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Subject specific hip geometry after THP influences hip joint reaction forces during gait
S62
Oral Presentations / Gait & Posture 24S (2006) S7–S97
O-37
3. Statement of clinical significance
Subject specific hip geometry after THP influences hip joint reaction forces during gait
A better insight in the biomechanical factors influencing hip loading during gait after THP will contribute to an enhanced understanding of the factors affecting initial implant fixation and eventually prevent implant loosening.
G. Lenaerts a,b,∗ , A. Spaepen a
I. Jonkers a ,
G. Van der Perre b ,
a
Department of Biomedical Kinesiologym FaBeR, Katholieke Universiteit Leuven, Belgium b Department of Mechanical Engineering, FTW, Katholieke Universiteit Leuven, Belgium
1. Summary/conclusions Subject specific hip geometry (especially NSA) after total hip joint replacement alters the joint reaction forces at the hip and affects implant loading.
2. Introduction Each year, 17,000 hip prostheses are implanted in Belgium. 5–10% need revision because of implant loosening. Several factors have been identified to predispose implant loosening. Musculoskeletal loading is often reported as an important factor affecting the biological processes involved in bone remodeling and primary fixation of implants. In patients with THP, the subject specific anatomy of the hip implant determines the moment generating capacity of the surrounding muscles. Our previous work reported a decrease in moment generating capacity of the hip abductors when a subject specific model was used that incorporates RX based values for femoral neck length (NL), femoral neck-shaft angle (NSA) and width of the pelvis (WP). As a result, we reported marked changes in calculated muscle (co-) activations using a static optimization approach. The present work evaluates to what extent hip contact forces during gait are influenced by subject-specific geometry of the hip and the resulting changes in muscle activation balance during gait.
4. Methods NL, NSA and WP were measured in 20 subjects, based on digitized post-operative RX-images (Imagica, GreyStone Inc). A deformable musculoskeletal model of the lower limb was adjusted to incorporate NL, NSA and WP for all patients (SIMM, Musculographics). NL varied from 41 to 86 mm, NSA between 113◦ and 144◦ , PW between 315 mm and 402 mm. Kinematic and kinetic data obtained from a normal gait trial were imposed to each individualised model to calculate (1) joint moments (2) individual muscle force generating capacity and (3) muscle moment arms over the gait cycle. Muscle activation patterns balancing the external joint moments were computed using a static optimisation algorithm, minimizing the sum of the muscle forces (Matlab, MathWorks Inc.). The 3D hip reaction forces were computed taking into account the muscle forces resulting from the muscle activation patterns, as well as external forces (the ground reaction forces—inertial forces and gravity). This analysis was repeated for a model with halve hip abductor force generating capacity, mimicking hip abductor weakness after surgery. The resulting changes in muscle activations were imposed [1]. Peak reaction forces during single limb stance as well as the associated inclination of the reaction force in the sagittal and the frontal plane are reported.
5. Results The peak reaction forces in the undeformed model are within the range reported in literature [2]. The changes in muscle activations due to the modified geometry introduced changes in peak reaction forces (Fig. 1). Consistent changes were most pronounced for the mediolateral component show-
Fig. 1. Changes in peak joint reaction forces during stance with increasing NSA. UM is the reference undeformed model.
Oral Presentations / Gait & Posture 24S (2006) S7–S97
S63
Fig. 2. Changes in inclination angle associated with peak joint reaction forces during stance with increasing NSA. UM is the reference undeformed model.
ing a decrease in the peak mediolateral component with increasing NSA. A distinct trend to increased peak vertical joint reaction forces with increased NSA was found. As a result, the inclination angle of the resultant reaction force in the frontal plane decreased substantially with decreasing NSA, introducing a more vertical alignment of the reaction force at peak loading (Fig. 2). Although, the sagittal plane angle showed variations in the individual model, no clear relation with the changes in NSA could be established. When halving the abductor muscle force generating capacity, all components of the reaction forces decreased. However, the previously described relations of the joint reaction forces with NSA were unchanged.
