TENSION BAND WIRING

Implants for patellar fractures have to resist high-tensile stress. Tension band wiring transforms distraction forces of the extensor mechanism to compression forces. The wires provide anchorage for 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, K-wires or cerclage wires is necessary.

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

Pre-operative 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 like abrasions arecommonandmay require debridement or delayed operation, in order to reduce the risk of infection.

• Assess neurovascular status of the leg.

Radiological assessment

• Analyse fracture geometryby standardanteroposterior (AP) and lateral X-rays, and a tangential patellar view (Fig. 11.1).

• Differentiate between fractures and growth abnormalities (e.g. a 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 an abnormal patellar position caused by isolatedquadriceps or patellartendonruptures.TheInsall index calculates the ratio of greatest patellar lengthand the distance between the distal patellar pole and the tibial tuberosity. Normal ratio = 1; a ratio < 1 suggests a patellar tendon rupture. If in doubt, compare with the lateral view of the contralateral side. Ultrasound reveals the tendon rupture site and haematoma.