25th Annual and Anniversary Meeting of the European Orthopaedic Research Society (EORS)

Overview Session Overview Sessionprint print  

09/14/2017 - Room A 202 | 1:30pm - 2:30pm 
Hip II

Chairs: Feng-Sheng Wang (TW); Jan Gosiewski (UK)

Radiographic evaluation of the proximal femur in sickle cell disease patients
Abstract text :

Avascular necrosis of the femoral head develops in 3-19% of patients with sickle cell disease and frequently this is bilateral. Intravascular sickling causes thrombosis and then ischemia, resulting in infarcts in the femoral head which progress to avascular necrosis. Total hip replacement is therefore indicated in such patients. However various studies have shown high complication rates in these groups of patients. There is no documented structural reason in the shape of the proximal femur in sickle cell disease patients which may cause implant loosening. The following are the objectives of this study-to assess the variation in the proximal femoral canal anatomy in sickle cell disease patients and compare with established documented findings in normal population and to also deduce if structural reasons could be the cause for implant loosening rate in this group of patients.

METHODS The standardized anterior posterior radiographs of forty-two (42) sickle cell disease patients with degenerative hip osteoarthritis secondary to avascular necrosis and another identical cohort of forty-two (42) patients with primary degenerative hip OA were initially taken and evaluated on a standard imaging software.  The following measurements were noted-proximal femoral canal(Y), mid-diaphysis canal(X), extra medullary canal (Z) diameters- in millimetres (mm) .The calcar-canal ratio (CC) and the cortical index (CI) was calculated as described by Dorr .


THE SICKLE CELL GROUP:The mean cortical index (CI) was moderately high -0.65(0.38-0.83), while the mean calcar to canal (CC) ratio was low-0.49(0.27-0.89) Using independent sample t-test, there was no significant difference in the cortical index (CI) and calcar canal ratio (CC) for males and females. ( p=0.9 for CC: p value>0.05 and p=0.6 for CI: p value >0.05).

OSTEOARTHRITIC GROUP:The mean cortical index (CI) was 0.49(0.19-0.79) and calcar canal ratio (CC) was 0.47(0.32-0.89). Using the independent t-test, there was no statistical difference between male and female cortical indices (t value- 0.29; degree of freedom (df)-0.221: p-0.76) . There was also no statistical difference in the calcar canal ratios between both genders. ( t value-0.153;df-0.20, p-0.87 with p value >0.05)

According to Dorr classification of types of variations in proximal femoral anatomy-xray measurements which show higher cortical indices and lower calcar to canal ratios suggest funnel shaped proximal femurs. This is clearly seen in the above measurements deduced in this sample of sickle cell disease patients. Their funnel shaped proximal femur allows for good implant fixation for both cemented and uncemented stems. These results therefore imply that the structural anatomy of these patients proximal femurs does not contribute to implant loosening and so other reasons for this should be sought. 

The effect of subject-specific loading patterns on hip cartilage shear stress
*Mariska Wesseling, Sanne Vancleef, Christophe Meyer , Jos Vander Sloten, Ilse Jonkers
Abstract text :


Modification in joint loading, and specifically shear stress, is found to be an important mechanical factor in the development of osteoarthritis (OA). Cartilage shear stresses can be investigated using finite element (FE) modelling, where typically in vivo joint loading as measured by an instrumented hip prosthesis is used as boundary condition. However, subject-specific gait characteristics substantially affect joint loading. The goal of this study is to investigate the effect of subject-specific joint loading as calculated using a subject-specific musculoskeletal model and integrated motion capture data on acetabular shear stress.


Three healthy control subjects walked at self-selected speed while measuring marker trajectories (Vicon, Oxford Metrics, UK) and force data (two AMTI force platforms; Watertown, MA). A subject-specific MRI-based musculoskeletal model consisting of 14 segments, 19 degrees of freedom and 88 musculotendon actuators, and including wrapping surfaces around the hip joint, was used. All analyses were performed in OpenSim 3.1. The model was scaled to the dimensions of each subject using the marker positions of a static pose. A kalman smoother procedure was used to calculate joint angles. Muscle forces were calculated using static optimization, minimizing the sum of squared muscle activations, and hip contact forces (HCF) were calculated and normalized to body weight (BW). To calculate shear stress, HCFs and joint angles calculated during the stance phase of gait were imposed to a hip finite element model (hip_n10rb) using FFEbio 2.5. In the model, femoral and acetabular cartilage were represented using the Mooney-Rivlin formulation (c1=6.817, bulk modulus=1358.86) and the pelvis and femur bones as rigid bodies. Peak HCF as well as maximal acetabular shear stress, magnitude and location, and the HCF at the time of maximal shear stress were compared between subjects.


