Lateral Gap Research Articles

Extension and flexion gap balancing and its correlation with alignment in navigated total knee arthroplasty.

Computer-assisted surgery was developed to improve the results of conventional total knee arthroplasty (TKA). The authors investigated the preoperative varus/valgus deformity influence on the production of balanced extension and flexion gaps using computer-assisted surgery. This study evaluated data from a prospective case series. A total of 132 patients (107 women and 25 men) underwent navigated TKA. Patients were divided into the following 3 groups according to the degree of the initial varus/valgus deformity: group 1, 0° to 3°; group 2, 3° to 9°; and group 3, greater than 9°. The final lower limb mechanical axis (LLMA) and the final flexion and extension gaps were measured. Knees exhibiting up to 3° of deviation on the frontal plane and a difference of up to 3 mm between the lateral and medial gaps were considered to be aligned and balanced, respectively. Average LLMA deviation decreased from 5.58° (± 4.80°) to 1.87° (± 1.66°). For knees with varus deviation, the percentage of balancing relative to the flexion gaps was 97.8% and that relative to the extension gap was 100% (P>.05). For knees with valgus deviation, the percentage of balancing relative to the flexion gaps was 95.1% and that relative to the extension gap was 97.6% (P>.05). Approximately 92% of the LLMA alignment was achieved in the group with varus deformity, whereas 71.4% was observed in the group with valgus deformity (P<.05). Computer-assisted TKA could attain proper flexion and extension balance regardless of coronal plane malalignment magnitude. Severe valgus and varus knees are more difficult to align using navigation. No difference was found in the balance of flexion or extension gaps in valgus or varus knees, independent of the severity.

Combinatorial color arrays based on optical micro-resonators in monolithic architecture.

We demonstrate two types of combinatorial color arrays based on the Fabry-Perot (FP) micro-resonators in monolithic architecture. Optical micro-resonators corresponding to color elements are constructed using a soluble dielectric material between two transreflective layers by transfer-printing in either a pattern-by-pattern or a pattern-on-pattern fashion. The color palette depends primarily on the thickness and the refractive index of a dielectric material embedded in the micro-resonator. A self-defined lateral gap between two adjacent color elements provides the functionality of light-blocking by the underlying background layer. A prototype of a liquid crystal display incorporated with our combinatorial color array is also demonstrated. This monolithic integration of different FP micro-resonators leads to a versatile platform to build up a new class of color arrays for a variety of visual applications including displays and coloration devices.

Flexion Gap Measured in 45 Degrees and 90 Degrees of Hip Flexion Positions during Total Knee Arthroplasty: Measurement by Navigation System.

PurposeTo evaluate the influence of thigh weight in different hip flexion positions on the knee flexion gap in total knee arthroplasty (TKA).Materials and MethodsWe evaluated 20 patients (25 knees) with osteoarthritis of the knee that underwent TKA using a navigation system from May 2010 to April 2011. After posterior cruciate ligament sacrificing, complete soft tissue balancing, and fixation of all components with cement, the flexion gaps were measured with the patello-femoral joint reduced. Medial and lateral flexion gaps were measured separately in both the 90°-90° and 45°-90° flexion positions of the hip-knee joints.ResultsThe medial and lateral flexion gaps in the 45°-90° flexion position of the hip-knee joints were 13.02±2.17 mm and 13.12±2.21 mm, respectively. The medial and lateral flexion gaps in the 90°-90° flexion position were 12.92±2.03 mm and 13.08±2.29 mm, respectively. The flexion gaps showed no significant (p>0.05) differences between the two different hip flexion positions.ConclusionsFlexion gaps in TKA were not influenced by hip flexion positions (45° or 90° of flexion). Therefore, soft tissue balancing and polyethylene thickness should not be affected by hip flexion positions during TKA.

Influence of tibial slope on extension and flexion gaps in total knee arthroplasty: increasing the tibial slope affects both gaps.

