Our knees are involved in almost every movement we make each day, from taking our first steps to struggling to climb a flight of stairs. They are not the same joint at 10, 30, or 70 years old , and this is evident both in the types of injuries that appear and in how they are treated. Far from the "it's just part of getting older" mentality, we now know that a significant portion of knee pain can be prevented, detected early, and managed with very specific strategies.
Throughout life, the knees go through very different phases: the childhood growth stage, the years of peak physical activity, adulthood with possible poorly healed sports injuries, and finally, the period in which degenerative changes in cartilage and osteoarthritis become prominent. Understanding what happens at each stage, why they hurt more at certain ages, and what treatment options exist—from exercise and physical therapy to advanced surgery or regenerative medicine—is key to maintaining quality of life for as long as possible.
How knees change with age
Current research using large MRI series has shown that the pattern of knee injuries varies according to age and sex . Studies with thousands of tests performed on people presenting with knee pain have identified striking differences between men and women, and between younger and older patients, in menisci, ligaments, and cartilage.
During childhood and adolescence, the skeleton is undergoing rapid development, and the growth plates around the knee contribute significantly to the final length of the femur and tibia. At this stage, many "normal variations" (bowlegs or knock-knees, in-toeing, nighttime growing pains) are common, causing considerable concern for families. However, these issues almost always resolve on their own and require only monitoring and accurate information.
Upon reaching adolescence and early adulthood, especially among athletes, traumatic injuries become more prevalent: meniscus tears, sprains or ligament ruptures (such as the ACL) , osteochondral fractures, chondromalacia patellae, or problems with tendon and bursa overload. An active lifestyle generally protects against chronic pain, but certain intense or poorly dosed activities can take their toll if injuries accumulate without proper treatment.
Around the age of 40-45, the effects of this history of impacts, minor traumas, and overuse become very common: degenerative changes in the cartilage (early osteoarthritis) , damaged menisci, chondromalacia, varus or valgus deformities, muscle weakness, and excess weight , all of which increase the load on the joint. From then on, the risk of knee osteoarthritis increases with age, with a clear peak in those over 70 and a higher incidence in women.
Another key finding from recent imaging studies is that the distribution of meniscal and ligamentous injuries differs between men and women throughout their lives. Meniscal and medial collateral ligament tears are more prevalent in men under 40 , while in older age groups, women more frequently present with meniscal tears, patellofemoral pathology, and signs of osteoarthritis.
Knees in children and adolescents: development, sport and pain
In pediatric consultations, a significant portion of the reasons for visits are related to the musculoskeletal system. In childhood, it is crucial to differentiate between normal maturation and what is truly pathological , because the knees change shape and alignment during the first years of life in a completely physiological manner.
In the early years, it is common to see developmental genu varum (bowlegs) that becomes more pronounced when the child begins to walk and usually corrects itself spontaneously before the age of 3. Then, around 3-4 years of age, many children develop genu valgum (knock-knees), which gradually normalizes until pre-adolescence, with a mild residual valgus that is somewhat more pronounced in adult women than in men.
Mild torsional deformities (internal or external rotation of the femur and tibia) are also common, manifesting as in-toeing or out-toeing. Most correct themselves with growth; the role of primary care is to monitor, reassure the family, and refer to a pediatric orthopedist only if the deviation is very pronounced, asymmetrical, or does not improve with age.
So-called " growing pains " are another common cause for concern. They usually appear between the ages of 3 and 10, at the end of the day or at night, in the thighs, lower back, or calves, without any objective joint involvement, and with normal examinations and tests. They are not directly related to growth spurts, are benign, and respond to simple measures such as local heat, massage, and reassurance for the family.
In adolescent athletes, the situation changes: the increased practice of soccer, basketball, handball, or other impact sports makes muscle, ligament, and meniscal injuries much more frequent. The knee, due to its complex biomechanics and its dependence on ligamentous and muscular support, is especially vulnerable to twisting movements, sudden stops, and repetitive jumping.
Typical knee injuries in childhood and adolescence
The list of conditions that can affect a young knee is long, but several are particularly characteristic. Knowing them helps avoid confusing minor discomfort with injuries that do require specialized testing (X-rays, ultrasound, MRI) or even surgery.
One of the most frequent disorders is patellar pathology . The patella acts as a pulley for the quadriceps and is subjected to great forces; if the vastus medialis (the inner portion of the quadriceps) is weak, if there is an increased Q angle, or biomechanical alterations (foot pronation, external tibial torsion, patella alta), the gliding of the patella over the femur becomes inefficient, and abnormal friction and pain appear.
