title: Per-operative vibration analysis: a valuable tool for defining correct stem insertion: preliminary report.
abstract: BACKGROUND
  Defining the stem insertion end point during total hip replacement still relies on the surgeon's feeling. When a custom-made stem prosthesis with an optimal fit into the femoral canal is used, the risk of per-operative fractures is even greater than with standard prostheses. Vibration analysis is used in other clinical settings and has been tested as a means to detect optimal stem insertion in the laboratory. The first per-operative use of vibration analysis during non-cemented custom-made stem insertion in 30 patients is reported here.
  
  
  METHODS
  Thirty patients eligible for total hip replacement with uncemented stem prosthesis were included. The neck of the stem was connected with a shaker that emitted white noise as excitation signal and an impedance head that measured the frequency response. The response signal was sent to a computer that analyzed the frequency response function after each insertion phase. A technician present in the operating theatre but outside the laminated airflow provided feed-back to the surgeon.
  
  
  RESULTS
  The correlation index between the frequency response function measured during the last two insertion hammering sessions was >0.99 in 86.7% of the cases. In four cases the surgeon stopped the insertion procedure because of a perceived risk of fracture. Two special cases illustrating the potential benefit of per-operative vibration analysis are described.
  
  
  CONCLUSIONS
  The results of intra-operative vibration analysis indicate that this technique may be a useful tool assisting the orthopaedic surgeon in defining the insertion endpoint of the stem. The development of a more user-friendly device is therefore warranted.
authors.affiliation: Department of Reconstructive Orthopaedic Surgery, University Hospitals Leuven, Belgium. Michiel.mulier@uz.kuleuven.ac.be
authors.forename: Michiel
authors.initials: M
authors.lastname: Mulier
authors.forename: Cesar
authors.initials: C
authors.lastname: Pastrav
authors.forename: Georges
authors.initials: G
authors.lastname: Van der Perre
mesh_terms: D019644:Arthroplasty, Replacement, Hip / Q000379:methods*; D017076:Computer-Aided Design; D005260:Female; D005269:Femur / Q000601:surgery*; D006622:Hip Prosthesis; D006801:Humans; D007430:Intraoperative Care / Q000379:methods*; D008297:Male; D008875:Middle Aged; D017755:Prosthesis Fitting; D014732:Vibration