What New Knee Research Means for Patients in Hillsboro, Beaverton, Aloha, and Nearby Towns

The following article is for learning only. It is not medical advice and should not be taken as such. Consult with a qualified orthopedic surgeon, sports medicine physician, or highly trained physical therapist in a high quality orthopedic/sports facility.

If you or your child has ever torn a knee ligament, you know how scary and confusing it can feel. Doctors use big words. There are many choices to make. And you just want to know one thing: will my knee get better?

Four recent medical studies looked closely at knee surgery and knee recovery. They studied things like which type of graft (the tissue used to rebuild a torn ligament) works best, how long it takes kids to get surgery, and how strong a knee really is years after surgery.

We examined all four studies from start to finish. In this article, we break them down in plain, simple words without overusing confusing medical words. We explain what each study found, what was studied, and what the researchers themselves said were the weak points of their own work. We also talk about what this means if you live in Hillsboro, Aloha, Beaverton, Cornelius, Forest Grove, North Plains, or Bethany areas, since knee injuries and ACL surgery are common in young athletes, weekend warriors, and active adults all across Washington County.

First, a Quick Lesson on the Knee

Before we jump into the studies, let's talk about a few simple facts. Your knee is held together by strong, rope-like bands called ligaments. One of the most important ones is the ACL, which stands for anterior cruciate ligament. Think of the ACL as a strong cord in the middle of your knee that stops your shin bone from sliding too far forward and keeps your knee from twisting too much.

The ACL gets torn a lot in sports like soccer, basketball, football, skiing, and volleyball. It can even get torn in car accidents and nasty falls. When it tears, many people (though not everyone) need a surgery called ACL reconstruction. During this surgery, a surgeon removes the torn ACL and replaces it with something called a graft.

Surgeons usually take this graft from one of a few places in your own body:

• The hamstring tendon, which comes from the back of your thigh.

• The quadriceps tendon, which comes from the front of your thigh, just above the kneecap.

• The patellar tendon, which connects your kneecap to your shin bone. Doctors often call this a bone-patellar tendon-bone graft, or BPTB, because small pieces of bone come along with it.

Choosing the right graft matters a lot. It can change how fast you heal, how strong your knee feels years later, and whether you might need a second surgery. This is exactly what our first two studies looked at.

Sometimes, a knee injury is even more serious than a single torn ACL. When two or more of the four main knee ligaments tear at the same time, doctors call this a multiligament knee injury. This is a much bigger injury, and it often happens with knee dislocations from car crashes, skiing accidents, or hard hits in contact sports. Our fourth study looked at how well people recover years after this kind of serious injury.

And finally, not every patient gets to surgery at the same speed. Our third study looked at children and teenagers with torn ACLs, and asked a hard question: does where a child lives, what kind of insurance they have, or their race affect how fast they get surgery, and does that delay cause more damage inside the knee?

Let's go through each study one at a time.

Study 1: Hamstring Tendon vs. Quadriceps Tendon, a Fair Head-to-Head Test

The first study we reviewed is a randomized controlled trial published in the Archives of Orthopaedic and Trauma Surgery in 2022, led by Dr. Hauke Horstmann and his team in Germany.[1] A randomized controlled trial is considered one of the strongest kinds of medical studies, because patients are placed into groups by chance, almost like a coin flip, so that the two groups being compared start out as similar as possible.

What they did: The researchers studied 51 adults, ages 18 to 50, who had a torn ACL. By chance, 27 patients received a hamstring tendon graft, and 24 patients received a quadriceps tendon graft. Doctors checked on these patients before surgery, and then again at 3 months, 6 months, 1 year, and 2 years after surgery. They measured how wobbly the knee was using a tool called an arthrometer, which gently pushes and pulls on the knee to measure how much it slides. They also measured muscle strength using something called an isokinetic machine (a machine that checks strength by matching the amount you push into it through the range and also checking your strength in one position), and they had patients fill out two well-known knee surveys called the IKDC score and the Lysholm score, which simply ask patients how their knee feels and works in daily life.

