Diagnosing a torn meniscus involves a combination of symptom assessment, hands-on physical examination, and imaging, usually an MRI. No single test is definitive on its own, but when a doctor combines findings from all three steps, the diagnosis is highly reliable. Here’s what to expect at each stage.
Symptoms That Point Toward a Tear
The most telling symptom is pain localized right along the joint line of your knee, either on the inner (medial) or outer (lateral) side. This tenderness occurs because the ligaments surrounding the meniscus become irritated when the cartilage is damaged. The exact point of tenderness often shifts toward the back of the knee as the joint bends.
Locking is another hallmark sign. The knee gets stuck, typically somewhere between 20 and 45 degrees as you try to straighten it. What’s happening is a loose or displaced fragment of meniscus wedging itself into the joint. A click or snap when the knee finally “unlocks” is actually a more reliable indicator of a tear than the locking itself. You may also feel the knee buckle or give way, as though it momentarily can’t support your weight.
Swelling shows up in roughly half of people with meniscus tears, but the amount of swelling doesn’t tell you much about the severity. Some significant tears produce minimal swelling, while minor injuries can swell noticeably. Full squatting is often painful or impossible, and you may struggle to fully straighten the knee if a torn fragment is blocking the motion.
What Happens During the Physical Exam
Your doctor will use a series of specific maneuvers to stress the meniscus and see if they reproduce your symptoms. The American Academy of Orthopaedic Surgeons (AAOS) considers physical examination, including joint line tenderness testing, the McMurray test, and the Thessaly test, effective for diagnosing acute meniscal tears. The tests become even more accurate when combined.
McMurray Test
You’ll lie on your back while the examiner bends your knee fully, then slowly straightens it while rotating your lower leg inward and outward. The goal is to trap a torn meniscus fragment between the bones. A palpable click, pop, or pain along the joint line during this motion suggests a tear.
Thessaly Test
You’ll stand on the affected leg with your foot flat on the ground while your provider holds your arms for balance. Then you’ll rotate your knee inward and outward three times. This is usually done twice: once with a slight knee bend and once with a deeper bend (around 20 degrees). Pain, locking, or catching along the joint line during the deeper bend is a positive result. Studies have reported sensitivity around 90 to 92% and specificity around 96 to 97% for this test, making it one of the more accurate bedside maneuvers.
Joint Line Tenderness
The simplest test is direct palpation. Your doctor presses along the medial and lateral joint lines while your knee is slightly bent. Sharp, localized pain at a specific point is a strong indicator, especially when it lines up with findings from the McMurray or Thessaly tests.
Why Your Doctor May Start With an X-Ray
X-rays don’t show the meniscus itself because cartilage doesn’t appear on standard radiographs. But a weight-bearing X-ray of the knee serves an important screening purpose: it reveals the degree of arthritis in the joint. This matters because if significant arthritis is present, it often drives the treatment plan regardless of what the meniscus looks like. In older adults especially, an X-ray can determine whether an MRI would even change the management approach. It also rules out fractures, loose bone fragments, and other structural problems that can mimic meniscus symptoms.
MRI: The Gold Standard
MRI is the preferred imaging tool for confirming a meniscus tear. The AAOS gives this a strong recommendation based on high-quality evidence. On MRI, radiologists look for two key findings that have remained the diagnostic standard since the late 1980s: abnormal signal within the meniscus that reaches the top or bottom surface of the cartilage, and any distortion of the meniscus’s normal triangular shape.
Healthy meniscus tissue appears as a uniform dark triangle on MRI. When degeneration or damage is present, brighter signals appear within that triangle. Radiologists grade these signals on a scale:
- Grade 1: A small, rounded bright spot inside the meniscus that doesn’t reach the surface. This represents early internal degeneration, not a tear.
- Grade 2: A linear bright signal inside the meniscus that still doesn’t reach the surface. Also degeneration, not a true tear.
- Grade 3: A bright signal that clearly extends to the top or bottom surface of the meniscus. This is what confirms a tear.
The distinction between Grade 2 and Grade 3 is the critical cutoff. Grade 1 and 2 findings are common, particularly as you age, and don’t require the same treatment considerations as an actual tear.
How Accurate Is MRI?
MRI performs better at detecting tears on the inner (medial) side of the knee than the outer (lateral) side. For medial meniscus tears, sensitivity runs around 93%, meaning it catches the vast majority of tears. Specificity sits around 76 to 82%, so there’s a small chance of a false positive. For lateral meniscus tears, sensitivity drops to about 68 to 69%, meaning MRI misses roughly a third of lateral tears, but specificity is high at 92 to 95%.
These numbers explain why doctors don’t rely on MRI alone. A negative MRI doesn’t completely rule out a lateral tear, and a positive MRI finding in an older patient with arthritis may represent age-related degeneration rather than a clinically meaningful injury. The physical exam findings and your symptom history help the doctor interpret what the MRI shows.
Conditions That Mimic a Meniscus Tear
Several knee problems produce symptoms that overlap with a torn meniscus, which is why the diagnostic process involves multiple steps rather than jumping to one test.
A medial collateral ligament (MCL) sprain causes pain along the inner joint line, much like a medial meniscus tear. The difference shows up when the examiner applies a sideways stress to the knee at 30 degrees of flexion. If the joint gaps open on the inner side, the MCL is the issue. Plica syndrome, where a fold of joint lining becomes irritated, produces pain near the kneecap rather than directly on the joint line, and sometimes a cord-like band can be felt along the inner edge of the kneecap. Osteochondral lesions, which are areas of damaged cartilage on the bone surface itself, can present almost identically to a meniscus tear and are typically distinguished only through MRI.
Ultrasound as an Alternative
Point-of-care ultrasound is emerging as a faster, cheaper option for evaluating suspected meniscus tears, particularly in emergency or urgent care settings. For medial meniscus tears, ultrasound has shown sensitivity around 89% and specificity around 90%, which approaches MRI-level accuracy. It can be performed immediately without scheduling delays and picks up other soft tissue injuries at the same time.
The limitations are real, though. Ultrasound is significantly better at detecting medial tears than lateral tears, and its accuracy depends heavily on the skill of the person performing it. It also hasn’t been well validated for penetrating injuries, complex trauma, or injuries more than five days old. Most doctors view it as a useful first-pass tool that can guide whether you need an MRI, not as a replacement for one.
Putting It All Together
The typical diagnostic sequence starts with your history and symptoms, moves to the physical exam maneuvers, and then proceeds to imaging if the clinical picture suggests a tear. For younger patients with a clear injury mechanism (a twist or pivot during activity), strong physical exam findings, and classic symptoms like locking and joint line tenderness, the diagnosis may be fairly straightforward before imaging even happens. For older adults or cases where the picture is less clear, an X-ray comes first to assess for arthritis, followed by MRI if it would change the treatment plan. In some cases, the definitive answer comes during arthroscopy, a minimally invasive procedure where a camera is inserted into the knee joint, which doubles as both the most accurate diagnostic tool and the route for surgical repair.