Chondromalacia patellae is the softening and progressive deterioration of the cartilage on the back of the kneecap. It is most common in adolescents and young adults who train on hard surfaces or participate in running and jumping sports. It causes pain in the front of the knee that worsens when going up and down stairs, running, or sitting for long periods with the knee bent, and may be accompanied by clicking or a grinding or popping sensation.
Another related condition is Sinding-Larsen-Johansson syndrome , an apophysitis of the inferior pole of the patella in highly active adolescents (11-13 years old, especially those involved in jumping sports). It is characterized by well-localized pain at the insertion of the patellar tendon after exercise, which improves with rest. Radiography and ultrasound allow visualization of the different stages of fragmentation and calcification in this area.
On the opposite side of the knee, the well-known Osgood-Schlatter disease affects the tibial tuberosity, where the patellar tendon inserts. It is typical in adolescent athletes; the pain is located in the bump immediately below the kneecap, increases with activity, and subsides with rest. It is due to repeated microtrauma to the growth plate in that area and usually resolves once growth is complete, but while it lasts, it may require reducing or modifying the sport.
Patellar dislocation or subluxation is relatively common in adolescent girls with marked genu valgum, weakness of the vastus medialis muscle, and sometimes excess weight. A twisting motion on a semi-flexed knee can abruptly displace the patella laterally, causing intense pain, inability to move the knee, and visible deformity. Many cases reduce spontaneously, but it is always necessary to assess the ligaments, the presence of effusion, and the risk of further dislocations, and to begin a specific muscle strengthening program as soon as possible.
Another injury that shouldn't be overlooked in adolescents is osteochondritis dissecans of the femoral condyle, especially the medial condyle. This involves an area of subchondral bone and cartilage that loses blood supply (ischemia) due to repeated microtrauma and can become partially or completely detached, causing locking, localized pain in the condyle, and limited extension. Magnetic resonance imaging (MRI) allows for classification of its severity and helps determine whether rest and physical therapy are sufficient or if arthroscopic treatment is necessary.
A Baker's cyst can appear in the popliteal fossa, behind the knee. This is simply a collection of synovial fluid that forms between muscles and fascia. In adolescents, it is often associated with muscle imbalances (weak vastus medialis, malaligned patella) that increase friction and fluid production. Although the mass is usually painless, it can feel tight. Treatment focuses on addressing the underlying biomechanical cause rather than surgery, as surgical procedures have a high recurrence rate.
Ligament and meniscal injuries can also occur in childhood, especially in pre-adolescent and adolescent athletes. A sudden twist with the foot planted can tear the collateral ligaments or the anterior cruciate ligament, or rupture a meniscus. These injuries manifest as sharp pain, swelling, a feeling of instability or locking, and, in the case of meniscal injuries, precise pain along the joint line and clicking sounds when performing maneuvers such as the McMurray test. At these ages, it is always important to assess the injury carefully, because extensive meniscectomy is associated with a higher risk of osteoarthritis later in life.
Knees in young and middle-aged adults: sports, work, and surgeries
Many people assume that knee pain is "something that only affects old people," but the reality is very different: more and more young and middle-aged adults are coming to the doctor with persistent knee pain , often related to previous sports injuries, work overload, excess weight, or misalignments that were not taken into account in time.
In this age group, large cohort MRI studies have observed a higher frequency of isolated anterior cruciate ligament (ACL) tears , as well as combinations of ACL injury with medial or lateral meniscus tears, especially in men between 20 and 40 years old. This finding challenges the previous notion that ACL tears are exclusive to young female athletes: when the entire population with knee pain is studied (not just athletes), men appear to accumulate more of these types of injuries.
In addition to ligament injuries, meniscus tears are very common . These can be traumatic (after a twist, a turn, or a fall) or degenerative (due to progressive wear and tear), as are focal chondral lesions and overuse syndromes such as iliotibial band syndrome , patellar tendinitis, pes anserine bursitis, or patellofemoral pain syndrome. These injuries often occur in people who participate in high-impact sports (soccer, running, basketball) or physically demanding jobs without adequate muscle conditioning.
When pain persists for more than three months, is accompanied by persistent swelling, difficulty climbing stairs, getting up from a chair or walking more than a few hundred meters, instability or a feeling that the knee "gives way" , or wakes up at night, it is a clear sign that there may be significant structural damage (cartilage, ligaments or bone) and an in-depth study is advisable.