What they found: Both grafts worked well. There was no meaningful difference between the hamstring tendon group and the quadriceps tendon group in knee stability, strength, or how patients rated their own knees. Patients who got the hamstring graft returned to sports in about 95 days on average. Patients who got the quadriceps graft returned to sports a bit sooner, in about 82 days on average, but this small difference was not considered statistically meaningful, which means it could have simply been due to chance rather than a true difference between the grafts. A small number of patients in each group had complications. Two patients in the hamstring group and three patients in the quadriceps group tore their new graft again within two years, and one patient in the quadriceps group developed an infection.

In plain words: This study suggests that when it comes to knee stability and how a knee feels a year or two after surgery, hamstring tendon grafts and quadriceps tendon grafts perform about the same for adults having their first ACL surgery.

Be cautious about this study, because: The researchers themselves pointed out some real weak spots. First, the study was small. Only 51 patients started the study, and by the two-year mark, 7 people had dropped out, leaving 44 patients. Small studies are more likely to miss real differences between treatments simply because there are not enough people to see a pattern clearly. Second, even though patients were assigned to groups by chance, the two groups ended up different in ways that matter. The quadriceps tendon group was, on average, younger, had more men, was taller, and received larger grafts than the hamstring tendon group. Since younger age, being male, and larger graft size can all affect how well a knee recovers, these differences make it harder to know for certain that the graft type alone caused the similar results. The authors admitted this could be due to what is called randomization bias, meaning that pure chance placed different kinds of patients unevenly between the two groups. Third, this study only followed patients for two years. A knee can look and feel fine at two years but still have problems show up later, which is exactly what our next study suggests.

Study 2: A Very Large Study Finds a Different Story for Quadriceps Tendon Grafts

Our second study is much, much bigger, and it comes to a more cautious conclusion about quadriceps tendon grafts. This 2026 study, published in The American Journal of Sports Medicine by Dr. Carolina Kekki and colleagues at a well-known sports medicine clinic in Stockholm, Sweden, looked at 5,653 ACL reconstruction surgeries performed between 2015 and 2022.[2] This is what is called a cohort study, meaning the researchers followed real-world groups of patients who already chose (with their surgeon) one of three graft types, rather than being randomly assigned like in Study 1. Because the graft choice was not random, a cohort study cannot prove that one graft causes better or worse results the way a randomized trial can, but a study this large can reveal patterns that a small study might miss.

What they did: Researchers sorted patients into three groups: 4,366 patients who received a hamstring tendon graft, 465 who received a patellar tendon (BPTB) graft, and 822 who received a quadriceps tendon graft. They then tracked, over two years, how many patients needed a second surgery, called a reoperation, and why. They also tracked patient-reported knee scores using a survey called the KOOS, which stands for Knee Injury and Osteoarthritis Outcome Score.

What they found: Patients with quadriceps tendon grafts needed a second surgery much more often than patients with hamstring tendon grafts. Overall, 19.2 percent of the quadriceps tendon group needed a second surgery within two years, compared to only 8.9 percent of the hamstring tendon group and 6.9 percent of the patellar tendon group. The single biggest reason for these extra surgeries was something called extension deficit or pain, meaning the patient could not fully straighten the knee or had ongoing pain from scar tissue, a condition sometimes called a cyclops lesion or arthrofibrosis, both of which simply mean extra scar tissue is blocking normal knee movement. This happened in 11.9 percent of quadriceps tendon patients, compared to 5.5 percent of hamstring tendon patients and 4.7 percent of patellar tendon patients. After accounting for other factors like age, sex, and graft size, patients with quadriceps tendon grafts were almost twice as likely to need this kind of second surgery compared to hamstring tendon patients.

