Drilling K-wires, what about the osteocytes? An experimental study in rabbits

The function of osteocytes regarding osteonecrosis has been underestimated for a long time. Recently it has been suggested that apoptosis of osteocytes results in strong osteoclastic bone resorption. Death of osteocytes due to drilling may therefore increase the risk of K-wire loosening. The purposes of our in vivo study were to assess the minimal drill time needed to notice disappearance of osteocytes and to measure the distance of the empty osteocyte lacunae surrounding the drill tract in relation with the insertion time, directly and 4 weeks after drilling Kirschner (K-) wires into the femur and tibia of rabbits.

Trocar tipped K-wires (70 mm length and 0.6 mm thickness) were drilled into the femur and tibia of 14 New Zealand white rabbits [mean body weight 2.81 kg (2.66-3.09 kg)]. Six rabbits were terminated following surgery (t = 0) and eight rabbits were terminated 4 weeks (t = 4) after surgery. Following termination, hematoxylin and eosin stained sections were cut from femur and tibia until the drill hole was visible. The sections were evaluated under a light microscope for the presence or absence of osteocytes in osteocyte lacunae surrounding the drill holes.

All osteocyte lacunae were empty around the K-wires in 50 and 87% of the cases, directly and 4 weeks after the surgery, respectively. The osteocytes disappeared especially beyond a drilling time of 37 s (P = 0.011) and 27 s (P = 0.008) at t = 0 and t = 4, respectively. Furthermore, a significantly positive correlation was seen between the distances of the empty osteocyte lacunae surrounding the drill holes in relation with time at t = 0 (P = 0.008) and t = 4 (P = 0.000).

Although only drilling without cooling was studied, short drilling times may prevent the disappearance of osteocytes in case cooling is not used in clinical practice as is the case in percutaneous K-wire insertion.