PD Dr. med. Stefan Rahm is a board-certified specialist in Orthopedic Surgery and Traumatology of the Musculoskeletal System with proven expertise in hip and pelvic surgery. As a partner at the Gelenkzentrum Zürich at the Privatklinik Bethanien, he treats patients with a wide range of hip-related conditions – from joint-preserving procedures to complex revision surgeries.
His medical career has taken him through several leading Swiss hospitals, including the Balgrist University Hospital and the Cantonal Hospital St. Gallen. He completed his habilitation in Orthopedics and Traumatology of the Musculoskeletal System in 2019 at the University of Zurich. A particular focus of his work is joint-preserving hip surgery, such as arthroscopic treatment of morphological abnormalities, as well as minimally invasive implantation and revision of hip prostheses. In doing so, he combines modern surgical techniques with individually tailored, patient-centered care. In addition to his clinical practice, PD Dr. Rahm is also deeply engaged in research.
His research has been published in numerous international peer-reviewed journals, and he regularly serves as a speaker and reviewer. He sees patients both at the Privatklinik Bethanien and in public hospitals in the Greater Zurich area.
The editorial team of Leading Medicine Guide spoke with hip specialist PD Dr. Rahm about the various causes of hip pain, the need for joint replacement, and potential revision surgeries.
The hip joint is subjected to enormous stress in everyday life – making early and accurate diagnosis of complaints all the more important. The most common causes of hip pain include femoroacetabular impingement (FAI) and coxarthrosis (hip osteoarthritis). While FAI primarily affects younger, active individuals and, if left untreated, can lead to premature joint wear, coxarthrosis is a degenerative disease that typically occurs at an older age. In both cases, surgical treatment may be necessary. Even after hip joint replacement, complications can arise over time that require a so-called revision surgery. A nuanced evaluation of the causes, diagnostics, and treatment options is therefore essential for sustainable care.
Femoroacetabular impingement (FAI) is a disorder of the hip joint in which an anatomical deformity restricts normal mobility and causes pain. Typically, there is a deviation at the acetabulum (pincer type) or the femoral head/neck junction (cam type), leading to narrowing of the articular cartilage and labrum during hip flexion and rotation. Over time, this chronic friction or repeated abutment can result in cartilage damage and ultimately osteoarthritis of the hip.
In femoroacetabular impingement (FAI), specific structural changes in the hip joint lead to a mechanical collision between the femoral neck and the acetabular rim in certain directions of motion.
„The typical patient with femoroacetabular impingement is usually a young person, most often between 18 and 25 years old, who likely participates in sports such as soccer, karate, or ice hockey. At first, they notice a feeling of tightness in the groin that appears only during training or a game. Over time, this groin pressure becomes noticeable even during prolonged sitting; it simply feels tight there, accompanied by mild groin pain. This pain usually subsides when the leg is moved and the seated position is changed. Symptoms often increase, and at some point the person consults a physician. Through clinical examination and analysis of the symptoms, it is usually possible to determine that the cause lies in restricted internal rotation at 90 degrees of hip flexion, making the area of impingement symptomatic and causing discomfort. An X-ray can further clarify the diagnosis by revealing the bony asphericity at the head–neck junction. This allows a clear determination that it is an impingement. For a three-dimensional assessment, an arthro–magnetic resonance examination (arthro-MR) is often performed—that is, an MRI with intra-articular contrast. This enables precise evaluation of the cartilage and whether the labrum has already been damaged. Especially in symptomatic patients, the labrum is usually torn in the superior-lateral region, which is explained and caused by the premature, repetitive abutment of the head–neck junction against the acetabular rim“, explains PD Dr. Rahm, continuing:
„The difference is that the labrum is a fibrocartilaginous ring with a function distinct from that of the articular cartilage itself. When the labrum is damaged by overuse, it is not directly related to osteoarthritis or a pre-arthritic condition. It is more of a localized lesion around the hip joint which, if treated appropriately (hip arthroscopy with femoral neck osteoplasty, acetabular rim trimming, and labral refixation), can heal very well. We refer to this as a so-called restorative surgery, in which—after a successful procedure—a near-perfect joint is created and the chances of long-term durability, i.e., 20 to 30 years, are very high. This type of hip procedure (hip arthroscopy with labral refixation) has only been performed since about 2010. Previously, surgeons began with open surgical hip dislocation, but with the development of hip arthroscopy—minimally invasive joint surgery—the open technique has been almost entirely replaced. Since about 2010, the current technique has been used, allowing the labrum to be precisely sutured and the head–neck junction to be optimally treated“. In the early phase of hip arthroscopy, the labrum was removed because it was not yet technically possible to refix it. 
