Surgeons commonly resect additional distal femur during primary total knee arthroplasty (TKA) to correct a flexion contracture to restore range of motion and knee function. However, the effect of joint line elevation on the resulting TKA kinematics including frontal plane laxity is unclear. Thus, our goal was to quantify the effect of additional distal femoral resection on passive extension and mid-flexion laxity. Six computational knee models with capsular and collateral ligament properties specific to TKA were developed and implanted with a contemporary posterior-stabilized TKA. A 10° flexion contracture was modeled by imposing capsular contracture as determined by simulating a common clinical exam of knee extension and accounting for the length and weight of each limb segment from which the models were derived (Figure 1). Distal femoral resections of 2 mm and 4 mm were simulated for each model. The knees were then extended by applying the measured knee moments to quantify the amount of knee extension. The output data were compared with a previous cadaveric study using a two-sample two-tailed t-test (p<0.05) [1]. Subsequently, varus and valgus torques of ±10 Nm were applied as the knee was flexed from 0° to 90° at the baseline, and after distal resections of 2 mm, and 4 mm. Coronal laxity, defined as the sum of varus and valgus angulation in response to the applied varus and valgus torques, was measured at 30° and 45°of flexion, and the flexion angle was identified where the increase in laxity was the greatest with respect to baseline.Introduction
Methods
In total knee arthroplasty (TKA), tibial insert thickness is determined intraoperatively by applying forces that generate varus-valgus moments at the knee and estimating the resulting gaps. However, how the magnitude of applied moments and the surgeon's perception of gaps affect the thickness selection is unclear. We determined this relationship using an in vitro human cadaveric model. Six pelvis-to-toe specimens (72±6 years old, four females) were implanted by an expert surgeon with a PS TKA using measured resection. Pliable sensors were wrapped around medial and lateral aspects of the foot and ankle to measure the applied forces. The forces were scaled by limb length to obtain the moments generated at the knee. Six surgeons with different experience levels independently assessed balance by applying moments in extension and 90° of flexion and choosing the insert they believed fit each knee. Peak moments and the accompanying extension and flexion gap openings as perceived by surgeons were recorded. The two measures were then related to insert choice using a generalized estimating equation.Introduction
Methods
Variation in pelvic tilt during postural changes may affect functional alignment. The primary objective of this study was to quantify the changes in lumbo-pelvic-femoral alignment from sitting to standing in patients undergoing THA. 144 patients were enrolled. Standing and sitting radiographs using the EOS imaging system were analyzed preoperatively and 1-year postoperatively. Pelvic incidence (PI), lumbar lordosis (LL), sacral slope (SS), proximal femoral angle (PFA) and spine/femoroacetabular flexion were determined. 38 patients had multilevel DDD (26%). Following THA, patients sat with increased anterior pelvic tilt demonstrated by a significant increase in sitting lumbar lordosis (28° preop vs 35° postop; p<0.01) and sacral slope (18° vs 23°; p<0.01). Following THA, patients flexed less through their spines (preop 26° vs postop 19°; p<0.01) and more through their hips (femoroacetabular flexion) (preop 60° vs postop 67°; p<0.01) to achieve sitting position. Patients with multilevel DDD sat with less spine flexion (normal 22° vs spine 13°; p<0.01), less change in sacral slope (more relative anterior tilt) (17° vs 9°; p<0.01), and more femoroacetabular flexion (64° vs 71°; p<0.01). For the majority of patients after THA, a larger proportion of lumbo-pelvic-femoral flexion necessary to achieve a sitting position is derived from femoroacetabular flexion with an associated increase in anterior pelvic tilt and a decrease in lumbar spine flexion. These changes are more pronounced among patients with multilevel DDD. Surgeons may consider orienting the acetabular component with greater anteversion and inclination in patients identified preoperatively to have anterior pelvic tilt or significant DDD.
Total hip arthroplasty (THA) is an effective operation for patients with hip osteoarthritis; however, patients with hip dysplasia present a particular challenge. Our novel study examined the effect of robotic-assisted THA in patients with hip dysplasia.. Nineteen patients at two centers presented with hip dysplasia. We found that components were placed according to the preoperative plan, there was a significant improvement in the modified Harris Hip Score from 31 to 84 (p<0.001), an improvement in hip range of motion (flexion improvement from 66 º to 91º, p<0.0001), a significant correction of leg length discrepancy (17.5 vs. 4 mm, p<.0002), and no short-term complications.. Robotic-assisted THA can be a useful method to ensure adequate component positioning and excellent outcomes in patients with hip dysplasia.