The quadriceps tendon group also reported feeling less satisfied with their knees. Fewer of these patients reached what researchers call the minimal important change, a score showing a real, meaningful improvement, and fewer reached what is called the patient acceptable symptom state, which simply means the patient felt their knee was good enough for daily life. More quadriceps tendon patients experienced what the researchers labeled treatment failure, meaning their knee scores stayed poor even after surgery and rehab.

There was one more interesting finding. Female patients who received larger grafts, between 9.5 and 12 millimeters wide, had 72 percent higher odds of needing a second surgery for extension problems or pain compared to those with smaller grafts. The researchers suggest this may be because a bigger graft can be too large for a smaller knee space, called the intercondylar notch, causing rubbing and irritation.

In plain words: In this large, real-world group of patients, the quadriceps tendon graft came with a real trade-off. It may still be a fine choice for some patients, especially when a surgeon has a specific reason to prefer it, but this study raises a caution flag that people considering this graft type should discuss the higher chance of needing a second surgery and possibly having a bit rockier recovery with their surgeon and physical therapist.

Be cautious about this study, because: This is a retrospective cohort study, not a randomized trial, so surgeons chose the graft type for each patient rather than a coin flip deciding it. This means the quadriceps tendon group might have included patients who already had more complex knee problems, since the study also found that this group had more meniscus tears and cartilage injuries to begin with. The researchers tried to adjust for this using statistics, but it is impossible to remove every hidden difference this way. Second, not everyone completed their follow-up surveys. Only about 38 to 45 percent of patients in each group actually completed their two-year KOOS surveys, meaning more than half of the patients did not report back, which could shift the results in either direction. Third, this study only measured reoperations that happened at this one clinic. Patients who had a second surgery somewhere else would not show up in this data, meaning the true reoperation rate could be even higher than reported. Finally, this study was done at a single clinic in Sweden, so results might look somewhat different at a clinic here in Oregon with different surgeons, different rehab protocols, and a different patient population.

Study 3: Why Some Kids Wait Much Longer for ACL Surgery, and Why That Matters

Our third study takes a different angle. Instead of comparing graft types, this 2026 study published in The American Journal of Sports Medicine by Dr. Christopher Hamad and his team at the University of California, Los Angeles, looked at something just as important: how long children and teenagers wait to get ACL surgery, and whether that wait causes more damage inside the knee.[3]

What they did: The researchers reviewed 443 pediatric patients, all younger than 18, who had ACL surgery at one academic hospital between 2013 and 2025. This hospital has a special walk-in orthopedic clinic just for kids, which the researchers say gives most children a fairly fast first appointment no matter their insurance type. Because of this, the researchers were able to separate two different kinds of delay: the time from injury to the first doctor visit, and the time from that first doctor visit to actual surgery. They looked at whether a child's race or ethnicity, insurance type (private insurance versus public insurance like Medicaid), and neighborhood made a difference in how long children waited, using a tool called the Childhood Opportunity Index, which measures things like school quality, safety, and health resources in a child's neighborhood.

What they found: The good news first. The time from injury to that first doctor visit was short for almost everyone, a median of just 5 days, and this part did not differ much by race, insurance, or neighborhood. This suggests the walk-in clinic model did its job of giving fast initial access to care.

The concerning news came next. Once a child was seen by a doctor, the wait to actual surgery was much longer, a median of 101 days, and this part of the wait was very unequal. About 38.6 percent of children experienced what the study called a prolonged delay, meaning more than 120 days between their first visit and surgery. Children who were non-Hispanic Black, Hispanic, or of another or unknown race and ethnicity were all significantly more likely to face this longer wait compared to non-Hispanic White children, even after the researchers adjusted for insurance and neighborhood factors. Kids with public insurance also waited significantly longer for surgery than kids with private insurance. And children living in lower-opportunity neighborhoods, meaning areas with fewer resources like good schools, safe housing, and nearby healthcare, waited longer too.

