Changes in talocrural joint contact stress characteristics after simulated rotationplasty

In order to assess the changes in talocrural joint contact stress after rotationplasty, 10 lower-leg cadaver specimens were axially loaded with 600 N and investigated in two loading situations: (1) Normal loading with a plantigrade foot; (2) in an equinus position of a simulated rotationplasty. Joint contact stress in the talar facet of the talocrural joint was determined with Fuji Prescale film cut to size and analyzed with digital image analysis for joint contact area, mean and peak pressure, contact force, and location of the load application on the trochlea tali. The results demonstrate a significant transfer on the loading zone to the posterior part of the talus (p = 0.005), a significant reduction of the contact area (p = 0.005) and force (p = 0.005), and a significant increase of the mean (p = 0.022) and maximum pressures (p = 0.013). These results indicate that the rotationplasty causes pronounced changes in joint loading characteristics.     

Innervation zone location of the biceps brachii,a comparison between genders and correlation with anthropometric measurements

Avoiding the innervation zone (IZ) is important when collecting surface electromyographic data. The purposes of this study were threefold: (1) to examine the precision of two different techniques for expressing IZ location for the biceps brachii, (2) to compare these locations between men and women, and (3) to determine if IZ movement with changes in elbow joint angle is related to different anthropometric measures. Twenty-four subjects (mean ± SD ages = 21.8 ± 3.5 yr) performed isometric contractions of the right forearm flexors at each of three separate elbow joint angles (90°, 120°, and 150° between the arm and forearm). During each contraction, the location of the IZ for the biceps brachii was visually identified using a linear electrode array. These IZ locations were expressed in both absolute (i.e. as a distance (mm) from the acromion process) and relative (i.e. as a percentage of humerus length) terms. The results suggested that the estimations of IZ location were more precise when expressed in relative versus absolute terms, and were generally different for men and women. The shift in IZ location with changes in elbow joint angle was not, owever, related to height, weight, or humerus length.     

Quadriceps cross-sectional area changes in young healthy men with different magnitude of Q angle

Knee pain and dysfunction have been often associated with an ineffective pull of the patella by the vastus medialis (VM) relative to the vastus lateralis (VL), particularly in individuals with knee joint malalignment. Such changes in muscular behavior may be attributed to muscle inhibition and/or atrophy that precedes the onset of symptoms. The aim of this study was to investigate possible effects of knee joint malalignment, indicated by a high quadriceps (Q) angle (HQ angle >15 degrees ), on the anatomic cross-sectional area (aCSA) of the entire quadriceps and its individual parts, in a group of 17 young asymptomatic men compared with a group of 19 asymptomatic individuals with low Q angle (LQ angle <15 degrees ). The aCSA of the entire quadriceps (TQ), VM, VL, vastus intermedius (VI), rectus femoris (RF), and patellar tendon (PT) were measured during static and dynamic magnetic resonance imaging (MRI) with the quadriceps relaxed and under contraction, respectively. A statistically significant lower aCSA was obtained in the HQ angle group, compared with the LQ angle group, for the TQ, VL, and VI in both static (TQ = 9.9%, VL = 12.9%, and VI = 9.1%; P < 0.05) and dynamic imaging (TQ = 10.7%, P < 0.001; VL = 13.4%, P < 0.01; and VI = 9.8%, P < 0.05) and the aCSA of the VM in dynamic MRI (11.9%; P < 0.01). The muscle atrophy obtained in the HQ angle group may be the result of a protective mechanism that inhibits and progressively adapts muscle behavior to reduce abnormal loading and wear of joint structures.     

