Mystery of knee joints 膝関節の不思議 

Believe it or not, our knee joint is a very interesting part of our body. It is interesting as it is not only a very important joint but also a very delicate and can be fragile.

According to NCBI (National Center for Biotechnology Information), the knee is the most commonly injured joint by adolescent athletes with an estimated 2.5 million sports-related injuries presenting to EDs annually.

It also reported that 6.6 million knee injuries were reported to United States emergency departments (EDs) from 1999 through 2008.

URL of NCBI article:


Obviously, we know that knee joint is important for us as we cannot stand up, let alone walk or run if we have any problems with our knees. Then, why is it so delicate and possibly fragile? According to Smithsonian National Museum of Natural History, approximately 300,000 years ago, Homo sapiens evolved in Africa. Ever since then, we have been walking on two legs. So why do we often have problems with our knee joint?


I am not a medical expert or an anthropologist or an expert in osteology. I am simply sharing my own thoughts and my hypothesis. If you believe in the theory of evolution, we evolved from the apes. The ancestors of the apes were four legged mammals (dogs, cats, cows, horses, etc.). When our ancestor (pre-Homo sapience) stood up on his two rear legs, the angle of the joint as well as the pressure point from the body weight had shifted dramatically. The burden was doubled when our body was supported by only two legs. In addition, standing on two legs requires a fine balancing act. They say that our body, though invisible to us, is always swaying in different directions in order to maintain our balance while we are standing up.


Now back to the injury subject.  Again according to NCBI, an estimated more than 6.6 million knee injuries occurred in a period of 9 years. This is an amazing rate of more than 2 knee injuries per 1,000 population. I am pretty sure that the readers will agree that these figures are quite high. In other words, the knee injuries are very common. These numbers are for the general population so the number of injuries will most likely go up significantly for the group who engages in athletics, dances and other physical activities including karate.

Here is an excellent article from the website of Full Potential Martial Arts, “Knee Pain in Martial Arts: Causes and Remedies” written by Brian, a martial arts instructor in Carmel Valley CA.


The reason I decided to write this essay was because I posted a short video of the dance rehearsal in 2017 by the Georgian National Ballet (Sukhishvili) team.

The video was titled “New Generation Of Sukhishvili”:


I was very impressed with the dance performed by the young men in Georgia. The dance involved not only many spins and turns but also the quick actions of kneeling down and jumping up. With the title and its URL I wrote, “This proves that if you train diligently and correctly, these kinds of moves will not result in knee problems.”


One reader who happens to be my karate colleague and who I respect very much wrote back saying that not all knees are the same. His point was that not everyone can dance as good as these dancers because our knees are different. I pushed back respectfully with the statement that I believed the knees are created the same in general among all the races in both men and women. I added “The difference is how you train your ligaments and the muscles in the legs, particularly around the knees. Anyone, provided they train correctly, can do what these dancers are doing. These skills can be adopted in the martial arts as well.”


To this comment, another karate colleague who I also respect very much provided me with an article written for USC News.

The title of the article is “All knees are not created equal”.

USC News is produced and edited by USC University Communications. Articles are written by University Communications staff and writers from USC schools and administrative units.


This article was written by the University Communications staff so it must be reliable. The title is opposed to what I had stated but was interesting so I read it. Here is what I had discovered from the article.


  1. It stated that each year, nearly half a million Americans receive knee replacements to relieve pain and disability. This statement confirms that a knee injury is very common and a knee replacement is done very often.
  2. According to a recent survey, two-thirds of the primary recipients are women because they tend to live longer than men, thereby incurring more joint wear.
  3. Surgeons have realized that the unique differences between the female and male anatomy of the knee were not being addressed with traditional knee replacement options.
  4. Donald Longjohn, assistant professor of orthopedic surgery at the Keck School of Medicine of USC said “The size and shape of the female knee bones, including the femur, tibia and patella, are significantly different from men”.

“Female knees are thinner and have a slight difference in angle between the femur and tibia than male knees, so the gender-specific knee ensures precise articulation that allows for a more natural movement”.

The rest of the article was that they developed the knee replacement specific to the gender needs which assures better and more successful knee replacement surgeries.


What I concluded from this article is that despite there being a difference in the knee joint between the sexes, it is mainly a size difference. There are more women who get knee replacement but they concluded it is mainly because they live longer than men. It is natural to see more joint problems as they become very old. Therefore, I did not see any message from this article that the difference of the knee joint between the sexes would put either sex inferior or to show more tendency to have knee problems.


