Total hip arthroplasty (THA) is a highly successful procedure that restores mobility and relieves chronic hip pain. Despite its effectiveness, a significant number of patients experience persistent or new-onset thigh pain following surgery. This discomfort, often called femoral stem pain, results from a complex interaction between the artificial implant, the surrounding bone, and the soft tissues. Understanding the origins of this pain—which can range from mechanical issues to soft tissue strain or severe complications—is essential for effective diagnosis and treatment.
Pain Stemming from Implant Integration
Thigh pain frequently arises from the body’s reaction to the metallic stem inserted into the femur, particularly with uncemented implants that rely on bone ingrowth for stability. Uncemented stems are associated with a higher initial incidence of thigh pain compared to cemented stems. The difference in material stiffness between the metal implant and the living bone is a major contributing factor to discomfort.
A primary mechanical cause is stress shielding, where the stiff femoral stem carries a disproportionate amount of the load, shielding the upper femur from normal stresses. This causes the bone density to decrease over time (osteolysis), which can weaken the proximal femur. The stress that is transferred distally can concentrate at the tip of the stem, causing localized mid-thigh pain often described as an ache during weight-bearing activities.
A separate, later-onset cause of pain is aseptic loosening, where the implant migrates or becomes unstable without infection. This occurs as the interface between the bone and the implant breaks down, often due to wear debris causing inflammation and bone loss. Loosening typically presents as “start-up” pain, felt when activity begins, suggesting micromotion at the bone-prosthesis interface.
Musculoskeletal and Soft Tissue Sources
Pain after THA is not always related to the implant itself but can originate from the surrounding muscles, tendons, and nerves disturbed during surgery. Changes in leg length or gait mechanics following the procedure can place abnormal tension on soft tissues, leading to inflammation.
Tendinopathy, or inflammation of the tendons, is a common source of persistent thigh discomfort. Iliopsoas tendinitis can develop when the psoas tendon rubs against an improperly positioned socket component, causing pain that radiates down the anterior thigh. Similarly, gluteal tendinopathy affects the hip abductor tendons near the greater trochanter, causing pain radiating down the lateral thigh.
Irritation or damage to peripheral nerves during the surgical approach is another significant cause of thigh pain. The lateral femoral cutaneous nerve is particularly vulnerable, and its irritation (meralgia paresthetica) results in numbness, burning, or tingling along the outer thigh. The femoral nerve can also be affected by scar tissue or retraction, leading to pain and sometimes weakness in the anterior thigh.
Inflammation of fluid-filled sacs, known as bursitis, also contributes to thigh pain. Trochanteric bursitis, involving the bursa over the bony prominence of the femur, causes pain on the side of the hip that may extend down the thigh. These soft tissue issues are often aggravated by specific movements and result from altered mechanics.
Urgent and Severe Post-Surgical Complications
While many causes of thigh pain after THA are chronic and manageable, some represent acute, severe complications that require immediate medical intervention. Recognizing the signs of these urgent issues is important for preserving the patient’s health and the longevity of the implant.
One serious complication is a Periprosthetic Joint Infection (PJI), which can manifest as persistent or worsening thigh pain. Acute infection symptoms often include systemic signs like fever and chills, accompanied by localized warmth, redness, and wound drainage. Even chronic, low-grade infections can present as unexplained, persistent pain, necessitating prompt blood work.
A Periprosthetic Fracture involves a break in the bone near the implant, which can occur during surgery or later due to a fall or stress. A sudden onset of severe, sharp thigh pain, often accompanied by the inability to bear weight, suggests this complication. These fractures compromise the stability of the implant and require complex surgical management.
Another concern is the formation of a Deep Vein Thrombosis (DVT), a blood clot usually forming in the deep veins of the leg or thigh. DVT presents as throbbing pain, tenderness, swelling, and redness in the affected limb. If a portion of this clot travels to the lungs, it causes a pulmonary embolism, which is a medical emergency.
Determining the Cause and Next Steps
The diagnostic process for thigh pain following hip replacement is a methodical investigation to pinpoint the specific source of discomfort. The initial step involves a thorough physical examination where the physician assesses the pain location, evaluates hip range of motion, and checks for signs of soft tissue irritation. This helps distinguish between pain originating from the joint itself and pain from surrounding musculoskeletal structures.
Radiographic imaging is the first-line investigation, beginning with plain X-rays of the pelvis and hip. These images evaluate the position of the femoral stem, check for signs of implant migration or loosening, and look for bone changes. Advanced imaging, such as MRI or Ultrasound, may be used if soft tissue pathology, like tendinopathy or bursitis, is suspected.
To rule out infection or systemic inflammation, blood work is routinely performed, specifically checking inflammatory markers like C-reactive protein (CRP) and the erythrocyte sedimentation rate (ESR). Elevated levels suggest an ongoing inflammatory process, which may indicate PJI. If infection is strongly suspected, a joint aspiration may be performed to analyze the fluid for bacteria.
Management strategies are tailored to the underlying cause. Soft tissue pain, such as tendinopathy or bursitis, often responds well to physical therapy adjustments, activity modification, and targeted anti-inflammatory treatments. If mechanical issues like stress shielding are the primary source, initial treatment is non-operative, focusing on pain management as the bone adapts. However, if imaging confirms implant loosening, a periprosthetic fracture, or an established infection, revision surgery becomes the necessary course of action.