The Knee for Dance or Disaster

Dr Kenneth Backhouse OBE
Illustrations by Lucy Kerr

In the two previous articles (Quadriceps Control of the Knee and The Knee Joint) the potential weaknesses of the knee joint have been stressed from the point of view of the bony structure, the heavy loading on a medially directed angulation and hence the vital dependence on the supporting muscles.

It is essential therefore, when considering the correct ways of using the joint, be it for dance, other forms of exercise or even everyday life, to ensure that the focus of activity should be on strength and avoidance of disruptive influences. The muscles must be strong and used effectively and all other structures in the joint need to be maintained in good physical state. The bones, in particular, in female dancers are often somewhat osteoporotic due to inadequate diet following efforts to maintain an often over slim state. This may readily lead to stress fracture but fortunately rarely involving the knee joint. The hyaline cartilage of joints is vulnerable to damage if overloaded without the joint lubrication being reactivated in the warming up process or, following illness, while even the temporary changes of an alcoholic 'hangover' can lead to disaster, especially in the knee joint. This will be discussed later.

Ligaments are particularly important in the knee joint. While the quadriceps muscles pull the knee into its firm straight state. It is the taut cruciate ligaments that produce the slight twist to lock the joint in extension. They also induce slight changes in the loading regions within the joint in movement: important to assist lubrication in such a heavily stressed joint. Likewise the thick, broad medial and the lateral ligaments, that are there to control the hinge activity, should remain taut at all times. Lax ligaments are more likely to be damaged. (Remember, when sewing, that it is difficult to break a tight thread; to break it you give quick pull when it is loose). Laxness of ligaments of genetic origin, as in people with sway back knees, offers extra control problems. Although ligaments always have active muscle support, the need becomes greater if ligaments are lax. If the laxness is due to improper stretching, as so often happens in the knee from forcing a flat turn-out, the results can lead to disaster.

Sway-Back Knee
Represents almost always a genetic laxity and is often associated with a general laxity of joint ligaments, such as an easy turn-out. As such it can have advantages in dance but must also add extra needs of control. If not too great it can give a lovely line in the working leg, as in arabesque, but in the supporting leg, if not controlled, it can throw the weight backwards which in turn can present problems for the feet, especially on full pointe. It can induce an increased pelvic tilt as well as a slowing in the speed of reaction. A small amount is of little consequence but if too great, instead of a simple pull up of the quadriceps into firm extension, a balance needs to be built-up between the extensors and flexors to limit the hyperextension.

In grand plié the quadriceps (A) pull the patella around the end of the femur under the full weight of the body, inducing enormous shear stresses on the cartilage (B). If the cartilage is not in good health and the joint well lubricated (effectively warmed-up), irreparable damage can occur.

Forced Flat Turn-Out
Is probably the cause of the highest proportion of knee disabilities, both early and long term in classical ballet dancers. Turn-out was never designed to position the feet but to allow freedom to maintain dance en face and to free the range of the legs to the side (à la seconde). The movement should arise purely from the hip joint for this purpose but the obvious focus on the feet has come to demand a flat turn-out. The Russians demand this, regardless of the damage to so many of their, often considered expendable, dancers. The Russian ethos, with their ballets and dancers, has spread abroad with equally dangerous results. Some years ago I was asked by a visiting company to explain why virtually all their Russian trained men had knee injuries. They had excellent flat turn-out but with knee-caps pointing forwards: much of the twist outwards was from the knee, the cause of their disability.

Britain has also suffered with professional schools demanding flat turn-out; even importing Russian teachers, with a considerable loss of potential talent and physical well-being of many young students. And the injuries are not limited to the knee as the efforts also induce rolling in of the feet as well as affecting pelvic tilt. Many dancers, fighting to achieve a better visual turn-out, are not only liable to suffer injuries but also fail to achieve, through concentration on a physical effort, their full artistic potential. As an example: a well-known English dancer with relatively poor turn-out was, in her earlier years, good but suffered far too many injuries. After leaving the company for a while she returned but decided not to fight for her turn-out but dance: she then became the supreme artist on which her reputation stands.

In extension the ligaments of the knee are taut and no active rotation should be possible. The rotation in extension is developed by rotating outwards in flexion and then, with the foot fixed on the ground straightening the leg, so gradually stretching and loosening the ligaments. The stability of this vulnerable joint is thus reduced. Under normal circumstances the menisci, particularly the lateral one, are adjusted to cope with the movements of the femur on the tibial tables so as not to become trapped between the bones. With loosening of the ligaments the adjustment becomes less effective so that a meniscus, usually the more fixed medial, may become trapped between the bones and split. The immediate effect is a locking of the joint that can be released by a helper repeatedly twisting the foot until the split cartilage slips back from between the bones; but the damage is done. Cartilage does not repair. Traditionally the whole cartilage was removed by major knee surgery. Although the surgery was reasonably effective early osteoarthritis of the knee was to be expected. Now the treatment may be less severe. An arthroscope, a small telescope with cutting and extracting instruments is inserted into the joint and if the damage is not too severe the split pieces of the cartilage may be removed. The long-term wear and tear damage may be correspondingly less severe but far better to be avoided. Nethertheless the resulting instability of forcing turn-out at the knee automatically leads to potential joint damage; immediate reduced efficiency and almost certainly expected future physical disability. Achieve an effective practical turn-out and look to a long artistically and physically satisfactory career.