Despite this conclusion, I decided to further investigate the differences in the knee joint structure between the sexes.


So, I came across an excerpt from an article in the book, “Women’s Strength Training Anatomy” written by Fredic Delavier. The author, studied morphology and anatomy for five years at the prestigious École des Beaux-Arts in Paris and studied dissection for three years at the Paris Faculté de Médecine.


The excerpt is on the skeletal difference between women and men. This is only one page and I believe the article is beneficial to the readers. I will quote the entire excerpt here.

The morphological differences between women and men are the result of differences in the volume and proportion of similar anatomical features. Generally speaking, the female skeleton is not as massive; it is smoother and more delicate with impressions—hollows or bumps—that serve as muscle insertions or provide passage for tendons, which are less accentuated. (The more highly developed musculature in men marks the skeleton more.) The female thoracic cage is generally more rounded, and not as big as in the male. Proportionately, the skeletal width of the shoulders is the same as in the male, but the larger muscular development of the latter makes it seem wider. The lumbar curve is greater in women and the pelvis is tilted anteriorly (anteversion), which makes for the sway-backed appearance often found in women. If the waist in women is longer and smaller, it is because the thorax is more constricted at the base and the pelvis is generally not as high.

The most important difference between the male and female skeletons is found at the level of the pelvis. The female pelvis is adapted for gestation: it is not as high and is proportionately wider than that of the male. The sacrum of the female is wider and the pelvic ring is wider and more circular to facilitate the passage of the newborn. As the pelvic ring is wider, the acetabula (the fossa in which the heads of the femurs lodge) are farther apart, which increases the distance between the greater trochanters and consequently the width of the hips.

Greater hip width in women influences the position of the femurs, which are often more angled than in men, giving them a slight X shape.

A wide pelvis with a significant angle of the femur can provoke genu valgum, accentuated all the more by the hyperlaxity toward which women tend. The legs then take on a typical X shape: the articulation at the knee is excessively solicited; the medial collateral ligament is overstretched; and the lateral meniscus, the cartilage-covered articular surfaces of the external condyle of the femur, and the lateral tuberosity of the tibia are subjected to excessive loads, which may lead to premature wear.

Pathological genu valgum is accompanied by medial collapse at the ankle and the disappearance of the plantar arch (flat foot), which may involve pain because of excessive stretching of certain muscles in the sole of the foot.

It is very important to take into account the individual morphologies and to remember that women are more often prone to genu valgum pathologies, whereas men more frequently suffer from bow-legs (genu varum). People with very noticeable genu valgum should therefore work out carefully, avoid training with heavy weights, and always perform the movements so as to avoid impacts that would aggravate knee and ankle problems.


“Women’s strength training Anatomy” from Human Kinetics site URL:



What I took away from this article is that

1. Generally speaking, the female skeleton is not as massive.

2. The most important difference between the male and female skeletons is found at the level of the pelvis.

3.  A wide pelvis with a significant angle of the femur can provoke genu valgum. In other words, a “knock knee” problem.

4. On the other hand, men more frequently suffer from bow-legs or genu varum.


I agree fully that the skeletal structure of a man is different from that of a woman. However, it does not mean that either sex has inferior bone structure including the knee joint. Women tend to have a knock knee problem but at the same time, men tend to have a bow legged knee problem. Thus, both sexes could develop some knee problem or injury either by accident or with age.


Before I make the final conclusion, I wanted to check one more article that is written by some Orthopedic Specialists. I found an article written by Dr. Brett Greenky and Dr. Seth Greenky.

Dr. Brett Greenky is an orthopedic surgeon in Fayetteville, New York and is affiliated with multiple hospitals in the area, including Crouse Hospital and St. Joseph’s Hospital Health Center. He received his medical degree from State University of New York Upstate Medical University and has been in practice for more than 20 years.

Dr. Seth Greenky has been an active surgeon and lecturer in the field of joint arthroplasty for 24 years. As associate professor in orthopedics at Upstate Medical University, Dr. Greenky has trained over 109 surgeons in the art of joint arthroplasty, while co-directing The Joint Replacement Program at St. Joseph’s Hospital in Syracuse. He specializes in Adult Reconstruction including Total Joint Replacement, Sports Injuries, and Fracture Care.


