Steven Leuridan

A glenoid reaming study: how accurate are current reaming techniques?

BACKGROUND Correct reaming of a degenerative glenoid can be a difficult procedure. We investigated how the quality of the reamed surface is influenced by different reamers, by the surgeons experience, and by glenoid erosion patterns. MATERIAL AND METHODS Three shoulder surgeons performed reaming procedures with different types of reamers (flat, convex, K-wire guided, and nipple guided) on a series of similarly sized uniconcave and biconcave glenoids. The reproducibility of reaming and the effect of different reamers on different-shaped glenoids were measured and evaluated. RESULTS The center and direction of reaming were constant for all surgeons in the case of type A glenoids. For type B2 glenoids, the center and direction of reaming differed significantly between surgeons. The congruity of the reamed surface was better after flat reaming than after convex reaming. Whether the reamers were guided by a central K-wire or by a nipple had no significant effect on the reamed surface. The experience of the surgeon had no effect on the congruity of reaming. CONCLUSIONS Reaming of a uniconcave glenoid is reproducible, but reaming of a biconcave glenoid seems much more difficult. Erosion and deformity of the glenoid influence the accuracy of reaming the most. Surgical experience plays a less important role. We conclude that there is a need for guidance in reaming of biconcave glenoids.

Development of an acoustic measurement protocol to monitor acetabular implant fixation in cementless total hip Arthroplasty: A preliminary study

In cementless total hip arthroplasty (THA), the initial stability is obtained by press-fitting the implant in the bone to allow osseointegration for a long term secondary stability. However, finding the insertion endpoint that corresponds to a proper initial stability is currently based on the tactile and auditory experiences of the orthopedic surgeon, which can be challenging. This study presents a novel real-time method based on acoustic signals to monitor the acetabular implant fixation in cementless total hip arthroplasty. Twelve acoustic in vitro experiments were performed on three types of bone models; a simple bone block model, an artificial pelvic model and a cadaveric model. A custom made beam was screwed onto the implant which functioned as a sound enhancer and insertor. At each insertion step an acoustic measurement was performed. A significant acoustic resonance frequency shift was observed during the insertion process for the different bone models; 250 Hz (35%, second bending mode) to 180 Hz (13%, fourth bending mode) for the artificial bone block models and 120 Hz (11%, eighth bending mode) for the artificial pelvis model. No significant frequency shift was observed during the cadaveric experiment due to a lack of implant fixation in this model. This novel diagnostic method shows the potential of using acoustic signals to monitor the implant seating during insertion.

Consequences of reaming with flat and convex reamers for bone volume and surface area of the glenoid; a basic science study

BackgroundThe effect of reaming on bone volume and surface area of the glenoid is not precisely known. We hypothesize that (1) convex reamers create a larger surface area than flat reamers, (2) flat reamers cause less bone loss than convex reamers, and (3) the amount of bone loss increases with the amount of version correction.MethodsReaming procedures with different types of reamers are performed on similar-sized uniconcave and biconcave glenoids created from Sawbones foam blocks. The loss of bone volume, the size of the remaining surface area, and the reaming depth are measured and evaluated.ResultsReaming with convex reamers results in a significantly larger surface area than with flat reamers for both uniconcave and biconcave glenoids (p = 0.013 and p = 0.001). Convex reamers cause more bone loss than flat reamers, but the difference is only significant for uniconcave glenoids (p = 0.007).ConclusionsIn biconcave glenoids, convex reamers remove a similar amount of bone as flat reamers, but offer a larger surface area while maximizing the correction of the retroversion. In pathological uniconcave glenoids, convex reamers are preferred because of the conforming shape.

