Does pin configuration matter in modified tension band wiring for transverse patellar fracture? A biomechanical study

Modified tension band wiring has been widely used for the treatment of transverse patellar fractures. The optimal position of a Kirschner wire (K-wire) in modified tension band wiring, however, has not yet been determined. The purpose of the present study was to evaluate biomechanically the effect of K-wire position in a modified tension band wiring technique.Forty-two polyurethane foam patellae with a midway transverse fracture were assigned to six different fixation groups regarding different pin configurations in tension band wiring. The depth or sagittal position of the K-wire was divided into anterior and posterior. The coronal position of the K-wire was divided into central, medial and lateral. A specially designed set up simulated a knee with 60° flexion. All specimens were tested under axial traction. Loads at 2 mm and 4 mm fracture displacement and at the failure of the construct were recorded.At 2 mm fracture displacement, anterolateral (AL) placement of K-wires revealed significantly less durability when compared with five other groups (P < 0.001). At 4 mm fracture displacement, the AL group also revealed inferior biomechanical strength when compared with other groups. Posteromedial (PM) K-wire placement group revealed more durability when compared with the posterolateral (PL) group (P < 0.05). At failure of the osteosynthesis, anteromedial (AM) and anterocentral (AC) groups revealed superior biomechanical strengths (P < 0.05).The coronal and sagittal position of K-wire affects the biomechanical characteristics of modified tension band wiring. Anterolateral placement of K-wires revealed inferior strength to all other constructs in modified anterior tension band wiring.