Increasing the tibial slope is often performed if the flexion gap is narrower than the extension gap. The main hypothesis of this study is that increasing the tibial slope coincidentally enlarges the extension gap. Twenty formalin-fixed cadaveric knees were obtained for study. After CT in full extension and 90° flexion, the data of each specimen were entered into a standardized coordinate system and virtual bone cuts were performed with incrementally increasing the posterior slope. Gaps were measured at tibiofemoral contact points in 90°-flexion and full extension in the medial and lateral compartment. Increasing the tibial slope did significantly widen both the extension and the flexion gaps (p < 0.001). In extension, the opening rates, i.e. the gap increase per degree of slope increase, were equal medially and laterally (0.5mm ±0.1) medial vs 0.6mm (±0.0) lateral), whereas in flexion the lateral gap did open significantly more than the medial one (0.6mm ±0.1) medial vs 0.9mm (±0.1) lateral (p < 0.001), resulting in a significantly greater flexion gap laterally. Increasing the tibial slope beyond the pre-operative planning in order to widen a tight flexion gap intra-operatively is not recommended as doing so will increase the extension gap simultaneously and will make the medial and lateral flexion gaps unequal.

Measured Resection Versus Gap Balancing for Total Knee Arthroplasty

The number of TKAs performed in the United States is expected to increase substantially in the next two decades [6]. Additionally, surgeons are performing TKAs in younger and more active patients. While many articles discuss the importance of radiographic alignment, soft-tissue balancing is essential to a successful TKA. There remains great controversy in how surgeons obtain correct alignment and soft-tissue tensioning. Some surgeons utilize a measured resection technique, while other surgeons favor a gap-balancing technique. As such, I have invited two internationally known orthopaedic surgeons to discuss these two approaches, both of which seek to achieve the same general goal — a well-aligned and well-balanced TKA. Bryan D. Springer MD is an attending joint replacement surgeon at the OrthoCarolina Hip and Knee Center in Charlotte, NC, USA, and a member of The Knee Society. Dr. Springer is the recipient of numerous Knee Society Awards, and has extensive experience with the gap-balancing technique. Sebastien Parratte MD, PhD is an attending joint replacement surgeon and assistant professor of orthopedic surgery at the University Hospital of Marseille in Marseille, France. Dr. Parratte likewise has received numerous Knee Society and Hip Society Awards, and has considerable experience with the measured resection technique. Matthew P. Abdel MD:What do you each see as the advantages of the gap-balancing or measured resection techniques, in terms of achieving ligament balance? Bryan D. Springer MD: Instability following TKA remains one of the most common modes of early failure. The gap-balancing technique is based on the progressive release of ligaments to create equal and symmetric flexion and extension gaps. It is imperative that one understands what structures affect extension, flexion, and both in order to create proper balance. One of the fundamental differences between the gap-balancing technique and measured resection technique lies in setting the rotation of the femoral component to achieve a symmetric flexion gap. Measured resection relies on arbitrary bony landmarks (surgical transepicondylar axis, posterior condylar axis, and anteroposterior (AP) axis of the femur) in order to set rotation. While bony landmarks may occasionally provide accurate rotation of the femoral component, one major disadvantage is the surgeon’s inability to accurately and reproducibly find them intraoperatively. Research has suggested there is wide variability in femoral component rotation when using bony landmarks, which leads to asymmetry of the flexion space and condylar lift off (Fig. 1) in flexion [3]. Open in a separate window Fig. 1 This schematic depicts condylar lift off that occurs when there is asymmetry of the flexion space. Published courtesy of Bryan D. Springer MD.

Does patella position influence ligament balancing in total knee arthroplasty?