Vibration-based fixation assessment of tibial knee implants: A combined in vitro and in silico feasibility study

The preoperative diagnosis of loosening of cemented tibial knee implants is challenging. This feasibility study explored the basic potential of a vibration-based method as an alternative diagnostic technique to assess the fixation state of a cemented tibia implant and establish the methods sensitivity limits. A combined in vitro and in silico approach was pursued. Several loosening cases were simulated. The largest changes in the vibrational behavior were obtained in the frequency range above 1500 Hz. The vibrational behavior was described with two features; the frequency response function and the power spectral density band power. Using both features, all experimentally simulated loosening cases could clearly be distinguished from the fully cemented cases. By complementing the experimental work with an in silico study, it was shown that loosening of approximately 14% of the implant surface on the lateral and medial side was detectable with a vibration-based method. Proximal lateral and medial locations on the tibia or locations toward the edge of the implant surface measured in the longitudinal direction were the most sensitive measurement and excitation locations to assess implant fixation. These results contribute to the development of vibration-based methods as an alternative follow-up method to detect loosened tibia implants.

Determination of replicate composite bone material properties using modal analysis

Replicate composite bones are used extensively for in vitro testing of new orthopedic devices. Contrary to tests with cadaveric bone material, which inherently exhibits large variability, they offer a standardized alternative with limited variability. Accurate knowledge of the composites material properties is important when interpreting in vitro test results and when using them in FE models of biomechanical constructs. The cortical bone analogue material properties of three different fourth-generation composite bone models were determined by updating FE bone models using experimental and numerical modal analyses results. The influence of the cortical bone analogue material model (isotropic or transversely isotropic) and the inter- and intra-specimen variability were assessed. Isotropic cortical bone analogue material models failed to represent the experimental behavior in a satisfactory way even after updating the elastic material constants. When transversely isotropic material models were used, the updating procedure resulted in a reduction of the longitudinal Youngs modulus from 16.00GPa before updating to an average of 13.96 GPa after updating. The shear modulus was increased from 3.30GPa to an average value of 3.92GPa. The transverse Youngs modulus was lowered from an initial value of 10.00GPa to 9.89GPa. Low inter- and intra-specimen variability was found.

Vibration Analysis of the Biomechanical Stability of Total Hip Replacements

In cases of severe rheumatoid arthritis or osteoarthritis, the hip joint is substituted by an artificial joint composed of a femoral stem fitted with a spherical head that can rotate inside a cup inserted in the acetabulum. This procedure is called total hip replacement (THR) and is one of the most frequently performed orthopaedic surgeries. For a cementless femoral implant, the fixation is achieved by preparing a slightly undersized bone bed, and the implant is forcefully hammered into the bone. The initial stability at the time of surgery is one of the most important factors to establish long-term survival of the implant. With each surgical hammer blow, the fixation of the implant in the bone increases. However, introducing an implant with a diameter wider than the bones inner canal contour (i.e., press fit) introduces stresses in the cortical bone, which can cause femoral fracture. In response to mechanical excitations (i.e., hammer blows or external vibrations), a femur–implant structure will display vibration modes and frequencies, just like any other mechanical structure. Changes in material properties or boundary conditions of a femur–implant structure will change its vibration modes and frequencies, which can be obtained numerically and experimentally. Therefore, this chapter explains how to perform vibration analysis on a THR component (i.e., the femoral implant) in order to assess femur–implant stability, as well as how to analyze, present, and interpret results.

A biomechanical testing system to determine micromotion between hip implant and femur accounting for deformation of the hip implant: Assessment of the influence of rigid body assumptions on micromotions measurements

