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

Early failure of a highly cross-linked polyethylene inlay after total hip arthroplasty probably due to insufficient irradiation

Highly cross-linked polyethylene (XLPE) is a major advance in total hip arthroplasty (THA), as it suffers from less wear and thus is associated with lower revision rates than standard ultra-high molecular weight polyethylene. Early failures are reported rarely, and associated with specific design or manufacturing issues. We report a case requiring early revision due to adverse reaction to polyethylene particles. Investigations identified insufficient irradiation as the most probable cause of failure. Here are reported the features of a clinical case with determination of the material properties of the retrieved XLPE liner and establishment of the appropriate calibration curves as reference. Periprosthetic joint infection could be ruled out with appropriate sampling as cause for the inflammatory periarticular tumour. Histology identified a massive macrophagic reaction to micrometric polyethylene particles. No component malposition was present, nor any third-body wear. The trans-vinylene index (TVI) indicated insufficient and potentially detrimental irradiation of the polyethylene, while gel content, crystallinity, melting temperature and oxidation index remained within expected ranges. Histologically proven failure of a XLPE THA liner was identifiable despite correct implantation of the components. The cause of failure most probably was an inadequate irradiation, as indicated by determination of the TVI. This case underscores the importance of histologic workup even in aseptic revisions, and of detailed analysis of retrievals. The calibration curves provided are essential for analysis of other retrievals.

Subject-Specific Surgical Planning for Hip Replacement: A Novel 2D Graphical Representation of 3D Hip Motion and Prosthetic Impingement Information

Prosthetic impingement (PI) following total hip arthroplasty (THA), which arises due to the undesirable relative motion of the implants, results in adverse outcomes. Predicting PI through 3D graphical representation is difficult to comprehend when all activities are combined for different implant positions. Therefore, the aim of the paper was to translate this 3D information into a 2D graphical representation for improved understanding of the patient’s hip motion. The method used planned implanted geometry, positioned onto native bone anatomy, and activity definitions as inputs to construct the 2D polar plot from 3D hip motion in four steps. Three case studies were performed to highlight its potential use in (a) combining different activities in a single plot, (b) visualising the effect of different cup positions and (c) pelvic tilt on PI. A clinical study with 20 ‘Non-Dislocators’ and 20 ‘Dislocators’ patients after 2 years of THA was performed to validate the method. The results supported the study hypothesis, in that the incidence of PI was always higher in the ‘Dislocators’ compared to the ‘Non-Dislocators’ group. The proposed 2D graphical representation could assist in subject-specific THA planning by visualising the effect of different activities, implant positions, pelvic tilt and related aspects on PI.

What is the tolerated width of periacetabular osteophytes to avoid impingement in cementless THA?: a three-dimensional simulation study

BACKGROUNDS

Impingement is a risk factor for instability and prosthetic failure following total hip arthroplasty (THA). If the periacetabular osteophytes are not removed at surgery, impingement could occur between the osteophytes and the femoral stem following THA. However, excessive removal of the osteophytes could lead to bleeding from the bone. The aim of our study, therefore, was to locate the site of the impingement and to determine the width of tolerable osteophytes, which does not induce impingement during activities of daily living (ADL), using a three-dimensional simulation.

METHODS

On 35 hip models, virtual THA was performed. The acetabular cups were positioned at 45° abduction and 20° anteversion, and the anteversion of femoral stems was 15°. Circular osteophytes with a 30-mm rim were built around the acetabular cup. Fourteen ADL motions were simulated, and the osteophytes were removed until there was no impingement. A clock face was used to map the location and the width of tolerable osteophytes.

RESULTS

The impingement mainly occurred in antero-superior and posterior portions around the acetabular cup. Only 4.2-6.2-mm osteophytes were tolerable at the antero-superior portion (12-3 o'clock) and 6.3-7.2-mm osteophytes at the posterior portion (8-10 o'clock) following a total hip arthroplasty. In antero-inferior and postero-superior portions, over-20-mm osteophytes did not induce any impingement.

CONCLUSION

Osteophytes in the antero-superior and posterior portion of the acetabulum should be excised during a THA to avoid impingement of the femur-stem construct on the acetabular osteophytes during ADLs.

Biomechanical model based evaluation of Total Hip Arthroplasty therapy outcome

OBJECTIVE

Total-hip-arthroplasties are performed to treat patients with osteoarthritis. Surgical planning is usually based on specific radiographs. These information could also be used as data for biomechanical modelling.

METHODS

Models are rarely used during clinical practice. Our aim was to analyze model-based the pre- and postoperatively hip-biomechanic. Pre- and postoperative X-rays of 30 patients were examined by using 4 biomechanical-models.

RESULTS

The received results showed variations e.g. an increase and decrease of hip-load pre- and postoperative.

CONCLUSION

With the data of these models it would be possible to integrate the amplitude and orientation of the hip-joint-resultant-force into the therapeutical approach.

Effect of femoral neck modularity upon the prosthetic range of motion in total hip arthroplasty

In total hip arthroplasty, aseptic loosening and dislocation are associated with not being able to achieve the correct prosthetic component orientation. Femoral neck modularity has been proposed as a solution to this problem by allowing the surgeon to alter either the neck-shaft or version angle of the prosthetic femoral component intra-operatively. A single replicate full factorial design was used to evaluate how effective a modular femoral neck cementless stem was in restoring a healthy prosthetic range of motion in comparison with a leading fixed-neck cementless stem with the standard modular parameters. It was found that, if altered to a large enough degree, femoral neck modularity can increase the amount of prosthetic motion as well as alter its position to where it is required physiologically. However, there is a functional limit to the amount that can be corrected and there is a risk with regard to the surgeon having to select the optimum modular neck before any benefit is realised.

