Although total knee replacement became a widespread procedure for the purpose of knee reconstruction, osteotomies around the knee were regularly performed. Total knee arthroplasty should be performed for advanced arthritis of the knee. With the advent of biplanar open wedge high tibial osteotomy (HTO) combined with locking plate fixation, HTO has been expanded and its surgical outcome has been improved in recent years. However, post-operative joint-line obliquity has been raised as a concern with this procedure, which may affect the outcome especially in the knees with severe varus deformity. Hence the purpose of this study is to analyze the compression and shear stresses in the knee cartilage with joint line obliquity after HTO. Using a three-dimensional computer aided design software, the digital knee model with soft tissues was developed. The geometrical bone data used in this study were derived from commercially available human bone digital anatomy media (3972 and 3976, Pacific Research Laboratories, Inc., WA, USA). The three-dimensional knee model was transferred to finite element model. Material properties of the soft tissues and bones were derived from previous studies. The loading condition was adjusted to the load during a single-leg stance of the gait cycle, which resulted in an axial compressive load of 1200 N. Two different conditions were subjected to the analysis: normal alignment and joint-line obliquity after HTO. For the normal alignment, a static force of 1200 N was applied along the mechanical axis. For the joint-line obliquity models, a single force of 1200 N was applied rotating force directions in the frontal plane from the normal direction by 2.5º, 5º, 7.5º, and 10º, respectively.Introduction
Methods
Although total hip arthroplasty (THA) has been one of the most successful, reliable and common prosthetic techniques since the introduction of cemented low-friction arthroplasty by Charnley in the early 1960s, aseptic loosening due to stem-cement and cement-bone interface failures as well as cement fractures have been known to occur. To overcome this loosening, the stem should be mechanically retentive and stable for long term repetitive loading. Migration studies have shown that all stems migrate within their cement mantle, sometimes leading to the stem being debonded from the cement [1]. If we adopt the hypothesis that the stems debond from the cement mantle, the stem surface should be polished. For the polished stem, the concept of a double taper design, which is tapered in the anteroposterior (AP) and mediolateral (ML) planes, and a triple-tapered design, which has trapezoidal cross-section with the double tapered, have been popularized. Both concepts performed equally well clinically [2]. In this study, we aimed to analyze stress patterns for both models in detail using the finite element (FE) method. An ideal cemented stem with bone was made using three dimensional FE analyses (ANSYS 13). The cortical bone was 105 mm long and 7 mm thick and the PMMA cement mantle was 5 mm in thickness surrounding the stem. Young's modulus was set at 200 GPa for the bone and 2.2 GPa for the cement. Poisson's ratio was 0.3 for both materials. The bone-cement interface was completely bonded and cement-stem interface was not bonded in cases where a polished stem surface was used. The two types of stems were compared. One being the double tapered (Fig 1 left) and the other the triple tapered (Fig 1 right). The coefficient of friction (μ) at the stem-cement interface was set at 0 for both models. The distal ends of the stems were not capsulated by the PMMA and therefore the stems were free to subside. All materials were assumed to be linearly isotropic and homogeneous. The distal ends of the bone were completely constrained against any movements and rotations. An axial load of 1200 N and a transverse load of 600 N were applied at the same time simulating the bending condition [3].Introduction
Methods
Reverse total shoulder arthroplasty (RTSA) is a commonly performed operation for a variety of pathologies. Despite excellent short-term outcomes, complications are commonly encountered. Recurrent instability occurs in up to 31% of cases, often due to components placed with too little tension. Acromial stress fractures can occur in up to 7% of cases, often due to components placed in too much tension. Despite these concerns, there is little evidence evaluating the intraoperative tension and glenohumeral contact forces (GHCF) during RTSA. The purpose of this study was to measure the intraoperative GHCF during RTSA. 26 patients were enrolled after obtaining IRB approval. Inclusion criteria were patients undergoing primary RTSA. An instrumented strain gauge implant was designed to attach to an Exactech Equinoxe (Gainesville, FL) baseplate during RTSA. A specially designed trial glenosphere was then attached to the instrumented baseplate. Wires from the strain gauges were connected to a 24-bit analog input and placed outside the operative field to a computer that measure the forces. After joint reduction, GHCF were measured in neutral, passive flexion, passive abduction, passive scaption and passive external rotation (ER). Five patients were excluded due to wire calibration issues.Introduction
Methods
