| BackgroundCalcaneal fractures are the common injury of foot in middle-young people from 20 to 40 years accounting for 70% of all tarsal fractures, about 75% refers to intra-articular fractures, most of which are caused by the longitudinal vertical violence on the heel. Due to the complexity of the calcaneus and the surrounding anatomical structures and the poor quality of local soft tissue coverage, so the treatment of intra-articular calcaneal fractures is difficult with many of morbidities. The correct classification of intra-articular calcaneal fractures has the guiding significance for the right diagnosis and treatment. So far the sanders classification is the most commonly used method in clinics. Chinese medicine has proposed the "three period syndrome differentiation" principles of the management of the fractural injury, in order that it can promot flow of Qi and blood, improve the new and repair the injury, make the bones and tendons stronger. Open reduction and internal fixation has become the most commonly used methods of the treatment of the displaced intra-articular calcaneal fractures.So far there are two kinds of plates appling in the fixation of the calcaneal fractures:locking plates and nonlocking plates, but there still is a lot of controversy which of two can offer the optimal mechanical stability. It has tendon and nerves at the medial surface of the calcaneus facing open reduction and internal fixation adopted the lateral approach. It would exist a certain of possibility of the iatrogenic injury of the medial soft tissue if the surgeons has the intraoperative slightly improper operation. To reduce the risk of the effect of the screw insertion during the surgery on the the medial soft tissue, can we use the locking plate for single cortical fixed? To reduce the risk of the complications of open reduction and internal fixation, can locking fixationg replace the internal position with the external position in the management of the calcaneal fractures? The concept of "equal emphasis on bones and tendon" proposed early by chinese medicine and "minimally invasive" proposed by conventional medicine make the orthopedics & traumatology boost the new treatment level. May minimally invasive percutaneous cement fixation minimally invasive percutaneous screw fixation and mini locking plate fixation have the equivalent mechanical stability with the conventional locking plate fixation adopted by the open reduction? After the recent 40 years of development, finite element analysis has become the major method of mechanics analysis of the musculoskeletal system around the globe. As for focusing on the these clinical problems described above, we will analyse the biomechanical properties of different fixation methods for the intra-articular calcaneal fractures by finite element and discuss their clinical biomechanics significance. In additon, Because of the existence of the anteversion and extraversion angles of the sustentaculum tali, it may not be satisfied when the sustentaculum tali screw is inserted from the lateral aspenc to the medial aspect of the calcaneus, even may damage the medial anatomy structues. Based on.this, A kind of director helping accurate placement of sustentaculum tali screw needs to be developed.Part I Construction and validation of three dimensional finiteelement model of adult normal calcaneusObjectiveThe finite element model of the adult normal calcaneus is constructed. The stress distribution of the normal calcaneus is analysed and validated in order to offer the base of the further research.MethodsUsing two-dimensional continuous CT data of the normal calcaneus, the 3D finite element model of the calcaneus was constructed by Mimicsl4.0 software, Geomagic Studio2012 software, Solidworks2013 software and Ansys 14.0 software. The stress distribution of the normal calcaneus was analysed, and the finite element model was validated by reviewing previous research and clinical observation.ResultsThe main stress concentration areas were around the calcaneal tuberosity、 at the posterior talar articular surface, at the sustentaculum tali, at the medial aspect of anterior talar articular surface. The scondary stress zone appeared from posterior talar articular surface to the calcaneal tuberosity descending through the lateral aspect of sustentaculum tali to the posterior 1/3 part of the bottom of the calcaneus. The stress value of the calcaneus was significantly smaller at the lateral surface than at the medial surface, the central zone at the lateral surface of the calcaneus was a little smaller. The high stress values appeared at the the Gissane’s Angle supporting the load and playing the pivotal role in the conduction. The relative high stress appeared at the posterior 1/3 part of the medial bottom of the calcaneus.ConclusionThe 3D finite element model of the calcaneus was constructed successfully, and the stress distribution of the calcaneus in the neutral position under the vertical load was analysed. In contrast with the previous experimental and clinical data, this model not only had normal calcaneal anatomic morphology, but can get the precise stress distribution of the normal calcaneus in the