Steerable Mechanical Joint for High Load Transmission in Minimally Invasive Instruments

As minimally invasive operations are performed through small portals, the limited manipulation capability of straight surgical instruments is an issue. Access to the pathology site can be challenging, especially in confined anatomic areas with few available portals, such as the knee joint. The goal in this paper is to present and evaluate a new sideways-steerable instrument joint that fits within a small diameter and enables transmission of relative high forces (e.g., for cutting of tough tissue). Meniscectomy was selected as a target procedure for which quantitative design criteria were formulated. The steering mechanism consists of a crossed configuration of a compliant rolling-contact element that forms the instrument joint, which is rotated by flexural steering beams that are configured in a parallelogram mechanism. The actuation of cutting is performed by steel wire that runs through the center of rotation of the instrument joint. A prototype of the concept was fabricated and evaluated technically. The prototype demonstrated a range of motion between À22 and 25 with a steering stiffness of 17.6 Nmm/rad (min 16.9 -max 18.2 Nmm/rad). Mechanical tests confirmed that the prototype can transmit an axial load of 200 N on the tip with a maximum parasitic deflection of 4.4 . A new sideways steerable mechanical instrument joint was designed to improve sideways range of motion while enabling the cutting of strong tissues in a minimally invasive procedure. Proof of principle was achieved for the main criteria, which encourages the future development of a complete instrument

Does Perception of Usefulness of Arthroscopic Simulators Differ with Levels of Experience?

Some commercial simulators are available for training basic arthroscopic skills. However, it is unclear if these simulators allow training for their intended purposes and whether the perception of usefulness relates to level of experience. We addressed the following questions: (1) Do commercial simulators have construct (times to perform tasks) and face validity (realism), and (2) is the perception of usefulness (educational value and user-friendliness) related to level of experience? We evaluated two commercially available virtual reality simulators (Simulators A and B) and recruited 11 and nine novices (no arthroscopies), four and four intermediates (one to 59 arthroscopies), and seven and nine experts (> 60 arthroscopies) to test the devices. To assess construct validity, we recorded the median time per experience group for each of five repetitions of one identical navigation task. To assess face validity, we used a questionnaire to judge up to three simulator characteristic tasks; the questionnaire asked about the realism, perception of educational value, and perception of user-friendliness. We observed partial construct validity for Simulators A and B and considered face validity satisfactory for both simulators for simulating the outer appearance and human joint, but barely satisfactory for the instruments. Simulators A and B had equal educational value according to the participants. User-friendliness was judged better for Simulator B although both were graded satisfactory. The perception of usefulness did not differ with level of experience. Our observations suggest training on either simulator is reasonable preparation for real-life arthroscopy, although there is room for improvement for both simulators. These simulators provide training in surgical skills without compromising patient safet

A comparison of 3-D CT and 2-D plain radiograph measurements of the wrist in extra-articular malunited fractures of the distal radius

Two-dimensional (2-D) plain radiographs may be insufficient for the evaluation of distal radial malunion, as it is a three-dimensional (3-D) deformity. This study introduced a 3-D measuring method that outputs radial inclination, ulnar variance, palmar tilt and axial rotation. To this end, a standardized and clearly defined coordinate system was constructed that allowed 3-D measurements closely resembling the conventional 2-D method in 35 patients. Mean differences between 3-D and 2-D measurements in affected wrists were 1.8° for radial inclination, 0.8 mm for ulnar variance and 3.7° for palmar tilt. In addition, inter- and intra-observer reproducibility of all 3-D and 2-D measurements were good or excellent (intraclass correlation coefficient &gt;0.75), with 3-D reproducibility always better than 2-D. Axial rotation was present in all patients with a mean of 7.9° (SD 6.9). Although the differences between 2-D and 3-D measurements were small, 3-D evaluation enables the assessment of axial rotation and brings us closer to a routine 3-D evaluation of malunion.</p

Measuring hindfoot alignment radiographically: the long axial view is more reliable than the hindfoot alignment view

BACKGROUND: Hindfoot malalignment is a recognized cause of foot and ankle disability. For preoperative planning and clinical follow-up, reliable radiographic assessment of hindfoot alignment is important. The long axial radiographic view and the hindfoot alignment view are commonly used for this purpose. However, their comparative reliabilities are unknown. As hindfoot varus or valgus malalignment is most pronounced during mid-stance of gait, a unilateral weight-bearing stance, in comparison with a bilateral stance, could increase measurement reliability. The purpose of this study was to compare the intra- and interobserver reliability of hindfoot alignment measurements of both radiographic views in bilateral and unilateral stance. MATERIALS AND METHODS: A hindfoot alignment view and a long axial view were acquired from 18 healthy volunteers in bilateral and unilateral weight-bearing stances. Hindfoot alignment was defined as the angular deviation between the tibial anatomical axis and the calcaneus longitudinal axis from the radiographs. Repeat measurements of hindfoot alignment were performed by nine orthopaedic examiners. RESULTS: Measurements from the hindfoot alignment view gave intra- and interclass correlation coefficients (CCs) of 0.72 and 0.58, respectively, for bilateral stance and 0.91 and 0.49, respectively, for unilateral stance. The long axial view showed, respectively, intra- and interclass CCs of 0.93 and 0.79 for bilateral stance and 0.91 and 0.58 for unilateral stance. CONCLUSION: The long axial view is more reliable than the hindfoot alignment view or the angular measurement of hindfoot alignment. Although intra-observer reliability is good/excellent for both methods, only the long axial view leads to good interobserver reliability. A unilateral weight-bearing stance does not lead to greater reliability of measuremen

