d.1 Aplicaciones del valor de resistencia al flujo en soluciones acústicas

Also known as diaphyseal aclasia, this is strongly hereditary condition in which the bones develop exostoses of cancellous bone, capped with cartilage and arising from the region of the epiphysis. The exostosis typically points away from the end of the bone due to the direction of long bone growth (Fig. 9.3 ). Multiple swellings can be palpated and these increase in size with the child. The long bones, iliac crests and scapulae are most usually affected. The swellings may be excised as necessary. The risk of malignancy occurring in adult life is rare and is proportional to the number of lesions.

Achondroplasia

A hereditary condition in 20% of cases (autosomal dominant) and in 80% it occurs sporadically. This

mately one - third of patients however, present for the fi rst time with no family history. These patients require a full and detailed haematological investi- gation of the clotting factors to assess the precise nature of the defect and its severity.

Treatment and p rophylaxis

The mainstay of treatment is replacement of the defective factor. This usually relieves the pain and bleeding dramatically. Factor replacement is also needed in planned orthopaedic procedures which hitherto would have been prohibited by the risks of bleeding. Joint replacement in haemophiliacs is becoming more commonplace.

The factor can be supplied in several forms. 1 Fresh frozen plasma . This can be given as an outpatient procedure, but is most effective within 4 hours of the onset of bleeding.

2 Cryoprecipitate . This material is a cold precipi- tate of fi brinogen containing considerable Factor VIII activity (but not Factor IX). It can be reconsti- tuted to give a potent preparation.

3 Freeze - dried human AHG (Factor VIII) concen- trate. This can be stored for long periods. 4 Animal antihaemophilic globulin .

5 Recombinant tissue factors , artifi cially created by genetic engineering.

The use of some of these products has been com- plicated by the transmission of human immunode- fi ciency virus (HIV) infection to the patients, and since 1986 all blood products are now appropri- ately treated by heat and screened. Concerns regarding transmission of new variant Creutzfelt Jacob disease (nvCJD) has resulted in the increased usage of recombinant tissue factors; in the UK all Factor VIII given is now recombinant. Since 1998 all children in the UK have been treated with recombinant factors.

A restoration of 15 – 20% factor level is adequate for most minor to moderate bleeds. Levels of 30% or more may be needed for severe bleeds or bleeds in dangerous situations. At this level of cover, almost any surgical procedure can be carried out.

Acute self - administration of factor therapy reduces the risk of severe bleeding after injury in those with severe disease.

injuries, with a tendency to develop extreme bruising or swelling. Small wounds such as pin- pricks may not bleed abnormally, but extraction of a tooth may be followed by a dangerous haemorrhage.

Haemorrhages tend to track along fascial planes and fi ll tissue compartments, and may result in nerve compression or vascular occlusion. Bleeding within the iliacus sheath is a common example of this phenomenon, and is often accompanied by paralysis of the femoral nerve. Median and ulnar palsies are also relatively common, usually associ- ated with bleeds into the forearm muscular compartments.

The main orthopaedic problems are those relat- ing to the development of acute haemarthroses and large intramuscular collections. These occur spontaneously in severe haemophiliacs and are a frequent reason for hospital admission. The knee, elbow and ankle are the commonest joints involved. There may be a defi nite injury, but in many cases the bleeding appears to be truly spon- taneous and may occur during sleep. Haemarthroses tend to be more common in young patients, par- ticularly adolescents.

Recurrent bleeding in the same joint is common and leads to gradual destruction of the articular cartilage, with internal fi brosis and a tendency to develop contractures — haemoarthropathy.

The haemarthroses are usually extremely painful and accompanied by severe muscle spasm. The joint is distended, except in those patients where repeated bleeds have produced so much fi brosis that distension is impossible. There is usually a local increase in temperature, and tenderness over the synovium. In chronic cases the range of move- ment may be diminished, with almost total destruction of the joint.

Large soft - tissue collections of blood may fail to reabsorb (so called pseudo - tumours) and may, indeed, increase in size, forming cysts which may compress surrounding structures and even pene- trate bone.

Diagnosis

The patient is often aware of his condition and may have similarly affected relatives. Approxi-

Pathology

The aetiology of Paget ’ s disease is not known, but characteristic inclusion bodies can be found in the bone cells, suggesting a viral origin. This virus may rest dormant from childhood, only being manifest later in life. Others postulate a genetic inheritance, although affected families are rare. Further research in this area is ongoing. The main feature of Paget ’ s disease is a disordered architec- ture of the bone. The bones most often affected are shown in Figure 9.4 .

1 Deformities are common, especially in weight - bearing bones. The tibiae become characteristically bowed.

2 Long bones become thickened, especially the cortex, and the distinction between cortex and medulla becomes lost. The trabeculae are coars- ened, disordered and exaggerated.

3 The skull can become enormously thickened (Fig. 9.5 ), sometimes with areas of osteolysis (oste- oporosis circumscripta).

4 The bones are vascular and bleed freely. 5 Fractures are common in the long bones and are typically transverse.

to reduce the risk of permanent damage to the articular cartilage by the blood in the joint. Cover is needed until bleeding has obviously stopped. After this, the blood usually re - absorbs and the joint becomes comfortable to move. At this point, mobilization can be started, but it is normally nec- essary to give a further period of cover, particularly if physiotherapy or manipulation is necessary to regain movements. The chronically damaged knee is very prone to repeated bleeds and a caliper or splint may be tried in the hope of diminishing the need for hospitalization and preventing unneces- sary damage to the joint.

Nerve palsies are usually treated conservatively, although a severe bleed into a closed fascial space may need surgical decompression.

It should be remembered that, after severe bleed- ing, transfusion of blood may be necessary for replacement of blood volume, independently of factor replacement. Some patients eventually develop inhibitors in the plasma, and no longer respond to Factor VIII concentrate. At this point, risks from fatal bleeding are much intensifi ed, and many patients die eventually from renal complications.