Understanding the relationship between knee specific tissue behavior and joint contact mechanics remains an area of focus. Seminal work from 1990's established the possibility to optimize tissue properties for recreation of laxity driven kinematics (Mommersteeg et al., 1996). Yet, the uniqueness and validity of such predictions could be strengthened, especially as they relate to joint contact conditions. Understanding this interplay has implications for the long term performance of joint replacements. Development of instrumented knee implants, highlighted by a single use tibial insert trial with embedded sensor technology (VERASENSE, Orthosensor Inc.), may offer an avenue to establish the relationship between tissue state and joint mechanics. Utilization of related data also has the potential to confirm computational predictions, where both rigid body motions and associated reactions are explicitly accounted for. Hence, the goal of this work was to evaluate an approach for optimization of ligament properties using joint mechanics data from an instrumented implant during laxity style testing. Such a framework could be used to inform joint balancing techniques, improve long term implant performance, and alternatively, qualify factors that may lead to poor outcomes
The INTRODUCTION
METHODS
Achieving balance in TKA is critical in assuring favorable outcomes. But, in order to achieve quantifiably balanced loading values, is it more advantageous to make bony corrections or release soft-tissue? The answer to this question will be paramount in evaluating the most appropriate surgical techniques for use with new dynamic technology, thereby maximizing favorable clinical outcomes. Therefore, the purpose of this investigation was to evaluate a possible quantitative loading threshold, using intraoperative sensors, which may dictate surgical correction of bone versus soft-tissue release. A retrospective analysis of 122 multicenter patients, in receipt of sensor-assisted primary TKA, was conducted. 40 lbs. was used as a threshold, above which bone was corrected; below which soft-tissue was corrected. All patients were categorized in to the following groups: Group A – candidates for bony correction, but received soft-tissue correction; Group B – candidates for soft-tissue/receiving soft-tissue; Group C – candidates for bony correction/receiving bony correction.INTRODUCTION
METHODS
Patient-reported satisfaction is a critical measure in understanding the clinical success of total knee arthroplasty. Yet, satisfaction levels in TKA patients are generally lower than THA patients; and surgeon-patient agreeability regarding clinical success is typically in discordance. Thus, the purpose of this evaluation was to report on the one-year satisfaction data of a group of sensor-assisted TKA patients, and compare that data to the average satisfaction reported in literature, as measured by a meta-analysis. One hundred and thirty five patients received TKA utilizing intra-operative sensing technology to evaluate soft-tissue balance as part of a prospective multicenter study. Patients were classified by two groups: “balanced” and “unbalanced”. Quantitative “balance” was defined as a mediolateral intercompartmental loading difference of ≤ 15 pounds; all loading exceeding 15 pounds was classified as “unbalanced”. At the one-year follow-up visit, a 7-question patient satisfaction survey was administered. The answering schema of this survey was modeled using a modified five-point Likert scale, ranging from “True” to “False” (or “Very Satisfied” to “Very Dissatisfied,” where appropriate). A meta-analysis of literature was performed and studies selected for inclusion in this analysis were required to meet the following criteria: all patients were in receipt of a primary TKA; satisfaction data was collected post-operatively; and the proportion of patients who were “satisfied” to “very satisfied” was statistically described.INTRODUCTION
METHODS
The cost associated with the TKA revision burden is projected to reach 13 billion dollars, annually. Complications reported by post-TKA patients include: pain (44%, multilocational), sensation of instability (21% reason for revision), and joint stiffness (17% reason for revision); problems that may be attributed to soft-tissue imbalance. One of the possible reasons for the substantial prevalence of such complications is the subjectivity associated with defining soft-tissue balance. A priority must be placed on developing new objective methods with which to avoid costly post-operative complications, including the integration of intraoperative sensing technology. The purpose of this evaluation was to report on the disparity between the patient-reported outcomes scores of quantitatively balanced versus unbalanced patients, at 1-year, using a group of 135 multicenter patients. 135 prospective patients, from 8 U.S. sites, have had primary TKA performed with the use of intraoperative sensors. Patients were classified by two groups: “balanced” and “unbalanced”. Quantitative “balance” was defined as a mediolateral intercompartmental loading difference of ≤ 15 pounds; all loading exceeding 15 pounds was classified as “unbalanced”. For all patients, the following kinematic data was captured: varus/valgus stability, anteroposterior stability, flexion contracture (if any), extension lag (if any), anatomic alignment, and ROM. Also at each clinical follow-up visit, activity levels and two patient-reported outcomes measures were administered, including: the American Knee Society Score (KSS), and the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC).INTRODUCTION
METHODS
