Investigating the Effects of Knee Flexion during the Eccentric Heel-Drop Exercise

This study aimed to characterise the biomechanics of the widely practiced eccentric heel-drop exercises used in the management of Achilles tendinosis. Specifically, the aim was to quantify changes in lower limb kinematics, muscle lengths and Achilles tendon force, when performing the exercise with a flexed knee instead of an extended knee. A musculoskeletal modelling approach was used to quantify any differences between these versions of the eccentric heel drop exercises used to treat Achilles tendinosis. 19 healthy volunteers provided a group from which optical motion, forceplate and plantar pressure data were recorded while performing both the extended and flexed knee eccentric heel-drop exercises over a wooden step when barefoot or wearing running shoes. This data was used as inputs into a scaled musculoskeletal model of the lower limb. Range of ankle motion was unaffected by knee flexion. However, knee flexion was found to significantly affect lower limb kinematics, inter-segmental loads and triceps muscle lengths. Peak Achilles load was not influenced despite significantly reduced peak ankle plantarflexion moments (p < 0.001). The combination of reduced triceps lengths and greater ankle dorsiflexion, coupled with reduced ankle plantarflexion moments were used to provide a basis for previously unexplained observations regarding the effect of knee flexion on the relative loading of the triceps muscles during the eccentric heel drop exercises. This finding questions the role of the flexed knee heel drop exercise when specifically treating Achilles tendinosis

Development of a foot and ankle musculoskeletal model: implications for achilles tendinopathy

This thesis investigates the mechanics behind Achilles tendinopathies and their respective treatments using a musculoskeletal modelling approach. Specifically, the eccentric heel-drop exercise used to treat Achilles tendinosis and orthotic heel wedges used to treat Achilles tendonitis were investigated, as the mechanics which drive tendon healing are not currently understood, but are believed to work by directly altering the mechanical loading of the Achilles tendon. An inverse dynamics model of the lower limb including the hip, knee ankle and MTP joints was developed to include a musculoskeletal foot and ankle model. An existing muscle geometry dataset was used, but a new algorithm to account for soft tissue and bony constraints at the ankle to ensure physiological musculo-tendon paths around the foot and ankle was developed. Optical motion, forceplate and instrumented pressure insole data was used to derive independent 3D ground reaction vectors necessary for the data inputs for each of the two foot segments modelled. In addition to the moments of the hip and knee, foot and ankle muscle forces and ankle joint reaction forces were also estimated. A cohort of 19 healthy individuals performed the eccentric heel-drop exercise used to treat Achilles tendinosis and walked on a level and up and down an inclined (10°) surface barefoot and in running shoes with and without prefabricated orthotic heel wedges used to treat Achilles tendonitis. Clinical questions regarding changes in lower limb mechanics due to variants of the eccentric heel-drop exercise and orthotic heel wedges were considered as well as model sensitivity to foot models and sources of centre of pressure (CoP) data. CoP data source and number of foot segments modelled did not consistently change the model outputs, with greater or worse similarity between sources depending on the specific phase of stance considered. An example of this are the reduced knee and hip extension moments and increased ankle dorsiflexion moments at heel-strike, but consistent peak ankle joint reaction and Achilles tendon forces due to different CoP inputs. Across all walking conditions, heel wedges were found to have minimal impact on Achilles tendon force, but had a significant impact on knee moments and secondary plantarflexors such as Tibialis Posterior and the toe flexor muscles. The ability of heel wedges to reduce Achilles tendon load during walking was not supported by this thesis. Key observations regarding the eccentric heel-drop exercise were the reductions in peak Achilles tendon force achieved when performing the exercise in running shoes compared to barefoot and with a flexed compared to extended knee. Given the increased difficulty in performing the flexed knee exercise, this questioned the efficacy of the flexed knee version of the task and possible changes to the rehabilitation protocol, incorporating the effect of shoes on peak Achilles tendon force were suggested.Open Acces

Viscoelastic adaptation of tendon graft material to compression: biomechanical quantification of graft preconditioning

