Hip resurfacing is an alternative to total hip arthroplasty for the young and active patient likely to outlive traditional means of hip joint replacement. The acetabular cup is implanted in much the same fashion as an uncemented total hip arthroplasty, however, implantation of the femoral component is unique to hip resurfacing, presenting both distinct benefits and limitations. Hip resurfacing spares much of the proximal femur including the femoral neck and portions of the femoral head. This may be advantageous if the patient requires revision surgery; however, preservation of the femoral neck bears with it the risk of femoral neck fracture. The exact mechanism of neck fracture is not fully understood. Avoiding potential fracture risks is vital to ensuring optimal patient outcomes. The current work investigated mechanical femoral head preparatory factors that may predispose to femoral neck fracture. Intra-operative computer navigation is emerging as the gold-standard in orthopaedic care. In hip resurfacing, navigation may improve the surgeon’s ability to optimally implant the resurfacing prosthesis; however, much of this technology is still in its infancy and requires investigation into the accuracy and repeatability of this peri-operative tool. Pre-operative planning can assist the surgeon in optimally determining the size and position of the resurfacing components, specifically in reference to the patient’s unique anatomy, prior to performing the operation. This may aid in correct implant selection and provide a basis on which to conduct intra-operative navigation. However, the accuracy and repeatability of pre-operative planning for hip resurfacing has not yet been established. Thus, this body of work looked to establish a clear methodology for pre-operative planning, intra-operative computer navigation and surgical technique in order to optimize preparation of the femoral head, ultimately reducing the risk of femoral neck fracture in hip resurfacing.

Hip resurfacing is an alternative to total hip arthroplasty for the young and active patient likely to outlive traditional means of hip joint replacement. The acetabular cup is implanted in much the same fashion as an uncemented total hip arthroplasty, however, implantation of the femoral component is unique to hip resurfacing, presenting both distinct benefits and limitations. Hip resurfacing spares much of the proximal femur including the femoral neck and portions of the femoral head. This may be advantageous if the patient requires revision surgery; however, preservation of the femoral neck bears with it the risk of femoral neck fracture. The exact mechanism of neck fracture is not fully understood. Avoiding potential fracture risks is vital to ensuring optimal patient outcomes. The current work investigated mechanical femoral head preparatory factors that may predispose to femoral neck fracture. Intra-operative computer navigation is emerging as the gold-standard in orthopaedic care. In hip resurfacing, navigation may improve the surgeon’s ability to optimally implant the resurfacing prosthesis; however, much of this technology is still in its infancy and requires investigation into the accuracy and repeatability of this peri-operative tool. Pre-operative planning can assist the surgeon in optimally determining the size and position of the resurfacing components, specifically in reference to the patient’s unique anatomy, prior to performing the operation. This may aid in correct implant selection and provide a basis on which to conduct intra-operative navigation. However, the accuracy and repeatability of pre-operative planning for hip resurfacing has not yet been established. Thus, this body of work looked to establish a clear methodology for pre-operative planning, intra-operative computer navigation and surgical technique in order to optimize preparation of the femoral head, ultimately reducing the risk of femoral neck fracture in hip resurfacing.

