For those who are interested in learning more about hip and knee issues:
Knee Anatomy and Function
- Knee vs. Hip Joint: The knee joint is inherently more unstable than the hip joint, which is a true ball-and-socket joint.
- Key Structures:
- Patella (Kneecap): The rounded bone at the front of the knee. The quadricep tendon attaches to its top, and the patellar tendon continues from it to attach to the tibia.
- Cartilage: Covers the ends of all bones in the joint, allowing smooth gliding. Maintaining cartilage is crucial because its disappearance leads to problems. Chondrocytes (cartilage cells) respond to pressure by making more matrix and proteins, meaning a pressured chondrocyte is "happy," while an unpressured one will break down.
- Ligaments: Provide stability to the joint.
- Cruciate Ligaments: The anterior cruciate ligament (ACL) and posterior cruciate ligament (PCL) cross within the knee. The ACL is a commonly torn ligament.
- Collateral Ligaments: Medial collateral ligament (MCL) and lateral collateral ligament (LCL) are on the sides of the knee.
- Menisci: Two semicircular structures (medial and lateral menisci) that are imperative for distributing force across the knee and preventing cartilage wear. They distribute about 30% of the load through the knee joint. Without them, there's "point loading" or "edge loading," which rapidly degenerates cartilage.
- Bones: Femur (thigh bone), Tibia (shin bone, the platform on which the knee sits), and Fibula (smaller bone on the outside, attaching to the tibia and LCL).
Forces on the Knee and Activity
- Amplified Forces: Activities like running and squatting significantly amplify forces on the knee. When squatting, the pressure behind the kneecap can be about seven times greater than body weight. Running can exert eight times body weight force on the knee. Walking up or down stairs can also place significant load (four to seven times body weight) on the knee.
- Activity vs. Inactivity: No activity is inherently "horrible" for cartilage. Inactivity is detrimental, as cartilage matrix content significantly depresses in a casted leg. Cartilage health follows an inverted U-shaped curve: some activity is good, more is better, but "too far" leads to decline. It's not a perfect Goldilocks zone, and individual factors are crucial.
- Biomechanics and Alignment:
- Good Mechanical Alignment: A plumb line from the center of the hip through the center of the knee (cutting the patellar tendon in half) to the center of the ankle indicates good alignment, reducing the risk of degeneration.
- Poor Alignment: Conditions like knock-knees (valgus) or bow-legs (varus) increase force through one compartment of the knee, raising the risk of degeneration.
ACL Injuries
- Impact on Cartilage: An ACL-deficient knee experiences substantially greater compressive force on its cartilage than an ACL-intact knee. Even after reconstruction, the loads through the joint often change permanently.
- Risk of Arthritis: Approximately 50% of people who have an ACL tear (whether reconstructed or not) show signs of arthritis within 15 to 20 years. It's a "baked-in-the-cake" problem from the initial injury. Some studies suggest a potentially higher risk of arthritis after reconstruction, possibly because it enables individuals to return to high-impact activities.
- Purpose of ACL Surgery: The primary reasons for ACL surgery are to protect the meniscus (which can tear if the knee is unstable) and to allow individuals to participate in sports and activities they enjoy.
- Injury Mechanisms:
- Non-contact injuries are the majority.
- Women have a higher risk due to factors like strength differences and neuromuscular control, often landing with a valgus (knees inward) and extended position, weak gluteus medius, and adducted hip.
- The mechanism often involves a valgus landing (knee moving inward), causing condylar liftoff (stretching the MCL), internal tibial rotation, and quadricep contraction, shifting the knee out of place.
- Hyperextension and trunk lean to one side during planting can also contribute.
- Prevention: Injury prevention programs, focusing on neuromuscular training and strengthening glutes, can reduce risk but require treating many individuals (90 people to prevent 1 ACL tear).
- Surgical Timing: It is generally preferred to wait until the knee is "quiet" (initial inflammation has come down) and the patient has done some prehab, though immediate surgery shows no adverse long-term effect.
- Graft Options:
- Autograft (patient's own tissue): Patellar tendon (gold standard, central third with bone from patella and tibia), hamstring (semitendinosus, sometimes with gracilis), and quadricep tendon (newer, less research).