neutral position, which was already very close to the actual characteristics of human calcaneus. So it offered the scientific basis about the further analysis and research of different fixation methods of calcaneal fractures.Part Ⅱ The finite element analysis of locking and non locking plate fixation of Sanders Ⅱ and Ⅲ calcaneal fracturesObjectiveA biomechanical comparison of locking and nonlocking plates for the fixation of calcaneal fractures of Sanders type Ⅱ and type Ⅲ by finite element method.MethodsThe solid models of calcaneal fractures of Sanders type Ⅱ and type Ⅲ and plate and screws were constructed by Solidworks2013 software. The finite element models of calcaneal fractures of Sanders type Ⅱ and type Ⅲ fixed with plate and screws were also constructed. Locking fixation and nonlocking fixation were stimulated by setting the parameters in the Ansys software, and were applied with the axial loads. The displacement of the fracture lines、 the stress of the fractural fragments of the calcaneus、the displacement and stress of the plate and screws in the two fixation models were assessed.ResultsThe maximum displacement at the lateral or middle fractural fragments of the subtalar joint surface were at the fracture lines, and the displacement of the fractural fragments of the subtalar joint surface gradually increased from the later to the midial aspect, and the maximum displacement appeared at the fractural fragments of the sustentaculum tali in all fixation models. The maximum displacement at the fracture lines in the locking and nonlocking plate fixation of the two models located at the subtalar joint surface were not significantly changed, were less than fracture lines displacement requirement greater than 1 mm (Sanders II:locking fixation 0.103mm, nonlocking fixation 0.111mm. SandersⅢ:locking fixation 0.151mm, nonlocking fixation 0.163mm). The maximum stress at the calcaneus in the locking and nonlocking plate fixation of the two models located around the cortical bones of calcaneal tuberosity were not significantly changed, were less than the yield strength of 95 Mpa (Sanders Ⅱ:locking fixation 61.244Mpa, nonlocking fixation 61.43Mpa. Sanders Ⅲ:locking fixation 87.858Mpa, nonlocking fixation 83.017Mpa). The stress of the fractural fragments of the subtalar joint surface gradually increased from the later to the midial aspect, and the maximum stress appeared around the hole of the sustentaculum tali in all fixation models. The maximum stress at the internal fixation system in the two fracture models located at the middle-posterior part of plates were not significantly changed, were less than the internal fixation failure strength of 225 MPa(Sanders Ⅱ:locking fixation 157.57Mpa, nonlocking fixation 155.37Mpa. Sanders Ⅲ: locking fixation 190.37Mpa, nonlocking fixation 170.75Mpa), and The maximum displacement of the internal fixation system in the two fracture models were at the distal part of the sustentaculum tali screw.ConclusionIn the finite element model of Sanders type Ⅱ and type Ⅲ calcaneal fractures, locking plate fixation did not provide a biomechanical advantage over nonlocking plate fixation, and both had the equal mechanical properties.Part Ⅲ The finite element analysis of locking plates using unicortical and bicortical fixiation of Sanders Ⅱ and Ⅲ calcaneal fracturesObjectiveA biomechanical comparison of locking plates using unicortical or bicortical fixiation of calcaneal fractures of Sanders type II and type III by finite element method, and discussion on their clinical significance.MethodsThe solid models of calcaneal fractures of Sanders type II and type III fixed with locking plates using unicortical and bicortical fixiation were constructed by Solidworks2013 software. The finite element models of calcaneal fractures of Sanders type II and type III fixed with plate and screws were also constructed, and were applied with the axial loads. The displacement of the fracture lines、the stress of the fractural fragments of the calcaneus^ the displacement and stress of the plate and screws in the two fixation models were assessed.ResultsThe maximum displacement at the lateral or middle fractural fragments of the subtalar joint surface were at the fracture lines, and the displacement of the fractural fragments of the subtalar joint surface gradually increased from the later to the midial aspect, and the maximum displacement appeared at the fractural fragments of the sustentaculum tali in all fixation models. The maximum displacement at the fracture lines in the locking plate using unicortical or bicortical fixiation of the two models located at the subtalar joint surface were not significantly changed, were less than fracture lines displacement requirement greater than 1 mm (Sanders Ⅱ:bicortical fixation 0.103mm, unicortical fixation 0.108mm. SandersⅢ:bicortical fixation 0.151mm, unicortical fixation 0.163mm). The maximum stress at the calcaneus in the locking bicortical fixiation of the two models were around the posterior part of the calcaneus (calcaneal tuberosity), while it in the other fixiation of the two models were at the anterior part of the calcaneus. The maximum stress in the both fixation of the