Search

BACKGROUND: The practice of cement augmentation in pedicle screw fixation is well established. However, there is a lack of consensus regarding the optimal screw design or cement type. This remains a clinically important question given the incidence of cement augmentation-associated complications. While fenestrated screws have become widely used in clinical practice, the relationship between fenestration placement along the screw axis and cement plume geometry and pullout strength have yet to be clarified. This study was designed to evaluate the mechanical and geometric properties of different fenestrated screw designs and cement viscosities in pedicle screw fixation. METHODS: Three different screw fenestration configurations and 2 different cement viscosities were examined in this study. Axial pullout tests were conducted in both foam blocks and cadaveric vertebrae. All vertebral specimens underwent tests of bone mineral density. In the foam blocks, 6 tests were conducted for each augmentation combination and also for nonaugmented controls. In the cadaveric testing, 36 lumbar vertebrae were instrumented with a cemented and uncemented control screw to compare features of fixation. Computed tomography (CT) images were taken to assess the geometric profile of the cement plumes in both the foam blocks and the cadaveric vertebrae. RESULTS: In both foam blocks and vertebral specimens, cementation was shown to confer a significant increase in pullout strength. Significant correlations existed between the anterior-posterior and lateral cement plume diameters and pullout strength in cadaveric vertebra and foam blocks, respectively. Within instrumented vertebra, variables such as the width of the vertebral body and screw insertion were found to significantly correlate with enhanced fixation. CT analysis of the instrumented vertebra demonstrated that a centrally distributed pattern of fenestrations was found to result in a cement plume with consistently predictable distribution within the vertebral body, without evidence of leak. CONCLUSION: Cementation of fenestrated pedicle screws increases overall pullout forces; however, there is an unclear relationship between the geometric properties of the cement plume and the overall strength of the screw-bone interface. This study demonstrates that the plume diameter, vertebral body width, and angle of screw insertion are correlated with enhanced pullout strength. Furthermore, varying the fenestration design of injectable screws resulted in a set of predictable plume patterns, which may be associated with fewer complications. Further investigation is required to clarify the optimal geometric and biomechanical properties of injectable pedicle screws and their role in establishing the cement-bone interface. CLINICAL RELEVANCE: This study is relevant to currently practicing spinal surgeons and biomechanical engineers. LEVEL OF EVIDENCE: 5.

Given the common occurrence of residual laxity and re-injury post anterior cruciate ligament reconstruction (ACLR), additional anterolateral procedures are increasingly used in combination with an ACLR. Despite the perception that there is a risk of over-constraining the lateral tibiofemoral (LTF) compartment, potentially leading to osteoarthritis, assessment on their effect on intra-articular compartment pressures is still lacking. Our objective was therefore, through a pilot biomechanical study, to compare LTF contact pressures after the most commonly used anterolateral procedures.A controlled laboratory pilot study was performed using 4 fresh-frozen cadaveric whole lower limbs. Through 0° to 90° of flexion, LTF contact pressures were measured with a Tekscan sensor, located under the lateral meniscus. Knee kinematics were obtained in 3 conditions of rotation (NR: neutral, ER: external and IR: internal rotation) to record the position of the knees for each loading condition. A Motion Analysis system with a coordinate system based on CT scans 3D bone modelling was used. After an ACLR, defined as the reference baseline, 5 anterolateral procedures were compared: anterolateral ligament reconstruction (ALLR), modified Ellison, deep Lemaire, superficial Lemaire and modified MacIntosh procedures. The last 3 procedures were randomised. For each procedure, the graft was fixed in NR at 30° of flexion and with a tension of 20 N.Compared with isolated ACLR, addition of either ALLR or modified Ellison procedure did not increased the overall LTF contact pressure (all p0.05) through the full range of flexion for the IR condition. Conversely, deep Lemaire, superficial Lemaire and modified MacIntosh procedure (all p0.05) did increase the overall LTF contact pressure compared with ACLR in IR. No significant difference was observed in ER and NR conditions.This pilot study, comparing the main anterolateral procedures, revealed that addition of either ALLR or modified Ellison procedure did not change the overall contact pressure in the LTF compartment through 0° to 90° of knee flexion. In contrast, the deep and superficial Lemaire, and modified MacIntosh procedures significantly increased overall LTF contact pressures when the knee was internally rotated.