In vivo comparative gap measurements were performed in three different patella positions (reduced, subluxated and everted) using offset-type-force-controlled-spreader-system. Prospectively, 50 knees were operated by total knee arthroplasty using a navigation-assisted gap-balancing technique. The offset-type-force-controlled-spreader-system was used for gap measurements. This commercially available instrument allows controllable tension in patella-reduced position. The mediolateral gaps of knee extension (0°) and flexion (90°) angle were recorded in three different patella positions; reduced, subluxated and everted. Any gap differences of more than 3 mm were considered as a meaningful difference. Correlation between the difference with the demographic data, preoperative radiologic alignment and intraoperative data was analysed. For statistical analysis, ANOVA and Pearson's correlation test were used. The gaps in patella eversion demonstrated smaller gaps both in knee extension and flexion position compared to the gaps of patella reduction position. The amount of decreased gaps was more definite in knee flexion position. Statistically significant difference was observed for the lateral gap of patella eversion compared to gap of patella reduction in knee flexion position (p < 0.05). There were notable cases of variability in knee flexion position. Significant portion of 12 (24 %) knees of patella subluxation and 33 (66 %) knees of patella evertion demonstrated either increased or decreased gaps in knee flexion position compared to the gaps of patella reduction position. The gaps in patella eversion demonstrated smaller gaps both in knee extension and flexion position compared to the gaps of patella reduction position. The amount of decreased gaps was more definite in knee flexion position. Therefore, the intraoperative patellar positioning has influence on the measurement of the joint gap. Keeping the patella in reduced position is important during gap balancing. I.

Biomechanical Stability of Open-Wedge High Tibial Osteotomy: Comparison of Two Locking Plates

Introduction: Recently, new plates with locking screws have been developed and used for medial open-wedge high tibial osteotomy (HTO). The purpose of this study was to evaluate and compare biomechanical properties of different internal fixations in open-wedge HTO using the two currently available locking plates. Methods: Eight paired fresh-frozen cadaveric lower extremities were vertically embedded in steel boxes. The axial compression load was applied to the legs using the mechanical testing machine. The axial compression load test from 0 N to 550 N and the failure test were performed before and after HTO. One side of the leg of a specimen was fixed with the Puddu locking plate and the other side was fixed with the TomoFix plate to compare the two plates using the same specimen. A mode of failure and vertical displacement of the medial and lateral parts of the tibia at the osteotomy gap was recorded using a video camera in the failure test. The load–displacement data were analyzed to calculate stiffness, failure load, and displacement at failure. Results: The mean failure load was 1471.4 N and 1692.3 N and total vertical displacement at failure was 3.1 mm and 2.9 mm with the Puddu and TomoFix plates, respectively. During axial compression loading, displacements mainly occurred at the lateral osteotomy gap, while the medial gap was well preserved. No significant differences were observed in the failure load, displacement, or mode of failure between the two plates. Conclusions: The Puddu and TomoFix plates had similar biomechanical properties in open-wedge HTO. The results indicated reliable stability after open-wedge HTO without fibular osteotomy.

Is it true that intra-operative medial and lateral joint gaps should be equal in TKA?

Is it true that intra-operative medial and lateral joint gaps should be equal in TKA?

Analysis of the Lateral Gap Maintaining behavior of Vehicles in Heterogeneous Traffic Stream

In India, vehicular traffic is heterogeneous and vehicles do not follow lane discipline and can move anywhere on the available free space of the road. Lateral gaps maintained by the vehicles play major role in the passing/overtaking behavior of the following vehicles. For a detailed understanding of the lateral gap maintaining behavior huge data, covering various traffic scenarios, are required. In this study a detailed methodology for collecting the microscopic traffic data has been presented. It has been observed that the lateral clearance between two adjacent vehicles significantly vary depending on several traffic conditions. Speed of the subject vehicle, speed and type of the adjacent vehicle, and road width, were found to be significantly influencing the lateral gap. It has been found that the lateral gap maintained by vehicles, moving with similar speeds, can be modeled with normal distribution. Similarly, lognormal distribution can be used in modeling the gaps maintained by a vehicle moving with certain speed with respect to any speed of the adjacent vehicle.

