Changes In Joint Loading Research Articles

Feasibility of predicting changes in gait biomechanics following muscle strength perturbations using optimal control in patients with transfemoral amputation

Bone-anchored limbs (BALs) are socket prosthesis alternatives, directly fixing to residual bone via osseointegrated implant. There is a need to quantify multi-level effects of rehabilitation for transfemoral BAL users (i.e. changes in joint loading and movement patterns). Our primary objective was determining feasibility of using optimal control to predict gait biomechanics compared to ground-truth experimental data from transfemoral BAL users. A secondary objective was examining biomechanical effects from estimated changes in hip abductor muscle strength. We developed and validated a workflow for predicting gait biomechanics in four transfemoral BAL users and investigated the biomechanical effects of altered hip abductor strengths.

Influence of Walking Over Unexpected Uneven Terrain on Joint Loading for Individuals With Transtibial Amputation.

Individuals with transtibial amputation (TTA) experience asymmetric lower-limb loading which can lead to joint pain and injuries. However, it is unclear how walking over unexpected uneven terrain affects their loading patterns. This study sought to use modeling and simulation to determine how peak joint contact forces and impulses change for individuals with unilateral TTA during an uneven step and subsequent recovery step and how those patterns compare to able-bodied individuals. We expected residual limb loading during the uneven step and intact limb loading during the recovery step would increase relative to flush walking. Further, individuals with TTA would experience larger loading increases compared to able-bodied individuals. Simulations of individuals with TTA showed during the uneven step, changes in joint loading occurred at all joints except the prosthetic ankle relative to flush walking. During the recovery step, intact limb joint loading increased in early stance relative to flush walking. Simulations of able-bodied individuals showed large increases in ankle joint loading for both surface conditions. Overall, increases in early stance knee joint loading were larger for those with TTA compared to able-bodied individuals during both steps. These results suggest that individuals with TTA experience altered joint loading patterns when stepping on uneven terrain. Future work should investigate whether an adapting ankle-foot prosthesis can mitigate these changes to reduce injury risk.

The influence of induced gait asymmetry on joint reaction forces

Chronic injury- or disease-induced joint impairments result in asymmetric gait deviations that may precipitate changes in joint loading associated with pain and osteoarthritis. Understanding the impact of gait deviations on joint reaction forces (JRFs) is challenging because of concurrent neurological and/or anatomical changes and because measuring JRFs requires medically invasive instrumented implants. Instead, we investigated the impact of joint motion limitations and induced asymmetry on JRFs by simulating data recorded as 8 unimpaired participants walked with bracing to unilaterally and bilaterally restrict ankle, knee, and simultaneous ankle + knee motion. Personalized models, calculated kinematics, and ground reaction forces (GRFs) were input into a computed muscle control tool to determine lower limb JRFs and simulated muscle activations guided by electromyography-driven timing constraints. Unilateral knee restriction increased GRF peak and loading rate ipsilaterally but peak values decreased contralaterally when compared to walking without joint restriction. GRF peak and loading rate increased with bilateral restriction compared to the contralateral limb of unilaterally restricted conditions. Despite changes in GRFs, JRFs were relatively unchanged due to reduced muscle forces during loading response. Thus, while joint restriction results in increased limb loading, reductions in muscle forces counteract changes in limb loading such that JRFs were relatively unchanged.

