Hip pain after knee replacement surgery can be confusing. While the procedure focuses on alleviating knee discomfort, the body is an interconnected system. Pain can emerge in areas seemingly unrelated to the surgical site, leading to unexpected hip symptoms.
Understanding Referred Pain
Referred pain is a neurological phenomenon where discomfort originating in one part of the body is perceived in a different location. This occurs because nerves from various bodily regions converge as they enter the spinal cord. The brain can misinterpret the true source of the pain signals, attributing them to a different area along the same nerve pathway.
For instance, the nerves supplying the knee and hip joints share common origins in the lumbar spine, specifically the femoral and obturator nerves. This shared innervation means that irritation or inflammation in the knee area following surgery can send signals that the brain interprets as pain coming from the hip. The saphenous nerve, a branch of the femoral nerve, innervates both the anterior and medial aspects of the knee and contributes to this referred sensation.
Compensatory Mechanics and Gait Alterations
The body instinctively adapts its movement patterns to protect an injured or recovering joint, and knee replacement is no exception. These adaptations, while initially helpful, can place abnormal stress on other joints, particularly the hip. Altered walking patterns, or gait changes, are common after knee replacement as the body adjusts to the new joint and recovers from surgical trauma. Patients may limp, favor the operated leg, or walk slower, which can cause uneven weight distribution and increased loading on the hip joint.
Muscle imbalances frequently develop or become more pronounced following surgery. Pre-existing weakness in muscles like the gluteals or core, combined with disuse or altered movement patterns during recovery, can strain the hip. For example, if the quadriceps muscles on the front of the thigh are too dominant, they can compress the knee joint and transfer stress to the hip. An increase in activity or incorrect exercise during rehabilitation can also lead to overuse of hip structures.
Pre-existing or Unmasked Hip Conditions
Sometimes, hip pain after knee replacement is not a direct consequence of the knee surgery itself, but rather an underlying hip condition that was present but overshadowed by more severe knee pain. Osteoarthritis of the hip, a common degenerative joint condition, might have been developing simultaneously with knee arthritis. Before knee replacement, the intense knee pain often masked the less prominent hip discomfort, making it noticeable only once the primary knee issue is resolved.
Conditions such as trochanteric bursitis or gluteal tendinopathy can also become apparent or exacerbated post-surgery. Trochanteric bursitis involves inflammation of the bursa, a fluid-filled sac located on the outer side of the hip, and can cause pain that radiates down the thigh. Changes in biomechanics or muscle imbalances after knee replacement can increase stress on this area, contributing to bursitis. Spinal issues in the lower back can also refer pain to the hip, and these symptoms might become more pronounced as the patient’s focus shifts from the knee.
When to Seek Medical Advice
If hip pain persists or worsens after knee replacement surgery, or if new symptoms emerge, consulting a healthcare professional is advisable. Pain that does not gradually improve with time or significantly interferes with daily activities or rehabilitation progress warrants evaluation. New symptoms such as swelling, redness, warmth, fever, or an inability to bear weight should prompt immediate medical attention, as these could indicate a more serious issue like infection.
Any numbness, tingling, or a sensation of the joint “giving out” are also important signs to report. A healthcare provider can accurately diagnose the cause of the hip pain through a comprehensive examination, which may include physical tests, imaging studies like X-rays or MRI, and sometimes diagnostic injections. Identifying the specific cause is important for determining the most appropriate course of action.