Joint Compressive Forces Research Articles

An FE investigation simulating intra-operative corrective forces applied to correct scoliosis deformity

BackgroundAdolescent idiopathic scoliosis (AIS) is a deformity of the spine, which may require surgical correction by attaching a rod to the patient’s spine using screws implanted in the vertebral bodies. Surgeons achieve an intra-operative reduction in the deformity by applying compressive forces across the intervertebral disc spaces while they secure the rod to the vertebra. We were interested to understand how the deformity correction is influenced by increasing magnitudes of surgical corrective forces and what tissue level stresses are predicted at the vertebral endplates due to the surgical correction.MethodsPatient-specific finite element models of the osseoligamentous spine and ribcage of eight AIS patients who underwent single rod anterior scoliosis surgery were created using pre-operative computed tomography (CT) scans. The surgically altered spine, including titanium rod and vertebral screws, was simulated. The models were analysed using data for intra-operatively measured compressive forces – three load profiles representing the mean and upper and lower standard deviation of this data were analysed. Data for the clinically observed deformity correction (Cobb angle) were compared with the model-predicted correction and the model results investigated to better understand the influence of increased compressive forces on the biomechanics of the instrumented joints.ResultsThe predicted corrected Cobb angle for seven of the eight FE models were within the 5° clinical Cobb measurement variability for at least one of the force profiles. The largest portion of overall correction was predicted at or near the apical intervertebral disc for all load profiles. Model predictions for four of the eight patients showed endplate-to-endplate contact was occurring on adjacent endplates of one or more intervertebral disc spaces in the instrumented curve following the surgical loading steps.ConclusionThis study demonstrated there is a direct relationship between intra-operative joint compressive forces and the degree of deformity correction achieved. The majority of the deformity correction will occur at or in adjacent spinal levels to the apex of the deformity. This study highlighted the importance of the intervertebral disc space anatomy in governing the coronal plane deformity correction and the limit of this correction will be when bone-to-bone contact of the opposing vertebral endplates occurs.

Biomechanical consequences of a posterior root tear of the lateral meniscus: stabilizing effect of the meniscofemoral ligament

The purpose of this study was to evaluate the effects of different types of lateral meniscus root tears in terms of tibiofemoral contact stress. Ten porcine knees each underwent five different testing conditions with the menisci intact, a simulated lateral posterior root tear with and without cutting the meniscofemoral ligament and with an artificial tear of the posterior root of the medial meniscus. Biomechanical testing was performed at 30° of flexion with an axial load of 100N. A pressure sensor (st Sensor Type S2042, Novel, Munich) was used to measure the tibiofemoral contact area and the tibiofemoral contact pressure. Data were analyzed to assess the differences in contact area and tibiofemoral peak contact pressure among the five meniscal conditions. There was no significant difference in mean contact pressure between the state with the menisci intact and an isolated posterior root tear of the lateral meniscus. In case of a root tear and a tear of the meniscofemoral ligament, the contact area decreased in comparison with the intact state of the menisci. After additional cutting of the meniscofemoral ligament, the tibiofemoral contact pressure was significantly higher in comparison with the intact state and the avulsion injury. In the medial compartment, joint compression forces were significantly increased in comparison with the intact state after cutting the posterior root of the medial meniscus (P<0.05). The consequence of a medial meniscus root tear is well known and was verified by this analysis. The results of the present study show that the biomechanical consequences of a lateral meniscus root tear depend on the state of the meniscofemoral ligament. An increase in tibiofemoral contact pressure is only to be expected in combined injuries of the meniscus root and the meniscofemoral ligaments. Posterior lateral meniscus root tear might have a better prognosis in terms of the development of osteoarthritis when the meniscofemoral ligament is intact.

Does knee external rotation differ according to frontal plane knee alignment and the presence of patellofemoral osteoarthritis after anterior cruciate ligament reconstruction?

Does knee external rotation differ according to frontal plane knee alignment and the presence of patellofemoral osteoarthritis after anterior cruciate ligament reconstruction?