Why does this matter for a child's knee? Because every extra day of waiting was linked to a small but real increase in the chance of a more serious cartilage injury found during surgery. Cartilage is the smooth, cushiony covering on the ends of your bones inside the knee joint, and once it's badly damaged, called a high-grade injury, it does not heal back to normal the way skin or bone can. Every extra 120 days of delay increased the odds of severe cartilage damage by about 57 percent. This is a similar pattern to what other researchers have found before: waiting longer for ACL surgery, especially past about 3 to 6 months, tends to allow more of that unstable, wobbly knee time to bang around and grind down cartilage and the meniscus, which are the two soft cushions inside the knee joint.

The study also looked at recovery after surgery. Among kids followed for at least a year, those with public insurance and those from lower-opportunity neighborhoods tended to show worse balance and symmetry between their two legs during hop testing, a common way therapists check if a knee is ready to return to sports.

In plain words: This study is a strong reminder that getting a child in front of an orthopedic doctor quickly is only half the battle. The bigger gap in fairness happened after that first visit, in the weeks and months it took to actually schedule and get surgery. Families facing insurance hurdles, scheduling barriers, or fewer local resources were more likely to have a long wait, and that wait appeared to come with real added risk to the child's knee.

Be cautious about this study, because: This was a study done at a single hospital, and the researchers themselves noted that their patient group was unusual: mostly Hispanic (about 61 percent) and mostly on public insurance (about 74 percent), which is very different from many other ACL research studies where patients tend to be mostly White and privately insured. This is actually a strength in some ways, since it studied a group that is often left out of research, but it also means the exact numbers might look different at a hospital with a different mix of patients, insurance systems, or scheduling systems, including clinics here in Oregon. Second, information about a patient's race, ethnicity, and insurance came from medical records, which can sometimes be incomplete or mislabeled, and the researchers grouped many different backgrounds together under an "other or unknown" category, which hides a lot of variety. Third, neighborhood opportunity scores measure the whole neighborhood, not each family, so this method cannot know exactly what happened in any one household, like whether a parent had trouble taking time off work or trouble reaching a pharmacy or imaging center. Fourth, this study could only include children who did eventually have surgery at this hospital. Kids whose families gave up, went elsewhere, or never got surgery at all are missing from this data, which could actually make the true unfairness gap even bigger than what was measured. Finally, the part of the study looking at graft failure had only 14 total failure events, which is too small a number to draw firm conclusions from.

Study 4: Even Years Later, Many Knees Have Not Fully Regained Their Strength

Our final study looks far down the road, well beyond the usual one or two year check-in that most ACL and knee ligament research relies on. This 2026 study, published in The American Journal of Sports Medicine by Ingrid Trøan and colleagues at Oslo University Hospital in Norway, studied patients an average of 7 years after surgery for a multiligament knee injury, meaning two or more of the four main knee ligaments were torn at the same time.[4] This kind of injury is much more severe than a single torn ACL and often happens with a knee dislocation.

What they did: Researchers invited 124 patients who had surgery for this serious injury between 2013 and 2020, and 90 of them, or 72 percent, agreed to come back in for detailed muscle strength and movement testing years later. Testers used a machine called a dynamometer to measure the exact strength of the quadriceps muscle (front of thigh) and hamstring muscle (back of thigh) on both the injured leg and the healthy leg, then compared the two using something called a limb symmetry index, or LSI. An LSI of 90 percent or higher is generally considered a normal, healthy result, meaning the injured leg is nearly as strong as the healthy leg. Patients also performed hop tests, like hopping as far as possible on one leg, which show how confident and capable a leg feels during real movement, not just when sitting in a machine.

What they found: Even a full 7 years after surgery, many knees were still noticeably weaker than the uninjured leg. 54 percent of patients had not regained normal quadriceps strength, and 46 percent had not regained normal hamstring strength. On average, the injured leg's quadriceps muscle was about 87 to 92 percent as strong as the healthy leg, depending on how fast the muscle was tested. When it came to hopping tests, 44 percent of patients could not hop as far or as symmetrically on their injured leg as researchers consider normal.

