The effect of the extracorporeal shock wave lithotriptor on bone cement

Trackerless ultrasound-integrated bone cement detection using a modular minirobot in revision total hip replacement

Medical robots are superior to freehand manipulation if an accurate, precise, and time-efficient implementation of a preplanned intervention is required. In the first part of this contribution a new modular minirobot for automatic ultrasound-based bone cement detection followed by subsequent cement milling in revision total hip replacement is presented. A minirobot integrated ultrasound module eliminates the need for external position tracking (e.g. by an optical system) as well as patient registration since the scanned contours can be directly provided within the robot's coordinate system. Further, the modular minirobot concept allows kinematics, workspace, and mechanical parameters to be easily adapted to the requirements of related or even new surgical applications. In the experimental part, the impact of ultrasound module integration on the implementation of optimized scanning strategies is investigated and evaluated in a laboratory set-up. As wave mode conversion and refraction artefacts due to angular sound incidence influence the detection accuracy, the transducer alignment can be optimized with respect to the number of degrees of freedom (DOFs) provided by the minirobot. A model-based scanning approach using two degrees of freedom (2DOFs), three degrees of freedom (3DOFs), and four degrees of freedom (4DOFs) respectively is presented. For automated scanning path calculation, a 2DOF distal-proximal prescan has been performed to estimate the principal components of the cement cavity's geometry using either a model-based or a statistical approach. In a cadaver study, the model-based approach consistently outperformed the statistical approach. The 3DOFs and 4DOFs scanning strategies yielded a significantly higher scanning accuracy if compared with the 2DOFs approach whereas the 3DOFs approach represents a trade-off between system complexity and detection accuracy.

Retrograde cement removal in periprosthetic fractures following hip arthroplasty

INTRODUCTION

Revision of cemented hip arthroplasty after periprosthetic fractures of the femur is a demanding procedure. Many different technical devices have been developed for this purpose. This paper presents a new surgical technique of cement removal avoiding excessive exposure of the fracture site.

MATERIALS AND METHODS

In six patients with periprosthetic fractures of the femur following hip arthroplasty (Johansson Type II and III) cement removal was performed by means of advancing a retrograde nail through the intercondylar notch of the knee.

RESULTS

In all cases the cement was removed completely. Intraoperative complications or significant knee problems were not observed.

CONCLUSION

The intracondylar approach provides a simple, rapid and less invasive technique for cement removal in revision hip arthroplasty.

A-mode ultrasound-based intra-femoral bone cement detection and 3D reconstruction in RTHR

Due to the difficulty of determining the 3D boundary of the cement-bone interface in Revision Total Hip Replacement (RTHR), the removal of the distal intra-femoral bone cement can be a time-consuming and risky operation. Within the framework of computer- and robot-assisted cement removal, the principles and first results of an automatic detection and 3D surface reconstruction of the cement-bone boundary using A-mode ultrasound are described. Sound propagation time and attenuation of cement were determined considering different techniques for the preparation of bone cement, such as the use of a vacuum system (Optivac, Biomet). A laboratory setup using a rotating, standard 5-MHz transducer was developed. The prototype enables scanning of bisected cement-prepared femur samples in a 90 degrees rotation range along their rotation axis. For system evaluation ex vivo, the distal femur of a human cadaver was prepared with bone cement and drilled (Ø 10 mm) to simulate the prosthesis cavity in a first approximation. The sample was cut in half and CT scanned (0.24 mm resolution; 0.5 mm distance; 0.5 mm thickness), and 3D voxel models of the manually segmented bone cement were reconstructed, providing the ground truth. Afterwards, 90 degrees segments of each ex-vivo sample were scanned by the A-mode ultrasound system. To obtain better ultrasound penetration, we used coded signal excitation and pulse compression filtering. A-mode ultrasound signal detection, filtering and segmentation were accomplished fully automatically. Subsequently, 3D voxel models of each sample were calculated. Accuracy evaluation of the measured ultrasound data was performed by ICP matching of each ultrasound dataset ( approximately 8000 points) to the corresponding CT dataset and calculation of the residual median distance error between the corresponding datasets. Prior to each ICP matching, an initial pre-registration was calculated using prominent landmarks in the corresponding datasets. This method yielded a median distance error in the region of 0.25 mm for the cement-bone interface in both femur halves.

Shock wave therapy (Orthotripsy) in musculoskeletal disorders

Extracorporeal shock wave therapy, which now is used routinely for urolithiasis, has gained increasing acceptance in Europe for some musculoskeletal problems and has led to the inception of clinical studies in the United States. The authors have reviewed the available literature to assess the biologic effects of shock waves on human musculoskeletal tissues, the credibility of published studies on therapeutic applications, and the potential for more widespread application of this modality to various skeletal and near-skeletal disorders. The primary advantage of extracorporeal shock wave therapy is its noninvasive nature and seemingly minimal complications when applied to musculoskeletal tissues.

Use of extracorporeal shock waves in the treatment of pseudarthrosis, tendinopathy and other orthopedic diseases

PURPOSE

The use of shock waves in orthopedic diseases was reviewed with special regard to the clinical applications.

MATERIALS AND METHODS

Findings in the literature and results from our own studies were analyzed and summarized.

RESULTS

Extracorporeal shock waves induced osteoneogenesis in animal models with intact and fractured bones. Based on these findings shock waves were used for the treatment of pseudarthrosis in humans. Most patients had at least 1 unsuccessful operation before shock wave therapy. Complete reunion was noted in 62 to 91% of cases and shock waves are recommended by some as the first choice of treatment for hypertrophic pseudarthrosis. After failed nonoperative therapy shock waves were used for the treatment of patients with various diseases as secondary treatment. The success rate for treatment of tendinopathies, such as tennis elbow, periarthritis humeroscapularis or calcaneal spur, was approximately 80%. For calcific tendinitis shock wave therapy seems to be superior to all other minimal or noninvasive techniques without compromising a potential later operation.

CONCLUSIONS

Shock waves have changed medical therapy substantially. Accounting for the epidemiology of the treated diseases, this new change may equal or even surpass the impact of extracorporeal shock wave lithotripsy.