marco spinelli - Academia.edu (original) (raw)

Papers by marco spinelli

Case-based Reasoning (CBR) is a mature tech- nology for building knowledge-based systems. Unlike ... more Case-based Reasoning (CBR) is a mature tech- nology for building knowledge-based systems. Unlike with reasoning approaches making use of deductive inference, CBR-based applica- tions are capable to produce useful results even if no answer matches the query exactly. Result sets presented to users are ordered by means of similarity and utility. However, for knowledge intensive domains we discovered that results sets enriched by calculated similarity values for particular answers are not sufficient for ex- perts. Such users have a demand for additional information and explanations making the pro- posed results more transparent. By presenting additional explanations to them, their confi- dence in the result set increases and possible deficiencies, e.g. in the weight model, can be revealed and corrected. In this position paper we investigate explanation approaches for CBR from the user level perspective. Besides identifying potential uses cases, we sketch techniques for creating different kinds of ex- planations and relate them to already existing approaches from other areas of CBR research, e.g. conversational CBR.

Proceedings of The Institution of Mechanical Engineers Part H-journal of Engineering in Medicine, 2010

Recent in vivo studies have identified variations in knee prosthesis function depending on prosth... more Recent in vivo studies have identified variations in knee prosthesis function depending on prosthesis geometry, kinematic conditions, and the absence/presence of soft-tissue constraints after knee replacement surgery. In particular, unicondylar knee replacements (UKR) are highly sensitive to such variations. However, rigorous descriptions of UKR function through experimental simulation studies, performed under physiological force-controlled conditions, are lacking. The current study evaluated the long-term functional performance of a widely used fixed-bearing unicompartmental knee replacement, mounted in a bi-unicondylar configuration (Bi-UKR), utilizing a force-controlled knee simulator during a simulated (ISO 14243) walking cycle. The wear behaviour, the femoral-tibial kinematics, and the incurred damage scars were analysed. The wear rates for the medial and the lateral compartments were 10.27 +/- 1.83 mg/million cycles and 4.49 +/- 0.53 mg/million cycles, respectively. Although constant-input force-controlled loading conditions were maintained throughout the simulation, femoral-tibial contact point kinematics decreased by 65 to 68 per cent for average anterior/posterior travel and by 58 to 74 per cent for average medial/lateral travel with increasing cycling time up to 2 million cycles. There were no significant differences in damage area or damage extent between the medial and the lateral compartments. Focal damage scars representing the working region of the femoral component on the articular surface extended over a range of 16-21 mm in the anterior-posterior direction. Kinematics on the shear plane showed slight variations with increasing cycling time, and the platform exhibited medial pivoting over the entire test. These measures provide valuable experimental insight into the effect of the prosthesis design on wear, kinematics, and working area. These functional assessments of Bi-UKR under force-controlled knee joint wear simulation show that accumulated changes in the UKR articular conformity manifested as altered kinematics both for anterior/posterior translations and internal/external rotations.

Proceedings of The Institution of Mechanical Engineers Part H-journal of Engineering in Medicine, 2008

ABSTRACT The wear of metal-on-metal bearings is affected by various design parameters, such as th... more ABSTRACT The wear of metal-on-metal bearings is affected by various design parameters, such as the clearance or surface roughness. It would be very useful to have a significant indicator of wear according to these design parameters, such as the Λ ratio. Three different batches of cast high- and low-carbon cobalt-chromium hip implants (28mm, 32mm, and 36mm diameters) were tested in a hip joint simulator for 2×106 cycles. Bovine calf serum was used as lubricant, and the samples were weighed at regular intervals during the test. The predictive role of the Λ ratio on the wear behaviour was investigated. Three different configurations were tested to explore the wear rate for a broad range of Λ ratios. The results of these studies clearly showed that the femoral heads of 36mm diameter had the best wear behaviour with respect to the other two smaller configurations tested. From a predictive point of view, the Λ ratios associated with the configurations tested could clearly indicate that the femoral heads of 36mm diameter worked in the mixed-lubrication regime (Λ>1); all the smallest configurations (28mm size) had Λ <1, thus showing their aptitude to work in the boundary lubrication regime, with substantially higher volume depletion due to wear. The Λ values associated with the 32mm size varied in a range around 1 (0.95<Λ<1.16), suggesting the possibility of operating in the mixed-lubrication regime.