Maximal shear stress was lower for S3 compared to S1 and S2 (9.14, 9.48 and 7.14 MPa for S1, S2 and S3 respectively). Nevertheless, HCF at the time instance of peak stress as well as peak HCF were highest for S3 (S1: 2.40/4.54 BW, S2: 2.97/4.78 BW and S3: 3.13/6.46 BW respectively). Maximal shear stress also occurred earlier in the stance phase for S3 compared to S1 and S2 (31, 26 and 11% of the stance phase for S1, S2 and S3 respectively). In addition, the location of the peak maximal shear stress was found to be more superior for S3.


Subject-specific loading patterns clearly influence the calculated maximal shear stress in the acetabular cartilage, affecting both the magnitude and the location of the stress. In addition, higher shear stresses are not coinciding with higher HCFs. This finding highlights the need of subject-specific rather than generic loading patterns when assessing cartilage shear stresses and associated risk in OA development in individual patients.

A Novel Powered Acetabular Revision System vs. Manual Osteotome: an in Vitro Comparison.
*Louis Kwong, Fabrizio Billi, Scott Keller, Aaron Kavanaugh, Andrew Luu, Jessica Ward, Cris Salinas, Wayne Paprosky
Abstract text :

Introduction: The objective of this study was to compare the performance of the Explant Acetabular Cup Removal System (Zimmer), which has been the favored system for many surgeons during hip revision surgery, and the new EZout Powered Acetabular Revision System (Stryker).

Methods: 54mm Stryker Trident® acetabular shells were inserted into the foam acetabula of 24 composite hemi-pelvises (Sawbones). The hemi-pelvises were mounted on a supporting apparatus enclosing three load cells. Strain gauges were placed on the hemipelvis, on the posterior and the anterior wall, and on the internal ischium in proximity to the acetabular fossa. A thermocouple was fixed onto the polar region of the acetabular component. One experienced orthopaedic surgeon and one resident performed mock revision surgery 6 times each per system.

Results: Statistical analysis was conducted using Tukey's range test (HSD). The maximum force transferred to the implant was more than 4X lower with the EZout System regardless the surgeon experience (p=1.0E-08). Overall, recorded strains were lower for the EZout System with the higher decrease in strain (5X) observed at the posterior wall region(p=2E-08). The temperature at the interface was higher for the EZout System but never more than 37°C. Total removal time was on average reduced by a third with the EZout System (p=0.01). The calculated torque was lower for the EZout System. The amount of foam left on the cup after removal, which mimics the compromised bone, was 2.5X higher on average for the Explant System with most of the foam concentrated in the polar region. Lastly, it was observed that the polar region of each implant was reached by rotating the EZout System handpiece within a very narrow cylinder of space centered along the axis of the acetabular component compared to the Explant System, which required movement of the pivoting osteotomes within a large cone-shaped operating envelope.

Discussion: Quantitatively, the EZout System required lower force, producing lower strains in the surrounding composite bone. Higher impact forces and associated increased strains may increase fracture risk. Qualitatively, the Explant System required a greater cone of movement than the EZout System requiring more space for the surgeon to leverage the handle of the tool. In addition, both surgeon and resident felt substantially greater exhaustion after using the Explant System vs. the EZout System. The resident compensated for the increased workload of the Explant with time, the experienced surgeon with force. The learning curve for both experienced surgeon and resident was also much shorter with the EZout System as shown by the close force values between the experienced surgeon and resident.

