Mechanisms to attenuate load in the intact limb of transtibial amputees when 4 performing a unilateral drop landing 5 6

19 Individuals with unilateral transtibial amputations experience greater work demand and loading 20 on the intact limb compared to the prosthetic limb, placing this limb at a greater risk of knee 21 joint degenerative conditions. It is possible that increased loading on the intact side may occur 22 due to strength deficits and joint absorption mechanics. This study investigated the intact limb 23 mechanics utilised to attenuate load, independent of prosthetic limb contributions and 24 requirements for forward progression, which could provide an indication of deficiencies in the 25 intact limb. Amputee and healthy control participants completed three unilateral drop landings 26 from a 30 cm drop height. Joint angles at touchdown, range of motion, coupling angles, peak 27 powers, and negative work of the ankle, knee and hip were extracted together with isometric 28 quadriceps strength measures. No significant differences were found in the load or movement 29 mechanics (p ≥ .312, g ≤ 0.42), despite deficits in isometric maximum (20%) and explosive 30 (25%) strength (p ≤ .134, g ≥ 0.61) in the intact limb. These results demonstrate that, when the 31 influence from the prosthetic limb and task demand are absent, and despite deficits in strength, 32 the intact limb adopts joint mechanics similar to able-bodied controls to attenuate limb loading. 33


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Previous research on individuals with a transtibial amputation (ITTAs) has suggested 39 that the mechanics of the prosthetic limb may influence the intact limb mechanics, and 40 subsequently the magnitude and rate of load experienced in walking 1,2 , running 3,4 , and start-41 stop tasks. 5 This is postulated to result from the inability of the prosthesis to generate the 42 propulsion required to continue forward progression 1 or, in bilateral jump landings, from 43 inadequate absorption of high forces through the prosthesis. 6 These interactions between the 44 prosthetic and intact limb mechanics may explain the altered shock absorption approach 45 observed in the intact limb (i.e., reduced joint angles and powers) during the initial loading 46 response phase of running, step/stair negotiation, and bilateral jump landing. 4,6-8 Thus, the 47 intact limb must perform greater work to either continue forward progression or arrest the 48 lowering of the centre of mass 9 , which results in high load compared to the prosthetic limb. 10 49 However, no research has assessed the shock absorption approach of the intact limb to attenuate 50 load without the influence of the prosthetic limb and the requirement to continue forward 51 progression. This could provide an indication of deficiencies in the intact limb following 52 amputation, which may be useful for informing rehabilitation protocols. 53 A unilateral drop landing onto the intact limb can be used to examine joint mechanics 54 and load attenuation in response to a consistent vertical momentum. Reducing vertical 55 momentum is required in many movements such as walking, running, and jump landings, and 56 occurs through joint flexion and eccentric work to efficiently absorb rapid impact forces. 57 Deficiencies in muscle strength of the knee extensors may also play a role in load attenuation. 58 Decreased maximum muscle strength has been identified as a key risk factor accompanying 59 degenerative loading diseases 11 and has been suggested as an indication of increased limb 60 loading. 12,13 Furthermore, frontal plane knee valgus motion can be increased 3-fold from 61 decreased quadriceps muscle force, 14,15 which has been identified as a risk factor associated 62 with joint degeneration. 16 Increasing trunk flexion when landing has been found as a 63 compensatory strategy to reduce the reliance on the eccentric contraction of the quadriceps. 64 Greater trunk flexion is related to greater flexion at all lower-limb joints when landing from a 65 jump which could aid in reducing knee joint loading. 17,18 Substantial deficits in quadriceps 66 muscle strength of 30-39% have previously been reported in the intact limb of ITTAs compared 67 to able-bodied individuals; 13,19 however, it is currently unknown how the intact limb may 68 accommodate for decreased quadriceps strength. 69 When landing from a jump, the time to develop muscular force to control joint motion 70 is limited. Generation of rapid muscle force has been shown to be important for re-stabilisation 71 of the lower-limb joints following mechanical perturbations. [20][21][22] The inability to stabilise and 72 prevent the rapid flexion of the knee joint during jump landings can lead to various acute and 73 repetitive knee overloading injuries, e.g. osteoarthritis and non-specific knee pain. 23 Rapid 74 muscle force production has not been examined in ITTAs yet could provide important 75 information on the ability to initially stabilise the joints upon landing.

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A study assessing bilateral jump landings 6 found that the intact limb of ITTAs 77 underwent a smaller range of motion (ROM) at all lower-limb joints compared to the control 78 population and experienced significantly greater peak vertical ground reaction force (vGRF).

