INVESTIGADORES
COINTRY Gustavo Roberto
congresos y reuniones científicas
Título:
Non-invasive biomechanical analysis of the whole human tibia in sedentary people, trained long-distance runners, and chronic paraplegic patients. A serial (19-scan) pQCT study
Autor/es:
SARA FELDMAN; RICARDO FRANCISCO CAPOZZA; PABLO ANDRÉS MORTARINO; IVAN YELIN; PAOLA REINA; V TOLFREY; HANS SCHIESSL; JOERN RITTWEGER; JOSÉ LUIS FERRETTI; GUSTAVO ROBERTO COINTRY
Lugar:
Bad Liebenzell (Alemania)
Reunión:
Congreso; V BLACK FOREST FORUM OF MUSCULOSKELETAL INTERACTIONS; 2009
Institución organizadora:
Int Soc of Musculoskeletal & Neuronal Interactions (ISMNI)
Resumen:
NON-INVASIVE BIOMECHANICAL ANALYSIS OF THE WHOLE HUMAN TIBIA IN SEDENTARY PEOPLE, TRAINED LONG-DISTANCE RUNNERS, AND CHRONIC PARAPLEGIC PATIENTS. A SERIAL (19-SCAN) pQCT STUDY. Feldman S1, Capozza R1, Mortarino P1, Yelin I1, Reina P1, Tolfrey VL2, Schiessl H3, Rittweger J4, Ferretti JL1, Cointry G1. 1.Center for P-Ca Studies (CEMFoC), Natl Univ of Rosario, Argentina; 2. Loughborough Univ, UK; 3. Stratec GmbH, Pforzheim, Germany; 4. Inst for Biomed Res into Human Movement & Health, Manchester Metropol Univ, UK GENERAL AIMS, SAMPLES AND METHODS     We were interested to study the impact of the mechanical environment on the anatomy and structure of the tibia. Calf muscles induce variable amounts of stress at different levels of the tibia. Stress patterns vary from almost pure uniaxial compression close to the heel to a combination of compression, torsion an bending stresses, of progressively increasing complexity toward the knee. Importantly, the tibio-talar knee joint can be loaded in valgus stress-mode, where the load is transmitted via the medial condyle. pQCT technology permits the serial musculoskeletal study of the entire human leg. This resource allows a biomechanical analysis of tibial anatomy and structure from the tibio-talar joint to the knee and the corresponding interactions with the calf musculature.    Aiming to understand the biomechanical role of the tibial structure in different physiological and pathological conditions, we have performed such study in the legs of         a. young men and women with sedentary habits  (10 males and 10 females aged 20-40 yr, living in Rosario, Argentina) or        b. trained long-distance runners (9 males and 6 females aged 20-40 yr, living also in Rosario) who were voluntarily recruited, and also         c. in 9 men aged 20-50 yr with chronic male paraplegia resulting from a spinal cord injury, with  age-, height-, and gender- matched able-body control people, all of these living in the Manchester region, UK.    In all individuals, cross-sectional images were obtained with identical XCT-2000 scanners in Rosario and Manchester, at regular intervals equivalent to 5% of the right tibia’s length. We have numbered the scans from S5 (5% site, next to the tibio-talar joint) to S95 (95% site, next to the knee joint) resulting in 19 scans for the entire bone. The parameters selected for all sectional images were contmode 2, peelmode 2, and cortmode 1. Threshold values for total and cortical bone were selected at 398.5 and 700.0 mg/cm3, respectively. Suitable indicators of bone mass (cortical area, CtA; total BMC, ToC; cortical BMC, CtC; trabecular vBMD, vTbD), diaphyseal design (periosteal perimeter, PeriC; endocortical perimeter, EndoC; cortical thickness, CtTh, and A-P-bending, lateral-bending and torsional or polar moments of inertia, xMI, yMI, pMI; circularity; eccentricity), and material “quality” (PVE-adjusted cortical vBMD, vCtD), and of muscle mass (muscle area, MA) were determined in each scan as allowed.     The respective aims of the three studies were: a. to describe the basic structural patterns of bone mass, design and material “quality” variation along the whole tibia length in relation with the proposed mechanical patterns of natural stimulation; b. to assess the impact of a low-intensity, high-volume chronic mechanical stimulation of the leg on the described structural patterns, and c. to compare the effects of that stimulation with the (expectedly symmetrical) opposed effects of a chronic immobilization. RESULTS    a. Sedentary individuals. Patterns of variation along the tibia were very similar between males and females for each indicator. However, with exception of vCtD, values were higher for males than females. Importantly, these gender-related differences disappeared when both