An in vivo comparison of the orientation of the transverse acetabular ligament and the acetabulum

Aligning the acetabular component with the Transverse Acetabular Ligament (TAL) to ensure optimal anteversion has been reported to reduce dislocation rates. However, to our knowledge in vivo measurement of the TAL angle has not yet been reported in a large cohort of normal hips. CT scans of 218 normal hips were analyzed. The TAL and four acetabular rim anteversion angles were measured (superiorly to inferiorly) relative to the anterior pelvic plane. The mean TAL anteversion angle was 20.5° ± 7.0°, and the acetabular rim angles from superior to inferior were 11.0° ± 12.9°, 19.9° ± 8.8°, 20.9° ± 6.2° and 25.1° ± 6.2° respectively. Both the TAL and the acetabular rim were significantly more anteverted in females than in males. The TAL anteversion angle was comparable to the predominant orientation (central rim section) of the native acetabulum while the superior acetabulum was comparatively retroverted and the inferior was relatively more anteverted.

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.

Effects of design parameters of total hip components on the impingement angle and determination of the preferred liner skirt shape with an adequate oscillation angle

The oscillation angle (OsA), which is the sum of the impingement angles on the two sides when the prosthetic neck sways from the neutral axis of the acetabular cup to the liner rim, is one of the most important factors that can affect the range of motion of an artificial hip joint. The aim of this study was to determine the influence of total hip component design on the impingement angle. Our findings show that an increase in cup depth of the liner restricts the motion of the neck and results in a reduced impingement angle, while an increase in chamfer angle increases the impingement angle until it reaches a critical value when a further increase no longer results in an increase in impingement angle. The impingement angle is not only dependent on the head/neck ratio, but also on the head size itself. For most arbitrarily chosen cup depths and chamfer angles, the neck only impacts at one point on the liner. This study proposes a suitable combination of cup depth and chamfer angle and a preferred impact mode, which, if impingement does occur, enables the neck to impinge on the liner rim over a large area. Cup-neck combinations that have an adequate OsA with maximum femoral head coverage are presented.

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.

Use of an ultrasound-based navigation system for an accurate acetabular positioning in total hip arthroplasty: a prospective, randomized, controlled study

The purpose of this study was to compare an ultrasound-based navigation system with an imageless navigation system with surface registration in the postoperative acetabular cup position. A prospective randomized controlled study of 2 groups of 40 patients each was performed. In the first group, cup positioning was assisted by an ultrasound-based navigation system, and in the second group, the cup was assisted by imageless navigation system with surface registration. There was significantly more outliers in the imageless navigation group. In addition, there was statistical significance in the anteversion angles and in the anteversion error between the imageless navigation and ultrasound-based navigation groups. Ultrasound-based navigation improves cup positioning in total hip arthroplasty better than an imageless navigation system by reducing the outliers, achieving a higher accuracy of anteversion.

Establishing a range of motion boundary for total hip arthroplasty

Range of motion of the hip joint is a major contributor to dislocation post total hip replacement. Impingement is often treated as a surrogate for dislocation and occurs – prosthetically – when the neck of the femoral component contacts with the rim of the pelvic acetabular cup. This impingement is caused by movement of the leg during activities of daily living. This article analyses hip joint range of motion and its implication for impingement. A systematic literature review was undertaken with the purpose of establishing a range of motion benchmark for total hip replacement. This paper proposes a method by which a three-dimensional range of motion boundary established from the literature can be presented. The nominal boundary is also validated experimentally using a number of configurations of a neutral hip joint coordinate frame.

A three-dimensional parameterized and visually kinematic simulation module for the theoretical range of motion of total hip arthroplasty

BACKGROUND

Proper option and optimal alignment of implants are major factors in obtaining the desired range of motion of total hip arthroplasty. It would be very useful if a tool is available to assist clinicians to preoperatively determine proper implants and their optimal intraoperative alignment for individual patient.

METHODS

Based on the secondary development function of ADAMS/VIEW, a three-dimensional parameterized module was developed to simulate six motions of implants for total hip arthroplasty. Total eight parameters (stem abduction, acetabular size, head size, general head-neck ratio, stem-neck angle, acetabular anteversion, acetabular inclination and femoral antetorsion) were included and three definitions of acetabular orientations (operative, radiographic and anatomical) were available. Any initial position of implants and simulation precision could be defined on the demand.

FINDINGS

After entering these eight parameters, a special model of total hip arthroplasty would be constructed. Single or combined motion until the prosthetic impingement could be simulated visually and the corresponding maximal rotation angle would be quantified.

INTERPRETATION

Clinical factors, such as patients with severe deformity of hip joint or a large range of motion demand, should be considered during total hip arthroplasty. This module can provide references for clinicians on proper option and intraoperative implantation of components, and be suitable for postoperative evaluation. Furthermore, it is a tool to investigate the "safe-zones" of total hip arthroplasty and also can be employed for the design of new implant system.