Spinal osteomyelitis in patients with rheumatoid arthritis following total knee arthroplasty—two case reports

C. O. Nnene1 and P. Hickling

Departments of Orthopaedics and Rheumatology, Mount Gould Hospital Plymouth, Plymouth, UK


    Introduction
 Top
 Introduction
 Case 1
 Case 2
 Discussion
 Note added in proof
 References
 
Spinal osteomyelitis is a relatively common problem in areas where tuberculosis is endemic. Other, non-tuberculous causes are rare but carry significant morbidity and mortality. It is a rare complication of peripheral joint sepsis.

We present two cases of spinal osteomyelitis occurring in patients with rheumatoid arthritis who developed sepsis in their total knee replacements more than a year after surgery. Both patients' spinal abscesses were successfully treated with intravenous antibiotic therapy, but one patient required a revision knee arthroplasty 18 months after presentation.


    Case 1
 Top
 Introduction
 Case 1
 Case 2
 Discussion
 Note added in proof
 References
 
A 75-yr-old lady underwent bilateral non-synchronous total knee replacements in 1994. Her rheumatoid arthritis had been well controlled on non-steroidal anti-inflammatory agents, but in November 1995 she had a polyarticular relapse of her disease and was started on prednisolone 7.5 mg daily. Three months prior to this relapse she gave a history of a cat bite on her left leg with resulting superficial infection which apparently settled. Despite treatment of her relapse the patient remained unwell and in January 1996 was referred to the Rheumatology Department. She was apyrexial but had bilateral, hot, tender knee effusions. Investigations revealed haemoglobin (Hb) 7.6 g/dl; white blood cell count (WBC) 14.2 (88% neutrophils), plasma viscosity (PV) 2.01 and C-reactive protein (CRP) 134 mg/l.

Both knees were aspirated and yielded turbid, straw-coloured fluid. Microscopy of both fluids showed pus cells ++ but Gram stain was negative. Staphylococcus aureus was grown on culture of the synovial fluid and blood. Intravenous flucloxacillin and gentamycin were commenced with oral fucidin and the knees were re-aspirated frequently. Shortly after admission the patient complained of right scapular pain and examination showed thoracic scoliosis and wasting of the scapular muscles. The thoracic spine radiograph revealed disc space narrowing and vertebral end plate irregularity and sclerosis in C7/T1 vertebrae. Magnetic resonance imaging (MRI) confirmed an inflammatory mass, slightly compressing the spinal cord at C7 and T1 (Fig. 1Go). A neurosurgical opinion was obtained and conservative management recommended. She was fitted with a supportive collar, given a further 4 weeks of intravenous antibiotics and eventually made a good recovery.



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FIG. 1 MRI scan of cervical spine in case 1 showing an inflammatory mass with bony involvement slightly compressing the spinal cord at C7 and T1.

 
A MRI scan 1 month later revealed resolution of the pre-vertebral collection and destruction of the C7/T1 intervertebral disc with auto-fusion of the cervicothoracic junction. At follow-up 6 months later she had good mobility in both knees with no neck pain and her CRP had fallen to 30 mg/dl. She remains well 3 yr after her septic presentation.


    Case 2
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 Introduction
 Case 1
 Case 2
 Discussion
 Note added in proof
 References
 
A 49-yr-old lady with a 21-yr history of aggressive rheumatoid arthritis necessitating right and left total knee replacements in May 1987 and March 1988, right and left elbow replacements in May 1993 and September 1994, and a left total shoulder replacement in July 1995. She also had a history of degenerative lumbar spine disease. For 7 yr until 1995 she had been treated with intravenous sodium aurothiomaleate, but had never taken oral steroids. Her medication at presentation comprised indomethacin 75 mg b.d. and co-proxamol.

She was admitted in March 1996 complaining of feeling generally unwell with lumbar pain for 4 days. There were no urinary symptoms. She was pyrexial and local tenderness was noted in the lumbar spine at L4/5. She had a hot swollen right knee and a mildly swollen cool left knee. Investigations revealed a erythrocyte sedimentation rate (ESR) of 90 mm/h, CRP 333 mg/l, Hb 10.9 g/dl and WBC 4.3 x 10/l. Blood cultures yielded S. aureus. Twenty millilitres of turbid fluid were aspirated from her right knee. Microscopy showed pus cells +++ and Gram-positive cocci and subsequently grew S. aureus. She was started on intravenous vancomycin due to allergies to penicillin and cephalosporins. Lumbar spine radiographs demonstrated marked degenerative changes at the L4/5 disc with less severe changes at L3/4 and L5/S1. A MRI scan showed destructive lesions in the bodies of L4 and L5 and soft tissue swelling encasing the L4/5 disc (Fig. 2Go).