ASSESSMENT OF TIBIOFEMORAL AND ALLOGRAFT LOADING AFTER OSTEOCHONDRAL ALLOGRAFT TRANSPLANTATION USING SHELL GRAFTS

In this study, we aimed to investigate tibiofemoral and allograft loading parameters after OCA transplantation using tibial plateau shell grafts to characterize the clinically relevant biomechanics that may influence joint kinematics and OCA osseointegration after transplantation. The study was designed to test the hypothesis that there are significant changes in joint loading after tibial plateau OCA transplantation that may require unique post-operative rehabilitation regimens in patients to restore balance in the knee joint.Fresh-frozen cadaveric knees (n=6) were thawed and mounted onto a 6 DOF KUKA robot. Specimens were size matched to +2 mm for the medial-to-lateral width of the medial tibial hemiplateaus. Three specimens served as allograft recipient knees and three served as donor knees. Recipient knees were first tested in their native state and then tested with size-matched medial tibial hemiplateau shell grafts (n=3) prepared from the donor knees using custom-cut tab-in-slot and subchondral drilling techniques. Tekscan sensors were placed in the joint spaces to evaluate the loading conditions under 90N biaxial loading at full extension of the knee before and after graft placement. The I-Scan system used in conjunction analyzed the total force, pressure distribution, peak pressure, and center of force within the joint space.Data demonstrated significant difference (p<0.05) in joint space loading after graft implantation compared to controls in both lateral and medial tibial plateaus. The I-Scan pressure mapping system displayed changes in femoral condylar contact points as well.The results demonstrated that joint space loading was significantly different (p<0.05) between all preoperative and postoperative cadaveric specimens. Despite the best efforts to size match grafts, slight differences in the host's joint geometry resulted in shifts of contact areas between the tibial plateau and femoral condyle therefore causing either an increase or decrease in pressure measured by the sensor. This concludes that accuracy in graft size matching is extremely important to restoring close to normal loading across the joint and this can be further ensured through postoperative care customized to the patient after OCA surgery.

Comparison between conventional MRI and weight-bearing positional MRI reveals important differences in radiological measurements of the patellofemoral joint.

To compare radiological measurements of the patellofemoral joint (PFJ) morphology and measurement reproducibility across the following scanning modalities: (a) 3 T supine MRI, (b) 0.25 T supine MRI and (c) standing 0.25 T MRI. Forty patients referred to MRI of the knee were scanned by high field 3 T MRI in supine position and low field 0.25 T positional (pMRI) in supine and standing positions. Radiological measurements for assessment of femoral trochlear morphology, patellar tracking, patellar height and knee flexion angle were compared across scanning situations by one-way repeated-measures ANOVA. Measurement reliability and agreement were assessed by calculation of ICC, SEM and MDC. Patellar tracking differed across scanning situations, particularly between 3.0 T supine and 0.25 T standing position. Mean differences are the following: patella bisect offset (PBO): 9.6%, p ≤ 0.001; patellar tilt angle (PTA): 3.1°, p ≤ 0.001; tibial tuberosity-trochlear groove distance (TT-TG): 2.7 mm, p ≤ 0.001). Measurements revealed slight knee joint flexion in supine and slight hyperextension in the standing position (MD: 9.3°, P ≤ 0.001), likely related to the observed differences in patellar tracking. Reproducibility was comparable across MRI field strengths. In general, PBO, PTA and TT-TG were the most robust measurements in terms of reproducibility and agreement across scanning situations (ICC range: 0.85-0.94). Significant differences in important patellofemoral morphology measurements were observed between supine and standing MRI scanning positions. These were unlikely due to physiological factors such as changes in joint loading but rather induced by slight differences in knee flexion angle. This emphasises the need to standardise knee positioning during scanning, particularly for weight-bearing positional MRI before clinical use.

Knee flexion in terminal stance is associated with changes in joint loading in patients with isolated, increased femoral anteversion

Knee flexion in terminal stance is associated with changes in joint loading in patients with isolated, increased femoral anteversion

Biomechanical evaluation of total ankle arthroplasty. Part I: Joint loads during simulated level walking.

In total ankle arthroplasty, the interaction at the joint between implant and bone is driven by a complex loading environment. Unfortunately, little is known about the loads at the ankle during daily activities since earlier attempts use two- or three-dimensional models to explore simplified joint mechanics. Our goal was to develop a framework to calculate multi-axial loads at the joint during simulated level walking following total ankle arthroplasty. To accomplish this, we combined robotic simulations of level walking at one-quarter bodyweight in three cadaveric foot and ankle specimens with musculoskeletal modeling to calculate the multi-axial forces and moments at the ankle during the stance phase. The peak compressive forces calculated were between 720 and 873 N occurring around 77%-80% of stance. The peak moment, which was the internal moment for all specimens, was between 6.1 and 11.6 N m and occurred between 72% and 88% of the stance phase. The peak moment did not necessarily occur with the peak force. The ankle joint loads calculated in this study correspond well to previous attempts in the literature; however, our robotic simulator and framework provide an opportunity to resolve the resultant three-dimensional forces and moments as others have not in previous studies. The framework may be useful to calculate ankle joint loads in cadaveric specimens as the first step in evaluating bone-implant interactions in total ankle replacement using specimen specific inputs. This approach also provides a unique opportunity to evaluate changes in joint loads and kinematics following surgical interventions of the foot and ankle.