male and female data were expressed as percentages of the minimal values shown for each indicator in every individual studied. CtA and CtC increased largely from S5 to S45; remained virtually constant until S75, and fell dramatically more proximally. The CtTh varied in direct association with CtA and CtC between S5 and S45, but then it decayed substantially until S95. The PeriC decreased proximally from the heel down to a minimum between S25 and S55 and then increased consistently up to maximal values close to the knee. The MIs were minimal between S5 and S25. Then they increased markedly, pMI from S25, xMI from S35, and yMI from S45, up to the knee. Up to S45, the MIs grew in direct relationship with CtC, CtA or CtTh. However, from S50 to S80 they grew inversely with these indicators, and directly with the PeriC. Cortical bone contributed significantly to the MIs only from S25 to S45. From S55 to S70 the MIs increased while cortical mass remained constant, and from S75 to S90 the MIs increased despite of a substantial reduction of cortical mass. Linear, direct relationships were observed between MIs (y) and CtC (distribution/mass, “d/m” curves) at every site, parallel for men and women but with higher intercepts for the latter. Negative, hyperbolic relationships were shown between MIs (y) and vCtD (distribution/quality, “d/q” curves) at every site and also for all sites together. The ToC decayed about 33% from S5 to S15, where minimal ToC values and variance and maximal circularity were observed. More proximally, ToC increased with an almost constant slope until S45, reaching the original S5 value at S40. The ToC remained virtually constant from S50 to S80 and then increased abruptly up to the knee.     b. Long-distance runners. The above-referred, gender-related differences were also observed in this case for all indicators. Despite of their intense physical activity, long-distance runners did not show larger MA tan sedentary individuals. Instead, runners had larger CtC and Mis, either in absolute values (ANOVA, p<0.001) or adjusted to a same MA value (ANCOVA, p<0.001), especially close to the mid-diaphyses. However, the vCtD, always higher in females than males, was reduced in both groups of runners (p<0.01). Nevertheless, d/m and d/q curves showed always larger MIs’ values for runners for the same CtC or vCtD values, respectively (ANCOVA, p<0.001).     c. Paraplegic patients. Paraplegic individuals had lower  CtA, CtC, vTbD, Mis and vCtD and larger EndoC values than their healthy controls (-50%, -7%, -23%, -28%, -30%, +10%, respectively, always p<0.001) at all scan levels. The d/m (MIs/CtC) curves obtained for paraplegic patients, always linear and positive, were parallel to those shown by their local controls (ANCOVA, p>0.05) but showed lower values of both MIs (y) and CtC (x) and a shift to the left in the graphs, i.e. larger MIs’ values for paraplegic than controls for the same CtC level (ANCOVA, p<0.01). The d/q (MIs/vCtD) relationships, negative and hyperbolic for the controls, showed a significant shift to the lower-left region of the graphs, with lower values of both MIs and vCtD for paraplegic than control individuals (in paraplegic subjects the MIs seemed to have been little affected by the EndoC enhancement), with no evident correlation. This behavior of the paraplegic men with respect to their healthy controls was not symmetrically opposed to that shown by the long-distance runners with respect to their sedentary controls. In fact, compared with the sedentary males, male runners showed 1. Inverse changes to those of the British paraplegic men concerning CtA, CtC, vTbD and Mis (all of them increased in Arg runners and reduced in paraplegics), but not vCtD (reduced in runners as it was in paraplegics); 2. Increased PeriC (not EndoC as shown by paraplegics) values, and 3. Shifts to only the upper region of the graphs in the d/m curves (showing larger MIs’ values for the same CtC level), and toward the upper-left region in the d/q curves (showing larger MIs corresponding to lower vCtD values), again not mirroring the differences shown between the British groups. DISCUSSION    a. Sedentary individuals. Results suggest that the observed gender-related differences in all indicators but the vCtD reflect a predominantly allometric relationship. However, both d/m and d/q curves show that men seem to be more efficient distributors of the available cortical mass than women, perhaps keeping an inverse relationship with bone material “quality” (vCtD, proportional to tissue stiffness), shown to be higher in the latter. The minimal amount and variance of bone mass (ToC) and MIs and the largest circularity at S15 observed in both genders suggest that the natural stress pattern for the species at that level should be virtually in pure compression.        