Problems originating in the hip can cause pain felt in the knee, a phenomenon known as referred pain. This occurs because the brain interprets a pain signal from one location as coming from another due to shared nerve pathways. A dysfunction in the hip joint also alters movement patterns, creating a mechanical chain reaction that places undue stress on the knee joint below it.
How the Hip and Knee Are Connected
The knee and hip joints are linked by a complex network of muscles, tendons, and nerves that ensure coordinated movement of the leg. This integrated system means that an issue in the hip can directly impact the alignment and loading of the knee. For example, a hip condition can cause a slight change in the way a person walks, creating an abnormal distribution of force that stresses the knee joint.
The most direct reason for referred pain is the shared sensory nerve supply. Both joints receive nerve branches from the femoral and obturator nerves, which originate in the lower spine. When irritation or inflammation occurs in the hip, these nerves transmit a pain signal that the brain mistakenly localizes to the end of the nerve branch, often around the knee.
The saphenous branch of the femoral nerve supplies both the hip joint capsule and sensation to the inner and front part of the knee. Because of this neurological overlap, pain signals traveling along this common pathway are frequently perceived as pain in the anterior or medial knee, even when the knee itself appears normal.
Common Hip Conditions That Cause Knee Pain
One of the most frequent causes of referred knee pain in older adults is hip osteoarthritis (OA), a degenerative condition involving the wear and tear of the joint cartilage. As the cartilage breaks down, the resulting friction and inflammation trigger pain signals that radiate down the thigh to the knee. Studies show that many patients with confirmed hip OA report knee pain as their primary or only symptom.
Femoroacetabular Impingement (FAI)
In younger, active individuals, FAI is a common structural problem that can manifest as anterior knee pain. FAI occurs when the ball and socket of the hip joint have an irregular shape, causing abnormal rubbing during movement. This altered joint mechanics can force the femur into external rotation, leading to increased stress and pain around the kneecap.
Labral Tears and IT Band Syndrome
A hip labral tear involves the ring of cartilage lining the hip socket. A tear in this structure typically produces pain deep in the groin, but this discomfort can radiate down the front of the thigh to the knee. Similarly, iliotibial band syndrome (ITBS) causes pain on the outer side of the knee, though the root of the problem is often tightness or dysfunction in the hip and pelvic muscles where the IT band originates.
Signs Your Knee Pain Originates in the Hip
Several indicators suggest that knee pain is actually being referred from the hip joint. A primary sign is the relative lack of physical findings directly at the knee itself. If the knee is not swollen, red, or tender to the touch, and there is no instability or mechanical catching, the pain source is less likely to be the knee.
Pain that is reproduced or worsened by specific movements of the hip is a strong clue. When a medical professional gently rotates the hip inward or outward, pain felt in the knee during this maneuver points toward a hip origin. This movement directly stresses the hip joint and surrounding structures, which are often compromised in conditions like hip arthritis.
The location of the pain can be revealing; hip-related knee pain is most often felt on the anterior (front) or inner side of the knee. Patients may also report associated stiffness or a deep ache in the groin, buttock, or side of the hip, even if the knee pain is the most noticeable complaint. Difficulty with activities that require deep hip flexion, such as putting on socks or shoes, further suggests the hip is the true source of the discomfort.
Seeking Medical Diagnosis and Treatment
If knee pain is persistent and lacks clear signs of injury or local tenderness, consulting an orthopedic specialist or physical therapist is the appropriate next step. A thorough physical examination assesses the range of motion in both the hip and the knee to identify limitations or pain reproduction during hip movements. Limited internal rotation of the hip, for instance, is a highly indicative sign of underlying hip pathology.
Diagnostic imaging often begins with standard X-rays of the hip, even if the patient only complains of knee pain. These images can reveal structural issues like joint space narrowing, indicating hip osteoarthritis, or abnormal bone shapes characteristic of FAI. In some cases, a magnetic resonance imaging (MRI) scan may be ordered to evaluate soft tissues, such as the labrum or cartilage within the hip joint.
Treatment for hip-originating knee pain focuses entirely on addressing the problem at its source. Physical therapy is a common approach, aiming to restore hip strength, flexibility, and stability to normalize the mechanics of the entire leg. Anti-inflammatory medications and joint injections can help manage acute pain, but for advanced conditions like severe hip osteoarthritis, total hip replacement surgery may be necessary to eliminate the referred knee pain.