During primary total knee arthroplasty, the surgeon may encounter excessive medial collateral ligament tension while addressing a varus knee. This may be due to medial ligament/capsular complex contractures, and/or, due to the creation of a 0 degree mechanical axis in a varus knee. This tension leads to increased loading in the medial compartment, which contributes to an unbalanced extension and flexion gap. If uncorrected, this imbalance can lead to unfavorable clinical outcomes, including: pain, accelerated polyethylene degradation, joint instability, and limited ROM. Currently, intercompartmental soft-tissue balance is obtained by a subjective surgeon's “feel”. However, this method of judging soft-tissue tension is both variable and unreliable. Most surgeons can detect gross instability, but judging ligament tension is difficult. The following technique describes the integration of intraoperative microelectronic tibial inserts to assess and modify ligament tension, utilizing real-time dynamic sensor feedback 500 TKAs were performed between September 2012 and April 2013, by three collaborating surgeons. All surgeons used the same implant system, compatible with an embedded microelectronic tibial insert with which to receive real-time feedback of femoral contact points and joint kinetics. Intraoperative kinematic data, displayed loading patterns consistent with identifiable intercompartmental imbalance through a full ROM. All mediolateral imbalance, secondary to an excessively tight medial compartment, was addressed with the technique described herein.Introduction
Methods
Most cases of hip osteoarthritis (OA) are believed to be caused by alterations in joint contact mechanics resulting from pathomorphologies such as acetabular dysplasia and acetabular retroversion. Over the past 13 years, our research group has focused on developing approaches for patient-specific modeling of cartilage and labrum in the human hip, and applying these approaches to study hip pathomorphology. The long term objective is to improve the understanding of the etiology of OA related to hip pathomorphology, and to improve diagnosis and treatment. The objectives of this presentation are to provide a summary of our subject-specific modeling approach, and to describe the results of our analysis of hips from three populations of subjects: normal, traditional dysplastic, and retroverted. A combined experimental and computational protocol was used to investigate contact mechanics in ten normal subjects (normal center edge angles (CEA), no history of hip pain), ten subjects with hip pain secondary to acetabular dysplasia (CEA less than 25°), and ten patients with a radiographic crossover sign, pain and clinical exams consistent with acetabular retroversion. CT arthrography was used to image cartilage and bone. Volumetric image data were segmented and discretized, and subject-specific finite element models were produced using validated methods [Fig. 1]. Boundary and loading conditions were obtained from instrumented implant and gait data. Contact mechanics were evaluated on the acetabular cartilage and labrum. Labrum contact area and peak contact stress were evaluated. Cartilage contact area, peak and average contact stress were evaluated in six anatomical regions in the acetabulum.Introduction:
Methods:
Post-operative clinical outcomes of TKA are dependent on a multitude of surgical and patient-specific factors. Malrotation of the femoral and/or tibial component is associated with pain, accelerated wear of the tibial insert, joint instability, and unfavorable patellar tracking and dislocation. Using the transepicondylar axis to guide implantation of the femoral component is considered to be an accurate anatomical reference and is widely used. However, no gold standard currently exists with respect to ensuring optimal rotation of the tibial tray. Literature has suggested that implantation methods, which reference the tibial tubercle, reduce positioning outliers with more consistency than other anatomical landmarks. Therefore, the purpose of this evaluation is to use data collected from intraoperative sensors to assess the true rotational accuracy of using the mid-medial third of the tibial tubercle in 98 TKAs. The data for this evaluation was retrieved from 98 consecutive patients who underwent primary TKA from the same highly experienced surgeon. Femoral component rotation was verified in every case via the use of the Whiteside line, referencing the transepicondylar axis, and confirming appropriate patellar tracking. Tibial tray rotation was initially established by location of the mid-medial third of the tibial tubercle. Rotational adjustments of the tibial tray were evaluated in real-time, as the surgeon corrected any tibiofemoral incongruency and tray malpositioning. The initial and final angles of tibial tray rotation were captured with intraoperative video feed, and recorded. A z-test of differences between pre- and post-rotational correction was performed to assess the statistical significance of malrotation present in this cohort.Introduction
Methods
This presentation will provide an overview of the interdisciplinary research program on hip pathomorphology at the University of Utah, including studies of dysplasia and femoracetabular impingement. The discussion will emphasize the implications of the research findings for hip preserving surgery
A large percentage of the patients who present for unilateral TKA have bilateral disease. Performing simultaneous, bilateral TKA has been debated and currently there is no consensus on the risks and benefit of this approach. In addition, specific selection criteria have not been defined to more accurately identify which patients are potentially appropriate candidates for this approach. The purpose of this study was to evaluate the clinical outcomes and peri-operative complications in simultaneous, bilateral TKA's using pre-operative patient selection criteria.Background:
Objectives:
