Wireless Orthopedic Pin for Bone Healing and Growth: Antenna Development

A slotted waveguide antenna, as part of a wireless battery system for a bone fixation implant called the Echidna Pin is proposed. The antenna has 3-dB beamwidth of 65° in both E- and H-planes and its gain is 7.7 dBi at 21 GHz. The proposed antenna is conformal to the body of the pin and uses the pin as a waveguide. It is shown that placing a small Perspex plate after the waveguide launcher allows satisfactory return loss performance at all resonant frequencies as the length of the waveguide changes. The pin is used in distraction osteogenesis and allows the distance between the two surgically broken pieces of bone to be changed, thus expanding both soft tissue and bone volume simultaneously. The wireless battery system allows reception of RF power and eliminates the need for daily manipulations on an externally fitted device, or an operation on the body to change the length of the pin. It also makes the treatment significantly less painful for the patient and reduces the risk of infection.