Neutral mechanical alignment in TKA has been shown to be an important consideration for survivorship, wear, and aseptic loosening. However, native knee anatomy is described by a joint line in 3° of varus, 2–3° of mechanical distal femoral valgus, and 2–3° of proximal tibia varus. Described kinematic planning methods replicate native joint alignment in extension without changing tibiofemoral alignment, but do not account for native alignment through a range of motion. An asymmetric TKA femoral component with a thicker medial femoral condyle and posterior condylar internal rotation paired with an asymmetric polyethylene insert aligns the joint line in 3° of varus while maintaining distal femoral and proximal tibial cuts perpendicular to mechanical axis. The asymmetric components recreate an anatomic varus joint line while avoiding tibiofemoral malalignment or femoral component internal rotation, a risk factor for patellofemoral maltracking. The study seeks to determine how many patients would be candidates for a kinematically planned knee without violating the principle of a neutral mechanical axis (0° ± 3°). A cohort comprised of 55 consecutive preoperative THA patients with asymptomatic knees and 55 consecutive preoperative primary unilateral TKA patients underwent simultaneous biplanar radiographic imaging. Full length coronal images from the thoracolumbar junction to the ankles were measured by two independent observers for the following: mechanical tibiofemoral angle (mTFA), mechanical lateral distal femoral angle (mLDFA), and mechanical medial proximal tibial angle (mMPTA). Patients who met the following conditions: mTFA 0°±3°; mLDFA 87°±3°; and mMPTA 87°±3°, were considered candidates for TKA with an asymmetric implant that would achieve a kinematic joint line and neutral mechanical axis. Similarly, patients with the following conditions: mTFA 0°±3°; mLDFA 90°±3°; and mMPTA 90°±3°, were considered candidates for TKA with a symmetric implant that would achieve a kinematic joint line and neutral mechanical axis.Introduction
Methods
The longevity of total hip arthroplasty (THA) is dependent on acetabular component position. We measured the reliability and accuracy of a CT-based navigation system to achieve the intended acetabular component position and orientation using three dimensional imaging. The purpose of the current study was to determine if the CT-guided robotic navigation system could accurately achieve the desired acetabular component position (center of rotation (COR)) and orientation (inclination and anteversion). The postoperative orientation and location of the components was determined in 20 patients undergoing THA using CT images, the gold standard for acetabular component orientation. Twenty primary unilateral THA patients were enrolled in this IRB-approved, prospective cohort study to assess the accuracy of the robotic navigation system. Pre- and post-operative CT exams were obtained and aligned 3D segmented models were used to measure the difference in center of rotation and orientation (anteversion and inclination). Patients with pre-existing implants, posttraumatic arthritis, contralateral hip arthroplasty, septic arthritis, or previous hip fracture were excluded. All patients underwent unilateral THA using robotic arm CT-guided navigation (RIO Makoplasty; MAKO Surgical Corp).Introduction
Methods
Medial unicompartmental knee arthroplasty (UKA) restores mechanical alignment and reduces lateral subluxation of the tibia. However, medial compartment translation remains abnormal compared to the native knee in mid-flexion Intra-operative adjustment of implant thickness can modulate ligament tension and may improve knee kinematics. However, the relationship between insert thickness, ligament loads, and knee kinematics is not well understood. Therefore, we used a computational model to assess the sensitivity of knee kinematics, and cruciate and collateral ligament forces to tibial component thickness with fixed bearing medial UKA. A computational model of the knee with subject-specific bone geometries, articular cartilage, and menisci was developed using multibody dynamics software (Fig 1a). The ligaments were represented with multiple non-linear, tension-only force elements, and incorporated mean structural properties. The 3D geometries of the femoral and tibial components of the Stryker Triathlon fixed-bearing UKA were captured using a laser scanner. An arthroplasty surgeon aligned the femoral and tibial components to the articular surfaces within the model (Fig 1b). The intact and UKA models were passively flexed from 0 to 90° under a 10 N compressive load. The tibial polyethylene insert was modeled by the orthopaedic surgeon to create a “balanced” knee. The modeled polyethylene insert thickness was then increased by 2 mm and decreased 2mm (in increments of 1mm) to simulate over- and under-stuffing, respectively. Outcomes were anterior-posterior (AP) translation of the femur on the tibia in the medial compartment, and forces seen by the ACL and MCL during mid-flexion (from 30 to 60° flexion). The mean differences between the intact knee model and all other experimental conditions for each outcome were calculated across mid-flexion.Introduction
Methods