Flexion instability of the knee accounts for, up to, 22% of reported revisions following TKA. It can present in the early post-operative phase or present— secondary to a rupture of the PCL— in the late post-operative phase. While most reports of instability occur in conjunction with cruciate retaining implants, instability in a posterior-stabilized knee is not uncommon. Due to the prevalence of revision due to instability, the purpose of constructing the following techniques is to utilize intraoperative sensors to quantify flexion gap stability. 500 posterior cruciate-retaining TKAs were performed between September 2012 and April 2013, by four collaborating surgeons. All surgeons used the same implant system, compatible with a microelectronic tibial insert with which to receive real-time feedback of femoral contact points and joint kinetics. Intraoperative kinematic data, as reported on-screen by the VERASENSE™ knee application, displayed similar loading patterns consistent with identifiable sagittal plane abnormalities. These abnormalities were classified as: “Balanced Flexion Gap,” “Flexion Instability” and “Tight Flexion Gap.” All abnormalities were addressed with the techniques described herein.Introduction
Methods
Acetabular component positioning is highly correlated with total hip arthroplasty (THA) outcomes. Multiple reports however indicate that less than 50% of acetabular cups are placed within surgeon-desired ranges for abduction and anteversion angles when using conventional cup positioning techniques. Issues with improper placement include instability-dislocation, impingement and impact on range of motion, polyethylene wear, leg length discrepancy, and gait mechanics. Accuracy in placement of the acetabular component is complicated by the need to estimate cup impactor angles to create desired cup position. A low cost approach to THA using Image-based Ultrasonic Guidance (IUG) (Orthosensor, Sunrise, FL) coupled to existing surgical tools is presented. IUG utilises acoustic measurement techniques for achieving optimal component positioning and leg length. A precisely machined Hip Test Fixture (HTF) has been built to simulate the anatomical pelvis, acetabular cup, and femur to validate system accuracy. The IUG was affixed to the HTF to demonstrate placement of the cup during THA. The HTF was loaded onto a 27-inch Graphic User Interface (GUI) providing three-dimensional CAD data of the HTF. Registration points included the Iliac Crest and 10 points around the acetabular cup. These points were mapped to the CAD data by the GUI. The HTF was set to 45° of abduction and 0° of version to begin testing. Abduction and version were measured over a +15° range in 1-degree increments while leg length and offset were measured over a +5mm range in 2mm increments. A high-resolution coordinate measurement machine (FaroArm EDGE) verified the accuracy and margin of error for inclination, version, leg length and offset at each increment. The HTF provided a precise means for evaluating IUG system accuracy of simulated THA in a controlled environment. Acceptable margins of error were reported on the HTF: mean error for version was 0.36° (SD 0.02°; 0.25° to 0.38°); mean error for inclination was 1.04° (SD 0.52°; 0.48° to 1.66°); mean error for leg length and offset were respectively 0.36mm (SD 0.86mm; −0.65 to 1.55mm) and 0.41mm (SD 0.28; 0.05 to 0.80mm). IUG provides a means for achieving acceptable precision and accuracy in component placement during THA as evaluated with the HTF. Further study is however necessary to correlate accuracy of IUG with clinical utility and short-term clinical outcomes.
Optimized tibial tray rotation during a total knee replacement (TKR) is critical for tibiofemoral congruency through full range of motion, as it affects soft tissue tension, stability and patellar tracking. Surgeons commonly reference the tibial tubercle, or the “floating tibial tray,” while testing the knee in flexion and extension. Utilization of embedded sensors may enable the surgeon to more accurately assess tibiofemoral contact points during surgery. The malrotation of the tibiofemoral congruency when utilizing the mid to medial 1/3 of the tibial tubercle for tibial rotation was evaluated in 50 posterior cruciate ligament-retaining TKRs performed by an experienced, high-volume surgeon. Sensors were embedded in the tibial trials; the rotation of the tibial tray was defined, and the femoral contact points in each compartment were captured. The surgical procedure was performed to size and then appropriately rotate the tibial tray. The anterior medial tray was pinned to control anterior-posterior and medio-lateral displacement, and allow internal and external rotation of the tray. With the capsule closed and patella reduced, the knee was reduced with trial implants. The femoral contact points and medial-lateral soft tissue tension were documented. Patellar tracking and changes in soft tissue tension were also documented.Introduction
Methods
Infection rates following arthroplasty surgery are reported between 1–4%, with considerably higher rates in revision surgery. The associated costs of treating infected arthroplasty cases are over 4 times the cost of primary arthroplasties, with significantly worse functional and satisfaction outcomes. In addition, multiple antibiotic resistant bacteria are developing, so to reduce the infection rates and costs associated with arthroplasty surgery, new preventative methods are required. HINS-light is a novel blue light inactivation technology which kills bacteria through a photodynamic process, and is proven to have bactericidal activity against a wide range of species. The aim of this study was to investigate the efficacy of HINS-light for the inactivation of bacteria isolated from infected arthoplasty cases. Specimens from hip and knee arthroplasty infections are routinely collected in order to identify possible causative organisms and susceptibility patterns. This study tested a range of these isolates for sensitivity to HINS-light. During testing, bacterial suspensions were exposed to increasing doses of HINS-light of (66mW/cm2 irradiance). Non-light exposed control samples were also set-up. Bacterial samples were then plated onto agar plates and incubated at 37°C for 24 hours before enumeration.Introduction