The study also compared two groups: patients whose injury involved just one of the two major central ligaments, called cruciate ligaments (this includes the ACL and PCL, or posterior cruciate ligament), versus patients whose injury involved both of these ligaments at once, called a bicruciate injury. The bicruciate injury group, which is the more severe pattern, had significantly weaker quadriceps muscles and performed significantly worse on a timed hopping test compared to the less severe group.

Interestingly, stronger quadriceps muscles were weakly linked to patients feeling better about their knee overall, using surveys like the IKDC and KOOS, but quadriceps strength on its own did not predict whether someone actually returned to their sport. This tells us that getting back to sport depends on more than just muscle strength alone. It likely also depends on confidence, fear of re-injury, and other factors.

In plain words: This study is powerful because it looked much further down the road than most knee research does. It shows that for a serious, multi-ligament knee injury, some amount of muscle weakness can stick around for years, even after a person feels mostly recovered day to day. This is especially true for the more severe, bicruciate injuries.

Be cautious about this study, because: This is what is called a cross-sectional study, meaning researchers tested each patient just once at one point in time, rather than tracking the same patients again and again over the years. Because of this, we cannot know exactly how or when the strength loss happened along the way, only where things stood at the 7-year mark. Second, nearly one-third of eligible patients chose not to participate, which always raises the question of whether the people who came back for testing were different in some way from those who did not, though the researchers noted no major age or injury differences between the two groups. Third, and maybe most important for anyone reading this as a patient, the study did not track how much physical therapy each patient actually did, how often, or for how long. Since physical therapy and consistent strength training are widely believed to be some of the biggest drivers of long-term knee strength after this kind of injury, not measuring this is a real gap. It means we cannot say from this study alone how much of the ongoing weakness might have been reduced with more complete rehabilitation. Finally, most patients in this study were hurt during sports or skiing, which are generally considered lower-energy injuries, so results might not apply as well to more severe, high-energy injuries like those from car accidents, which tend to cause even more damage.

What This Means If You Live in Hillsboro, Beaverton, Aloha, Cornelius, Forest Grove, North Plains, or Bethany

Reading through all four of these studies together, a few clear lessons stand out for anyone in our local Washington County and greater Portland communities who is facing a knee ligament injury, whether that's a soccer player in Hillsboro, a high schooler in Beaverton, a weekend hiker in Forest Grove, a youth athlete in Cornelius, a rec-league player in Aloha, a family in North Plains, or someone recovering in Bethany.

First, graft choice is a real conversation to have with your surgeon, not just a small detail. The research shows that hamstring tendon grafts and quadriceps tendon grafts can perform similarly in the first two years for some patients, but the larger, real-world study found that quadriceps tendon grafts came with a meaningfully higher chance of needing a second surgery for stiffness or pain, along with somewhat lower patient satisfaction. This does not mean one graft is wrong for everyone. It means it is worth a real conversation about your own body, your sport, your age, and your goals before deciding.

Second, for families anywhere in the Hillsboro, Beaverton, Aloha, Cornelius, Forest Grove, North Plains, or Bethany area with a child or teenager who has torn their ACL, this research is a strong reminder to move quickly once a diagnosis is made. Getting that first appointment fast matters, but so does staying on top of insurance approvals, imaging appointments, and surgery scheduling in the weeks that follow. Every month of unnecessary delay may allow more wear and tear on the cartilage and meniscus inside a growing child's knee.

Third, and this is something we care deeply about as physical therapists, full recovery from a serious knee ligament injury does not happen in a few weeks or even a few months. The long-term study on multiligament knee injuries found that muscle weakness can quietly linger for years if it is not actively addressed. This is exactly why consistent physical therapy, ongoing strength testing, and honest hop test and limb symmetry checks matter so much, not just right after surgery, but well into the following months and years, especially for anyone returning to sports or physical work in Hillsboro, Beaverton, or the surrounding towns.