Influence of intentional femoral component flexion in navigated TKA on gap balance and sagittal anatomy

Navigation has proven its ability to accurately restore coronal leg axis; however, for a good clinical outcome, other factors such as sagittal anatomy and balanced gaps are at least as important. In a gap-balanced technique, the size of the flexion gap is equalled to that of the extension gap. Flexion of the femoral component has been described as a theoretical possibility to balance flexion and extension gap. Aim of this study was to assess whether intentional femoral component flexion is helpful in balancing TKA gaps and in restoring sagittal anatomy. One hundred and thirty-one patients with TKA were included in this study. Implantation was performed in a navigated, gap-balanced, tibia-first technique. The femoral component flexion needed to equal flexion to extension gap was calculated based upon the navigation data. The sagittal diameter, the anterior and posterior offset were measured pre- and postoperatively based on the lateral radiographs. Medial and lateral gaps in extension and flexion as well as flexion/extension gap differences pre- and postoperatively were analysed. Additionally range of motion (ROM) and patient satisfaction (SF 12) were obtained. To achieve equal flexion and extension gap, the femoral component was flexed in 120 out of 131 patients showing mean flexion of 2.9° (SD 2.2°; navigation data) and 3.1° (SD 2.0°; radiological analysis), respectively. Based on this technique, it was possible to balance the extension gap (<2 mm difference) in 130 out of 131 patients (99%) and the flexion gap in 119 out of 131 (91%). The difference between extension and flexion gap was reduced from 39 to 24 out of 131 patients (81%) on the medial side and from 69 to 28 on the lateral side (79%). The sagittal diameter was restored in 114 out of 131 cases (87%); however, anterior offset was significantly reduced by 1.3 mm (SD 3.9°), and posterior offset was significantly increased by 1.6 mm (SD 3.3°). No correlation between any navigation and radiological parameter was found with ROM and SF 12. The navigation-based, gap-balanced technique allows intentional flexion of the femoral component in order to balance gaps in more than 90% of primary TKA cases. Simultaneously, the sagittal diameter is restored in 87% of patients. However, to achieve equal gaps, the posterior offset is significantly increased by 1.6 mm and the femoral component is flexed by 3°. To evaluate the effect of this technique on the clinical outcome, future studies are needed. II.

Navigation-Guided Lateral Gap Arthroplasty as the Treatment of Temporomandibular Joint Ankylosis

This article presents a novel method of navigation-guided lateral gap arthroplasty (LGA) in the treatment of temporomandibular joint ankylosis (TMJA). Six patients with unilateral TMJA from 2007 through 2011 were included in this study. Presurgical planning was performed to determine the amount and extent of ankylosed bone to be resected using the simulation platform. Minimum follow-up was 6 months. Patients were monitored for complications and signs of recurrence. Maximum mouth opening (MO) was measured and compared intra- and postoperatively. Preoperative planning was performed at the STN or Accu-Navi workstation. The amount and extent of ankylosed bone to be resected was determined. All 6 LGAs were completed successfully using real-time instrument- and pointer-based navigation. Measurements performed intraoperatively showed that the mean for maximum MO was about 35 to 40 mm and remained the same postoperatively. Follow-up evaluation showed remarkable improvement in function and esthetics, with no signs of recurrence. Navigation-guided LGA can be regarded a viable option for performing this delicate and complicated surgical procedure.

Flexion and extension gaps created by the navigation-assisted gap technique show small acceptable mismatches and close mutual correlations