Probing forces of menisci: what levels are safe for arthroscopic surgery

Purpose To facilitate effective learning, feedback on performance during arthroscopic training is essential. Less attention has been paid to feedback on monitoring safe handling of delicate tissues such as meniscus. The goal is to measure in vitro probing forces of menisci and compare them with a theoretical maximum probing force (TMPF). Method Menisci samples of ten cadavers were mounted on force platforms to measure probing forces up to 20 N in three directions. Nineteen subjects participated: six novices (experience 60 arthroscopies), and three faculty (>250 a year). All had to perform three tasks on each meniscus sample with an arthroscopic probe: push three times on the superior meniscal surface, perform one continuous run on the superior meniscal surface, and push three times on the inferior meniscal surface. The absolute maximum probing force (AMPF) was determined for each condition. A multivariable linear regression analysis was performed to assess the influence of experience on the force magnitude (P < 0.05). AMPFs were compared to the TMPF (estimated to be 8.5 N). Results The AMPF of the push task was on average 2.8 N (standard deviation (SD) of 0.8 N), of the continuous run task 2.5 N (SD 0.9 N), and of the pull task 3.9 N (SD 2.0 N). Significant difference was present between experts and novices (P < 0.05). The AMPFs are in the same order of magnitude as the TMPF. Conclusion The results indicate the necessity of using a safety level for tissue manipulation when training arthroscopy and a value for is magnitude.Biomechanical EngineeringMechanical, Maritime and Materials Engineerin

Biomechanical evaluation of fixation of comminuted olecranon fractures: one-third tubular versus locking compression plating

New concepts in plate fixation have led to an evolution in plate design for olecranon fractures. The purpose of this study was to compare the stiffness and strength of locking compression plate (LCP) fixation to one-third tubular plate fixation in a cadaveric comminuted olecranon fracture model with a standardised osteotomy. Five matched pairs of cadaveric elbows were randomly assigned for fixation by either a contoured LCP combined with an intramedullary screw and unicortical locking screws or a one-third tubular plate combined with bicortical screws. Construct stiffness was measured by subjecting the specimens to cyclic loading while measuring gapping at the osteotomy site. Construct strength was measured by subjecting specimens to ramp load until failure. There was no significant difference in fixation stiffness and strength between the two fixation methods. All failures consisted of failure of the bone and not of the hardware. Contoured LCP and intramedullary screw fixation can be used as an alternative treatment method for comminuted olecranon fractures as its stiffness and strength were not significantly different from a conventional plating techniqu

Direction of the oblique medial malleolar osteotomy for exposure of the talus

A medial malleolar osteotomy is often indicated for operative exposure of posteromedial osteochondral defects and fractures of the talus. To obtain a congruent joint surface after refixation, the oblique osteotomy should be directed perpendicularly to the articular surface of the tibia at the intersection between the tibial plafond and medial malleolus. The purpose of this study was to determine this perpendicular direction in relation to the longitudinal tibial axis for use during surgery. Using anteroposterior mortise radiographs and coronal computed tomography (CT) scans of 46 ankles (45 patients) with an osteochondral lesion of the talus, two observers independently measured the intersection angle between the tibial plafond and medial malleolus. The bisector of this angle indicated the osteotomy perpendicular to the tibial articular surface. This osteotomy was measured relative to the longitudinal tibial axis on radiographs. Intraclass correlation coefficients (ICC) were calculated to assess reliability. The mean osteotomy was 57.2 ± 3.2° relative to the tibial plafond on radiographs and 56.5 ± 2.8 on CT scans. This osteotomy corresponded to 30.4 ± 3.7° relative to the longitudinal tibial axis. The intraobserver (ICC, 0.90-0.93) and interobserver (ICC, 0.65-0.91) reliability of these measurements were good to excellent. A medial malleolar osteotomy directed at a mean 30° relative to the tibial axis enters the joint perpendicularly to the tibial cartilage, and will likely result in a congruent joint surface after reductio

The preferred technique for knee synovium biopsy and synovial fluid arthrocentesis

For knee osteoarthritis and related conditions, analysis of biomarkers hold promise to improve early diagnosis and/or offer patient-specific treatment. To compare biomarker analyses, reliable, high-quality biopsies are needed. The aim of this work is to summarize the literature on the current best practices of biopsy of the synovium and synovial fluid arthrocentesis. Therefore, PubMed, Embase and Web of Science were systematically searched for articles that applied, demonstrated, or evaluated synovial biopsies or arthrocentesis. Expert recommendations and applications were summarized, and evidence for superiority of techniques was evaluated. Thirty-one studies were identified for inclusion. For arthrocentesis, the superolateral approach in a supine position, with a 0°-30° knee flexion was generally recommended. 18-gage needles, mechanical compression and ultrasound-guidance were found to give superior results. For blind and image-guided synovial biopsy techniques, superolateral and infrapatellar approaches were recommended. Single-handed tools were preconized, including Parker-Pearson needles and forceps. Sample quantity ranged approximately from 2 to 20. Suggestions were compiled for arthrocentesis regarding approach portal and patient position. Further evidence regarding needle size, ultrasound-guidance and mechanical compression were found. More comparative studies are needed before evidence-based protocols can be developed