Dislocation continues to be a common complication of total hip arthroplasty (THA) [1]. Although many factors affect the prevalence of dislocation, achieving proper intraoperative soft tissue tension is one of the main surgical goals to reduce this risk. However, a sensor to measure the soft tissue of ball joints i.e. hip and shoulder has not yet been developed. The sensor enables surgeons to adjust the size or position of the implants depending on soft tissue tension. Hence, we have developed a sensor-instrumented modular femoral head for THA to measure soft-tissue tension intraoperatively [2]. This study demonstrates the possibility of a soft tissue tension and joint angle data connection using a wireless system. The sensor-instrumented modular femoral head that we developed was made of epoxy resin with linear strain gauges (BTM-1C, Tokyo Sokki, Japan) inside the head and a triple-axis gyroscope (MPU-6500). Strain outputs and angle data from the gyroscope were transferred to a computer via a 2.4 GHz wireless link (RN42, Bluetooth Module). Data logging was performed by a custom program using C++ (Microsoft Visual Studio 2012) via both wired and wireless link. The strain gauges were embedded inside the head. For the calibration study, the sensor was fixed in a clamping block of an angle vice to permit changes in the direction of force. The calibration jig with the angle vice was placed on top of a low-friction two-dimensional translation table that eliminated horizontal constraints. A constant vertical force was applied using a vertical die set. The experimental setup is shown in Fig. 1. Instead of a portable battery, a DC electric power supply is used (bottom left). A picture of the Gyroscope and the radio module is inserted (bottom right). The force values and applied angles were changed recording strain gauge and angle outputs.Introduction
Materials and Methods
Dislocation continues to be a common complication of total hip arthroplasty (THA). Many factors affect the prevalence of dislocation after THA, including soft tissue laxity, surgical approach, component position, patient factors, and component design [1]. Achieving proper intraoperative soft tissue tension is one of the surgical goals to reduce the risk of the dislocation. However, reports of the intraoperative soft tissue tension measurements have not been enough yet. One way to quantify the intraoperative soft tissue tension is to measure joint forces using an instrumented prosthesis. Hence, we have developed a sensor-instrumented modular femoral head of THA to measure the soft-tissue tension intraoperatively. The goal of this study was to design and calibrate the sensor. The sensor-instrumented modular femoral head that we developed was made of polycarbonate with four linear strain gauges (BTM-1C, Tokyo Sokki Kenkyujo Co., Ltd., JP). To fabricate the sensor, four penetrant holes (1.6 millimeter in diameter), parallel to the coordinate axes were produced (Fig1). The strain gauges were embedded on inside wall of these holes. Finally, the holes were filled by epoxy resin (A-2 adhesive, Tokyo Sokki Kenkyujo Co., Ltd., JP). For calibration study, the sensor was fixed in a clamping block of an angle vice to permit change of force directions. The calibration jig with the angle vice was placed on top of a low-friction x-y translation table that eliminated horizontal constrains. Known forces (Fi) were applied by a standard material testing machine (Instron4204, INSTRON, Norwood, MA) through a polyethylene insert (Fig. 2). Two different series of forces were applied. One is that force values were increased from zero to 600 N on the z axis. And the other force pattern is 600 N forces were applied by changing force angles. The external force vector (Fi) can be expressed in terms of the strain gauge outputs as follows: Fi = T Si where T is a calibration matrix and Si corresponds to the outputs of the strain gauges. Calibration errors were calculated according to well-established methods [2].Introduction
Materials and Methods
Persistent problems and relatively high complication rates with reverse total shoulder arthroplasty (RTSA) are reported (1, 2). It is assumed that some of these complications are affected by improper intraoperative soft tissue tension. Achieving proper intraoperative soft tissue tension is an obvious surgical goal. However, intraoperative soft tissue tension measurements and methods for RTSA have not been reported. One way to quantify soft tissue tension is to measure intraoperative joint forces using an instrumented prosthesis. Hence, we have developed an instrumented RTSA to measure shoulder joint forces intraoperatively. The goal of this study was to measure intraoperative shoulder joint forces during RTSA. The instrumented shoulder prosthesis measures the contact force vector between the glenosphere and humeral tray. This force sensor is a custom instrumented trial implant that can be used with an existing RTSA system (EQUINOXE, Exactech Inc, Gainesville, FL) just as a standard trial implant is used. Four uniaxial foil strain gauges (QFLG-02-11-3LJB, Tokyo Sokki Kenkyujo Co., Ltd., JP) are instrumented inside the sensor. Using a calibration matrix, the three force components were calculated from four strain gauge outputs (3). Sixteen patients who underwent RTSA took part in this IRB approved study. All patients were greater than 50 years of age and willing to review and sign the study informed consent form. After obtaining informed consent for surgery, a standard deltopectoral approach to the shoulder was performed. The instrumented trial prostheses were assembled on the glenoid baseplate instead of a standard glenosphere. After the joint was reduced, joint forces were recorded during cyclic rotation, flexion, scapular plane movement (scaption), and adduction of the shoulder. Strain gauge outputs were recorded during these movements as well as the neutral position just before movements. Mean values of forces with each motion were compared by one-way analysis of variance (ANOVA). A multiple comparisons test was subsequently performed to examine differences between motions.Introduction
Materials and Methods