In real life, immediately after joint replacement, the artificial joint is actually bathed in blood (and clotted blood) instead of synovial fluid. Blood contains large molecules and cells of size ~ 5 to 20 μm suspended in plasma and considered to be a non-Newtonian (pseudoplastic) fluid with density of 1060 Kg/m³ and viscosity ~ 0.01 Pas at shear rates of 3000 s⁻¹ (as obtained in this work). The effect of these properties on friction and lubrication is not fully understood and, so far to our knowledge, hardly any studies have been carried out regarding friction of metal-on-metal bearings with various clearances in the presence of lubricants such as blood or a fluid containing macromolecules such as hyaluronic acid (HA) which is a major component of synovial fluid increasing its viscosity and lubricating properties. In this work, therefore, we have investigated the frictional behaviour of a group of Smith and Nephew Birmingham Hip Resurfacing implants with a nominal diameter of 50mm and diametral clearances in the range ~ 80 μm to 300 μm, in the presence of blood (clotted and whole blood), a combination of bovine serum (BS) with hyaluronic acid (HA) and carboxymethyl cellulose (CMC, as gelling agent) adjusted to a range of viscosities (~0.001-0.2 Pas), and bovine serum with CMC adjusted to a similar range of viscosities. These results suggested that reduced clearance bearings have the potential to generate high friction especially in the presence of blood which is indeed the in vivo lubricant in the early weeks after implantation. Friction factors in higher clearance bearings were found to be lower than those of the lower clearance bearings using blood as the lubricant. Similar trends, i.e. increase in friction factor with reduction in diametral clearance, were found to be also the case using a combination of BS+CMC or BS+HA+CMC as lubricants having viscosities in the range 0.1-0.2 and 0.03-0.14 Pas, respectively. On the other hand, all the lubricants with lower viscosities in the range 0.001-0.0013 and 0.001-0.013 Pas for both BS+CMC and BS+HA+CMC, respectively, showed the opposite effect, i.e. caused an increase in friction factor with increase in diametral clearance. Another six large diameter (50mm nominal) BHR deflected prostheses with various clearances (~ 50-280μm after cup deflection) were friction tested in vitro in the presence of blood and clotted blood to study the effect of cup deflection on friction. It was found that the biological lubricants caused higher friction factors at the lower diametral clearances for blood and clotted blood as clearance decreased from 280μm to 50μm (after deflection). The result of this investigation has suggested strongly that the optimum clearance for the 50 mm diameter MOM BHR implants to be ≥150μm and <235μm when blood lubricant used, so as to avoid high frictions (i.e. avoid friction factors >0.2) and be able to accommodate a mixed lubrication mode and hence lower the risk of micro- or even macro-motion specially immediately after hip implantation. These suggested optimum clearances will also allow for low friction (i.e. friction factors of <0.2-0.07) and reasonable lubrication (dominantly mixed regime) for the likely cup deflection occurring as a result of press-fit fixation.

In real life, immediately after joint replacement, the artificial joint is actually bathed in blood (and clotted blood) instead of synovial fluid. Blood contains large molecules and cells of size ~ 5 to 20 2m suspended in plasma and considered to be a non-Newtonian (pseudoplastic) fluid with density of 1060 Kg/m3 and viscosity ~ 0.01 Pas at shear rates of 3000 s-1 (as obtained in this work). The effect of these properties on friction and lubrication is not fully understood and, so far to our knowledge, hardly any studies have been carried out regarding friction of metal-on-metal bearings with various clearances in the presence of lubricants such as blood or a fluid containing macromolecules such as hyaluronic acid (HA) which is a major component of synovial fluid increasing its viscosity and lubricating properties. In this work, therefore, we have investigated the frictional behaviour of a group of Smith and Nephew Birmingham Hip Resurfacing implants with a nominal diameter of 50mm and diametral clearances in the range ~ 80 2m to 300 2m, in the presence of blood (clotted and whole blood), a combination of bovine serum (BS) with hyaluronic acid (HA) and carboxymethyl cellulose (CMC, as gelling agent) adjusted to a