Evidence for early loading of osseointegrated implants for bone conduction at 4 weeks.

INTRODUCTION: The purpose of our study was to directly measure the stability of the abutment using resonance frequency analysis (RFA) and to report on the change in stability over time for implants loaded 4 weeks postoperatively.
MATERIALS AND METHODS: The principle behind RFA is to obtain a numerical value relating to stability. The Osstell RFA recording device measures the resonance in a magnetic field of a 1 cm commercially manufactured attachment (SmartPeg) that is screwed onto the bone conduction device abutment. RFA measurements were obtained at surgery, 1, 4, and 16 weeks after implant surgery. The degree of movement (vibration) is inversely proportional to the stability of the abutment, and a numerical figure, the implant stability quotient (ISQ), is derived. Patients were fitted with the new Cochlear Bone-Anchored Hearing Aid (BAHA) BI300 series implant using a 1-stage procedure and loaded 4 weeks postoperatively.
RESULTS: Prospectively 68 consecutive patients were recruited with a male to female ratio of 23:45. Nineteen patients had bilateral BAHA devices fitted, giving a total of 88 implants. The average ISQ change (delta) for the cohort gives a value of 0 at time of surgery. The change in ISQ at 1 week was -0.10 (95% confidence interval [CI], 0.74), at 4 weeks was 1.21 (95% CI, 0.59), and at 16 weeks was 1.60 (95% CI, 0.77). DISCUSSION: Successful early loading of the BAHA sound processor has been achieved. RFA provides a reliable means of assessing stability for loading and measuring implant stability in the longer term. These data support the evidence for early loading at 4 weeks with good clinical safety.