The clinical relevance of sound changes produced during cementless hip arthroplasty: a correctly sized femoral broach creates a distinctive pattern of audio frequencies directly related to bone geometry.

AIMS: Cementless femoral stems must be correctly sized and well-seated to obtain satisfactory biological fixation. The change in sound that occurs during impaction of the femoral broach is said to indicate good fit, but this has not been widely studied. We set out to find whether the presence or absence of these sound changes could predict correct sizing. PATIENTS AND METHODS: We recorded the sound generated during femoral broaching for 105 cementless total hip arthroplasties using the Corail stem. Four cases were excluded, leaving 101 recordings for analysis. There were 36 male patients and 65 female patients, with a mean age of 69.9 years (sd 12.3) and median body mass index (BMI) of 29 kg/m 2 (interquartile range (IQR) 26 to 32). The recordings were analyzed to identify the frequencies of the sounds produced during impaction of the femoral broach. RESULTS: The emergence of a low-frequency band of sound in the 1 kHz range, during the final femoral broaching, was a strong predictor of a well-sized implant stem. The frequency was related to femoral length, supporting our hypothesis that the sound arose from the bone itself. CONCLUSION: The low-frequency sound generated during femoral broaching can be monitored spectrographically, its frequency can be predicted from femoral length, and it is a good predictor of appropriate stem sizing.