Arthroscopic partial meniscectomy for a degenerative tear

Arthroscopic partial meniscectomy is a short operation: the surgeon trims the torn part of a meniscus back to a stable rim and leaves the rest. The reasoning is intuitive. A flap of torn tissue is catching in the joint, so remove the flap.

That reasoning has been tested more rigorously than almost anything else in orthopaedic surgery, including in the way surgical procedures are hardest to test — against a sham.

The sham-controlled trial

FIDELITY randomised 146 adults aged 35 to 65 with a degenerative medial meniscus tear, confirmed on both MRI and arthroscopy, and no knee osteoarthritis. Everyone went to theatre and had a diagnostic arthroscopy. Then, in the same operation, half had the tear resected and half had a simulated procedure matching the sounds, the sensations and the time in the operating room. Nobody — patient, carer or assessor — knew which.

At twelve months the Lysholm score had improved 21.7 points in the resected group and 23.3 in the sham group. WOMET improved 24.6 and 27.1. Knee pain after exercise improved 3.1 and 3.3. Every between-group interval spanned zero.

At two years the picture held, and the trial went looking for the patients who should have benefited. Two subgroups were examined in advance: people reporting mechanical symptoms, and people with an unstable tear. Neither separated from the trial as a whole.

The mechanical-symptom question, asked directly

Catching and locking are the reasons most often given for operating, so the trial analysed them on their own. Before surgery, 32 patients (46%) in the resection group and 37 (49%) in the sham group reported catching or locking. At follow-up the numbers were 34 (49%) and 33 (43%) — a risk difference of 0.03. Among the 69 people who had the symptom to begin with, 0.07.

The authors draw the conclusion carefully, and it is the more interesting one: this questions whether a degenerative tear is what causes the symptom it is being resected for.

Five years, and what the structure did

Both arms of FIDELITY were still doing well at five years, and still doing equally well: WOMET, Lysholm and pain after exercise all sat within a couple of points of each other.

The radiographs moved. Seventy-two percent of the resected knees and 60% of the sham knees had progressed at least one Kellgren-Lawrence grade — an adjusted absolute risk difference of 13%, with a 95% confidence interval from -2% to 28%. The OARSI sum score moved in the same direction by 0.7 points, and that interval did not include zero. Mechanical symptoms at five years were reported by 20 of 68 patients (29%) after resection and 9 of 74 (12%) after the sham, a risk difference of 18%.

Then the MRI arm of that follow-up did something more precise, and its result is the one worth carrying. Reading subregion by subregion, the odds ratio in the resected arm was 2.86 for osteophyte progression, 1.31 for cartilage damage and 1.43 for bone marrow lesions — and only the osteophyte interval excluded 1. The radiographic difference is being driven by osteophytes rather than by measured cartilage loss. That has not been replicated, and it is the most cartilage-specific randomised measurement this literature contains.

The trials against exercise and physical therapy

Three separate teams asked a different question — surgery or conservative care — and arrived in the same place.

MeTeOR randomised 351 patients aged 45 and over with a meniscal tear and mild-to-moderate osteoarthritis. WOMAC physical function improved 20.9 points with surgery and 18.5 with physical therapy. Thirty percent of the physical-therapy arm crossed over to surgery within six months, and once they did, their twelve-month function matched the surgical arm's.

OMEX randomised 140 people, mean age 49.5, nearly all without definitive radiographic osteoarthritis, to twelve weeks of supervised exercise or to surgery alone. The two-year difference in KOOS4 was 0.9 points. Thigh muscle strength improved in the exercise arm at three months, which is the one place the trial separated cleanly. At ten years, radiographic osteoarthritis had appeared in 23% of the surgical arm and 20% of the exercise arm.

ESCAPE randomised 321 patients aged 45 to 70 in nine Dutch hospitals, as a noninferiority trial. At five years IKDC had improved 29.6 points after surgery and 25.1 after sixteen sessions of exercise-based physical therapy — a difference of 3.5 points against a noninferiority threshold of 11. Radiographic osteoarthritis progressed at comparable rates.

Pooling five randomised trials in knees with mild or no osteoarthritis — 296 knees operated, 284 treated conservatively or with a sham — found no gain in functional activity and no significant reduction in pain.

Where the line actually falls

The conventional defence of this operation is that the trials enrolled the wrong patients: degenerative tears in middle-aged knees, rather than traumatic tears in young ones.

That population has been randomised once, and the trial tested timing rather than necessity. A hundred patients aged 18 to 45, mean age 35, a third of them competitive or elite athletes, with a recent traumatic isolated tear and no osteoarthritis, were assigned to early surgery or to physical therapy with the option of delayed surgery. At two years both groups scored 78 on IKDC. Forty-one percent of the physical-therapy arm took the delayed operation, and both arms improved by a clinically meaningful margin.

So the young traumatic tear has one trial, and what it establishes is that waiting costs nothing measurable at two years — not that the operation is never needed. Locked knees have never been randomised at all, and root tears are a different operation with a different literature, covered in the repair entry.

Reading a scan against the base rate

One number is worth holding alongside all of this. In an unselected Framingham sample aged 50 to 90, 61% of the people found to have a meniscal tear on MRI had reported no knee pain, aching or stiffness in the previous month. Among people who did have radiographic osteoarthritis, a tear was present in 63% of those with pain and 60% of those without.

A tear on the scan and pain in the knee are both common in the same people, and the scan cannot tell you which one is doing the talking.

What would change this

The variable the surgeon actually controls — how much meniscus comes out — has never been randomised, while it is consistently the strongest predictor in the observational literature. The osteophyte-versus-cartilage split at five years needs a second trial to confirm it. And nobody has enrolled a truly locked knee, which is the presentation every guideline still treats as surgical and which no randomised evidence covers. Any of the three would tell a reader something the current evidence cannot.