range of viscosities (~0.001-0.2 Pas), and bovine serum with CMC adjusted to a similar range of viscosities. These results suggested that reduced clearance bearings have the potential to generate high friction especially in the presence of blood which is indeed the in vivo lubricant in the early weeks after implantation. Friction factors in higher clearance bearings were found to be lower than those of the lower clearance bearings using blood as the lubricant. Similar trends, i.e. increase in friction factor with reduction in diametral clearance, were found to be also the case using a combination of BS+CMC or BS+HA+CMC as lubricants having viscosities in the range 0.1-0.2 and 0.03-0.14 Pas, respectively. On the other hand, all the lubricants with lower viscosities in the range 0.001-0.0013 and 0.001-0.013 Pas for both BS+CMC and BS+HA+CMC, respectively, showed the opposite effect, i.e. caused an increase in friction factor with increase in diametral clearance. Another six large diameter (50mm nominal) BHR deflected prostheses with various clearances (~ 50-2802m after cup deflection) were friction tested in vitro in the presence of blood and clotted blood to study the effect of cup deflection on friction. It was found that the biological lubricants caused higher friction factors at the lower diametral clearances for blood and clotted blood as clearance decreased from 2802m to 502m (after deflection). The result of this investigation has suggested strongly that the optimum clearance for the 50 mm diameter MOM BHR implants to be ¿1502m and <2352m when blood lubricant used, so as to avoid high frictions (i.e. avoid friction factors >0.2) and be able to accommodate a mixed lubrication mode and hence lower the risk of micro- or even macro-motion specially immediately after hip implantation. These suggested optimum clearances will also allow for low friction (i.e. friction factors of <0.2-0.07) and reasonable lubrication (dominantly mixed regime) for the likely cup deflection occurring as a result of press-fit fixation. / Smith & Nephew Orthopaedics Ltd.

Depuis les dernières années, la prévalence de personnes souffrant de dégénérescence des cartilages articulaires, communément appelée ostéoarthrite (OA), ne cesse d’augmenter. Les douleurs articulaires et les raideurs musculaires associées à cette pathologie mènent à des limitations des capacités fonctionnelles, à une perte de mobilité et d’autonomie affectant grandement la qualité de vie de ces personnes. Afin de soulager les personnes souffrant de cette pathologie, l’arthroplastie de la hanche est une procédure chirurgicale fréquemment utilisée. À la suite de cette chirurgie, une amélioration de la qualité de vie et une reprise des capacités fonctionnelles sont souvent observées. Cependant, comparativement à des sujets sains, la vitesse de marche est diminuée, une faiblesse des muscles abducteurs de la hanche est constatée et des mouvements compensatoires au niveau du tronc sont persistants. L’objectif de cette thèse est d’évaluer le patron locomoteur chez des patients qui subiront une arthroplastie de la hanche. Plus spécifiquement, les adaptations locomotrices pré et post-opératoires seront quantifiées dans le but d’apporter des modifications aux programmes de réhabilitation pour ainsi favoriser un patron locomoteur sans déficit. Afin de répondre à cet objectif, trois études distinctes ont été effectuées. Dans le cadre de la première étude, l’impact de l’implantation d’une prothèse totale de la hanche avec une tête fémorale de large diamètre et une prothèse de resurfaçage a été évalué par rapport aux sujets sains lors de la locomotion. Au cours de cette étude, le contrôle du tronc a été analysé en utilisant la distance entre le centre de masse corporel et le centre articulaire de la hanche opérée. Suite aux résultats obtenus, aucune différence majeure n’existe entre les deux types de prothèses en ce qui a trait au contrôle du tronc et ce, à un an post-opératoire. Lors de la deuxième étude, la symétrie des paramètres biomécaniques des membres inférieurs lors de la locomotion chez des patients ayant bénéficié de l’implantation d’une prothèse de la hanche a été caractérisée suite à un programme d’exercices péri-opératoires (pré et post-opératoire). Lors de cette étude, le programme d’exercices péri-opératoires était complémentaire au protocole de réadaptation du centre hospitalier. D’après les résultats obtenus lors de cette étude exploratoire, ce programme d’exercices péri-opératoires semble