Andrew D. Speirs

Reliability of knee joint muscle activity during weight bearing force control

We developed a novel approach that requires subjects to produce and finely tune ground reaction forces (GRFs) while standing. The aim of this study was to examine the reliability of electromyographic data recorded during these tasks. Healthy young adults stood with their dominant leg in a boot fixed to a force platform. A target matching protocol required subjects to control both the direction and magnitude of GRF along the horizontal plane while maintaining constant inferior-superior loads of 50% body-weight (BW). Each target matching task was repeated three times in a random order. Subjects were retested with the same protocol 2-3 days later. Normalised electromyography data of eight muscles crossing the knee joint was collected for each successful target match. A random model, single measures intra-class correlation analysed the reliability for both test-retest and intra-day results, in addition to inter-subject reliability. The GRFs required to meet the targets were comparable to a range of activities of daily living, ranging from 0.48 to 0.58 N/kg of BW in the horizontal plane while maintaining 50% BW in the vertical plane. We observed moderate to high ICC values (0.60-0.993) for most muscles in most directions, indicating low within-subject variance. In addition, moderate to high between-subject reliability was observed in all eight muscle activation profiles, indicating subjects used similar neuromuscular control strategies to achieve the desired GRFs. In conclusion, our protocol identifies non-random weight-bearing motor control strategies while generating direction dependent GRFs. These results provide reliable insight into knee joint stabilisation strategies during weight bearing.

Joint stabilisers or moment actuators: The role of knee joint muscles while weight-bearing

Previous investigations have identified the roles of knee joint muscles in supporting external loads during non-weight-bearing tasks and found these to depend on moment arm orientation (MAO). However, during weight-bearing tasks ground reaction forces (GRF) are transferred up through the knee, subjecting it to large multi-directional forces and stability is dependent on articular geometry, loading, and muscle activation. The purpose of this study was to investigate activation strategies used by healthy individuals to generate and support highly controlled GRF during weight-bearing. Twenty healthy males (23.9±1.9 yrs) stood with their foot in a boot fixed to a force platform. Subjects controlled an onscreen cursor by modulating normalised GRF and were required to produce 30% of their maximal force in 12 directions of the horizontal plane while maintaining 50% body weight on the test leg. Lower limb electromyography, kinematics and kinetics were recorded for each trial. Mean muscle activation was plotted in polar coordinates based on GRF orientation. Muscle activation symmetry was determined and when applicable, the mean direction of activation and muscle specificity index reported. The measured GRF were comparable to activities of daily living (0.48-0.58±0.17-0.19 N/kg in horizontal plane). Muscle activations were repeatable (ICCs: 0.78-0.98), however, only semitendinosus (ST) activation was indicated by its MAO. Considering the joint moments and activations patterns we therefore classified muscles as: (1) general joint stabilisers (vastus lateralis and medialis), (2) specific joint stabiliser (BF), and (3) moment actuators (ST and rectus femoris). General joint stabilisers were active in all load directions; specific stabilisers were active in directions opposite their MAO; moment actuators had higher specificities and activations corresponding to their MAO. We suggest the stabiliser muscles create a rigid mechanical linkage at the knee which allows the actuators of the hip and knee to modulate GRF.

Stress distribution and consolidation in cartilage constituents is influenced by cyclic loading and osteoarthritic degeneration