Objective The optimal anterolateral procedure to control anterolateral rotational laxity of the knee is still unknown. The objective was to compare the ability of five anterolateral procedures performed in combination with anterior cruciate ligament reconstruction (ACLR) to restore native knee kinematics in the setting of a deficient anterior cruciate ligament (ACL) and anterolateral structures. Methods A controlled laboratory study was performed using 10 fresh-frozen cadaveric whole lower limbs with intact iliotibial band. Kinematics from 0° to 90° of flexion were recorded using a motion analysis three-dimensional (3D) optoelectronic system, allowing assessment of internal rotation (IR) and anteroposterior (AP) tibial translation at 30° and 90° of flexion. Joint centres and bony landmarks were calculated from 3D bone models obtained from CT scans. Intact knee kinematics were assessed initially, followed by sequential section of the ACL and anterolateral structures (anterolateral ligament, anterolateral capsule and Kaplan fibres). After ACLR, five anterolateral procedures were performed consecutively on the same knee: ALLR, modified Ellison, deep Lemaire, superficial Lemaire and modified MacIntosh. The last three procedures were randomised. For each procedure, the graft was fixed in neutral rotation at 30° of flexion and with a tension of 20 N. Results Isolated ACLR did not restore normal overall knee kinematics in a combined ACL plus anterolateral-deficient knee, leaving a residual tibial rotational laxity (p=0.034). Only the ALLR (p=0.661) and modified Ellison procedure (p=0.641) restored overall IR kinematics to the normal intact state. Superficial and deep Lemaire and modified MacIntosh tenodeses overconstrained IR, leading to shifted and different kinematics compared with the intact condition (p=0.004, p=0.001 and p=0.045, respectively). Compared with ACLR state, addition of an anterolateral procedure did not induce any additional control on AP translation at 30° and 90° of flexion (all p>0.05), except for the superficial Lemaire procedure at 90° (p=0.032). Conclusion In biomechanical in vitro setting, a comparison of five anterolateral procedures revealed that addition of either ALLR or modified Ellison procedure restored overall native knee kinematics in a combined ACL plus anterolateral-deficient knee. Superficial and deep Lemaire and modified MacIntosh tenodeses achieved excellent rotational control but overconstrained IR, leading to a change from intact knee kinematics. Level of evidence The level-of-evidence statement does not apply for this laboratory experiments study.

Background: Preoperative quantification of bone loss has a significant effect on surgical decision making and patient outcomes. Various measurement techniques for calculating glenoid bone loss have been proposed in the literature. To date, no studies have directly compared measurement techniques to determine which technique, if any, is the most reliable. Purpose/Hypothesis: To identify the most consistent and accurate techniques for measuring glenoid bone loss in anterior glenohumeral instability. Our hypothesis was that linear measurement techniques would have lower consistency and accuracy than surface area and statistical shape model–based measurement techniques. Study Design: Controlled laboratory study. Methods: In 6 fresh-frozen human shoulders, 3 incremental bone defects were sequentially created resulting in a total of 18 glenoid bone defect samples. Analysis was conducted using 2D and 3D computed tomography (CT) en face images. A total of 6 observers (3 experienced and 3 with less experience) measured the bone defect of all samples with Horos imaging software using 5 common methods. The methods included 2 linear techniques (Shaha, Griffith), 2 surface techniques (Barchilon, PICO), and 1 statistical shape model formula (Giles). Intraclass correlation (ICC) using a consistency model was used to determine consistency between observers for each of the measurement methods. Paired t tests were used to calculate the accuracy of each measurement technique relative to physical measurement. Results: For the more experienced observers, all methods indicated good consistency (ICC > 0.75; range, 0.75-0.88), except the Shaha method, which indicated moderate consistency (0.65 < ICC < 0.75; range, 0.65-0.74). Estimated consistency among the experienced observers was better for 2D than 3D images, although the differences were not significant (intervals contained 0). For less experienced observers, the Giles method in 2D had the highest estimated consistency (ICC, 0.88; 95% CI, 0.76-0.95), although Giles, Barchilon, Griffith, and PICO methods were not statistically different. Among less experienced observers, the 2D images using Barchilon and Giles methods had significantly higher consistency than the 3D images. Regarding accuracy, most of the methods statistically overestimated the actual physical measurements by a small amount (mean within 5%). The smallest bias was observed for the 2D Barchilon measurements, and the largest differences were observed for Giles and Griffith methods for both observer types. Conclusion: Glenoid bone loss calculation presents variability depending on the measurement technique, with different consistencies and accuracies. We recommend use of the Barchilon method by surgeons who frequently measure glenoid bone loss, because this method presents the best combined consistency and accuracy. However, for surgeons who measure glenoid bone loss occasionally, the most consistent method is the Giles method, although an adjustment for the overestimation bias may be required. Clinical Relevance: The Barchilon method for measuring bone loss has the best combined consistency and accuracy for surgeons who frequently measure bone loss.

