Containment versus impingement: finding a compromise for cup placement in total hip arthroplasty

Evaluation of range of motion restriction within the hip joint

In total hip arthroplasty, determining the impingement free range of motion requirement is a complex task. This is because in the native hip, motion is restricted by both impingement as well as soft tissue restraint. The aim of this study is to determine a range of motion benchmark which can identify motions which are at risk from impingement and those which are constrained due to soft tissue. Two experimental methodologies were used to determine motions which were limited by impingement and those motions which were limited by both impingement and soft tissue restraint. By comparing these two experimental results, motions which were limited by impingement were able to be separated from those motions which were limited by soft tissue restraint. The results show motions in extension as well as flexion combined with adduction are limited by soft tissue restraint. Motions in flexion, flexion combined with abduction and adduction are at risk from osseous impingement. Consequently, these motions represent where the maximum likely damage will occur in femoroacetabular impingement or at most risk of prosthetic impingement in total hip arthroplasty.

Validation of the femoral anteversion measurement method used in imageless navigation

Total hip arthroplasty restores lost mobility to patients suffering from osteoarthritis and acute trauma. In recent years, navigated surgery has been used to control prosthetic component placement. Furthermore, there has been increasing research on what constitutes correct placement. This has resulted in the definition of a safe-zone for acetabular cup orientation. However, there is less definition with regard to femoral anteversion and how it should be measured. This study assesses the validity of the femoral anteversion measurement method used in imageless navigation, with particular attention to how the neutral rotation of the femur is defined. CT and gait analysis methodologies are used to validate the reference which defines this neutral rotation, i.e., the ankle epicondyle piriformis (AEP) plane. The findings of this study indicate that the posterior condylar axis is a reliable reference for defining the neutral rotation of the femur. In imageless navigation, when these landmarks are not accessible, the AEP plane provides a useful surrogate to the condylar axis, providing a reliable baseline for femoral anteversion measurement.

The association between Femoral Tilt and impingement-free range-of-motion in total hip arthroplasty

Background

There is a complex interaction among acetabular component position and antetorsion of the femoral stem in determining the maximum, impingement-free prosthetic range-of-motion (ROM) in total hip arthroplasty (THA). By insertion into the femoral canal, stems of any geometry follow the natural anterior bow of the proximal femur, creating a sagittal Femoral Tilt (FT). We sought to study the incidence of FT as measured on postoperative computed tomography scans and its influence on impingement-free ROM in THA.

Methods

The incidence of the postoperative FT was evaluated on 40 computed tomography scans after cementless THA. With the help of a three-dimensional computer model of the hip, we then systematically analyzed the effects of FT on femoral antetorsion and its influence on calculations for a ROM maximized and impingement-free compliant stem/cup orientation.

Results

The mean postoperative FT on CT scans was 5.7° ± 1.8°. In all tests, FT significantly influenced the antetorsion values. Re-calculating the compliant component positions according to the concept of combined anteversion with and without the influence of FT revealed that the zone of compliance could differ by more than 200%. For a 7° change in FT, the impingement-free cup position differed by 4° for inclination when the same antetorsion was used.

Conclusions

A range-of-motion optimized cup position in THA cannot be calculated based on antetorsion values alone. The FT has a significant impact on recommended cup positions within the concept of “femur first” or “combined anteversion”. Ignoring FT may pose an increased risk of impingement as well as dislocation.

Ultrasound-based computer navigation of the acetabular component: a feasibility study

INTRODUCTION

This feasibility study investigated the accuracy of anterior pelvic reference plane (APP) registration and acetabular cup orientation in two cadavers with different BMIs.

METHOD

Five observers each registered the APP five times in the 2 cadavers (BMIs: 32 kg/m(2) and 25 kg/m(2)) using an ultrasound-based navigation system. By comparison against the CT-derived reference landmarks, the errors in determining the individual landmarks defining the APP, as well as the resulting errors in the orientation of the APP and the acetabular cup orientation were determined.

RESULTS

Across all measurements obtained with the ultrasound navigation system, the errors in rotation and version in determining the APP were 0.5° ± 1.0° and -0.4° ± 2.0°, respectively. The cup abduction and anteversion errors determined from all measurements of the five investigators for both cadavers together were -0.1° ± 1.0° and -0.4° ± 2.7°, respectively. The data further demonstrated a high reproducibility of the measurements for the resulting cup adduction and anteversion angle.

CONCLUSION

Our preliminary results confirm that ultrasound navigation is a highly accurate tool that allows a reproducible registration of the APP and thereby enables accurate and precise intraoperative determination of the acetabular cup orientation also in patients with increased BMI.

