A posterior horn tear of the medial meniscus is a tear in the back portion of the C-shaped cartilage pad on the inner side of your knee. This is one of the most common locations for meniscus injuries, partly because the posterior horn is thicker than the front portion and bears a disproportionate share of your knee’s load during movement. These tears range from minor fraying that heals with rest and physical therapy to severe disruptions that accelerate cartilage breakdown and may need surgery.
Why the Posterior Horn Matters
Your medial meniscus sits between your thighbone and shinbone on the inner side of the knee. It acts as a shock absorber, distributes your body weight across the joint, and helps stabilize the knee during motion. The meniscus is anchored to the top of the shinbone at two points: the front (anterior horn) and the back (posterior horn). These anchoring ligaments are made of tough type I collagen fibers that keep the meniscus locked in position.
The posterior horn is thicker than the anterior horn, reflecting its larger role in keeping the meniscus properly positioned. More importantly, the rear attachment is critical for maintaining what’s called “hoop stress,” a tension mechanism that allows the meniscus to spread forces evenly across the joint surface rather than concentrating them in one spot. When the posterior horn tears, this force distribution breaks down, and the cartilage lining your joint starts absorbing loads it wasn’t designed to handle alone.
What Causes These Tears
Posterior horn tears happen through two main pathways: acute trauma and gradual degeneration.
Acute tears typically occur during sports or physical activity. A sudden pivot, a deep squat under load, or a twisting motion while your foot is planted can shear the posterior horn. These injuries can happen with or without contact from another person. Younger, active people are more likely to experience this type of tear.
Degenerative tears develop over time as the meniscus loses its resilience with age. The tissue becomes brittle and prone to damage from ordinary movements. Something as simple as an awkward twist when standing up from a chair can be enough to tear an aging posterior horn. These tears are common in people over 40 and often show up alongside early signs of knee arthritis.
Symptoms to Recognize
With smaller tears, pain and swelling may not appear for 24 hours or more. Larger tears tend to announce themselves quickly. Common symptoms include:
- Pain along the inner knee, especially when twisting, squatting, or rotating the joint
- Swelling or stiffness that develops gradually over the first day
- A popping sensation at the time of injury
- Locking, where the knee feels stuck and won’t straighten fully
- Catching or giving way, a sensation that the knee buckles or can’t support your weight
Locking and catching are considered “mechanical symptoms” and tend to signal a more significant tear, sometimes one where a flap of torn meniscus is physically blocking normal knee motion.
How It’s Diagnosed
Your doctor will typically start with a physical exam. One common test, the McMurray test, involves bending and rotating your knee while feeling for a click or pain along the joint line. For medial meniscus tears specifically, this test picks up about 54% of cases, with relatively good accuracy when it does come back positive (79% specificity). Joint line tenderness, or pain when pressing along the inner knee, catches about 50% of tears. Because neither test is perfect on its own, imaging usually follows.
MRI is the standard for confirming a posterior horn tear. It shows the tear’s exact location, size, and pattern, and reveals whether surrounding structures like ligaments or cartilage are also damaged. On MRI, a true tear appears as a bright signal line that extends to the surface of the meniscus. Radiologists also look for signs of meniscal extrusion, where the damaged meniscus has started to squeeze out from between the bones, a red flag for more serious joint consequences.
Root Tears: A More Serious Subtype
Not all posterior horn tears carry the same weight. A root tear, defined as a radial tear within one centimeter of where the meniscus attaches to the shinbone, is particularly damaging. It severs the circumferential fibers that maintain hoop stress, effectively disabling the meniscus’s ability to distribute load. The torn meniscus can then extrude outside the joint space, creating a situation functionally comparable to having no meniscus at all.
The consequences are significant. A root tear can reduce the contact area between your thighbone and shinbone by 40 to 75%, which may increase the pressure on your joint cartilage by 200 to 300%. This dramatically accelerates cartilage wear. Research has found that meniscal root tears with extrusion carry roughly 4.6 times the odds of progressing to osteoarthritis compared to knees without this injury, with visible joint changes appearing in as few as four years even in knees that previously showed no signs of arthritis.
Treatment: Conservative vs. Surgical
The right approach depends on the type of tear, your age, your activity level, and whether you’re experiencing mechanical symptoms like locking or catching.
Degenerative tears in older patients without mechanical symptoms often respond well to a structured physical therapy program as the first line of treatment. Supervised exercise focuses on strengthening the muscles around the knee, restoring range of motion, and gradually reintroducing load-bearing activity. If symptoms persist after a dedicated course of rehab, surgery can still be considered later.
Surgical options fall into two categories. Meniscal repair stitches the torn tissue back together and is best suited for younger patients with tears located in the outer portion of the meniscus, where blood supply is better and healing is more likely. Repair shows about an 80% clinical success rate at two years. Tears that run vertically or longitudinally and are longer than one centimeter are the best candidates. A partial meniscectomy, where the damaged portion is trimmed away, is used for tears in the inner zone (where blood supply is poor) or tears that aren’t repairable due to their shape or severity. Trimming preserves as much healthy meniscus as possible while removing the source of mechanical symptoms.
What the Numbers Show for Repair
At five years after meniscal repair, about 72.5% of patients show complete clinical healing, with functional scores averaging around 91 out of 100 on standard knee assessment scales. On follow-up MRI, however, only about 58% of repaired menisci appear fully healed on imaging, suggesting that some repairs function well despite not looking perfect on a scan. Patients who had their meniscus repaired alongside reconstruction of the anterior cruciate ligament (ACL) had the best healing rates, around 89% clinical success, likely because the post-surgical rehabilitation protocols for ACL reconstruction also protect the meniscal repair.
Recovery Timeline
Recovery after meniscal repair follows a phased progression. The first six weeks focus on protecting the repair. For tears in the posterior horn root or radial patterns, this means no weight on the leg initially, while vertical or longitudinal tears may allow weight-bearing right away as tolerated. Pain control, gentle range-of-motion exercises, and reactivating the quadriceps muscle are the priorities in this phase.
Between weeks six and nine, you transition off crutches and begin building tolerance for load. The goal is a normal walking pattern without a limp. From weeks nine through sixteen, rehabilitation shifts toward restoring full knee range of motion, adding external resistance, and introducing balance training.
Return to sport typically begins no earlier than four months and can extend to nine months or longer depending on the sport and the tear type. This final phase includes progressive jogging, plyometric exercises, and sport-specific drills. Return timelines are guided by objective testing, not just how the knee feels, because healing on the inside often lags behind how the knee performs on the outside.
After a partial meniscectomy, recovery is considerably faster. Most people return to normal daily activities within a few weeks and sport within six to eight weeks, since there’s no repair that needs to heal.