The Effect of Foot Progression Angle on Knee Joint Compression Force During Walking

It is unclear how rotations of the lower limb affect the knee joint compression forces during walking. Increases in the frontal plane knee moment have been reported when walking with internally rotated feet and a decrease when walking with externally rotated feet. The aim of this study was to investigate the knee joint compressive forces during walking with internal, external and normal foot rotation and to determine if the frontal plane knee joint moment is an adequate surrogate for the compression forces in the medial and lateral knee joint compartments under such gait modifications. Ten healthy males walked at a fixed speed of 4.5 km/h under three conditions: Normal walking, internally rotated and externally rotated. All gait trials were recorded by six infrared cameras. Net joint moments were calculated by 3D inverse dynamics. The results revealed that the medial knee joint compartment compression force increased during external foot rotation and the lateral knee joint compartment compression force increased during internal foot rotation. The increases in joint loads may be a result of increased knee flexion angles. Further, these data suggest that the frontal plane knee joint moment is not a valid surrogate measure for knee joint compression forces but rather indicates the medial- to-lateral load distribution.

Changing sagittal plane body position during single-leg landings influences the risk of non-contact anterior cruciate ligament injury

To examine the effects of different sagittal plane body positions during single-leg landings on biomechanics and muscle activation parameters associated with risk for anterior cruciate ligament (ACL) injury. Twenty participants performed single-leg drop landings onto a force plate using the following landing styles: self-selected, leaning forward (LFL) and upright (URL). Lower extremity and trunk 3D biomechanics and lower extremity muscle activities were recorded using motion analysis and surface electromyography, respectively. Differences in landing styles were examined using 2-way Repeated-measures ANOVAs (sex × landing conditions) followed by Bonferroni pairwise comparisons. Participants demonstrated greater peak vertical ground reaction force, greater peak knee extensor moment, lesser plantar flexion, lesser or no hip extensor moments, and lesser medial and lateral gastrocnemius and lateral quadriceps muscle activations during URL than during LFL. These modifications of lower extremity biomechanics across landing conditions were similar between men and women. Leaning forward while landing appears to protect the ACL by increasing the shock absorption capacity and knee flexion angles and decreasing anterior shear force due to the knee joint compression force and quadriceps muscle activation. Conversely, landing upright appears to be ACL harmful by increasing the post-impact force of landing and quadriceps muscle activity while decreasing knee flexion angles, all of which lead to a greater tibial anterior shear force and ACL loading. ACL injury prevention programmes should include exercise regimens to improve sagittal plane body position control during landing motions.

Patellofemoral joint compression forces in backward and forward running

Patellofemoral pain (PFP) is a common injury and increased patellofemoral joint compression forces (PFJCF) may aggravate symptoms. Backward running (BR) has been suggested for exercise with reduced PFJCF.The aims of this study were to (1) investigate if BR had reduced peak PFJCF compared to forward running (FR) at the same speed, and (2) if PFJCF was reduced in BR, to investigate which biomechanical parameters explained this. It was hypothesized that (1) PFJCF would be lower in BR, and (2) that this would coincide with a reduced peak knee moment caused by altered ground reaction forces (GRFs).Twenty healthy subjects ran in forward and backward directions at consistent speed. Kinematic and ground reaction force data were collected; inverse dynamic and PFJCF analyses were performed.PFJCF were higher in FR than BR (4.5±1.5; 3.4±1.4BW; p<0.01). The majority of this difference (93.1%) was predicted by increased knee moments in FR compared to BR (157±54; 124±51Nm; p<0.01). 54.8% of differences in knee moments could be predicted by the magnitude of the GRF (2.3±0.3; 2.4±0.2BW), knee flexion angle (44±6; 41±7) and center of pressure location on the foot (25±11; 12±6%) at time of peak knee moment. Results were not consistent in all subjects.It was concluded that BR had reduced PFJCF compared to FR. This was caused by an increased knee moment, due to differences in magnitude and location of the GRF vector relative to the knee. BR can therefore be used to exercise with decreased PFJCF.