Background: Suture pullout during rehabilitation may result in loss of tension in the inferior glenohumeral ligament (IGHL) and contribute to recurrent instability after capsular plication, performed with or without labral repair. To date, the suture pullout strength in the IGHL is not well-documented. This may contribute to recurrent instability. Purpose/Hypothesis: A cadaveric biomechanical study was designed to investigate the suture pullout strength of sutures in the IGHL. We hypothesized that there would be no significant variability of suture pullout strength between specimens and zones. Additionally, we sought to determine the impact of early mobilization on sutures in the IGHL at time zero. We hypothesized that capsular plication sutures would fail under low load. Study Design: Descriptive laboratory study. Methods: Seven fresh-frozen cadaveric shoulders were dissected to isolate the IGHL complex, which was then divided into 18 zones. Sutures in these zones were attached to a linear actuator, and the resistance to suture pullout was recorded. A suture pullout strength map of the IGHL was constructed. These loads were used to calculate the load applied at the hand that would initiate suture pullout in the IGHL. Results: Mean suture pullout strength for all specimens was 61.6 ± 26.1 N. The maximum load found to cause suture pullout through tissue was found to be low, regardless of zone of the IGHL. Calculations suggest that an external rotation force applied to the hand of only 9.6 N may be sufficient to tear capsular sutures at time zero. Conclusion: This study did not provide clear evidence of desirable locations for fixation in the IGHL. However, given the low magnitude of failure loads, the results suggest the timetable for initiation of range-of-motion exercises should be reconsidered to prevent suture pullout through the IGHL. Clinical Relevance: From this biomechanical study, the magnitude of force required to cause suture pullout through the IGHL is met or surpassed by normal postoperative early range-of-motion protocols.

Direct anterior approach (DAA) arthroplasty has generated great interest because of its minimally invasive and muscle sparing nature. Obese patients are reported to be associated with greater incidence of complications in primary joint replacement. The purpose of this study was to compare patient outcomes and complication rates between obese and non-obese patients undergoing primary total hip arthroplasty (THA) through a Bikini direct anterior incision. This retrospective, single surgeon study compared the outcome of 258 obese patients and 200 non-obese patients undergoing DAA THA using a Bikini incision, over a 5-year period. The average follow-up was 3.2 years (range 1.1–5.6 years). There was no statistically significant differences in the complication rate between the two groups. The obese group recorded 2 major (venous thromboembolism and peri-prosthetic fracture) and 2 minor complications (superficial wound infection), compared with the non-obese group, which recorded 2 major (deep-wound infection and peri-prosthetic fracture) and 1 minor complication (superficial wound infection). Patient-reported outcomes (WOMAC and Harris Hip Scores) showed significant post-operative improvements (p

BACKGROUND: To assess whether lumbar pedicle screw placement with a minimally invasive surgical (MIS) vs. open technique imparts different biomechanical parameters and thus may affect failure rates. METHODS: Human cadaveric disarticulated lumbar vertebrae 1–5 were stabilised in cement. Pedicle screws were inserted either via the ‘MIS’ or ‘open’ technique, based on previously described anatomical landmarks. Each vertebra had one ‘MIS’ and one ‘open’ technique screw. Specimens were tested with an Instron mechanical testing machine, positioned to allow for testing of direct coaxial force. Load was applied until failure occurred, and load-displacement curves generated for each screw. RESULTS: Average failure load was found to be 685±399 N for MIS, versus 661±323 N for open technique (P=0.75). The average ultimate failure load was 748±421 N for MIS, versus 772±326 N for open (P=0.74). Average displacement until failure was 0.95±0.49 mm for MIS as compared to 0.95±0.62 mm for open (P=0.996). Axial stiffness was 936±217 N/mm for MIS and 1,016±263 N/mm for open (P=0.19). Average work required to result in failure was 0.84±1.09 J for MIS and 0.82±1.05 J for open (P=0.94). CONCLUSIONS: There was no significant difference in the biomechanical properties of the MIS as compared with open lumbar pedicle screws, when tested until failure under direct coaxial force. The clinical implication may be that there is no significant advantage in the biomechanical properties of MIS versus open lumbar pedicle screw insertion techniques.

Background In anterior cruciate ligament reconstruction, quadrupled semitendinosus (Quad ST) grafts have potential advantages over doubled semitendinosus–gracilis (ST/G) including larger diameter and gracilis preservation, however the ideal tibial fixation method of the resultant shorter Quad ST graft remains elusive if a fixed-loop suspensory fixation device is used on the femur. We investigated whether the tibial fixation biomechanical properties of a Quad ST fixed indirectly with polyethylene terephthalate tape tied over a screw in a full outside-in created tunnel was superior to a ST/G graft fixed with an interference screw. Materials and methods In a controlled laboratory study, six cadaveric matched pairs of each construct were subjected to cyclic loading to mimic physiologic loading during rehabilitation. This included preconditioning cycling, cyclic loading to 220 N for 500 cycles, then cyclic loading to 500 N for 500 cycles. Results High standard deviations across the measured parameters occurred with no significant difference between measured parameters of elongation for the different constructs. Elongation of the Quad-ST construct was greater at 10 and 100 cycles, but not statistically different. Four of the six Quad-ST constructs failed below 100 cycles, compared with two failures below 100 cycles in the ST/G construct. There was a strong correlation between cycles to failure and bone mineral density for the Quad ST-tape constructs. Conclusions Tibial fixation of Quad ST with a tied tape–screw construct in a full-length tunnel was not biomechanically superior to ST/G graft fixed with an interference screw, exhibited greater nonsignificant construct elongation with earlier failure, and was more reliant on bone mineral density. Level of evidence In vitro laboratory study.