Background: Accurate pre‐clinical evaluation of the initial stability of new cementless hip stems using in vitro micromotion measurements is an important step in the design process to assess the new stems potential. Several measuring systems, linear variable displacement transducer‐based and other, require assuming bone or implant to be rigid to obtain micromotion values or to calculate derived quantities such as relative implant tilting. Methods: An alternative linear variable displacement transducer‐based measuring system not requiring a rigid body assumption was developed in this study. The system combined advantages of local unidirectional and frame–and–bracket micromotion measuring concepts. The influence and possible errors that would be made by adopting a rigid body assumption were quantified. Furthermore, as the system allowed emulating local unidirectional and frame–and–bracket systems, the influence of adopting rigid body assumptions were also analyzed for both concepts. Synthetic and embalmed bone models were tested in combination with primary and revision implants. Single‐legged stance phase loading was applied to the implant – bone constructs. Findings: Adopting a rigid body assumption resulted in an overestimation of mediolateral micromotion of up to 49.7 &mgr;m at more distal measuring locations. Maximal average relative rotational motion was overestimated by 0.12° around the anteroposterior axis. Frontal and sagittal tilting calculations based on a unidirectional measuring concept underestimated the true tilting by an order of magnitude. Interpretation: Non‐rigid behavior is a factor that should not be dismissed in micromotion stability evaluations of primary and revision femoral implants. Highlights:Implant and bone motion can be measured simultaneously at several locations.Non‐rigid behavior has a major influence on implant stability measurement results.Under a rigid body assumption, distal micromotion was overestimated by up to 49.7 &mgr;m.Under a rigid body assumption, relative rotational motion was overestimated by up to 0.12°.

A nondestructive method to verify the glenosphere-baseplate assembly in reverse shoulder arthroplasty

BACKGROUND Glenoid dissociation is a rare postoperative complication in reverse shoulder arthroplasty that has severe consequences for the patient and requires revision in most cases. A mechanically compromised Morse taper is hypothesized to be the main cause of this complication, with bony impingements and soft tissue interpositioning being cited as the most important problems. Intraoperative assessment of the taper assembly is challenging. Current methods require applying considerable torque to the glenosphere or relying on radiographs. MATERIALS AND METHODS This in vitro study demonstrates how the assembly quality can be accurately determined in a nondestructive way by exploiting the implant-specific relation between screw and Morse taper characteristics by measuring the angular rotation-torque curve. RESULTS The feasibility of the method is demonstrated on 2 reverse implant models. Several data features that can statistically discriminate between optimal and suboptimal assemblies are proposed. CONCLUSION Suboptimal assemblies can be detected using the method presented, which could easily be integrated in the current surgical workflow. Clinical recommendations based on the methods rationale are also presented, allowing detection of the most severe defect cases with surgical instruments currently in use.

Modal frequency and shape curvature as a measure of implant fixation: A computer study on the acetabular cup

Modal parameters are often investigated in order to assess the initial fixation of an implant. Most of studies are focused on the natural frequencies and frequency response function. Usually the femoral stem is tested although the acetabular cup fixation is important as well. The results of implant stability assessment are inconsistent and seem to suggest that frequency as a stability indicator is not sufficiently sensitive. In this study the sensitivity of the modal properties to changes in the bone-implant interface was investigated with the help of the finite element method (FEM). A novel fixation index based on modal shape curvature was investigated as a potential measure of the implant fixation. Modal frequencies are sensitive to interface changes in some manner, but suffer from insensitivity to local changes at bone-implant interface. The sensitivity up to 44% of natural frequencies to stiffness change due insertion steps was observed. The tested damage indicators are able to detect localized small changes in peripheral stiffness (5% stiffness reduction) with 95% confidence under the noise up to 1%. The modal shapes and their curvatures have a great potential to be a robust fixation indicator.

Review of a Pilot Internet System Dynamics Course

The University of Cincinnati has offered a Ph.D. level System Dynamics Course since the early 1980s. Originally, the course was concerned with experimental modeling aspects (impedance and modal modeling) and was complemented by a Fourier Analysis (Digital Signal Processing) and a Finite Element course sequence. In the 1990s, this course morphed from a lecture based course to a project based self study course with reduced formal lectures and more mentoring. The students in the course were broken up into groups of 3–5 students and they were required to use MATLAB to program the signal processing, parameter estimation and modeling algorithms. In 2006, this course was offered for the first time as an Internet Course to students at other universities and institutions. The main reason is that at any single site or university there are not enough students to justify offering such a course. This paper will review the progress of this effort.