The aim of this study was to investigate the mechanism underlying the development of gap differences in total knee arthroplasty using the navigation-assisted gap technique and to assess whether these gap differences have statistical significance. Ninety-two patients (105 knees) implanted with cruciate-retaining prostheses using the navigation-assisted gap balancing technique were prospectively analysed. Medial extension and flexion gaps and lateral extension and flexion gaps were measured at full extension and at 90° of flexion. Repeated measures analysis of variance was used to compare the mean values of these four gaps. The correlation coefficient between each pair of gaps was assessed using Pearson's correlation analysis. Mean intra-operative medial and lateral extension gaps were 20.6 ± 2.1 and 21.7 ± 2.2 mm, respectively, and mean intra-operative medial and lateral flexion gaps were 21.6 ± 2.7 and 22.1 ± 2.5 mm, respectively. The pairs of gaps differed significantly (P < 0.05 each), except for the difference between the medial flexion and lateral extension gaps (n.s.). All four gaps were significantly correlated with each other, with the highest correlation between the medial and lateral flexion gaps (r = 0.890, P < 0.001) and the lowest between the medial flexion and lateral extension gaps (r = 0.701, P < 0.001). Medial and lateral flexion and extension gaps created using the navigation-assisted gap technique differed significantly, although the differences between them were <2 mm, and the gaps were closely correlated. These narrow ranges of statistically acceptable gap differences and the strong correlations between gaps should be considered by surgeons, as should the risks of soft tissue over-release or unintentional increases in extension or flexion gap after preparation of the other gap.

Tibial internal rotation is affected by lateral laxity in cruciate-retaining total knee arthroplasty: an intraoperative kinematic study using a navigation system and offset-type tensor

The purpose of this study was to test the hypothesis that intraoperative soft-tissue balance assessed by an offset-type tensor influences post-operative knee kinematics after cruciate-retaining (CR) total knee arthroplasty (TKA). The influence of intraoperative soft-tissue balance on knee kinematics in CR-TKA was retrospectively analysed in 30 patients. Intraoperative soft-tissue balance parameters such as varus angle (varus ligament balance), joint component gap (centre gap), and medial and lateral compartment gaps were measured in the navigation system while applying 40-lb joint distraction force at 0°, 10°, 30°, 60°, 90°, and 120° of knee flexion using an offset-type tensor with the patella reduced. Tibial internal rotation and tibial anterior translation were measured as the differences between the values at 60° and 120° of flexion using the navigation system. Correlations between the soft-tissue parameters and post-operative knee kinematics were analysed. The varus ligament balance was positively correlated with tibial internal rotation at 60° and 90° of flexion (R=0.54, P<0.05; R=0.60, P<0.01, respectively). Furthermore, the joint component gap was positively correlated with tibial internal rotation at 90° of flexion (R=0.44, P<0.05), and the lateral compartment gap was positively correlated with tibial internal rotation at 60°, 90°, and 120° of knee flexion. The intraoperative varus ligament balance and joint component gap values were factors that predicted post-operative knee kinematics after CR-TKA. Lateral laxity at mid-to-deep knee flexion plays a significant role in tibial internal rotation. III.

Intersecting Circuits Generate Precisely Patterned Retinal Waves

The developing retina generates spontaneous glutamatergic (stage III) waves of activity that sequentially recruit neighboring ganglion cells with opposite light responses (ON and OFF RGCs). This activity pattern is thought to help establish parallel ON and OFF pathways in downstream visual areas. The circuits that produce stage III waves and desynchronize ON and OFF RGC firing remain obscure. Using dual patch-clamp recordings, we find that ON and OFF RGCs receive sequential excitatory input from ON and OFF cone bipolar cells (CBCs), respectively. This input sequence is generated by crossover circuits, in which ON CBCs control glutamate release from OFF CBCs via diffusely stratified inhibitory amacrine cells. In addition, neighboring ON CBCs communicate directly and indirectly through lateral glutamatergic transmission and gap junctions, both of which are required for wave initiation and propagation. Thus, intersecting lateral excitatory and vertical inhibitory circuits give rise to precisely patterned stage III retinal waves.

Layer-By-Layer Assembly of Ag Nanowires into 3D Woodpile-like Structures to Achieve High Density “Hot Spots” for Surface-Enhanced Raman Scattering