Cup positioning in total hip arthoplasty: spatial alignment of the acetabular entry plane

PURPOSE

Correct cup positioning is one of the keys for successful total hip replacement. There are mechanical and computer assistant guides for correct cup positioning in the market. To optimize the cup positioning, the use of navigation systems is recommended. The aim of this study was to compare spatial orientation of the acetabulary entry plane in relation to tables plane which is used by mechanical guides as well as anterior pelvic plane used for cup orientation by navigation systems.

METHODS

CT raw data of 80 Caucasians (160 acetabuli) (done in supine position) with osteoartritic hips were collected. 3-D pelvic reconstruction was generated using Amira software (Visage Imaging Berlin, Germany). Anterior pelvic plane and acetabulary entry plane were defined by reliable anatomical landmarks. Spatial orientation were calculated by a custom made program code for the Amira software.

RESULTS

There were no differences between anterior pelvic plane and table's plane as well as spatial orientation of acetabulary entry plane of both acetabuli in relation to anterior pelvic plane or table's plane. Furthermore, there was no correlation between age, sex or body mass index and spatial orientation of the acetabulary entry plane as well.

CONCLUSIONS

The use of mechanical alignment guides for cup orientation during total hip arthroplasty based on table's plane in patient's supine position is a successful method to achieve proper cup orientation.

Minimally invasive computer-navigated total hip arthroplasty, following the concept of femur first and combined anteversion: design of a blinded randomized controlled trial

BACKGROUND

Impingement can be a serious complication after total hip arthroplasty (THA), and is one of the major causes of postoperative pain, dislocation, aseptic loosening, and implant breakage. Minimally invasive THA and computer-navigated surgery were introduced several years ago. We have developed a novel, computer-assisted operation method for THA following the concept of "femur first"/"combined anteversion", which incorporates various aspects of performing a functional optimization of the cup position, and comprehensively addresses range of motion (ROM) as well as cup containment and alignment parameters. Hence, the purpose of this study is to assess whether the artificial joint's ROM can be improved by this computer-assisted operation method. Second, the clinical and radiological outcome will be evaluated.

METHODS/DESIGN

A registered patient- and observer-blinded randomized controlled trial will be conducted. Patients between the ages of 50 and 75 admitted for primary unilateral THA will be included. Patients will be randomly allocated to either receive minimally invasive computer-navigated "femur first" THA or the conventional minimally invasive THA procedure. Self-reported functional status and health-related quality of life (questionnaires) will be assessed both preoperatively and postoperatively. Perioperative complications will be registered. Radiographic evaluation will take place up to 6 weeks postoperatively with a computed tomography (CT) scan. Component position will be evaluated by an independent external institute on a 3D reconstruction of the femur/pelvis using image-processing software. Postoperative ROM will be calculated by an algorithm which automatically determines bony and prosthetic impingements.

DISCUSSION

In the past, computer navigation has improved the accuracy of component positioning. So far, there are only few objective data quantifying the risks and benefits of computer navigated THA. Therefore, this study has been designed to compare minimally invasive computer-navigated "femur first" THA with a conventional technique for minimally invasive THA. The results of this trial will be presented as soon as they become available.

TRIAL REGISTRATION NUMBER

DRKS00000739.

Improving cup positioning using a mechanical navigation instrument

BACKGROUND

Although surgical navigation reduces the rate of malpositioned acetabular cups in total hip arthroplasty (THA), its use has not been widely adopted. As a result of our perceived need for simple and efficient methods of navigation, we developed a mechanical navigation device for acetabular cup orientation.

QUESTIONS/PURPOSES

We assessed accuracy of cup orientation (mean error of cup inclination and anteversion) of a novel mechanical navigation device, percentage of outliers, length of operation, and compared the results with a series of CT-based computer-assisted THAs.

METHODS

Cup orientation of 70 THAs performed using the mechanical navigation device was compared with a historical control group of 146 THAs performed using CT-based computer navigation. Postoperative cup orientation was measured using a validated two-dimensional/three-dimensional matching method. An outlier was defined outside a range of ± 10° from the planned inclination and/or anteversion.

RESULTS

Using the mechanical navigation device, we observed a decrease in the errors of inclination (1.3° ± 3.4° [range, -6.6° to 8.2°] versus 3.5° ± 4.2° [-12.7° to 6.9°]), errors of anteversion (1.0° ± 4.1° [-8.8° to 9.5°] versus 3.0° ± 5.8° [-11.8° to 19.6°]), percentages of outliers (0% versus 9.6%), and length of operation (112 ± 22 [78-184] minutes versus 132 ± 18 [90-197] minutes) compared with CT-based navigation.