While implant designs and surgical techniques have improved in total knee arthroplasty (TKA), approximately 20% of patients remain dissatisfied. The purpose of this study was to determine if reproduction of anatomic preoperative measurements correlated to improved clinical outcomes in TKA. We retrospectively reviewed95 patients (106 knees) who underwent a TKA between 2012 −2013 with a minimum of one year follow-up. All patients had a pre and post-operative SF-12 and WOMAC scores. Pre and 6 week post-operative radiographs were reviewed to compare restoration of coronal plane alignment, maintenance of joint line obliquity, and maintenance of tibial varus. Coronal alignment was defined as the angle formed between the mechanical axis of the femur and the the tibia. Joint line obliquity was defined as the angle between the mechanical axis of the limb and the line which best parallels the joint space at the knee. Tibial varus was compared between the preoperative proximal lateral tibial angle and the angle formed by the mechanical axis of the tibia and tibial component postoperatively.Introduction
Methods
Implant position plays a major role in the mechanical stability of a total hip replacement. The standard modality for assessing hip component position postoperatively is a 2D anteroposterior radiograph, due to low radiation dose and low cost. Recently, the EOS® X-Ray Imaging Acquisition System has been developed as a new low-dose radiation system for measuring hip component position. EOS imaging can calculate 3D patient information from simultaneous frontal and lateral 2D radiographs of a standing patient without stitching or vertical distortion, and has been shown to be more reliable than conventional radiographs for measuring hip angles[1]. The purpose of this prospective study was to compare EOS imaging to computer tomography (CT) scans, which are the gold standard, to assess the reproducibility of hip angles. Twenty patients undergoing unilateral THA consented to this IRB-approved analysis of post-operative THA cup alignment. Standing EOS imaging and supine CT scans were taken of the same patients 6 weeks post-operatively. Postoperative cup alignment and femoral anteversion were measured from EOS radiographs using sterEOS® software. CT images of the pelvis and femur were segmented using MIMICS software (Materialise, Leuven, Belgium), and component position was measured using Geomagic Studio (Morrisville, NC, USA) and PTC Creo Parametric (Needham, MA). The Anterior Pelvic Plane (APP), which is defined by the two anterior superior iliac spines and the pubic symphysis, was used as an anatomic reference for acetabular inclination and anteversion. The most posterior part of the femoral condyles was used as an anatomic reference for femoral anteversion. Two blinded observers measured hip angles using sterEOS® software. Reproducibility was analysed by the Bland-Altman method, and interobserver reliability was calculated using the Cronbach's alpha (∝) coefficient of reliability.Introduction
Materials and Methods
Sagittal pelvic tilt (PT) has been shown to effect the functional position of acetabular components in patients with total hip replacements (THR). This change in functional component position may have clinical implications including increased likelihood of wear or dislocation. Surgeons can use computer-assisted navigation intraoperatively to account for a patient's pelvic tilt and to adjust the position of the acetabular component. However, the accuracy of this technique has been questioned due to the concern that PT may change after THR. The purpose of this study was to measure the change in PT after THR, and to determine if preoperative clinical and radiographic parameters can predict PT changes after THR. 138 consecutive patients who underwent unilateral THR by one surgeon received standing bi-planar lumbar spine and lower extremity radiographs preoperatively and six weeks postoperatively. Patients with prior contralateral THR, conversion THR and instrumented lumbosacral fusions were excluded. PT and pelvic incidence (PI) were measured preoperatively for each patient, and PT was measured on the postoperative imaging. A negative value for PT indicated posterior pelvic tilt. Patient demographics were collected from the chart. Average age was 56.8±10.9 years, average BMI was 28.3±6.0 kg/m2, and 67 patients (48.6%) were female. Mean preoperative pelvic tilt was 0.6°±7.3° (range: −19.0° to 17.9°). We found greater than 10° of sagittal PT in 23 out of 138 (16.6%) patients in this sample. Mean post-operative pelvic tilt was 0.3°±7.4° (range: −18.4° to 15.0°). Mean change in pelvic tilt was −0.3°±3.6° (range: −9.6° to 13.5°). PT changed by less than 5° in 119 of 138 patients (86.2%). The mean difference in pre-operative and post-operative PT is not statistically significant (p = 0.395). Pre-operative PT was strongly correlated with post-operative PT (r2 = 0.88, p = 0.0001) (Figure 1). There was not a statistically significant relationship between PI and change in PT (r2 = −0.16, p = 0.06). In conclusion, based on the variability in pelvic tilt in this study population and the relatively small change in pelvic tilt following THA tilt-adjustment of the acetabular component position based on standing pre-operative imaging is likely to be of benefit in the majority of patients undergoing navigated THA. However, we have been unable to predict the relatively rare occurrence of a large change in pelvic tilt, which would confound tilt-adjusted component position.