Mobility of the conceptus and uterine contractions in the mare

Location of the embryonic vesicle within the uterus of mares was recorded every. five minutes for two consecutive hours (25 location determinations per trial) in three experiments. In Experiment 1 (n=7), the number of location changes among nine uterine segments (three body segments and three segments for each horn) was greater (P<0.05) on Day 13 than on Day 10. The vesicle was located in the body more frequently (P<0.05) and tended (P<0.1) to move to a more caudal position more frequently on Day 10 than on Day 13. Fixation occurred on Day 15 in four of seven mares and on Day 16 in the remaining three mares. The number of location changes was not significantly different between two days prior to fixation and one day prior to fixation. In Experiment 2, the effect of clenbuterol, a B₂ sympathomimetic blocker of uterine contractions, was studied on Days 12 or 13 of pregnancy. Location changes occurred less frequently (P<0.05) in treated mares (n=9) than in controls (n=10), indicating involvement of uterine contractions in the mobility of the embryonic vesicle. In Experiment 3, when the initial direction of location changes was caudal within a horn and cranial within the uterine body, the vesicle was more likely (P<0.05) to continue moving in the same direction than in the opposite direction. However, when the direction within a horn was cranial, the next location change was as likely to be in the opposite direction as in the same direction (not significantly different from equality). When the direction within the uterine body was caudal, the next location change was more likely (P<0.05) to be in the opposite direction.     

Effects of electrode location on myoelectric conduction velocity and median frequency estimates

The effect of surface electrode location on the estimates of the median frequency and conduction velocity of the myoelectric signal was investigated. The locations were identified with respect to the innervation zone and the tendonous portion of the tibialis anterior muscle. Considerable modifications in the median frequency and conduction velocity parameters were noted. The highest values of the median frequency occurred at the region of the innervation zone and tendonous insertion of the muscle, and decreased proportionally with distance from these areas. The rate of change of median frequency was not effected by electrode location. Estimates of conduction velocity were most stable in a region between the distal tendon and the adjacent innervation zone. This region also provided the best linear fit when comparing conduction velocity to median frequency estimates. The implications for signal detection procedures are discussed.     

Length-tension properties of ankle muscles in chronic human spinal cord injury

Contracture, or loss of range of motion (ROM) of a joint, is a common clinical problem in individuals with spinal cord injury (SCI). In order to measure the possible contribution of changes in muscle length to the loss of ankle ROM, the active force vs. angle curves for the tibialis anterior (TA) and gastrocnemiussoleus (GS) were measured in 20 participants, 10 with SCI, and 10 gender and age matched, neurologically intact (NI) individuals. Electrical stimuli were applied to the TA and GS motor nerves at incremented angles of the entire ROM of the ankle and the resulting ankle and knee torques were measured using a multi-axis load cell. The muscle forces of the TA and GS were calculated from the torque measurements using estimates of their respective moment arms and the resulting forces were plotted against joint angle. The force–angle relation for the GS at the ankle (GSA) was significantly shifted into plantar flexion in SCI subjects, compared to NI controls (t-test, p<0.001). Similar results were obtained based upon the GS knee (GSK) force–angle measurements (p<0.05). Conversely, no significant shift in the force–angle relation was found for the TA (p=0.138). Differences in the passive ROM were consistent with the force–angle changes. The ROM in the dorsiflexion direction was significantly smaller in SCI subjects compared to NI controls (p<0.05) while the plantar flexion ROM was not significantly different (p=0.114). Based upon these results, we concluded that muscle shortening is an important component of contracture in SCI.     

Elbow helical axes of motion are not the same in physiologic and kinetic joint simulators

Physiologic and kinetic joint simulators have been widely used for investigations of joint mechanics. The two types of simulator differ in the way joint motion is achieved; through prescribed motions and/or forces in kinetic joint simulators and by tendon loads in physiologic joint simulators. These two testing modalities have produced important insights, as in elucidating the importance of soft tissue structures to joint stability. However, the equivalence of the modalities has not been tested. This study sequentially tested five cadaveric elbows using both a physiologic simulator and a robot/6DOF system. Using position data from markers on the humerus and ulna, we calculated and compared the helical axes of motion of the specimens as the elbows were flexed from full extension. Six step size increments were used in the helical axis calculation. Marker position data at each test's full extension and full flexion point were also used to calculate a datum (overall) helical axis. The angles between the datum axis and step-wise movements were computed and stored. Increasing step size monotonically decreased the variability and the average conical angle encompassing the helical axes; a repeated measures ANOVA using test type (robot or physiologic simulator) and step size found that both type and step caused statistically significant differences (p<0.001). The large changes in helical axis angle observed for small changes in elbow flexion angle, especially in the robot tests, are a caveat for investigators using similar control algorithms. Controllers may need to include increased joint compliance and/or C(1) continuity to reduce variability.     