The understanding of load support mechanisms in cartilage has evolved with computational models that better mimic the tissue ultrastructure. Fibril-reinforced poroelastic models can reproduce cartilage behaviour in a variety of test conditions and can be used to model tissue anisotropy as well as assess stress and pressure partitioning to the tissue constituents. The goal of this study was to examine the stress distribution in the fibrillar and non-fibrillar solid phase and pressure in the fluid phase of cartilage in axisymmetric models of a healthy and osteoarthritic hip joint. Material properties, based on values from the literature, were assigned to the fibrillar and poroelastic components of cartilage and cancellous and subchondral compact bone regions. A cyclic load representing walking was applied for 25 cycles. Contact stresses in the fibrillar and non-fibrillar solid phase supported less than 1% of the contact force and increased only minimally with load cycles. Simulated proteoglycan depletion increased stresses in the radial and tangential collagen fibrils, whereas fibrillation of the tangential fibrils resulted in increased compressive stress in the non-fibrillar component and tensile stress in the radial fibrils. However neither had an effect on fluid pressure. Subchondral sclerosis was found to have the largest effect, resulting in increased fluid pressure, non-fibrillar compressive stress, tangential fibril stress and greater cartilage consolidation. Subchondral bone stiffening may play an important role in the degenerative cascade and may adversely affect tissue repair and regeneration treatments.

Surgical Correction of Cam Deformity in Association with Femoroacetabular Impingement and Its Impact on the Degenerative Process within the Hip Joint

Background: Cam morphology in association with femoroacetabular impingement (FAI) is a recognized cause of hip pain and cartilage damage and proposed as a leading cause of arthritis. The purpose of this study was to analyze the functional and biomechanical effects of the surgical correction of the cam deformity on the degenerative process associated with FAI. Methods: Ten male patients with a mean age of 34.3 years (range, 23.1 to 46.5 years) and a mean body mass index (and standard deviation) of 26.66 ± 4.79 kg/m2 underwent corrective surgery for cam deformity in association with FAI. Each patient underwent a computed tomography (CT) scan to assess acetabular bone mineral density (BMD), high-resolution T1&rgr; magnetic resonance imaging (MRI) of the hips to assess proteoglycan content, and squatting motion analysis as well as completed self-administered functional questionnaires (Hip disability and Osteoarthritis Outcome Score [HOOS]) both preoperatively and 2 years postoperatively. Results: At a mean follow-up of 24.5 months, improvements in functional scores and squat performance were seen. Regarding the zone of impingement in the anterosuperior quadrant of the acetabular rim, the mean change in BMD at the time of follow-up was −31.8 mg/cc (95% confidence interval [CI], −11 to −53 mg/cc) (p = 0.008), representing a 5% decrease in BMD. The anterosuperior quadrant also demonstrated a significant decrease in T1&rgr; values, reflecting a stabilization of the cartilage degeneration. Significant correlations were noted between changes in clinical functional scores and changes in T1&rgr; values (r = −0.86; p = 0.003) as well as between the BMD and maximum vertical force (r = 0.878; p = 0.021). Conclusions: Surgical correction of a cam deformity in patients with symptomatic FAI not only improved clinical function but was also associated with decreases in T1&rgr; values and BMD. These findings are the first, to our knowledge, to show that alteration of the hip biomechanics through surgical intervention improves the overall health of the hip joint. Level of Evidence: Therapeutic Level IV. See Instructions for Authors for a complete description of levels of evidence.

Acetabular and spino-pelvic morphologies are different in subjects with symptomatic cam femoro-acetabular impingement: ACETABULAR AND SPINOPELVIC MORPHOLOGY IN FAI

