Computer-assisted hip navigation offers the potential for more accurate placement of hip components, which is important in avoiding dislocation, impingement, and edge-loading. The purpose of this study was to determine if the use of computer-assisted hip navigation reduced the rate of dislocation in patients undergoing revision THA. We retrospectively reviewed 72 patients who underwent computer-navigated revision THA [Fig. 1] between January 2015 and December 2016. Demographic variables, indication for revision, type of procedure, and postoperative complications were collected for all patients. Clinical follow-up was performed at 3 months, 1 year, and 2 years. Dislocations were defined as any episode that required closed or open reduction or a revision arthroplasty. Data are presented as percentages and was analyzed using appropriate comparative statistical tests (z-tests and independent samples t- tests).Introduction
Methods and Materials
Acetabular component position is considered a major factor affecting the etiology of hip dislocation. The ‘Lewinnek safe zone’ has been the most widely accepted range for component position to avoid hip dislocation, but recent studies suggest that this safe zone is outdated. We used a large prospective institutional registry to ask: 1) is there a ‘safe zone’ for acetabular component position, as measured on an anteroposterior radiograph, within which the risk of hip dislocation is low?, and 2) do other patient and implant factors affect the risk of hip dislocation? From 2007 to 2012, 19,449 patients (22,097 hip procedures) were recorded in an IRB approved prospective total joint replacement registry. All patients who underwent primary THA were prospectively enrolled, of which 9,107 patients consented to participate in the registry. An adverse event survey (80% compliance) was used to identify patients who reported a dislocation event in the six months after hip replacement surgery. Postoperative AP radiographs of hips that dislocated were matched with AP radiographs of stable hips, and acetabular position was measured using Ein Bild Röntgen Analyse software. Dislocators in radiographic zones (± 5°, ± 10°, ± 15° boundaries) were counted for every 1° of anteversion and inclination angles.Introduction
Materials and Methods
Pelvic flexion and extension in different body positions can affect acetabular orientation after total hip arthroplasty, and this may predispose patients to dislocation. The purpose of this study was to evaluate functional acetabular component position in total hip replacement patients during standing and sitting. We hypothesize that patients with degenerative lumbar disease will have less pelvic extension from standing to sitting, compared to patients with a normal lumbar spine or single level spine disease. A prospective cohort of 20 patients with primary unilateral THR underwent spine-to-ankle standing and sitting lateral radiographs that included the lumbar spine and pelvis using EOS imaging. Patients were an average age of 58 ± 12 years and 6 patients were female. Patients had (1) normal lumbar spines or single level degeneration, (2) multilevel degenerative disc disease or (3) scoliosis. We measured acetabular anteversion (cup relative to the horizontal), sacral slope angle (superior endplate of S1 relative to the horizontal), and lumbar lordosis angles (superior endplates of L1 and S1). We calculated the absolute difference in acetabular anteversion and the absolute difference in lumbar lordosis during standing and sitting (Figure 1).Introduction
Methods
Tranexamic acid (TXA) has been shown to reduce post-operative blood loss, but the dosage and method of administration remains controversial. The purpose of our study was to study the effectiveness of topical TXA in a cohort of patients (n=224) undergoing TKA by a single surgeon. Two groups of patients who received topical TXA were compared to patients who did not receive TXA. Patients that received topical TXA had the least early postoperative blood loss, with patients that received topical TXA with a tourniquet and a drain having the least. Patients receiving TXA required fewer transfusions than patients who did not receive TXA and there was no difference in the rate of symptomatic DVT/PE. Our results support the use of topical TXA during TKA.