Is there a low-back cost to hip-centric exercise? Quantifying the lumbar spine joint compression and shear forces during movements used to overload the hips

The aim of this study was to quantify joint compression and shear forces at L4/L5 during exercises used to overload the hips. Nine men performed 36 “walking” trials using two modalities: (1) sled towing and (2) exercise bands placed around the ankles. Participants completed forward, backward, and lateral trials with bent and straight legs at three separate loads. Surface electromyography (EMG) was recorded bilaterally from eight torso and thigh sites, upper body and lumbar spine motion were quantified, and hand forces were measured. An EMG-driven musculoskeletal model was used to estimate the muscular contribution to joint compression and shear. Peak reaction, muscle and joint compression and shear forces, and peak gluteus medius and maximus activity were calculated. Significant differences were noted in each dependent measure; however, they were dependent on direction of travel, leg position, and load. The highest joint compression and shear forces for the sled and band conditions were 4378 N and 626 N, and 3306 N and 713 N, respectively. In general, increasing the band tension had little effect on all dependent measures, although a load-response was found during the sled conditions. Before using any exercise to improve hip function, the potential benefits should be weighed against “costs” to neighbouring joints.

The role of footwear in attenuating impact loads in individuals with knee osteoarthritis

The role of footwear in attenuating impact loads in individuals with knee osteoarthritis

드롭랜딩 시 높이에 따른 슬개대퇴 압박력의 차이

Patellofemoral pain syndrome is the most common problem involving the knee, accounting for 25% of knee injuries. Repetitive, overuse activities cause increased force at the patellofemoral joint, resulting in pain during flexion and extension activities. Most research have been conducted in exploring the patellofemoral compressive force in gait, squat and lunges, even though in real cases, possibilities in landing exist. The purpose of this study was to compare the differences in patellofemoral compressive force according to two different height. Sixteen collegiate male students(age: 22.25 <TEX>${\pm}$</TEX> 3.30 yrs, height: 177.25 <TEX>${\pm}$</TEX> 4.44 cm, weight: 77.50 <TEX>${\pm}$</TEX> 8.18 kg) were chosen. The subjects performed drop landings in 45 cm, 60 cm. The findings demonstrated that higher height showed peak knee extension moment, quadriceps contraction force, patellofemoral compressive force with increased VGRF. Regarding the patellofemoral joint compressive force, it increased by quadriceps contraction force with knee flexion during landing, yet, it showed no difference in maximal knee flexion. To minimize patellofemoral joint stress and reduce the likelihood of developing PFPS, we recommend that predesigned quadriceps and hip muscle group strengthening are needed during conditioning and training.

Arthroscopic Fixation of Matrix-Associated Autologous Chondrocyte Implantation: Importance of Fixation Pin Angle on Joint Compression Forces

The aim of the study was to investigate the effect of pin fixation perpendicular and 30° tilted to the matrix surface on the joint compression forces. In a porcine knee model, joint compression forces were recorded with a digital pressure sensor above the medial meniscus and with axial compression of 100 N by use of a material testing machine. The forces were recorded for an intact femoral condyle, as well as a standardized cartilage defect of 25 × 20 mm, after matrix-associated autologous chondrocyte implantation (m-ACI) (BioSeed C; Biotissue Technologies, Freiburg, Germany), fixed by use of a conventional suture technique and pin fixation with a biodegradable pin perpendicular and 30° tilted to the matrix surface. In knees with cartilage defects, the peak compression forces (mean, 824 kPa) were significantly increased compared with the intact knee joint (564 kPa). After m-ACI implantation with a chondral suture (581.3 kPa) and perpendicular pin fixation, the joint compression forces of the cartilage defect were significantly decreased (630.7 kPa). There were no significant differences compared with the intact knee. After 30° tilted pin insertion, mean joint compression forces were significantly increased (1,740 kPa). This study shows that after chondral suture and perpendicular pin fixation, there are no increased compression forces in the knee joint in comparison to an intact knee. Thirty degree tilted pin insertion contributes to increased joint compression forces. A tilted insertion during pin fixation in m-ACI should be avoided because it may lead to increased joint compression forces, especially after cartilage defect lesions on the tibial side.