Molecular and morphological adaptations in compressed articular cartilage by polarized light microscopy and Fourier-transform infrared imaging

Fifteen articular cartilage-bone specimens from one canine humeral joint were compressed in the strain range of 0-50%. The deformation of the extracellular matrices in cartilage was preserved and the same tissue sections were studied using polarized light microscopy (PLM) and Fourier-transform infrared imaging (FTIRI). The PLM results show that the most significant changes in the apparent zone thickness due to 'reorganization' of the collagen fibrils based on the birefringence occur between 0% and 20% strain values, where the increase in the superficial zone and decrease in the radial zone thicknesses are approximately linear with the applied strain. The FTIRI anisotropy results show that the two amide components with bond direction perpendicular to the external compression retain anisotropy (amide II in the superficial zone and amide I in the radial zone). In contrast, the measured anisotropy from the two amide components with bond direction parallel to the external compression changes their anisotropy significantly (amide I in the superficial zone and amide II in the radial zone). Statistical analysis shows that there is an excellent correlation (r=0.98) between the relative depth of the minimum retardance in PLM and the relative depth of the amide II anisotropic cross-over. The changes in amide anisotropies in different histological zones are explained by the strain-dependent tipping angle of the amide bonds. These depth-dependent adaptations to static loading in cartilage's morphological structure and chemical distribution could be useful in the future studies of the early diseased cartilage.     

UKA与TKA治疗膝关节内侧单间室骨性关节炎的临床对比

目的:探究膝关节单髁置换术(UKA)与全膝关节置换术(TKA)治疗膝关节内侧单间室骨性关节炎的临床治疗效果。方法:将2011年4月-2015年7月期间因膝关节单间室骨性关节炎入院接受治疗的89例患者纳入本研究,随机分为研究组和对照组,研究组44例,行UKA手术,对照组45例,采用TKA手术方式治疗。对两组患者进行术后随访,对比临床治疗效果。结果:两组术前均有明显膝关节疼痛,术后膝关节疼痛均明显改善,组间差别无显著统计学意义(X2=1.323,P=0.2500.05);术后膝关节屈曲角度、HSS评分相对于术前均显著改善,研究组术后膝关节屈曲角度(111.2±18.8)度高于对照组的(98.6±14.7)度,差异有统计学意义(P0.05);HSS评分(87.6±13.7)分高于对照组的(73.2±16.8)分,差异有统计学意义(P0.05);研究组膝关节屈曲至90度时间比对照组短,数据差异有统计学差异(t=-2.303,P=0.0240.05)。结论:膝关节内侧单间室骨性关节炎采用UKA与TKA均能取得一定临床效果,减轻患者痛苦,改善膝关节功能,但UKA临床疗效较好,手术创伤较小,术后恢复较快。     

Analysis of Jumping-Landing Manoeuvers after Different Speed Performances in Soccer Players