6. Discussion The interaction between hip geometry, muscle moment generating capacity and hip loading can be analyzed using inverse dynamics based on personalized musculoskeletal modeling. Our results show an important interaction between NSA and mediolateral reaction forces, causing a more vertical inclination angle in the frontal plane during gait. This therefore will result in a more vertical loading of the implant when peak reaction forces are applied during gait. Although we did not analyze the interaction between NSA, NL and PW, our findings do suggest that a minimal NSA angle needs to be preserved in order to limit the mediolateral force component and limit the resulting bending stress in the femoral shaft. The calculation of individual hip loading by use of musculoskeletal modeling and inverse analysis may contribute to understanding the effect of hip joint loading on bone remodeling and implant load shearing.
O-38 Biomechanical and metabolic performance of a new orthotic knee joint principle for stance phase safety T. Schmalz a,∗ , S. Blumentritt a , H. Drewitz b a b
Department of Research, Otto Bock Health Care, Duderstadt, Germany Orthopaedic Workshop, Rehabilitation Centre, G¨ottingen, Germany
1. Summary Recently developed orthotic knee joints that are integrated into a knee–ankle–foot–orthosis (KAFO) stabilize the paralyzed knee in stance phase while permitting natural flexion and extension at the knee during swing phase. The functional advantages for these patients can be documented by metabolic and biomechanical parameters.
2. Introduction For many patients with lower limb weakness or paralysis, functional mobility is achieved by means of a KAFO. In traditional orthoses, the knee joint is locked throughout the complete gait cycle (knee completely locked, KTL) to guarantee safety during stance phase. Over the last few years, five new orthotic systems [1] have been developed worldwide which stabilize the knee joint during stance phase without interfering with knee flexion in swing (knee locked during stance, KLDS). In the present study, KAFOs utilizing KTL and KLDS principles are compared based on metabolic and biomechanical parameters.
References 3. Statement of clinical significance [1] Lenaerts G, Jonkers I, Spaepen A. Gait Post 2005;22(1):S19. [2] Stansfield BW, Nicol AC. Clin Biomech 2002;17:130–9.
doi:10.1016/j.gaitpost.2006.11.045
This study investigates and documents the functional advantages that patients with lower limb weakness or paralysis can anticipate from orthoses utilizing the new KLDS principles.
Oral Presentations / Gait & Posture 24S (2006) S7–S97
O-37
3. Statement of clinical significance
Subject specific hip geometry after THP influences hip joint reaction forces during gait
A better insight in the biomechanical factors influencing hip loading during gait after THP will contribute to an enhanced understanding of the factors affecting initial implant fixation and eventually prevent implant loosening.
G. Lenaerts a,b,∗ , A. Spaepen a
I. Jonkers a ,
G. Van der Perre b ,
a
Department of Biomedical Kinesiologym FaBeR, Katholieke Universiteit Leuven, Belgium b Department of Mechanical Engineering, FTW, Katholieke Universiteit Leuven, Belgium
1. Summary/conclusions Subject specific hip geometry (especially NSA) after total hip joint replacement alters the joint reaction forces at the hip and affects implant loading.
2. Introduction Each year, 17,000 hip prostheses are implanted in Belgium. 5–10% need revision because of implant loosening. Several factors have been identified to predispose implant loosening. Musculoskeletal loading is often reported as an important factor affecting the biological processes involved in bone remodeling and primary fixation of implants. In patients with THP, the subject specific anatomy of the hip implant determines the moment generating capacity of the surrounding muscles. Our previous work reported a decrease in moment generating capacity of the hip abductors when a subject specific model was used that incorporates RX based values for femoral neck length (NL), femoral neck-shaft angle (NSA) and width of the pelvis (WP). As a result, we reported marked changes in calculated muscle (co-) activations using a static optimization approach. The present work evaluates to what extent hip contact forces during gait are influenced by subject-specific geometry of the hip and the resulting changes in muscle activation balance during gait.