As the use of glenoid suture anchors in arthroscopic and open reconstruction, for instability after Bankart lesions of the shoulder, increases, an emerging problem has been the incidence of glenoid rim fractures through suture drill holes. Very little is known regarding the effect of the Hill–Sachs lesion on the glenoid's susceptibility to fracture and how drill hole location can further affect this. This study used finite element modeling techniques to investigate the risk of fracture of the glenoid rim in relation to variable sized Hill–Sachs defects impacting on the anterior glenoid edge with suture anchor holes placed in varying positions. The distribution of Von Mises (VM) stresses and the factor of safety (FOS) for each of the configurations were calculated. The greatest peak in VM stresses was generated when the glenoid was loaded with a small Hill–Sachs lesion. The VM stresses were lessened and the FOS increased (reducing likelihood of failure) with increasing size of the Hill–Sachs lesion. Placement of the suture drill holes at 2 mm from the glenoid rim showed the highest risk of failure; and when combined with a medium sized Hill–Sachs lesion, which matched the central line of the drill holes, a potentially clinically significant configuration was presented. The results of this study are useful in assisting the surgeon in understanding the interaction between the Hill–Sachs lesion size and the placement of suture anchors with the purpose of minimizing the risk of subsequent rim fracture with new injury.

The occurrence of audible squeaking in some patients with ceramic-on-ceramic (CoC) hip prostheses is a cause for concern. Considering multifactor contributing to this phenomenon, many studies have been conducted over the last decade. Great efforts have been put on understanding the mechanics of the hip squeaking to gain a deep insight into factors resulting in sound emission from hip articulation. Disruption of fluid-film lubrication and friction were reported as main potential causes of hip squeaking, while patient and surgical factors as well as design and material of hip implants were identified as affecting factors. This review article therefore summarised the recent available literature on this subject to provide a platform for future developments. Moreover, high wear rates and ceramic liner fracture as viable consequences of hip squeaking were discussed., The first author gratefully acknowledges Macquarie University for International Macquarie University Research Excellence Scholarship (iMQRES)-No. 2010017. The second author would like to thank to the Portuguese Foundation for Science and Technology through the project UID/EEA/04436/2013.

OBJECTIVE To assess the accuracy and suitability of dual-energy computed tomography (DECT) in scanning metals used in orthopedic implants. MATERIALS AND METHODS Four metal phantoms (Cobalt Chrome, Titanium Grade 5, Stainless Steel 316, and Stainless Steel 630), commonly used materials in orthopedic implants, were scanned by conventional, polychromatic CT as well as Gemstone Spectrum Imaging (GSI) DECT, with and without metal artefact reduction software (MARS). Scans were assessed for artefact based on Hounsfield unit values; and surfaces generated, based on a Canny edge detection algorithm. Two separate metal implants were also scanned and assessed for dimensional accuracy. RESULTS Conventional, polychromatic CT, and GSI DECT (without MARS) scans displayed major beam hardening in the presence of all four metals. The GSI DECT with MARS showed very clear and reproducible boundaries with minimal noise surrounding the metal phantoms. However, geometric analysis found overestimation of the dimensions, volume, and surface area for most of the metal phantoms. Titanium displayed the least artefact, compared to the other metals, in all scan scenarios. CONCLUSIONS Although metal artefact reduction using GSI DECT looks superior to conventional CT, when measured objectively, it was shown to overestimate geometries and skew dimensions. The GSI DECT with MARS should be used with caution, especially when assessing questions of implant shape or wear.

