Percutaneous fixation of scaphoid fractures has become popular in recent years, mainly due to its reduced complexity compared to open surgical approaches. Fluoroscopy is currently used as guidance for this percutaneous approach, however, as a projective imaging modality, it provides only a 2D view of the complex 3D anatomy of the wrist during surgery, and exposes both patient and physician to harmful X-ray radiation. To avoid these drawbacks, 3D ultrasound has been suggested to provide imaging for guidance as a widely available, real-time, radiation-free and low-cost modality. However, the blurred, disconnected, weak and noisy bone responses render interpretation of the US data difficult so far. In this work, we present the integration of 3D ultrasound with a statistical wrist model to allow development of an improved ultrasound-based guidance procedure. For enhancement of bone responses in ultrasound, a phase symmetry based approach is used to exploit the symmetry of the ultrasound signal around the expected bone location. We propose an improved estimation of the local phase symmetry by using the local spectrum variation of the ultrasound image. The statistical wrist model is developed through a group-wise registration based framework in order to capture the major modes of shape and pose variations across 30 subjects at different wrist positions. Finally, the statistical wrist model is registered to the enhanced ultrasound bone surfaces using a probabilistic registration approach. Feasibility experiments are performed using two volunteer wrists, and the results are promising and warrant further development and validation to enable ultrasound guided percutaneous scaphoid fracture reduction.
The impact of cement leakage during percutaneous vertebroplasty has not been well characterized. This study aimed to quantify and compare cement leakage and its clinical significance in osteoporotic and metastatic vertebrae treated with vertebroplasty. Cement leakage was quantified using semi-automated thresholding of digital CT scans for fouteen metastatic and nineteen osteoporotic vertebrae and compared to pain scores. Cement leakage was present in 90.9% of vertebrae. Cement leaked predominantly into the disc in the osteoporotic vertebrae but yielded more diffuse leakage patterns in the metastatic cases. Despite cement leakage, there was significant improvement in pain immediately following vertebroplasty for all patients. This study aimed to quantify cement leakage in osteoporotic and metastatic vertebrae post-vertebroplasty and to determine whether leakage has clinical significance at follow-up. Despite high incidences of cement leakage, both osteoporotic and metastatic patients experienced significant immediate pain relief post-vertebroplasty. Cement leakage is investigated as a possible rationale for the higher rates of pain relief seen in osteoporotic vs metastatic patients undergoing percutaneous vertebroplasty. Cement leakage was present in 90.9% of the vertebrae treated. The percent volume of cement leakage was 11.6±10.6 in the osteoporotic vertebrae and 19.4±19.1 in the metastatic vertebrae (p=0.144). Cement leaked predominantly into the disc in the osteoporotic vertebrae whereas leakage was more diffuse in the metastatic vertebrae. Pain scores were high prior to vertebroplasty and decreased significantly following the procedure in both groups irrespective of leakage (p<
0.05). Digital CT scans were retrieved for osteoporotic (n=19) and metastatic (n=14) patients treated with percutaneous vertebroplasty. Volume of cement injected directly into the vertebral body and location of cement leakage (pedicle, disc, periphery, canal) was quantified using semi-automated thresholding techniques. Pain scores were collected at four stages of treatment (pre, immediately post, one day post, one week post-vertebroplasty). Disruption of the endplate in the osteoporotic spine provides an easily accessible pathway for the leakage of cement into the disc. Elevated pressurization during cement injection into metastatically involved vertebrae may account for the more diffuse cement leakage seen in the metastatic group. Clinically, pain scores improved irrespective of leakage.
Vertebroplasty (VP) is currently used to improve spinal stability in patients with vertebral metastases. This study assessed the effects of Laser Induced Thermo Therapy (LITT), a minimally invasive technique used to ablate tumor tissue prior to vertebroplasty. Load-induced canal narrowing (LICN) was measured pre and post-vertebroplasty in twelve paired spinal motion segments with simulated lytic metastases. LICN improved post-vertebroplasty for all specimens treated with LITT. In all specimens, cement location was an important factor in post-vertebroplasty stability. Reduction of the tumor volume pre-vertebroplasty resulted in more reliable defect filling. To investigate the effect of tumor ablation using Laser Induced Thermo Therapy (LITT) prior to vertebroplasty (VP) on cement distribution and vertebral stability. Tumor volume reduction using LITT prior to cement injection improves defect filling and consistently reduces Load Induced Canal Narrowing (LICN). A simple, minimally invasive procedure providing accurate tissue destruction pre-vertebroplasty may result in more reliable cement fill, reduce cement extravasation and improve post-vertebroplasty stability. Following verebroplasty, LICN improved in all specimens treated with LITT and in those VP alone specimens with cement located posterior to the tumor tissue (33%). LITT treated vertebrae exhibited a trend toward reduced posterior wall motion post-vertebroplasty (LICN=29.7±27.1%) versus specimens treated with VP alone (LICN=248.7±253%). In the LITT+VP group, cement was fully contained within the vertebral body while cement extravasation into the canal was noted in 33% of the specimens treated without LITT. Twelve paired cadaveric thoracolumbar spinal motion segments with simulated lytic metastases were randomized for treatment with VP alone or LITT+VP. In the LITT+VP group, a laser fibre inserted through a transpedicular approach was used to ablate the tumor tissue prior to cement injection. The specimens were axially loaded to 800N pre and post-treatment. LICN was used as a measure of vertebral stability. Cement location was assessed post-testing through axial sectioning. Location of cement is an important factor in determining post-VP stability. Vertebroplasty is effective in decreasing LICN if the tumor is ablated or surrounded posteriorly with cement.
In percutaneous vertebroplasty, clinically significant complications occur predominantly in patients with spinal metastases. This higher rate of complication may be associated with increased pressurization that has been reported due to the presence of lytic tissue during vertebroplasty. To date, there has been no research investigating techniques aimed at reducing this pressurization. This study investigated the potential of tumour volume reduction using laser induced thermo therapy ablation within the metastatic spine. This novel technique proved to be capable of efficient tissue shrinkage (average 60%) with little or no pressurization (average 1.3mmHg) and moderate levels of temperature elevation (average increase of 15.1°C). This study aims to investigate the potential of minimally invasive tumour volume reduction using laser induced thermo therapy ablation within the metastatic spine. Volume reduction of tumour tissue prior to cement injection may provide a method to reduce pressurization, reduce the likelihood of tumour extravasation and improve cement fill during percutaneous vertebroplasty. In percutaneous vertebroplasty, clinically significant complications occur predominantly in patients with spinal metastases (10%). Laser-induced thermo therapy condensed and coagulated the simulated tumour. Volume shrinkage of the tumour tissue averaged 60%. Pressures generated within the vertebral body only rose an average of 1.3mmHg during the procedure. Maximum temperatures on the posterior body wall increased by 15.1°C, with average temperatures 6.8°C above the baseline. A simulated lytic defect created using breast tissue was introduced into the vertebral body of a calf spine to model a metastatically involved vertebra. A pre-charred surgical fibre coupled to a diode laser delivering 1750J of energy was inserted through an eleven-guage needle into the centre of the tumour using an intrapedicular technique. During treatment, the temperature at the posterior body wall and intravertebral pressure were measured. Following ablation, the volume of the remaining tissue was measured. The results suggest that this novel technique is capable of reproducible, uniform, and effective tissue destruction with little to no pressurization and moderate levels of temperature elevation. Both pressures and temperatures generated during our study were lower than reported values during percutaneous vertebroplasty and suggest little risk of complications.
