In Germany, more than 2 million people currently live with a hip prosthesis and over 1.5 million with a knee prosthesis. Altogether, this amounts to approximately 3.5 to 4 million people who have an artificial hip or knee joint. Sometimes these prostheses need to be replaced. Around 19,000 hip revision surgeries and roughly 10,000–12,000 knee revision surgeries are performed each year. The editorial team of the Leading Medicine Guide spoke with Prof. Dr. Konstantinos Anagnostakos, a specialist in hip and knee endoprosthetics, about the specific challenges of revision surgeries and what patients need to be aware of.
A hip or knee prosthesis must definitely be replaced when certain problems arise that significantly impair the function or comfort of the joint. The most common reason for a revision is loosening of the implant, which can occur after several years due to wear and mechanical stress.
“There are many reasons why a prosthesis—whether hip or knee—needs to be replaced. The most common cause is loosening of the implant after some years. This loosening results from wear and continuous mechanical load. For the hip joint, infections, dislocations, and periprosthetic fractures are additional factors. Interestingly, we do not have more infections in Germany today than we used to; rather, diagnostics have improved significantly in recent years. This allows us to identify that many cases in which we previously did not know why the prosthesis caused pain were often due to an underlying infection. For the knee joint, stability also plays an important role in addition to implant loosening. There are various types of knee prostheses, some of which rely on the posterior cruciate ligament, while others require the collateral ligaments to ensure stability. If one of these ligaments does not function properly, it leads to instability of the prosthesis and may necessitate revision surgery. The urgency of revision depends on the underlying cause. In cases of acute infection or fracture, the prosthesis must be replaced promptly. However, if it is only classic loosening that has been identified over weeks or months, the orthopedic surgeon will typically recommend an elective revision. This is not an emergency procedure that must be carried out immediately. It is important to distinguish between the different causes and their urgency,” explains Prof. Dr. Anagnostakos as he begins.
Individual bone quality significantly affects primary stability, osseointegration, and the long-term risk of loosening in hip and knee implants. Low bone density, disrupted microarchitecture, and reduced mineralization lead to increased micromotion at the implant–bone interface, promote fibrous rather than bony ingrowth, and increase the likelihood of aseptic loosening.
“There are various reasons why an infection can occur in a hip prosthesis that has already been in the body for some time. In general, we distinguish between three types of infections: acute infections, so-called low-grade infections, and late infections. An acute infection typically occurs within the first four to six weeks after surgery. During this period, the connection to the operation is clear. If a patient has recently undergone surgery and develops symptoms after a week, two weeks, or a month—such as redness, fever, or signs of infection—we know that the infection is directly related to the procedure. Late infections, however, may occur years after surgery. These are often hematogenous, meaning that the patient has an infection elsewhere in the body that spreads through the bloodstream to the prosthesis site. A temporary weakening of the immune system can trigger the infection on the implant. Low-grade infections are more diffuse and may also be related to the initial surgery. If the immune system is functioning well or bacterial counts are low, these infections may not produce acute symptoms immediately. Instead, they may cause mild, nonspecific complaints over a longer period. These symptoms are often so subtle that patients do not associate them with an infection—rather, they experience general issues such as mild pain, swelling, or redness. In such cases, the typical signs of infection such as fever, chills, or pus formation are absent, making diagnosis more challenging,” explains Prof. Dr. Anagnostakos regarding the causes of infection.
Modern hip and knee prostheses are advanced medical devices designed for long service life. Studies show that more than 80% of knee prostheses and around 60% of hip prostheses remain functional after 25 years. However, various factors can affect their longevity..jpg "Partially cemented right hip endoprosthesis with multiple osteolyses (“arrows”) in the stem area indicating a possible infection.")
Partially cemented right hip endoprosthesis with multiple osteolyses (“arrows”) in the stem area indicating a possible infection.
Patient behavior after surgery is also crucial. Excess weight increases mechanical load and accelerates wear, while a normal body weight reduces stress on the prosthesis. Regular, joint-friendly activities such as swimming, cycling, or Nordic walking strengthen muscles and stabilize the joint without excessive strain on the prosthesis. In contrast, high-impact sports such as jogging or skiing may shorten implant longevity. Regular medical check-ups are equally important to detect early signs of loosening or misalignment.
“First and foremost, it is important that the patient understands—ideally during a conversation with the surgeon before the procedure—what goals can realistically be achieved. Patients should remain realistic and take their biological age and any comorbidities into account. Identifying shared goals—whether pain reduction, restoring joint function, or improving mobility—is crucial. After the operation, these goals should be pursued actively. If a patient tries to push for unrealistic outcomes or overloads the joint too early, this may overstrain not only the affected joint but the entire lower extremity. Such overload can significantly slow and complicate the healing process. Furthermore, early excessive weight-bearing—depending on the type of implant, whether cemented or cementless—can also lead to implant loosening,” emphasizes Prof. Dr. Anagnostakos.