Wear, 2009

One of the most recent advances in knee replacement surgery is the Unicompartmental Knee Prosthes... more One of the most recent advances in knee replacement surgery is the Unicompartmental Knee Prosthesis that involves the substitution of only one compartment. Uncertainties on the survivorship of such design led to the improvement of pre-clinical mechanical simulation. To effectively support this market phase with clinically relevant wear data it is important to be able to accurately quantify it and the consequent knee prostheses functionality.

Wear, 2011

Replaced hip joints are normally expected to last 15-20 years. However, although the procedure is... more Replaced hip joints are normally expected to last 15-20 years. However, although the procedure is nowadays successfully performed, up to 10% of procedures carried out are revision operations to replace joints, which have failed prematurely, mainly in case of polymeric or metallic bearing surfaces. In fact, particulate debris, generated by wear of the bearing surfaces, are "attacked" by the immune system which results in the death of surrounding bone tissue which in turn leads to loosening of the joint and pain to the patient. All-ceramic hip replacements were introduced to eliminate this mechanism and reduce wear.

Tribology International, 2010

New cross-linked polyethylene acetabular cups, obtained by thermo-compression process, were compa... more New cross-linked polyethylene acetabular cups, obtained by thermo-compression process, were compared with conventional and traditional commercially available cross-linked polyethylene in terms of wear behaviour in a hip simulator for 10 million cycles using bovine calf serum as lubricant.

Proceedings of The Institution of Mechanical Engineers Part H-journal of Engineering in Medicine, 2010

Hip joint wear simulators are used extensively to simulate the dynamic behaviour of the human hip... more Hip joint wear simulators are used extensively to simulate the dynamic behaviour of the human hip joint and, through the wear rate, gain a concrete indicator about the overall wear performance of different coupled bearings. Present knowledge of the dynamic behaviour of important concurrent indicators, such as the coefficient of friction, could prove helpful for the continuing improvement in applied biomaterials. A limited number of commercial or custom-made simulators have been designed specifically for friction studies but always separately from wear tests; thus, analysis of these two important parameters has remained unconnected. As a result, a new friction sensor has been designed, built, and integrated in a commercial biaxial rocking motion hip simulator. The aim of this study is to verify the feasibility of an experimental set-up in which the dynamic measurement of the friction factor could effectively be implemented in a standard wear test without compromising its general accuracy and repeatability. A short wear test was run with the new set-up for 1 x 10(6) cycles. In particular, three soft-bearings (metal-on-polyethylene, phi = 28 mm) were tested; during the whole test, axial load and frictional torque about the vertical loading axis were synchronously recorded in order to calculate the friction factor. Additional analyses were performed on the specimens, before and after the test, in order to verify the accuracy of the wear test. The average friction factor was 0.110 +/- 0.025. The friction sensors showed good accuracy and repeatability throughout. This innovative set-up was able to reproduce stable and reliable measurements. The results obtained encourage further investigations of this set-up for long-term assessment and using different combinations of materials.

Proceedings of The Institution of Mechanical Engineers Part H-journal of Engineering in Medicine, 2010

Modification of knee joint wear simulation methods has included 'anatomic attachm... more Modification of knee joint wear simulation methods has included 'anatomic attachment' of unicondylar knee replacements (UKR) onto synthetic femurs with material properties and morphology similar to human femurs. The present study assesses the effect of such modification by comparing the damage patterns on UKR polyethylene inserts after in vitro simulation using standard and modified simulation methods with those on inserts retrieved after in vivo function. Three groups of UKR inserts were evaluated after retrieval (Explant Group, n = 17) or after knee joint wear simulation with the components attached to standard metal blocks (Standard Group, n = 6) or synthetic femurs (Anatomic Group, n = 6). All UKR had similar non-conforming articular surfaces. Articular damage patterns (mode, frequency, and area) were quantified using digital image photogrammetry. Although some common damage modes were noted, knee joint wear simulation with standard or 'anatomic' attachment did not generate damage pattern sizes similar to the explanted UKR. A focal damage pattern consistent with contact between the metal femoral articular surface and the polyethylene inserts was evident on all inserts, but only the Explant Group had evidence of dispersed damage dominated by abrasive modes. Synthetic femurs added complexity to the wear simulation without generating wear patterns substantially more similar to those observed on retrieved inserts.