Digital templating is a critical part of preoperative planning for total hip arthroplasty (THA) that is increasingly used by orthopaedic surgeons as part of their preoperative planning process. Digital templating has been used as a method of reducing hospital costs by eliminating the need for acetate films and providing an accurate method of preoperative planning. Pre-operative templating can help anticipate and predict appropriate component sizes to help avoid postoperative leg length discrepancy, failure to restore offset, femoral fracture, and instability. A preoperative plan using digital radiographs for surgical templating for component size can improve intraoperative accuracy and precision. While templating on conventional and digital radiographs is reliable and accurate, the accuracy of templating on digital images acquired with a novel biplanar imaging system (EOS Imaging Inc, Cambridge, MA, USA) remains unknown. EOS imaging captures whole body images of a standing patient without stitching or vertical distortion, less magnification error and exposes patients to less radiation than a pelvis AP radiograph. Therefore, the purpose of this study was to compare EOS imaging and conventional anteroposterior (AP) xrays for preoperative digital templating for THA, and compare the results to the implant sizes used intraoperatively. Forty primary unilateral THA patients had preoperative supine AP xrays and standing EOS imaging. The mean age for patients was 61 ± 8 years, the mean body mass index 29 ± 6 kg/m2 and 21 patients were female. All patients underwent a THA with the same THA system (R3 Acetabular System and Synergy Cementless Stem, Smith & Nephew, TN, USA) by a single surgeon. Two blinded observers preoperatively templated using both AP xray and EOS imaging for each patient to predict acetabular size, femoral component size, and stem offset. All templating was performed by two observers with standard software (Ortho Toolbox, Sectra AB, Linköping, Sweden) [Figure 1] one week prior to surgery, and were compared using the Cronbach's alpha (∝) coefficient of reliability. The accuracy of templating was reported as the average percent agreement between the implanted size and the templated size for each component.Background
Methods
Obesity is a risk factor for acetabular malposition when total hip arthroplasty (THA) is performed with manual orientation techniques. However, conflicting evidence exists regarding the usefulness of computer-assisted surgery for performing THA in obese patients. The purpose of this study was to compare the precision and accuracy of imageless navigation for acetabular component placement in obese versus non-obese patients. After institutional review board approval, 459 THA performed for primary hip osteoarthritis were reviewed retrospectively. The same imageless navigation system was used for acetabular component placement in all THA. During surgery the supine anterior pelvic plane was referenced superficially. THA was performed via posterolateral approach in the lateral position. A hemispherical acetabular component was used, with target inclination of 40° and target anteversion of 25°. Computer software was used to determine acetabular orientation on postoperative anteroposterior pelvic radiographs. Obese patients (BMI ≥ 30 kg/m2) were compared to non-obese patients. A 5° difference in mean orientation angles was considered clinically significant. Orientation error (accuracy) was defined as the absolute difference between the target orientation and the measured orientation. Student's t test was used to compare means. Hartley's test compared variances of the mean differences (precision). Fisher exact tests examined the relationship between obesity and component placement in the target zone (target ± 10°) for inclination and version. All statistical tests were two-sided with a significance level of 0.05. Differences in mean inclination and anteversion between obese and non-obese groups were 1.1° (p=0.02 and p=0.08, respectively), and not clinically significant. Inclination accuracy trended toward improvement for non-obese patients (p=0.06). Inclination precision was better for non-obese patients (p=0.006). Accuracy and precision for anteversion were equal between the two groups (p=0.19 and p=0.95, respectively). There was no relationship between obesity and placement of the acetabulum outside of the target ranges for inclination (p=0.13), anteversion (p=0.39) or both (p=0.99), with a trend toward more inclination outliers in obese patients versus non-obese patients (7.3% versus 3.9%). The observed differences in mean acetabular orientation angles were not clinically significant (< 5°), although inclination orientation was less accurate and precise for obese patients. In contrast to existing literature, we found no difference in the accuracy and precision with regard to anteversion in obese and non-obese patients. We propose that accurate superficial registration of landmarks in obese patients is achievable, and the use of imageless navigation likely improves acetabular positioning in obese and non-obese patients.