permettre d’améliorer la symétrie de la puissance et du travail musculaire au niveau de la hanche, du genou et de la cheville favorisant ainsi un patron de marche avec de minimes compensations. Finalement, dans le cadre de la troisième étude, l’approche prédictive et l’approche fonctionnelle, utilisées pour localiser le centre articulaire de la hanche, ont été comparées aux mesures radiographiques, chez des patients à la suite d’un remplacement articulaire de la hanche. À la suite de cette étude, les résultats démontrent que l’utilisation de l’approche fonctionnelle est plus appropriée chez des patients ayant bénéficié d’une arthroplastie de la hanche. En effet, cette approche individualisée est plus précise ce qui, par conséquent, permettra d’obtenir des résultats de plus grande qualité lors d’analyses biomécaniques de la locomotion. / In recent years, the prevalence of people suffering from joint cartilage degeneration, called osteoarthritis (OA), still increases. The joint pain and muscle stiffness related to this pathology have an impact on patients’ quality of life by limiting their functional capacities, mobility and autonomy. In order to relieve these patients, hip arthroplasty is a frequently used surgical procedure. Even if there is an improvement in quality of life and a restoration of functional capacities in these patients, some impairment seem to persist during the post-operative period. The walking velocity is slower when compared to healthy subjects, a hip abductor muscle weakness is observed and trunk compensations lasted during the post-operative period. The aim of this thesis is to evaluate patients undergoing hip arthroplasty during locomotion. More specifically, gait pattern adaptations will be quantified pre and post-operatively to revise rehabilitation programs in order to promote a healthy gait pattern. Three separate studies were conducted to meet this objective. The first study compared the effect of a large femoral head hip prosthesis and a hip resurfacing prosthesis to healthy subjects. During this study, the trunk control was analyzed using the distance between the body center of mass and the hip prosthetic joint center. The results obtained show no major difference between the two types of prosthesis and the healthy control one year post-operatively. During the second study, biomechanics parameter symmetry of the lower limb of gait pattern in patients undergoing hip arthroplasty was characterized following a peri-operative (pre and post-operatively) exercise program. The exercise program was complementary to the medical center standard rehabilitation program. Based on the results of this exploratory study, the peri-operative exercise program seems to improve the symmetry of the muscular power and work of the hip, knee and ankle which promote a healthy gait pattern without compensations. Finally, for the third study, the predictive and the functional approaches, used to locate the hip joint center, were compared to radiographic measurements in patients undergoing hip arthroplasty. The results of this study demonstrated that the functional approach was more appropriate for these patients. This individualized approach is more accurate which leads to quality improvement during biomechanical analysis of gait pattern.

Depuis les dernières années, la prévalence de personnes souffrant de dégénérescence des cartilages articulaires, communément appelée ostéoarthrite (OA), ne cesse d’augmenter. Les douleurs articulaires et les raideurs musculaires associées à cette pathologie mènent à des limitations des capacités fonctionnelles, à une perte de mobilité et d’autonomie affectant grandement la qualité de vie de ces personnes. Afin de soulager les personnes souffrant de cette pathologie, l’arthroplastie de la hanche est une procédure chirurgicale fréquemment utilisée. À la suite de cette chirurgie, une amélioration de la qualité de vie et une reprise des capacités fonctionnelles sont souvent observées. Cependant, comparativement à des sujets sains, la vitesse de marche est diminuée, une faiblesse des muscles abducteurs de la hanche est constatée et des mouvements compensatoires au niveau du tronc sont persistants. L’objectif de cette thèse est d’évaluer le patron locomoteur chez des patients qui subiront une arthroplastie de la hanche. Plus spécifiquement, les adaptations locomotrices pré et post-opératoires seront quantifiées dans le but d’apporter des modifications aux programmes de réhabilitation pour ainsi favoriser