Muscle and joint‐contact loading at the glenohumeral joint after reverse total shoulder arthroplasty

The purposes of this study were to determine the contributions of each shoulder muscle to glenohumeral joint force during abduction and flexion in both the anatomical and post-operative shoulder and to identify factors that may contribute to the incidence of glenoid component loosening/failure and joint instability in the shoulder after reverse shoulder arthroplasty (RSA). Eight cadaveric upper extremities were mounted onto a testing apparatus. Muscle lines of action were measured, and muscle forces and muscle contributions to glenohumeral joint forces were determined during abduction and flexion of the pre-operative anatomical shoulder and of the shoulder after arthroplasty. Muscle forces in the middle deltoid during abduction and those in the middle and anterior deltoid during flexion were significantly lower in the reverse shoulder than the pre-operative shoulder (p < 0.017). The resultant glenohumeral joint force in the reverse shoulder was significantly lower than that in the pre-operative shoulder; however, the superior shear force acting at the glenohumeral joint was significantly higher (p < 0.001). Reverse total shoulder arthroplasty reduces muscle effort in performing lifting and pushing tasks; however, reduced joint compressive force has the potential to compromise joint stability, while an increased superior joint shear force may contribute to component loosening/failure. Because greater superior shear force is generated in flexion than in abduction, care should be taken to avoid excessive shoulder loading in this plane of elevation.

Weight Loss Reduces Biomechanically Modeled Knee Joint And Muscle Forces

Obesity is characterized by excessive body mass relative to height and is a predictor of knee osteoarthritis (OA). Despite the assumption that reduced body mass reduces knee joint loads and knee OA risk, these loads have not been identified in obese people or in formerly obese people after weight loss. PURPOSE: To identify the effects of weight loss on knee joint and muscle forces in obese adults. METHODS: Ground reaction forces and 3D kinematics were measured during walking prior to (baseline, BMI = 43.2) and 6 (BMI = 31.6) and 12 months (BMI = 28.6) after bariatric surgery in 10 adults. Musculoskeletal modeling was applied to these data to predict knee joint and muscle forces which were analyzed with 1-way ANOVA and post-hoc tests comparing baseline vs 6 months and 6 vs 12 months. All subjects gave written informed consent. RESULTS: Body mass decreased 27% from baseline to 6 months and 9% more at 12 months (126 vs 92 vs 84 kg, both p<0.05). Self-selected walking speed was statistically unchanged at 6 months (1.30 vs 1.35 m/s, N.S.) but increased 7% from 6 to 12 months (1.45 m/s, p<0.05). Maximum knee compressive force decreased 18% (2,943 vs 2,417, p<0.05) at 6 months then was statistically unchanged at 12 months (2,557 N). Maximum hamstrings (661 vs 550 N, p<0.05) and gastrocnemius (1,055 vs 805 N, p<0.05) forces were reduced at 6 months compared to baseline. Quadriceps force was statistically unchanged. CONCLUSIONS: Reduced body weight was the primary mechanism in changing knee joint compressive force. Indeed, knee force and body weight were correlated at r=0.82. Knee force most likely did not change from 6 to 12 months because increased walking speed probably counteracted the effect of reduced weight. Speed was correlated to knee force at r=0.49. Quadriceps force went unchanged despite weight loss most likely because step length (r=0.72 with quadriceps force) and knee flexion (r=0.44 with quadriceps force) both increased through the trial (data not shown) increasing quadriceps demand. Our data suggest 1) reduced weight led to reduced hamstrings and gastrocnemius forces which then led to reduced knee force and 2) reduced body weight may serve as a protective mechanism against knee OA incidence by reducing knee joint forces.