Surgeons often target the Lewinnek zone (40°±10° of inclination; 15°±10° of anteversion) for acetabular orientation during total hip arthroplasty (THA). However, matching native anteversion (20°-25°) may achieve optimal stability. The purpose of this study was to (1) determine incidence of early dislocation with increased target acetabular anteversion, and (2) report the accuracy of imageless navigation for achieving target acetabular position in a large, single-surgeon cohort. A posterolateral approach with soft tissue repair was performed in the 553 THA meeting the inclusion criteria. The same imageless navigation system was used for acetabular component placement in all THA. Target acetabular orientation was 40° ± 10° of inclination and 25° ± 10° of anteversion. Computer software was used to measure acetabular positioning on 6-week postoperative anteroposterior pelvic radiographs. Incidence of dislocation within 6 months of surgery was determined. Repeated measures multiple regression using the Generalised Estimating Equations approach was used to identify baseline patient characteristics (age, gender, BMI, primary diagnosis, and laterality) associated with component positioning outside of the targeted ranges for inclination and anteversion. Fisher exact tests were used to examine the relationship between dislocation and component placement in either the Lewinnek safe zone or the targeted zone. All tests were two-sided with a significance level of 0.05. Mean inclination was 42.2° ± 4.9°, and mean anteversion was 23.9° ± 6.5°. 82.3% of cups were placed within the target zone. Variation in anteversion accounted for 67.3% of outliers. Only body mass index was associated with inclination outside the target range (p = 0.017), and only female gender was associated with anteversion outside the target range (p = 0.030). Six THA (1.1%) experienced early dislocation, and 3 THA (0.54%) were revised for multiple dislocations. There was no relationship between dislocation and component placement in either the Lewinnek zone (p = 0.224) or the target zone (p = 0.287). This study demonstrates that increasing target acetabular anteversion using the posterolateral approach does not increase the incidence of early THA dislocation. However, the long-term effects on bearing surface wear and stability must be elucidated. The occurrence of instability even in patients within our target zone emphasises the importance of developing patient-specific targets for THA component alignment.
Conventional, extramedullary (EM) tibial alignment guides are only 65%–88% accurate in creating a tibial resection within 2° of perpendicular to the tibial mechanical axis in total knee arthroplasty (TKA). The purpose of this study was to compare the overall, tibial component alignment, and the surgeon's ability to achieve a specific, intraoperative goal for alignment between a portable, navigation system (KneeAlign™) and conventional, EM alignment guides. One hundred patients were enrolled in a prospective, randomized controlled study. Fifty patients received a TKA using the KneeAlign™ to perform the tibial resection, and 50 patients an EM alignment guide. Standing AP hip-to-ankle radiographs and lateral knee-to-ankle radiographs were obtained at the first, postoperative visit.Background:
Methods:
Successful total joint arthroplasty requires accruate and reproducible acetabular component position. Acetabular component malposition has been associated with complications inlcuding dislocation, implant loosening, and increased wear. Recent literature had demonstrated that high-volume fellowship trained arthroplasty surgeons are in the “safe zone” for cup inclination and anteversion only 47% of the time. (1) Computer navigation has improved accuracy and reproducibility but remains expensive and cumbersome to many hospital and physicians. Patient specific instrumentation (PSI) has been shown to be effective and efficient in total knee replacements. The purpose of this study was to determine in a cadaveric model the anteversion and inclination accuracy of acetabular guides compared to a pre-operitive plan. 8 fresh-frozen cadaveric pelvis specimens underwent Computer Tomography (CT) in order to create a 3D reconstruction of the acetabulum. Based on these 3D reconstruction, a pre-operative plan was made positioning the patient specific acetabulum guides at 40 degrees of inclination and 20 degrees of anteversion in the pelvis.(Figure 1) The guides were created based on the specific bony morphology of the acetabular notch and rim. The guides were created using a 3D printer which allowed for precise recreation of the virtual model. 7 cadaveric specimens underwent creation and implantation of a acetabular guide specific to each specimens bony morphology. Ligamentum, pulvinar, and labum were removed for each cadaver prior to implantation to prevent soft tissue obstruction. The guides were inserted into the acetabular notch with the final position based on the fit of the guide in the notch. (Figure 2) Post-implantation CT was then performed and inclination and anteversion of the implanted guide measured and compared to the preoperative plan.Introduction:
