A 51-year-old female presented with left knee pain since several months and was posted for left total knee arthroplasty. MRI done a month back showed bone marrow oedema in the lateral tibial condyle. Total leucocyte count (TLC) was 4420 mm3 and C-reactive protein (CRP) was 20.9 mg/L.
A plain radiograph showed a well-defined subarticular lytic lesion in the lateral tibial condyle (Figure 1).
A repeat MRI (magnetic resonance imaging) was done, which showed a well-defined oval lesion in the lateral proximal tibial metaepiphysis. The centre of the lesion was hypointense on the T1WI (T1-weighted image (Figure 2) and hyperintense on T2WI (Figure 3). The penumbra sign was seen with an inner wall, hyperintense on T1WI. The outer wall was hypointense on both T1WI and T2WI. Osteoarthritic (OA) changes were seen with thinning of the articular cartilage and subchondral cystic changes.
There was surrounding perilesional bone marrow oedema, hyperintense on proton density fat-saturated (PDFS) images (Figure 4). Mild synovial effusion was seen (Figure 5).
CT (computed tomography) showed a well-defined lucent lesion with surrounding sclerosis and a breach of the articular surface (Figures 6a and 6b). Post-operative X-rays showed antibiotic beads filling the cavity (Figures 7a and 7b).
Background
Tuberculous osteomyelitis and arthritis generally arise from the reactivation of bacilli lodged in the body during primary infection through a haematogenous route. The infection involves the metaphysis of long bones and vertebral end plates due to their rich vascular supply.
Clinical Perspective
Making a timely diagnosis is difficult as patients present with vague complaints of pain and may not show any signs of systemic illness, unlike pyogenic osteomyelitis. Tuberculous osteomyelitis occurs in the elderly in developed countries but can occur in children and young adults in endemic regions. Pyogenic osteomyelitis and Brodie’s abscess are common in children and young adults.
Imaging Perspective
MRI is the imaging modality of choice for the investigation of osteomyelitis. Bone marrow oedema is the earliest feature of acute osteomyelitis and can be detected as early as 1 to 2 days after the onset of the infection [1].
Tuberculous osteomyelitis can present as a lytic lesion in the metaphysis of long bones with surrounding sclerosis and can mimic Brodie’s abscess. An intraosseous abscess demonstrates the classic penumbra sign on MRI formed by pus in the centre, which is hyperintense on T2, surrounded by granulation tissue, which is hyperintense on T1 and enhances intensely following contrast administration. This sign has been reported to be highly specific for osteomyelitis [2].
Periosteal reaction is usually not a typical feature of adult tuberculous infections [3]. Transphyseal spread of infection into the joint is common in tuberculosis, unlike pyogenic infections. In pyogenic arthritis, joint space narrowing is early and significant, while in tuberculosis, it is late and mild [4].
Outcome
The management of intraosseous abscess consists of curettage, cancellous bone grafting or filling the abscess cavity with antibiotic-impregnated polymethylmethacrylate (PMMA) beads [5]. This is followed by a prolonged course of parenteral or oral antibiotics, and in the case of tuberculosis, administration of antitubercular drugs for 6–9 months or an extended period of 18 months [6].
In our patient, CT-guided aspiration from the tibial lesion was done, which revealed pus. Synovial fluid revealed a total leucocyte count of 95,000 mm3. The culture was negative. Post-curettage bone and synovial tissue histopathology revealed necrosis and multiple confluent and discrete granulomas s/o tuberculous inflammation (Figure 8).
Take Home Message
Not every cause of knee pain in the elderly can be attributed to degenerative changes; imaging helps in making an accurate diagnosis of osteomyelitis or bone abscess.
All patient data have been completely anonymised throughout the entire manuscript and related files.
Intraosseous cold abscess
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1. X-ray: An irregularly shaped radiolucent area can be seen in the subcortical region of the lateral condyle of the left tibia, surrounded by varying degrees of sclerotic margins. The joint space is generally preserved, with no obvious signs of soft tissue swelling.
2. CT: A round-like low-density lesion can be seen in the lateral condyle of the tibia, surrounded by sclerotic bone. The lesion boundary is relatively clear, showing a “cavitary” appearance, suggesting possible pus or necrotic debris inside.
3. MRI:
- On T1WI, the lesion appears as a relatively low signal area, with a slightly higher signal peripheral ring (possibly indicative of granulation tissue or a gliosis-like reaction).
- On T2WI and STIR sequences, the lesion center shows a marked high signal, with a higher signal band around it, and significant bone marrow edema.
- The lesion involves the surrounding cortical bone, and reactive thickening can be observed in the adjacent joint synovium, indicating possible inflammatory changes or effusion in the joint cavity.
Based on the above imaging findings, along with the patient’s history (51-year-old female with chronic pain in the lateral condyle of the tibia), the following conditions should be considered:
In summary, tuberculous osteomyelitis and bacterial osteomyelitis are the primary differential diagnoses. Correlation with clinical history, laboratory findings (TLC, CRP), and subsequent pathological results will help determine the nature of the lesion.
Taking into account the patient’s age, clinical symptoms (chronic knee pain), test indicators (slightly elevated CRP, relatively low TLC), imaging features (MRI showing typical bone marrow edema and abscess cavity), and histopathological results (necrosis and granuloma consistent with tuberculous inflammation), the most likely final diagnosis is:
Tuberculous Osteomyelitis (Tuberculosis Infection of the Lateral Condyle of the Tibia).
Further aspiration or histopathological examination confirming tuberculosis is key to diagnosis. In this case, positive pathological results support this diagnosis.
1. Treatment Strategy Overview:
- Anti-tuberculosis medication: A combination regimen including isoniazid, rifampicin, etc., is typically recommended for at least 6–9 months. For bone and joint tuberculosis, treatment may extend to 12–18 months.
- Surgical intervention: For patients with extensive lesions and abscess formation, surgical debridement (curettage) of the lesion and pathological tissue may be required. In some cases, bone grafting or antibiotic-impregnated bone cement may be used to fill the cavity.
- Supportive therapy: Includes nutritional support and boosting immune function.
2. Rehabilitation and Exercise Prescription (FITT-VP Principle):
Additionally, in patients with fragile bones or limited cardiopulmonary function, the rehabilitation process should be slowed down and conducted under professional supervision to prevent accidental injury or fractures.
This report is based solely on the existing imaging and pathological materials, intended to provide a reference. Specific diagnosis and treatment require correlation with clinical examination and specialist consultation. This report does not replace hospital visits or professional medical advice.
Intraosseous cold abscess