Alterations in articular cartilage T2 star relaxation time following mechanical disorders: in vivo canine supraspinatus tendon resection models

BackgroundThe role of altered joint mechanics on cartilage degeneration in in vivo models has not been studied successfully due to a lack of pre-injury information. We aimed 1) to develop an accurate in vivo canine model to measure the changes in joint loading and T2 star (T2*) relaxation time before and after unilateral supraspinatus tendon resections, and 2) to find the relationship between regional variations in articular cartilage loading patterns and T2* relaxation time distributions.MethodsRigid markers were implanted in the scapula and humerus of tested dogs. The movement of the shoulder bones were measured by a motion tracking system during normal gaits. In vivo cartilage contact strain was measured by aligning 3D shoulder models with the motion tracking data. Articular cartilage T2* relaxation times were measured by quantitative MRI scans. Articular cartilage contact strain and T2* relaxation time were compared in the shoulders before and 3 months after the supraspinatus tendon resections.ResultsExcellent accuracy and reproducibility were found in our in vivo contact strain measurements with less than 1% errors. Changes in articular cartilage contact strain exhibited similar patterns with the changes in the T2* relaxation time after resection surgeries. Regional changes in the articular cartilage T2* relaxation time exhibited positive correlations with regional contact strain variations 3 months after the supraspinatus resection surgeries.ConclusionThis is the first study to measure in vivo articular cartilage contact strains with high accuracy and reproducibility. Positive correlations between contact strain and T2* relaxation time suggest that the articular cartilage extracellular matrix may responds to mechanical changes in local areas.

Longitudinal changes in lower limb joint loading up to two years following tibial plateau fracture

BackgroundTibial plateau fractures are one of the most common intra-articular fractures resulting from high or low energy impact trauma. Few studies have assessed postoperative outcomes of these fractures with respect to changes in knee joint loading post-surgery. This gait analysis study compared lower limb joint loading up to two years post-surgery. MethodsTwenty patients (range 27–67 years; 9:11(male:female)) were treated with open reduction internal fixation and instructed to weight bear as tolerated immediately following surgery. Joint loading at the hip, knee and ankle were assessed at six time points post-operatively up to two years. Gait analyses were performed at each time point and a musculoskeletal model was used to compute external joint moments for the lower limb. ResultsHip flexion and extension (P = <0.001, P = <0.001), knee flexion (P = 0.014) and ankle plantarflexion moments (P = <0.001) showed significant increases with time. The hip flexion moment increased between six months and one year (mean difference = 0.16 Nm/kg) but did not increase thereafter (mean difference = 0.01 Nm/kg). Knee flexion and extension, and ankle plantarflexion moments increased up to six months (mean difference = 0.22 Nm/kg, 0.14 Nm/kg, 0.80 Nm/kg, respectively), but no further differences were seen with time from six months postoperative. DiscussionThe greatest changes in joint loads were observed at the hip and ankle within the first six months, likely a result of mechanical adaptations attempting to account for limited motion at the knee. Knee joint loading plateaued beyond six months suggesting functional outcomes are largely reliant on postoperative management within the initial three months while the bone is healing.

Variable responses in pain and function 1 month after platelet-rich plasma injection are related to changes in joint loading during gait

Purpose: Platelet-rich plasma (PRP) injections are receiving increasing interest as a treatment for knee osteoarthritis (OA). PRP is prepared by centrifugation of whole blood, resulting in greater concentrations of platelets and associated growth factors than whole blood. Despite encouraging preclinical results and clinical reports of improvements in pain, there remain questions regarding the efficacy of PRP for knee OA due to methodological concerns and heterogeneity between studies. The lack of objective tools for assessing interventions is a critical barrier towards evaluating therapies for knee OA.

