Dr Matthew BroadheadOrthopaedic Surgeon · Sydney & Coffs Harbour

Journal Club · October 2026

Does a cartilage tumour found by chance need surgery?

128 cartilage tumours of the long bones were watched with MRI for four years on average. 87% stayed the same or shrank, and none became a high-grade cancer.

It is one of the more unsettling ways to learn you have a tumour: an MRI of your knee or shoulder, ordered for arthritis or a sore rotator cuff, comes back describing a lesion in the bone that the radiologist thinks is made of cartilage. The report may say enchondroma, or atypical cartilaginous tumour, or hedge with the phrase low-grade chondrosarcoma cannot be excluded. The natural question is whether something that might be a cancer should be taken out. This pair of studies from a Dutch sarcoma centre is the best evidence on what happens if it is not.

What the study looked at

Two kinds of cartilage tumour grow inside the shaft and ends of the long bones. An enchondroma is benign and very common; small ones are found in a few per cent of knee MRIs done for other reasons. An atypical cartilaginous tumour (ACT) is one step along, with a little more cellular activity under the microscope. Until 2013 it was called grade 1 chondrosarcoma, and the older name still appears in reports. In the long bones it is now classed as locally aggressive rather than malignant, because it essentially never spreads. The two are hard to tell apart on a scan, and often on a biopsy as well, which is why for years the safe-seeming answer was to scrape them out.

The Radboud University sarcoma unit in Nijmegen stopped doing that for lesions that were not causing symptoms, and instead followed them with MRI. The 2016 paper, reviewed here as background, was their first report: 49 patients watched for at least two years. The 2021 paper is the larger follow-up: 128 tumours in 124 patients, each with at least two years between their first and last MRI and an average of just over four years. The scans were scored for size, for scalloping of the inner surface of the bone, for enhancement, and for one feature that turns out to matter a great deal, fat trapped within the lesion, which is a sign of a tumour being replaced by normal marrow.

What they found

  • Almost all were incidental. 125 of the 128 (97.7%) were found on scans done for something else, most often knee or shoulder problems unrelated to the tumour. Only two patients had pain that might have come from the lesion, and in both it settled.
  • Over four years, 87% stayed the same or got smaller. 65 tumours (51%) were unchanged. 46 (36%) regressed, typically by filling in with fat, and in 17 of those the lesion measurably shrank, by 8 mm on average.
  • 13% showed some progression, 17 tumours. The definition was deliberately strict: any growth counted, including 5 mm or less. None developed the features of a high-grade chondrosarcoma. Five of the seventeen were operated on because they had grown, and none turned out to be high-grade under the microscope.
  • Fat in the lesion was the reassuring sign. 87% of the tumours that regressed had entrapped fat on the first scan, and no tumour lost its fat over time. Where a lesion with fat did grow, the growth was tiny (median 3 mm).
  • The ones that grew were the small ones, in younger people. Progressing tumours measured 12 to 64 mm at diagnosis and the patients averaged 39 years old, against the mid-fifties in the other groups. Size was not a reason to operate: the authors recommend surveillance regardless of how large the lesion is.
  • The earlier series told the same story. Of 49 patients followed from 2016, 8 had surgery, but only 3 (6%) for a medical reason: growth in two, pain in one. The other five were operated on at their own request or because the limb needed surgery for something else.

What it means for you

If a cartilage lesion has been found by chance in the long bone of your arm or leg, is not causing pain, and has no worrying features on the scan, the current approach in sarcoma units is to watch it, not remove it. This is what the evidence supports. The operation to scrape out a cartilage tumour is not trivial: it weakens the bone, it can fracture, and it commits you to a recovery for a lesion that, in this series, was more likely to shrink than to grow. Surgery is reserved for the lesion that grows and hurts, or that develops features of something more aggressive, such as breaking through the cortex of the bone or forming a soft-tissue mass.

What watching looks like, in the authors’ proposal, is a repeat MRI at six months, which also answers the understandable anxiety of the first few months. If nothing has changed, the next scan is two years later, and the interval can lengthen from there. If the lesion is shrinking, a scan at three years. If it has grown but still looks benign, another scan within the year. This is their scheme, drawn from their own data, rather than a national guideline, and the schedule you are given may differ. What should not differ is that the follow-up happens: surveillance is only safe if someone is actually looking.

Two things this paper does not cover. Cartilage tumours of the pelvis, spine and shoulder blade behave more aggressively and are treated differently; this evidence is for the long bones only. And a lesion that is painful, where the pain is clearly from the lesion rather than the arthritis or tendon problem that prompted the scan, is a different conversation, and should be had with a sarcoma service.