Purpose: The tensile viscoelastic behaviour of tendon tissue is of central biomechanical importance and well examined. However, the viscoelastic tendon adaptation to external compression, such as when a tendon graft is fixated with an interference screw, has not been investigated before. Here, we quantify this adaptive behaviour in order to develop a new method to mechanically precondition tendon grafts and to better understand volumetric changes of tendinous tissue. The hypothesis of this study was that under compressive loads, tendon grafts will undergo a temporary volumetric (and therefore diametric) reduction, due to the extrusion of water from the tendon. Methods: Compressive testing was performed on a material testing machine and load applied through the use of a custom-made mould, with a semi-circular cross section to accommodate the tendon graft. The effects of different compressive forces on the length, diameter and weight of tendon grafts were measured by calipers and a weighing scale, respectively. Further, different strain rates (1 vs. 10mm/min) (n=6, per rate), compression method (steady compression vs. creep) (n=15 for each method) and different compression durations (1, 5, 10min) (n=5 for each duration) were tested to identify the most effective combination to reduce graft size by preserving its macroscopic structure. Results: The effect of compression on volume reduction (75% of initial volume and weight) reached a plateau at 6,000N on an 8-mm tendon bundle. Length thereby increased by approximately 10%. Both steady compression and creeping were able to reduce dimensions of the graft; however, creeping was more effective. There was no difference in effect with different durations for compression (p>0.05) in both methods. Conclusion: The viscoelastic behaviour of hamstring tendon grafts under pressure allows preconditioning of the grafts for reduction of volume and diameter and therefore to drill a smaller bone tunnel, retaining more of the original bone. At the same time, the collagen content of the transplant is preserved and a tight fit of the transplant in the bone tunnel achieve

Energy flow analysis of amputee walking shows a proximally-directed transfer of energy in intact limbs, compared to a distally-directed transfer in prosthetic limbs at push-off

Reduced capacity and increased metabolic cost of walking occurs in amputees, despite advances in prosthetic componentry. Joint powers can quantify deficiencies in prosthetic gait, but do not reveal how energy is exchanged between limb segments. This study aimed to quantify these energy exchanges during amputee walking. Optical motion and forceplate data collected during walking at a self-selected speed for cohorts of 10 controls, 10 unilateral trans-tibial, 10 unilateral trans-femoral and 10 bilateral trans-femoral amputees were used to determine the energy exchanges between lower limb segments. At push-off, consistent thigh and shank segment powers were observed between amputee groups (1.12W/kg vs. 1.05W/kg for intact limbs and 0.97W/kg vs. 0.99W/kg for prosthetic limbs), and reduced prosthetic ankle power, particularly in trans-femoral amputees (3.12W/kg vs. 0.87W/kg). Proximally-directed energy exchange was observed in the intact limbs of amputees and controls, while prosthetic limbs displayed distally-directed energy exchanges at the knee and hip. This study used energy flow analysis to show a reversal in the direction in which energy is exchanged between prosthetic limb segments at push-off. This reversal was required to provide sufficient energy to propel the limb segments and is likely a direct result of the lack of push-off power at the prosthetic ankle, particularly in trans-femoral amputees, and leads to their increased metabolic cost of walking

Embossing of a screw thread and TCP granules enhances the fixation strength of compressed ACL grafts with interference screws

Purpose: Fixation of soft tissue grafts with interference screws relies on the friction of the graft between the screw and the bone tunnel. The goal of this study was to precondition such grafts by mechanical compression in order to reduce anticipated and undesired viscoelastic adaptation of the graft to screw pressure. Further, the otherwise slippery graft surface was modified with impressed tricalcium phosphate granules (TCP) to improve friction and mechanical hold. Methods: Fresh flexor digitorum tendons from young bovines were used to create bundles with a diameter of 8-9mm and were divided into 10 groups to compare the pullout strength and bone damage in a variety of construct scenarios. Specifically, the effects of graft precompression to reduce preimplantation graft diameter were investigated. Further the effects of impressing TCP granules and/or a screw thread into the tendon surface during the compression process were studied. Results: In sawbone tests, radial graft compression allowed for a smaller bone tunnel (7mm), but resulted in a significantly lower pullout strength of 174N (95% CI: 97, 250), compared with controls [315N (204, 426)]. In contrast, TCP coated [402N (243, 561)], screw embossed grafts [458N (302, 614)], and the combination of TCP and embossing [409N (274, 543)] achieved higher pullout strengths when compared to the standard technique. In porcine bone, untreated grafts using an 8mm screw pulled out at 694±93N, significantly higher loads were required to pullout compressed grafts with or without TCP coating (870±74 and 878±131N), yet fixed with a 7mm screw. Conclusion: Modification of the tendon graft surface has a large influence on the biomechanical performance of interference screw fixation and results in less bone damage inflicted during insertion to a smaller tunnel diameter, while simultaneously achieving superior pullout strengt

Embossing of a screw thread and TCP granules enhances the fixation strength of compressed ACL grafts with interference screws

