattern of proximal femur

Trabecular pattern of proximal femur refers to the five groups of trabeculae that are demonstrable within the femoral head and neck.

Basic concept

Trabecula is a supportive and connective tissue element which form in cancellous bone. Trabeculae develop in a normal bone and also in a healing bone. The trabecular pattern of growth follows the course of stress lines along the bone and maximum trabeculae develop along the lines of maximum stress.

To understand the progress of trabecular pattern, it is imperative that we understand the concept put forth by Julius Wolff, known as the Wolff’s Law ³.

Wolff's Law

Wolff's law suggests that there are dynamic internal forces as well as static and dynamic external forces acting on the bone. These static forces are imposed by gravity and the dynamic forces by weight bearing. Wolff's Law implies a reaction of a living bone to the mechanical forces on a bone segment ³.

If the loading on a particular bone increases, then the bone will remodel itself over time to become stronger and resist the loading in that particular bone segment and for that particular force of loading.

The proximal femur is an apt example to show the trabecular pattern based on Wolf’s law. Both tensile and compressive forces are present and correspond to the lines of forces.

Types of trabeculae

1. principal tensile trabeculae
2. principal compressive/medial compressive trabeculae
3. secondary compressive/lateral compressive trabeculae
4. secondary tensile trabeculae
5. greater trochanteric trabeculae

Principal tensile trabeculae

• it is in the form of an arc
• extends from the lateral margin of the greater trochanter to the inferior aspect below the fovea
• the arc traverses through the superior cortex of the neck and the femoral head

Principal compressive /medial compressive trabeculae

• it is vertically orientated and has a triangular configuration
• extends from the medial cortex of the head into the femoral neck

Secondary compressive/lateral compressive trabeculae

• it has a fan-like configuration
• extends from the calcar and lesser trochanter to the greater trochanter

A central area bounded by the three trabecular patterns is referred to as the Ward triangle ⁴.

Importance of trabecular pattern

As per the Garden classification of subcapital femoral fractures, the displacement is graded as per the position of the medial compressive trabecular ⁴.

• stage I: medial trabeculae form an angle greater than 180°
• stage II: medial trabeculae of head form an angle of approximately 160° with femoral neck
• stage III: medial trabeculae are out of alignment with those of pelvis
• stage IV: medial trabeculae are in alignment with those of pelvis

Etymology

It is derived from Latin word trabs meaning beam or bar.