Cyclic Damage Accumulation in the Femoral Constructs Made With Cephalomedullary Nails

Background: The purpose of this study was to evaluate the risk of peri-prosthetic fracture of constructs made with cephalomedullary (CM) long and short nails. The nails were made with titanium alloy (Ti-6Al-4V) and stainless steel (SS 316L). Methods: Biomechanical evaluation of CM nail constructs was carried out with regard to post-primary healing to determine the risk of peri-implant/peri-prosthetic fractures. Therefore, this research comprised of, non-fractured, twenty-eight pairs of cadaveric femora that were randomized and implanted with four types of fixation CM nails resulting in four groups. These constructs were cyclically tested in bi-axial mode for up to 30,000 cycles. All the samples were then loaded to failure to measure failure loads. Three frameworks were carried out through this investigation, Michaelis–Menten, phenomenological, and probabilistic Monte Carlo simulation to model and predict damage accumulation. Findings: Damage accumulation resulting from bi-axial cyclic loading in terms of construct stiffness was represented by Michaelis–Menten equation, and the statistical analysis demonstrated that one model can explain the damage accumulation during cyclic load for all four groups of constructs (P \u3e 0.05). A two-stage stiffness drop was observed. The short stainless steel had a significantly higher average damage (0.94) than the short titanium nails (0.90, P \u3c 0.05). Long titanium nail group did not differ substantially from the short stainless steel nails (P \u3e 0.05). Results showed gender had a significant effect on load to failure in both torsional and bending tests (P \u3c 0.05 and P \u3c 0.001, respectively). Interpretation: Kaplan–Meier survival analysis supports the use of short titanium CM nail. We recommend that clinical decisions should take age and gender into consideration in the selection of implants

Imaging Mechanical Muscle–Bone Relationships: How to See the Invisible

The ontogenetic adaptation of bones to their habitual loads offers a rationale for imaging muscle–bone relationships. Provided that bones adapt to strains that are chiefly determined by muscle contractions, information from muscle and bone scans allows comparing measures of bone stiffness and strength with surrogate measures for muscular force generation. Prediction of the mechanical behavior of bone is nowadays well possible by peripheral quantitative computed tomography (pQCT). However, prediction of muscle forces is not currently feasible. pQCT offers the opportunity to outline gross muscle cross-sectional area (CSA) as a surrogate measure of the force-generating capacity of muscle groups. Ultrasound and magnetic resonance (MR) imaging allow identification of single muscles. In addition, ultrasound also offers the possibility to assess muscle architecture and thus to assess physiological CSA as a more likely predictor of muscle forces than anatomical CSA. Although there is currently no single technique in use to simultaneously assess muscle volume, CSA, and architecture at the level of single muscles, this could in future be possible by MR diffusion imaging. Current attempts to quantify muscle “quality” are not directly related to the force-generating capacity and thus only of indirect help. Hence, one should hope that better imaging assessments of muscle will be possible in future. However, despite these current limitations, muscle–bone strength indicators have been defined that can already be used today in order to differentiate primary and secondary bone disorders thus underlining the validity of the “muscle–bone” approach.Fil: Rittweger, Jorn. German Aerospace Agency; AlemaniaFil: Ferretti, Jose Luis. Universidad Nacional de Rosario. Facultad de Ciencias Médicas. Centro de Estudios de Metabolismo Fosfocálcico; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin

Cyclic Damage Accumulation in the Femoral Constructs Made With Cephalomedullary Nails

Background: The purpose of this study was to evaluate the risk of peri-prosthetic fracture of constructs made with cephalomedullary (CM) long and short nails. The nails were made with titanium alloy (Ti-6Al-4V) and stainless steel (SS 316L). Methods: Biomechanical evaluation of CM nail constructs was carried out with regard to post-primary healing to determine the risk of peri-implant/peri-prosthetic fractures. Therefore, this research comprised of, non-fractured, twenty-eight pairs of cadaveric femora that were randomized and implanted with four types of fixation CM nails resulting in four groups. These constructs were cyclically tested in bi-axial mode for up to 30,000 cycles. All the samples were then loaded to failure to measure failure loads. Three frameworks were carried out through this investigation, Michaelis–Menten, phenomenological, and probabilistic Monte Carlo simulation to model and predict damage accumulation. Findings: Damage accumulation resulting from bi-axial cyclic loading in terms of construct stiffness was represented by Michaelis–Menten equation, and the statistical analysis demonstrated that one model can explain the damage accumulation during cyclic load for all four groups of constructs (P \u3e 0.05). A two-stage stiffness drop was observed. The short stainless steel had a significantly higher average damage (0.94) than the short titanium nails (0.90, P \u3c 0.05). Long titanium nail group did not differ substantially from the short stainless steel nails (P \u3e 0.05). Results showed gender had a significant effect on load to failure in both torsional and bending tests (P \u3c 0.05 and P \u3c 0.001, respectively). Interpretation: Kaplan–Meier survival analysis supports the use of short titanium CM nail. We recommend that clinical decisions should take age and gender into consideration in the selection of implants

