Acoustic analysis to monitor implant seating and early detect fractures in cementless THA: An in vivo study

Automatic breach detection during spine pedicle drilling based on vibroacoustic sensing

Pedicle drilling is a complex and critical spinal surgery task. Detecting breach or penetration of the surgical tool to the cortical wall during pilot-hole drilling is essential to avoid damage to vital anatomical structures adjacent to the pedicle, such as the spinal cord, blood vessels, and nerves. Currently, the guidance of pedicle drilling is done using image-guided methods that are radiation intensive and limited to the preoperative information. This work proposes a new radiation-free breach detection algorithm leveraging a non-visual sensor setup in combination with deep learning approach. Multiple vibroacoustic sensors, such as a contact microphone, a free-field microphone, a tri-axial accelerometer, a uni-axial accelerometer, and an optical tracking system were integrated into the setup. Data were collected on four cadaveric human spines, ranging from L5 to T10. An experienced spine surgeon drilled the pedicles relying on optical navigation. A new automatic labeling method based on the tracking data was introduced. Labeled data was subsequently fed to the network in mel-spectrograms, classifying the data into breach and non-breach. Different sensor types, sensor positioning, and their combinations were evaluated. The best results in breach recall for individual sensors could be achieved using contact microphones attached to the dorsal skin (85.8%) and uni-axial accelerometers clamped to the spinous process of the drilled vertebra (81.0%). The best-performing data fusion model combined the latter two sensors with a breach recall of 98%. The proposed method shows the great potential of non-visual sensor fusion for avoiding screw misplacement and accidental bone breaches during pedicle drilling and could be extended to further surgical applications.

Acoustical determination of primary stability of femoral short stem during uncemented hip implantation

BACKGROUND

Preparing the medullary space of the femur aims to create an ideal form-fitting of cementless implants to provide sufficient initial stability, which is crucial for osseous integration, ensuring good long-term results. Hammering the implant into the proximal femur creates a press-fit anchoring of the endoprosthesis in the medullary space. Implanting the optimal size of the shaft for best fitting should avoid damage to the bone. Modified acoustic signals in connection with implantation are being detected by surgeons and might be related to the primary stability of the implant.

METHODS

This study aims to explore the relationship between frequency sound patterns and the change in stem stability. For this purpose, n = 32 Metha® short stems were implanted in a clinical setting by the same surgeon. During implantation, the sounds were recorded. To define a change in the acoustic system response during the operation, the individual blows of the implantation sequence were correlated with one another.

FINDINGS

An algorithm was able to subdivide through sound analysis two groups of hammer blows (area 1 and area 2) since the characteristics of these groups showed significant differences within the frequency range of 100 Hz to 24 kHz. The edge between both groups, detected by the algorithm, was validated with expert surgeons' classifications of the same data.

INTERPRETATION

In conclusion, monitoring, the hammer blows sound might allow quantification of the primary stability of the implant. Sound analysis including patient parameters and a classification algorithm could provide a precise characterization of implant stability.

Detection of periprosthetic fractures around the femoral stem by resonance frequency analysis: An in vitro study

Periprosthetic femoral bone fractures are frequent complications of Total Hip Arthroplasty (THA) and may occur during the insertion of uncemented Femoral Stems (FS), due to the nature of the press-fit fixation. Such fracture may lead to the surgical failure of the THA and require a revision surgery, which may have dramatic consequences. Therefore, an early detection of intra-operative fractures is important to avoid worsening the fracture and/or to enable a peroperative treatment. The aim of this in vitro study is to determine the sensitivity of a method based on resonance frequency analysis of the bone-stem-ancillary system for periprosthetic fractures detection. A periprosthetic fracture was artificially created close to the lesser-trochanter of 10 femoral bone mimicking phantoms. The bone-stem-ancillary resonance frequencies in the range (2-12) kHz were measured on an ancillary instrumented with piezoelectric sensors, which was fixed to the femoral stem. The measurements were repeated for different fracture lengths from 4 to 55 mm. The results show a decrease of the resonance frequencies due to the fracture occurrence and propagation. The frequency shift reached up to 170 Hz. The minimum fracture length that can be detected varies from 3.1±1.7 mm to 5.9±1.9 mm according to the mode and to the specimen. A significantly higher sensitivity (p = 0.011) was obtained for a resonance frequency around 10.6 kHz, corresponding to a mode vibrating in a plane perpendicular to the fracture. This study opens new paths toward the development of non-invasive vibration-based methods for intra-operative periprosthetic fractures detection.