PurposeRunning at high speed and sudden change in direction or activity stresses the knee. Surprisingly, not many studies have investigated the effects of sprinting on knee’s kinetics and kinematics of soccer players. Hence, this study is aimed to investigate indices of injury risk factors of jumping-landing maneuvers performed immediately after sprinting in male soccer players.MethodsTwenty-three collegiate male soccer players (22.1±1.7 years) were tested in four conditions; vertical jump (VJ), vertical jump immediately after slow running (VJSR), vertical jump immediately after sprinting (VJFR) and double horizontal jump immediately after sprinting (HJFR). The kinematics and kinetics data were measured using Vicon motion analyzer (100Hz) and two Kistler force platforms (1000Hz), respectively.ResultsFor knee flexion joint angle, (p = 0.014, η = 0.15) and knee valgus moment (p = 0.001, η = 0.71) differences between condition in the landing phase were found. For knee valgus joint angle, a main effect between legs in the jumping phase was found (p = 0.006, η = 0.31), which suggests bilateral deficit existed between the right and left lower limbs.ConclusionIn brief, the important findings were greater knee valgus moment and less knee flexion joint angle proceeding sprint (HJFR & VJFR) rather than no sprint condition (VJ) present an increased risk for knee injuries. These results seem to suggest that running and sudden subsequent jumping-landing activity experienced during playing soccer may negatively change the knee valgus moment. Thus, sprinting preceding a jump task may increase knee risk factors such as moment and knee flexion joint angle.     

Gender differences in musculotendinous stiffness and range of motion after an acute bout of stretching

The purpose of the present study was to examine musculotendinous stiffness (MTS) and ankle joint range of motion (ROM) in men and women after an acute bout of passive stretching. Thirteen men (mean ± SD age = 21 ± 2 years; body mass = 79 ± 15 kg; and height = 177 ± 7 cm) and 19 women (21 ± 3 years; 61 ± 9 kg; 165 ± 8 cm) completed stretch tolerance tests to determine MTS and ROM before and after a stretching protocol that consisted of 9 repetitions of passive, constant-torque stretching. The women were all tested during menses. Each repetition was held for 135 seconds. The results indicated that ROM increased after the stretching for the women (means ± SD pre to post: 109.39° ± 10.16° to 116.63° ± 9.63°; p ≤ 0.05) but not for the men (111.79° ± 6.84° to 113.93° ± 8.15°; p > 0.05). There were no stretching-induced changes in MTS (women's pre to postchange in MTS: -0.35 ± 0.38; men's MTS: +0.17 ± 0.40; p > 0.05), but MTS was higher for the men than for the women (MTS: 1.34 ± 0.41 vs. 0.97 ± 0.38; p ≤ 0.05). electromyographic amplitude for the soleus and medial gastrocnemius during the stretching tests was unchanged from pre to poststretching (p > 0.05); however, it increased with joint angle during the passive movements (p ≤ 0.05). Passively stretching the calf muscles increased stretch tolerance in women but not in men. But the stretching may not have affected the viscoelastic properties of the muscles. Practitioners may want to consider the possible gender differences in passive stretching responses and that increases in ROM may not always reflect decreases in MTS.     

Acute effects of static stretching on maximal eccentric torque production in women

The purpose of this study was to examine the acute effects of static stretching on peak torque (PT) and the joint angle at PT during maximal, voluntary, eccentric isokinetic muscle actions of the leg extensors at 60 and 180 degrees x s(-1) for the stretched and unstretched limbs in women. Thirteen women (mean age +/- SD = 20.8 +/- 0.8 yr; weight +/- SD = 63.3 +/- 9.5 kg; height +/- SD = 165.9 +/- 7.9 cm) volunteered to perform separate maximal, voluntary, eccentric isokinetic muscle actions of the leg extensors with the dominant and nondominant limbs on a Cybex 6000 dynamometer at 60 and 180 degrees x s(-1). PT (Nm) and the joint angle at PT (degrees) were recorded by the dynamometer software. Following the initial isokinetic assessments, the dominant leg extensors were stretched (mean stretching time +/- SD = 21.2 +/- 2.0 minutes) using 1 unassisted and 3 assisted static stretching exercises. After the stretching (4.3 +/- 1.4 minutes), the isokinetic assessments were repeated. The statistical analyses indicated no changes (p > 0.05) from pre- to poststretching for PT or the joint angle at PT. These results indicated that static stretching did not affect PT or the joint angle at PT of the leg extensors during maximal, voluntary, eccentric isokinetic muscle actions at 60 and 180 degrees x s(-1) in the stretched or unstretched limbs in women. In conjunction with previous studies, these findings suggested that static stretching may affect torque production during concentric, but not eccentric, muscle actions.     