Acetabular and spino‐pelvic (SP) morphological parameters are important determinants of hip joint dynamics. This prospective study aimed to determine whether acetabular and SP morphological differences exist between hips with and without cam morphology and between symptomatic and asymptomatic hips with cam morphology. A cohort of 67 patients/hips was studied. Hips were either asymptomatic with no cam (Controls, n = 18), symptomatic with cam (n = 26) or asymptomatic with cam (n = 23). CT‐based quantitative assessments of femoral, acetabular, pelvic, and spino‐pelvic parameters were performed. Measurements were compared between controls and those with a cam deformity, as well as between the three groups. Morphological parameters that were independent predictors of a symptomatic cam were determined using a regression analysis. Hips with cam deformity had slightly smaller subtended angles superior‐anteriorly (87° vs. 84°, p = 0.04) and greater pelvic incidence (53° vs. 48°, p = 0.003) compared to controls. Symptomatic cams had greater acetabular version (p < 0.01), greater subtended angles superiorly and superior‐posteriorly (p = 0.01), higher pelvic incidence (p = 0.02), greater alpha angles and lower femoral neck‐shaft angles compared to asymptomatic cams (p < 0.01) and controls (p < 0.01). The four predictors of symptomatic cam included antero‐superior alpha angle, femoral neck‐shaft angle, acetabular depth, and pelvic incidence. In conclusion, this study illustrates that symptomatic hips had a greater amount of supero‐posterior coverage; which would be the contact area between a radial cam and the acetabulum, when the hip is flexed to 90°. Furthermore, individuals with symptomatic cam morphology had greater PI. Acetabular‐ and SP parameters should be part of the radiological assessment of femoro‐acetabular impingement.

Recent Trends in Newly Developed Plasma-Sprayed and Sintered Coatings for Implant Applications

The current paper aims to review recent trends (2011 to 2015) in newly developed plasma-sprayed and sintered coatings for implant applications. Recent developments in plasma-sprayed and sintered coatings have focused on improving biological performance, bacterial growth resistance, and mechanical properties, predominantly of HA and glass ceramics. The majority of these improvements are attributed to the addition of dopants. To improve biological performance, trace elements, such as Zn and Mg, both of which are found in bone, were added to replicate the functions they provide for the skeletal system. Though bacterial growth resistance is traditionally improved by Ag dopant, the addition of new dopants such as CeO2 and Zn were explored as well. Great effort has also been made to improve coating adherence and reduce stresses by minimizing coefficient of thermal expansion mismatch between the coating and substrate through the addition of elements such as Zn and Mg or the inclusion of a buffer layer. For sintering process in particular, there was an emphasis on reducing sintering temperature through modification of 45S5 Bioglass. New plasma spray and sintering technologies aimed at reducing high-temperature exposure are briefly introduced as well. These include microplasma spray and spark plasma sintering.

Properties of the cartilage layer from the cam-type hip impingement deformity

Femoro-acetabular impingement (FAI) is associated with significant acetabular cartilage damage and degenerative arthritis. To understand the contact stress and thus biomechanical mechanisms that may contribute to degeneration, the material behaviour of the cartilage layer is required. The objective of this study is to determine the fibril-reinforced poroelastic properties and composition of cartilage from cam deformities and to compare to those of normal cartilage. Patients undergoing surgical treatment of a symptomatic cam FAI deformity were recruited from the clinical practice of one of the authors. Osteochondral specimens were retrieved from the deformity during surgery using a trephine. Control specimens were retrieved from the anterior femoral head bearing surface during autopsy procedures. Indentation stress-relaxation tests were performed to determine the modulus (ES), Poissons ratio (ν) and permeability (k0) of the poroelastic component, and the strain-independent (E0) and -dependent (Eε) moduli of the fibril-reinforcement using finite element analysis and optimization. Safranin-O staining was used to quantify proteoglycan content. ES and ν were 71% and 37% lower, respectively, in Cam specimens compared to controls, and k0 was approximately triple that of Control specimens (p<0.05). No significant differences were seen in the fibrillar components, E0 and Eε. Proteoglycan content was substantially depleted in Cam specimens, and was correlated with ES, ν and k0. This study showed that cartilage from the cam deformity exhibits severe degeneration in terms of the mechanical behaviour and composition changes, and is consistent with osteoarthritis. This further supports the hypothesis that FAI is a cause of hip osteoarthritis.