Modeling the debonding process of osseointegrated implants due to coupled adhesion and friction

Cementless implants have become widely used for total hip replacement surgery. The long-term stability of these implants is achieved by bone growing around and into the rough surface of the implant, a process called osseointegration. However, debonding of the bone-implant interface can still occur due to aseptic implant loosening and insufficient osseointegration, which may have dramatic consequences. The aim of this work is to describe a new 3D finite element frictional contact formulation for the debonding of partially osseointegrated implants. The contact model is based on a modified Coulomb friction law by Immel et al. (2020), that takes into account the tangential debonding of the bone-implant interface. This model is extended in the direction normal to the bone-implant interface by considering a cohesive zone model, to account for adhesion phenomena in the normal direction and for adhesive friction of partially bonded interfaces. The model is applied to simulate the debonding of an acetabular cup implant. The influence of partial osseointegration and adhesive effects on the long-term stability of the implant is assessed. The influence of different patient- and implant-specific parameters such as the friction coefficient [Formula: see text], the trabecular Young's modulus [Formula: see text], and the interference fit [Formula: see text] is also analyzed, in order to determine the optimal stability for different configurations. Furthermore, this work provides guidelines for future experimental and computational studies that are necessary for further parameter calibration.

A parametric numerical analysis of femoral stem impaction

Press-fitted implants are implanted by impaction to ensure adequate seating, but without overloading the components, the surgeon, or the patient. To understand this interrelationship a uniaxial discretised model of the hammer/introducer/implant/bone/soft-tissues was developed. A parametric analysis of applied energy, component materials and geometry, and interactions between implant and bone and between bone and soft-tissues was performed, with implant seating and component stresses as outcome variables. To reduce the impaction effort (energy) required by the surgeon for implant seating and also reduce stresses in the hardware the following outcomes were observed: Reduce energy per hit with more hits / Increase hammer mass / Decrease introducer mass / Increase implant-bone resistance (eg stem roughness). Hardware stiffness and patient mechanics were found to be less important and soft tissue forces, due to inertial protection by the bone mass, were so low that their damage would be unlikely. This simple model provides a basic understanding of how stress waves travel through the impacted system, and an understanding of their relevance to implantation technique and component design.

Influence of Artificial Soft Tissue on Intra-Operative Vibration Analysis Method for Primary Fixation Monitoring in Cementless Total Hip Arthroplasty

In cementless Total Hip Arthroplasty (THA), achieving high primary implant fixation is crucial for the long-term survivorship of the femoral stem. While orthopedic surgeons traditionally assess fixation based on their subjective judgement, novel vibration-analysis fixation-monitoring techniques show promising potential in providing the surgeon with objective and quantifiable fixation measurements. This study presents a dynamic response measurement protocol for implant endpoint insertion and evaluates this protocol in the presence of artificial soft tissue. After the artificial femur was prepared in accordance with the THA protocol, the implant was inserted and progressively hammered into the cavity. The Pearson Correlation Coefficient (PCC) and Frequency Response Assurance Criterion (FRAC) corresponding to each insertion hammer hit were derived from the Frequency Response Functions (FRF) corresponding to each insertion step. The protocol was repeated with the artificial femur submerged in artificial soft tissue to imitate the influence of anatomical soft tissue. The FRAC appeared overall more sensitive than the PCC. In the presence of the artificial soft tissue the technique yielded higher PCC and FRAC values earlier in the insertion process. The measurements with artificial soft tissue produced FRFs with fewer peaks, lower resonance frequencies, and overall higher damping factors. The soft tissue appears to limit the fixation-change detection capabilities of the system and a promising potential remedy to this limitation is suggested.

Using Acoustic Vibrations as a Method for Implant Insertion Assessment in Total Hip Arthroplasty

The success of total hip arthroplasty depends on the experience of the surgeon, and one of the ways the surgeon currently determines the final implant insertion depth is to listen to the change in audible pitch of the hammering sound. We investigated the use of vibration emissions as a novel method for insertion quality assessment. A non-invasive contact microphone-based measurement system for insertion depth estimation, fixation and fracture detection was developed using a simplified in vitro bone/implant (n = 5). A total of 2583 audio recordings were analyzed in vitro to obtain energy spectral density functions. Out of the four main resonant peaks under in vitro conditions, broach insertion depth statistically correlates to increasing 3rd and 4th peak frequencies. Degree of fixation was also observed as higher goodness of fit (0.26–0.78 vs. 0.12–0.51 between two broach sizes, the latter undersized). Finally, however, the moment of fracture could not be predicted. A cadaveric in situ pilot study suggests comparable resonant frequencies in the same order of magnitudes with the bone model. Further understanding of the signal patterns are needed for an early warning system diagnostic system for imminent fractures, bone damage, improving accuracy and quality of future procedures.

