In cementless THA the incidence of intraoperative fracture has been reported to be as high 28% [1]. To mitigate these surgical complications, investigators have explored vibro-acoustic techniques for identifying fracture [2–5]. These methods, however, must be simple, efficient, and robust as well as integrate with workflow and sterility. Early work suggests an energy-based method using inexpensive sensors can detect fracture and appears robust to variability in striking conditions [4–5]. The orthopaedic community is also considering powered impaction as another way to minimize the risk of fracture [6– 8], yet the authors are unaware of attempts to provide sensor feedback perhaps due to challenges from the noise and vibrations generated during powered impaction. Therefore, this study tests the hypothesis that vibration frequency analysis from an accelerometer mounted on a powered impactor coupled to a seated femoral broach can be used to distinguish between intact and fractured bone states. Two femoral Sawbones (Sawbones AB Europe, SKU 1121) were prepared using standard surgical technique up to a size 4 broach (Summit, Depuy Synthes). One sawbone remained intact, while a calcar fracture approximately 40mm in length was introduced into the other sawbone. Broaching was performed with a commercially available pneumatic broaching system (Woodpecker) for approximately 4 secs per test (40 impactions/sec) with hand-held support. Tests were repeated 3 times for fractured and intact groups as well as a ‘control’ condition with the broach handle in mid-air (ie not inserted into the sawbone). Two accelerometers (PCB M353B18) positioned on the femoral condyle and the Woodpecker impactor captured vibration data from bone-broach-impactor system (Fig1). Frequency analysis from impaction strikes were postprocessed (Labview). A spectrogram and area under FFT (AUFFT) [4] were analysed for comparisons between fractured and intact bone groups using a nested ANOVA.Introduction
Methods
In Total Hip Arthroplasty (THA), proper bone preparation technique is fundamental to preventing intraoperative fracture. Anecdotally, surgeons suggest they can avoid fracture by listening for changes in the pitch of a mallet strike during broaching. Consequently, it is not surprising that researchers have explored vibroacoustic methods to prevent [1] and identify bone fractures [2, 3]. For instance, a shift in frequency of the acoustic signals during impaction has been correlated with initial stability [4, 5]. In-spite of these research-based successes, we are unaware of an intraoperative application for THA. We submit that idiosyncratic variability during impaction [6] may overwhelm analytical techniques developed in a controlled laboratory environment. The purpose of this test, therefore, was to evaluate the effect of several strike parameters on the vibro-acoustic response during impaction. Specifically, we hypothesized that the A Sawbones femur (SKU1121, Medium) was prepared and broached using standard surgical technique for the Summit hip system (DePuy Synthes) progressing from size 0 to 4. The size 4 broach was firmly seated and impacted ten times (n=10) for each of the prescribed conditions (Table 1) while securely holding the femur by hand. Vibroacoustic data from an accelerometer attached distally on the femur and a directional microphone located within 1 metre (Figure 1) were acquired at a sampling rate of 40kHz and postprocessed using LabView. Spectrograms were generated for qualitative comparisons, while fast fourier transform (FFT) with normalised amplitudes for each strike facilitated quantitative analysis of the area under the FFT curve (AU-FFT). Strike conditions were monitored to ensure the groups were consistent and distinct (Table 1).Introduction
Methods
Dislocation is one of the most frequent complications in total hip arthroplasty (THA), affecting an estimated 1% to 5% of THA patients. Malposition of the acetabular cup is thought to be a likely contributor. As the field searches for solutions, new experimental methods can help engineers, scientists, and surgeons better understand the problem as well as evaluate novel techniques and products. Create a laboratory simulation to assess patient positioning and pelvic motion during THA. Apply this simulation to assess (1) variation in patient positioning; (2) various methods to identify the pelvic plane via palpated anatomic landmarks.INTRODUCTION
OBJECTIVES
For many patients, total knee replacement (TKR) provides pain relief and restores motion for many years [1]. Some patients, however, experience early failures and require revision surgery. One of the suggested contributors to early failure has been excessive wear due to malalignment [2]. Previous work has shown that varus-valgus malalignment results in extreme condylar loading and could lead to high wear [3]. The purpose of this experiment, therefore, was to evaluate medial/lateral load sharing in an in vitro wear simulation. Wear testing was conducted on midsized Attune and Sigma fixed bearing cruciate substituting TKR components (DePuy Synthes). The two systems differ in many aspects; notably, Attune employs antioxidant-stabilized moderately-crosslinked polyethylene and a gradually changing sagittal femoral curvature while Sigma uses remelted moderately-crosslinked polyethylene and a mulit-radius femoral design. Wear was evaluated across a wide range of medial/lateral (M/L) load splits: 10/90, 60/40, and 90/10 using an AMTI six-station knee simulator (Figure 1). Simulation was conducted for 3 million cycles using at 1 Hz using previously described methods [4] with ‘High Kinematic’ displacement controlled inputs in 25% bovine calf serum (Hyclone) at 37 ± 2°C supplemented with sodium azide and EDTA. Polyethylene wear was determined gravimetrically with load soak compensation every 0.5 Mcyc.Introduction
Methods
Knee simulators are being used to evaluate wear. The current international standards have been developed from clinical investigations of the normal knee [1, 2] or from a single TKA patient [3, 4]. However, the forces and motions in a TKA patient differ from a normal knee and, furthermore, the resulting kinematic outcomes after TKA will depend on the design of the device [5]. Consequently, these standard tests may not recreate in-vivo conditions; therefore, the goal of this study was to perform a novel wear simulation using design-specific inputs that have been derived from fluoroscopic images of a deep knee bend. A wear simulation was developed using fluoroscopic data from a pool of eighteen TKA patients performing a deep knee bend. All patients had a Sigma CR Fixed Bearing implant (DePuy) and were well functioning (Knee Society Score > 90). A single patient was selected that represented the typical motions, which was characterized by early rollback followed by anterior motion with an overall modest internal tibial rotation (Figure 1). The relative motion between the femoral and tibial components was transformed to match the coordinate system of an AMTI knee wear simulator [6] and a compressive load input was derived using inverse dynamics [7]. The resulting force and motions (Figure 2) were then applied in a wear simulation with 5 MRad crosslinked and remelted polyethylene for 3 Mcyc at 1 Hz. Components were carefully positioned and each joint (n=3) was tested in 25% bovine calf serum (Hyclone Laboratories), which was recirculated at 37±2°C [3]. Serum was supplemented with sodium azide and EDTA. Wear was quantified gravimetrically every 0.5 Mcyc using a digital balance (XP250, Mettler-Toledo) with load soak compensation.INTRODUCTION
METHODS