The clinical examination, X-rays, and MRI usually provide sufficient information to assess the situation.
„Sometimes I complement the diagnostics with a 3D CT scan to gain a more detailed overview. If clinical findings deviate or the situation appears complex, I use this additional imaging to better understand where interventions may be necessary. Particularly with pronounced impingement morphologies, 3D CT enables a detailed overview of which areas need to be addressed or adjusted during surgery. Another important point in the workup is to include the knee in the MRI or CT to measure femoral torsion. Femoral torsion is a key factor in impingement: if it is very low, especially below zero, it is called retroversion. This can cause impingement on its own, even without pronounced cam or pincer lesions. In such cases, arthroscopic correction is difficult. An open procedure may be indicated, in which torsion is corrected via a so-called subtrochanteric femoral anteverting rotational osteotomy. The severity of cartilage damage is the most important prognostic factor for long-term outcomes of joint-preserving hip arthroscopy. In young patients, around age 20, hip arthroscopy is usually still performed even if cartilage damage is already present. For patients in their 30s, the goal remains to preserve the joint as much as possible if the damage allows. In older patients, from about 40 years onward, the likelihood of achieving a satisfactory result after a joint-preserving procedure is significantly reduced because the damage is too advanced. In such cases, hip arthroscopy is generally no longer advisable, as the actual benefit is too small due to existing coxarthrosis, which cannot be addressed by cartilage repair techniques. Instead, one should consider total hip arthroplasty, whose outcomes are excellent across all age groups today. Age and the extent of joint damage are therefore the most important prognostic factors: for younger patients, joint-preserving surgery is always preferable; for older patients, replacement is favored, as the likelihood of durable, good function is then highest“, says PD Dr. Rahm.
Patient-specific factors that increase the risk of a later revision after hip prosthesis implantation are diverse and involve physical condition, lifestyle, and comorbidities.
Relevant risk factors include, among others, younger patient age, high activity level, pronounced anatomical deformities, obesity, and systemic diseases such as rheumatoid arthritis or diabetes mellitus. Poor bone quality, for example due to osteoporosis, can also increase the risk of loosening or periprosthetic fractures. Preexisting infections, prior surgery on the affected hip, or suboptimal musculature and muscle imbalance after the primary operation likewise play a role.
„Modern hip endoprostheses are generally extremely durable, so the need for revisions is relatively rare. Nevertheless, specific risks must be considered in revision surgery. These procedures require substantially greater expertise, as they are more complex and must be planned precisely. For revisions, choosing the right approach is important, and anterior approaches have proven effective because muscles and tendons do not have to be cut, allowing faster recovery. However, the first few weeks after revision surgery should be approached cautiously to optimally support osseointegration of the new implant. In principle, rehabilitation after a revision takes longer than after a primary hip replacement. Sports are usually permitted only after several months—once the prosthesis has integrated well, the X-ray is unremarkable, and the patient is satisfied. If these conditions are met, there are good prospects that the prosthesis will last a very long time, even a lifetime. The materials used today, such as highly cross-linked polyethylene and ceramic heads, are very durable, even though we do not yet have 30-year data. The results so far are nonetheless so convincing that, after a good first year, problems are unlikely“, emphasizes PD Dr. Rahm, adding:
„If a revision does become necessary, for example due to loosening or wear, this is usually a clear indication. Such cases are, however, very rare. To detect these late sequelae early, I see my patients every five years for follow-up, including an X-ray. In a revision, I can usually use the same approach, i.e., the anterior approach, and replace only individual components, such as the head or the polyethylene liner. This allows short, straightforward procedures that are usually very effective and get patients back on their feet quickly. To proactively reduce the risk of a revision, careful preoperative planning is essential. This includes detailed imaging, precise prosthetic alignment considering individual anatomy, and, if necessary, preoperative measures to optimize bone health or reduce weight. A structured postoperative rehabilitation program with targeted muscle strengthening and training of joint function also contributes significantly to the stability and longevity of the prosthesis. In the long term, patient-specific education about joint-sparing behavior and possible warning signs plays a central role in recognizing complications early and avoiding revision surgery whenever possible“. 
Surgical strategies for primary hip replacement differ markedly from those in revision arthroplasty–in technique and complexity as well as in postoperative outcomes.
In primary hip arthroplasty, the operative workflow is usually well defined, with standardized implants and procedures. In most cases, the anatomical structures are still largely intact, enabling more precise implant positioning and relatively predictable biomechanics. Modern minimally invasive techniques and muscle-sparing approaches can further facilitate postoperative rehabilitation and reduce the risk of complications. Functional outcomes are generally very good in primary procedures, with high patient satisfaction and long implant survivorship. By contrast, revision arthroplasty is characterized by substantially higher surgical demands.