Methods
Skills simulation is increasingly used as a training tool in postgraduate surgical training. Trainee's perception of the value of this experience has not previously been investigated. The aim of this investigation was to investigate the value of surgical simulation training delivered by an arthroscopy skills course. We constructed a subject-specific, self-assessment questionnaire based around the ISCP Peer Assessment Tool. The questionnaire was administered to candidates before and after attending the Plymouth Arthroscopy Skills Course. Participant demographic data was recorded. Questionnaire data was interrogated to give an overview of the course, as well as the benefit of site-specific skills stations. Statistical analysis showed the data to be normally distributed. The paired T-test was used to compare mean values. Twelve surgical trainees attended the course – CT2 trainees (n=4); ST3 trainees (n=7); ST4 trainee (n=1). 11 candidates completed both administered questionnaires giving a 92% response rate. The global mean score at the beginning of the course was 2.39. The global mean score at the end of the course was 3.90. The mean improvement was 1.51 (p<0.01; 95% CI= 0.96-2.07). Skill station specific scores all showed improvement with the greatest effect in wrist arthroscopy. CT trainees had a lower mean score compared to ST trainees. Both groups completed the course with similar mean scores. This study shows that arthroscopy simulation improves trainee-reported ratings of surgical skill. It also shows that less experienced candidates derived the greatest benefit from the training. Further research is required to compare self-assessed performance against objective benchmarks using validated assessment tools.
Military patients have high functional requirements of the upper limb and may have lower pre-operative PROM scores than civilian patients i.e. their function is high when benchmarked, but still insufficient to perform their military role thereby mandating surgery. Our aim was to compare the pre-operative Oxford Shoulder Instability Scores in military and civilian patients undergoing shoulder stabilisation surgery. We undertook a prospective, blinded cohort-controlled study (OCEBM Level 3b). The null hypothesis was that there was no difference in the Oxford Shoulder Instability Scores between military and civilian groups. A power calculation showed that 40 patients were required in each group to give 95% power with 5% significance. A clinical database (iParrot, ByResults Ltd., Oxford, UK) was interrogated for consecutive patients undergoing shoulder stabilisation surgery at a single centre. The senior author - blinded to the outcome score - matched patients according to age, gender and diagnosis. Statistical analysis showed the data to be normally distributed so a paired samples t-test was used to compare the two groups. 110 patients were required to provide a matched cohort of 80 patients. There were 70 males and 10 females. Age at the time of surgery was 16-19yrs (n=6); 20-24yrs (n=28); 25-29 (n=16); 30-34(n=12); 35-49(n=12); 40-44(n=6). 72 patients (90%) had polar group one and 8 patients (10%) had polar group two instability. The mean Oxford Shoulder Instability Score in the civilian group was 17 and the in military group was 18. There was no statistical difference between the two groups (p=0.395). This study supports the use the Oxford Shoulder Instability Score to assess military patients with shoulder instability.
To assess whether prosthetic femoral stem centralisers have a detrimental effect on the macroporosity of the cement mantle, and if so, whether this is independent of their design and the rate of implantation, 30 identically cast moulded prosthetic femora were divided into 3 groups. Group 1: no centraliser (control), Group 2: centraliser A and Group 3: centraliser B. Using third generation cementation techniques and pressure monitoring, Charnley C-stems +/− the appropriate centraliser were implanted to a constant depth. Half in each group were implanted as rapidly as possible and the other half over 90 seconds. The stems were removed and the cement mantle then underwent a preliminary arthroscopic examination prior to being sectioned transversely at 3 constant levels. Each level was then photographed and digitally enlarged to a known scale to allow examination and determination of any cement voids (macropores) surface area. There were no significant pressure fluctuations between the groups. Preliminary arthroscopic examination revealed that cement voids appeared more common when a centraliser was used. This difference was confirmed (p=0.002) following sectioning of the specimens, with cement voids found in 85% of femora when a centraliser was used and only 20% in the control group. Centraliser B performed worst with cement voids of a larger volume and more frequent occurrence (p=0.002). The macroporosity of the cement mantle was independent of the rate of implantation (p=0.39). The use of femoral stem centralisers is helpful in preventing malposition of the implant but results in increased macroporosity of the cement mantle. This may have implications regarding the longevity of an implant in terms of early loosening and therefore their design and use must always be carefully considered.