The Development of Appendicular joint cartilages in Alligator mississippiensis: Evolutionary and Biomechanical Implications for Archosauria

Crocodylians and birds are the two surviving lineages within Archosauria, a clade of morphologically and ecologically diverse vertebrates that evolved highly disparate locomotor postures. The appendicular joints of crocodylians and birds differ substantially, thus complicating inferences of ancestral morphology and evolutionary transitions. Recent studies have indicated that the American alligator, an extant crocodylian, use a wide spectrum of cartilaginous and other connective tissues to construct the hip joint. However, little is known about the distribution and use of cartilage throughout other appendicular joints, as well the ontogenetic transition of the crocodilian chondro‐osseous interface during early development. In particular, the hyaline cartilage on the proximal femur of late embryonic alligators possesses a convex, cone‐like extension that inserts deep into the metaphysis. This morphology is not seen in juvenile and adults, but is superficially similar to the cartilage cone‐metaphyseal trough articulation inferred in early members of multiple archosaurian groups. The method by which alligators and other archosaurs reduced the cartilage cone during ontogeny and evolution, as well as the functional significance of the cartilage cone itself, are poorly understood.This study examined the ontogenetic transitions of proximal appendicular joints in the American alligator, spanning from in ovo stages to the first year of life. We used dissection, histology, and imaging techniques to assess the articular soft tissue anatomy at the chondro‐osseous junction of the proximal‐ and distal epiphyses of the femur and humerus. Additionally, osteological correlates for joint cartilage were identified on fully skeletonized limb bone elements and compared with bony morphology seen in fossil archosauromorphs.At the onset of hatching, the alligator did not reduce the cartilage cone via decreasing the “depth” of cartilaginous extension into the metaphysis, as inferred for early archosaurs. Instead, neonatal alligators regress the cartilage cone via multiple invasion fronts of trabecular bones, such that the subchondral growth plate of hatchlings presents a convex surface perforated by numerous cartilage canals, similar to those found in young birds. These results suggest that the ontogenetic loss of cartilage cone in the alligator is different from the evolutionary loss of cartilage cone hypothesized for early archosaurs. Instead, the role of cartilage thinning, fibrocartilage sleeve development and calcified epiphyseal cartilage may be highly associated within different sauropsid lineages in response to evolutionary changes in joint loading regimes.Support or Funding InformationThis research is supported by the Missouri State University Faculty Research Grant

Changes in knee joint load indices from before to 12 months after arthroscopic partial meniscectomy: a prospective cohort study

Patients undergoing arthroscopic partial meniscectomy (APM) are at increased risk of knee osteoarthritis (OA). Meniscal damage and/or surgery may alter knee joint loading to increase OA risk. We investigated changes in knee joint loading following medial APM surgery, compared with the contra-lateral leg. We estimated indices of knee joint loading (external peak knee adduction moment (KAM), KAM impulse and peak knee flexion moment (KFM)) normalized to body size (i.e., body mass (BM) and height (HT)) using 3D gait analysis in 23 patients (17 men, mean (SD) 46.2 (6.4) years, BMI 25.8 (3.4)kg/m(2)) without radiographic knee OA before and 12 months after medial APM. Static alignment was assessed by radiography and self-reported outcomes by Knee injury and Osteoarthritis Outcome Score (KOOS). Peak KAM and KAM impulse increased in the APM leg compared to the contra-lateral leg from before to 12 months after surgery (change difference: 0.38Nm/BM*HT% 95% CI 0.01 to 0.76 (P=0.049) and 0.20 Nm*s/BM*HT% 95% CI 0.10 to 0.30 (P<0.001)). Patients self-reported improvements on all KOOS subscales (KOOS pain improvement: 22.8 95% CI 14.5 to 31.0 (P<0.01)). A relative increase in indices of medial compartment loading was observed in the leg undergoing APM compared with the contra-lateral leg from before to 12 months after surgery. This increase may contribute to the elevated risk of knee OA in these patients. Randomized trials including a non-surgical control group are needed to determine if changes in joint loading following APM are caused by surgery or by changes in symptoms.

Activity and Loading Influence the Predicted Bone Remodeling Around Cemented Hip Replacements

