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Imaging Changes

The radiological findings are as follows: (1) localized osteoporosis; (2) subperiosteal reaction; (3) concentric bone absorption; (4) soft tissue absorption; (5) acute infection and pathological fractures; (6) changes in the lower leg; (7) changes in the joints.

1. Localized osteoporosis under the infected area, with hazy bone destruction, is sometimes due to the soft tissue reaction and hyperemia but in other cases results from early, direct bone infection.

2. A subperiosteal reaction can be due to bone infection, which is seen radiologically as destruction of the trabeculae within the medulla and the production of small sequestrae. At this stage the changes are those of osteomyelitis. Healing can occur with little deformity if treatment is initiated rapidly, and the resulting radiographic appearance of the bone may return to normal. More frequently, permanent deformity results and the condition progresses (Fig. 34.18). The patient, who is without pain, continues to live his life, inflicting further damage. Healing is unlikely, but if further infection can be prevented, bone destruction does not progress. The radiographic appearances are misleading; the bones are often very hard and dense despite the gross changes.

3. Concentric absorption of the outer layers of the bone is often associated with new bone laid down within the medulla. There are two theories to explain this process. It may be that this is the normal process of bone replacement and osteoblastic activity within the medulla, consequent on a good blood supply maintained by movement of the patient. However, angiography suggests that the blood supply to the foot is in fact reduced and slowed, and has demonstrated local vascular granulomas in close proximity to the bones. It does seem more likely that this granulomatous reaction causes absorption by extrinsic pressure. Owing to the functional ischemia of the foot and the osteoblastic reaction, the medullary space narrows as endosteal new bone is laid down. Eventually the extrinsic absorption causes a fracture at the apex of the metatarsal shaft (the process is not dissimilar to the constricting band of ainhum). This narrowing is not always an "hour glass" shape. In other patients there is cupping of the proximal interphalangeal joint surfaces and the metatarsal heads become absorbed, with consequent subluxation increasing the deformity.

4. The absorption of soft tissues is very considerable in leprosy. As the ends of the bones are also absorbed there may be a large gap between the remaining bones, which are pulled together, adding to the distortion. Imbalance results because not all the muscles are paralyzed and the deformity is increased even further. This is likely to produce ulceration in a different site; the continued variations in the pressure areas inevitably lead to progressive ulceration. In the feet, as the metatarsals diminish in length by this process of concentric bone absorption, the entire foot shortens (Figs. 34.21-34.24). There is nearly always associated recurrent ulceration of the sole of the foot near the metatarsal heads. The toes remain attached as useless appendages and may actually fall or be rubbed off. One of the major problems in the tropics, where leprosy patients sleep on mats with their feet uncovered, is that rats nibble away the insensitive toes or fingers while the patient sleeps.

5. Acute infection also occurs in the hands and there may be severe osteolytic destruction (Fig. 34.23; see also Fig. 34.20). Because the hand is used abnormally to compensate for paralysis or difficulty in walking, it suffers the same stress as the feet. The whole process of infection, absorption, shortening, and soft tissue contraction continues, made worse by pathological fractures.

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Fig. 34.21 A-J. The pattern of tapering and tuft resorption in leprosy. This usually indicates anesthesia, often without motor paralysis. When there is concentric bone resorption, there is often soft tissue ulceration under the metatarsal head; some phalanges eventually disappear; others are left with a characteristic spindle shape. This pattern is much the same in children and adults, but it may be altered by secondary infection. These patients came from Africa, India, the Caribbean, and the Pacific regions. A AFIP 69-42152; H AFIP 68-36423; I AFIP 69-33103.

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Fig. 34.22 A-E. The end result of leprosy. The change in gait has altered the site of trophic ulceration. The heel ulcers cause large areas of bone absorption, and eventually secondary infection. D-EAs the talus disintegrates, with weight-bearing, there is complete disruption of the foot. The combined effect of leprosy and secondary infection leaves little normal anatomy or function.

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