Fabrication and validation of reference structures for the localization of subdural standard- and micro-electrodes in MRI.

OBJECTIVE: Report simple reference structure fabrication and validate the precise localization of subdural micro- and standard electrodes in magnetic resonance imaging (MRI) in phantom experiments. APPROACH: Electrode contacts with diameters of 0.3 mm and 4 mm are localized in 1.5 T MRI using reference structures made of silicone and iron oxide nanoparticle doping. The precision of the localization procedure was assessed for several standard MRI sequences and implant orientations in phantom experiments and compared to common clinical localization procedures. MAIN RESULTS: A localization precision of 0.41 ± 0.20 mm could be achieved for both electrode diameters compared to 1.46 ± 0.69 mm that was achieved for 4 mm standard electrode contacts localized using a common clinical standard method. The new reference structures are intrinsically bio-compatible, and they can be detected with currently available feature detection software so that a clinical implementation of this technology should be feasible. SIGNIFICANCE: Neuropathologies are increasingly diagnosed and treated with subdural electrodes, where the exact localization of the electrode contacts with respect to the patient's cortical anatomy is a prerequisite for the procedure. Post-implantation electrode localization using MRI may be advantageous compared to the common alternative of CT-MRI image co-registration, as it avoids systematic localization errors associated with the co-registration itself, as well as brain shift and implant movement. Additionally, MRI provides superior soft tissue contrast for the identification of brain lesions without exposing the patient to ionizing radiation. Recent studies show that smaller electrodes and high-density electrode grids are ideal for clinical and research purposes, but the localization of these devices in MRI has not been demonstrated.

It's the little things: On the complexity of planar electrode heating in MRI.

Neurological disorders are increasingly analysed and treated with implantable electrodes, and patients with such electrodes are studied with MRI despite the risk of radio-frequency (RF) induced heating during the MRI exam. Recent clinical research suggests that electrodes with smaller diameters of the electrical interface between implant and tissue are beneficial; however, the influence of this electrode contact diameter on RF-induced heating has not been investigated. In this work, electrode contact diameters between 0.3 and 4 mm of implantable electrodes appropriate for stimulation and electrocorticography were evaluated in a 1.5 T MRI system. In situ temperature measurements adapted from the ASTM standard test method were performed and complemented by simulations of the specific absorption rate (SAR) to assess local SAR values, temperature increase and the distribution of dissipated power. Measurements showed temperature changes between 0.8 K and 53 K for different electrode contact diameters, which is well above the legal limit of 1 K. Systematic errors in the temperature measurements are to be expected, as the temperature sensors may disturb the heating pattern near small electrodes. Compared to large electrodes, simulations suggest that small electrodes are subject to less dissipated power, but more localized power density. Thus, smaller electrodes might be classified as safe in current certification procedures but may be more likely to burn adjacent tissue. To assess these local heating phenomena, smaller temperature sensors or new non-invasive temperature sensing methods are needed.

Clinical and radiological outcome at mean follow-up of 11 years after hip arthroscopy.

INTRODUCTION: The use of hip arthroscopy (HA) has substantially increased over the last decade. However, while the benefits of HA after 1 year in patients with femoroacetabular impingement (FAI) are well documented, long-term data on the progression of osteoarthritis (OA) or patient-reported outcomes (PROMs) are lacking. OBJECTIVES: To evaluate long-term clinical and radiological outcomes after HA. MATERIALS AND METHODS: Preoperative clinical records, operative notes, and radiographs from all patients who underwent HA at our hospital between 1998 and 2006 were reviewed. Exclusion criteria were previous hip surgery or diagnostic HA. Primary endpoints were subsequent total hip arthroplasty (THA) or other hip surgery. Secondary endpoints were OA progression and PROMs. RESULTS: HA was performed in 92 consecutive patients from 1998 to 2006. Indications for HA were FAI, labral lesions, early OA, and focal osteochondral defects. Mean follow-up was 11.2 years (SD 2.5, range 7.9-16). Data from 43 patients were available for analysis; 38 patients were excluded, and 11 were lost to follow-up. 20 patients had subsequent hip surgery, of which 11 patients required THA. 33 patients (77%) stated that they would undergo HA again under the same circumstances. Longitudinal radiological analysis showed no significant OA progression in patients without THA. The Forgotten Joint Score-12 was the only PROM to significantly differ between patients who had no further surgery and patients who had undergone revision (p = 0.037). CONCLUSION: There was no significant OA progression on plain radiography at an average of 11 years post-HA. Sound indication criteria is essential, as 45% of patients required subsequent surgery.