Investigation of optimal follower load path generated by trunk muscle coordination

It has been reported that the center of rotation of each vertebral body is located posterior to the vertebral body center. Moreover, it has been suggested that an optimized follower load (FL) acts posterior to the vertebral body center. However, the optimal position of the FL with respect to typical biomechanical characteristics regarding spinal stabilization, such as joint compressive force, shear force, joint moment, and muscle stress, has not been studied. A variation in the center of rotation of each vertebra was formulated in a three-dimensional finite element model of the lumbar spine with 117 pairs of trunk muscles. Then, the optimal translation of the FL path connecting the centers of rotations was estimated by solving the optimization problem that was to simultaneously minimize the compressive forces, the shear forces, and the joint moments or to minimize the cubic muscle stresses. An upright neutral standing position and a standing position with 200N in both hands were considered. The FL path moved posterior, regardless of the optimization criteria and loading conditions. The FL path moved 5.0 and 7.8mm posterior in upright standing and 4.1mm and 7.0mm posterior in standing with 200N in hands for each optimization scheme. In addition, it was presented that the optimal FL path may have advantages in comparison to the body center FL path. The present techniques may be important in understanding the spine stabilization function of the trunk muscles.

Effects of an intensive weight loss program on knee joint loading in obese adults with knee osteoarthritis

To determine the effect of an intensive weight loss program on knee joint loads during walking in obese patients with knee osteoarthritis (OA). Participants included 157 obese knee OA patients that underwent a 16-week dietary intervention. Three-dimensional gait analyses were performed before and after the intervention at the participants' freely chosen walking speed. Knee joint compression forces, axial impulses, knee flexion angle and frontal and sagittal plane knee moments were calculated to determine the biomechanical effects of the weight loss. 157 subjects (89% of the initial cohort) completed the 16-week intervention. The average weight loss of 13.7 kg (P<.0001) corresponded to 13.5% of the baseline body weight. The weight loss resulted in a 7% reduction in knee joint loading, a 13% lower axial impulse, and a 12% reduction in the internal knee abductor moment (KAM). There were no clear effects on sagittal plane knee moments or peak knee flexion angle. Linear regression analyses adjusted for changes in walking speed showed that for every 1 kg in weight loss, the peak knee load was reduced by 2.2 kg. Thus, every kilo reduction in body weight was related to more than twice the reduction in peak knee force at a given walking speed. Weight loss is an excellent short-term investment in terms of joint loading for patients with combined obesity and knee OA. The effects of sustained weight loss on disease progression and symptoms in relation to biomechanical factors remain to be shown.

Is it possible to reduce the knee joint compression force during level walking with hiking poles?

Walking with hiking poles has become a popular way of exercising. Walking with poles is advocated as a physical activity that significantly reduces the loading of the hip, knee and ankle joints. We have previously observed that pole walking does not lead to a reduction of the load on the knee joint. However, it is unclear whether an increased force transmitted through the poles can reduce the load on the knee joint. Thus, the purpose of the present study was to investigate if an increased load transmitted through the arms to the poles could reduce the knee joint compression force during level walking with poles. We hypothesized that an increased pole force would result in a reduction of the knee joint compression force. Gait analyses from 10 healthy subjects walking with poles were obtained. The pole force was measured simultaneously during the gait analyses. The knee joint compression forces were estimated by using a biomechanical knee joint model. The results showed that the subjects were able to increase the pole force by 2.4 times the normal pole force. However, this did not lead to a reduction in the knee joint compressive force and we rejected our hypothesis. In conclusion, the use of poles during level walking does not seem to reduce knee joint compressive loads. However, it is possible that the use of poles in other populations (e.g. osteoarthritis patients) and in terrain would unload the knee joint. This should be investigated in the future.

주관절의 생역학

Purpose: Understanding elbow biomechanics is necessary to understand the pathophysiologic mechanism of elbow injury and to provide a scientific basis for clinical practice. This article provides a summary of key concepts that are relevant to understanding common elbow injuries and their management. Materials and Methods: The biomechanics of the elbow joint can be divided into kinematics, stability and force transmission through the elbow joint. Active and passive stabilizers include bony articular geometry; soft tissues provide joint stability, compression force and motion. Results and Conclusion: Knowledge of elbow biomechanics will help (i) advance surgical procedures and trauma management, (ii) develop new elbow prostheses and (iii) stimulate future research.

