3.2.3 Tension band principle

10.1055/b-0038-160826

3.2.3 Tension band principle

Markku Nousiainen

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1 Biomechanical principles

Early concepts of load transfer within bone were developed and described by Frederic Pauwels [1]. He observed that a curved, tubular structure under axial load always has a compression side as well as a tension side ( Fig/Animation 3.2.3-1 ). From these observations, the principle of tension band fixation evolved.

**Fig/Animation 3.2.3-1a–b** The tension band principle. a An eccentrically loaded bone has a tension and a compression side. b A tension band converts tension into compression at the opposite cortex.

A tension band converts tensile force into compression force at the opposite cortex. This is achieved by applying a device eccentrically, on the convex side of a curved bone.

The concept can most easily be understood by examining the femur under mechanical load ( Fig 3.2.3-2 ). If a fracture is to unite, it requires mechanical stability, which is obtained by compression of the fracture fragments. Conversely, distraction or tension interferes with fracture healing. Therefore, tension force on a bone must be neutralized or, ideally, converted into compression force to promote fracture healing. This is especially important in articular fractures, where stability is essential for early motion and good functional outcome. In fractures where muscle pull tends to distract the fragments, such as fractures of the patella or olecranon, the application of a tension band will neutralize these forces and even convert them into compression when the joint is flexed ( Fig 3.2.3-3a–b ). This is accomplished through the creation of a “hinge” at the side of the fracture occupied by the tension band construct. The subsequent application of distraction forces rotates the fracture around this hinge, producing a compression force opposite to it. Similarly, a bone fragment can be avulsed at the insertion of a tendon or ligament, as in the greater tuberosity of the humerus ( Fig 3.2.3-3c ), the greater trochanter of the femur, or the medial malleolus ( Fig 3.2.3-3d ). Here, too, a tension band can reattach the avulsed fragment, converting tensile forces generated by ligamentous pull into compression forces at the fracture surface.

**Fig 3.2.3-2a–e** When applied to the tension side of the bone, a plate acts as a dynamic tension band. a The mechanical axis of the bone is not necessarily within the center of the bone. b Under axial load the curved femur creates a tension force laterally and a compression force medially. c A plate positioned on the side of compressive forces cannot neutralize the tension force, and gapping will be observed opposite to the plate. A plate should not be applied in this position. d A tension band plate converts tensile force into compression on the opposite cortex. This cortex must provide a buttress. The plate remains under tension while the bone is compressed. e With a medial cortical defect, the plate will undergo bending stresses and eventually fail due to fatigue at a specific point (arrow). A tension band plate should not be used in this situation.

**Fig 3.2.3-3a–d** a Tension band principle applied to a fracture of the patella. The figure-of-eight wire loop lies anterior to the patella and fracture. Upon knee flexion, the tensile force (between the quadriceps muscle and the tibial tuberosity) is converted into compression at the articular surface. b In the olecranon fracture, the figure-of-eight wire loop acts as a tension band during flexion of the elbow. This is an example of a dynamic tension band. c Application of the tension band principle at the proximal humerus for an avulsion of the greater tubercle. The wire loop is anchored to the humerus by a 3.5 mm cortex screw. d Application of the tension band principle to the medial malleolus. The wire loop may be anchored to the tibia by a 3.5 mm cortex screw. This is an example of a static tension band.

2 Concepts of application

The tension band principle with wire loops is often applied to articular fractures of the patella and olecranon, converting tension from muscle pull into a compression force on the articular side of the fracture. In addition, small avulsion fractures may benefit from the principles of tension band fixation ( Fig 3.2.3-3c–d ).

The principle of tension band fixation with a plate can also be applied in diaphyseal fractures of curved bones, such as the femoral shaft. Application of a tension band construct to the tension side of the bone neutralizes distraction at this site, while promoting compression on the opposite side of the bone.

In curved long bones, the convex side of the diaphysis indicates the tension side.

Similarly, in delayed union or in nonunion, where the presence of angular deformity creates a tension side in the bone, adherence to the tension band mechanical principles is extremely important.

Whenever feasible, any internal or external fixation device should be applied to the tension side [2].

Bony union will then consistently occur. Loops of wire, cables, as well as absorbable or nonabsorbable suture material can function as a tension band. When appropriately placed, intramedullary nails, plates, and external fixators can also fulfill the function of a tension band ( Fig 3.2.3-4 ).

**Fig 3.2.3-4a–d** Clinical example of a plate acting as a tension band in a nonunion after intramedullary nailing of a femoral nonunion. **a–b** Symptomatic nonunion with broken nail—note the hypertrophic area around the fracture site. **c–d** After removal of the intramedullary nail, a tension band plate was applied on the lateral or convex side of the femur without bone grafting, and weight bearing was encouraged. The nonunion consolidated.

A tension band that produces compression at the time of application is called a static tension band, as the forces at the fracture site remain fairly constant during movement.

Tension band application to the medial malleolus is an example of a static tension band ( Fig 3.2.3-3d ).

If the compression force increases with motion, the tension band is a dynamic one.

A good example is the application of the tension band principle to a fracture of the patella. Upon knee flexion, the increased tensile force is converted to compression force ( Fig 3.2.3-3a , Fig 3.2.3-5 ).