Osteosclerosis

OSTEOSCLEROSIS, osteosclerosis (from Greek os-teon - bone and skleros - hard, dense), a term denoting the hardening of bone, occurring mainly due to an increase in the volume of the trabeculae of spongy substance. In the highest degree of such a condition, the bone marrow spaces completely disappear, and the entire bone is transformed into a homogeneous compact bone mass, which is designated as eburnation (from Latin ebur - ivory). In the compact layer of bone, osteosclerosis is expressed in the increase of bone substance along the walls of Haversian canals, which leads to their narrowing, and is usually combined with hyperostosis, i.e., thickening of this layer due to excessive periosteal and endosteal bone formation. Changes of this kind can occur in the most diverse lesions of the skeleton, and the degree of spread and localization of the sclerotic process, as well as the nature of the newly formed bone tissue, can be extremely different. In particular, the content of calcium salts in such proliferations is sometimes decreased, sometimes to their complete absence (as in rickets, osteomalacia, fibrous osteitis), sometimes normal (e.g., in inflammatory osteosclerosis), and even increased (as in Albers-Schönberg disease) (see Osteopathies).-Volkmann distinguishes 1) osteosclerosis restitutiva, observed e.g. at the site of former fractures, after sequestrectomies and generally in the outcome of various already completed destructive processes in bone; 2) osteosclerosis react iva, s. indurativa, developing around chronic osteomyelitic foci of various origins and even under the influence of chronic inflammatory processes in adjacent tissues (e.g., in chronic suppurative arthritis, ulcers of the leg, etc.), and 3) osteosclerosis idiopathica, for example in syphilis (without any inflammatory phenomena in the corresponding bones), in general venous stasis (osteosclerosis cyanotica - especially in the bones of the skull), in Albers-Schönberg disease, etc. Painful forms, in which (or during or in the outcome) osteosclerosis may be observed, are as follows: 1) rickets, osteomalacia, fibrous osteitis, deforming osteitis, achondroplasia (see), especially that form which is designated as chondrodystrophia hyperplastica (according to Kaufman's classification) and in which, in addition to the usually enhanced periosteal bone formation, there arise also irregular proliferations of cartilaginous mass of the epiphysis, whereby are formed although little increasing in length but very wide, irregularly shaped bone trabeculae; Albers-Schönberg disease (see Osteopathies). Occasionally osteosclerotic changes are also observed in acromegaly (see) and in the so-called osteoarthropathie hypertrophiante pneu-mique (see Marie's disease). 2) Various forms of osteomyelitis both specific (tuberculosis, syphilis, etc.) and non-specific (see Bone and Osteomyelitis). 3) Bone calluses developing after fractures (see). 4) Most cases of chronic (usually professional) poisoning by phosphorus and arsenic (proceeding with widespread osteosclerosis and hyperostosis). 5) Some primary and metastatic bone tumors, such as ossifying central sarcomas, osteosarcomas, osteochondromas, osteoplastic carcinomas (see Bone). 6) Some diseases of the blood and hematopoietic organs, namely - some forms of leukemia, aleukemia and anemia (see). As for leukemia, osteosclerosis has been described as a patho-anatomical finding in individual cases of both lymphatic and myeloid forms. In this case, the condition of the bone marrow, located in the narrowed bone marrow spaces, can be different, i.e., it can either represent changes usually characteristic of this form of disease, or have an aplastic nature, being represented by fibrous or fatty tissue with only small scattered foci of hematopoiesis here and there (the so-called leukemias with aplastic bone marrow). All other diseases of the blood and hematopoietic organs, accompanied by osteosclerosis, are usually combined into the group of so-called osteosclerotic anemias (a term introduced by Ass-mapp in 1927), since the anemic syndrome is always more or less sharply expressed in them. However, a modern analysis of the few cases belonging here shows that this group is undoubtedly a collective one, including besides essential anemias also diseases of the aleukemia type and hemorrhagic aleukemia; moreover, the number of proper anemias in it cannot even be called predominant, and also according to the general picture these anemias usually turn out to be atypical, standing closer to secondary forms than to the classic Biermer's form.-The pathogenesis of osteosclerotic changes in all the above-mentioned diseases remains very unclear to this day. By some they are interpreted as a special indurative process, often analogous to the induration of the spleen frequently encountered in the same diseases. In other cases, they speak of the replacement proliferation of bone tissue, arising¹ as a result of atrophy of the bone marrow, etc. In any case, most authors consider osteosclerosis here as a secondary phenomenon, developing on the basis of one or another disorder of the bone marrow hematopoietic apparatus.