- Allograft (cadaveric tissue): Can be bone-tendon-bone or soft tissue. Not recommended for younger patients (under 34) due to higher re-rupture risk, as it takes longer to mature and strengthen. Easier recovery initially, suitable for older, less active individuals.
- Recovery and "Inflamma-type": Some individuals experience prolonged, low-burn chronic inflammation (elevated IL-1, IL-6 in synovial fluid) after an ACL injury, impacting recovery. This "inflamma-type" may also apply to other injuries and total knee replacements.
Arthritis (Osteoarthritis)
- Definition: There's a difference between radiographic arthritis (cartilage loss visible on X-ray) and symptomatic arthritis (pain). Arthritis is a "whole joint disease" involving cartilage breakdown, inflammatory reaction in the synovium, and bone changes, not just isolated cartilage narrowing.
- Symptom Onset: People can have severe radiographic arthritis with no symptoms for a long time until a "traumatic event" (stumble, twist, lift) "flips the switch," leading to sudden, severe pain.
- Body Weight: Excess body weight is a significant driver of arthritis due to amplified forces on the knee. Even small weight loss can significantly reduce the load.
Meniscus Tears
- Treatment Principle: For a meniscus tear without existing arthritis, strongly consider fixing it to prevent future arthritis.
- Types of Tears and Treatment:
- Peripheral Tears: Good blood flow, can be sewn back together.
- Bucket Handle Tears: A piece flips over, often locking the knee. Primarily repaired by sewing it back.
- Radial Tears: May be sutured if close to the rim, but often require trimming the torn piece (meniscectomy).
- Controversy of Sham Surgery: Studies showing meniscal surgery is no better than sham surgery primarily apply to patients with pre-existing degeneration or arthritis, where the meniscus tissue itself is unhealthy and cannot be effectively repaired. For young individuals without arthritis, fixing a repairable meniscus tear is crucial.
Patellofemoral Syndrome (Anterior Knee Pain)
- Cause: Overloading the cartilage in the patellofemoral joint (behind the kneecap), often due to increased running duration or mileage. Pain can come from the patellar tendon, quad tendon, cartilage, bone, or even the fat pad.
- Treatment: Physical therapy (PT) focusing on strengthening the quadriceps (can be challenging if it causes pain), hip strengthening (especially gluteus medius to correct leg adduction), and sometimes Blood Flow Restriction (BFR) training to allow for lower load quad strengthening.
Total Knee Replacement (TKR)
- Indications: Advanced arthritis in multiple knee compartments, failed conservative treatments (PT, injections, bracing), and significantly poor quality of life, provided the patient is healthy enough for surgery.
- Procedure: Involves making cuts in the distal femur and proximal tibia to fit metal implants, often with a high molecular weight polyethylene insert. The patellar surface may also be replaced with a plastic button.
- Recovery: Takes about one year for full recovery, with improvements continuing even longer, though it is often non-linear (80% better in six months). Post-operative pain can be significant, but perioperative pain management has improved. Patient satisfaction (around 85%) is lower than for hip replacements, and many don't feel it's a "normal knee". Factors like pre-op muscle strength and "inflamma-type" may differentiate recovery rates.
- Limitations Post-TKR: Patients are generally advised against contact sports due to the risk of devastating fractures around the implant, but activities like tennis (singles or doubles) and skiing are often permitted, with the understanding that the polyethylene will wear out over time.
- Mechanical Alignment: Surgeons often use computer navigation to ensure precise cuts and optimal mechanical alignment during TKR, which helps the new knee function correctly.
Other Knee Concerns and General Principles
- Non-Surgical Cases: Patellar tendon or quadriceps tendon ruptures require immediate surgery as the leg cannot be extended otherwise. However, some meniscus tears and even ACL tears can be managed conservatively in individuals who do not participate in pivoting or rotational "level one" sports (e.g., biking, running) and cope well.
- Ankle Arthritis: Less common than hip or knee arthritis because the ankle joint is highly congruent, and the plumb line of force goes "right down the center." However, traumatic events like ankle sprains and fractures significantly increase the risk.
- Importance of Mechanics and Activity: A recurring theme is that inactivity or poor biomechanics are root causes of many knee problems. Correcting these through strengthening and proper movement is fundamental to knee health.