un patron locomoteur sans déficit. Afin de répondre à cet objectif, trois études distinctes ont été effectuées. Dans le cadre de la première étude, l’impact de l’implantation d’une prothèse totale de la hanche avec une tête fémorale de large diamètre et une prothèse de resurfaçage a été évalué par rapport aux sujets sains lors de la locomotion. Au cours de cette étude, le contrôle du tronc a été analysé en utilisant la distance entre le centre de masse corporel et le centre articulaire de la hanche opérée. Suite aux résultats obtenus, aucune différence majeure n’existe entre les deux types de prothèses en ce qui a trait au contrôle du tronc et ce, à un an post-opératoire. Lors de la deuxième étude, la symétrie des paramètres biomécaniques des membres inférieurs lors de la locomotion chez des patients ayant bénéficié de l’implantation d’une prothèse de la hanche a été caractérisée suite à un programme d’exercices péri-opératoires (pré et post-opératoire). Lors de cette étude, le programme d’exercices péri-opératoires était complémentaire au protocole de réadaptation du centre hospitalier. D’après les résultats obtenus lors de cette étude exploratoire, ce programme d’exercices péri-opératoires semble permettre d’améliorer la symétrie de la puissance et du travail musculaire au niveau de la hanche, du genou et de la cheville favorisant ainsi un patron de marche avec de minimes compensations. Finalement, dans le cadre de la troisième étude, l’approche prédictive et l’approche fonctionnelle, utilisées pour localiser le centre articulaire de la hanche, ont été comparées aux mesures radiographiques, chez des patients à la suite d’un remplacement articulaire de la hanche. À la suite de cette étude, les résultats démontrent que l’utilisation de l’approche fonctionnelle est plus appropriée chez des patients ayant bénéficié d’une arthroplastie de la hanche. En effet, cette approche individualisée est plus précise ce qui, par conséquent, permettra d’obtenir des résultats de plus grande qualité lors d’analyses biomécaniques de la locomotion. / In recent years, the prevalence of people suffering from joint cartilage degeneration, called osteoarthritis (OA), still increases. The joint pain and muscle stiffness related to this pathology have an impact on patients’ quality of life by limiting their functional capacities, mobility and autonomy. In order to relieve these patients, hip arthroplasty is a frequently used surgical procedure. Even if there is an improvement in quality of life and a restoration of functional capacities in these patients, some impairment seem to persist during the post-operative period. The walking velocity is slower when compared to healthy subjects, a hip abductor muscle weakness is observed and trunk compensations lasted during the post-operative period. The aim of this thesis is to evaluate patients undergoing hip arthroplasty during locomotion. More specifically, gait pattern adaptations will be quantified pre and post-operatively to revise rehabilitation programs in order to promote a healthy gait pattern. Three separate studies were conducted to meet this objective. The first study compared the effect of a large femoral head hip prosthesis and a hip resurfacing prosthesis to healthy subjects. During this study, the trunk control was analyzed using the distance between the body center of mass and the hip prosthetic joint center. The results obtained show no major difference between the two types of prosthesis and the healthy control one year post-operatively. During the second study, biomechanics parameter symmetry of the lower limb of gait pattern in patients undergoing hip arthroplasty was characterized following a peri-operative (pre and post-operatively) exercise program. The exercise program was complementary to the medical center standard rehabilitation program. Based on the results of this exploratory study, the peri-operative exercise program seems to improve the symmetry of the muscular power and work of the hip, knee and ankle which promote a healthy gait pattern without compensations. Finally, for the third study, the predictive and the functional approaches, used to locate the hip joint center, were compared to radiographic measurements in patients undergoing hip arthroplasty. The results of this study demonstrated that the functional approach was more appropriate for these patients. This individualized approach is more accurate which leads to quality improvement during biomechanical analysis of gait pattern.