Relationships Among Knee Loads During Gait and C-Reactive Protein In Knee Osteoarthritis: A Preliminary Study

Knee osteoarthritis (OA) is associated with biomechanical and physiological factors including lower extremity joint moments and knee joint forces during gait and inflammatory markers such as C-reactive protein (CRP) supporting the existence of both biomechanical and physiological pathways to disease progression and possibly amelioration. Little is know however about the relationships among these pathways. PURPOSE: To identify the relationships among anthropometric measures of body weight and BMI, gait biomechanical measures of knee joint abductor moment and compressive force, and the inflammatory marker CRP in older adults with knee OA. METHODS: Data were obtained from a subset of 210 older adults (age: 66 yrs, mass: 93 kg, BMI: 33 kg/m2) out of 450 participants having radiographically diagnosed knee OA enrolled in the Intensive Dietary Restriction with Exercise in Arthritis (IDEA) trial. 3D inverse dynamics analysis of the lower extremity was used to calculate knee abductor moment and compressive force during level walking. Serum levels of CRP were determined using an automated immunoanalyzer and were log-transformed for analyses. Pearson product moment correlations among these variables were calculated to identify the relationships among the biomechanical and physiological variables (p<0.05). RESULTS: Knee joint compressive force was relatively strongly related to body mass (r=0.65) and walking speed (r=0.48) and moderately related to BMI (r=0.27) and peak knee abductor moment (r=0.17). CRP was moderately related to BMI (r=0.22) but had statistically non-significant relationships with knee compressive force (r=0.03) and peak knee moment (r=-0.09). CONCLUSIONS: The data showed a surprisingly minimal relationship between established biomechanical and physiological pathways associated with knee OA. The moderate-strength relationships between BMI and both biomechanical (knee compressive force) and physiological (CRP) variables suggest a possible, if only tenuous, connection between the two pathways. Our data are limited to a single measure of inflammation and it is possible other pro-inflammatory cytokines including interleukin 6 or tumor necrosis factor-alpha may show a stronger connection between biomechanical and physiological pathways in knee OA. Supported by NIH R01 AR052528.

The Biomechanical Effects of Variation in the Maximum Forces Exerted by Trunk Muscles on the Joint Forces and Moments in the Lumbar Spine: A Finite Element Analysis

The weakening of trunk muscles is known to be related to a reduction of the stabilization function provided by the muscles to the lumbar spine; therefore, strengthening deep muscles might reduce the possibility of injury and pain in the lumbar spine. In this study, the effect of variation in maximum forces of trunk muscles on the joint forces and moments in the lumbar spine was investigated. Accordingly, a three-dimensional finite element model of the lumbar spine that included the trunk muscles was used in this study. The variation in maximum forces of specific muscle groups was then modelled, and joint compressive and shear forces, as well as resultant joint moments, which were presumed to be related to spinal stabilization from a mechanical viewpoint, were analysed. The increase in resultant joint moments occurred owing to decrease in maximum forces of the multifidus, interspinales, intertransversarii, rotatores, iliocostalis, longissimus, psoas, and quadratus lumborum. In addition, joint shear forces and resultant joint moments were reduced as the maximum forces of deep muscles were increased. These results from finite element analysis indicate that the variation in maximum forces exerted by trunk muscles could affect the joint forces and joint moments in the lumbar spine.

Effects of Single-Bundle and Double-Bundle ACL Reconstruction on Tibiofemoral Forces and Joint Kinematics Under Dynamic Loading (SS-42)