Background: None of the anterolateral procedures used in combination with ACL reconstruction (ACLR) to control rotational laxity have demonstrated superiority. The objective was to compare the capacity of the main anterolateral procedures associated with ACLR to restore intact knee kinematics in case of combined ACL and anterolateral structure injury. Methods: The complete kinematics of 10 cadaveric knees, previously modelled by TDM, were recorded using a 3D Motion Analysis® system. Intact knee kinematics, including internal rotation (IR) of the tibial and anterior-posterior (AP) laxity at 30 and 90° flexion were initially assessed, followed by a sequential section of the ACL and anterolateral complex (ALC) (anterolateral ligament (ALL), ALL capsule and Kaplan fibers). After the ACLR, 5 anterolateral procedures were performed consecutively on the same knee: ALLR; Ellison; Deep Lemaire; Superficial Lemaire; and MacIntosh. The last three procedures were randomized. For each procedure, the graft was fixed in neutral rotation at 30° flexion with a tension of 20 N. Results: ACLR alone did not restore overall knee kinematics when there was an ACL+ALC injury, and resulted in residual rotational laxity of the tibia (p > 0.001). Only the ALLR (p=0.262) and modified Ellison (p=0.081) procedures restored normal global IR kinematics. Superficial/deep Lemaire and MacIntosh procedures resulted in over-constrained kinematic profiles (respectively: p=0.013, p=0.018 and p=0.030). In terms of ACLR, the addition of an anterolateral procedure did not provide additional control over AP translation at 30 and 90° (p > 0.05), exception for the surficial Lemaire procedure at 90° (p = 0.032). Discussion: ACLR alone was not sufficient to restore normal kinematics in ACL and ALC-deficient knees. ALLR and Ellison procedures restored physiological kinematics, unlike the MacIntosh procedure which caused additional control of IR and thereby induced over-constraint. Conclusion: The addition of ALLR or the modified Ellison procedure, which restore intrinsic kinematics, might be useful during primary ACL reconstruction to avoid repeated injury without a risk of over-constraint. The superficial/deep Lemaire and MacIntosh procedures resulted in over-constrained kinetics but provided additional rotation control that could be useful in revision surgery.

Intraoperative periprosthetic femoral fractures (IPPFF) occur in approximately 3-5% of all cementless total hip arthroplasty (THA) surgeries. This study aimed to identify the critical impaction load to cause an IPPFF during implant implementation. This critical load may be used as a guideline for surgeons as well as a parameter for the design of future surgical tools and procedures. This study concerned a single femur of a healthy 60 year old female with an anatomical femoral stem implant, thus the effects of patient specific variables (such as osteoporosis, amount of bone resorption, bone damage, implant geometry, age and gender) were not considered. The eXtended Finite Element Method (XFEM) was used to analyse the fracture. From CT scan data, a user-defined subroutine is used to assign heterogeneous isotropic material properties to the femur. It was computed that IPPFF would take place at an impaction load of 18.5 kN.

Introduction Parmi les differentes procedures anterolaterales utilisees en association avec une reconstruction du LCA (LCAR) et visant a controler la laxite rotatoire, aucune n’a fait preuve de sa superiorite. L’objectif etait de comparer la capacite des principales procedures anterolaterales, combinee a une LCAR, a restaurer une cinematique de genou natif sur des genoux avec une lesion combinee du LCA et des structures anterolaterales. Methodes Les cinematiques completes de 10 genoux cadaveriques, au prealablement modelises par TDM, ont ete enregistrees a l’aide d’un systeme 3D de Motion Analysis®. Les cinematiques de genou intact, incluant la rotation tibiale interne (RI) et la laxite antero-posterieure (AP) a 30 et 90° de flexion ont ete initialement evaluees, suivie d’une section sequentielle du LCA et du complexe anterolateral (CAL) (ligament anterolateral (LAL), capsule AL et fibres de Kaplan). Apres la LCAR, 5 interventions anterolaterales ont ete effectuees consecutivement sur le meme genou : LALR ; Ellison ; Lemaire-profond ; Lemaire-superficiel ; et MacIntosh. Les trois dernieres procedures ont ete randomisees. Pour chaque procedure, le greffe a ete fixee en rotation neutre a 30° de flexion avec une tension 20 N. Resultats La LCAR isolee ne permettait pas de retablir la cinematique globale du genou lorsqu’il existait une lesion combinee du LCA + CAL, laissant une laxite rotatoire tibiale residuelle (p > 0,001). Seules les procedures LALR (p = 0,262) et Ellison modifiee (p = 0,081) ont permis de retablir des cinematiques de RI globale normales. Les interventions de Lemaire superficiel/profond et de MacIntosh, induisaient des profils cinematiques hypercontraints (respectivement : p = 0,013, p = 0,018 et p = 0,030). Par rapport a l’etat LCAR, l’ajout d’une procedure anterolaterale n’induisait pas de controle supplementaire sur la translation AP a 30 et 90° (p > 0,05), a l’exception de la procedure de Lemaire-superficiel a 90° (p = 0,032). Discussion La LCAR isolee n’etait pas suffisante pour restaurer une cinematique normale dans un genou LCA et du CAL deficient. Les procedures de LALR ou d’Ellison permettaient une restauration des cinematiques physiologique, a l’inverse des procedures et de MacIntosh, qui en entrainant un controle supplementaire de la RI, induisaient une hyper-contrainte. Conclusion L’ajout de la procedure LALR ou de l’Ellison modifiee, en retablissant des cinematiques natives, peuvent etre utile lors de la reconstruction primaire du LCA afin d’eviter une lesion iterative sans risquer une hypercontrainte. Les procedures de Lemaire superficiel/profond et de MacIntosh conduisent a des cinematiques hypercontraintes mais permettent un controle de rotation supplementaire pouvant etre utile en chirurgie de revision.