Specificity of joint angle in isometric training

Six healthy women (21.8 +/- 0.4 y) did isometric strength training of the left plantarflexors at an ankle joint angle of 90 degrees. Training sessions, done 3 times per week for 6 weeks, consisted of 2 sets of ten 5 s maximal voluntary contractions. Prior to and following the training, and in random order, voluntary and evoked isometric contraction strength was measured at the training angle and at additional angles: 5 degrees, 10 degrees, 15 degrees, and 20 degrees intervals in the plantarflexion and dorsiflexion directions. Evoked contraction strength was measured as the peak torque of maximal twitch contractions of triceps surae. Training increased voluntary strength at the training angle and the two adjacent angles only (p less than 0.05). Time to peak twitch torque was not affected by training. Twitch half relaxation time increased after training (p = 0.013), but the increase was not specific to the training angle. There was a small (1.1%, p less than 0.05) increase in calf circumference after training. Evoked twitch torque did not increase significantly at any joint angle. It was therefore concluded that a neural mechanism is responsible for the specificity of joint angle observed in isometric training.     

Surface EMG: The issue of electrode location

This paper contributes to clarifying the conditions under which electrode position for surface EMG detection is critical and leads to estimates of EMG variables that are different from those obtained in other nearby locations. Whereas a number of previous works outline the need to avoid the innervation zone (or the muscle belly), many authors place electrodes in the central part or bulge of the muscle of interest where the innervation zone is likely to be. Computer simulations are presented to explain the effect of the innervation zone on amplitude, frequency and conduction velocity estimates from the signal and the need to avoid placing electrodes near it. Experimental signals recorded from some superficial muscles of the limbs and trunk (abductor pollicis brevis, flexor pollicis brevis, biceps, upper trapezius, vastus medialis, vastus lateralis) were processed providing support for the findings obtained from simulations. The use of multichannel techniques is recommended to estimate the location of the innervation zone and to properly choose the optimal position of the detection point(s) allowing meaningful estimates of EMG variables during movement analysis.     

Muscle-damaging exercise affects isokinetic torque more at short muscle length

The aim of this study was to investigate the differences in the length-dependent changes in quadriceps muscle torque during voluntary isometric and isokinetic contractions performed after severe muscle-damaging exercise. Thirteen physically active men (age = 23.8 ± 3.2 years, body weight = 77.2 ± 4.5 kg) performed stretch-shortening cycle (SSC) exercise comprising 100 drop jumps with 30-second intervals between each jump. Changes in the voluntary and electrically evoked torque in concentric and isometric conditions at different muscle lengths, muscle soreness, and plasma creatine kinase (CK) activity were assessed within 72 hours after SSC exercise. Isokinetic knee extension torque decreased significantly (p < 0.05) at all joint angles after SSC exercise. At 2 minutes and at 72 hours after SSC exercise, the changes in knee torque were significantly smaller at 80° (where 180° = full knee extension) than at 110-130°. At 2 minutes after SSC exercise, the optimal angle for isokinetic knee extension torque shifted by 9.5 ± 8.9° to a longer muscle length (p < 0.05). Electrically induced torque at low-frequency (20-Hz) stimulation decreased significantly more at a knee joint angle of 130° than at 90°. The subjects felt acute muscle pain and CK activity in the blood increased to 1,593.9 ± 536.2 IU·L?1 within 72 hours after SSC exercise (p < 0.05). This study demonstrates that the effect of muscle-damaging exercise on isokinetic torque is greatest for contractions at short muscle lengths. These findings have practical importance because the movements in most physical activities are dynamic in nature, and the decrease in torque at various points in the range of motion during exercise might affect overall performance.     