Methods:
Numerous studies have reported the importance of acetabular component positioning in decreasing dislocation rates, the risk of liner fractures, and bearing surface wear in total hip arthroplasty (THA). The goal of improving acetabular component positioning has led to the development of computer-assisted surgical (CAS) techniques, and several studies have demonstrated improved results when compared to conventional, freehand methods. Recently, a computed tomography (CT)-based robotic surgery system has been developed (MAKO™ Robotic Arm Interactive Orthopaedic System, MAKO Surgical Corp., Fort Lauderdale, FLA, USA), with promising improvements in component alignment and surgical precision. The purpose of this study was to compare the accuracy in predicting the postoperative acetabular component position between the MAKO™ robotic navigation system and an imageless, CAS system (AchieveCAS, Smith and Nephew Inc., Memphis, TN, USA). 30 THAs performed using the robotic navigation system (robotic cohort) were available for review, and compared to the most recent 30 THAs performed using the imageless, CAS system (CAS cohort). The final, intraoperative reading for acetabular abduction and anteversion provided by each navigation system was recorded following each THA. Einsel-Bild-Roentgen analysis was used to measure the acetabular component abduction and anteversion based on anteroposterior pelvis radiographs obtained at each patient's first, postoperative visit (Figure 1). Two observers, blinded to the treatment arms, independently measured all the acetabular components, and the results were assessed for inter-observer reliability. Comparing the difference between the final, intraoperative reading for both acetabular abduction and anteversion, and the radiographic alignment calculated using EBRA analysis, allowed assessment of the intraoperative predictive capability of each system, and accuracy in determining the postoperative acetabular component position. In addition, the number of acetabular components outside of the “safe zone” (40° + 10° of abduction, 15° + 10° of anteversion), as described by Lewinnek et al., was assessed. Lastly, the operative time for each surgery was recorded.Background:
Materials and Methods:
Wasted implants represent both an increased risk and cost to our healthcare system. In our institution, a sterilely packaged implant that is opened and not implanted is wasted in one out of 20 primary total knee replacement procedures. The cost of these wasted implants exceeds $1 million per year. We propose the introduction of a novel, computer based, e.Label and compatibility system to reduce implant-related medical errors and waste in total knee arthroplasty. We hypothesize that the implementation of this system will help reduce medical errors and wasted implants by improving and standardizing the visual markers and by ensuring that parts are compatible so that implant mismatches and inappropriate laterality are prevented. A software program was implemented which creates an e.Label for all components (Figure 1) and checks imbedded, manufacturer provided, compatibility charts to ensure that parts are of appropriate laterality, and are compatible with each other. Upon implementation, the program was studied prospectively for seven months and compared to a retrospective cohort in regards to number, type, and cost of wasted implants. Critical errors that were detected were also recorded.INTRODUCTION
METHODS
The aim of this study was to quantitatively analyze the amount coronal plane laxity in mid-flexion that occurs in a well-balanced knee with an elevated joint line of 4 mm. In the setting an elevated joint line, we hypothesized that we would observe an increased varus and/or valgus laxity throughout mid flexion. After obtaining IRB approval, nine fresh-frozen cadaver legs from hip-to-toe underwent TKA with a posterior stabilized implant (APEX PS, OMNIlife Science, Inc.) using a computer navigation system equipped with a robotic cutting-guide, in this controlled laboratory cadaveric study. After the initial tibial and femoral resections were performed, the flexion and extension gaps were balanced using navigation, and a 4 mm recut was