Differential atrophy of the lower-limb musculature during prolonged bed-rest

Patients with medical, orthopaedic and surgical conditions are often assigned to bed-rest and/or immobilised in orthopaedic devices. Although such conditions lead to muscle atrophy, no studies have yet considered differential atrophy of the lower-limb musculature during inactivity to enable the development of rehabilitative exercise programmes. Bed-rest is a model used to simulate the effects of spaceflight and physical inactivity. Ten male subjects underwent 56-days of bed-rest. Magnetic resonance imaging of the lower-limbs was performed at 2-weekly intervals during bed-rest. Volume of individual muscles of the lower-limb and subsequently, rates of atrophy were calculated. Rates of atrophy differed (F = 7.4, p 0.081). Differential rates of atrophy were seen in synergistic muscles (e.g. adductor magnus > adductor longus, p = 0.009; medial gastrocnemius > lateral gastrocnemius, p = 0.002; vastii > rectus femoris, p = 0.0002). These results demonstrate that muscle imbalances can occur after extended periods of reduced postural muscle activity, potentially hampering recovery on return to full upright body position. Such deconditioned patients should be prescribed "closed-chain" simulated resistance exercises, which target the lower-limb antigravity extensor muscles which were most affected in bed-rest

Effects of Six-Week Resistance Training with or without Vibration on Metabolic Markers of Bone Metabolism

Acute and protracted effects of resistive exercise (RE) and resistive exercise with whole-body vibration (RVE) on metabolic markers of bone metabolism were investigated. Twenty-six men participated in a randomized training program including RE (n = 13; age = 23.4 +/- 1.4 years) or RVE (n = 13; age = 24.3 +/- 3.3 years). During the first session, acute C-terminal telopeptide of type I collagen (CTX) responses decreased by 12.9% (standard deviation, SD 13.7%) after 2 min, followed by a 15.5% (SD 36.0%) increase at 75 min after exercise (both p < 0.001). Procollagen type I amino terminal propeptide (P1NP) increased by 12.9% (SD 9.1%) at 2 min (p < 0.001) but no change occurred at 75 min. Sclerostin showed prolonged responses from 2 to 75 min post-exercise in the first session (p < 0.001). Acute responses at the first session were comparable between groups for CTX and P1NP, acute sclerostin responses were substantially greater in RE than in RVE (p = 0.003). No significant differences were noted in the resting baseline levels of CTX, P1NP, or sclerostin from the beginning to the end of the six-week progressive training. The present study therefore did not demonstrate any sizeable enhancement of bone turnover that could match the effects that have been repeatably made in response to countermeasure exercise during bed rest

Intracranial and Intraocular Pressure During Various Degrees of Head-Down Tilt

BACKGROUND: More than half of astronauts develop ophthalmic changes during long-duration spaceflight consistent with an abnormal intraocular and intracranial pressure (IOP, ICP) difference. The aim of our study was to assess IOP and ICP during head-down tilt (HDT) and the additive or attenuating effects of 1% CO2 and lower body negative pressure (LBNP). METHODS: In Experiment I, IOP and ICP were measured in nine healthy subjects after 3.5 h HDT in five conditions: -6 degrees, -12 degrees, and -18 degrees HDT, -12 degrees with 1% CO2, and -12 degrees with -20 mmHg LBNP. In Experiment II, IOP was measured in 16 healthy subjects after 5 min tilt at +12 degrees, 0 degrees, -6 degrees, -12 degrees, -18 degrees, and -24 degrees, with and without-40 mmHg LBNP. RESULTS: ICP was only found to increase from supine baseline during -18 degrees HDT (9.2 +/- 0.9 and 14.4 +/- 1 mmHg, respectively), whereas IOP increased from 15.7 +/- 0.3 mmHg at 0 degrees to 17.9 +/- 0.4 mmHg during -12 degrees HDT and from 15.3 +/- 0.4 mmHg at 0 degrees to 18.7 +/- 0.4 mmHg during-18 degrees HDT. The addition of -20 mmHg LBNP or 1% CO2 had no further effects on ICP or IOP. However, the use of -40 mmHg LBNP during HDT lowered IOP back to baseline values, except at 24 degrees HDT. DISCUSSION: A small, posterior intraocular-intracranial pressure difference (IOP > ICP) is maintained during HDT, and a sustained or further decreased difference may lead to structural changes in the eye in real and simulated microgravity

Serum sclerostin and DKK1 in relation to exercise against bone loss in experimental bed rest

The impact of effective exercise against bone loss during experimental bed rest appears to be associated with increases in bone formation rather than reductions of bone resorption. Sclerostin and dickkopf-1 are important inhibitors of osteoblast activity. We hypothesized that exercise in bed rest would prevent increases in sclerostin and dickkopf-1. Twenty-four male subjects performed resistive vibration exercise (RVE; n&nbsp;=&nbsp;7), resistive exercise only (RE; n&nbsp;=&nbsp;8), or no exercise (control n&nbsp;=&nbsp;9) during 60 days of bed rest (2nd Berlin BedRest Study). We measured serum levels of BAP, CTX-I, iPTH, calcium, sclerostin, and dickkopf-1 at 16 time-points during and up to 1&nbsp;year after bed rest. In inactive control, after an initial increase in both BAP and CTX-I, sclerostin increased. BAP then returned to baseline levels, and CTX-I continued to increase. In RVE and RE, BAP increased more than control in bed rest (p&nbsp;&le;&nbsp;0.029). Increases of CTX-I in RE and RVE did not differ significantly to inactive control. RE may have attenuated increases in sclerostin and dickkopf-1, but this was not statistically significant. In RVE there was no evidence for any impact on sclerostin and dickkopf-1 changes. Long-term recovery of bone was also measured and 6-24 months after bed rest, and proximal femur bone mineral content was still greater in RVE than control (p&nbsp;=&nbsp;0.01). The results, while showing that exercise against bone loss in experimental bed rest results in greater bone formation, could not provide evidence that exercise impeded the rise in serum sclerostin and dickkopf-1 levels