Initial biomechanical studies have determined that the double-bundle technique significantly improved upon the single-bundle method: it better resists an externally applied moment and the stress distribution between the two grafts closely matches that of the normal ACL. However, there have not been any studies to evaluate the long-term effects of double-bundle ACL reconstruction on joint contact mechanics or articular cartilage integrity. Before this can be studied however, a direct measurement of joint contact forces must be examined. This study was conducted to establish a baseline relationship between ACL reconstructive techniques on joint kinematics and compressive forces. The purpose of this study was to compare the tibiofemoral joint kinematics and contact forces between single-bundle (SBR) and double-bundle (DBR) ACL reconstructive techniques during simulated squatting using a cadaver model. Twelve matched pairs of fresh frozen human cadaver knees (7 female and 3 male) with no evidence of knee pathology were stored at −20° C following harvest. The mean age of the specimens was 58 years (range 16 – 80). The specimens consisted of the distal third of the femur and the proximal two thirds of the tibia. Threaded rods (0.5-inch diameter Stainless Steel, McMaster-Carr, Los Angeles, CA) were inserted into the intramedullary canal of the femur and tibia and secured through an epoxy resin (Smooth-Cast 300, Smooth-On Inc, Easton, PA) for attachment to a test fixture which allows for dynamic simulated squatting. Additionally, the quadriceps tendon and semimembranosus and biceps femoris hamstrings were sutured to allow attachment to the test fixture for dynamic loading. An Optotrak Image Analysis System (Northern Digital; Waterloo, Ontario) with Optotrak Digitizer software (NDI 6D Architect) was used to track the position of the tibia with respect to the femur for kinematic measurements. K-Scan thin-film pressure sensors (4000; Maximum Pressure Range: 10,342 KPa, Sensing Area: 27.9 mm x 33 mm, Sensels per square cm: 62; Tekscan Inc, South Boston, MA) were used to simultaneously measure the tibiofemoral compressive forces in both compartments of the knee. The “I-scan” software program (Tekscan, Inc., South Boston, MA) was used to gather sensor data. Measurements were made in the intact knee and after the experimental procedure at each of 11 angles (0, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100). For each outcome measure, two-way repeated measures analysis of variance was used to test for differences between the two experimental procedures with respect to the mean change from intact state. The model also included factors representing the effect of angle and an angle by procedure interaction. F-tests corresponding to simple effects were used to evaluate procedure differences in outcome within each angle when appropriate. One sample t-tests, which were based on the error term derived from the ANOVA, were used to evaluate significant change from intact state for each experimental procedure both across and within test angle. Analyses were performed using SAS statistical software Version 8. Statistical significance was based on p = 0.05. Rotation kinematics were different from the intact knee throughout the range of motion in the SBR group, while DBR was different at only high flexion angles while recreating proper rotation at low angles (p=0.004). In the medial compartment, both techniques successfully recreated joint contact forces (P=0.0006). In the lateral compartment, DBR failed to reapproximate native compressive forces throughout all flexion angles while SBR more closely reapproximated native compressive forces at high flexion angles. This study suggests compressive load is better restored with single-bundle than double-bundle ACL reconstruction. Joint kinematics are better restored with double-bundle reconstruction but still did not completely recreate the native ACL.

Effects Of Drop Landing Height On Lower Extremity Joint Contact Forces

The impact phase of loading has long been associated with osteogenisis and lower extremity skeletal injuries. Although reaction forces increase with drop landing height, they comprise only a small portion of the joint loading environment. The true loading experienced by the joints can only be realized when muscle forces are taken into consideration. PURPOSE: To determine the effects of drop landing height on lower extremity joint contact forces METHODS: Nine subjects completed ten landings from three heights in a random order (26, 39, and 52 cm). Electromyographical, force platform and kinematic data were collected concurrently. Musculoskeletal modeling and computer optimization techniques were used to determine muscle forces of the lower extremity. Electromyographical data were used to validate muscle optimizations, and joint contact forces at the hip, knee, and ankle were calculated by summing the reaction and muscle forces at each joint. Peak instantaneous joint contact forces during the impact phase (200 ms) were determined. Differences in joint contact forces were compared between conditions using a repeated measures ANOVA with Tukey‘s post-hoc tests. RESULTS: The knee and hip contact forces significantly increased with drop height. The ankle contact force during the 52 cm drop height was significantly larger than the 26 cm drop height. Respectively, joint compressive contact forces for the 26, 39, and 52 cm drop heights were as follows: ankle 6.8, 7.7, and 8.7 body weight (BW), knee 9.5, 10.5, 12.1 BW, hip 8.6, 9.9, 11.8 BW. Ground reaction forces contributed 20 to 28% of joint contact forces during drop landings. CONCLUSION: The results show an evident increase in ground reaction forces and joint contact forces with an increase in drop landing height. However, ground reaction forces account for only a small portion of joint loading during drop landings. Muscle forces substantially contribute to the joint loading environment. The results suggest that conventional methods using external forces and ground reaction forces may drastically underestimate force experienced by the joint.