Focused Ultrasound Thalamotomy with Dentato-Rubro-Thalamic Tractography in Patients with Spinal Cord Stimulators and Cardiac Pacemakers.

Magnetic resonance image-guided high-intensity focused ultrasound (MRgFUS)-based thermal ablation of the ventral intermediate nucleus of the thalamus (VIM) is a minimally invasive treatment modality for essential tremor (ET). Dentato-rubro-thalamic tractography (DRTT) is becoming increasingly popular for direct targeting of the presumed VIM ablation focus. It is currently unclear if patients with implanted pulse generators (IPGs) can safely undergo MRgFUS ablation and reliably acquire DRTT suitable for direct targeting. We present an 80-year-old male with a spinal cord stimulator (SCS) and an 88-year-old male with a cardiac pacemaker who both underwent MRgFUS for medically refractory ET. Clinical outcomes were measured using the Clinical Rating Scale for Tremor (CRST). DRTT was successfully created and imaging parameter adjustments did not result in any delay in procedural time in either case. In the first case, 7 therapeutic sonications were delivered. The patient improved immediately and durably with a 90% CRST-disability improvement at 6-week follow-up. In our second case, 6 therapeutic sonications were delivered with durable, 75% CRST-disability improvement at 6 weeks. These are the first cases of MRgFUS thalamotomy in patients with IPGs. DRTT targeting and MRgFUS-based thermal ablation can be safely performed in these patients using a 1.5-T MRI.

The relevance of skull density ratio in selecting candidates for transcranial MR-guided focused ultrasound.

OBJECTIVE: Transcranial MR-guided focused ultrasound (MRgFUS) is a minimally invasive treatment for movement disorders. Considerable interpatient variability in skull transmission efficiency exists with the current clinical devices, which is thought to be dependent on each patient's specific skull morphology. Lower skull density ratio (SDR) values are thought to impede acoustic energy transmission across the skull, attenuating or preventing the therapeutic benefits of MRgFUS. Patients with SDR values below 0.4 have traditionally been deemed poor candidates for MRgFUS. Although considerable anecdotal evidence has suggested that SDR is a reliable determinant of procedural and clinical success, relationships between SDR and clinical outcomes have yet to be formally investigated. Moreover, as transcranial MRgFUS is becoming an increasingly widespread procedure, knowledge of SDR distribution in the general population may enable improved preoperative counseling and preparedness. METHODS: A total of 98 patients who underwent MRgFUS thalamotomy at the authors' institutions between 2012 and 2018 were analyzed (cohort 1). The authors retrospectively assessed the relationships between SDR and various clinical outcomes, including tremor improvement and adverse effects, as well as procedural factors such as sonication parameters. An SDR was also prospectively obtained in 163 random emergency department patients who required a head CT scan for various clinical indications (cohort 2). Patients' age and sex were used to explore relationships with SDR. RESULTS: In the MRgFUS treatment group, 17 patients with a thalamotomy lesion had an SDR below 0.4. Patients with lower SDRs required more sonication energy; however, their low SDR did not influence their clinical outcomes. In the emergency department patient group, about one-third of the patients had a low SDR (< 0.4). SDR did not correlate with age or sex. CONCLUSIONS: Although lower SDR values correlated with higher energy requirements during MRgFUS thalamotomy, within the range of this study population, the SDR did not appreciably impact or provide the ability to predict the resulting clinical outcomes. Sampling of the general population suggests that age and sex have no relationship with SDR. Other variables, such as local variances in bone density, should also be carefully reviewed to build a comprehensive appraisal of a patient's suitability for MRgFUS treatment.

Enhanced adhesion of plasma-sprayed commercially pure titanium porous coatings to polished Mg-PSZ ceramic substrates.

The purpose of this study was to evaluate the suitability of a plasma sprayed titanium porous coating on polished magnesia-stabilized zirconia (Mg-PSZ) ceramic surfaces. We hypothesized that diffusion bonding was responsible for the adhesion of the coating to the ceramic substrate. Mg-PSZ tensile test coupons were vibratory polished (roughness Sa = 0.50 µm) or vibratory polished/lapped (Sa = 0.12 µm) before coating and testing. The exposed surfaces after tensile testing were examined by energy dispersive X-ray (EDX) analysis. Mg-PSZ shear test coupons were vibratory polished (Sa = 0.48 µm). As the surface roughness of the ceramic substrate decreased by a factor of 4.175, the coating tensile strength increased from 62.6 to 66.8 MPa, comparable to that of porous coated cobalt chromium (CoCr) and titanium (Ti-6Al-4V) coupons. EDX analyses found titanium everywhere on the ceramic surface after the titanium layer was pulled off with tensile testing, even on areas that appeared to be "clean" to the naked eye. This suggested that titanium oxide compounds were present at the interface, where the oxygen required could only result from diffusion bonding across the interface. Diffusion bonding may also explain the significantly higher amounts of zirconium on the coating surface that had been pulled off the smoother lapped ceramic coupons. The measured shear strength of porous-coated ceramic coupons was significantly higher than that of CoCr and Ti-6Al-4V coupons. The superior adherence of the titanium coating to Mg-PSZ suggests this process has great clinical potential in arthroplasty, especially for patients with metal sensitivity. © 2019 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 107A: 1925-1932, 2019.

