A review of work o d o o t h deformatiohnd load sharing in non-metallic gears is presented. Ahnite element analys;&employing the flexibility method for contacting bodies is used to model tooth deflections and contact patterns 'Betweenheshing g e a r y For metallic gears the change in contact ratio between the theoretical and running values is shown to be small. However, for low modulus, non-Y t a l l i c gears the change in contact ratio is large and cangive cause for concern. The benefits and disadvantages of this increase in +.Qperating contact r a t i a s stated. Finally, the possibility of characterizing the change in operating contact ratio in a non-dimensional form is discussed.
Study design: A single case study. Objectives: To compare proximal tibia trabecular bone mineral density (BMD) of a participant with complete spinal cord injury (SCI), long-termed functional electrical stimulation-rowing (FES-R) trained, with previously reported SCI and non-SCI group norms. To estimate lower limb joint contact forces (JCFs) in the FES-R trained participant. Setting: UK University and orthopaedic hospital research centre. Methods: Bilateral proximal tibial trabecular BMD of the FES-R trained participant was measured using peripheral quantitative computerised tomography, and the data were compared with SCI and non-SCI groups. An instrumented four-channel FES-R system was used to measure the lower limb JCFs in the FES-R trained participant. Results: Structurally, proximal tibial trabecular BMD was higher in the FES-R trained participant compared with the SCI group, but was less than the non-SCI group. Furthermore, left (184.7 mg cm À3 ) and right (160.7 mg cm À3 ) BMD were well above the threshold associated with non-traumatic fracture. The knee JCFs were above the threshold known to mediate BMD in SCI, but below threshold at the hip and ankle. Conclusion: As pathological fractures predominate in the distal femur and proximal tibia in chronic SCI patients, the fact that the FES-R trained participant's knee JCFs were above those known to partially prevent bone loss, suggests that FES-R training may provide therapeutic benefit. Although the elevated bilateral proximal tibial BMD of the FES-R participant provides circumstantial evidence of osteogenesis, this single case precludes any statement on the clinical significance. Further investigations are required involving larger numbers and additional channels of FES to increase loading at the hip and ankle. Spinal Cord (2014) 52, S4-S5; doi:10.1038/sc.2014.112
INTRODUCTIONOsteoporosis is a known secondary complication of spinal cord injury (SCI) characterised by low bone mineral density (BMD), which results in a high incidence of pathological fractures in the distal femur and proximal tibia. 1 Physical therapy is one strategy under investigation to mediate bone loss in SCI by increasing muscle-induced skeletal loading. 2 In the SCI model, functional electrical stimulation (FES) is required to activate paralysed muscle. Although the dose-response in the SCI model is unknown, compressive loads of 1-2 times body weight, delivered by FES-induced muscle contractions, have been found to partially prevent bone loss after SCI. 2 The aims of this study were to: (1) compare the lower limb BMD of a participant with long-term FESrowing (FES-R) trained with SCI and non-SCI groups, using peripheral quantitative computerised tomography imaging and (2) establish the magnitude of joint contact forces (JCFs) in the lower limbs of the FES-R trained participant.
MATERIALS AND METHODSThe participant for these trials (Table 1), and author of this paper, had been FES-R trained for 48 years as described in reference 3 using quadriceps and hamstring controlled FES-activation. Th...
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