Total Hip Arthroplasty (THA) involves replacing a diseased or damaged hip joint with an artificial implant made of metal, plastic, or ceramic components. This operation is highly effective for relieving pain and restoring mobility for millions suffering from severe arthritis. However, these implants are subject to wear over time and are not designed to last indefinitely. The eventual necessity of replacing a failed implant leads to revision surgery, raising the question of how many times this cycle can be repeated.
The Expected Durability of a Primary Hip Replacement
Modern total hip replacements are highly successful, with the majority of patients experiencing significant long-term relief. Current data indicates that approximately 80% of primary hip implants function well for 20 years or longer. Advancements in materials science, such as highly cross-linked polyethylene components, mean some implants may last 25 years or more.
Implants eventually require revision for several reasons, the most common being aseptic loosening. This occurs when the bond between the implant and the bone fails, often due to the body’s reaction to microscopic wear debris. Other frequent causes of failure include mechanical wear, dislocation, and periprosthetic infection.
Aseptic loosening and wear-related failure typically occur many years after the initial procedure. In contrast, complications like dislocation and deep infection can happen much earlier. The patient’s age and activity level significantly influence the longevity of the implant, as younger, more active patients place greater stress on the artificial joint.
Addressing the Numerical Limit of Revision Surgery
There is no specific, fixed number of times a hip can be replaced, as the constraint is biological, determined by the condition of the patient’s surrounding bone and soft tissues. Each subsequent revision procedure becomes progressively more complex and carries an increased risk profile.
The success rate and expected lifespan of the replacement implant decrease significantly with every re-operation. For instance, a primary hip replacement may last over 20 years, but a second revision might last only seven years, and a third only three years. This trend of diminishing returns limits the number of total procedures.
Revision surgery is associated with a substantially higher risk of complications compared to the initial operation. The risk of deep periprosthetic joint infection can be two to five times higher than in a primary surgery. Surgeons often limit major revisions to three or four, as further attempts offer a poor trade-off between risk and functional outcome.
The Impact of Repeated Procedures on Bone Stock
The ultimate biological constraint on the number of hip replacements is the degradation of the patient’s own bone, referred to as “bone stock.” Removing a failed implant requires removing host bone to prepare the site for new hardware, and this cumulative loss weakens the hip structure.
This degradation is exacerbated by stress shielding, where the rigid implant prevents normal mechanical forces from reaching the surrounding bone. This lack of stress signals the body to resorb the unused bone, leading to thinning of the femur and acetabulum. Severe bone loss makes it difficult to securely anchor a new implant, compromising its stability.
When bone stock is severely deficient, surgeons use specialized techniques, including bone grafts to rebuild damaged areas. Alternatively, they may implant custom-made metal cages or modular stems that bypass the weakened bone and anchor into healthier tissue.
Non-Replacement Options for End-Stage Joint Failure
When bone stock is too depleted or the risk of infection is high, further revision arthroplasty may be ill-advised. In these end-stage scenarios, surgeons consider two primary surgical alternatives that do not involve implanting a new hip joint. These salvage options are intended to control pain rather than restore full function.
Hip Fusion (Arthrodesis)
Hip fusion, or arthrodesis, involves surgically welding the femur and the pelvis together to eliminate movement in the joint. While this results in a permanently stiff hip, it provides excellent pain relief and stability, allowing patients to bear weight without pain. Arthrodesis is considered a better option for younger, active individuals who can tolerate the resulting gait change and increased stress on their lower back and knee.
Resection Arthroplasty (Girdlestone Procedure)
The Girdlestone procedure, or resection arthroplasty, is often reserved as a final resort, particularly in cases of uncontrollable infection. This operation involves removing the femoral head and neck without replacement, leaving a space where the hip joint once was. The leg is shortened and supported by muscle and scar tissue, resulting in a flail, unstable hip. The functional outcome is often poor, requiring patients to use walking aids or a wheelchair. However, the procedure is effective at eliminating infection and providing a pain-free, albeit functionally limited, outcome.