Conclusion: Based on the results of this in vitro model, the EZout Powered Acetabular Removal System may be a reasonable alternative to manual removal techniques

Quantification of cortical and cartilage thickness in the proximal tibia of osteoarthritis patients using micro-computed tomography
*Klemens Trieb, Sascha Senck
Abstract text :

Due to the increasing life expectancy the incidence of gonarthrosis, the degeneration of articular cartilage and bone in the knee joint, is increasing worldwide. Although the success rate of knee arthroplasties is high, complications like the loosening of the implant necessitate subsequent treatments. Moreover, the morphology and microstructure of the knee joint varies considerably between patients, therefore the anatomical expertise of orthopedic surgeons is essential. In this analysis we therefore investigate the variation and micro-architectural alterations in subchondral bone in osteoarthritis (OA) patients undergoing a knee replacement surgery.

We investigate OA bone degenerations using clinical X-rays and micro-computed tomography (micro-CT). Tibial bone samples are collected from 100 patients undergoing a total knee arthroplasty at the Klinikum Wels-Grieskirchen. Images are obtained using an industrial micro-CT scanner RayScan 250E. Microstructural parameters include bone volume fraction and cortical thickness of the subcondral bone and are obtained from micro-CT images with isometric voxel sizes of 50 µm.

Using micro-CT, we show a high morphological variation in relation to cortical thickness, both within the respective condyle as well as between the medial and lateral condyle. Cortical thickness seems to correlate with cartilage thickness and knee joint alignment. The results are incorporated into a gonarthrosis database that integrates microstructural parameters via a combined analysis of X-ray and micro-CT data. This database aims to facilitate the assessment of osteoarthritis, i.e. in relation to cartilage degeneration, in future patients on the basis of the investigated patient collective.

Subject-specific hip joint kinetics during deep squatting in young, athletic adults
*Jan Van Houcke, Pavel E.  Galibarov, Sigrid Fauconnier, Christophe Pattyn, Emmanuel E. Audenaert
Abstract text :

Introduction: A deep squat (DS) is a challenging motion at the level of the hip joint generating substantial reaction forces (HJRF). During DS, the hip flexion angle approximates the functional range of hip motion. In some hip morphologies this femoroacetabular conflict has been shown to occur as early as 80° of hip flexion. So far in-vivo HJRF measurements have been limited to instrumented hip implants in a limited number of older patients performing incomplete squats (< 50° hip flexion and < 80° knee flexion). Clearly, young adults have a different kinetical profile with hip and knee flexion ranges going well over 100 degrees. Since hip loading data on this subgroup of the population is lacking and performing invasive measurements would be unfeasible, this study aimed to report a personalised numerical model solution based on inverse dynamics to calculate realistic in silico HJRF values during DS.

M&M: Fifty athletic males (18-25 years old) were prospectively recruited for motion and morphological analysis. DS motion capture (MoCap) acquisitions and MRI scans of the lower extremities with gait lab marker positions were obtained. The AnyBody Modelling System (v6.1.1) was used to implement a novel personalisation workflow of the AnyMoCap template model. Bone geometries, semi-automatically segmented from MRI, and corresponding markers were incorporated into the template human model by an automated nonlinear morphing. Furthermore, a state-of-the-art TLEM 2.0 dataset, included in the Anybody Managed Model Repository (v2.0), was used in the template model.  The subject-specific MoCap trials were processed to compute squat motion by resolving an overdeterminate kinematics problem.  Inverse dynamics analyses were carried out to compute muscle and joint reaction forces in the entire body. Resulting hip joint loads were validated with measured in-vivo data from Knee bend trials in the OrthoLoad library. Additionally, anterior pelvic tilt, hip and knee joint angles were computed.

Results: A preliminary set of results (20 out of 50 subjects) was analysed. The average HJRF was 3.42 times bodyweight at the peak of DS (95% confidence interval: 2.99 - 3.85 %BW). Maximal hip and knee flexion angles were 113° (109.7°-116.8°)  and 116° (109.4 – 123.0°) respectively. The anterior pelvic tilt demonstrated a biphasic profile with peak value of 33° (28.1° - 38.4°).

Discussion: A non-invasive and highly personalised alternative for determining hip loading was presented.  Consistently higher HJR forces during DS in young adults were demonstrated as opposed to the Orthoload dataset. Similarly, knee and hip flexion angles were much higher, which could support the increase in HJRF. We can conclude that DS hip kinetics in young adults clearly differ from the typical total hip arthroplasty population.