Spine and pelvis are very important and complex structures able to provide structural support and flexibility to the human body. However, they can undergo several pathologies commonly associated with ageing such as adult scoliosis, high-grade spondylolisthesis, and sagittal imbalance, changing the physiological curvature of the spine. There are different surgical techniques that could be used in order to restore a physiological condition of the spine in select cases, such as spinal fixation and osteotomies. Despite the general good results obtained with standard treatments, postoperative complications and failures such as pseudoarthrosis, breaking and loosening of implants, sacroiliac joints pain, sagittal imbalance and so on, are very frequent. Nowadays, several in-vitro and in-silico studies are performed in order to understand and overcome the biomechanical complications and explore novel techniques and implants. However, a simplified loading scenario consisting of pure moments (sometimes in combination with follower load) is applied to the spine instead of realistic loading conditions, consisting of muscle forces, with potential major consequences on the numerical predictions. The aim of this project was to determine whether a simplified loading scenario (pure moments) is appropriate for the investigation of spinal fixation with respect to realistic loading conditions (muscle forces), and to use the most appropriate loads to study novel fixation techniques (also a multi-rod construct) by means of innovative implants with or without a L5 pedicle subtraction osteotomy. In the first part of this thesis, a comparison between simplified and realistic loading conditions is presented. Three standard spinal fixation techniques (lumbar, sacrolumbar and sacropelvic with S2 alar-iliac screws fixations) were implemented in a finite element model and subjected either to pure moments of 7.5 Nm (simplified loading conditions) or to muscle forces derived from a musculoskeletal simulation (realistic loading conditions). After the validation of the intact model under both loading conditions against two in-vitro studies and the validation of the instrumented musculoskeletal models against an in-vivo study, a comparison between these two loading conditions in terms of stresses in the implants was performed for each instrumented model. For the lumbar and the sacrolumbar model, simplified loading conditions were not sufficient to produce accurate results as those of realistic loading conditions, in particular for the posterior rods. For the sacropelvic model with S2 alar-iliac screws, instead, the results obtained with simplified loading conditions were very similar to those found with realistic loading conditions. Therefore, appropriate loading conditions for the lumbar and sacrolumbar fixation models were realistic loading conditions, while for the sacropelvic fixation model simplified loading conditions were sufficient. In the second part of this thesis, the use of a novel porous fusion/fixation implant to enhance sacropelvic fixation was explored with respect to a standard sacropelvic fixation technique. After the validation of the intact model, four spinal fixation techniques with novel implant were created and compared under appropriate loading conditions (simplified loading conditions). One of these models represented a standard sacropelvic fixation technique with S2 alar-iliac screws and was used as baseline. The validation of the intact model was performed against two in-vitro studies. The novel implant resulted in a similar stability of L5-S1 and SIJ motions with respect to the standard techniques, as well as a reduced risk of screws failure and in a similar risk of rod failure. The novel implant seems therefore effective in protecting the pedicle screws from excessive loading. In the third part of this thesis, the use of the novel porous fusion/fixation implant to enhance sacropelvic fixation and multi-rod construct was explored when also a L5 pedicle subtraction osteotomy was performed. The intact finite element model validated in the second part of this thesis was used as starting model for this part of the thesis. Three spinal fixation techniques with novel implants were created from the intact model after resection at L5 level and compared under appropriate loading conditions (simplified loading conditions). One of these models represented the multi-rod construct with four rods. Another model (thoracolumbar fixation with S1 pedicle screws) was used as baseline. The sacropelvic fixation with the novel implant resulted in an increase of the stability of L4-S1 and SIJ motions, a reduced risk of screws failure, and an increased risk of rod failure with respect to spinal technique without sacropelvic fixation. Using four rods (multi-rod construct) resulted in a slightly increase of the stability of L4-S1 and SIJ motions, a similar risk of screw failure, and a relevant decreased risk of rod failure with respect to other techniques with two rods. According to this, the novel implant demonstrated a good behavior for the stability of the spine and for screws also when a L5 pedicle subtraction osteotomy was performed, but not for the posterior rods. Sacropelvic fixation with the novel implants needed to be combined with multi-rod construct in order to have a protective effect on the posterior rods, especially when a L5 pedicle subtraction osteotomy was performed. Clinical evaluation should be performed to confirm the applicability of results to patient outcomes.