Introduction Le remplacement prothétique est le traitement ultime pour la dégénérescence avancée de la hanche. Cependant, l’usure prématurée des surfaces de frottement métal contre polyéthylène conventionnel (MoPc) réduit de façon importante sa longévité chez les patients jeunes et actifs. Pour surmonter ce problème, des surfaces de frottement alternatives ont été proposées, notamment les couples métal-métal (MoM) et céramique-céramique (CoC). Le but de cette étude est d'évaluer la survie à long terme de ces surfaces d'appui lors du remplacement total de la hanche (PTH) avec une articulation de petit diamètre MoM ou CoC et du resurfaçage de la hanche (RH) MoM. Méthodes La survie des implants a été évaluée à long terme dans deux études où les sujets ont été randomisées pour une PTH MoM 28 mm (99 hanches) ou un RH (104 hanches) dans l’étude 1 ou une PTH CoC (71 hanches) ou MoPc (69 hanches) dans l’étude 2. Les mesures d’efficacité principales comparés, au dernier recul, était le taux de révision, les taux de complications, score fonctionnels validés, et les signes radiographiques anormaux. Résultats Étude 1, après un suivi moyen de 15 ans, la survie avec révision pour toutes causes était de (89,2 % pour le RH versus 94,2 % pour la PTH MoM, p=0,292). Toutefois avec une révision aseptique comme critère d'évaluation, la survie était significativement plus élevée dans les PTH (97,4 % contre 89,2 % ; p=0,033). Les deux groupes ont obtenu des scores fonctionnels similaires. Étude 2, après un suivi moyen de 21 ans, la survie était significativement plus élevée (96,9% vs 73,6%, p<0,001) pour les PTH CoC versus MoPc. À l'évaluation radiographique, 13 % des MoPc étaient considérés descellées versus aucune CoC et 61 % des MoPc versus 6 % des CoC présentaient des signes d’ostéolyse (p<0,001). Les PTHs CoC avaient des scores moyens de WOMAC significativement plus élevés que le groupe MoPc (11.0 vs 19.4; p = 0.048). Conclusion L’utilisation de couples dur-dur MoM ou CoC en PTH ou RH ont offert une excellente survie et fonction à long terme chez une clientèle de sujets jeunes et actifs. En comparaison, le taux d’échec élevé du couple MoPc confirme qu’il doit être abandonné. Les résultats de cette étude doivent être mis en perspective avec les résultats futurs des nouveaux couples métal contre polyéthylènes réticulés. / Introduction Prosthetic replacement is the ultimate treatment for advanced hip degeneration. However, premature wear of the metal-on-conventional polyethylene (MoPc) bearing surfaces significantly reduces its longevity in young and active patients. To overcome this problem, alternative bearing surfaces have been proposed including metal-on-metal (MoM) and ceramic-on-ceramic (CoC) bearings. The aim of this study is to evaluate the long-term survival of these bearing surfaces during total hip replacement (THA) with a small diameter MoM or CoC bearings and hip resurfacing (HR) MoM. Methods Long-term implant survival was assessed in two studies where subjects were randomized to 28mm MoM THA (99 hips) or HR (104 hips) in Study 1, or CoC THA (71 hips) or MoPc (69 hips) in Study 2. The main outcome measures compared, at final follow-up, were revision rate, complications’ rate, validated functional scores, and abnormal radiographic signs. Results Study I: after a mean of 15 years, survivorship with endpoint all-cause revision was 89.2% for HR versus 94.2% for MoM THA MoM (p = 0.292). However, with aseptic revision as an endpoint, survivorship was significantly higher in MoM THA (97.4%) compared to (89.2%) in HR (p = 0.033). Both groups achieved similar functional scores. Study II: after a mean follow-up of 21 years, survivorship was significantly higher in CoC (96.9%) versus (73.6%) in MoPc THAs (p<0.001). On radiographic evaluation, 13% MoPc were considered loose versus non in CoC, and 61% MoPc versus 6% CoC showed osteolytic signs (p<0.001). CoC had better mean WOMAC scores than MoPc (11.0 vs 19.4; p = 0.048). Conclusion Good long-term survival and function for HR and MoM 28-mm THA implants with similar overall rates of complications and revisions. CoC provided excellent results compared to MoPc at more than 20-year follow-up.