Abstract
Introduction
Proper initial fixation of the stem in the femoral canal is important to achieve successful long-term clinical results in total hip arthroplasty (THA) and bipolar hemiarthroplasty (BHA). However, this factor fully relies on surgeon's experience and skill during the hammering process. The goal of this study is to evaluate the frequency of the stem hammering sound which enables the achievement of proper stem fixation and avoiding femoral bone fracture.
Materials and methods
57 patients who received BHA as a result of femoral neck fracture were evaluated. Intraoperative images of stem hammering were recorded using a digital video camera (Everio GZ-MG275, Victor, Japan). The frequency of the hammering sound was analyzed using a digital audio editor, GoldWave (GoldWave Inc.) (Figure 1). The frequency change during hammering was categorized into two groups, convergent and non-convergent, according to the frequency change pattern (Figure 2). The definition of “convergent group” is as follows: in the last five hammering sounds to finish the stem insertion, 1) Three consecutive hammering frequency shape and distribution 2) Formant peak frequency within the range of 3,000 Hz.
Two types of cementless stems, SYNERGY SELECT II (tapered) and ECHELON TITANIUM (cylindrical, both from Smith & Nephew, Inc.) were used. Stem hammering was conducted using the same stem inserter. Canal Flare Index (CFI), Cortical Index (CI), Singh Index (SI), canal filling ratio, and the total number of stem-cortex contact zones were evaluated on x-ray images. The Mann-Whitney U-test was used for statistical analysis.
Results
The number of contact zones was significantly different between convergent and non-convergent groups in both SYNERGY and ECHELON stems. However, no significant difference was found in CFI, CI, SI, and canal filling ratio. With the SYNERGY stem 24 cases showed convergence in hammering frequency and non-convergence in 16 cases. The mean total contact zones were 6.08±1.18 (convergent group) and 4.44±1.71 (non-convergent group). In the ECHELON group 9 cases showed convergence in hammering frequency and non-convergence in 8 cases. The total contact zones were 6.78±1.09 (convergent group) and 4.88±1.55 (non-convergent group) (Table 1).
Discussion
Regardless of femoral geometry and stem design, hammering sound frequency was convergent when the stem-bone contact area increased. Change in the hammering sound frequency can provide reliable information during the stem insertion in terms of stem-bone contact to prevent bone fracture.