The aim of this study was to quantify mid-flexion laxity in a total knee arthroplasty with an elevated joint line, as compared to a native knee and a TKA with joint line maintained. Our hypothesis was joint line elevation of 4mm would increase coronal plane laxity throughout mid-flexion in a pattern distinct from the preoperative knee or in a TKA with native joint line. Six fresh-frozen cadaver legs from hip-to-toe underwent TKA with a posterior stabilised 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 4mm recut was made in the distal femur. The remaining femoral cuts were made, the femoral component was downsized by resecting an additional 4mm of bone off the posterior condyles, and the polyethylene was increased by 4mm to create a situation of a well-balanced knee with an elevated joint line. 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(of flexion, when applying a standardised varus/valgus load of 9.8Nm across the knee using a 4kg spring-load located at 25cm distal to the knee joint line. Laxity was also measured in the native knee, as well as the native knee after a standard approach during TKA which included a medial release. Coronal plane laxity was defined as the absolute difference (in degrees) between the mean mechanical alignment angle obtained from applying a standardised varus and valgus stress at 0, 30, 45, 60 and 90(.Introduction
Methods
the mean medial gap was 1.5–2.5mm smaller than the mean lateral gap for all scenarios and forces tested (p<
0.05); everting the patella decreased the medial and lateral gaps by 1mm and 1.3mm with an intact PCL, and by 1mm and 2.7mm with the PCL resected, respectively; PCL resection resulted in increased flexion gap heights of ~1–2mm for both sides. During knee flexion from 30° to 90°, the PCL tended to squeeze the medial compartment by 1–2mm (p<
0.05). Increasing the force from 50N to 100N per side resulted in a mean gap increase of 0.5mm throughout the range of flexion.
A fluoroscopic based computer enhancement system was designed for accurate insertion of guide wires for hip fracture fixation while decreasing fluoroscopy time. A saw bone model was created. The femur was imaged with fluoroscopy and a three-dimensional computer model was created. The femur, fluoroscopy drum, and drill were tracked with an optical tracking device. Guide wire position was planned on the computer model. Using a tracked drill the guide wire was inserted. The number of fluoroscopic images was decreased by 85% and the number of passes required to place the guide wire in acceptable position was decreased by 60% using computer enhanced technique. A fluoroscopic based computer enhancement system was designed for accurate insertion of guide wires for hip fracture fixation while decreasing fluoroscopy time. The number of fluoroscopic images and passes required to place the guide wire in acceptable position were decreased using computer enhanced technique. Final guide wire position was not different between the two groups. Orthopedic surgeons are exposed to radiation from fluoroscopy on a daily basis. This system allowed us to insert guide wires using substantially less fluoroscopy, without compromising accuracy. An average of 13.5 images were taken for each standard technique trial compared to two images for each computer enhanced trial, representing a reduction in fluoroscopy of 85%. One pass was used for each computer enhanced trial. An average of 2.4 trials was used for standard technique. Average final error was 3.6mm using standard technique and 3.8mm using computer technique. A saw bone model with a soft tissue sleeve was created. A DRB (dynamic referencing body) was fixed to the femur. The DRB, fluoroscopy drum, and drill were tracked with an optical tracking device. The system created a 3D model from two orthogonal fluoroscopic images. Guide wire position was then planned on the computer model. Using a tracked drill the guide wire was inserted. Computer enhanced trials were compared to standard techniques in regards to number of fluoroscopic images taken, number of trials to obtain acceptable guide wire position, and accuracy of guide wire placement. Guide wire position was measured on AP and lateral x-rays.
