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.
Acetabular cup malpositioning has been implicated in instability and wear-related complications after total hip arthroplasty. Although computer navigation and robotic assistance have been shown to improve the precision of implant placement, most surgeons use mechanical and visual guides to place acetabular components. Authors have shown that, when using a bean bag positioner, mechanical guides are misleading as they are unable to account for the variability in pelvic orientation during positioning and surgery. However, more rigid patient positioning devices may allow for more accurate free hand cup placement. To our knowledge, no study has assessed the ability of rigid devices to afford surgeons with ideal pelvic positioning throughout surgery. The purpose of this study is to utilize robotic-arm assisted computer navigation to assess the reliability of pelvic position in total hip arthroplasty performed on patients positioned with rigid positioning devices. 100 hips (94 patients) prospectively underwent total hip Makoplasty in the lateral decubitus position from the posterior approach; 77 stabilized by universal lateral positioner, and 23 by peg board. After dislocation but prior to reaming, one fellowship trained arthroplasty surgeon manually placed the robotic arm parallel to both the longitudinal axis of the patient and the horizontal surface of the operating table, which, if the pelvis were oriented perfectly, would represent 0 degrees of anteversion and 0 degrees of inclination. The CT-templated computer software then generated true values of this perceived zero degrees of anteversion and inclination based on the position of the robot arm registered to a preoperative pelvic CT. Therefore, variations in pelvic positioning are represented by these robotic navigation generated values. To assure the accuracy of robotic measurements, cup anteversion and inclination at times of impaction were recorded and compared to those calculated via the trigonometric ellipse method of Lewinnek on standardized 3 months postoperative X-rays.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
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.