made in the distal femur. The remaining femoral cuts were made, the femoral component was downsized by resecting an additional 4 mm of bone off the posterior condyles, and the polyethylene was increased by 4 mm to create a situation of a well-balanced knee with an elevated joint line. Real implants were used in the study to eliminate any inherent error or laxity in the trials. The navigation system was used to measure overall coronal plane laxity by measuring the mechanical alignment angle at maximum extension, 30, 45, 60 and 90 degrees of flexion, when applying a standardized varus/valgus load of 9.8 [Nm] across the knee using a 4 kg spring-load located at 25 cm distal to the knee joint line (Figure 1). Coronal plane laxity was defined as the absolute difference (in degrees) between the mean mechanical alignment angle obtained from applying a standardized varus and valgus stress at 0, 30, 45, 60 and 90 degrees. Each measurement was performed three separate times. Two tailed student t-tests were performed to analyze whether there was difference in the mean mechanical alignment angle at 0°, 30°, 45°, 60°, and 90° between the well balanced scenario and following a 4 mm joint line elevation with an otherwise well balanced knee.Introduction
Methods
Traditional methods of component positioning in total hip replacement (THR) utilize mechanical alignment guides which estimate position relative to the plane of the operating room table. However, variations in pelvic tilt alter the relationship between the anatomic plane of the pelvis and that of the table such that components placed in optimal position relative the table may not land within the classic anatomic “safe zone” described by Lewinnek. It has been suggested that navigation software should incorporate adjustments for the degree of pelvic tilt. Current imageless navigation software has this capability, however there is a paucity of data regarding the accuracy of this technology. We aimed to assess the accuracy of intra-operative pelvic tilt adjusted anteversion measurements as compared to unadjusted measurements.Introduction
Purpose
Computer assisted surgery (CAS) systems have been shown to improve alignment accuracy in total knee arthroplasty (TKA), yet concerns regarding increased costs, operative times, pin sites, and the learning curve associated with CAS techniques have limited its widespread acceptance. The purpose of this study was to compare the alignment accuracy of an accelerometer-based, portable navigation device (KneeAlignÒ 2) to a large console, imageless CAS system (AchieveCAS). Our hypothesis is that no significant difference in alignment accuracy will be appreciated between the portable, accelerometer-based system, and the large-console, imageless navigation system. 62 consecutive patients, and a total of 80 knees, received a posterior cruciate substituting TKA using the Achieve CAS computer navigation system. Subsequently, 65 consecutive patients, and a total of 80 knees, received a posterior cruciate substituting TKA using the KneeAlignÒ 2 to perform both the distal femoral and proximal tibial resections (femoral guide seen in Figure 1, and tibial guide seen in Figure 2). Postoperatively, standing AP hip-to-ankle radiographs were obtained for each patient, from which the lower extremity mechanical axis, tibial component varus/valgus mechanical alignment, and femoral component varus/valgus mechanical alignment were digitally measured. Each measurement was performed by two, blinded independent observers, and interclass correlation for each measurement was calculated. All procedures were performed using a thigh pneumatic tourniquet, and the total tourniquet time for each procedure was recorded.Introduction
Methods
The aim of this study was to quantitatively analyze the amount coronal plane laxity in mid-flexion that occurs with a loose extension gap in TKA. In the setting of a loose extension gap, we hypothesized that although full extension is achieved, a loose extension gap will ultimately lead to increased varus and/or valgus laxity throughout mid flexion. After obtaining IRB approval, six fresh-frozen cadaver legs from hip-to-toe underwent TKA with a posterior stabilized implant (APEX PS OMNIlife Science, Inc.) using a computer navigation system equipped with a robotic cutting-guide, in this controlled laboratory cadaveric study. After the initial tibial and femoral resections were performed, and the flexion and extension gaps were balanced using navigation, a 4 mm distal recut was made in the distal femur to create a loose extension gap (using the same thickness of polyethylene as the well-balanced case). Real implants were used in the study to eliminate error