PURPOSE: Fixation of soft tissue grafts with interference screws relies on the friction of the graft between the screw and the bone tunnel. The goal of this study was to precondition such grafts by mechanical compression in order to reduce anticipated and undesired viscoelastic adaptation of the graft to screw pressure. Further, the otherwise slippery graft surface was modified with impressed tricalcium phosphate granules (TCP) to improve friction and mechanical hold. METHODS: Fresh flexor digitorum tendons from young bovines were used to create bundles with a diameter of 8-9 mm and were divided into 10 groups to compare the pullout strength and bone damage in a variety of construct scenarios. Specifically, the effects of graft precompression to reduce preimplantation graft diameter were investigated. Further the effects of impressing TCP granules and/or a screw thread into the tendon surface during the compression process were studied. RESULTS: In sawbone tests, radial graft compression allowed for a smaller bone tunnel (7 mm), but resulted in a significantly lower pullout strength of 174 N (95% CI: 97, 250), compared with controls [315 N (204, 426)]. In contrast, TCP coated [402 N (243, 561)], screw embossed grafts [458 N (302, 614)], and the combination of TCP and embossing [409 N (274, 543)] achieved higher pullout strengths when compared to the standard technique. In porcine bone, untreated grafts using an 8 mm screw pulled out at 694 ± 93 N, significantly higher loads were required to pullout compressed grafts with or without TCP coating (870 ± 74 and 878 ± 131 N), yet fixed with a 7 mm screw. CONCLUSION: Modification of the tendon graft surface has a large influence on the biomechanical performance of interference screw fixation and results in less bone damage inflicted during insertion to a smaller tunnel diameter, while simultaneously achieving superior pullout strength

Medial-lateral centre of mass displacement and base of support are equally good predictors of metabolic cost in amputee walking

Amputees are known to walk with greater metabolic cost than able-bodied individuals and establishing predictors of metabolic cost from kinematic measures, such as centre of mass (CoM) motion, during walking are important from a rehabilitative perspective, as they can provide quantifiable measures to target during gait rehabilitation in amputees. While it is known that vertical CoM motion poorly predicts metabolic cost, CoM motion in the medial-lateral (ML) and anterior-posterior directions have not been investigated in the context of gait efficiency in the amputee population. Therefore, the aims of this study were to investigate the relationship between CoM motion in all three directions of motion, base of support and walking speed, and the metabolic cost of walking in both able-bodied individuals and different levels of lower limb amputee. 37 individuals were recruited to form groups of controls, unilateral above- and below-knee, and bilateral above-knee amputees respectively. Full-body optical motion and oxygen consumption data were collected during walking at a self-selected speed. CoM position was taken as the mass-weighted average of all body segments and compared to each individual’s net non-dimensional metabolic cost. Base of support and ML CoM displacement were the strongest correlates to metabolic cost and the positive correlations suggest increased ML CoM displacement or Base of support will reduce walking efficiency. Rehabilitation protocols which indirectly reduce these indicators, rather than vertical CoM displacement will likely show improvements in amputee walking efficiency

A spatio-temporal and kinematic description of self-selected walking in adults with Achondroplasia

© 2020 Background: Achondroplasia is characterised by a shorter appendicular limb to torso ratio, compared to age matched individuals of average stature (controls). Despite the well documented shorter leg length of individuals with compared to controls, there are few complete descriptions of gait kinematics reported for the population. Aim: The aim of this study was to report the spatio-temporal and kinematic characteristics of self-selected walking (SSW) in a group with Achondroplasia (N = 10) and age matched group without Achondroplasia (controls, N = 17). Method: Whole body 3D analysis of both groups was conducted using a 14 camera VICON system. Spatio-temporal and kinematic variables were determined through a Plug-in-Gait model. SSW was obtained from an average of three trials equating to a total of ∼120 m walking. Results: The group with Achondroplasia were 23 % slower (P < 0.001), had a 29 % shorter stride length (P < 0.001) and a 13 % higher stride frequency (P < 0.001) compared to controls. There were no differences in time normalised temporal measures of left toe off (P = 0.365), right heel contact (P = 0.442) or the duration of double support (P = 0.588) between groups. A number of discrete joint kinematic differences existed between groups, resulting in the group with Achondroplasia having more ‘flexed’ lower limbs than controls throughout the gait cycle. Conclusion: Differences in absolute spatio-temporal variables between groups is likely due to the shorter leg length of the group with Achondroplasia, while their more flexed position of the lower limbs may facilitate toe-clearance during the swing phase