In these cases, a total knee replacement isn't always the first option. Today, the surgical range is very broad and is tailored to the patient's age, the type of damage, and their individual expectations. Arthroscopy allows for the repair or smoothing of meniscal tears, the removal of loose cartilage or bone fragments, and the treatment of certain focal lesions. Osteotomy realigns the weight-bearing axis in young patients with pronounced varus or valgus deformities, relieving pressure on the damaged area of cartilage. And when the damage is concentrated in a single compartment of the knee, partial replacement or unicompartmental arthroplasty preserves a large portion of the natural joint and promotes faster recovery.
For focal chondral lesions in patients under 40, cartilage restoration techniques such as microfracture, autologous chondrocyte implantation, and osteochondral grafts have been developed to regenerate damaged tissue. Beyond their own country of residence, there has been a growing interest in medical tourism to destinations that combine more affordable prices, short waiting times, and advanced surgical technology, such as some specialized centers in Turkey.
Knee osteoarthritis and joint aging
From the fifth decade of life onwards, especially if there are associated risk factors, the signs of knee osteoarthritis begin to become evident , a degenerative disease in which the articular cartilage thins and loses quality, progressively leaving less protection between the femur, tibia and patella.
The knee is a weight-bearing joint : it supports the weight of the body and whatever we carry when standing, walking, running, or climbing stairs. This is why knee osteoarthritis is one of the most common conditions in the body. Initially, the degenerative process is silent because cartilage has no nerve endings; pain appears when the subchondral bone, synovial membrane, ligaments, and capsule are affected.
There are two main types of knee osteoarthritis. Primary or idiopathic osteoarthritis is the most common, related to age and a combination of genetic and lifestyle factors (female sex, overweight, intense high-impact physical activity, muscle weakness, biomechanical abnormalities). It usually begins around age 40-50 and progresses slowly, with possible periods of acceleration or relative stability.
Secondary osteoarthritis arises as a consequence of other processes: extensive meniscectomies, anterior cruciate ligament ruptures that are not reconstructed or are poorly rehabilitated, intra-articular fractures, pronounced varus or valgus deformities, metabolic diseases such as gout or pseudogout, diabetes, or severe joint infections (septic arthritis). In these cases, the wear and tear can manifest even in relatively young people.
Epidemiological studies indicate that between 10 and 15% of the adult population suffers from some degree of knee osteoarthritis, with prevalence rates that clearly increase with age and are higher in women. In Spain, data such as those from the EPISER study place the prevalence of knee osteoarthritis at around 13-14% in people over 40, with a greater impact on women, people with obesity, and the elderly.
Risk factors: age, weight, sex, muscle mass, and physical activity
Age is obviously a key factor: the more years we accumulate, the greater the likelihood of cartilage deterioration . But it's not the only one, and more importantly, it's not modifiable. On the other hand, other factors can be addressed and make a significant difference in the risk of developing painful osteoarthritis.
Being female increases the risk of knee osteoarthritis, especially after menopause, probably due to hormonal changes, differences in biomechanics, and variations in muscle and fat distribution. In fact, knee pain due to wear and tear is up to three times more common in women than in men of the same age.
Overweight and obesity are among the most important and, fortunately, modifiable risk factors. Mechanically, each extra kilogram translates into several extra kilograms of load on the knee with each step (multiplied by 2-4 when walking). Metabolically, obesity is associated with a low-grade chronic inflammatory state that also affects the joints, explaining, for example, the high prevalence of osteoarthritis in the hands of obese people, even though the hands are not weight-bearing joints.
Muscle weakness , especially in the quadriceps and hamstrings, increases stress on the cartilage because the muscles are unable to properly cushion or stabilize impacts. This alters gait biomechanics, promotes joint instability, and creates a vicious cycle: less movement due to pain, more muscle is lost, the knee becomes even more unstable, and the pain worsens.
Regarding physical activity , the key is moderation. Light or moderate, low-impact activity (walking on level ground, cycling, swimming, water aerobics) improves cartilage nutrition, maintains joint range of motion, and strengthens muscles and ligaments. However, certain high-impact activities or professional training (soccer, basketball, volleyball) repeated for years without adequate prevention are associated with an increased risk of osteoarthritis after retirement, partly due to accumulated meniscus and ligament injuries.
Finally, biomechanical alterations (such as excessive bowing of the legs in varus or valgus, pronounced pronation of the feet, misaligned knees, and leg length discrepancies) unevenly redistribute the load and concentrate stress on specific areas of the cartilage, accelerating its wear. Custom insoles, orthotics, knee braces, and, in selected cases, corrective osteotomies can play a significant role in these patients.