A caveat worth knowing

This is a single centre looking back over its own patients, the lowest tier of evidence short of individual case reports, and it was chosen because nothing better exists. Only patients in whom the unit chose not to operate are included, and that choice became more permissive as the years went on, so a few early lesions that were removed for minor growth are missing from the surveillance group. Most tumours were never biopsied, so the series cannot say what proportion were enchondromas and what proportion were atypical cartilaginous tumours. Four years is mid-term: malignant change in these lesions is rare but, when it happens, can be late, and the authors themselves say longer follow-up is needed and that surveillance must not become an endless cycle of expensive scans. For now, the finding is consistent across both of their series and with the smaller studies they cite: left alone, the incidental cartilage lesion of a long bone usually does nothing, and often quietly disappears.

Assessing this studyA standardised appraisal for clinicians and registrars: study design, strength and validity.
Study design
Retrospective single-centre cohort from a Dutch tertiary sarcoma unit (Radboud University Medical Center, Nijmegen) of 128 central cartilaginous tumours of the long bones in 124 patients managed by active surveillance, with a minimum of 24 months between the first and last MRI. MRI features (size, endosteal scalloping, entrapped fat, septal enhancement, calcification) were scored and each tumour classified as unchanged, regressed or progressed. Read alongside the same group's 2016 series of 49 conservatively managed patients, the first natural-history report of its kind.
Level of evidence
OCEBM Level 4 (prognosis): a retrospective case series. There is no randomised or prospective inception-cohort evidence on surveillance of these tumours, and the authors argue a prospective study long enough to settle the question is impractical, so this is the best available tier.
Are the results valid?
The main threats are selection and definition. Only tumours in which surgery was withheld are included, and the unit's threshold for operating fell during the study period, so early cases that were resected for minor growth are absent from the surveillance arm. Most tumours were never biopsied, so enchondroma and atypical cartilaginous tumour cannot be told apart and the series is reported as one group. "Progression" was defined generously, counting growth of 5 mm or less, which inflates the progression group rather than hiding risk. Mean follow-up of 50 months is mid-term for a disease in which malignant change, when it occurs, can be late. 73% of patients were referred from other hospitals, which fits a tertiary practice but means the denominator of all incidental cartilage lesions is unknown. The MRI scoring was done at a single centre by the authors. No conflicts of interest were declared.
What are the results?
Of 128 tumours (mean age at diagnosis 52 years, range 20 to 76), 125 (97.7%) were incidental findings on scans done for something else, most often knee or shoulder complaints. At a mean of 50 months (range 25 to 138), 65 (51%) were unchanged, 46 (36%) had regressed and 17 (13%) had progressed on MRI. None developed features of high-grade chondrosarcoma. 87% of the tumours that regressed showed entrapped marrow fat at diagnosis; where fat was present in a tumour that later grew, the growth was minimal (median 3 mm). Progression occurred in smaller tumours (12 to 64 mm at diagnosis) and younger patients (mean 39 years, against 55 and 52 in the stable and regressing groups). Five tumours were operated on for growth; none showed high-grade chondrosarcoma on histology. In the 2016 series of 49 patients, 8 had surgery during follow-up but only 3 (6%) for a medical reason (growth in 2, pain in 1).
Do they apply to our patients?
Directly relevant to the common situation of a cartilage lesion reported on a knee or shoulder MRI done for arthritis, a meniscal tear or an injury. It applies to asymptomatic central lesions of the long bones without aggressive features. It does not apply to cartilage tumours of the pelvis, spine or shoulder blade, which behave differently and are managed surgically, nor to lesions with cortical destruction, a soft-tissue mass or pain that the lesion itself explains. The proposed surveillance scheme (MRI at six months, then two-yearly if stable, sooner if growing, surgery if growth is accompanied by persistent pain) is the authors' suggestion from their own data, not a validated guideline.
Bottom line
In the best available evidence, a single centre's mid-term MRI surveillance of 128 untreated enchondromas and atypical cartilaginous tumours of the long bones, the great majority stayed stable or shrank and none became high-grade; surveillance rather than surgery is a safe default for the asymptomatic incidental lesion, provided the lesion has no aggressive features and the follow-up actually happens.

Framework: study design graded with the Oxford Centre for Evidence-Based Medicine (OCEBM) Levels of Evidence; validity and applicability appraised in the CASP tradition.

This is a plain-language summary of published research, provided for general education. It is not medical advice and does not describe Dr Broadhead's own results. Whether any finding applies to you depends on your individual circumstances, so please discuss your care with your treating team.

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