To palpate the medial collateral ligament (MCL), you need to trace a band of tissue that runs from the bony bump on the inner side of the femur down to the inner shin, roughly 6 centimeters below the knee joint. The ligament sits just under the skin on the medial knee, making most of its length accessible to your fingers if you know the right landmarks and positioning.
Key Landmarks to Find First
The MCL has two layers, but the one you can feel is the superficial MCL. It originates at the medial femoral epicondyle, the prominent bony point on the inner side of the knee at thigh level. Its tibial attachment sits about 6 centimeters below the joint line on the inner shin. The deep MCL lies underneath, attaching much closer to the joint line (only about 6 millimeters below the tibial plateau), but it is difficult to isolate by touch because of its deep-seated position.
Before touching the ligament itself, identify three reference points:
- Medial femoral epicondyle: the bony prominence on the inner side of the distal thigh. This is where the superficial MCL begins.
- Adductor tubercle: a small bump just above and behind the epicondyle. Surgeons use it as a starting landmark for medial knee approaches, and it helps you orient to the top of the MCL.
- Medial joint line: the crease between the femur and tibia on the inner knee. You can find it by palpating the bottom edge of the kneecap with the knee bent to 90 degrees, then sliding your fingers straight medially.
Patient Positioning
Have the patient lie on their back with the affected leg relaxed. For general palpation of the ligament’s course, a slight bend in the knee (around 20 to 30 degrees) relaxes the surrounding muscles and makes the MCL easier to isolate under your fingers. Abducting the hip so the leg hangs off the side of the table can help if you plan to combine palpation with stress testing. For locating the joint line specifically, flex the knee to 90 degrees, which opens the medial compartment and makes the gap between the femur and tibia more obvious.
Step-by-Step Palpation
Start at the medial femoral epicondyle. Place your thumb or fingertip directly on that bony bump and press gently. The MCL’s femoral origin fans out over this point, so tenderness here can signal an injury at the ligament’s upper attachment, which is the most common tear location.
From the epicondyle, slide your fingers distally along the inner knee, following a line that angles slightly forward. You are tracing the body of the superficial MCL. It feels like a firm, flat band under the skin, distinct from the softer tissue around it. Maintain light to moderate pressure as you move down. Note any thickening, bogginess, or pain the patient reports along the way.
Cross the joint line. You should feel a subtle dip where the femur and tibia meet. Continue distally along the shin for about 6 centimeters. The tibial insertion sits here, along the inner surface of the proximal tibia. Press into this area and note any tenderness. The pes anserine tendons (a group of three muscle tendons) insert nearby but slightly lower and more toward the front, roughly 5 to 7 centimeters below the joint margin. Keep that distinction in mind so you don’t confuse the two.
Distinguishing MCL Pain From Other Structures
The inner knee is crowded with pain-generating structures, so location matters. MCL tenderness follows the ligament’s path: epicondyle, mid-substance over the joint line, or distal tibial attachment. Medial meniscus pain, by contrast, localizes specifically to the joint line itself. You can sharpen the distinction by externally rotating the shin and slowly extending the knee while pressing on the joint line. A painful, palpable click during this maneuver (the McMurray test) points toward a meniscal tear rather than an MCL problem.
Pes anserine bursitis produces tenderness that sits lower and more anterior than MCL pain, centered about 5 to 7 centimeters below the joint line at the spot where the conjoined tendons insert. MCL tenderness is typically located above and behind that point. Comparing the affected knee to the opposite side helps clarify whether tenderness is abnormal or just normal sensitivity.
Adding the Valgus Stress Test
Palpation alone tells you where the pain is, but the valgus stress test tells you whether the ligament is intact. With the patient supine and hip abducted, flex the knee to 30 degrees. Stabilize the thigh with one hand and use the other to push the ankle laterally, creating an inward (valgus) force at the knee. Feel for how much the medial side gaps open, and whether you reach a firm endpoint.
Repeat the test with the knee in full extension. At 30 degrees, you isolate the MCL because other stabilizers (the posterior capsule, cruciate ligaments) are relaxed. If the knee gaps open only at 30 degrees, the MCL is likely the sole injured structure. If it also gaps in full extension, suspect additional damage to the posterior capsule or cruciate ligaments.
While applying valgus stress, keep your palpating fingers on the medial joint line. You can often feel the joint opening under your fingertips, which makes the degree of laxity more tangible than watching from a distance.
Grading What You Feel
The amount of medial gapping during the valgus stress test at 30 degrees determines the injury grade:
- Grade I (mild): 3 to 5 millimeters of opening with a firm endpoint. The ligament is stretched but intact. These injuries typically heal within one to three weeks.
- Grade II (moderate): 6 to 10 millimeters of opening, still with some endpoint but noticeably looser than the other knee. Recovery generally takes four to six weeks.
- Grade III (severe): more than 10 millimeters of opening with no firm endpoint, meaning the ligament has completely torn. Healing takes six weeks or longer, and imaging is usually needed to check for associated injuries.
Always compare to the uninjured knee. Some people naturally have more joint laxity than others, so the absolute number matters less than the side-to-side difference.
Common Pitfalls
Pressing too hard too early can cause guarding, where the patient tenses the surrounding muscles and makes the ligament harder to feel. Start with light pressure and increase gradually. If the knee is acutely swollen, palpation becomes less reliable because fluid and inflammation obscure the normal tissue planes. In that scenario, the valgus stress test carries more diagnostic weight than palpation tenderness alone.
The deep MCL is essentially impossible to palpate directly because it sits beneath the superficial layer and blends with the joint capsule. If you suspect a deep layer injury (common in combined meniscal and ligament injuries), imaging is the better tool. Your fingers can reliably assess the superficial MCL and the bony landmarks it attaches to, but not the deeper structures beneath it.