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This suggests that ITTAs utilise a more extended landing strategy in the intact limb. However, 80 the ITTA study assessed a bilateral landing, thus, the restricted mechanics from the prosthesis 81 could have influenced the results. Reduced lower-limb joint flexion is possibly a compensation 82 to limit the eccentric work required from the knee joint musculature 24 , yet this may lead to the 83 impact forces being absorbed by the surrounding tissue structures. 25 Individuals who perform 84 a more extended landing strategy also utilise a different joint absorption approach as measured 85 by joint power and work. 26,27 While the knee joint is a consistent contributor to dissipating the 86 kinetic energy, the percentage contribution of the ankle and hip joint work can be altered as the 87 degree of knee flexion during landing changes. [26][27][28] These studies suggest that specific 88 coordination strategies of the lower-limb joints may be related to the load experienced. It is 89 possible that without the influence from the prosthetic limb, the intact limb may be able to 90 adopt a more flexed landing strategy thereby reducing the limb and joint load experienced.

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In ITTAs, the intact limb is at a greater risk of experiencing knee pain, subsequent joint 92 degeneration, and the development of comorbidities when compared to the prosthetic limb and 93 the general population. 29-31 The pathogenesis of joint degeneration is thought to stem from 94 repetitive overloading in a limb 32 , however, only one study has been conducted on landings in 95 the ITTA population 6 where only the peak vGRF was assessed. Research assessing overloading 96 injuries has examined various discrete features within the GRF 33 , knee joint moment 34,35 , and 97 knee intersegmental force 36,37 waveforms. There is no clear consensus on the most appropriate 98 reduction of these loading waveforms to assess overloading associated with joint degeneration.

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Statistical parametric mapping is an approach which analyses a waveform in its original 100 temporal-spatial format 38 to remove the bias from an a priori approach when assessing limb or 101 joint loading.

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The purpose of this study was, therefore, to investigate limb loading in the intact limb 103 of ITTAs compared to able-bodied controls during a unilateral drop landing, independent of 104 prosthetic limb interactions and the requirement of forward progression; and assess the 105 mechanisms underpinning any differences, including quadriceps maximal and rapid muscle 106 force production and joint absorption mechanics. It is hypothesised that, compared to the 107 control limb, the intact limb will 1) present with reduced quadriceps muscular strength and 108 rapid muscle force production, 2) experience a greater magnitude of load throughout the 109 absorption phase as assessed by examining the loading pattern using statistical parametric 110 mapping, and 3) perform altered discrete joint mechanics in the sagittal plane for the ankle, 111 knee, and hip joints and altered trunk flexion and knee joint valgus motion.

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Eight recreationally active ITTAs and twenty-one controls volunteered to participate in 114 the study (Table 1). Ethical approval was obtained from the University of Roehampton's Ethic 115 Committee (LSC 16/176) and the National Health Services Health Research Authority 116 (17/NW/0566). All participants provided written informed consent prior to any assessment.

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Inclusion criteria required all participants to be physically active (i.e. requiring moderate or 118 greater physical effort) a minimum of 2-3 days per week. Participants were excluded if they 119 had sustained a musculoskeletal injury in the six months prior or were experiencing pain in 120 their back or lower-extremities. ITTAs included in the study had a grading of K3/K4, as 121 determined by their physicians, to ensure that the participants could perform high impact 122 movements safely. A K3/K4 level is defined as an amputee that has the ability or potential to 123 negotiate environmental barriers and for prosthetic ambulation that exhibits high impact, stress, 124 or energy levels. ITTA participants had amputations due to traumatic incidents (e.g., 125 automobile accident) and were a minimum of 6-months post-amputation (mean ± SD: 12.2 ± 126 11.5, range: 1.5-29 years) (Table 1).   For the strength measures, there was a medium-to-large effect (g = 0.61) for MVT to 222 be lower in the intact limb although this difference was not statistically significant (Table 2).

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There was also a medium-to-large effect (g = 0.72) for peak RTD to be lower in the intact limb  However, these earlier studies included individuals whose amputation occurred due to vascular 257 diseases, thus, the greater deficiencies in muscular strength may be due to the effects of the   Figure 4B). Greater utilisation of the ankle joint to attenuate load has been found to be 308 associated with increases in peak vGRF, knee flexor moment, and anterior knee intersegmental 309 force magnitudes. 26,27,61 Healthy individuals who performed a more extended landing strategy 310 at all joints utilised the ankle joint to perform ~50% of the total joint work. 26,27 Rowley & 311 Richards 62 determined that an optimal ankle plantarflexion angle at touchdown between 20-312 30° would limit the peak vGRF and vGRF loading rate when landing from a jump.

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Additionally, within this optimal plantarflexion range, the lower-limb joints' contribution 314 relative to the support moment were found to be relatively equal (ankle, knee and hip joints