Validation of an alignment method using motion tracking system for in-vitro orientation of cadaveric hip joints with reduced set of anatomical landmarks

Accurate in-vitro orientation of cadaveric hip joints is challenging due to limited available anatomical landmarks. Published hip joint in-vitro investigations commonly lack details on methods used to achieve reported orientations and the accuracy with which the desired orientation has been achieved. The aim of this study was to develop an accurate method for orienting hip joints with limited anatomical landmarks for in-vitro investigations, and to compare this method against orientation using guiding axes and by visual approximation. The proposed orientation method resulted in orientation angles achieved to within one degree (SD ± 0.58°). For most specimens, orientation using physical tools resulted in errors of ±8° and ±12° in at least one of three orientation angles used to place the femur and pelvis in neutral orientation, respectively. Precision was also worse, with SDs ranging from ±1° to ±5° for orientation angles of femoral specimens and SDs ranging from ±1° to ±8° for pelvic specimens. The error in the orientation angles was worse for orientation by visual approximation and the range of SDs were greater for both the femur and pelvis. Finite element modeling was used to assess the effects of observed orientation errors, on prediction of fracture load. In most cases, the largest error in fracture load among all trials exceeded 30%, relative to a femur oriented without any error in the orientation angles.

Higher patient activity level and subchondral stiffening in asymptomatic cam femoroacetabular impingement subjects

ABSTRACT A cam deformity is proposed as a cause of idiopathic osteoarthritis. Increased subchondral bone mineral density (BMD) is associated with this degenerative process of osteoarthritis, and the patient’s activity level may contribute to it. Therefore, the correlation between activity level and subchondral BMD in subjects with cam deformity FAI was studied. In this study, 26 asymptomatic cam deformity subjects (Bump) were compared with 18 subjects with a normal alpha angle (Control). Anterosuperior subchondral femoral neck and acetabular rim BMD were measured using quantitative computed tomography. Activity level was determined using the UCLA activity score. The correlation between BMD and UCLA activity were analysed. The result was a significantly higher BMD for Bump subjects in almost all measured sections. The UCLA score of the Bump versus Control subjects were comparable (8.96 versus 8.77, P = 0.740). While the controls showed no correlation between UCLA and BMD, a positive correlation was found for the Bump subjects on several femoral and acetabular impingement locations. These results support the conclusion that mechanical loading causes subchondral stiffening at the anterosuperior head–neck junction of the femur and anterosuperior acetabular rim. The absence of a correlation between BMD versus UCLA in the Controls supports the hypothesis that activity level may serve as a predictor for higher subchondral BMD in a cam deformity hip joint.

Unravelling the hip pistol grip/cam deformity: Origins to joint degeneration: IS OSTEOARTHRITIS ASSOCIATED WITH CAM-FAI

This article reviews a body of work performed by the investigators over 9 years that has addressed the significance of cam morphology in the development of hip osteoarthritis (OA). Early hip joint degeneration is a common clinical presentation and preexisting abnormal joint morphology is a risk factor for its development. Interrogating Hills criteria, we tested whether cam‐type femoroacetabular impingement leads to hip OA. Strength of association was identified between cam morphology, reduced range‐of‐movement, hip pain, and cartilage degeneration. By studying a pediatric population, we were able to characterize the temporality between cam morphology (occurring 1st) and joint degeneration. Using in silico (finite element) and in vivo (imaging biomarkers) studies, we demonstrated the biological plausibility of how a cam deformity can lead to joint degeneration. Furthermore, we were able to show a biological gradient between degree of cam deformity and extent of articular damage. However, not all patients develop joint degeneration and we were able to characterize which factors contribute to this (specificity). Lastly, we were able to show that by removing the cam morphology, one could positively influence the degenerative process (experiment). The findings of this body of work show consistency and coherence with the literature. Furthermore, they illustrate how cam morphology can lead to early joint degeneration analogous to SCFE, dysplasia, and joint mal‐reduction post‐injury. The findings of this study open new avenues on the association between cam morphology and OA including recommendations for the study, screening, follow‐up, and assessment (patient‐specific) of individuals with cam morphology in order to prevent early joint degeneration. Statement of significance: By satisfying Hills criteria, one can deduct that in some individuals, cam morphology is a cause of OA.