two models were not significantly changed, were less than the yield strength of 95 Mpa (Sanders II:bicortical fixation 61.244Mpa, unicortical fixation 61.88Mpa. Sanders Ⅲ:bicortical fixation 87.858Mpa, unicortical fixation 85.732Mpa). The stress of the fractural fragments of the subtalar joint surface gradually increased from the later to the midial aspect, and the maximum stress appeared around the hole of the sustentaculum tali in all fixation models. The maximum stress and the maximum displacement at the internal fixation system in the two fracture models were at the middle-posterior part of plates and at the distal part of the sustentaculum tali screw. The maximum stress at the internal fixation system in the locking using bicortical and unicortical fixation of calcaneal fractures of Sanders type II were not significantly changed, were less than the internal fixation failure strength of 225 MPa(bicortical fixation 157.57Mpa, unicortical fixation 191.15Mpa). Compared with locking using bicortical fixation of calcaneal fractures of Sanders type Ⅲ, the maximum stress at the internal fixation system in the locking unicortical fixation increased by 36%, and exceeded the internal fixation failure strength of 225 MPa(bicortical fixation 190.37Mpa, unicortical fixation 259.82Mpa).ConelusionLocking plates using unicortical and bicortical fixiation of calcaneal fractures of Sanders type Ⅱ had the equivalent mechanical properties with, the former had the potential clinic application in the treatment of calcaneal fractures of Sanders type Ⅱ.Locking plate using bicortical fixiation of calcaneal fractures of Sanders type Ⅲ fixation had a biomechanical advantage over locking plate using unicortical fixiation.Part IV The finite element analysis of Sanders II and III calcaneal fractures fixed with locking plates in the internal and external position ObjectiveA biomechanical comparison of the calcaneal fractures of Sanders type II and type III fixed with locking plates in the internal and external position by finite element method, and discussion on their clinical significance.MethodsThe solid models of calcaneal fractures of Sanders type II and type III fixed with locking plates in the internal and external position were constructed by Solidworks2013 software. The finite element models of calcaneal fractures of Sanders type II and type III fixed with plate and screws were also constructed, and were applied with the axial loads. The displacement of the fracture lines、the stress of the fractural fragments of the calcaneus、 the displacement and stress of the plate and screws in the two fixation models were assessed.ResultsThe maximum displacement at the lateral or middle fractural fragments of the subtalar joint surface were at the fracture lines, and the displacement of the fractural fragments of the subtalar joint surface gradually increased from the later to the midial aspect, and the maximum displacement appeared at the fractural fragments of the sustentaculum tali in all fixation models. The maximum displacement at the fracture lines in the calcaneal fractures of Sanders type II and type III fixed with locking plates in the internal and external position were not significantly changed, were less than fracture lines displacement requirement greater than 1 mm(Sanders Ⅱ."internal fixation 0.103mm, external fixation 0.126mm. Sanders Ⅲ:internal fixation 0.151mm, external fixation 0.178mm). The maximum stress at the calcaneus in the calcaneal fractures of Sanders type Ⅱ fixed with locking plates in the internal and external position were around the posterior part of the calcaneus(calcaneal tuberosity), while they in the calcaneal fractures of Sanders type Ⅲ fixed with locking plates in the internal and external position were respectively around the posterior part of the calcaneus(calcaneal tuberosity) and around the fractue lines of the medial fragment. The maximum stress at the calcaneus in the calcaneal fractures of Sanders type Ⅱ fixed with locking plates in the internal and external position were not significantly changed, were less than the yield strength of 95 Mpa (internal fixation 61.244Mpa, external fixation 70.84Mpa). Compared with calcaneal fractures of Sanders type Ⅲ fixed with locking plates in the internal position, the maximum stress at the calcaneus in the calcaneal fractures fixed with locking plates in the external position increased by 22%, and exceeded the yield strength of 95 Mpa(internal fixation 87.858Mpa, external fixation 107.51Mpa). The stress of the fractural fragments of the subtalar joint surface gradually increased from the later to the midial aspect, the maximum stress appeared at the medial fractural fragments of the calcaneus (the maximum stress in the internal fixation located at the hole of sustentaculum tali screw, the maximum stress in the external fixation located at the fracture lines). The maximum stress at the internal fixation system in the two fracture models located at the middle-posterior part of plates were not significantly changed, were less than the internal fixation failure strength of 225 MPa(Sanders Ⅱ:internal fixation 157.57Mpa, external fixation 107.81Mpa. Sanders Ⅲ:internal fixation 