Overview
The lecture teaches Osteomyelitis through one clinical case: a 38 year old woman with thigh and left knee pain, knee swelling and night sweats. It follows her from presenting complaints and blood tests, through a first working diagnosis of septic arthritis that proved wrong, to reassessment with a repeat x-ray and a nuclear medicine bone scan, surgical drainage of pus from bone, and then the complications and psychosocial fallout of the illness. Running through the case are the lecturer’s learning points about listening to the patient, avoiding tunnel vision and preconceived ideas, and excluding the most serious possibility.
Clinical approach: the lecture’s learning points
Opening learning points:
- Listen to your patient.
- Avoid preconceived ideas.
- Avoid tunnel vision.
- Look for red flag symptoms. [slide does not elaborate: it does not say which symptoms count as red flags]
Learning points given mid-case, after things went wrong:
- Bad luck happens.
- Try to anticipate potential problems.
- Try not to contribute to bad luck.
Closing learning points:
- Listen to your patient.
- Avoid tunnel vision and preconceptions.
- Exclude the most serious possibility.
- Rare conditions happen.
- Bad luck happens but don’t contribute.
- Be supportive and compassionate.
The case: presentation, signs and investigations
Presenting complaints:
- Pain, which was constant and made sleep difficult, felt in the thigh and left knee, and not well localised.
- Swelling of the left knee.
- Night sweats.
Signs:
- Fever 37.9°
- Swollen knee and thigh
- Pain on movement of the knee
- Enlarged lymph nodes in the groin
Blood results, with normal ranges in brackets:
- Total leucocytes 19.4 (4.0 to 11.0)
- Neutrophils 17.6 (2.0 to 7.5)
- Monocytes 1.12 (0.2 to 1.0)
- The granulocytes showed a shift to immaturity.
- ESR 58 (2 to 12). ESR is a non specific indication of inflammation.
Important
Fever, pain and a raised white cell count together: assume bacterial infection. You must determine the site and treat urgently.
First working diagnosis and initial treatment
- Knee x-rays were normal.
- Presumed diagnosis: septic arthritis of the knee.
- Treatment: knee joint washout. No micro organisms were found.
- Best guess antibiotic: flucloxacillin, chosen because Staphylococcus aureus is the usual cause.
Microbiology and how infection spreads in bone
Key points:
- Staphylococcus aureus is the most common cause of musculoskeletal infection.
- Acute infections may follow haematogenous spread of organisms from an unrecognised source.
- Infection establishes itself in damaged or abnormal tissues.
Route of spread within a long bone, from the textbook figure reproduced in the lecture (Figure 60-4B):
- Infection sits in the medullary canal.
- It permeates outwards through the cortex.
- It collects beneath the periosteal membrane, as a subperiosteal collection.
A gross pathology photograph of a sectioned long bone is shown alongside this, with dark mottled, haemorrhagic-appearing areas in the medullary cavity and cortex. The slide carries no caption, so what the specimen is meant to demonstrate is not confirmed.
Monitoring progress and reassessing the diagnosis
- Progress is monitored by following temperature, pulse and symptoms. The observation chart shown (Dunedin Hospital) plots temperature, blood pressure and pulse rate over successive post-operative days.
- When the patient did not fit the working diagnosis, the instruction is to think again and repeat the x-ray. Two knee x-ray views of the distal femur and proximal tibia were repeated.
- Nuclear medicine bone scan: four views labelled R anterior L, L posterior R, L lateral and R lateral, showing asymmetric tracer uptake between the two limbs, used to localise the site of infection.
- A later chart of the same kind is captioned “Patient getting better now”, showing improvement in the observations during treatment.
Treatment of the bone infection
- Treatment step given: drain pus from bone, illustrated with two x-rays of the long bone.
- An intraoperative photograph shows a surgical wound held open with retractors, with forceps holding a pale piece of tissue in the exposed muscle field. The slide has no caption and the nature of the tissue is not stated.
- A further photograph shows the limb with an external fixator frame applied: multiple pins pass through the skin into the bone and connect to external rods and clamps, with a wound dressing pad over the surgical site.
Warning
Slides 13, 16, 18, 20, 22, 23 and 24 carry no title or caption, so the transcript describes them from visual appearance only and those readings are not confirmed by the lecture. They include an uncaptioned knee and distal femur x-ray whose place in the narrative is unclear; an x-ray with what appear to be surgical pins crossing the shaft; an x-ray in which no hardware is clearly visible; an x-ray with a faint linear lucent line along part of the shaft that could not be confidently characterised; and a pair of x-rays showing a plate with screws in one image and a rod or pin construct near the joint in the other, likely but not certainly follow-up imaging after fixation. No sequence of operations should be treated as taught content on the basis of these images.
Complications of osteomyelitis
- Failure to eradicate infection
- Sequestration, described as mechanical: in dead bone, with the protective cell wall of the micro organism. [slide does not elaborate beyond these points]
- Antibiotic resistance, for example MRSA.
- Unrecognised organisms, for example TB and anaerobes.
- Pathological fracture. Shown as an x-ray of a long bone with a fracture through the shaft. [slide gives the heading and the image only, with no definition or mechanism]
- Soft tissue scarring, causing joint stiffness and loss of muscle excursion and power.
