The pathology of osteomyelitis

Osteomyelitis is a particularly tragic preventable disease, which has almost disappeared from the industrial world, where it was once common, particularly among the poor. It is now almost entirely a disease of the disadvantaged children of the developing world, whom it often disables for life if it is treated late or inadequately. You can only treat osteomyelitis satisfactorily if you treat it early. Later treatment is difficult, expensive, and time-consuming.

There are several kinds: (1) Haematogenous osteomyelitis in which bacteria reach bone through the circulation, and which is the concern of most of this chapter. (2) Traumatic osteomyelitis, particularly following road accidents and war injuries, in which bacteria reach bone through a badly treated open fracture, as the result of: (a) an inadequate wound toilet (54.1), and (b) immediate instead of delayed wound closure (54.4). One of the main purposes of Chapter 54 is to prevent this preventable disaster, so nothing more will be said about it here. (3) Osteomyelitis following unskilled orthopaedic procedures in unsterile theatres, particularly the fixation of femur fractures with Kuntscher nails. The fracture methods described in Volume Two minimize this risk, and about the only possibility of it occurring with the methods described there is the osteomyelitis of the upper tibia that may occasionally follow the insertion of a Steinmann pin for skeletal traction (78.6). Fortunately, this is usually mild and localized.

Acute haematogenous osteomyelitis is a surgical emergency. It is also the supreme example of the axiom[md]''Where there is pus let it out'. Your challenge is to drill the site of infection and to let out the pus before it causes pressure necrosis of the bone, and to do so with the least possible delay. If you don't explore an infected bone early enough, or don't explore it at all, the patient may be severely disabled. Drilling is not difficult; but the sequestrectomy that may be necessary later if you fail to drill it will be very difficult.

Staphylococci are usually responsible. But if osteomyelitis complicates sickle-cell disease, or some other haemoglobinopathy, other organisms may cause it, particularly E. coli (common) and S. typhi (rare). If the patient is a neonate, streptococci or enterobacteria may be infecting him. The metaphysis of a long bone is the usual site. In decreasing order of frequency you are likely to see osteomyelitis in the proximal tibia, the distal femur, the proximal femur, the proximal end of the humerus, the distal radius or ulna, the distal tibia, or the calcaneus. But any bone can be involved, and sometimes several of them at the same time.

Infection thromboses the end arteries of a metaphysis, and so kills the bone that they supply. Pus accumulates under pressure, breaks out through a hole in the bone, and comes to lie under the periosteum. Pus then strips the periosteum off the shaft and deprives part of the bone of its blood supply, so that it dies and forms a sequestrum. The stripped periosteum responds by producing new bone, which is the beginning of the involucrum. Later, this may become so extensive that it forms a new shaft. If the disease progresses, large areas of bone, and perhaps even its entire shaft, become separated from their blood supply, die, and form one or more sequestra. These lie inside the involucrum, bathed in a pool of pus, which discharges through sinuses in the skin.

Occasionally, the disease does not go through this acute stage, and does not form sequestra, or sinuses. Instead, the infected bone becomes sclerotic, and its marrow cavity is obliterated (Brodie's abscess, A, Fig. 7-2).

Before the age of six months an epiphysis offers no barrier to the spread of infection, so that pus in a metaphysis rapidly spreads to a joint. After this age the cartilage of an epiphyseal plate limits the spread of infection, so that a joint is only infected if an infected metaphysis extends inside a joint capsule, as in the proximal femur. Osteomyelitis is uncommon later in life, after the epiphyses have fused.

JOHN (6 years) was admitted late on a Saturday night, in the days before antibiotics, to a London teaching hospital, with the typical symptoms of osteomyelitis. There was no registrar, so the house surgeon consulted his chief (who had gone off for the weekend) over the telephone and was told to ''Keep the boy until Monday morning'. By then it was too late. The boy was ill- nourished and from a poor home; he just went down and down, running pus from his joints, and getting thinner and thinner, until his iliac crests broke out through his skin, and one iliac epiphysis dropped off. He finally died of amyloid disease of his liver. LESSON This boy became a byword and a terrible example throughout the hospital of what can happen if osteomyelitis is ''cooked', and pus under pressure is not drained (a story told by H Leader Stirling). Fig. 7-3 INSTRUMENTS FOR CHRONIC OSTEOMYELITIS. The most important instrument for diagnosing early osteomyelitis[md]the bone drill[md]is shown in Fig. 70-12. You will need a bone drill (70.11), and you will find a pneumatic tourniquet useful. Here are the instruments you will need to remove sequestra.

OSTEOTOME, Swedish model, solid forged stainless steel, (a) 6 mm. (b) 10 mm. One only of each size. Use these for cutting the bones of children. An adult's bones are too hard to be cut by an osteotome alone. Weaken them first with a line of drill holes.

NIBBLER, bone, Read Jensen, one only.

GOUGES, Swedish model, solid forged stainless steel, (a) 6 mm, (b) 10 mm. One only of each size. These curved bone chisels must be sharp. If necessary, get them sharpened on a grindstone. Use them for deepening a cavity in a bone.

MALLET, stainless steel, 350 g, one only. This an adequate size of mallet, there is no need for a larger one.

BONE FILE or rasp, one only.

FORCEPS, bone cutting, Liston, angled on flat, 200 mm, one only. These are general-purpose bone cutters. You can also use them instead of special rib cutters.

FORCEPS, bone-holding, Hey Groves, 210 mm, one only. This is for small bones, such as the radius.

FORCEPS, bone-holding, Lane's 390 mm, one only. This is a heavier pair of forceps for larger bones such as the tibia.

FORCEPS, sequestrum, angled, 190 mm, one only. These are slender, angled forceps to remove sequestra.

CURETTE, or scoop, Volkmann, double ended, size C, four only. Use this to curette infected bone when you operate for osteomyelitis.

LEVERS, bone, Trethowan, 220 mm, four only. Put these round a bone to expose it.

LEVERS, bone heavy, 275 mm, four only

HOOK, bone, 220 mm, one only

ROUGINE, Faraboef, with curved end, chisel edge, one only. Use this to scrape the periosteum from a bone.

ELEVATOR, periosteal, large, one only.