Case-based Reasoning (CBR) is a mature tech- nology for building knowledge-based systems. Unlike ... more Case-based Reasoning (CBR) is a mature tech- nology for building knowledge-based systems. Unlike with reasoning approaches making use of deductive inference, CBR-based applica- tions are capable to produce useful results even if no answer matches the query exactly. Result sets presented to users are ordered by means of similarity and utility. However, for knowledge intensive domains we discovered that results sets enriched by calculated similarity values for particular answers are not sufficient for ex- perts. Such users have a demand for additional information and explanations making the pro- posed results more transparent. By presenting additional explanations to them, their confi- dence in the result set increases and possible deficiencies, e.g. in the weight model, can be revealed and corrected. In this position paper we investigate explanation approaches for CBR from the user level perspective. Besides identifying potential uses cases, we sketch techniques for creating different kinds of ex- planations and relate them to already existing approaches from other areas of CBR research, e.g. conversational CBR.

Proceedings of The Institution of Mechanical Engineers Part H-journal of Engineering in Medicine, 2010

Recent in vivo studies have identified variations in knee prosthesis function depending on prosth... more Recent in vivo studies have identified variations in knee prosthesis function depending on prosthesis geometry, kinematic conditions, and the absence/presence of soft-tissue constraints after knee replacement surgery. In particular, unicondylar knee replacements (UKR) are highly sensitive to such variations. However, rigorous descriptions of UKR function through experimental simulation studies, performed under physiological force-controlled conditions, are lacking. The current study evaluated the long-term functional performance of a widely used fixed-bearing unicompartmental knee replacement, mounted in a bi-unicondylar configuration (Bi-UKR), utilizing a force-controlled knee simulator during a simulated (ISO 14243) walking cycle. The wear behaviour, the femoral-tibial kinematics, and the incurred damage scars were analysed. The wear rates for the medial and the lateral compartments were 10.27 +/- 1.83 mg/million cycles and 4.49 +/- 0.53 mg/million cycles, respectively. Although constant-input force-controlled loading conditions were maintained throughout the simulation, femoral-tibial contact point kinematics decreased by 65 to 68 per cent for average anterior/posterior travel and by 58 to 74 per cent for average medial/lateral travel with increasing cycling time up to 2 million cycles. There were no significant differences in damage area or damage extent between the medial and the lateral compartments. Focal damage scars representing the working region of the femoral component on the articular surface extended over a range of 16-21 mm in the anterior-posterior direction. Kinematics on the shear plane showed slight variations with increasing cycling time, and the platform exhibited medial pivoting over the entire test. These measures provide valuable experimental insight into the effect of the prosthesis design on wear, kinematics, and working area. These functional assessments of Bi-UKR under force-controlled knee joint wear simulation show that accumulated changes in the UKR articular conformity manifested as altered kinematics both for anterior/posterior translations and internal/external rotations.

Proceedings of The Institution of Mechanical Engineers Part H-journal of Engineering in Medicine, 2008

ABSTRACT The wear of metal-on-metal bearings is affected by various design parameters, such as th... more ABSTRACT The wear of metal-on-metal bearings is affected by various design parameters, such as the clearance or surface roughness. It would be very useful to have a significant indicator of wear according to these design parameters, such as the Λ ratio. Three different batches of cast high- and low-carbon cobalt-chromium hip implants (28mm, 32mm, and 36mm diameters) were tested in a hip joint simulator for 2×106 cycles. Bovine calf serum was used as lubricant, and the samples were weighed at regular intervals during the test. The predictive role of the Λ ratio on the wear behaviour was investigated. Three different configurations were tested to explore the wear rate for a broad range of Λ ratios. The results of these studies clearly showed that the femoral heads of 36mm diameter had the best wear behaviour with respect to the other two smaller configurations tested. From a predictive point of view, the Λ ratios associated with the configurations tested could clearly indicate that the femoral heads of 36mm diameter worked in the mixed-lubrication regime (Λ>1); all the smallest configurations (28mm size) had Λ <1, thus showing their aptitude to work in the boundary lubrication regime, with substantially higher volume depletion due to wear. The Λ values associated with the 32mm size varied in a range around 1 (0.95<Λ<1.16), suggesting the possibility of operating in the mixed-lubrication regime.