Periprosthetic bone remodeling is frequently observed after total hip replacement. Reduced bone density increases the implant and bone fracture risk, and a gross loss of bone density challenges fixation in subsequent revision surgery. Computational approaches allow bone remodeling to be predicted in agreement with the general clinical observations of proximal resorption and distal hypertrophy. However, these models do not reproduce other clinically observed bone density trends, including faster stabilizing mid-stem density losses, and loss-recovery trends around the distal stem. These may resemble trends in postoperative joint loading and activity, during recovery and rehabilitation, but the established remodeling prediction approach is often used with identical pre- and postoperative load and activity assumptions. Therefore, this study aimed to evaluate the influence of pre- to postoperative changes in activity and loading upon the predicted progression of remodeling. A strain-adaptive finite element model of a femur implanted with a cemented Charnley stem was generated, to predict 60 months of periprosthetic remodeling. A control set of model input data assumed identical pre- and postoperative loading and activity, and was compared to the results obtained from another set of inputs with three varying activity and load profiles. These represented activity changes during rehabilitation for weak, intermediate and strong recoveries, and pre- to postoperative joint force changes due to hip center translation and the use of walking aids. Predicted temporal bone density change trends were analyzed, and absolute bone density changes and the time to homeostasis were inspected, alongside virtual X-rays. The predicted periprosthetic bone density changes obtained using modified loading inputs demonstrated closer agreement with clinical measurements than the control. The modified inputs also predicted the clinically observed temporal density change trends, but still under-estimated density loss during the first three postoperative months. This suggests that other mechanobiological factors have an influence, including the repair of surgical micro-fractures, thermal damage and vascular interruption. This study demonstrates the importance of accounting for pre- to postoperative changes in joint loading and patient activity when predicting periprosthetic bone remodeling. The study's main weakness is the use of an individual patient model; computational expense is a limitation of all previously reported iterative remodeling analysis studies. However, this model showed sufficient computational efficiency for application in probabilistic analysis, and is an easily implemented modification of a well-established technique.

Changes in joint loads, leptin, and MMP-3 subsequent to long-term intensive weight loss and exercise: secondary outcomes from the intensive diet and exercise for arthritis randomized clinical trial

Changes in joint loads, leptin, and MMP-3 subsequent to long-term intensive weight loss and exercise: secondary outcomes from the intensive diet and exercise for arthritis randomized clinical trial

Trunk muscle action compensates for reduced quadriceps force during walking after total knee arthroplasty

Patients with total knee arthroplasty (TKA) frequently exhibit changes in gait biomechanics post-surgery, including decreased ranges of joint motion and changes in joint loading; however, the actions of the lower-limb muscles in generating joint moments and accelerating the center of mass (COM) during walking are yet to be described. The aim of the present study was to evaluate differences in lower-limb joint kinematics, muscle-generated joint moments, and muscle contributions to COM accelerations in TKA patients and healthy age-matched controls when both groups walk at the same speed. Each TKA patient was fitted with a posterior-stabilized total knee replacement and underwent patellar resurfacing. Three-dimensional gait analysis and subject-specific musculoskeletal modeling were used to determine lower-limb and trunk muscle forces and muscle contributions to COM accelerations during the stance phase of gait. The TKA patients exhibited a ‘quadriceps avoidance’ gait pattern, with the vasti contributing significantly less to the extension moment developed about the knee during early stance (p=0.036). There was a significant decrease in the contribution of the vasti to the vertical acceleration (support) (p=0.022) and forward deceleration of the COM (braking) (p=0.049) during early stance; however, the TKA patients compensated for this deficiency by leaning their trunks forward. This significantly increased the contribution of the contralateral back extensor muscle (erector spinae) to support (p=0.030), and that of the contralateral back rotators (internal and external obliques) to braking (p=0.004). These findings provide insight into the biomechanical causes of post-operative gait adaptations such as ‘quadriceps avoidance’ observed in TKA patients.

Trunk And Lower Extremity Kinetics During Variations Of The Forward Lunge Exercise

