Biomechanical Study On Knee Injury And Its Prevention During Half-Squat Parachute Landing

Objective We aim to investigate the effects of different drop heights and knee braces on the kinematics and kinetics in the knee and ankle joint during half-squat parachute landing (HSPL) by using the Vicon motion capture system and the AMTI force platform. We can get to know the knee injury and knee brace prevention biomechanical mechanisms due to HSPL by analysising the datum from the research.We hope our study could provide guidance to prevent and reduce the knee injury and provide a theoretical basis for the design of the new knee support for the paratroopers.Methods We selected 20 active service paratroopers (male,age 18-30 years, height 170-180 cm,weight 60-80Kg) who had no history of serious lower-extremity injury and were familiar with HSPL to participate in the study.All the paratroopers wore the 07 style military parachute boots, and jumped from the platforms of two different heights of 40cm and 80cm and landed on the force platform in three different knee protection conditions(no brace, elastic knee brace, semi-rigid knee brace). The Vicon motion capture system and force platform record the datum of knee kinematics and ground reaction force (GRF). After the examination, we diverted the datum into the Visual 3D motion analysis software and finally we analysised the datum by using the two factor ANOVAin SPSS17.0 software.Results All the participates finished the test smoothly and no one was injuried.(1). The peak Vertical Ground-Reaction Force (peak vGRF) for the height of 80cm were higher than that of 40cm (P<0.01). No statistical differences of peak vGRF between the no brace, elastic knee brace, semi-rigid knee brace groups were found (P=0.22).(2). The peak knee flexion angle (peak KFA) and displacement (KFD)of the height of 80cm were higher than that of 40cm (P<0.01) and these two parameters for elastic knee brace, semi-rigid knee brace were lower than that of no brace (P<0.05),but there were no statistical differences between the datum of elastic knee brace and semi-rigid knee brace (p=0.103).(3).The peak knee abduction angle (peak KAA) and displacement (KAD)of the height of 80cm were higher than that of 40cm (P<0.01).There is no statistical difference between the elastic knee brace and no brace group for peak KAA (P=0.072),but semi-rigid knee brace group is lower than the other two groups (P<0.05). The parameter of KAD for elastic knee brace, semi-rigid knee brace were lower than that of no brace (P<0.05), but there were no statistical differences between the datum of elastic knee brace and semi-rigid knee brace (P=0.12).(4). The peak knee extorsion angle (peak KEA) and displacement (KED)for the height of 80cm were higher than that of 40cm (P<0.01) and the peak KEA for elastic knee brace, semi-rigid knee brace were lower than that of no brace,but there were no statistical differences between the datum of elastic knee brace and semi-rigid knee brace (P=0.91).No statistical differences of KED between the no brace, elastic knee brace, semi-rigid knee brace groups were found (p=0.097).Conclusion (1).During HSPL, the high peak vGRF,high flexion, abduction and extorsion angle and displacement may contribute to the knee unstability which may result in knee injury.(2). Neither the elastic nor semi-rigid knee braces could decrease the peak v-GRF. (3). Both the elastic and semi-rigid knee braces could decrease peak KFA and KFD for about 12-17°, and the semi-rigid knee brace decrease more which means that the semi-rigid knee brace works more effectively. (4). The semi-rigid knee brace could decrease peak KAA and KFD for about 3-6°,but elastic knee brace could only decrease the KFD.Thus,both the elastic and semi-rigid knee braces protect the stability of knee in coronal position, and the semi-rigid knee brace decrease more datum which means that the semi-rigid knee brace works more effectively.(5).Both the elastic and semi-rigid knee braces could decrease the datum of peak KEA, but they could only decrease 1.5 °for average, and neither the elastic nor semi-rigid knee braces could decrease the KED. Thus, these two knee brace could not protect the knee from erosion effectively. (6).To improve the comfortableness and protectiveness of the knee brace,we need to combine the good points of both the elastic and semi-rigid knee braces in designing new knee brace for the paratroopers.(7).Further research are needed to investigate the effects on the kinematics and kinetics on the nearby ankle and hip joints for wearing the knee braces.Objective To observe the expression of the main disc extracellular matrix(ECM) and mateix metallo proteinases-1,3(MMP-1,3) on the lumbar intervertebral disc in high load condition.Methods 40 healthy male New Zealand white rabbits of 7-8 months of age with the average weight of 3kg were randomly divided into control group,+Gz 4,8 and 12-week group. Each group has 10 rabbits.No any intervention in control group, all rabbits exposed in+7 Gz condition in each+Gz group.When the experiment time was approached,all the rabbits were killed.Pathological changes were observed on intervertebral discs(L6-S1) and grade classified.Immunohistochemisty was used to detect the content of Collagen I, II and MMP-1,3.Results The expression of type I Collagen and MMP-1,3 in+Gz groups was higher than control group,and the difference between the groups was statistically significant(P<0.05).And there was a statistically significant increasing trend from the control group to the 12-week group (P<0.05).But the expression of type II Collagen in each+Gz group was lower than control group,and the difference between the groups was statistically significant(P<0.05). And there was a statistically significant declining trend from the control group to the 12-week subgroup (P<0.05).Conclusion The frequent esposure to+Gz condition could really accelerate the lumbar disc degeneration process.The high expression alteration of ECM and MMP-1,3 in high load condition may be a routine leading intervertebral disc degeneration disease (IVDD)for the rabbits.