Dr. Thorsten Gehrke, MD is a nationally and internationally renowned specialist in joint surgery. He has built a reputation through his many years of experience and outstanding expertise, particularly in the field of hip and knee endoprosthetics. Since 2005, he has served as Medical Director and Chief of Orthopedics and Surgery at the prestigious ENDO Clinic in Hamburg, one of the world's leading specialty clinics for bone, joint, sports, and spinal surgery.
In his role, Dr. Gehrke oversees a wide range of orthopedic treatments that go well beyond conventional endoprosthetics. A particular focus of his practice lies in the implantation and revision of hip and knee prostheses—both in aseptic and septic cases. He is regarded as one of the leading global experts, especially when it comes to infected prostheses. In addition to these complex procedures, the ENDO Clinic also performs corrective osteotomies, arthroscopies, and ligament reconstructions.
The spectrum of endoprosthetic care also includes shoulder and elbow joints. The clinic further specializes in the treatment of foot disorders and injuries—such as through arthrodesis, corrective procedures, or the use of ankle prostheses—as well as spinal surgery, particularly for decompression, spinal fusion, and disc operations. This demonstrates the extensive surgical capabilities of the internationally renowned specialty clinic. The ENDO Clinic Hamburg, where Dr. Gehrke works, has a decades-long history as a center for highly specialized endoprosthetic care. Since its founding in 1976, more than 165,000 joint prostheses have been implanted there.
Each year, over 8,000 patients from both Germany and abroad seek treatment at the clinic. With this high volume of cases, an interdisciplinary team, and an uncompromising commitment to quality, the ENDO Clinic ranks among the world's leading institutions of its kind. In his daily work, Dr. Gehrke places great emphasis on providing individualized and holistic patient care. His goal is to restore the mobility and quality of life that may have been lost due to joint conditions or injuries. He combines surgical precision with cutting-edge technology, scientific grounding, and a high degree of empathy.
The editorial team at the Leading Medicine Guide had the opportunity to speak with Dr. Gehrke about complications in endoprosthetics—particularly with regard to potential infections.
Endoprosthetics, meaning the surgical replacement of joints with artificial implants, is now considered one of the most successful and frequently performed procedures in modern orthopedics. Hip and knee prostheses in particular provide many patients with advanced joint degeneration a significant improvement in quality of life, mobility, and pain relief. Despite high success rates and medical advancements, the procedure still carries inherent risks. As with any surgery, complications can occur—one of the most serious being periprosthetic infection, an infection in the area surrounding the implant. These infections pose a major challenge in endoprosthetics and require specialized diagnosis and treatment.
Periprosthetic infections are among the most serious complications in endoprosthetic procedures and represent a significant challenge for both patients and healthcare teams.
Despite major advancements in implant technology, surgical techniques, and perioperative care, infections cannot be entirely eliminated. They can lead to significant impairments in quality of life and often require lengthy revision surgeries along with intensive antibiotic therapy. This makes it all the more important to thoroughly assess and minimize individual infection risk prior to undergoing an endoprosthetic procedure.
“One of the most common and important risk factors is obesity—specifically morbid obesity. We know that when the BMI exceeds 40, the risk of infection increases exponentially. Another major risk factor is malnutrition—if the patient has poor nutritional status, or eats an unbalanced or incorrect diet. This can, for example, lead to bacterial colonization in the gallbladder, and those bacteria can eventually reach and infect a prosthesis. Nutrition truly plays a central role. This also includes diets or dietary changes before surgery—but we are still in the early stages in terms of clear recommendations.