Integrity Assessment of a Hybrid DBS Probe that Enables Neurotransmitter Detection Simultaneously to Electrical Stimulation and Recording.

Deep brain stimulation (DBS) is a successful medical therapy for many treatment resistant neuropsychiatric disorders such as movement disorders; e.g., Parkinson's disease, Tremor, and dystonia. Moreover, DBS is becoming more and more appealing for a rapidly growing number of patients with other neuropsychiatric diseases such as depression and obsessive compulsive disorder. In spite of the promising outcomes, the current clinical hardware used in DBS does not match the technological standards of other medical applications and as a result could possibly lead to side effects such as high energy consumption and others. By implementing more advanced DBS devices, in fact, many of these limitations could be overcome. For example, a higher channels count and smaller electrode sites could allow more focal and tailored stimulation. In addition, new materials, like carbon for example, could be incorporated into the probes to enable adaptive stimulation protocols by biosensing neurotransmitters in the brain. Updating the current clinical DBS technology adequately requires combining the most recent technological advances in the field of neural engineering. Here, a novel hybrid multimodal DBS probe with glassy carbon microelectrodes on a polyimide thin-film device assembled on a silicon rubber tubing is introduced. The glassy carbon interface enables neurotransmitter detection using fast scan cyclic voltammetry and electrophysiological recordings while simultaneously performing electrical stimulation. Additionally, the presented DBS technology shows no imaging artefacts in magnetic resonance imaging. Thus, we present a promising new tool that might lead to a better fundamental understanding of the underlying mechanism of DBS while simultaneously paving our way towards better treatments.

Should patients with brain implants undergo MRI?

Patients suffering from neuronal degenerative diseases are increasingly being equipped with neural implants to treat symptoms or restore functions and increase their quality of life. Magnetic resonance imaging (MRI) would be the modality of choice for the diagnosis and compulsory postoperative monitoring of such patients. However, interactions between the magnetic resonance (MR) environment and implants pose severe health risks to the patient. Nevertheless, neural implant recipients regularly undergo MRI examinations, and adverse events are rarely reported. However, this should not imply that the procedures are safe. More than 300 000 cochlear implant recipients are excluded from MRI, unless the indication outweighs the excruciating pain. For 75 000 deep brain stimulation (DBS) recipients quite the opposite holds true: MRI is considered an essential part of the implantation procedure and some medical centres deliberately exceed safety regulations, which they refer to as crucially impractical. Permanent MRI-related neurological dysfunctions in DBS recipients have occurred in the past when manufacturer recommendations were exceeded. Within the last few decades, extensive effort has been invested to identify, characterise and quantify the occurring interactions. Yet today we are still far from a satisfying solution concerning a safe and beneficial MR procedure for all implant recipients. To contribute, we intend to raise awareness of the growing concern, summon the community to stop absurdities and instead improve the situation for the increasing number of patients. Therefore, we review implant safety in the MRI literature from an engineering point of view, with a focus on cochlear and DBS implants as success stories of neural implants in clinical practice. We briefly explain fundamental phenomena which can lead to patient harm, and point out breakthroughs and errors made. Then, we end with conclusions and strategies to avoid future implants from being contraindicated in MR examinations. We believe that implant recipients should enter MRI, but before doing so, it should be made sure that the procedure is reasonable.

The influence of local bone quality on fracture pattern in proximal humerus fractures.