Increasing MIs and eccentricity toward the knee indicate the addition of progressively larger torsional, sagittal and frontal bending stresses, in this anatomical order. The necessary enhancement of bone mass to achieve these structural changes going proximally seems to have gone predominantly to increase CtTh in the lower third of the bone and dealth with the large enhancement in PeriC observed from the midshaft region upwards. In the more proximal regions, however, bone architecture (MIs) improved in consonance with bone PeriC while cortical mass and thickness actually decreased substantially. The study of bone/muscle relationships is discussed below.     b. Long-distance runners. In general terms, results suggest that bone mass and structure are achieved as a function of not only the mass of regional muscles (which was not enhanced in the studied runners), but also the intensity and volume of the mechanical use of those muscles. However, when the volume of that activity is exaggerated, as in these runners, the mechanical quality of cortical tissue (intrinsic stiffness, proportional to vCtD) can be impaired as a result of an excessive Haversian remodeling (an indication that tissue is no more able to self-repair the fatigue-induced microdamage). Nevertheless, the architectural distribution of cortical tissue, as assessed by the MIs as a function of tissue availability (d/m curves) and mechanical quality (d/q curves), seemed to have been sensitive to the volume of the mechanical use of the skeleton, perhaps as a natural resource to compensate for the reduction of bone material quality in the runners. This suggests that long-distance runners tend to show a reduced mechanical quality of their compact bone in the tibiae, but they also have a better architectural distribution of the diaphyseal tibial bone. As a result, runners’ tibiae tend to be more robust than those of their sedentary controls for a similar cortical mass or quality, or for the same calf muscle mass, perhaps as a function of the volume of mechanical use derived from muscle contractions. This mechanism would improve the tibial design in long-distance runners, but it would not necessarily enhance tibial strength, as long as runners’ leg bones are obviously more prone to suffer fatigue fractures.     c. Paraplegic patients. Results show that the chronic effects of the extreme lack and excess of  mechanical stimulation of the skeleton (of relatively low intensity but high volume in the long-distance runners) were not symmetrically opposed on every variable studied. While bone mass and epiphyseal design did impair in paraplegics and improve in athletes, bone material “quality” (as assessed by vCtD) decreased in both, as a result of an excessive intracortical remodeling. In the runners, the obvious reason for this apparently paradoxical effect is the need to repair the overuse-induced microdamage. In paraplegics, the cause is directly disuse. Within the conceptual field of the mechanostat theory, the modeling reaction to that common impairment would seem, on one side, to have overcompensated the diaphyseal structure in the runners (too high MI values), and on the other, to fail to achieve the necessary structural improvement in paraplegics (normal MI levels, or even lowered MI values because of an enhanced endocortical remodeling).         In other words: 1. The skeletal impacts of extreme mechanical use and disuse do not need to be strictly symmetrical on every mechanically relevant bone property. 2. One possible cause of such asymmetry can be the type of physical activity selected for comparison. 3. The mechanical quality of bone tissue can be deteriorated down to comparable levels (yet through different mechanisms) by changes apparently opposed in the mechanical environment. 4. The different impacts of the two described kinds of effects on bone structure could depend on two different patterns of evocation of modeling- or remodeling-based reactions of the bone mechanostat, which can be reflected (and evaluated) by the MIs and/or the vCtD.