Another very important factor is smoking. There are now clear recommendations that patients should stop smoking at least three months before surgery. Of course, that’s not always easy to implement. In countries like the U.S., it’s handled very strictly—they even test nicotine levels in the blood, and if they’re too high, surgery is not performed. We can’t enforce that as strictly here, but the scientific correlation is well established: smoking significantly increases the risk of infection. Interestingly, depression is also a risk factor. Many people wonder why, but depressed patients often struggle with hygiene or are less likely to follow medical advice—both of which increase the risk of complications,” explains Dr. Gehrke, adding:
“Another key issue is joint injections. If a patient has received an injection—such as corticosteroids—into the joint within three to six months prior to surgery, the risk of infection increases dramatically. Many people are unaware of this. Diabetes is also a major risk factor, especially if it is poorly managed. There are indicators, such as the HbA1c value, that show how well blood sugar is controlled. If this value is too high, the risk of infection also rises sharply. These are all factors that can be influenced—with discipline. Patients can actively help reduce their own risk. Of course, there are also inherent, non-modifiable risks—for instance, serious underlying illnesses or a weakened immune system. But overall, most relevant risk factors can be modified.”
When it comes to obesity, the risk is particularly striking—leaving one to wonder why it's so high. The exact cause is not fully understood.
Dr. Gehrke elaborates: “In patients with severe obesity, tissue circulation around the joint is often poor. This means the body’s immune cells can’t reach critical areas effectively. Additionally, the incisions tend to be larger, increasing the potential entry point for germs. This applies to all joints—whether hip, knee, shoulder, or foot. The spine is a bit of a special case. And again, we return to the issue of bacterial colonization in the gallbladder—which is a very real concern, with clear data supporting it. Patients with a BMI over 40 have an eight- to ten-fold increased risk of infection compared to normal-weight individuals. And it's not just obesity—underweight or extremely thin, cachectic patients with a BMI under 18 are also at significantly higher risk. Both extremes—overweight and underweight—substantially increase the risk.”
So-called hospital-acquired infections—or nosocomial infections—still exist. Anyone entering a hospital inherently carries the risk of exposure to pathogens.
“In specialized clinics like ours, that risk is much lower than in general hospitals. That’s simply because we exclusively treat well-prepared patients. We don’t take emergency cases, people straight off the street, from nursing homes, or accident victims—as is often the case in other facilities. Our patients are usually medically optimized before admission. Still, a residual risk remains. That’s why we take extensive hygiene precautions. It starts before surgery. Patients at increased risk—such as those from care facilities, agriculture, or veterinary professions—undergo swab testing. This determines whether the nose, throat, or other areas are colonized with problematic bacteria. If so, we pre-treat with special ointments or medications to prevent infection.
Additionally, we instruct all patients to thoroughly wash themselves with antiseptic soap the night before and the morning of surgery—from head to toe. That’s standard practice for us. We do a lot to minimize risk. Yet infections remain highly relevant. One can clearly say: roughly one-third of all post-surgical complications are infections. This remains a key issue in surgical medicine,” says Dr. Gehrke.
The clinical symptoms and diagnostic criteria of a periprosthetic infection differ significantly depending on whether it is an acute or chronic form. Both are serious complications in endoprosthetics but differ in terms of symptoms, timing, and diagnostic challenges.
“Pain is the hallmark symptom of any infection—that's a general rule. Of course, pain can have many causes, but if a patient initially has a pain-free interval after surgery and then pain suddenly returns, that should raise red flags. It’s a classic warning sign. On the first, second, or third day after surgery, an infection is usually not yet visible—it takes time to develop.
It’s extremely rare for an infection to become apparent immediately—on the same day or shortly thereafter. That only happens in exceptional cases. Most infections first appear at the wound site. If the wound is red, oozing, or continues to bleed, this can be a clear indicator of a developing infection. Such signs must always be taken seriously. Additionally, infections can be detected through specific blood markers. One of the most important is CRP, a marker of inflammation that is routinely monitored after surgery. A rising level can be another red flag. Then there are general symptoms like fatigue, fever, or night sweats—often the first systemic signs that something is wrong,” explains Dr. Gehrke.