CONCLUSIONS

Compared with CT-based surgical navigation, navigation of acetabular cup orientation using a mechanical device can be performed in less time, lower mean errors, and minimal equipment.

Effective incorporating spatial information in a mutual information based 3D-2D registration of a CT volume to X-ray images

This paper addresses the problem of estimating the 3D rigid poses of a CT volume of an object from its 2D X-ray projection(s). We use maximization of mutual information, an accurate similarity measure for multi-modal and mono-modal image registration tasks. However, it is known that the standard mutual information measures only take intensity values into account without considering spatial information and their robustness is questionable. In this paper, instead of directly maximizing mutual information, we propose to use a variational approximation derived from the Kullback-Leibler bound. Spatial information is then incorporated into this variational approximation using a Markov random field model. The newly derived similarity measure has a least-squares form and can be effectively minimized by a multi-resolution Levenberg-Marquardt optimizer. Experiments were conducted on datasets from two applications: (a) intra-operative patient pose estimation from a limited number (e.g. 2) of calibrated fluoroscopic images, and (b) post-operative cup orientation estimation from a single standard X-ray radiograph with/without gonadal shielding. The experiment on intra-operative patient pose estimation showed a mean target registration accuracy of 0.8mm and a capture range of 11.5mm, while the experiment on estimating the post-operative cup orientation from a single X-ray radiograph showed a mean accuracy below 2 degrees for both anteversion and inclination. More importantly, results from both experiments demonstrated that the newly derived similarity measures were robust to occlusions in the X-ray image(s).

Do large femoral heads reduce the risks of impingement in total hip arthroplasty with optimal and non-optimal cup positioning?

The purpose of this study was to assess whether large femoral heads (36-38 mm) improve the range of motion in total hip arthroplasty compared to standard (28-32 mm) femoral heads in the presence of optimal and non-optimal cup positioning. A mathematical model of the hip joint was generated by using a laser scan of a dried cadaveric hip. The range of motion was assessed with a cup inclination and anteversion of reference and with non-optimal cup positions. Large femoral heads increased the range of motion, compared to the 28-mm femoral head, in the presence of a hip prosthesis correctly implanted and even more so in the presence of non-optimal cup positioning. However, with respect to the 32-mm femoral head, large femoral heads showed limited benefits both in the presence of optimal and non-optimal cup positioning.

Computer-assisted total hip arthroplasty: coding the next generation of navigation systems for orthopedic surgery

This article outlines the scientific basis and a state-of-the-art application of computer-assisted orthopedic surgery in total hip arthroplasty (THA) and provides a future perspective on this technology. Computer-assisted orthopedic surgery in primary THA has the potential to couple 3D simulations with real-time evaluations of surgical performance, which has brought these developments from the research laboratory all the way to clinical use. Nonimage- or imageless-based navigation systems without the need for additional pre- or intra-operative image acquisition have stood the test to significantly reduce the variability in positioning the acetabular component and have shown precise measurement of leg length and offset changes during THA. More recently, computer-assisted orthopedic surgery systems have opened a new frontier for accurate surgical practice in minimally invasive, tissue-preserving THA. The future generation of imageless navigation systems will switch from simple measurement tasks to real navigation tools. These software algorithms will consider the cup and stem as components of a coupled biomechanical system, navigating the orthopedic surgeon to find an optimized complementary component orientation rather than target values intraoperatively, and are expected to have a high impact on clinical practice and postoperative functionality in modern THA.

Validation of a new method for determination of cup orientation in THA

Our goal was to validate accuracy, consistency, and reproducibility/reliability of a new method for determining cup orientation in total hip arthroplasty (THA). This method allows matching the 3D-model from CT images or slices with the projected pelvis on an anteroposterior pelvic radiograph using a fully automated registration procedure. Cup orientation (inclination and anteversion) is calculated relative to the anterior pelvic plane, corrected for individual malposition of the pelvis during radiograph acquisition. Measurements on blinded and randomized radiographs of 80 cadaver and 327 patient hips were investigated. The method showed a mean accuracy of 0.7 +/- 1.7 degrees (-3.7 degrees to 4.0 degrees) for inclination and 1.2 +/- 2.4 degrees (-5.3 degrees to 5.6 degrees) for anteversion in the cadaver trials and 1.7 +/- 1.7 degrees (-4.6 degrees to 5.5 degrees) for inclination and 0.9 +/- 2.8 degrees (-5.2 degrees to 5.7 degrees) for anteversion in the clinical data when compared to CT-based measurements. No systematic errors in accuracy were detected with the Bland-Altman analysis. The software consistency and the reproducibility/reliability were very good. This software is an accurate, consistent, reliable, and reproducible method to measure cup orientation in THA using a sophisticated 2D/3D-matching technique. Its robust and accurate matching algorithm can be expanded to statistical models.