La colonna vertebrale e la pelvi sono strutture molto importanti e complesse capaci di dare supporto strutturale e flessibilità al corpo umano, che, però, possono andare incontro a diverse patologie, comunemente associate con l’invecchiamento, come la scoliosi nell’adulto, la spondilolistesi degenerativa e lo squilibrio sagittale, cambiando la curva fisiologica della colonna vertebrale. Ci sono diverse tecniche chirurgiche che possono essere utilizzate per ristabilire una condizione fisiologica della colonna vertebrale in determinati casi, come la fissazione spinale e l’osteotomia vertebrale. Nonostante i buoni risulta ottenibili con questi trattamenti standard, complicazioni postoperatorie e fallimenti meccanici, come la rottura o la perdita degli impianti, dolore alle articolazioni sacroiliache, squilibrio sagittale e altre problematiche, sono molto frequenti. Negli ultimi anni diversi studi in-vitro e in-silico sono stati effettuati per capire e superare le complicazioni biomeccaniche e studiare nuove tecniche ed impianti per la fissazione spinale. Nonostante questo, condizioni di carico semplificate (momenti puri a volte in combinazione con follower load), vengono spesso utilizzate in questi studi, invece di condizioni di carico realistiche (forze muscolari) con potenziali conseguenze sulle predizioni numeriche. Il presente lavoro di tesi ha lo scopo di determinare se le condizioni di carico semplificate (momenti puri) sono appropriate per studiare tecniche di fissazione spinale rispetto alle condizioni di carico realistiche (forze muscolari), e di usare le condizioni di carico più appropriate per studiare nuove tecniche di fissazione spinale (con due o quattro barre spinali), utilizzando impianti innovativi con o senza una osteotomia peduncolare sottrattiva eseguita a livello L5. Nella prima parte di questa tesi è riportato un confronto tra condizioni di carico semplificate e condizioni di carico realistiche. Tre tecniche standard di fissazione spinale (lombare, sacrolombare e sacropelvica con le viti alari-iliache S2) sono state implementate in un modello ad elementi finiti e sottoposte sia a un momento puro di 7.5 Nm (condizioni di carico semplificate) sia a forze muscolare ottenute da un modello muscoloscheletrico (condizioni di carico realistiche). Dopo aver validato il modello intatto sottoposto a condizioni di carico sia semplificate che realistiche con due studi in-vitro e aver validato i modelli strumentati muscoscheletrici con uno studio in-vivo, è stato fatto un confronto degli sforzi negli impianti tra le due condizioni di carico per ciascun modello strumentato. Per il modello lombare e sacrolombare, le condizioni di carico semplificato non sono state sufficienti ad ottenere risultati simili a quelli ottenuti con le condizioni di carico realistiche, in particolare per le barre spinali. Per il modello sacropelvico con viti alari-iliache S2, invece, i risultati ottenuti con le condizioni di carico semplificate sono stati simili a quelli ottenuti con le condizioni di carico realistiche. Per questo motivo, le condizioni di carico realistiche risultano essere quelle appropriate per il modello lombare e quello sacrolombare. Le condizioni di carico semplificato, invece, risultano essere quelle appropriate per il modello sacropelvico. Nella seconda parte di questa tesi, è stato studiato l’uso di un nuovo impianto, chiamato porous fusion/fixation implant, per la fissazione sacropelvica in confronto a una tecnica standard di fissazione sacropelvica. Dopo aver fatto la validazione del modello intatto, quattro tecniche di fissazione spinale con il nuovo impianto sono state create e confrontate con condizioni di carico appropriate (condizioni di carico semplificate). Uno di questi modelli è stato creato per rappresentare la tecnica standard di fissazione sacropelvica con viti alari-iliache S2, ed è stato utilizzato come modello di riferimento. Il modello intatto è stato validato con due studi in-vitro. I modelli con il nuovo impianto mantenevano invariata la stabilità del movimento a livello L5-S1 e dell’articolazione sacroiliaca e il rischio di fallimento delle barre spinali, ma riducevano il rischio di fallimento delle viti rispetto al modello di riferimento (tecnica standard di fissazione spinale). Nella terza parte di questa tesi, è stato studiato il nuovo impianto, chiamato porous fusion/fixation implant, per la fissazione sacropelvica e una struttura con quattro barre spinali in presenza di una osteotomia peduncolare sottrattiva eseguita a livello L5. Il modello intatto utilizzato come modello di partenza in questa parte della tesi è stato validato nella seconda parte della tesi. Quattro tecniche di fissazione spinale con i nuovi impianti sono state create partendo dal modello intatto dopo la resezione a livello L5 e confrontate con condizioni di carico appropriate (condizioni di carico semplificate). Uno di questi modelli è stato creato per rappresentare la struttura con quattro barre spinali. Un altro di questi modelli (fissazione toracolombare con viti peduncolari in S1) è stato usato come modello di riferimento. I modelli con fissazione sacropelvica con il nuovo impianto aumentavano la stabilità del movimento a livello L4-S1 e dell’articolazione sacroiliaca, riducevano il rischio di fallimento delle viti ed incrementavano il rischio di fallimento delle barre spinali in confronto al modello di riferimento (senza fissazione sacropelvica). Il modello con quattro barre spinali aumentava leggermente la stabilità del movimento a livello L4-S1 e dell’articolazione sacroiliaca, manteneva invariato il rischio di fallimento delle viti e riduceva il rischio di fallimento delle barre spinale in confronto a quelle tecniche spinale con due barre spinali. In conclusione, il nuovo impianto (porous fusion/fixation implant) ha dimostrato un buon comportamento per la stabilità della colonna vertebrale e per le viti, anche in presenza della osteotomia peduncolare sottrattiva eseguita a livello L5, ma non per le barre spinali. La fissazione sacropelvica con i nuovi impianti ha bisogno di essere combinata con quattro barre spinali per avere un effetto protettivo sulle barre spinali, soprattutto in presenza di una osteotomia peduncolare sottrattiva.