PD Dr. Rahm comments: „Revisions always present a special challenge because they are something of a black box, where the exact problems become fully apparent only during the procedure. Thorough preparation for all possible scenarios is therefore essential. One must be prepared, for example, for a loose stem, greater wear, or the need to replace the cup because it is damaged or no longer stable. It is also important to have all available implants and materials on hand in the OR to respond flexibly. Sometimes additional steps are needed, such as bone grafting to stabilize bone loss (osteolysis). Moreover, different acetabular reinforcement shells, screwable or cemented stems, and longer revision stems are part of the plan to cover all contingencies. Another important issue in revisions is scarred tissue. Every second operation is influenced by scarring, which often impairs visualization and access. Therefore, it is crucial to know the operative report from the first surgery, if available. Sometimes it can still be found or requested. This lets you know where the scar is likely located and which approach is best. If the first procedure used a posterior approach, it is usually advisable to use the same approach for the revision. If the first operation was via the anterior route, one should decide individually and, if necessary, deviate, because the advantages of another (non-anterior) approach may outweigh those of the anterior approach in a revision setting. It is also possible to excise a scar while working from the back and create a small ‘working plane’ in front. The key is to prepare for all eventualities and carefully consider where the problem most likely lies and how best to ensure a stable THA with minimal soft-tissue damage, so that the patient can ultimately go home pain-free, mobile, and satisfied“.
Early treatment of femoroacetabular impingement (FAI) can significantly influence the risk of developing coxarthrosis later on. In FAI, anatomical deformities at the femoral head/neck (cam type), the acetabulum (pincer type), or a combination of both (mixed type) lead to repeated mechanical conflict between the femur and the acetabular rim. This mechanical stress, particularly in active or young patients, gradually damages the articular cartilage and the labrum, which is considered a potential pathway to osteoarthritis.
„In fact, the topic is not yet fully resolved in the scientific literature, but there are initial indications that successful impingement treatment can positively influence disease progression. For example, a young soccer player who undergoes timely surgery and is pain-free afterward. During the operation, one can directly assess the condition of the bone and cartilage. However, long-term comparative studies in which 100 patients were operated on and compared with another 100 who were not, with outcomes evaluated after 30 years, do not yet exist. There is growing evidence that early impingement surgery may slow the development of hip osteoarthritis. The word ‘prevent’ is used cautiously in clinical practice because the data are not yet strong enough. What is important for the patient is that the main indication for surgery is to relieve acute distress and pain. The data on slowing or preventing osteoarthritis are not yet definitive, whereas pain relief during sports and activity clearly supports early treatment“, says PD Dr. Rahm, offering guidance on possible preventive measures:
„Prevention of early osteoarthritis primarily involves having a specialist assess the range of motion of the hip joint. In young patients with the first twinges in the hip, a standard X-ray can provide valuable clues. If the hip joint is asymptomatic, the likelihood is high that it will remain healthy for a long time. Many patients present with pain only later in life, even though they previously had no symptoms. This shows that the hip joint often adapts to changes as long as it is not painful. If complaints arise, one should act early, as pain is usually a warning sign. Low-impact sports such as cycling, swimming, hiking, or walking are recommended, as they place less stress on the joint. High-intensity, abrupt movements or sports with sudden stop-and-go phases like karate or squash can increase risk and should be avoided. In general: the earlier one takes care of the hip joint and practices prevention, the better osteoarthritis can be delayed and long-term quality of life preserved“. 
Man in the park_AI generated
The Gelenkzentrum Zürich is among the leading centers for hip surgery. The focus is on state-of-the-art minimally invasive techniques, which account for about 80% of procedures and enable fast, gentle recovery. Over 95% of patients report a marked reduction in pain and a significant improvement in mobility after treatment.
„Here in Zurich, I currently perform about 200 hip replacements per year and around 80 arthroscopies. I can therefore say that we are highly specialized. My focus is exclusively on hip surgery; I do not operate on other joints. That is what sets me apart, as I am familiar with the entire spectrum of hip medicine, including the treatment of morphological abnormalities, primary arthroplasty, and revision arthroplasty. Nowadays, concentrating on one area is sensible in order to develop expert knowledge, recognize complex problems early, and prevent them in a targeted manner“, emphasizes PD Dr. Rahm, and with that we conclude our conversation.
Many thanks, Dr. Rahm, for these important insights!