Effects of gleno-humeral joint centre mislocation on gleno-humeral kinematics and kinetics

The gleno-humeral (GH) rotation centre is typically estimated using predictive or functional methods, however these methods may lead to location errors. This study aimed at determining a location error threshold above which statistically significant changes in the values of kinematic and kinetic GH parameters occur. The secondary aims were to quantify the effects of the direction of mislocation (X, Y or Z axis) of the GH rotation centre on GH kinematic and kinetic parameters.

Shoulder flexion and abduction movements of 11 healthy volunteers were recorded using a standard motion capture system (Vicon, Oxford Metrics Ltd, Oxford, UK), then GH kinematic and kinetic parameters were computed. The true position of the GH rotation centre was determined using a low dose x-ray scanner (EOS? imaging, France) and this position was transferred to the motion data. GH angles and moments were re-computed for each position of the GH rotation centre after errors of up to ± 20?mm were added in increments of ± 5?mm to each axis. The three-dimensional error range was 5?mm to 34.65?mm.

GH joint angle and moment values were significantly altered from 10?mm of three-dimensional error, and from 5?mm of error on individual axes. However, errors on the longitudinal and antero-posterior axes only caused very small alterations of GH joint angle and moment values respectively. Future research should develop methods of GH rotation centre estimation that produce three-dimensional location errors of less than 10?mm to reduce error propagation on GH kinematics and kinetics.     

前交叉韧带保留残端重建对患者术后膝关节本体感觉功能恢复的影响

目的:研究前交叉韧带保留残端重建对患者术后膝关节本体感觉功能恢复的影响。方法:选取2014年3月-2016年3月于我院行膝关节镜下前交叉韧带重建手术患者108例,采用随机数字表法将所有患者分为对照组(n=54)和研究组(n=54)。对照组给予非保留残端重建治疗,研究组给予保留残端重建治疗,两组患者均进行为期12个月的随访观察。分别比较两组患者术前、术后3个月、术后6个月、术后12个月膝关节功能以及本体感觉功能恢复情况。结果:术前、术后12个月两组患者膝关节Lysholm评分对比均无统计学差异(P0.05),术后3个月、术后6个月研究组膝关节Lysholm评分明显高于对照组,差异有统计学意义(P0.05)。术后各个时间两组患者膝关节Lysholm评分均高于术前,且随着时间的推移呈上升的趋势,差异有统计学意义(P0.05)。术前、术后12个月两组膝关节被动活动察觉阈值、被动角度再生试验结果对比无统计学差异(P0.05),术后3个月、术后6个月研究组的膝关节被动活动察觉阈值、被动角度再生试验结果明显低于对照组,差异有统计学意义(P0.05),术后各个时间两组患者膝关节被动活动察觉阈值、被动角度再生试验结果均低于术前,且随着时间的推移呈下降的趋势,差异有统计学意义(P0.05)。两组患者不良反应发生率均为1.85%,无统计学差异(P0.05)。结论:前交叉韧带保留残端重建有利于患者术后膝关节功能以及本体感觉功能早期恢复,安全性好,值得临床推广。     

Calcium sensitivity of vasospastic basilar artery after experimental subarachnoid hemorrhage