190.37Mpa, external fixation 172.84Mpa), and the maximum displacement of the internal fixation system in the two fracture models were at the distal part of the sustentaculum tali screw.ConclusionLocking plates in external position had the potential clinic application in the treatment of the intra-articular calcaneal fractures of Sanders typeII.Part V The finite element analysis of minimally invasive technology in treating Sanders II calcaneal fracturesObjectveA biomechanical comparison of the conventional locking plate fixations minimally invasive percutaneous cement fixation、minimally invasive percutaneous screw fixation and mini locking plate fixation of the fixation of calcaneal fractures of Sanders type II by finite element method, discussion on their clinical significance, and discussion on the relationship between the concept of "equal emphasis on bones and tendon" and the concept of "minimally invasive".MethodsThe finite element models of calcaneal fractures of Sanders type II and type III fixed with the conventional locking plate、minimally invasive percutaneous cement、minimally invasive percutaneous screw and mini locking plate were constructed, and were applied with the axial loads. The displacement of the fracture lines、the stress of the fractural fragments of the calcaneus、 the displacement and stress of the plate and screws in the two fixation models were assessed.ResultsThe maximum displacement at the lateral fractural fragments of the subtalar joint surface were at the fracture lines, and the displacement of the fractural fragments of the subtalar joint surface gradually increased from the later to the midial aspect, and the maximum displacement appeared at the fractural fragments of the sustentaculum tali in all fixation models. The maximum displacement at the fracture lines in the calcaneal fractures of Sanders type II fixed with different fixation were not significantly changed, were less than fracture lines displacement requirement greater than 1 mm (conventional locking plate fixation 0.103mm, percutaneous cement fixation 0.14mm, percutaneous screw fixation 0.108mm, mini locking plate fixation 0.061mm). The maximum stress at the calcaneus in the conventional locking plate fixation and mini locking plate fixation of calcaneal fractures of Sanders type II were around the posterior part of the calcaneus (calcaneal tuberosity), while it in the other fixiation of the calcaneal fractures were around the calcaneocuboidal joint. Compared with calcaneal fractures of Sanders type II fixed with conventional locking plates, the maximum stress at the calcaneus in the calcaneal fractures fixed with percutaneous screw and mini locking plate were not significantly changed, were less than the yield strength of 95 Mpa (conventional locking plate fixation 61.244Mpa, percutaneous screw fixation 87.404Mpa, mini locking plate fixation 79.857Mpa), but the maximum stress at the calcaneus in the calcaneal fractures fixed with the percutaneous cement fixation was 113 mpa exceeding the yield strength of 95 Mpa. The stress of the fractural fragments of the subtalar joint surface gradually increased from the later to the midial aspect, the maximum stress appeared at the medial fractural fragments of the calcaneus. The maximum stress at the plants in the calcaneal fractures fixed with conventional locking plate fixation、 percutaneous cement、percutaneous screw、mini locking plate were respectively at the middle part of the plate、the middle part of the cement、 the tip of screw around posterior talar articular surface、the middle part of the sustentaculum tali screw, and the one of percutaneous cement fixation had the minimum value while one of conventional locking plate fixation had the maximum value which was 156Mpa below the internal fixation failure strength of 225 MPa. The maximum displacement at the plants in the calcaneal fractures fixed with conventional locking plate fixation、percutaneous screw、mini locking plate were at the distal part of the sustentaculum tali screw while it in the calcaneal fractures fixed with percutaneous cement was at the top of the cement, and it of conventional locking plate fixation had the minimum value while it of percutaneous cement fixation had the maximum value which was lmm.ConclusionThe concept of "equal emphasis on bones and tendon" and the concept of "minimally invasive" were highly integrated. Minimally invasive percutaneous cement fixation of intra-articular calcaneal fractures had the stress concentration at the calcaneus with the high risk of the collapse and malunion of the subtalar joint surface. Minimally invasive percutaneous screw fixation and mini locking plate fixation of the fixation of calcaneal fractures, which had the potential clinic application in the treatment of the calcaneal fractures, had the equal mechanical properties with the conventional locking plate fixation, which. Mini locking plate of the calcaneus would be further developed.Part VI The accuracy assessment of aiding the placement of sustentaculum tali screw of the self-designed directorObjectiveThe design and production of a kind of director of sustentaculum tali screw, the assessment of its precision of aiding