The surface-enhanced Raman scattering (SERS) "hot spots" are highly localized regions of enhanced electromagnetic field within a SERS substrate that dominate the overall SERS intensity. This results in inhomogeneous distribution of SERS intensity in a SERS substrate, thus limiting their application as reproducible and ultrasensitive sensing platforms. Here, we address this challenge by fabricating Ag nanowires into three-dimensional (3D) woodpile-like platforms via layer-by-layer Langmuir-Blodgett assembly. We focus on promoting strong electromagnetic coupling between parallel and vertically stacked Ag nanowire pairs within the woodpile structure to achieve a high density of "hot spots" across the entire 3D SERS substrates. Raman mapping (x-y plane) demonstrates that all of the 3D Ag nanowire arrays exhibit a homogeneous SERS Raman intensity over a large area, whereas their monolayer counterpart experiences >50% of zero and/or an undetectable SERS signal. The SERS enhancement factor increases from 3.1 × 10(3) to 2.6 × 10(4), as the assembled Ag nanowire layer increases from monolayer to three layers, respectively. We attribute the homogeneous SERS signal to the high density of "hot spots" arising from the vertical and lateral gaps within the woodpile layers. The SERS signals plateau off when the number of layers increase from three to five, which can be attributed to limited laser penetration depth. The assembled multilayered silver nanowires demonstrate a larger SERS depth cross section and angle-independent SERS intensity, making such woodpile 3D SERS substrate more reliable and versatile for future sensing applications.

Influence of Gap Balance on the Sagittal Movement of a Specific Mobile Bearing Floating Platform Design in Total Knee Arthroplasty

We analyzed 119 knees implanted with mobile bearing floating platform prostheses using the navigation-assisted gap balancing technique to analyze the relationship between intraoperative sagittal movement of floating platforms and soft tissue balancing. The 95 (79.8%) knees were classified into the positive rollback group (mean insert posterior rollback 5.86 ± 1.24 mm), and the remaining 24 (20.2%) into the negative rollback group. Lateral flexion gap (LFG) differed significantly between knees with positive and negative rollback (20.5 ± 1.7 mm vs 22.1 ± 1.7 mm, P = .021). Only LFG significantly influenced the occurrence of bearing sagittal movement. Sagittal translation of the insert occurred in about 80% of knees implanted with mobile bearing floating platforms in TKA, and was affected by flexion gaps, especially on the lateral side.

Comparing navigation-based in vivo knee kinematics pre- and postoperatively between a cruciate-retaining and a cruciate-substituting implant

Individual physiological knee kinematics are highly variable in normal knees and are altered following cruciate-substituting (PS) and cruciate-retaining (CR) total knee arthroplasty (TKA). We wanted to know whether knee kinematics are different choosing two different knee designs, CR and PS TKA, during surgery using computer navigation. For this purpose, 60 consecutive TKA were randomised, receiving either CR (37 patients) or PS TKA (23 patients). All patients underwent computer navigation, and kinematics were assessed prior to making any cuts or releases and after implantation. Outcome measures were relative rotation between femur and tibia, measured medial and lateral gaps and medial and lateral condylar lift-off. We were not able to demonstrate a significant difference in femoral external rotation between either group prior to implantation (7.9° CR vs. 7.4° PS) or after implantation (9.0° CR vs. 11.3° PS), both groups showed femoral roll-back. It significantly increased pre- to postoperatively in PS TKA. In the CR group both gaps increased, the change of the medial gap was significantly attributable to medial release. In the PS group both gaps increased and the change of the medial and of the lateral gap was significant. Condylar lift-off was observed in the CR group during 20° and 60° of flexion. This study did not reveal significant differences in navigation-based knee kinematics between CR and PS implants. Femoral roll-back was observed in both implant designs, but significantly increased pre- to postoperatively in PS TKA. A slight midflexion instability was observed in CR TKA. Intra-operative computer navigation can measure knee kinematics during surgery before and after TKR implantation and may assist surgeons to optimise knee kinematics or identify abnormal knee kinematics that could be corrected with ligament releases to improve the functional result of a TKR, whether it is a CR or PS design. Our intra-operative finding needs to be confirmed using fluoroscopic or radiographic 3D matching after complete recovery from surgery.

