Introduction

Implants for patellar fractures have to resist high tensile stress. Tension band wiring transforms distraction forces of the extensor mechanism into compression forces. The wires provide anchorage of the tension band wire and neutralize the rotational forces.

Indications

• Transverse and multifragmental patellar fractures. In case of multifragmental fractures, often a combination of tension band wiring and cortical screws, lag screws, Kirschner wires (K-wires) or cerclage wires is necessary.

• A pair of lag screws can exert high compression forces to transverse fractures.

Preoperative planning

Clinical assessment

• Pain, swelling, deformity, haemarthrosis, loss of function.

• Palpate gap between the fragments. Rule out an injury of the quadriceps and patellar tendon.

• Soft tissue injuries such as abrasions are common and may require debridement or delayed operation, in order to reduce the risk of infection.

• Assess the neurovascular status of the leg.

Radiological assessment

• Analyse fracture geometry by standard anteroposterior and lateral x-rays, and tangential patellar view (Fig. 12.1.1).

• Diferentiate between fractures and growth abnormalities (e.g. bipartite patella is typically found on the proximal lateral quadrant of the patella, usually with sclerotic edges of the fragment, in contrast to fractures).

• Rule out abnormal patella position by isolated quadriceps or patellar tendon ruptures. The Insall index calculates the ratio of greatest patella length to the distance between distal patellar pole and tibial tuberosity. Normal ratio = 1, ratio < 1 suggests patellar tendon rupture. If in doubt, compare with the lateral view of the contralateral side. Ultrasound reveals tendon rupture site and haematoma.