The upper limb undergoes a large range-of-motion (ROM); and therefore, the mechanical testing techniques for the corresponding joint implants need to reflect these movements. The literature shows that aseptic loosening and implant instability are the main shoulder implant related reasons for revision surgery. Aseptic loosening occurs when excessively high stresses lead to degradation of the articular surface of the implant component, resulting in generation of wear debris and implant instability that is mostly caused by eccentric loading. Therefore shoulder implant testing generally falls under two different testing modes: wear testing and stability testing. Both anatomic and reverse type shoulder implants have been tested using a variety of different testing regimes including static and dynamic as well as constant loading, variable loading, and physiological loading. There are currently no standard mechanical testing protocols available for Elbow implants, with only a few reports of varus-valgus laxity test methods found in the literature.

It is still unclear how a vertebral fracture should be stabilised and strengthened without endangering the remaining intact bone of the augmented vertebra or the adjacent vertebrae. Numerical modelling may provide insight. To date, however, few finite element (FE) spine models have been developed which are both multi-segmental and capture a more complete anatomy of the vertebrae. A 3-D, two-functional unit, CT-based, lumbar spine, FE model was developed and used to predict load transfer and likelihood of fracture following balloon kyphoplasty. The fractured anterior wall and injected cement were modelled in a two-functional spinal unit model with osteoporotic bone properties. Parameters investigated included: cement stiffness, cement volume and height restoration. Models were assessed based on stresses and a user-defined fracture-predicting field. Augmentation altered the stress distribution; shielding was dependent on positioning of the cement; and fracture algorithm found incomplete height restoration to increase the likelihood of fracture, particularly in adjacent vertebrae.

The new generation short-stem hip implants are designed to encourage physiological-like loading, to minimize stress—strain shielding and therefore implant loosening in the long term. As yet there are no long-term clinical studies available to prove the benefits of these short-stem implants. Owing to this lack of clinical data, numerical simulation may be used as a predictor of longer term behaviour. This finite element study predicted both the primary stability and long-term stability of a short-stem implant. The primary implant stability was evaluated in terms of interface micromotion. This study found primary stability to fall within the critical threshold for osseointegration to occur. Longer term stability was evaluated using a strain-adaptive bone remodelling algorithm to predict the long-term behaviour of the bone in terms of bone mineral density (BMD) changes. No BMD loss was observed in the classical Gruen zones 1 and 7 and bone remodelling patterns were comparable with hip resurfacing results in the literature.

The aetiology of Kienböck's disease is unknown. Ulnar variance and lunate shape are possible mechanical risk factors. This study assessed the trabecular structure in 29 cadaveric lunates using microCT and correlated this with ulnar variance and lunate shape on plain radiographs and with bone density assessed using conventional CT. The bony trabeculae within the lunate were shown to run almost perpendicular to the proximal and distal joint surfaces in the coronal plane; these trabeculae met the subchondral bone at an angle between 72–102°. In lunates whose proximal and distal articular surfaces are not parallel, the trabecular orientation may be less able to resist compressive forces and more susceptible to fracture.

A ceramic-on-ceramic (CoC) hip prosthesis with clearance is modeled as a multibody dynamics system for the purpose of studying hip squeaking. A continuous contact force model provides the intrajoint forces developed at the hip joint. Friction effects due to the relative motion are also considered. A FFT analysis of the audible sounds from CoC hip acceleration is carried out to analyze hip squeaking. The effects of friction, hip implant size, and the head initial position on hip squeaking and the trajectory of femoral head are analyzed and discussed. It was shown that the causes of hip squeaking are stick/slip, friction-induced vibration, and the femoral head angular speed and force changes. [DOI: 10.1115/1.4028109]