in any laxity inherent to the trials. The navigation system was used to measure overall coronal plane laxity by measuring the mechanical alignment angle at maximum extension, 30, 45, 60 and 90 degrees of flexion, when applying a standardized varus/valgus load of 9.8 [Nm] across the knee using a 4 kg spring-load located at 25 cm distal to the knee joint line. (Figure 1). Coronal plane laxity was defined as the absolute difference (in degrees) between the mean mechanical alignment angle obtained from applying a standardized varus and valgus stress at 0, 30, 45, 60 and 90 degrees. Each measurement was performed three separate times. Two tailed student t-tests were performed to analyze whether there was difference in the mean mechanical alignment angle at 0°, 30°, 45°, 60°, and 90° between the well balanced scenario and following a 4 mm recut in the distal femur creating a loose extension gap.Introduction
Methods
The aims of this study were: 1) to quantitatively analyse the amount of knee extension that is achieved with +2mm incremental increases in the amount of distal femoral bone that is resected during TKA in the setting of a flexion contracture, 2) to quantify the amount of coronal plane laxity that occurs with each 2mm increase in the amount of distal femur resected. In the setting of a soft tissue flexion contracture, we hypothesized that although resecting more distal femur will reliably improve maximal knee extension, it will ultimately lead to increased varus and/or valgus laxity throughout mid-flexion. Seven fresh-frozen cadaver legs from hip-to-toe underwent TKA with a posterior stabilized implant using a measured resection technique with computer navigation system equipped with a robotic cutting-guide, in this IRB approved, controlled laboratory study. After the initial tibial and femoral resections were performed, the posterior joint capsule was sutured (imbricated) through the joint space under direct visualization until a 10° flexion contracture was obtained with the trial components in place, as confirmed by computer navigation. Two distal femoral recuts of +2mm each where then subsequently made and after the remaining femoral cuts were made, the trail implants were reinserted. The navigation system was used to measure overall coronal plane laxity by measuring the mechanical alignment angle at maximum extension, 30°, 60° and 90° of flexion, when applying a standardized varus/valgus load of 9.8 [Nm] across the knee using a 4kg spring-load located at 25cm distal to the knee joint line.(Figure 1) Coronal plane laxity was defined as the absolute difference (in °) between the mean mechanical alignment angle obtained from applying a standardized varus and valgus stress at 0°, 30, 60° and 90°. Each measurement was performed three separate times and averaged. The maximal extension angle achieved following each 2mm distal recut was also recorded. Two-tailed student's t-tests were performed to analyze whether there was difference in the mean laxity at each angle and if there was a significant improvement in maximal extension with each recut. P-values < 0.05 were considered significant.Aims/Hypothesis
Methods
Our aim was to compare the passive kinematics and coronal plane stability throughout flexion in the native and the replaced knee, using three different TKA designs: posterior stabilized (PS), bi-cruciate substituting (BCS), and ultracongruent (UC). Our hypotheses were: 1.) a guided motion knee replacement (BCS) offers the closest replication of native knee kinematics in terms of femoral rollback 2.) the replaced knee will be significantly more stable in the coronal plane than the native knee; 3.) No difference exists in coronal plane stability between the 3 implants/designs throughout flexion. After IRB approval, two cadaveric specimens were used for a pilot study to determine sample size. Five fresh-frozen hip-to-toe cadaveric specimens then underwent TKA using an anatomic measured resection technique with a computer-navigated robotic femoral cutting-guide. The PS, BCS, and UC TKA designs were implanted in each knee using the same distal and posterior femoral cuts to standardize the position of the implants. Computer navigation was then utilized to record the varus/valgus laxity of each implant at 0°, 30°, 60° and 90° of flexion while applying a standardized 9.8Nm moment. Passive tibiofemoral kinematics were measured in a continuous passive motion machine from 10° to 110°. Femoral rollback on the tibia was calculated for the native and replaced knees by measuring the closest point (CP) on the femoral condyle to a transverse plane perpendicular to the mechanical axis of the tibia at each flexion angle.Purpose
Methods