Surgical Technique: Computer-assisted Sliding Medial Condylar Osteotomy to Achieve Gap Balance in Varus Knees During TKA

Extensive posteromedial release to correct severe varus deformity during TKA may result in mediolateral or flexion instability and may require a constrained implant. We describe a technique combining computer navigation and medial condylar osteotomy in severe varus deformity to achieve a primary goal of ligament balance during TKA. The goal of this procedure was to achieve mediolateral gap balance in varus knees with rigid, recalcitrant medial contracture, with or without excessive lateral laxity, not amenable to extensive medial soft tissue releases. A sliding medial condylar osteotomy (SMCO) was performed under navigation guidance and the condylar block internally fixed using cancellous screws. We prospectively evaluated mediolateral laxity, Knee Society scores, and knee ROM after SMCO in 12 varus arthritic knees in 11 patients (five men, six women) undergoing TKA with a minimum followup of 2 years (mean, 2 years; range, 2-2.5 years). The degree of mediolateral knee laxity improved from Grade 2 (in four knees) and Grade 3 (in eight knees) preoperatively to Grade 1 (< 5 mm) in all knees at last followup. Mean Knee Society score improved from 30 (range, 10-54) to 92 (range, 86-100). Mean knee flexion improved from 106° (range, 90°-120°) to 112° (range, 100°-124°), and no knee had any extensor lag or residual flexion deformity (> 5°). Three knees had asymptomatic fibrous union at the osteotomy site. Computer-assisted SMCO in varus knees with recalcitrant medial contracture achieves improved mediolateral stability and knee function after TKA. Our technique uses navigation to accurately reposition the medial condylar block to equalize medial and lateral gaps, thereby ensuring a stable well-aligned knee without deploying constrained implants.

Realization of Micro-EDM under Ultra-Small Discharge Energy by Applying Ultrasonic Vibration to Machining Fluid

Although micro-EDM has its potential in micro tool and part manufacturing, the machining speed is quite low due to short -circuits and abnormal discharges, because of the difficult debris removal from the narrow gap -width. Especially, the machining becomes impossible under ultra-small discharge energy, for example, a low open voltage and the stray capacitor in the RC discharge circuit. In this study, the effect of applying ultrasonic vibration to the machining fluid in micro-EDM was experimentally investigated, in order to realize higher machining speed and deep -hole drilling. It was found that a significant increase in the machining speed was realized by applying ultrasonic vibration. Also, with the vibration of the machining fluid, micro-hole drilling with ultra-small discharge energy became possible. In addition, the exp erimental results show that the lateral gap width between the tool electrode and workpiece was shortened, and the tool wear ratio became smaller.

Lateral soft tissue laxity increases but medial laxity does not contract with varus deformity in total knee arthroplasty.

In TKA, soft tissue balance (the joint gap) depends on the amount of resected bone and soft tissue release. Some studies report preoperative bony deformity correlates with soft tissue balance evaluated intraoperatively and that the medial tissues are contracted with varus deformity. However, these studies did not take into account the amount of resected bone and did not describe whether the soft tissue was tight or loose. Therefore, it remains unclear whether in varus deformity the soft tissues on the medial side are contracted. We compared (1) intraoperative joint gap, (2) amount of resected bone, and (3) intraoperative soft tissue laxity on the lateral and medial sides according to severity of preoperative varus deformity. We retrospectively reviewed 70 patients with osteoarthritis and varus deformities who underwent 90 TKAs. We retrospectively divided the 90 knees into three groups according to degree of preoperative alignment: mild varus group (<10°), moderate varus group (10°-20°), and severe varus group (>20°). To evaluate intraoperative soft tissue tension, we calculated the soft tissue gap by subtracting the thickness of the resected bone from the joint gaps on the medial and lateral sides, respectively. We then explored the relationship between the soft tissue gap and preoperative alignment. The lateral soft tissue gap was larger in the severe varus group than in the mild and moderate varus groups. The medial soft tissue gap was larger in the severe varus group than in the mild varus group, but there were no differences in the medial joint gaps among the groups. After the bone is resected, the soft tissue on the lateral side is more lax; however, the soft tissue on the medial side is not shorter with greater preoperative varus deformity.