Modal Analysis of the Ancillary During Femoral Stem Insertion: A Study on Bone Mimicking Phantoms

The femoral stem primary stability achieved by the impaction of an ancillary during its insertion is an important factor of success in cementless surgery. However, surgeons still rely on their proprioception, making the process highly subjective. The use of Experimental Modal Analysis (EMA) without sensor nor probe fixation on the implant or on the bone is a promising non destructive approach to determine the femoral stem stability. The aim of this study is to investigate whether EMA performed directly on the ancillary could be used to monitor the femoral stem insertion into the bone. To do so, a cementless femoral stem was inserted into 10 bone phantoms of human femurs and EMA was carried out on the ancillary using a dedicated impact hammer for each insertion step. Two bending modes could be identified in the frequency range [400-8000] Hz for which the resonance frequency was shown to be sensitive to the insertion step and to the bone-implant interface properties. A significant correlation was obtained between the two modal frequencies and the implant insertion depth (R² = 0.95 ± 0.04 and R² = 0.94 ± 0.06). This study opens new paths towards the development of noninvasive vibration based evaluation methods to monitor cementless implant insertion.

Acoustic characteristics of broaching procedure for post-operative stem subsidence in cementless total hip arthroplasty

PURPOSE

Avoiding stem subsidence is crucial for achieving better outcome for cementless total hip arthroplasty (THA). The aim of this study was to develop a prediction model for the incidence of post-operative stem subsidence using full quantitative acoustic parameters in hammering sound during the broaching procedure and to assess the accuracy of this prediction model.

METHODS

The acoustic parameters of the hammering sounds during a broaching procedure for 55 hips in 49 patients who underwent THAs with cementless taper-wedged stem were analysed. The stem subsidence was assessed at one month post-operatively, and the relationship between the acoustic parameters and the value of stem subsidence was investigated.

RESULTS

The average stem subsidence was 2.15 ± 2.91 mm. The subsidence 3 mm or more was observed in eleven hips (20%), and 5 mm or more was observed in seven hips (12.7%). Basic patient's characteristics, preoperative femoral morphology and immediate post-operative canal fill ratio and stem alignment were not significantly related to the volume of stem subsidence. Nine acoustic parameters were significantly correlated with the value of subsidence. The prediction model for post-operative subsidence using only acoustic parameters during broaching procedure was established, and this model showed a positive prediction value of 100% and a negative prediction value of 90.6% for post-operative stem subsidence at 5 mm or more.

CONCLUSION

Post-operative stem subsidence can be predicted by using acoustic parameters of the hammering sound during the broaching procedure. Our results suggest that we are at the start of a new era in which novel and innovative smart technologies can be used to assist in orthopaedic surgery.

Development of an Instrument to Assess the Stability of Cementless Femoral Implants Using Vibration Analysis During Total Hip Arthroplasty

Objective: The level of primary implant fixation in cementless total hip arthroplasty is a key factor for the longevity of the implant. Vibration-based methods show promise for providing quantitative information to help surgeons monitor implant fixation intraoperatively. A thorough understanding of what is driving these changes in vibrational behavior is important for further development and improvement of these methods. Additionally, an instrument must be designed to enable surgeons to leverage these methods. This study addresses both of these issues. Method: An augmented system approach was used to develop an instrument that improves the sensitivity of the vibrational method and enables the implementation of the necessary excitation and measurement equipment. The augmented system approach took into account the dynamics of the existing bone-implant system and its interaction with the added instrument. Results: Two instrument designs are proposed, accompanied by a convergence-based method to determine the insertion endpoint. The modal strain energy density distribution was shown to affect the vibrational sensitivity to contact changes in certain areas. Conclusion: The augmented system approach led to an instrument design that improved the sensitivity to changes in the proximal region of the combined bone-implant-instrument system. This fact was confirmed both in silico and in vitro. Clinical Impact: The presented method and instruments address practical intraoperative challenges and provide perspective to objectively support the surgeon’s decision-making process, which will ensure optimal patient treatment.