In-silico comparison of innovative spinal fixation techniques under appropriate loading conditions
Matteo, Panico
2022
Abstract
Spine and pelvis are very important and complex structures able to provide structural support and flexibility to the human body. However, they can undergo several pathologies commonly associated with ageing such as adult scoliosis, high-grade spondylolisthesis, and sagittal imbalance, changing the physiological curvature of the spine. There are different surgical techniques that could be used in order to restore a physiological condition of the spine in select cases, such as spinal fixation and osteotomies. Despite the general good results obtained with standard treatments, postoperative complications and failures such as pseudoarthrosis, breaking and loosening of implants, sacroiliac joints pain, sagittal imbalance and so on, are very frequent. Nowadays, several in-vitro and in-silico studies are performed in order to understand and overcome the biomechanical complications and explore novel techniques and implants. However, a simplified loading scenario consisting of pure moments (sometimes in combination with follower load) is applied to the spine instead of realistic loading conditions, consisting of muscle forces, with potential major consequences on the numerical predictions. The aim of this project was to determine whether a simplified loading scenario (pure moments) is appropriate for the investigation of spinal fixation with respect to realistic loading conditions (muscle forces), and to use the most appropriate loads to study novel fixation techniques (also a multi-rod construct) by means of innovative implants with or without a L5 pedicle subtraction osteotomy. In the first part of this thesis, a comparison between simplified and realistic loading conditions is presented. Three standard spinal fixation techniques (lumbar, sacrolumbar and sacropelvic with S2 alar-iliac screws fixations) were implemented in a finite element model and subjected either to pure moments of 7.5 Nm (simplified loading conditions) or to muscle forces derived from a musculoskeletal simulation (realistic loading conditions). After the validation of the intact model under both loading conditions against two in-vitro studies and the validation of the instrumented musculoskeletal models against an in-vivo study, a comparison between these two loading conditions in terms of stresses in the implants was performed for each instrumented model. For the lumbar and the sacrolumbar model, simplified loading conditions were not sufficient to produce accurate results as those of realistic loading conditions, in particular for the posterior rods. For the sacropelvic model with S2 alar-iliac screws, instead, the results obtained with simplified loading conditions were very similar to those found with realistic loading conditions. Therefore, appropriate loading conditions for the lumbar and sacrolumbar fixation models were realistic loading conditions, while for the sacropelvic fixation model simplified loading conditions were sufficient. In the second part of this thesis, the use of a novel porous fusion/fixation implant to enhance sacropelvic fixation was explored with respect to a standard sacropelvic fixation technique. After the validation of the intact model, four spinal fixation techniques with novel implant were created and compared under appropriate loading conditions (simplified loading conditions). One of these models represented a standard sacropelvic fixation technique with S2 alar-iliac screws and was used as baseline. The validation of the intact model was performed against two in-vitro studies. The novel implant resulted in a similar stability of L5-S1 and SIJ motions with respect to the standard techniques, as well as a reduced risk of screws failure and in a similar risk of rod failure. The novel implant seems therefore effective in protecting the pedicle screws from excessive loading. In the third part of this thesis, the use of the novel porous fusion/fixation implant to enhance sacropelvic fixation and multi-rod construct was explored when also a L5 pedicle subtraction osteotomy was performed. The intact finite element model validated in the second part of this thesis was used as starting model for this part of the thesis. Three spinal fixation techniques with novel implants were created from the intact model after resection at L5 level and compared under appropriate loading conditions (simplified loading conditions). One of these models represented the multi-rod construct with four rods. Another model (thoracolumbar fixation with S1 pedicle screws) was used as baseline. The sacropelvic fixation with the novel implant resulted in an increase of the stability of L4-S1 and SIJ motions, a reduced risk of screws failure, and an increased risk of rod failure with respect to spinal technique without sacropelvic fixation. Using four rods (multi-rod construct) resulted in a slightly increase of the stability of L4-S1 and SIJ motions, a similar risk of screw failure, and a relevant decreased risk of rod failure with respect to other techniques with two rods. According to this, the novel implant demonstrated a good behavior for the stability of the spine and for screws also when a L5 pedicle subtraction osteotomy was performed, but not for the posterior rods. Sacropelvic fixation with the novel implants needed to be combined with multi-rod construct in order to have a protective effect on the posterior rods, especially when a L5 pedicle subtraction osteotomy was performed. Clinical evaluation should be performed to confirm the applicability of results to patient outcomes.File | Dimensione | Formato | |
---|---|---|---|
PhD_Thesis_PanicoMatteo.pdf
accesso solo da BNCF e BNCR
Dimensione
36.31 MB
Formato
Adobe PDF
|
36.31 MB | Adobe PDF |
I documenti in UNITESI sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
https://hdl.handle.net/20.500.14242/207586
URN:NBN:IT:POLIMI-207586