Symptoms of osteoarthritis and examination of the knee
Knee osteoarthritis can begin insidiously, with pain that only appears with exertion (going downhill, carrying heavy objects, walking long distances) and mild morning stiffness that lasts only a few minutes. Over time, the pain becomes more constant, occurs with minor activities, limits walking, and requires the use of canes or walkers.
In addition to pain, other notable symptoms include decreased mobility (difficulty fully flexing or extending the knee), stiffness after periods of rest, a feeling of instability, crepitus (cracking or grating sounds), and the appearance of joint effusion (fluid accumulation within the knee) which results in swelling, especially in the suprapatellar region. In advanced stages, evident morphological changes may be observed: pronounced varus or valgus knees, increased volume, deformity, and a clear loss of strength and function.
During the clinical examination, the practitioner assesses leg alignment, the presence of quadriceps atrophy, ligamentous stability using specific maneuvers (anterior and posterior drawer tests, Lachman test, forced valgus-varus tests), selective tenderness along the joint line (indicative of meniscus injury), and overall range of motion. A thorough medical history and a well-executed systematic examination allow for a general diagnosis even before resorting to imaging tests.
Weight-bearing X-rays are the first-line test for confirming osteoarthritis, as they show narrowing of the joint space (cartilage loss), osteophyte formation, subchondral bone sclerosis, and possible deformities. Magnetic resonance imaging (MRI) and CT scans are reserved for a more thorough assessment of the menisci, ligaments, and focal chondral lesions, or when another associated pathology is suspected.
Treatments: from lifestyle changes to knee replacements
The approach to osteoarthritis and knee pain in general is stepwise and multidisciplinary. Not all patients need the same treatment or at the same time , and surgery should be considered the last resort after exhausting reasonable conservative options, without delaying it so long as to rob patients of years of quality life.
In the initial stages, non-pharmacological measures are the cornerstone: weight reduction in cases of obesity, an adapted physical exercise program (walking, cycling, swimming, progressive strength exercises) , physiotherapy to improve mobility and muscle control, postural education, and the use of technical aids (canes, knee pads, insoles) when indicated.
From a pharmacological standpoint, treatment usually begins with simple analgesics such as paracetamol at adjusted doses, although their long-term effectiveness is limited. Oral nonsteroidal anti-inflammatory drugs (NSAIDs) can be useful during more intense pain flare-ups, always taking into account cardiovascular, digestive, and renal risks. Topical NSAIDs (creams, gels) are also used, with fewer systemic effects.
When pain control is insufficient, intra-articular injections of corticosteroids (for specific inflammatory flare-ups, limited in number per year) or hyaluronic acid (viscosupplementation) can be considered. Hyaluronic acid acts as a lubricant and shock absorber and can provide relief for several months in certain patients. The so-called SYSADOAs (glucosamine, chondroitin, diacerein) are slow-acting drugs with variable results according to studies, but they are well-tolerated and used in long-term regimens.
In recent years, regenerative medicine applied to the knee has gained prominence, with the use of platelet-rich plasma (PRP) and, in certain contexts, mesenchymal stem cells. These therapies aim to modulate inflammation and stimulate tissue repair; they can delay the need for knee replacement in some patients, although research is still being refined to determine which profiles respond best and with which protocols.
When pain is severe, significantly limiting daily life despite physiotherapy, medication, injections, and lifestyle changes, and advanced wear and tear is confirmed by imaging, surgery becomes the most reasonable option , regardless of age. Sometimes, postponing a prosthesis is considered for people who are "too young," but this implies accepting years of limited life, as illustrated by the cases of 50-year-old patients who are told to wait another ten years while pain prevents them from dancing, walking, or working normally.
Modern total knee replacements often have a lifespan exceeding 20 years when the appropriate model is chosen and a precise surgical technique is performed, tailored to the type of deformity, ligament stability, and muscle condition. Various designs (cruciate retaining, posteriorly stabilized, constrained prostheses, etc.) are available, which the surgeon selects to optimize stability and longevity. And when a prosthesis wears out or fails, prosthetic replacement is possible.
After a knee replacement, the goal is not for the patient to return to top-level competition or contact sports like football, but rather to be able to walk without pain, climb stairs, live independently, and participate in moderate recreational activities . Again, rehabilitation and the patient's commitment to strength and mobility training are just as important as the surgery itself.
Knee health throughout life depends on a combination of factors, ranging from genetics and body shape to weight, muscle mass, physical activity, and how injuries are managed when they occur. With good information, reasonable prevention, early detection of structural damage, and intelligent use of available therapeutic tools (including surgery when necessary, not years later), it is entirely possible to reach advanced age with knees that, while not perfect, allow you to continue moving freely and maintain a good quality of life.
