The Mechanical Behavior Of The Lisfranc Ligaments In The Forfoot

Objective: To study mechanical properties of the Lisfranc ligament stabilizing the medial tarsometatarsal joints in the forfoot under normal conditions.Methods: Six fresh-frozen cadaveric foot specimens were studied. Four specimens were from men and two were from women.The mean age is 40 years old and the mean weight is 62.5 kilogram. There was no evidence of previous trauma or arthrosisin any of the specimens. The specimens were packaged with the double-deck plastic bags,then conserved in the refrigerator where the temperature was -20 centi-degree. There was no obviously change about the biologic character of the bone and ligament under this temperature[1]. the specimens were taken out 12 hours before tests and defrosted naturally under the room temperature.Desecteding the tibia and fibula 20 centimeters above the ankle joint,and to reject the skin,muscle and other soft tissue 5 centimeter around the proximate carefully,retaining the Z-line between the tibia and the fibula.The dissected proximal aspects of the tibia and fibula were then potted in the custom jig while the foot was maintained in a neutral stance position.Marking the corpse specimen,which is advantageous for the later test and the statistical analysis. To eliminate abnormity,serious osteoporosis and other pathologic abnormality through the naked eye and X optical.The dissected proximal aspects of the tibia and fibula were then potted in the custom jig while the foot was maintained in a neutral stance position.The specimen maintained in orthostatism all the time in the model manufacture process,so that the specimen can stand under load steadily,to ensure the experiment precision.During the testing procedure,the specimens were kept moist with saline solution.The specimens were attached to the vitodynamics machine ,underneath the specimen through the specially skid resistant contact surface,place above connected the charger. The articulating surfaces of the first and second tarsometatarsal joints were exposed by making one incision into the tarsometatarsal joint spaces.dissecting carefully to reduce the damage on soft tissue as far as possible in order to guarantee the specimen close to normal physiology structure as far as possible.The ankle joint was held in 30 degrees of plantar flexion with external fixation when the foot with neutral inversion and eversion. The displacements of the first and second metatarsal heads were measured using linear variable differential transducers,which was set in the dorsal aspect of the the first and second metatarsal base.Mechanical testing was performed with the CSS-44020 vitodynamics machine. The feet were preloaded with 10N,ten load cycles were applied at arate of 10N/s to a maximum load of 100N,the load was maintained for five seconds and then was released.To maintain the tibia and fibula was vertical to the horizontal plane when loading.Dorsal ligament,Lisfranc ligament and plantar ligaments were next sharply sectioned,then loaded.The displacement changes between the first and second metatarsal base under different load of the four groups(group with initial specimens,group specimens with sectioned dorsal ligaments,group specimens with sectioned dorsal ligaments and Lisfranc ligament group specimens with sectioned all ligaments)were record by computer.After each test,let the specimen revert to the initial state by taking a 5 minutes rest in order to eliminate the effect because of the creep. In the experiment loads 100N is the maximum pressure under which the specimen can maintain 30 degrees of plantar flexion. During the testing procedure,the specimens were kept moist with saline solution to decrease the organism denaturation owing to the test,so that the experimental results were precise and commeasurable. To input the four groups data and carry on statistics analysis with sas the v9 (two way ANOVA).Results: There were differences for displacement of four groups(group with initial specimens,group specimens with sectioned dorsal ligaments,group specimens with sectioned dorsal ligaments and Lisfranc ligament group specimens with sectioned all ligaments). In group with initial specimens,the mean displacement was 0.00058±0.00013mm/N ; In group specimens with sectioned dorsal ligaments,the mean displacement was 0.00072±0.00015mm/N;In group specimens with sectioned dorsal ligaments and Lisfranc ligament,the mean displacement was 0.00216±0.00053mm/N;In group specimens with sectioned all ligaments,the mean displacement was 0.00214±0.00062mm/N. Between specimens within pairs within either group,the displacement of initial specimens (0.00058±0.00013mm/N)and specimens with sectioned dorsal ligaments (0.00072±0.00015mm/N)were significantly different than that of the specimens with sectioned dorsal ligaments and Lisfranc ligament (0.00216±0.00053mm/N)and specimens with sectioned all ligaments (0.00214±0.00062mm/N). There was no significant difference in the displacement between initial specimens (0.00058±0.00013mm/N)and specimens with sectioned dorsal ligaments (0.00072±0.00015mm/N);There was no significant difference in the displacement between specimens with sectioned dorsal ligaments and Lisfranc ligament (0.00216±0.00053mm/N)and specimens with sectioned all ligaments (0.00214±0.00062mm/N).Conclusions:the stability between the medial cuneiform and the second metatarsal depend on three ligaments:the dorsal ligament,the Lisfranc ligament and the plantar ligament. The Lisfranc ligament is most important in maintaining the stability between the medial cuneiform and the second metatarsal among three ligaments.the Injuries with rupture of the Lisfranc ligament may induce destabilizing between the medial cuneiform and the second metatarsal. The dorsal ligament and the plantar ligament are less important than The Lisfranc ligament,the injuries with isolated rupture of the dorsal ligament may not be as destabilizing as injuries with ruptured Lisfranc ligament or plantar ligaments,that the former may be managed nonoperatively;When the transverse arch of foot become low because of incurring enormous load or tarsoptosis or talipes cavus,what are the contributions of the three ligaments to maintaining the stability between the medial cuneiform and the second metatarsal,we have need of further stady.