Whether you are recovering from a routine ACL tear or a more serious multiligament knee injury, working closely with a physical therapist who tracks your actual strength numbers, not just how you feel, gives you the best shot at closing that strength gap before it becomes a long-term problem. If you live in Hillsboro, Aloha, Beaverton, Cornelius, Forest Grove, North Plains, Bethany, or anywhere nearby in the Portland metro area and you are recovering from knee surgery or trying to decide on a graft type, talking with a local physical therapist alongside your surgeon can help you build a realistic, honest plan for getting your strength and confidence all the way back.

Key Takeaways

A well-designed but small study of adults found that hamstring tendon and quadriceps tendon ACL grafts performed about the same after two years, though the study groups ended up unevenly matched by age, sex, and graft size, which is an important limitation to keep in mind.

A much larger, real-world study of over 5,600 patients found that quadriceps tendon grafts came with meaningfully higher rates of needing a second surgery, mostly for stiffness and pain, along with somewhat lower patient satisfaction scores compared to hamstring tendon grafts.

Among children and teenagers, race, insurance type, and neighborhood resources were all linked to longer waits between diagnosis and actual surgery, and each additional day of delay was linked to a small but real increase in serious cartilage damage found during surgery.

Even 7 years after surgery for a serious multiligament knee injury, more than half of patients had not fully regained normal quadriceps strength, and this gap was even larger for the most severe injury patterns, underscoring how important long-term physical therapy and strength tracking really are.

A Note on These Numbers

Throughout this article, you'll notice terms like "statistically significant," "odds ratio," and "confidence interval." In plain terms, a statistically significant result means the pattern researchers found was unlikely to have simply happened by chance. An odds ratio compares how much more or less likely something is to happen in one group versus another; a ratio of 1.0 means no difference, while a ratio of 2.0 roughly means about twice as likely. A confidence interval gives a likely range for the true answer, and when that range does not cross the number 1.0 (for odds ratios) or zero (for other comparisons), researchers usually consider the finding meaningful rather than random noise. We share these terms here so you can understand them if you ever read the original research studies yourself.

Disclaimer

This article is for general education only. It is a plain-language summary of four published medical research studies, and it is not a substitute for medical advice, diagnosis, or treatment from a qualified doctor, surgeon, or physical therapist. Every knee injury and every patient is different. Please talk with your own orthopedic surgeon or highly trained orthopedic physical therapist before making any decisions about surgery, graft choice, rehabilitation, or return to sport. Nothing in this article should be used to delay seeking medical care.

References

1. Horstmann H, Petri M, Tegtbur U, Felmet G, Krettek C, Jagodzinski M. Quadriceps and hamstring tendon autografts in ACL reconstruction yield comparably good results in a prospective, randomized controlled trial. Arch Orthop Trauma Surg. 2022;142(2):281-289.

2. Kekki C, Cristiani R, Stålman A, von Essen C. Quadriceps tendon autografts are associated with increased short-term reoperation rates for extension deficit or pain and inferior patient-reported outcomes compared with hamstring tendon autografts: an analysis of 5653 cases of primary anterior cruciate ligament reconstruction. Am J Sports Med. 2026;54(11):2658-2667.

3. Hamad CD, Wu S, Joachim K, Chung E, Liu T, Silva M, Bowen R, Baghdadi S. Sociodemographic predictors of postpresentation delay to pediatric ACL reconstruction and associated intra-articular injury severity. Am J Sports Med. 2026;54(11):2668-2679.

4. Trøan I, Holm I, Moatshe G, LaPrade RF, Engebretsen L, Bere T. Quadriceps and hamstring muscle strength recovery after a multiligament knee injury: a long-term follow-up. Am J Sports Med. 2026;54(11):2722-2731.