They wrote an article with the title of “Gender Differences in Joint Replacement”.

They stated joint replacement surgery is increasingly common in the United States. Converging social and medical realities are making the incidence of degenerative joint disease of the weight bearing joints (hip and Knee) increasingly prevalent. It is estimated that more than 1 Million Knee replacement and nearly 600,000 Hip replacements will be done yearly by 2020.


They continued on to cover the gender differences.

Women more commonly need Total Knee Replacement compared to men. The need for Hip Replacement is about even between the sexes.  Age matched men versus women: Men put on slightly more miles per year on their joints. Men average a million steps per year at age 65 while women average about 800,000 steps during the same time frame.  The number of steps per year goes down about 3% annually in both genders. Men weigh more, so the wear placed on the joints is certainly higher than women.  Women have a higher incidence of inflammatory arthritis like Rheumatism (actually nearly 9:1).


Here is the link to the article in full:


Once again the experienced surgeons stated that men have more problems with their knee joints because they walk more than women in general. Another reason for the more frequent problem is due to the body weight (men being heavier than women in general). There was no mention of the inferiority of the knee joint of either sex.


It is true that the knee joint of men and women are created differently. The osteology experts tell us that women’s knees are generally smaller. Due to the difference in the pelvis width, the angle of the femur to the tibia is different between the sexes. The extreme tilt, either inward or outward, could cause a potential knee joint problem. However, the risk is the same or very similar for both sexes.


In addition, I have not discovered any medical or osteology research finding that there is any structural differences between the nationalities and races. In other words, the knee joint of a Japanese person is basically identical to that of an American, European, African, etc.


I do believe however, the cultural differences, particularly of the living styles, can take an effect. For instance, your knees will not bend too much by sitting in a chair. On the other hand, sitting in a seiza found in Japanese martial arts will require hyper bending of the knees and much stretching of the knee ligaments. This way of sitting was very common and popular in the Japanese life style but now it is disappearing lately.


Many western karateka falsely believe that the Japanese have a superior knee structure. Unfortunately, this is incorrect. Many of the Japanese children have the life style of sitting only in chairs these days. They no longer sit on the floor any more. What do you think will happen to them consequently? They cannot do the bunny hops and sit in a seiza position. They now have as many knee joint problems as the western children.


It is true that the knee problem often occurs from the extreme twist of the leg, excessive impact to the joint, hyper extension, etc. Karate training involves lots of body shifting, turning, as well as kicking. This means the practitioners should prepare their physical ability to match the training requirement.



The practitioners must learn the correct stances and body shifting method. They also should warm up the joints before each training. In addition, they must supplement the warm ups with some specific exercises to strengthen the muscles and ligaments that are holding the knee joint. The practitioners must advance only gradually in the training and the more challenging techniques. They must not engage in the exercises and training that would cause any pain to the joints. The sense of pain is an indication that something is wrong.



The dance performed by the Georgian National Ballet team seems extreme and dangerous to the audience who never trained for it. However, by preparing their physical condition and muscles, anyone can learn to dance like those ballet dancers, even though not everyone can become good enough to be a team member.


On the same token, some of the Asai ryu physical exercises such as bunny hops, one leg squats, jump from seiza, etc. seem extreme and even dangerous to the karate practitioners who have never trained for them. I request the readers not dismiss it or to categorize without fair trials that they are unhealthy or dangerous. I have written an essay relating to this subject. The title is “Are the ASAI exercises really necessary? 浅井空手の運動が必要な理由”.


Here is the link to the essay, if you are interested in reading it.




I want to emphasize very strongly that almost anyone can become a karate expert without ruining their knees if they exercise well and train correctly. The writer, I am 71 years old and I can demonstrate any of these Asai exercises. I am not an exception or a superman. I have been training regularly and have trained under some excellent instructors. Thus, I never experienced any joint injury including knee and hips in my life. In addition, I train 3 to 4 hours daily even to this date to keep my condition and prepare myself for action. Training this much time may be too difficult for most of the practitioners. They can spend much less time and they can avoid joint problems if they train in karate properly.


On the other hand, if you claim that you are an instructor or call yourself Sensei, then you are obligated to dedicate your time to make yourself worthy of the title. If you already have a knee or hip joint problem, the least you can do is to teach and train your students correctly so that they will not suffer the same problem. I believe this is the universal obligation of a Sensei. Am I asking too much? What do you think?



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