Bone quality plays a decisive role in the long-term stability of hip and knee prostheses. If bone density is reduced or the microstructure is compromised due to osteoporosis, the risk increases that the implant will not achieve solid fixation and will loosen over time.
This is especially important for cementless implants, which rely on direct anchoring in the bone. If micromotion occurs between implant and bone, a soft fibrous tissue layer may form instead of stable bony ingrowth, compromising stability. Wear particles from implant materials may also trigger osteolysis through inflammatory processes, further weakening bone strength and increasing the risk of loosening.
Regarding this, Prof. Anagnostakos states: “Especially in cases of suspected osteoporosis, a bone density assessment is useful to better evaluate implant stability. Preoperative diagnostics are crucial, and the surgeon depends on the information provided by the patient. If a patient is known to have osteoporosis, they must inform the surgeon so that an appropriate fixation technique can be chosen. In addition to clinical history, imaging such as X-rays is routinely performed. If these raise suspicion of inadequate bone quality, comprehensive osteoporosis diagnostics—laboratory tests and bone density measurements—are indicated. If reduced bone quality is confirmed, a cemented implant may be more suitable, as it reduces the risk of complications. It is extremely rare that no prosthesis can be implanted due to poor bone density. Medical advances and implant innovations now allow for longer cemented stems that distribute forces more evenly and reduce fracture risk. It is crucial that the surgeon can recognize when a cemented versus a cementless implant is appropriate. Typically, this concerns older patients, often aged 70 or above, who may already have osteoporosis without knowing it. In such cases, diagnosis is often made only during treatment of injuries or within the scope of more extensive examinations.”
To identify these risks early, careful preoperative diagnostics are essential. Bone density is typically measured via DXA (Dual-Energy X-ray Absorptiometry), a method used to assess bone mass and body composition. Supplemental methods such as quantitative CT or high-resolution peripheral CT can provide detailed insights into regional bone structure and trabecular architecture. Laboratory tests, including markers of bone metabolism or vitamin D levels, help identify metabolic disturbances or secondary causes of impaired bone quality. Based on these findings, a personalized decision can be made for cemented or cementless fixation. In practice, patients with good bone quality benefit from cementless systems, while cemented systems are often safer when stability is limited. Precise surgical technique—potentially supported by navigation—also optimizes load distribution and reduces the risk of loosening.
Fracture of the femur in the presence of a cementless bipolar prosthesis (“periprosthetic femur fracture”).
Revision surgeries on hip and knee prostheses are among the most challenging procedures in endoprosthetics due to the unique complexities involved. Unlike primary implantation, the surgeon must work with altered bone conditions, scar tissue, and often significant bone defects. To minimize risks, certified EndoProthetic Centers play a crucial role.
“The challenges of revision surgery vary greatly depending on the specific reason for the procedure. In cases of implant loosening, the main challenges involve managing bone defects, achieving stable fixation of the new implant, and restoring joint function and mobility. In contrast, the priority in infection cases is eradication of the infection. For hip dislocations, restoring joint stability is paramount, while fractures require both fracture management and secure fixation of the new implant components. Careful preoperative analysis and planning are essential to identify and address potential complications. When the surgeon is well prepared and thoroughly evaluates imaging studies, most challenges of revision surgery can be anticipated,” explains Prof. Dr. Anagnostakos, adding:
“One of the greatest risks is underestimating the complexity of the revision procedure—whether due to lack of knowledge or insufficient experience. This can lead to serious problems during surgery. Therefore, it is advisable to undergo revision surgery in specialized centers. These facilities handle higher case volumes and thus possess greater expertise, which significantly improves outcomes and reduces complications such as intraoperative fractures, dislocations, or infections. In Germany, certified endoprosthetic centers such as the Nardini Clinic have distinguished themselves with high procedure numbers and corresponding expertise. Studies show that hospitals with higher caseloads tend to have lower complication rates. For elective procedures, it is worthwhile for patients to seek out specialized facilities even if this requires traveling farther. In acute situations, however, there is no time for long travel, and immediate care is essential.”
At the Nardini Clinic in Rhineland-Palatinate, with two locations (Zweibrücken and Landstuhl), more than 1,200 prosthesis operations are performed each year. This is an impressive number and reflects the clinic’s extensive experience and expertise.
To better illustrate patient considerations, Prof. Dr. Anagnostakos explains: “For patients choosing a hospital, it is not uncommon to select the nearest facility—sometimes without fully considering the quality of care offered. Today, however, patients have far better access to information via the internet and social media. Thirty or forty years ago, such information was extremely limited, and patients often had to rely solely on proximity. Despite today’s wealth of information, medical laypersons should remain cautious, as not everything found online is reliable. Two points are important: First, many health insurers recommend not relying on just one opinion but obtaining a second opinion—an invaluable opportunity for informed decision-making. Second, during the initial consultation with the physician or surgeon, patients should feel well taken care of. There should be a sense of trust and human connection. Patients should never feel like something is being sold to them; the focus must always be on improving their quality of life. A strong doctor–patient relationship is essential for treatment success and patient well-being.”