Wear, 2009

One of the most recent advances in knee replacement surgery is the Unicompartmental Knee Prosthes... more One of the most recent advances in knee replacement surgery is the Unicompartmental Knee Prosthesis that involves the substitution of only one compartment. Uncertainties on the survivorship of such design led to the improvement of pre-clinical mechanical simulation. To effectively support this market phase with clinically relevant wear data it is important to be able to accurately quantify it and the consequent knee prostheses functionality.

Wear, 2011

Replaced hip joints are normally expected to last 15-20 years. However, although the procedure is... more Replaced hip joints are normally expected to last 15-20 years. However, although the procedure is nowadays successfully performed, up to 10% of procedures carried out are revision operations to replace joints, which have failed prematurely, mainly in case of polymeric or metallic bearing surfaces. In fact, particulate debris, generated by wear of the bearing surfaces, are "attacked" by the immune system which results in the death of surrounding bone tissue which in turn leads to loosening of the joint and pain to the patient. All-ceramic hip replacements were introduced to eliminate this mechanism and reduce wear.

Tribology International, 2010

New cross-linked polyethylene acetabular cups, obtained by thermo-compression process, were compa... more New cross-linked polyethylene acetabular cups, obtained by thermo-compression process, were compared with conventional and traditional commercially available cross-linked polyethylene in terms of wear behaviour in a hip simulator for 10 million cycles using bovine calf serum as lubricant.

Proceedings of The Institution of Mechanical Engineers Part H-journal of Engineering in Medicine, 2010

Hip joint wear simulators are used extensively to simulate the dynamic behaviour of the human hip... more Hip joint wear simulators are used extensively to simulate the dynamic behaviour of the human hip joint and, through the wear rate, gain a concrete indicator about the overall wear performance of different coupled bearings. Present knowledge of the dynamic behaviour of important concurrent indicators, such as the coefficient of friction, could prove helpful for the continuing improvement in applied biomaterials. A limited number of commercial or custom-made simulators have been designed specifically for friction studies but always separately from wear tests; thus, analysis of these two important parameters has remained unconnected. As a result, a new friction sensor has been designed, built, and integrated in a commercial biaxial rocking motion hip simulator. The aim of this study is to verify the feasibility of an experimental set-up in which the dynamic measurement of the friction factor could effectively be implemented in a standard wear test without compromising its general accuracy and repeatability. A short wear test was run with the new set-up for 1 x 10(6) cycles. In particular, three soft-bearings (metal-on-polyethylene, phi = 28 mm) were tested; during the whole test, axial load and frictional torque about the vertical loading axis were synchronously recorded in order to calculate the friction factor. Additional analyses were performed on the specimens, before and after the test, in order to verify the accuracy of the wear test. The average friction factor was 0.110 +/- 0.025. The friction sensors showed good accuracy and repeatability throughout. This innovative set-up was able to reproduce stable and reliable measurements. The results obtained encourage further investigations of this set-up for long-term assessment and using different combinations of materials.

Proceedings of The Institution of Mechanical Engineers Part H-journal of Engineering in Medicine, 2010

Modification of knee joint wear simulation methods has included 'anatomic attachm... more Modification of knee joint wear simulation methods has included 'anatomic attachment' of unicondylar knee replacements (UKR) onto synthetic femurs with material properties and morphology similar to human femurs. The present study assesses the effect of such modification by comparing the damage patterns on UKR polyethylene inserts after in vitro simulation using standard and modified simulation methods with those on inserts retrieved after in vivo function. Three groups of UKR inserts were evaluated after retrieval (Explant Group, n = 17) or after knee joint wear simulation with the components attached to standard metal blocks (Standard Group, n = 6) or synthetic femurs (Anatomic Group, n = 6). All UKR had similar non-conforming articular surfaces. Articular damage patterns (mode, frequency, and area) were quantified using digital image photogrammetry. Although some common damage modes were noted, knee joint wear simulation with standard or 'anatomic' attachment did not generate damage pattern sizes similar to the explanted UKR. A focal damage pattern consistent with contact between the metal femoral articular surface and the polyethylene inserts was evident on all inserts, but only the Explant Group had evidence of dispersed damage dominated by abrasive modes. Synthetic femurs added complexity to the wear simulation without generating wear patterns substantially more similar to those observed on retrieved inserts.