4. Methods NL, NSA and WP were measured in 20 subjects, based on digitized post-operative RX-images (Imagica, GreyStone Inc). A deformable musculoskeletal model of the lower limb was adjusted to incorporate NL, NSA and WP for all patients (SIMM, Musculographics). NL varied from 41 to 86 mm, NSA between 113◦ and 144◦ , PW between 315 mm and 402 mm. Kinematic and kinetic data obtained from a normal gait trial were imposed to each individualised model to calculate (1) joint moments (2) individual muscle force generating capacity and (3) muscle moment arms over the gait cycle. Muscle activation patterns balancing the external joint moments were computed using a static optimisation algorithm, minimizing the sum of the muscle forces (Matlab, MathWorks Inc.). The 3D hip reaction forces were computed taking into account the muscle forces resulting from the muscle activation patterns, as well as external forces (the ground reaction forces—inertial forces and gravity). This analysis was repeated for a model with halve hip abductor force generating capacity, mimicking hip abductor weakness after surgery. The resulting changes in muscle activations were imposed [1]. Peak reaction forces during single limb stance as well as the associated inclination of the reaction force in the sagittal and the frontal plane are reported.
5. Results The peak reaction forces in the undeformed model are within the range reported in literature [2]. The changes in muscle activations due to the modified geometry introduced changes in peak reaction forces (Fig. 1). Consistent changes were most pronounced for the mediolateral component show-
Fig. 1. Changes in peak joint reaction forces during stance with increasing NSA. UM is the reference undeformed model.
Oral Presentations / Gait & Posture 24S (2006) S7–S97
S63
Fig. 2. Changes in inclination angle associated with peak joint reaction forces during stance with increasing NSA. UM is the reference undeformed model.
ing a decrease in the peak mediolateral component with increasing NSA. A distinct trend to increased peak vertical joint reaction forces with increased NSA was found. As a result, the inclination angle of the resultant reaction force in the frontal plane decreased substantially with decreasing NSA, introducing a more vertical alignment of the reaction force at peak loading (Fig. 2). Although, the sagittal plane angle showed variations in the individual model, no clear relation with the changes in NSA could be established. When halving the abductor muscle force generating capacity, all components of the reaction forces decreased. However, the previously described relations of the joint reaction forces with NSA were unchanged.
6. Discussion The interaction between hip geometry, muscle moment generating capacity and hip loading can be analyzed using inverse dynamics based on personalized musculoskeletal modeling. Our results show an important interaction between NSA and mediolateral reaction forces, causing a more vertical inclination angle in the frontal plane during gait. This therefore will result in a more vertical loading of the implant when peak reaction forces are applied during gait. Although we did not analyze the interaction between NSA, NL and PW, our findings do suggest that a minimal NSA angle needs to be preserved in order to limit the mediolateral force component and limit the resulting bending stress in the femoral shaft. The calculation of individual hip loading by use of musculoskeletal modeling and inverse analysis may contribute to understanding the effect of hip joint loading on bone remodeling and implant load shearing.
O-38 Biomechanical and metabolic performance of a new orthotic knee joint principle for stance phase safety T. Schmalz a,∗ , S. Blumentritt a , H. Drewitz b a b
Department of Research, Otto Bock Health Care, Duderstadt, Germany Orthopaedic Workshop, Rehabilitation Centre, G¨ottingen, Germany
1. Summary Recently developed orthotic knee joints that are integrated into a knee–ankle–foot–orthosis (KAFO) stabilize the paralyzed knee in stance phase while permitting natural flexion and extension at the knee during swing phase. The functional advantages for these patients can be documented by metabolic and biomechanical parameters.
2. Introduction For many patients with lower limb weakness or paralysis, functional mobility is achieved by means of a KAFO. In traditional orthoses, the knee joint is locked throughout the complete gait cycle (knee completely locked, KTL) to guarantee safety during stance phase. Over the last few years, five new orthotic systems [1] have been developed worldwide which stabilize the knee joint during stance phase without interfering with knee flexion in swing (knee locked during stance, KLDS). In the present study, KAFOs utilizing KTL and KLDS principles are compared based on metabolic and biomechanical parameters.
References 3. Statement of clinical significance [1] Lenaerts G, Jonkers I, Spaepen A. Gait Post 2005;22(1):S19. [2] Stansfield BW, Nicol AC. Clin Biomech 2002;17:130–9.
doi:10.1016/j.gaitpost.2006.11.045
This study investigates and documents the functional advantages that patients with lower limb weakness or paralysis can anticipate from orthoses utilizing the new KLDS principles.