Wear plays a key role in primary failure of artificial hip articulations. Thus, the main goal of this work is to investigate the influence of friction-induced vibration on the predicted wear of hard hip arthroplasties. This desideratum is reached by developing a three-dimensional multibody dynamic model for a hip prosthesis taking the spatial nature of the physiological loading and motion of the human body into account. The calculation of the intra-joint contact forces developed is based on a continuous contact force approach that accounts for the geometrical and materials properties of the contacting surfaces. In addition, the friction effects due to the contact between hip components are also taken into account. The vibration of the femoral head inside the cup associated with stick-slip friction, negative-sloping friction and dynamic variation in intra-joint contact force has been also incorporated in the present hip articulation model. The friction-induced vibration increases the sliding distance of the contact point between the head and cup surfaces by altering its micro and macro trajectories, and consequently affects the wear. In the present work, the Archard’s wear law is considered and embedded in the dynamic hip multibody model, which allows for the prediction of the wear developed in the hip joint. With the purpose of having more realistic wear simulation conditions, the geometries of the acetabular cup and femoral head are updated throughout the dynamic analysis. The main results obtained from computational simulations for ceramic-on-ceramic and metal-on-metal hip prostheses are compared and validated with those available in the best-published literature. Finally, from the study performed in the present work, it can be concluded that that an important source of the high wear rates observed clinically may be due to friction-induced vibration., The first author gratefully acknowledges Macquarie University for his International Macquarie University Research Excellence Scholarship (iMQRES)-No. 2010017. The second author would like to thank the Portuguese Foundation for Science and Technology (FCT) through the project UID/EEA/04436/2013.

Wear can influence the lifetime and performance of implants and has been found to be a key factor in primary failure of artificial hip joints. The present study aims to present a spatial multibody dynamic model to predict wear in ceramic- on-ceramic hip implants. The problem was formulated by developing a spatial multibody dynamic model of a hip prosthesis taking three-dimensional physiological loading and motion of the human body into account. Then, the Archard wear model was integrated into the dynamic calculation of the hip implant to predict wear. Additionally, geometries of the cup and head were updated throughout the simulation to generate a more realistic wear simulation. The results were validated against current literature. Finally it was illustrated that friction-induced vibration caused excessive wear of hip implant components.

The main objective of this work is to study the effect of friction-induced vibration and contact mechanics on the maximum contact pressure and moment of artificial hip implants. For this purpose, a quasi-static analysis and a multibody dynamic approach are considered. It is shown that the multibody dynamic model is effective at predicting contact pressure distribution and moment of hip implants from both accuracy and time-consuming points of view. Finally, from the computational simulations performed, it can be observed that the friction-induced vibration influences the contact pressure and the moment in hip implants by introducing an oscillating behaviour in the system dynamics., Fundação para a Ciência e a Tecnologia (FCT)

The present study investigates nonlinear vibration and dynamic behaviour of a ceramic on ceramic hip implant. The aim of this research is to firstly gain a better understanding of hip squeaking and vibration and secondly to investigate the effect of friction on contact point path during normal gait. For this purpose, a spatial multibody dynamic hip model was developed, using a friction-velocity constitutive law combined with a Hertzian contact model. Furthermore, the physiological three-dimensional rotation angles and forces are taken into account to calculate tangential and normal contact forces, respectively. Comparing the outcomes with that available in the literature allowed for the validation of our approach. It was shown that the cause of hip squeaking is friction-induced vibration owing to different phenomena such as stick-slip friction, negative-sloping friction and contact force changes. Moreover, friction-induced vibration does significantly change contact point path during the gait when compared to non-friction analysis., Fundação para a Ciência e a Tecnologia (FCT)

In vitro mechanical testing of orthopedic implants provides information regarding their mechanical performance under simulated biomechanical conditions. Current in vitro component stability testing methods for reverse shoulder implants are based on anatomical shoulder designs, which do not capture the dynamic nature of these loads. With glenoid component loosening as one of the most prevalent modes of failure in reverse shoulder replacements, it is important to establish a testing protocol with a more realistic loading regime. This paper introduces a novel method of mechanically testing reverse shoulder implants, using more realistic load magnitudes and vectors, than is currently practiced. Using a custom made jig setup within an Instron mechanical testing system, it is possible to simulate the change in magnitude and direction of the joint load during arm abduction. This method is a step towards a more realistic testing protocol for measuring reverse shoulder implant stability.

Introduction. Osteonecrosis may be triggered by bone temperatures above 47 °C during routine orthopaedic bone cuts using power-driven saws with potentially negative impacts on bone healing. A new oscillating-tip saw blade design (Precision®; Stryker, Kalamazoo, USA) has been recently developed with a saw blade design that may influence the amount of heat generated. We have, therefore, sought to compare the bone temperature achieved using this new blade design with a standard oscillating saw during a standardized cutting task. Method. Six human cadaveric femora were obtained. Each femur was clamped and a distal femoral cutting jig was applied. An initial cut was performed to visualize the distal metaphyseal bone. The cutting block was then moved 2 mm proximal and a further cut performed, measuring the temperature of the bone with an infrared camera. This was repeated, moving the block 2 mm proximal with each cut, alternating between a standard oscillating saw blade (12 cuts) and the Precision® saw blade (12 cuts). The bone density at the level of each slice was established from a CT scan of each specimen which had been performed prior to the experiment. Results. The two blades did not differ with respect to the integrated mean temperature calculated for each cut (p = 0.89). The average peak temperatures were not significantly different between blades (p = 0.14). There was no significant difference between blades for peak heating rate (p = 0.7), although the area of bone heated above the 47 deg osteonecrotic threshold was significantly (p = 0.04) less for the standard saw blade. Conclusions. The Precision® blade may have advantages over standard oscillating blade, but reduced heat generation was not observed in this study. Indeed, the Precision® blade generated heat that exceeded the bony osteonecrosis threshold in a greater proportion of bone than the standard blade, questioning its use for osteotomy or uncemented knee arthroplasty. Further work should examine modifications to the blade design to better optimize the requirements of speed, accuracy and heat generation.