the placement of sustentaculum tali screw through experiment study and clinical trials, and discussion on the significance of fracture healing of "three Period syndrome differentiation" principles proposed by chinese medicine.MethodsA kind of director aiding the insertion of sustentaculum tali screw was designed and made. Three 1.5mm kirschner wires were inserted in the foot specimens with the help of director of sustentaculum tali screw. Between June 2014 and October 2015,50 feet(42 patients) underwent surgical treatment of intra-articular calcaneal fractures, and the clinical data were analyzed. According to the fracture fixations with or without using director of sustentaculum tali screw, All the patients were assigned randomly into two groups:Group A(the bared-handed group,25 feet of 21cases), Group B(the director group,25feet of 21cases). All the patients had to take the chinese herb after surgery in accordance with the principle of"three period syndrome differentiation". The two groups were comparable in base data, showing no significant differences(p>0.05). The operation time、luoroscopy frequency、 rate of accurate screwing、Bohler’s angle and Gissane’s angle at pre- and post-operation、fractural union time and AOFAS foot scores were compared between the two groups.ResultsThe director of sustentaculum tali screw was successfully made. Three 1.5mm kirschner wires were inserted in the foot specimens with the help of director of sustentaculum tali screw. CT scan indicated that there was no kirschner wire within the talocalcaneal joint, and that the two kirschner wires were within sustentaculum tali but the other one was below the sustentaculum tali. All the patients were followed after surgery. No significant difference was found between the two groups regarding the average follow-up time (Group A:7.9±1.9 months, Group B:7.6±1.5 months, t=0.130, p >0.05). One patient in Group A was complicated with skin incision swelling, but no necrosis and infection was found after alcohol wet and medicine. All wound incision in Group B healed primarily without the necrosis and infection. Both groups had no delayed union and nonunion, and no significant difference was found between the two groups regarding the bone union time (Group A:2.4± 0.3 months, Group B:2.3±0.2 months, r=1.566, p>0.05). The operation time of Group B was smaller than that of Group A, and the differences were statistically significant (Operation time:Group A,94.6±6.1 min; Group B, 85.6+12.6 min, t=3.222, p<0.05. Fluoroscopy frequency:Group A,2.2±0.9 times, Group B,1.5+0.7 times, t=3.251, p<0.05). The fluoroscopy frequency during surgery of Group B was smaller than that of Group A, and the differences were statistically significant (Z=2.269,p<0.05). No significant difference was found between the two groups regarding the Gissane’s angle at post-operation (Group A 113.4±8.7°, Group B 117.3±11.2°, t=1.375, p>0.05). Group B had higher Bohler’s angle at post-operation than Group A, the differences was statistically significant (Group A 21.5±5.2°, Group B 28.1 ±8.2°, t=3.406, p<0.05). The Bohler’s angle and Gissane’s angle were improved significantly from pre-operatively to post-operatively (Bohler’s angle in Group A:pre-operatively -2.3±14.2°, post-operatively 21.5±5.2°, t=8.721, p<0.05; Bohler’s angle in Group B:pre-operatively 3.9±16.5°, post-operatively 28.1±8.2°, t=1.376,p<0.05; Gissane’s angle in Group A:pre-operatively 97.4±7.9°, post-operatively 113.4±8.7°, t=7.336, p< 0.05; Gissane’s angle in Group B:pre-operatively 98.7±12.9 °, post-operatively 117.3±11.2°, t=6.762,p<0.05). Radiographic examination showed 14 screws in the Group A were accurately implanted into the middle of the sustentaculum tali except 6 screws which penetrated into the inferior of the sustentaculum tali and 2 screws which penetrated into the posteriorinferior of the sustentaculum tali and 3 screws which penetrated into the anteriorinferior of the sustentaculum tali. The accurate rate of screw implant was 64%.21 screws in the Group B were accurately implanted into the middle of the sustentaculum tali except 3 screws which penetrated into the inferior of the sustentaculum tali and 1 screws which penetrated into the posteriorinferior of the sustentaculum tali. The accurate rate of screw implant was 84%. Group B had a higher rate of accurate screwing than Group A, the differences was statistically significant(x2=4.667, p< 0.05). The results of Group A were excellent in 2 feet, good in 12 feet, fair in 10 feet, poor in 1 foot. The results of Group B were excellent in 11 feet, good in 11 feet, fair in 2 feet, poor in 1 foot. Group B was better than Group A in AOFAS score, the differences was statistically significant (Z=3.318, p<0.05).ConelusionThe take of chinese herb on the basis of "three period syndrome differentiation" principles proposed by Chinese medicine could promote fracture healing, shorten fracture healing time. The designed director of sustentaculum tali screw could obviously improve the precision of the insertion of screw, which had the potential clinic application, especially suitable for patients whth normal or thin patients. |
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