Activities of daily living after total hip arthroplasty. Is a 32-mm femoral head superior to a 26-mm head for improving daily activities?

Range of motion (ROM) of the hip joint after total hip arthroplasty (THA) could be increased by using a larger prosthetic femoral head, but it is not known whether the activities of daily living (ADL) are influenced by THA with different head sizes. Our objective was to compare postoperative ADL in patients who underwent THA using a head diameter of 26 mm or 32 mm. We assessed the range of motion and the mode of ADL after cementless primary THA. Comparison was performed between 25 joints of 24 patients who underwent THA with a 26-mm femoral head (26-mm group) and 24 joints of 20 patients with a 32-mm head (32-mm group). The postoperative range of flexion and abduction was significantly larger in the 32-mm group than in the 26-mm group. With respect to the mode of performing selected ADL such as putting on and removing pants, socks, and cutting toenails, many patients adopted the compensatory position of lumbar flexion with hip flexion plus knee extension in the 26-mm group, while a majority of the patients from the 32-mm group employed the mode of hip flexion with knee flexion. Patients with the 32-mm head showed better postoperative ADL of the ipsilateral side compared with the 26-mm head.

Navigated cup implantation in hip arthroplasty

BACKGROUND AND PURPOSE

Many studies have suggested that navigation-based implantation can improve cup positioning in total hip arthroplasty (THA). We conducted a systematic review and meta-analysis to compile the best available evidence, and to overcome potential shortcomings because of small sample sizes in individual studies.

METHODS

The search strategy covered the major medical databases from January 1976 through August 2007, as well as various publishers' databases. The internal validity of individual studies was evaluated independently by 3 reviewers. We used random-effects modeling to obtain mean differences in cup angulation and relative risk (RR) of cup positioning outside Lewinnek's safe zone.

RESULTS

Of 363 citations originally identified, 5 trials of moderate methodology enrolling a total of 400 patients were included in the analysis. Mean cup inclination and anteversion were not statistically significantly different between the conventional groups and the navigated groups. Navigation reduced the variability in cup positioning and the risk of placing the acetabular component beyond the safe zone (RR = 0.21, CI: 0.13-0.32).

INTERPRETATION

Based on the current literature, navigation is a reliable tool to optimize cup placement, and to minimize outliers. However, long-term outcomes and cost utility analyses are needed before conclusive statements can be drawn about the value of routine navigation in THA.

Cup positioning in THA: current status and pitfalls. A systematic evaluation of the literature

The correct determination of cup orientation in THA regarding the intraoperative as well as the postoperative assessment due to the pelvic tilt and rotation with inexact incorporation of the pelvis is uncertain. The anterior pelvic plane (APP) seems to be the most reliable reference frame and computer-assisted navigation systems seem to provide the best tool for correct implantation to date. For the intraoperative assessment of the APP, the exact determination of the bony landmarks is mandatory. For the standard plain radiography, standardized positioning of the patient and approximation of pelvic tilt by a lateral view are mandatory. An additional CT must be carried out for certain indications. More emphasis has to be given to the individuality of pelvic tilt and range of motion.

Optimal orientation of implanted components in total hip arthroplasty with polyethylene on metal articulation

BACKGROUND

In many studies related to the total hip arthroplasty, it has been found that incorrect alignment of the total hip component is one of the major factors influencing mechanical failures. Although various recommendations for cup orientation have been presented, there were few studies that seek to determine a proper orientation of the implants based on the human motion data. The objective of this study is to determine an optimum orientation of the hip implant considering various daily activities.

METHODS

Firstly, the cup orientations free of impingement were calculated for a given set of implant geometric parameters and the required range of motion for daily activities measured in 10 subjects. Next, the optimum values for the cup orientation and stem anteversion avoiding impingement and minimizing cup wear were determined for the proposed motion criteria.

FINDINGS

Different cup orientation was obtained as optimum for each combination of the neck angles (40 degrees and 50 degrees) and oscillation angles (120 degrees and 135 degrees). The corresponding optimum stem anteversion was also different when different neck angle was used.

INTERPRETATION

As the margin for the impingement-free orientation of the cup was small, the optimum cup orientation and stem anteversion should be adopted specific for each combination of the neck angle and oscillation angle.