A knee injury can lead to pain experienced in the hip, a phenomenon frequently observed in clinical practice. The human body is an interconnected mechanical system, and a problem in one joint rarely remains isolated. When the knee is injured, painful, or unstable, the body immediately alters its movement patterns to protect the compromised joint. This change in mechanics shifts strain and load up the leg to the hip joint and surrounding musculature, often resulting in secondary pain.
The Biomechanical Link: Understanding the Kinetic Chain
The connection between the knee and hip is understood through the concept of the lower extremity kinetic chain. This chain describes how the joints of the foot, ankle, knee, and hip function as a linked system, where motion at one segment affects all others. The femur, or thigh bone, is the segment shared by both the hip and knee joints, making their functional relationship direct.
The hip is a ball-and-socket joint providing multiplanar motion, while the knee functions primarily as a hinge joint. When a knee injury, such as a meniscal tear or ligament sprain, causes pain or restricts movement, the body must adjust how it uses the entire limb to maintain balance and locomotion. These adjustments are executed by the muscles and joints higher up the chain, particularly the pelvis and the hip.
The stability of the hip, pelvis, and trunk is necessary for proper mechanics at the knee. When the knee is compromised, the hip musculature must compensate by stabilizing the thigh bone to reduce stress on the knee. This protective action places demands on the hip’s muscles, leading to strain and discomfort.
Compensation Patterns That Overload the Hip
The most common mechanism for knee-induced hip pain involves the body adopting altered movement patterns to avoid pain. This is often referred to as an antalgic gait, or limping, which changes how weight is distributed across the lower limb. The stance phase, when the foot is on the ground, becomes shorter on the injured side to quickly offload the painful knee.
This uneven weight bearing causes the hip abductor muscles, particularly the gluteus medius and gluteus minimus, to work harder. These muscles keep the pelvis level during walking, and their overuse from compensating for a painful knee can lead to localized hip pain, often felt on the side of the hip or toward the buttocks. This strain can manifest as tendinopathy (irritation of the tendons) or trochanteric bursitis, a common cause of lateral hip pain.
A knee injury that prevents full extension or flexion forces the hip to absorb more shock than the knee normally manages. If the knee cannot straighten completely due to swelling or damage, the hip flexor muscles may become chronically tight and overactive to stabilize the shortened limb. This constant tension can lead to muscle strain or irritation of the hip joint.
The protective changes in movement can result in a pelvic shift or tilt. To offload the injured leg, the body may lean or shift its center of gravity, which unevenly loads the muscles of the hip and lower back. Over time, this mechanical imbalance places strain on the hip joint capsule and surrounding ligaments, leading to chronic discomfort perceived as hip pain originating from the underlying knee problem.
Diagnosis and Management
Recognizing that hip pain may be secondary to a knee issue requires a thorough differential diagnosis. The physical examination involves assessing the patient’s gait and checking the range of motion and specific pain points at both the knee and the hip. Pain reproduced by specific knee movements or palpation of the knee is a strong indicator that the hip symptoms are compensatory.
Clinicians look for characteristic signs such as weakness in the hip abductor muscles on the injured side, confirming a protective compensation pattern. Imaging studies of the hip may appear normal or show only mild changes, supporting the conclusion that the pain is referred or mechanical, rather than a primary hip pathology like severe arthritis.
Effective treatment must focus on correcting the source of the problem: the original knee injury and subsequent altered mechanics. Physical therapy is the standard management approach, concentrating on improving the function and stability of the knee joint. This includes strengthening the muscles that support the knee, such as the quadriceps and hamstrings, to restore its ability to bear weight.
A rehabilitation program simultaneously targets the hip and core musculature to reverse the compensatory patterns. Exercises focus on strengthening the gluteus medius and other hip stabilizers to allow the pelvis to remain level during movement. By restoring normal biomechanics to the entire lower extremity, the load on the hip is relieved, allowing the secondary hip pain to resolve once the underlying knee dysfunction is addressed.