Every patient’s anatomy is unique, and during revision surgery, it is often difficult to predict the exact extent of bone loss that may occur when removing an implant.
Prof. Anagnostakos emphasizes: “This is why I cannot commit 100 percent—even with preoperative planning—to using prosthesis A, B, or C. A certain degree of flexibility is always required to respond appropriately to intraoperative findings. Depending on what unexpected conditions arise, the surgeon must be able to proceed with option A, B, or C. Therefore, it is crucial that all potentially needed implants and instruments are available on site. It must not happen that the surgical team relies solely on Plan A and does not have Plan B available if unforeseen challenges occur. Interrupting a surgery for this reason would reflect poor preparation, lack of experience, or organizational failure—regardless of the cause.”
In recent years, the number of revision surgeries has not decreased overall, but the underlying causes have shifted. Classic revisions due to aseptic loosening are becoming less dominant, while improved diagnostics have led to increased detection of infections, resulting in more septic revision procedures. At the same time, an aging population contributes to more fractures. Clinics must therefore be well prepared and have sufficient implants and instruments available to handle unexpected emergencies without delay, as any postponement directly affects patient care.
Modern techniques such as navigation-assisted implantation and robotic assistance have significantly advanced endoprosthetics in recent years.
In navigation-assisted surgery, the surgeon is supported by computer systems that use imaging or intraoperative sensors to display the exact positioning of implant components. This helps avoid alignment errors and allows implants to be placed with millimeter precision.
“Navigation-assisted operations and robotics are playing an increasingly important role in medical progress, especially in endoprosthetics. Robotic systems have gained popularity in recent years, both in Germany and worldwide. Existing studies show that robotic-assisted procedures demonstrate good implant longevity and low revision rates. However, it is important to note that these are mid-term results. Long-term data—20 or 30 years after the use of robotic systems—are still pending. It remains to be seen how long-term outcomes will compare, including differences among various robotic platforms. Currently, the positive results we observe pertain primarily to primary implant surgeries, as robotic systems are not yet approved for complex revision surgeries. Nevertheless, I am optimistic that with growing experience and more data, revision endoprosthetics will also benefit from these technologies. When exactly this will happen, and whether hip or knee applications will lead the way, cannot yet be predicted. It is also important to consider dependence on industry developments. Navigation and robotics already offer substantial advantages in primary endoprosthetics, and we can expect innovations in revision surgery as well—though the timeline remains uncertain,” says Prof. Dr. Anagnostakos.
However, robotic systems involve higher costs and significant training requirements. Not every hospital has the necessary equipment, and benefits must be balanced against economic considerations. Nonetheless, the combination of navigation and robotics represents a major advancement that makes endoprosthetic surgery safer and more successful.
Material science in endoprosthetics has made tremendous progress in recent years, aiming to extend the longevity of hip and knee implants and significantly reduce the number of revision surgeries.
“In recent years, major advances have been made affecting many individual components. One example is polyethylene—the material used in the liners of artificial hip cups or certain prosthetic components. Manufacturers now offer highly cross-linked polyethylene, which significantly improves wear resistance and increases implant longevity. Similarly, ceramic components have seen remarkable improvements. Both hip cups and other implants now benefit from enhanced surface coatings, optimized macro-porosity, and improved microstructure. These innovations not only ensure excellent primary stability but also significantly enhance long-term bone ingrowth, resulting in outstanding implant survival. And I believe this development is far from complete. The industry will continue to explore new materials—and this is necessary. Experience has shown that some implants become loose or fail over time for various reasons. Therefore, continuous innovation is essential. Anyone who rests on past achievements risks decreasing quality—and ultimately, this always impacts patients,” emphasizes Prof. Dr. Anagnostakos, concluding our discussion.
Thank you very much, Professor Dr. Anagnostakos, for these valuable insights into revision surgery!
- Specialist in Orthopedics and Trauma Surgery
- Specialization: Endoprosthetics (hip, knee), revision surgery, minimally invasive techniques
- Since September 15, 2025, Chief Physician of the Department of Joint Surgery and Sports Traumatology at Nardini Klinikum Zweibrücken (together with Dr. Burkhardt Muschalik)
- Focus areas: Implantation and revision of hip and knee prostheses; management of complex revision cases (loosened, infected, defective implants); arthroscopic knee, shoulder, and ankle procedures; treatment of acute and chronic sports injuries; minimally invasive techniques for tissue preservation and faster rehabilitation; navigation-assisted implantation for precise prosthesis placement
- Director of a certified EndoProthetic Center (EndoCert® since 2014) with the highest quality standards
- Internationally recognized for expertise in endoprosthetics and revision surgery
