An original view on the pathogenesis of Perthes'
disease (femoral head osteochondropathy, Legg-Calvé-Perthes disease).
By the onset of Perthes disease, the hip joint is generally formed, and the femoral head and acetabulum represent bone structures. From our perspective, the initiating factor is trauma, specifically, damage to the ligamentum capitis femoris (LCF). This can be its rupture (most commonly), detachment from its attachment point, or irreversible plastic elongation. In other words, the amount of mechanical energy acting on the LCF, at a certain moment, exceeds the amount that it can absorb. Another option is possible when individual LCF fibers are damaged. Bioeffective stresses arise and increase in it, inducing biological processes that transform the LCF (for more details, see the Law of Bioinduction). As a result, it is either permanently damaged or significantly lengthened.
Due to damage or uncompensated lengthening of the LCF, the statics and dynamics of the hip joint are disrupted. In the single-support phase of gait and in the single-support posture, it no longer functions as a second-class lever, but as a first-class lever. In the upper sector of the femoral head and acetabulum, the value of the actual average daily stresses increases, which turns out to be greater than optimal stresses. Bioeffective stresses emerge. The volume of the femoral head is smaller than the volume of the pelvic bone, therefore the magnitude of the effective stresses, and therefore the average daily stresses in it is greater. Accordingly, bioeffective stresses are higher in the head of the femur and biological processes are more active.
Due to mechanical phenomena and biological processes in the upper sector
of the femoral head, an area of compression of the spongy substance is formed
with its subsequent restructuring. Partially the bone tissue atrophies, its
mass in the upper sector decreases. The presence of bioeffective stresses
induces adaptive processes in the femoral head. The granulation tissue that
appears at the site of damage through the processes of metaplasia is gradually
transformed into fibrous and then into bone tissue. With a satisfactory course
of adaptive processes in the head of the femur, not only qualitative, but also
quantitative changes are observed. The trabecular systems are rearranged, the
shape of the femoral head changes, which increases in size.
Changes in the head of the femur neutralize bioeffective stresses in it. This is achieved by eliminating zones of stress concentration, increasing the contact area of the femoral head and acetabulum, strengthening their upper sectors due to subchondral sclerosis, thickening and increasing the number of trabeculae. As these changes develop, the optimal average daily stresses for the newly formed femoral head are equalized with the actual stresses, and the bioeffective stresses are leveled. After this, the ongoing adaptive processes induced by bioeffective stresses fade away. The hip joint acquires a different structure from the norm, and the kinematics of locomotion also changes.
Keywords: ligamentum capitis femoris, ligamentum teres, ligament of head of femur, hip joint, biomechanics, osteochondropathy, Perthes' disease, pathogenesis
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The first version of the text in:
Архипов-Балтийский СВ. Рассуждение о морфомеханике. Норма. В 2 т. Т. 2. Гл. 5-6. испр. и доп. изд. Калининград, 2004. (Archipov-Baltic SV. Reasoning about Morphomechanics. The norm – Kaliningrad, 2004. [Rus]) [aleph.rsl.ru]
ETIOLOGY AND PATHOGENESIS
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