INTRODUCTION: Bone mineral density and fracture morphology are widely discussed and relevant factors when considering the different treatment options for proximal humerus fractures. It was the aim of this study to investigate the influence of local bone quality on fracture patterns of the Neer classification as well as on fracture impaction angle in these injuries. MATERIALS AND METHODS: All acute, isolated and non-pathological proximal humerus fractures admitted to our emergency department were included. The fractures were classified according to Neer and the humeral head impaction angle was measured. Local bone quality was assessed using the Deltoid Tuberosity Index (DTI). The distribution between DTI and fracture pattern was analysed. RESULTS: 191 proximal humerus fractures were included (61 men, mean age 59 years; 130 women, mean age 69.5). 77 fractures (40%) were classified as one-part, 72 (38%) were two-part, 24 (13%) were three- and four-part and 18 (9%) were fracture dislocations. 30 fractures (16%) were varus impacted, whereas 45 fractures (24%) were classified as valgus impacted. The mean DTI was 1.48. Valgus impaction significantly correlated with good bone quality (DTI ≥ 1.4; p = 0.047) whereas no such statistical significance was found for the Neer fracture types. DISCUSSION: We found that valgus impaction significantly depended on good bone quality. However, neither varus impaction nor any of the Neer fracture types correlated with bone quality. We conclude that the better bone quality of valgus impacted fractures may be a reason for their historically benign amenability to ORIF. On the other hand, good local bone quality does not prevent fracture comminution.

The extended medial elbow approach-a cadaveric study.

BACKGROUND: The two most commonly used approaches to expose medial elbow structures are the flexor carpi ulnaris split and the Hotchkiss over-the-top approach. The aim of this study was to define the extended medial approach to the elbow, featuring advantages of over-the-top (proximal exposure) and additional complete exposure of the coronoid and proximal medial ulna, while respecting the internervous plane between the flexor pronator mass and flexor carpi ulnaris muscle. METHODS: In this comparative anatomic study, 12 fresh frozen cadaveric elbows were dissected alternately to study the distal limitation and exposed area of the extended medial elbow approach compared with splitting the flexor carpi ulnaris. RESULTS: Proximal ulna exposure area was comparable between the extended medial elbow approach (average, 840 mm(2)) and the flexor carpi ulnaris split (average, 810 mm(2); P = .44). The extended medial approach was limited distally by the posterior recurrent ulnar artery (mean 68 mm from medial epicondyle), whereas the first motor branch for the flexor carpi ulnaris muscle limited the second approach in 75% of the specimens (mean 29 mm from medial epicondyle, P < .001). CONCLUSIONS: The extended medial elbow approach is a single approach allowing full exposure of the medial elbow and combining the advantages of the over-the-top approach with a safe distal extension to the medial ulna. In contrast to the flexor carpi ulnaris split, our approach respects the internervous plane.

Periprosthetic fractures around polished collarless cemented stems: the effect of stem design on fracture pattern.

BACKGROUND: Predictable patterns of periprosthetic fracture have been observed around polished double tapered stems. Finite element studies have suggested that triple-tapered stems cause less cement strain in torsion compared to double-tapered stems. Hence, we hypothesised that the in vitro behaviour of implanted double- and triple-tapered polished stems, like the CPT (Zimmer, Warsaw, USA) or C-Stem (DePuy, Leeds, U.K.) when subjected to pathological torsional loads may cause different patterns of periprosthetic fractures. METHODS: Ten double-tapered stems (CPT) and ten triple-tapered stems (C-Stem) were cemented into synthetic femur bones. A constant axial compression load of 100 N and a torsional pre-load of 0.1 N.m were applied using a biaxial testing machine. The distal femur was then loaded in external rotation at 45 degrees until failure. RESULTS: Seven of the 10 CPT stems fractured at the level of the stem body while fracturing the cement mantle at the same level. In three of ten of the CPT stems and all ten C-Stems, the synthetic bone fractured at the tip of the prosthesis while the cement mantle remained intact. This was significant for the resulting fracture pattern (P=0.001). There was no significant difference between the groups for either torque (P=0.13) or angle at failure (P=0.49). INTERPRETATION: This biomechanical study indicates that the CPT and C-Stem create a different fracture pattern under the same loading condition. The C-Stem (a triple tapered stem) may produce lower strain in torsion to the cement mantle of a cemented THA. However, fractures that do occur may be more difficult to treat than those produced around a stem like the CPT subjected to comparable loading.