The forward lunge (FL) is commonly used for rehabilitation, injury prevention, and improving athletic performance. While the FL is an effective functional exercise, it trains movement primarily in the sagittal plane and previous research has shown that the hip extensors have relatively low activation compared to the knee extensors. By altering the FL, it is possible to increase the activation of the sagittal plane hip extensors and the frontal plane hip abductors/adductors. PURPOSE: To observe the changes in the kinetics of the trunk and lower extremities due to variations of the FL. METHODS: Eleven healthy males participated in the study (age 25±3 yr, height 180±5 cm, mass 84±15 kg). Four types of lunges were completed with 2 hand-held dumbbell loads (13.6, 27.2 kg): FL, FL with trunk forward (FLTF), wide step lunge at 30° (WSL), and WSL with trunk forward (WSLTF). Each lunge was performed 3 times (24 total trials). Lunges were performed on 2 portable force platforms while 33 retroreflective markers were tracked. Joint moments were calculated at the knee, hip, and L5/S1 joints, then normalized to body mass (Nm/kg). Multivariate ANOVA was used to test for significant differences (p<0.05). RESULTS: WSL and WSLTF had higher hip adduction (0.89±0.26 vs. 0.32±0.23), knee varus (0.51±0.21 vs. 0.29±0.13) and knee valgus moments (0.48±0.10 vs. 0.28±0.18) than FL and FLTF. FL and FLTF had higher hip abduction moments (0.56±0.32 vs. 0.09±0.07) than WSL and WSLTF. FLTF and WSLTF had higher hip extension (2.85 ± 0.43 vs. 2.40 ± 0.33) and L5/S1 extension moments (1.96 ± 0.42 vs. 1.38 ± 0.38) than FL and WSL. Higher dumbbell load resulted in higher peak hip extension (2.85 ± 0.43 vs. 2.40 ± 0.33) and L5/S1 extension moments (1.83 ± 0.53 vs. 1.51 ± 0.40) than lower dumbbell load. CONCLUSION: Wide step lunges may strengthen hip adductor muscles, but increased knee varus and valgus moments may be harmful to the knee joint. Trunk forward lunges and doubling the dumbbell load increased hip and L5/S1 extension moments without increasing knee varus and valgus moments. Trunk forward lunges and increased dumbbell loads may strengthen hip extensors while sparing the knee joints, but may be harmful to the lower back. Changes in joint loading as a function of lunge technique should be considered when training and when rehabilitating knee, hip, and low back injuries.

Changes in collagen fibril network organization and proteoglycan distribution in equine articular cartilage during maturation and growth

The aim of this study was to record growth-related changes in collagen network organization and proteoglycan distribution in intermittently peak-loaded and continuously lower-level-loaded articular cartilage. Cartilage from the proximal phalangeal bone of the equine metacarpophalangeal joint at birth, at 5, 11 and 18 months, and at 6-10 years of age was collected from two sites. Site 1, at the joint margin, is unloaded at slow gaits but is subjected to high-intensity loading during athletic activity; site 2 is a continuously but less intensively loaded site in the centre of the joint. The degree of collagen parallelism was determined with quantitative polarized light microscopy and the parallelism index for collagen fibrils was computed from the cartilage surface to the osteochondral junction. Concurrent changes in the proteoglycan distribution were quantified with digital densitometry. We found that the parallelism index increased significantly with age (up to 90%). At birth, site 2 exhibited a more organized collagen network than site 1. In adult horses this situation was reversed. The superficial and intermediate zones exhibited the greatest reorganization of collagen. Site 1 had a higher proteoglycan content than site 2 at birth but here too the situation was reversed in adult horses. We conclude that large changes in joint loading during growth and maturation in the period from birth to adulthood profoundly affect the architecture of the collagen network in equine cartilage. In addition, the distribution and content of proteoglycans are modified significantly by altered joint use. Intermittent peak-loading with shear seems to induce higher collagen parallelism and a lower proteoglycan content in cartilage than more constant weight-bearing. Therefore, we hypothesize that the formation of mature articular cartilage with a highly parallel collagen network and relatively low proteoglycan content in the peak-loaded area of a joint is needed to withstand intermittent stress and shear, whereas a constantly weight-bearing joint area benefits from lower collagen parallelism and a higher proteoglycan content.

Mechanical properties of the long‐head of the biceps tendon are altered in the presence of rotator cuff tears in a rat model

Rotator cuff tears are disabling conditions that result in changes in joint loading and functional deficiencies. Clinically, damage to the long-head of the biceps tendon has been found in conjunction with rotator cuff tears, and this damage is thought to increase with increasing tear size. Despite its importance, controversy exists regarding the optimal treatment for the biceps. An animal model of this condition would allow for controlled studies to investigate the etiology of this problem and potential treatment strategies. We created rotator cuff tears in the rat model by detaching single (supraspinatus) and multiple (supraspinatus + infraspinatus or supraspinatus + subscapularis) rotator cuff tendons and measured the mechanical properties along the length of the long-head of the biceps tendon 4 and 8 weeks following injury. Cross-sectional area of the biceps was increased in the presence of a single rotator cuff tendon tear (by approximately 150%), with a greater increase in the presence of a multiple rotator cuff tendon tear (by up to 220%). Modulus values decreased as much as 43 and 56% with one and two tendon tears, respectively. Also, multiple tendon tear conditions involving the infraspinatus in addition to the supraspinatus affected the biceps tendon more than those involving the subscapularis and supraspinatus. Finally, biceps tendon mechanical properties worsened over time in multiple rotator cuff tendon tears. Therefore, the rat model correlates well with clinical findings of biceps tendon pathology in the presence of rotator cuff tears, and can be used to evaluate etiology and treatment modalities.