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Fig. 2 MRI scan of lumbar spine in case 2 showing involvement of the bodies of L4/5 with associated soft tissue swelling.

 
Her initial response to treatment was incomplete and her antibiotic regime changed to clindamycin and fusidic acid which she continued for 4 weeks. Her back pain subsided and she regained good mobility in her knee joints. One month post-discharge from hospital her Hb was 10.4 g/dl, WBC 5.9 x 10/l, CRP 68 mg/l. Four months later she remained well although her long-term antibiotics were recommenced when her CRP was noted to be rising. A revision knee arthroplasty was subsequently performed 18 months after initial presentation for a recurrence of S. aureus infection with sinus formation.


    Discussion
 Top
 Introduction
 Case 1
 Case 2
 Discussion
 Note added in proof
 References
 
Non-tuberculous vertebral osteomyelitis is an uncommon occurrence but is seen most frequently in association with infective discitis. Haematogenous spread is the mode of transfer and S. aureus is the most common organism [1, 2]. Septic arthroplasties have rarely been reported as a source of infection in these cases.

Delayed sepsis in knee arthroplasties is also uncommon, occurring in 2–4% of all cases [3, 4] and S. aureus is the causative organism in 41%. Rheumatoid arthritis has a higher incidence of delayed infection than osteoarthritis [5, 6] and is a significant factor in the late development of sepsis in arthroplasties [4, 7] but rarely in the development of spinal osteomyelitis or abscess [1]. In the absence of any other association and with sepsis clearly demonstrated in the total knee prostheses, these can be presumed to be the focus of infection in the two cases reported here. The relevance of the cat bite in case 1 remains speculative. However, the possibility that a staphylococcal bacteraemia from a source other than the knees was responsible for metastatic infection in the spine and arthroplasties in both patients cannot be ruled out.

The diagnosis of sepsis in rheumatoid patients is not always easy to make, as septic arthritis can mimic a rheumatoid flare. This is especially illustrated in case 1, where the patient was apyrexial at presentation, probably as a result of her steroid medication. Similarly, the back symptoms of the second patient could have been attributed to her established degenerative spinal disease and an infective aetiology missed. MRI proved an invaluable guide to diagnosis.

Both patients responded well to early, intensive and prolonged antibiotic therapy. Resolution of the vertebral osteomyelitis was monitored by MRI scan and computed tomography (CT)-guided aspiration was not required as a likely causative organism had already been isolated. Both patients continue long-term follow-up.

The possibility of metastatic infection in the presence of an infected joint must always be considered when a patient develops back pain especially when the patient may be immunologically compromised.


    Note added in proof
 Top
 Introduction
 Case 1
 Case 2
 Discussion
 Note added in proof
 References
 
Since submission of this article patient 2 has had two episodes of S. aureus joint sepsis in her left elbow arthroplasty which were managed with drainage and antibiotics. Her peripheral blood count now shows persistent neutropenia and thrombocytopenia which may herald the onset of Felty syndrome.


    Notes
 
1 Correspondence to: C. O. Nnene, 37 Oakfield Gardens, Edmonton, London N18 1NY, UK. Back


    References
 Top
 Introduction
 Case 1
 Case 2
 Discussion
 Note added in proof
 References
 

  1. Isdale AH, Foley-Nolan DF, Butt WP, Birkenhead D, Wright V. Psoas abscess in rheumatoid arthritis—an inperspicious diagnosis. Br J Rheumatol 1994;33:853–8.[ISI][Medline]
  2. Madsen SR, Rosenberg AE. A 27 year old woman with pain in the neck and shoulder and clumsiness in the hand. N Engl J Med 1992;326:1070–6.[ISI][Medline]
  3. Rodriguez J, Sadler S, Edelman S, Ranawat CS. Long-term results of total knee arthroplasty in class 3 & 4 rheumatoid arthritis. J Arthroplasty 1996;II:141–5.
  4. Wymenga AB, van Horn J, Theeuwes A, Muytgens HL, Sloof TJH. Perioperative factors associated with septic arthritis after arthroplasty. Acta Orthopaedica Scand 1992;63:665–71.
  5. Laskin RS. Total condylar knee replacement in patients who have rheumatoid arthritis. J Bone Joint Surg 1990;72A:529–35.[Abstract]
  6. Kristensen O, Nafei A, Kjaersgaard-Andersen P, Hvid I, Jensen J. Long-term results of total condylar knee arthroplasty in rheumatoid arthritis. J Bone Joint Surg 1992;74B:803–6.
  7. Bengston S. Prosthetic osteomyelitis with special reference to the knee. Ann Med 1993;25:523–9.[ISI][Medline]
Submitted 7 April 1998; revised version accepted 8 September 1999.



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