Focused Ultrasound Thalamotomy for Essential Tremor in the Setting of a Ventricular Shunt: Technical Report.

BACKGROUND: A recent randomized controlled trial of magnetic resonance imaging (MRI)-guided focused ultrasound (FUS) for essential tremor (ET) demonstrated safety and efficacy. Patients with ventricular shunts may be good candidates for FUS to minimize hardware-associated infections. OBJECTIVE: To demonstrate feasibility of FUS in this subset of patients. METHODS: A 74-yr-old male with medically refractory ET, and a right-sided ventricular shunt for normal pressure hydrocephalus, underwent FUS to the right ventro-intermedius (VIM) nucleus. The VIM nucleus was directly targeted using deterministic tractography. Clinical outcomes were measured using the Clinical Rating Scale for Tremor. RESULTS: Shunt components required 6% of the total ultrasound transducer elements to be shut off. Eight therapeutic sonications were delivered (maximum temperature, 64°), leading to a 90% improvement in hand tremor and a 100% improvement in functional disability at the 3-mo follow-up. No complications were noted. CONCLUSION: This is the first case of FUS thalamotomy in a patient with a shunt. Direct VIM targeting and achievement of therapeutic temperatures with acoustic energy is feasible in this subset of patients.

Transcranial magnetic resonance imaging-guided focused ultrasound thalamotomy for tremor: technical note.

Although the use of focused ultrasound (FUS) in neurosurgery dates to the 1950s, its clinical utility was limited by the need for a craniotomy to create an acoustic window. Recent technological advances have enabled efficient transcranial delivery of US. Moreover, US is now coupled with MRI to ensure precise energy delivery and monitoring. Thus, MRI-guided transcranial FUS lesioning is now being investigated for myriad neurological and psychiatric disorders. Among the first transcranial FUS treatments is thalamotomy for the treatment of various tremors. The authors provide a technical overview of FUS thalamotomy for tremor as well as important lessons learned during their experience with this emerging technology.

Thin-Walled Cross-Linked Acetabular Liners Need Not Exhibit Reduced Locking Strength.

Use of larger diameter femoral heads has emerged as a promising strategy to reduce the risk of dislocation after total hip arthroplasty, but thinning the walls of cross-linked ultra-high-molecular-weight polyethylene (UHMWPE) acetabular liners to accommodate these larger heads may compromise the locking mechanism of the liner. The purpose of this study was to test the mechanical integrity of the locking mechanism in cross-linked and re-melted UHMWPE acetabular components with reduced wall thickness. The locking mechanism of cross-linked (100 kGy/re-melted) acetabular liners in sizes 50/28, 50/36, and 52/36 mm of 1 design was evaluated by lever-out tests and torsion tests. Torsion tests were performed at 2 angles to isolate the liner's locking tabs independent of the contribution of its central post. Lever-out testing demonstrated nominally reduced failure strength in 50/36-mm liners (13.3 N · m) compared with 50/28-mm liners (12.3 N · m; P=.0502), whereas the lever-out strength of 52/36-mm liners was 12.2±0.94 N · m. Failure torques were similar between 50/28- and 50/36-mm liners at 45° and 90°, but the failure torque of size 52/36-mm liners was significantly higher at each angle. The use of larger diameter femoral heads does not compromise the locking mechanism of thinned MicroSeal (Signal Medical Corp, Marysville, Michigan) acetabular liners. Use of a cross-linked UHMWPE acetabular liner, with a locking mechanism that is not compromised when the liner is thinned to a thickness of at least 2.86 mm, appears to be a biomechanically sound construct when articulated with large diameter femoral heads.

Reduced UHMWPE wear using magnesia-stabilized zirconia instead of CoCr femoral components in a knee simulator.

Magnesia-stabilized zirconia (Mg-PSZ) is stable and maintains a scratch-resistant surface in hip replacement, but is untested in knees. We assessed whether using Mg-PSZ instead of cobalt-chromium (CoCr) femoral components resulted in less tibial insert wear, and evaluated changes in topography and roughness of the femoral components. Inserts bearing against CoCr or Mg-PSZ were tested using standard (9 Mc) and aggressive (6 Mc) waveforms. Femoral component surface topography and roughness were evaluated before and after testing by optical profilometry. When bearing against Mg-PSZ, UHMWPE wear rate decreased by 73% (standard) and by 59% (aggressive conditions). After 15 Mc, CoCr components featured deep scratches, and roughness increased five-fold, while Mg-PSZ components were unchanged. Mg-PSZ femoral components may be indicated for high-demand patients and those with metal sensitivity.