Background:Arthritis of the metatarsophalangeal (MTP) joint is characterized by loss of MTP joint range of motion (ROM) and pain. Joint arthroplasty is one treatment option, and while results can be satisfactory, there is still room for improvement. The aim was to use cadaveric model to compare the sagittal kinematics and articulating contact properties of 4 different first metatarsal head designs of an MTP joint implant.Methods:Six cadaveric feet were each prepared with a single modular first MTP joint total arthroplasty. A standard cyclic load, which induced hallux dorsiflexion, was applied and motion measured from high resolution images. Contact behavior was collected simultaneously using a pressure transducer. Data collected compared the native joint with 4 different reconstructed cases. Each reconstructed joint used a different metatarsal-head-component while reusing the same phalangeal component to compare the 4 alternative metatarsal head designs.Results:All reconstructed joints displayed greater ROM compared with the intact joint. Of the 4 metatarsal head components, the grooved, anatomical design demonstrated the greatest dorsiflexion when compared to the standard design, 31.6 degrees (SD ± 8.6 degrees), P < .05. All reconstructed joints displayed contact areas lower than the intact (~50%, P < .001). The grooved metatarsal-head-component experienced the least contact force ( P < .015), and the eccentric component underwent the greatest contact pressure ( P < .05) when compared to the intact case.Conclusions:In this study of a first metatarsophalangeal joint replacement design, ROM was shown to be better for the more anatomically designed metatarsal head, while contact properties did not vary across different designs.Clinical Relevance:This information may be useful in the development of new metatarsal components.

Background: The frictional properties between bone and uncemented orthopedic implants are important for initial stability. Accurate frictional data are used in computer modeling to improve implant design. Unfortunately, friction data derived from standardized testing methods is rare. We aimed to validate two testing methods and to provide friction data. Method: Two experimental designs for testing friction (Sled and Rotation) were investigated. One (Sled) employed a friction testing standard (ASTM D4518) while the other (Rotation) was a novel design. Both designs were initially validated using metal and polymer surfaces of known friction coefficients. The effect of variables, speed and normal force was evaluated. Finally trabecular bone from fresh frozen cadaveric femurs ([Formula: see text]) was tested against four commonly used orthopedic surfaces. Porosity of each bone sample was obtained using micro-CT and we reviewed the correlation between porosity and friction coefficient. Results: Based on the validation experiments, the Rotation method delivered more accurate friction estimates, and was less affected by normal force and speed, than the Sled method. The testing of bone against implant surfaces produced a variety of different force displacement curves and a wide range of friction coefficients (range 0.19–0.78). Bone excised from the lateral femoral condyle produced a higher friction coefficient than bone from the medial femoral condyle (p-value [Formula: see text]). Trabecular bone samples yielded a range of porosities (91.30–79.03%) as determined by micro-CT. A weak positive correlation was observed between bone porosity and friction coefficient. Conclusion: This study demonstrated the importance of a validated testing method when determining frictional properties between bone and orthopedic implants. Specific testing standards should therefore be created, to ensure accurate and reproducible data. The data produced in this study will be utilized for further experimental studies and computer modeling.

Balloon kyphoplasty (BKP) and vertebroplasty (VP) are clinically effective procedures. However, BKP has been occasionally associated with failure, although the cause has not been established thus far. We believe that, especially in patients with severe osteoporosis and osteonecrosis, BKP fails due to the so-called stress shielding effect and the stiffness of cement. In these patients, other bone-preserving kyphoplastic procedures and vertebroplasty, as well as recently introduced cements adjusted to the severity of osteoporosis, might be beneficial. Furthermore, it is essential to achieve complete straightening intraoperatively when performing BKP, because any persistent residual kyphosis will aggravate the burden on the adjacent vertebral bodies following the creation of a cavity filled with cement. Therefore, it would be meaningful to consider alternative bone-preserving kyphoplastic measures instead of BKP. In cases of older fractures, one should consider the use of VP and the recently introduced cements.