However, most infections do not occur immediately after surgery but develop later—often one or two weeks post-op. The majority are known as late infections, which can even appear months or years after the procedure. “We differentiate between acute and late infections: acute infections develop within the first three to four weeks after surgery. Anything beyond that is considered a late infection. But regardless of timing, pain is almost always the main symptom. So if pain returns or worsens, the treating physician must take action. Targeted diagnostics then follow—such as blood tests or joint fluid analysis—to identify the cause and begin treatment early if needed,” Dr. Gehrke emphasizes.
Biofilms play a central role in the pathogenesis of periprosthetic infections and represent one of the greatest therapeutic challenges.
A biofilm is a complex cluster of microorganisms that attach to the surface of an implant and embed themselves in a self-produced matrix of extracellular polymers. This structure protects the bacteria from the body’s immune system and from systemically administered antibiotics, as the medications often cannot adequately penetrate the biofilm.
“The biofilm is absolutely central—that’s what it all comes down to. Let me explain briefly: every implanted prosthesis—whether hip, knee, shoulder, or another joint—is a potential site for infection. And this applies not just to prostheses, but also to foreign bodies like heart valves or permanent catheters. The reason is simple: it’s foreign material. Most prostheses are made of metal. And metal has no defense mechanisms—it can’t protect itself against bacteria. The body does have very effective defense strategies—phagocytes, immune cells, all of that works very well in native tissue. But none of that applies on the surface of a prosthesis. That’s where foreign-body infections occur.
The bacteria reach the prosthesis, adhere to the metal surface—there are various ways they do this—and then begin to form a mucus layer around themselves. That’s the so-called biofilm. Bacteria love mucus, warmth, and moisture—and they create exactly that environment on the prosthesis. Once they’re established, they produce this slimy matrix in which they can multiply efficiently. They gradually coat the entire prosthesis with this biofilm. In the beginning, the patient notices nothing. The real danger starts when bacteria escape from the biofilm and spread throughout the body. Then they can release toxins that trigger severe—sometimes life-threatening—infections,” explains Dr. Gehrke.
“The next obvious question is: can this biofilm be treated with antibiotics? Unfortunately, the harsh truth is: no. Within that mucus, the bacteria are extremely well protected—they are up to a thousand times more resistant to antibiotics than free-floating bacteria in the bloodstream. The antibiotic dose needed to penetrate the biofilm would be intolerable for the human body. It simply doesn’t work. That means: as long as the bacteria remain in the biofilm on the prosthesis, no antibiotic in the world will help. In such cases, there is only one solution—the prosthesis must be removed. Only then can the biofilm and its bacteria be completely eliminated. Timing is critical: if the infection is detected within the first three weeks after surgery, the biofilm may not yet be fully formed.
Then, there’s still a chance to reopen the wound, thoroughly flush the joint, remove all infected tissue, and use antiseptic solutions. With some luck and targeted treatment, the infection can be controlled without replacing the prosthesis. But if the infection appears later—after three or four weeks—the biofilm is fully established. Flushing is no longer sufficient. In such cases, complete removal of the prosthesis is the only option. This highlights how important early detection is—the sooner we intervene, the better the chance of preserving the prosthesis.”
Evaluating the effectiveness of single-stage versus two-stage revision procedures for infected knee and hip prostheses is a central topic in the treatment of endoprosthetic infections.
“Anyone with a prosthesis is fundamentally at risk if they develop a bacterial infection elsewhere in the body. Take, for example, a bladder infection—which many women experience more frequently. That’s a bacterial infection—we’re only talking about bacteria here, not viruses or the flu. If such bacteria are present in the body, they can travel through the bloodstream to the prosthesis and colonize it, causing an infection. That’s why any bacterial infection, such as a bladder infection, must be treated promptly and thoroughly with antibiotics.
Here’s an important point: when we talk about replacing an infected prosthesis, many assume that the new prosthesis remains at risk. And unfortunately, that’s true. There’s no way around removing the infected prosthesis. After that, we aim to eliminate all risk factors. There are two surgical strategies: first, the single-stage revision—in which the old, biofilm-covered prosthesis is removed, the surrounding tissue is cleaned, and a new prosthesis is implanted in the same operation. Second, the two-stage revision—where the prosthesis is removed, everything is thoroughly disinfected, and the patient goes several months without a prosthesis until we are certain the infection is gone. Only then is a new prosthesis implanted.
