Bringing the knee toward the chest, known as deep hip flexion, is a common action that can provoke pain in the hip joint. This motion often includes slight internal rotation and adduction, causing the “ball” of the upper thigh bone to press deeply into the hip socket. Since the hip is a ball-and-socket joint, this deep compression can reveal structural issues inside the joint or soft tissue problems surrounding it. Pain during this specific movement indicates that the joint’s mechanics are being challenged during activities like kneeling, sitting low, or stretching.
Primary Structural Causes of Pain
The most common structural issue causing pain during deep hip flexion is Femoroacetabular Impingement (FAI). FAI is a condition where the hip bones have an irregular shape, leading to abnormal contact. This structural mismatch causes the bones to rub against each other, particularly when the knee is drawn toward the chest, which is the position of maximum impingement.
Cam impingement involves an abnormal bump on the femoral head (the ball of the joint). This bump prevents smooth rotation within the socket, causing grinding forces on soft tissues during deep flexion. Pincer impingement results from an excess rim of bone on the hip socket (acetabulum), creating over-coverage of the femoral head. This over-coverage leads to the socket rim pinching soft tissues during the knee-to-chest motion.
Many individuals present with Mixed impingement, where both Cam and Pincer deformities are present simultaneously. The chronic friction and mechanical stress from FAI frequently damage the acetabular labrum. The labrum is a ring of fibrocartilage lining the rim of the hip socket, functioning like a gasket to deepen the socket and provide joint stability.
A labral tear often results from the repetitive pinching caused by FAI, causing sharp, clicking, or catching pain during deep flexion. When the labrum is torn, joint stability and shock absorption capacity are reduced, and the torn tissue can get caught between the moving bones. Cartilage damage, commonly associated with Osteoarthritis, also contributes to pain. This involves general wear and tear of the articular cartilage, which is the smooth tissue covering the bone ends. Pain from cartilage damage is exacerbated by the deep compression of the joint during the knee-to-chest movement.
Muscular and Soft Tissue Contributors
Pain during hip flexion can originate from issues outside the joint capsule, involving surrounding muscles, tendons, and fluid-filled sacs. A common cause is Iliopsoas Tendinitis or Bursitis, affecting the iliopsoas muscle—the primary hip flexor. Tendinitis is inflammation of the tendon, while bursitis is inflammation of the bursa, a cushioning sac located near the tendon in the front of the hip.
Both conditions cause a deep, aching pain in the front of the hip or groin that worsens when the knee is raised toward the chest. This pain often results from overuse or repetitive hip flexion, such as in sports involving kicking or running. Snapping Hip Syndrome is sometimes associated with the iliopsoas tendon snapping over underlying structures as the hip moves. This snapping can become painful if the tendon or bursa is already inflamed.
Another muscular issue is a Hip Flexor Strain, frequently involving the Rectus Femoris muscle, one of the four quadriceps muscles. The rectus femoris is unique because it crosses both the hip and knee joints, making it a powerful hip flexor. A strain is a pull or tear in the muscle or tendon, often caused by a sudden, forceful movement like sprinting or kicking.
A strain presents with sudden, sharp pain at the front of the hip. Subsequent swelling and muscle weakness make lifting the knee toward the chest particularly difficult and painful. Unlike structural causes, these soft tissue issues are characterized by inflammation and tenderness in the muscle or tendon area.
Immediate Self-Care and Medical Triage
For immediate self-care, modify activity and avoid the deep hip flexion movement that causes pain. Temporarily avoid activities like deep squatting, kneeling, or prolonged sitting in low chairs to prevent further irritation. Over-the-counter non-steroidal anti-inflammatory drugs (NSAIDs), such as ibuprofen or naproxen sodium, can be taken as directed to manage pain and reduce inflammation.
Use ice or a cold pack for 10 to 20 minutes, several times a day, especially in the first 48 to 72 hours following acute pain or swelling. If the pain is chronic or related to muscle stiffness, applying moist heat or a warm bath for 10 to 20 minutes can help relax tight muscles and promote circulation. Maintain mobility with gentle, low-impact activities, such as swimming or cycling, that do not force the hip into the painful deep flexion position.
Knowing when to transition from self-care to professional evaluation is important for accurate diagnosis. Seek medical attention if the pain persists for more than two weeks despite consistent self-care efforts. Immediate medical care is necessary if you experience red flag symptoms. These include:
- An inability to bear weight on the leg.
- Sudden and severe pain.
- Signs of a systemic infection, such as fever or chills.
A locking or catching sensation in the hip joint, which suggests a possible labral tear or loose body, also warrants a medical visit. The diagnostic process begins with a physical examination where a doctor tests your range of motion and attempts to reproduce the pain. This is followed by imaging, such as X-rays, to assess bone structure for conditions like FAI or arthritis. An MRI may also be used to visualize soft tissue damage like labral tears or tendinitis.