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. 2013 Aug;84(4):410-4.
doi: 10.3109/17453674.2013.810521. Epub 2013 Jun 25.

The natural course of spontaneous osteonecrosis of the knee (SPONK): a 1- to 27-year follow-up of 40 patients

Jan Juréus  1 , Anders Lindstrand, Mats Geijer, Otto Robertsson, Magnus Tägil
Affiliations

The natural course of spontaneous osteonecrosis of the knee (SPONK): a 1- to 27-year follow-up of 40 patients

Jan Juréus et al. Acta Orthop. 2013 Aug.

Abstract

Background and purpose: Spontaneous osteonecrosis of the knee (SPONK) is a painful lesion in the elderly, frequently leading to osteoarthritis and subsequent knee surgery. We evaluated the natural course and long-term consequences of SPONK in terms of need for major knee surgery.

Methods: Between 1982 and 1988, 40 consecutive patients were diagnosed with SPONK. The short-term outcome has been reported previously (1991). After 1-7 years, 10 patients had a good radiographic outcome and 30 were considered failures, developing osteoarthritis. In 2012, all 40 of the patients were matched with the Swedish Knee Arthroplasty Register (SKAR) and their medical records were reviewed to evaluate the long-term need for major knee surgery.

Results: At the 2012 review, 33 of the 40 patients had died. The mean follow-up time from diagnosis to surgery, death, or end of study was 9 (1-27) years. 17 of 40 patients had had major knee surgery with either arthroplasty (15) or osteotomy (2). All operated patients but 1 were in the radiographic failure group and had developed osteoarthritis in the study from 1991. 6 of 7 patients with large lesions (> 40% of the AP radiographic view of the condyle) at the time of the diagnosis were operated. None of the 10 patients with a lesion of less than 20% were ever operated.

Interpretation: It appears that the size of the osteonecrotic lesion can be used to predict the outcome. Patients showing early signs of osteoarthritis or with a large osteonecrosis have a high risk of later major knee surgery.

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Figures

Figure 1.
Figure 1.
An 83-year-old woman developed osteonecrosis and secondary osteoarthritis in the medial femur condyle. The initial radiographs at diagnosis (A) and those after 1 year (B) showed a small but typical radiolucent subchondral lesion in the weight-bearing area of the medial femoral condyle. The patient had a total knee arthroplasty 2 years after diagnosis (C).
Figure 2.
Figure 2.
MR image showing bone marrow edema of the medial femur condyle with a focal subchondral lesion typical of osteonecrosis.
Figure 3.
Figure 3.
Kaplan-Meier failure estimate showing the proportion of patients requiring knee surgery with arthroplasty or high tibial osteotomy over the years.
See this image and copyright information in PMC

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