Arteries that develop vasospasm after subarachnoid hemorrhage (SAH) may have altered contractility and compliance. Whether these changes are due to alterations in the smooth muscle cells or the arterial wall extracellular matrix is unknown. This study elucidated the location of such changes and determined the calcium sensitivity of vasospastic arteries. Dogs were placed under general anesthesia and underwent creation of SAH using the double-hemorrhage model. Vasospasm was assessed by angiography performed before and 4, 7, or 21 days after SAH. Basilar arteries were excised from SAH or control dogs (n = 8-52 arterial rings from 2-9 dogs per measurement) and studied under isometric tension in vitro before and after permeabilization of smooth muscle with alpha-toxin. Endothelium was removed from all arteries. Vasospastic arteries demonstrated significantly reduced contractility to KCl with a shift in the EC(50) toward reduced sensitivity to KCl 4 and 7 days after SAH (P < 0.05, ANOVA). There was reduced compliance that persisted after permeabilization (P < 0.05, ANOVA). Calcium sensitivity was decreased during vasospasm 4 and 7 days after SAH, as assessed in permeabilized arteries and in those contracted with BAY K 8644 in the presence of different concentrations of extracellular calcium (P < 0.05, ANOVA). Depolymerization of actin with cytochalasin D abolished contractions to KCl but failed to alter arterial compliance. In conclusion, it is shown for the first time that calcium sensitivity is decreased during vasospasm after SAH in dogs, suggesting that other mechanisms are involved in maintaining the contraction. Reduced compliance seems to be due to an alteration in the arterial wall extracellullar matrix rather than the smooth muscle cells themselves because it cannot be alleviated by depolymerization of smooth muscle actin.     

Bilateral differences in the net joint torques during the squat exercise

Bilateral movements are common in human movement, both as exercises and as daily activities. Because the movement patterns are similar, it is often assumed that there are no bilateral differences (BDs; differences between the left and right sides) in the joint torques that are producing these movements. The aim of this investigation was to test the assumption that the joint torques are equal between the left and right lower extremities by quantifying BDs during the barbell squat. Eighteen recreationally trained men (n = 9) and women (n = 9) completed 3 sets of 3 repetitions of the squat exercise, under 4 loading conditions: 25, 50, 75, and 100% of their 3 repetition maximum, while instrumented for biomechanical analysis. The average net joint moment (ANJM) and maximum flexion angle (MFA) for the hip, knee, and ankle as well as the average vertical ground reaction force (AVGRF) and the average distance from the ankle joint center to the center of pressure (ADCOP) were calculated. Group mean and individual data were analyzed (alpha = 0.05). At each joint, there was a significant main effect for side and load, no main effect for gender, with few significant interactions. The hip ANJM was 12.4% larger on the left side, the knee ANJM was 13.2% larger on the right side, and the ankle ANJM was 16.8% larger on the left side. Differences in MFAs between sides were less than 2 degrees for all 3 joints (all p > 0.20 except for the knee at 75% [p = 0.024] and 100% [p = 0.025]), but the AVGRF and the ADCOP were 6% and 11% larger on the left side. Few subjects exhibited the pattern identified with the group mean data, and no subject exhibited nonsignificant BDs for all 3 joints. These findings suggest that joint torques should not be assumed to be equal during the squat and that few individual subjects follow the pattern exhibited by group mean data.     

Localized damage in vertebral bone is most detrimental in regions of high strain energy density

It was hypothesized that damage to bone tissue would be most detrimental to the structural integrity of the vertebral body if it occurred in regions with high strain energy density, and not necessarily in regions of high or low trabecular bone apparent density, or in a particular anatomic location. The reduction in stiffness due to localized damage was computed in 16 finite element models of 10-mm-thick human vertebral sections. Statistical analyses were performed to determine which characteristic at the damage location--strain energy density, apparent density, or anatomic location--best predicted the corresponding stiffness reduction. There was a strong positive correlation between regional strain energy density and structural stiffness reduction in all 16 vertebral sections for damage in the trabecular centrum (p < 0.05, r2 = 0.43-0.93). By contrast, regional apparent density showed a significant negative correlation to stiffness reduction in only four of the sixteen bones (p < 0.05, r2 = 0.47-0.58). While damage in different anatomic locations did lead to different reductions in stiffness (p < 0.0001, ANOVA), no single location was consistently the most critical location for damage. Thus, knowledge of the characteristics of bone that determine strain energy density distributions can provide an understanding of how damage reduces whole bone mechanical properties. A patient-specific finite element model displaying a map of strain energy density can help optimize surgical planning and reinforcement of bone in individuals with high fracture risk.