The Effect of Medial and Lateral Heel Wedge Orthotics on Knee Joint Loading during Gait

1647 Osteoarthritis (OA) affects an estimated 21 million Americans and is responsible for more than 7 million physician visits per year. Knee OA is a debilitating condition that frequently transforms physically active individuals into sedentary persons. Heel wedge orthotics are designed to mechanically lower the magnitude of the tibiofemoral joint loads in order to reduce pain and disability in knee OA patients. Heel wedge orthotics have been shown to effectively reduce knee pain but few studies have compared the biomechanical effects of both medial and lateral orthotics on tibiofemoral joint loading. PURPOSE: To characterize the effects of medial and lateral heel wedges on tibiofemoral joint loading and knee joint motion during gait. METHODS: Ten healthy volunteers (6 females, 4 males; mean age, 24 ± 7 yr) with no history of knee injury participated in the study. Three-dimensional kinematic data (6-camera, Vicon Motion Systems, 120 Hz) and ground reaction forces (2 Kistler force plates, 1080 Hz) were collected as subjects ambulated at a self-selected pace along a 10m walkway. Using a counterbalanced repeated measures ANOVA design, each subject was tested under 3 conditions (5 trials per condition): lateral wedge (LW), medial wedge (MW) and no wedge (CONTROL). Peak knee joint angles and peak knee moments (inverse dynamics approach) were calculated during the stance phase of gait. The knee adduction moment was used as an estimate of medial tibiofemoral joint loading, and was separated into two peaks: early stance (EARLY) and late stance (LATE). RESULTS: The knee adduction moment during EARLY (0.57 ± 0.12 Nm/kg) was significantly higher than during LATE (0.41 ± 0.13 Nm/kg) in all conditions (p<0.05). During LATE, the MW knee adduction moment was higher than both the LW and CONTROL knee adduction moments (0.44 ± 0.12 Nm/kg vs. 0.39 ± 0.11 Nm/kg and 0.40 ± 0.13 Nm/kg, respectively). No significant differences were found between sagittal plane knee moments. The sagittal, frontal, and transverse plane knee joint angles were not significantly different between conditions. CONCLUSIONS: Lateral wedge orthotics did not reduce medial tibiofemoral joint loading in our group of healthy subjects. In contrast, the short-term use of medial wedge orthotics did positively affect tibiofemoral joint loading while maintaining normal knee kinematics. This latter finding is encouraging and suggests that heel wedge orthotic use may benefit knee OA patients. Specifically, changes in joint loading from long-term orthotic use may be more apparent in subjects with knee OA. Future studies should include subjects with knee OA and evaluate the effects of orthotics longitudinally.

Validated numerical modeling of the effects of combined orthodontic and orthognathic surgical treatment on TMJ loads and muscle forces.

Investigations of the changes in the mechanics of the craniomandibular system as a result of treatment have been limited by the lack of validated models of this system. The aims of this project were to (1) validate numerical model predictions of temporomandibular joint (TMJ) eminence morphology and muscle forces produced during molar biting and (2) use the validated models to calculate the changes in TMJ and muscle forces as a consequence of treatment involving orthognathic surgery. Ten volunteers participated; their combined orthodontic and orthognathic surgical treatments were completed. Three-dimensional anatomical data from each subject were used in computer models to predict the sagittal TMJ eminence morphology and joint and muscle forces for each subject, consistent with the neuromuscular objectives of minimizing joint loads and muscle effort. The actual shape of the eminence in each subject was measured with jaw tracking. Surface electromyographic recordings were a measure of the muscle forces involved in static molar biting. Model predictions were compared with measured data from the subjects for eminence shape (R(2) = 0.96) and for muscle activity ratios (R(2) = 0.98). The strength of these relationships validated the models for use in calculating changes in joint loads and muscle forces after treatment. The results suggested that the mechanics of the masticatory system are affected by the combined treatments. The TMJ loads increased in 8 subjects. The average increases in condylar and muscle forces were 4% relative to the applied bite force, but in 1 case the increases were up to 20%. Therefore, although average increases in the forces were small, some persons may experience biologically significant increases in joint and muscle forces as a result of treatment.