Two computer assisted techniques (CT and a fluoro-guide based system) were used to insert the femoral component of the Oxford Unicompartmental Knee arthroplasty. The accuracy and variability of component positioning were compared. Clinical data was collected pre-operatively and is being collected post-operatively. Standing AP and lateral knee X-rays as well as skyline X-rays were collected pre-operatively and post-operative full length AP and lateral femur X-rays were completed in order to measure alignment of the femoral component. Results are showing accurate insertions of the Oxford knee femoral component using both systems. To review two computer-assisted techniques for inserting Oxford Unicompartmental Knee arthroplasties. CT based and fluro based techniques were compared with regards to accuracy and variability of component positioning. Currently we are able to use either a CT based system or a fluro based system to accurately insert the femoral component of the Oxford Unicompartmental Knee arthroplasty. Computer assist techniques are allowing us to perform minimally invasive arthroplasty procedures with great accuracy. Patients were all seen in a pre-admission clinic where pre-operative clinical survey data were collected. All patients had standing AP and lateral knee X-rays as well as skyline X-rays pre-operatively. Post-perative full length AP and lateral femur X-rays were completed in order to measure alignment of the femoral component. Patients are being followed post-operatively with SF-36, WOMAC, Knee Society Scores, and X-rays. Patients being operated on with the CT based system had pre operative CT scans. Intra-operatively a DRB was fixed to the patient’s femur and the chosen computer assisted technique was used to direct the rotation of the tibial cut as well as the alignment of the femoral cutting jig. To date we have completed seventeen computer assisted Oxford Unicompartmental Knee Arthroplasties. The average error in the AP plane using CT based system was 3.2 degrees and 2.1 degrees for the lateral plane. The average error in the AP plane using the fluro-based system was 2.2 degrees and 1.3 degree for the lateral plane.
Two computer assisted techniques (CT and a fluoro-guide based system) were used to insert the femoral component of the Oxford Unicompartmental Knee arthroplasty. The accuracy and variability of component positioning were compared. Clinical data was collected pre-operatively and is being collected post-operatively. Standing AP and lateral knee X-rays as well as skyline X-rays were collected pre-operatively and post-operative full length AP and lateral femur X-rays were completed in order to measure alignment of the femoral component. Results are showing accurate insertions of the Oxford knee femoral component using both systems. To review two computer-assisted techniques for inserting Oxford Unicompartmental Knee arthroplasties. CT based and fluro based techniques were compared with regards to accuracy and variability of component positioning. Currently we are able to use either a CT based system or a fluro based system to accurately insert the femoral component of the Oxford Unicompartmental Knee arthroplasty. Computer assist techniques are allowing us to perform minimally invasive arthroplasty procedures with great accuracy. Patients were all seen in a pre-admission clinic where pre-operative clinical survey data were collected. All patients had standing AP and lateral knee X-rays as well as skyline X-rays pre-operatively. Post-perative full length AP and lateral femur X-rays were completed in order to measure alignment of the femoral component. Patients are being followed post-operatively with SF-36, WOMAC, Knee Society Scores, and X-rays. Patients being operated on with the CT based system had pre operative CT scans. Intra-operatively a DRB was fixed to the patient’s femur and the chosen computer assisted technique was used to direct the rotation of the tibial cut as well as the alignment of the femoral cutting jig. To date we have completed seventeen computer assisted Oxford Unicompartmental Knee Arthroplasties. The average error in the AP plane using CT based system was 3.2 degrees and 2.1 degrees for the lateral plane. The average error in the AP plane using the fluro-based system was 2.2 degrees and 1.3 degree for the lateral plane.