Knock-Knee (Geni Valgum)
The femur approaches the knee joint from the side of the pelvis so the knee naturally has an angle on the vertical tibia. As a result the load tends to push the knee inwards. Ideally this is prevented by the action of the inner thigh muscles (Sartorius, Gracilis and Semitendinosus) in support of the strong medial ligament of the knee joint. A degree of laxity in this support allows the knee to fall in to some extent, a problem greater in females due to the wider pelvis and the increased angle of the knee from the straight. A very high proportion of the adult female population suffer from a degree of knock-knee and this is a major problem if present in a dancer. Hence the constant need to stress pulling up on the inside of the thigh. Not only does poor control of knock-knee induce strain on, particularly, the medial ligament but it also induces rolling in of the foot and the major problems associated with that.

Although the inner thigh muscles support the knee from falling in, their tendons run behind the medial condyle of the femur and then turn forwards into the tibia, where they can act as medial rotators at the knee joint, normally only when the joint is flexed. If the knee is forced into a lateral twist to achieve a flat turn-out, these muscles must relax to allow it to occur, so losing control of and compounding the dangers to the inner side of the knee; adding to the problems within the joint as well as the ensuing problems of rolling in of the foot.

Twisting of the knee under full load can lead to trapping of a semi-lunar cartilage (more usually the medial) and to irreparable damage

The Patella
is a bone in the tendons of vastus intermedius and rectus femoris components of the quadriceps. It acts to improve the leverage of the tendons over the lower part of the femur and hence the efficiency of these muscles as extensors at the knee joint. However, due to the angle of the femur on the tibia, the pull of the muscles through the patella to the patellar tendon and into the tibia is also not direct. Hence there is a tendency for the patella to be pulled laterally as the muscles contract. The patella runs in a groove between the two condyles of the femur. The lateral condyle is rather more prominent and so acts to some extent in preventing the patella tracking laterally. The real control of the tracking of the patella however comes from the oblique portion of vastus medialis. As the quadriceps contracts this muscle should control the tracking of the patella, preventing the stesses to the outside and even more importantly preventing lateral dislocation. Due to the greater angulation at the knee in females, the risk of tracking problems and even spontaneous dislocation of the patella is common; problems aggravated in knock-knee.

By pulling up on the inside of the thigh to support the inner side of the knee the oblique portion of vastus medialis is also activated to control the tracking. Failure to do so will add tracking stresses to the hyaline cartilage on the under side of the patella where it is related to that on the femur. Subsequent damage results in pain, particularly when extending the knee. At an immediate level there is maybe a spontaneous lateral dislocation so that the patella comes to lie outside the lateral condyle of the femur. Although a common problem, particularly in females, it is easy to reduce. With the knee straight the patella can usually be pushed back over the lateral condyle of the femur: better to be avoided! Maintain an inner side pull up!

With the leg in extension, the patella lies on the front of the lower part of the femur with their contact surfaces covered by hyaline cartilage. As the knee bends the patella tracks round the lower end of the femur so with the knee at 90 degrees it lies on the end of the femur and in full flexion (grand plié) it is even farther round. Thus the loading between the femur and the patella as it is pulled round to straighten under the full weight of the body is enormous. Traditionally 'bunny-hopping' i.e. bouncing with the knees in full flexion, was a popular way in physical exercise to strengthen the quadriceps muscles. So common was damage to the cartilage beneath the patella that the exercise was abandoned. There have even been demands that the grand plié should also be banned on similar grounds. It would be impractical to do so without gross limitation to the potentials in dance. However the warning is there and care should be exercised. If all is well with the cartilage and reasonable levels of activity are maintained there should be little risk. In good health the cartilage should be able to cope but in ilness - even with a hang-over, the cartilage may be vulnerable. It is also important that the joint lubrication is effective so a good warm-up is vital before exercising the grand plié. Problems can induce damage to the cartilage creating retro patellar pain: or fragments can be broken off to give free bodies in the joint that interfere with painless movement.

Muscle control in joint injury
One of the body's natural response to injury is to bring in a protective reduction in muscular activity and this is particularly so for the knee. Possibly this is in recognition of the basic vulnerability of the joint. Even a very minor injury around the knee joint will result in a central (i.e. the brain) inhibition of quadriceps activity that in turn quickly leads to a reduction in muscle bulk and power. In the knee this can lead to further problems if care is not taken. In view of the large expanse of synovial membrane in the knee even minor injury can lead to synovitis - water on the knee. This must be treated with TOTAL REST, when the problem is likely to clear in 48 hours or so. If allowed to go on synovitis can persist, adhesions can form and be a chronic problem.

But with the rest, firm quadriceps exercise with the knee remaining straight is vital i.e. muscle exercise without movement. However the synovitis can occur secondary to other forms of injury if the knee is exercised without good quadriceps control. Always remember that the knee is a vulnerable joint that has to accept a great deal of stress whatever activities are required of it. If the stresses are not controlled then, although short term problems may not be obvious, the longer term may lead to disaster and early disability. Dance has often been blamed for the early onset of knee disability. It is often an improper blame. The blame commonly lies in the classroom with the demands of teachers with little understanding of the human body, the instrument of dance, or sometimes at a professional level from the unreasonable requests of choreographers. Dance from strength and enjoy a long and successful future.