- Psychosocial considerations: length of time in hospital, disruption to family life, loss of income, loss of job, and “why me?”
Summary of osteomyelitis
- Usually Staph aureus.
- May occur in a healthy person.
- Haematogenous spread often.
- Direct spread from an open wound.
- Relatively common in children.
- Bone pain plus fever equals osteomyelitis.
Self-test
- List the presenting complaints in this case, including the character and site of the pain.
- List the signs found on examination, including the recorded temperature.
- Give the blood results with their normal ranges, and state what the ESR result indicates.
- A patient has fever, pain and a raised white cell count. State what the lecture says you should assume, and what you must then do.
- Describe the first working diagnosis in this case, what the initial knee x-rays showed, and what the joint washout yielded.
- Name the best guess antibiotic used and explain the reasoning behind that choice.
- State the three learning points the lecture gives about the organisms causing musculoskeletal infection and how infection establishes itself.
- Describe, in order, how infection spreads within a long bone according to the textbook figure reproduced in the lecture.
- List the parameters the lecture says to follow to monitor progress, and state what the observation chart shown actually plots.
- The patient did not improve after the knee washout. Describe the two imaging steps taken next, and state what the bone scan was for.
- List the four categories of complication of osteomyelitis given in the lecture.
- Under failure to eradicate infection, list the three mechanisms given, including what the lecture says about sequestration.
- Describe the consequences of soft tissue scarring that the lecture lists.
- List the psychosocial considerations the lecture raises.
- Summarise the lecture’s key facts about osteomyelitis, including its diagnostic rule of thumb.
- List the learning points about clinical approach given on the closing slide.
- A 38 year old woman has constant, poorly localised thigh and left knee pain that disturbs sleep, a swollen knee, night sweats, fever 37.9°, enlarged groin nodes, neutrophils 17.6 and ESR 58, with normal knee x-rays. A washout for presumed septic arthritis finds no organisms and she does not improve. Explain what this case teaches about the next step and about the reasoning error to avoid.
- Explain what can and cannot be concluded from the uncaptioned pair of x-rays late in the case, which show surgical hardware.
Answers
Reveal answers
- Pain that was constant and made sleep difficult, felt in the thigh and left knee, and not well localised; swelling of the left knee; night sweats.
- Fever 37.9°, a swollen knee and thigh, pain on movement of the knee, and enlarged lymph nodes in the groin.
- Total leucocytes 19.4 (normal 4.0 to 11.0), neutrophils 17.6 (normal 2.0 to 7.5), monocytes 1.12 (normal 0.2 to 1.0), with the granulocytes showing a shift to immaturity; ESR 58 (normal 2 to 12). The ESR is a non specific indication of inflammation.
- Assume bacterial infection. You must determine the site of the infection and treat it urgently.
- The presumed diagnosis was septic arthritis of the knee; the knee x-rays were normal; the knee joint washout found no micro organisms.
- Flucloxacillin, as a best guess antibiotic, because Staphylococcus aureus is the usual cause.
- Staph aureus is the most common cause of musculoskeletal infection; acute infections may follow haematogenous spread of organisms from an unrecognised source; infection establishes itself in damaged or abnormal tissues.
- Infection in the medullary canal permeates outwards through the cortex and then collects beneath the periosteal membrane.
- Temperature, pulse and symptoms. The observation chart shown (Dunedin Hospital) plots temperature, blood pressure and pulse rate across successive post-operative days.
- The x-ray was repeated (two knee views of the distal femur and proximal tibia), and a nuclear medicine bone scan was done, with four views showing asymmetric tracer uptake between the limbs; the bone scan was used to localise the site of infection.
- Failure to eradicate infection; pathological fracture; soft tissue scarring; psychosocial considerations.
- Sequestration, described as mechanical, in dead bone, with the protective cell wall of the micro organism (the slide gives no more than this); antibiotic resistance, for example MRSA; unrecognised organisms, for example TB and anaerobes.
- Joint stiffness, and loss of muscle excursion and power.
- Length of time in hospital, disruption to family life, loss of income, loss of job, and the patient’s “why me?”.
- Osteomyelitis is usually caused by Staph aureus, may occur in a healthy person, often follows haematogenous spread, may spread directly from an open wound, and is relatively common in children. The rule of thumb is that bone pain plus fever equals osteomyelitis.
- Listen to your patient; avoid tunnel vision and preconceptions; exclude the most serious possibility; rare conditions happen; bad luck happens but don’t contribute to it; be supportive and compassionate.
- Fever, pain and a raised white cell count mean you assume bacterial infection and must determine the site and treat urgently. A normal knee x-ray and a washout that grows nothing do not settle the matter, so the step is to think again: repeat the x-ray and do a nuclear medicine bone scan to localise the site of infection, after which treatment became draining pus from the bone. The error to avoid is tunnel vision and preconceived ideas: listen to the patient, exclude the most serious possibility, and remember that bone pain plus fever equals osteomyelitis.
- Only that the two views show a long bone with surgical hardware in place, a plate with screws in one image and a rod or pin construct near the joint in the other. The slide has no title or caption, so this is visual interpretation only: it is likely follow-up imaging after fixation, but that is not confirmed, and no order or sequence of operations can be concluded from it.