The position and number of screws influence screw perforation of the humeral head in modern locking plates: a cadaver study.

OBJECTIVES: Screw perforation of the humeral head in locking plate osteosynthesis occurs in up to 30% of cases. The current study compared different fixation possibilities (eg, number and position of screws) to reduce screw perforation in the humeral head. METHODS: A humeral head fracture with a missing medial support was created in 30 fresh-frozen cadavers and fixed with a polyaxial locking plate (NCB PH; Zimmer, Warsaw, IN). The constructs were loaded with increasing force and the number of cycles until screw perforation was recorded. Four different fixation methods were tested: group 1 five screws with fixed angle, group 2 five screws in polyaxial position according to bone strength, group 3 three screws, and group 4 five screws with 1 as an inferomedial support screw. RESULTS: More screws in the humeral head significantly increased the number of cycles before screw perforation. An inferomedial support screw further increased the number of cycles. Polyaxial screw placement compared with fixed-angle placement had no effect on the screw perforation phenomenon. CONCLUSIONS: We recommend to position an inferomedial support screw, and at least 5 screws in the head fragment, when using a locking plate in proximal humerus fractures with disrupted medial hinge.

The treatment of periprosthetic fractures with locking plates: effect of drill and screw type on cement mantles: a biomechanical analysis.

INTRODUCTION: Periprosthetic fractures after cemented hip replacement are a challenging problem to manage. Biomechanical studies have suggested the benefit of using locking screws for plate fixation, but there are concerns whether screws damage the cement mantle and promote crack propagation leading to construct failure. METHOD: In this biomechanical study, different screw types were implanted into the cement mantle after pre-drilling holes of different sizes, in unicortical and bicortical configuration. The presence of cracks and the pull-out resistance of these screws were then evaluated. RESULTS: No unicortical screw induced cracks. Screws with a shortened tip, smaller flutes and double threads were significantly better for pull-out resistance. Bicortical screws were associated with a risk of local cement mantle damage, but also with a significantly greater holding power. By increasing the drill diameter, the onset of cracks decreased, but so does the pull-out resistance.

Early results in the treatment of proximal humeral fractures with a polyaxial locking plate.

OBJECTIVES: We report early results using a second generation locking plate, non-contact bridging plate (NCB PH((R)), Zimmer Inc. Warsaw, IN, USA), for the treatment of proximal humeral fractures. The NCB PH combines conventional plating technique with polyaxial screw placement and angular stability. DESIGN: Prospective case series. SETTING: A single level-1 trauma center. PATIENTS: A total of 50 patients with proximal humeral fractures were treated from May 2004 to December 2005. INTERVENTION: Surgery was performed in open technique in all cases. MAIN OUTCOME MEASURES: Implant-related complications, clinical parameters (duration of surgery, range of motion, Constant-Murley Score, subjective patient satisfaction, complications) and radiographic evaluation [union, implant loosening, implant-related complications and avascular necrosis (AVN) of the humeral head] at 6, 12 and 24 weeks. RESULTS: All fractures available to follow-up (48 of 50) went to union within the follow-up period of 6 months. One patient was lost to follow-up, one patient died of a cause unrelated to the trauma, four patients developed AVN with cutout, one patient had implant loosening, three patients experienced cutout and one patient had an axillary nerve lesion (onset unknown). The average age- and gender-related Constant Score (n = 35) was 76. CONCLUSIONS: The NCB PH combines conventional plating technique with polyaxial screw placement and angular stability. Although the complication rate was 19%, with a reoperation rate of 12%, the early results show that the NCB PH is a safe implant for the treatment of proximal humeral fractures.