Our clinic is internationally recognized for having perfected the single-stage revision so successfully that our outcomes are just as good—or even better—than those of the two-stage approach. This is a major relief for patients, because going months without a hip or knee is incredibly burdensome. However, this method requires a high level of expertise. It’s not just the surgeon who matters, but the entire team: infectious disease specialists, microbiologists, nursing staff, physical therapists—everyone works together closely. This approach is called the multidisciplinary model, which, unfortunately, is consistently implemented in only a few specialized centers worldwide,” emphasizes Dr. Gehrke.
Infections can, in the worst cases, lead to limb loss or even life-threatening sepsis. That’s why this topic must never be taken lightly.
“Given how frequently these operations are performed—we’re talking about several hundred thousand procedures annually in Germany—it’s all the more important to prepare each patient as thoroughly as possible. This includes strict hygiene measures before and during surgery, careful monitoring of risk factors such as blood sugar levels, and targeted preparation of patients in high-risk groups, like those from nursing homes or agricultural settings.
Despite all this, the infection rate in primary procedures is not at zero, but typically around one in one hundred cases. That sounds small but amounts to several thousand infections per year—a significant number. Especially in severely obese patients—with a BMI over 40—the risk of infection is so high that I insist on weight reduction before proceeding with surgery. This may include recommending bariatric surgery (like gastric operations) or the use of new weight-loss injections.
As the responsible surgeon, I simply cannot justify an operation under such high-risk conditions. The patient may be suffering greatly, in pain, and barely able to walk—but without weight reduction, the risk would be too high. Of course, there are exceptions: if someone is severely obese, nearly immobile, and in extreme distress, we must evaluate the risks and benefits carefully on an individual basis. In such cases, surgery may be performed earlier under strict medical guidance and hygiene protocols. But that is the exception, not the rule. Most of the time, patients can be prepared within three to six months to significantly reduce the surgical risk and allow the prosthesis to be implanted safely,” says Dr. Gehrke.
In general, the rule is: the more specialized a hospital is in such procedures, the lower the risk of infection. There is a well-documented correlation between the number of surgeries performed and the infection rate.
Clinics that perform these types of operations only occasionally typically have significantly higher infection rates. That’s why choosing the right hospital is a crucial factor in minimizing infection risks. In facilities like the ENDO Clinic, where most procedures are planned, the bacterial burden is entirely different—and significantly lower—than in hospitals that treat many emergency patients, such as trauma victims. There, the exposure to pathogens is much higher, which increases the risk.
“For patients with infections, it is therefore essential to seek care at a specialized center. There are not many of these in Germany, and the ENDO Clinic is one of the largest worldwide. Internationally, the importance of this issue is growing. In the U.S., as well as in countries like France and Spain, efforts are being made to consolidate infection cases and refer patients with severe complications to specialized centers with experienced teams. There have been repeated attempts to coat prostheses with antibacterial substances such as antibiotics, iodine, or silver. So far, however, these approaches have not proven successful. The main reason is that bacteria are incredibly smart. There are countless strains, constantly evolving new resistances and behaving differently in the body—so they can't be easily eradicated.
Silver and gold do have antibacterial properties, but a prosthesis made entirely of gold is simply unrealistic. And silver, while effective, is toxic to surrounding tissue and can cause side effects. So there is no truly practical solution yet. That’s why it’s all the more important to maintain good overall health and prepare the body as best as possible before surgery. The average infection rate is around one percent, at most two percent. In highly specialized clinics like the ENDO Clinic, it's even lower—usually under one percent,” concludes Dr. Gehrke.
Dr. Gehrke – thank you very much for your valuable insights and explanations!
