The knee joint is very vulnerable because of its basic structure, which is a hinge with long levers on either side . The knee is really two joints, one between the femur and the tibia, the other between the patella and the anterior surface of the lower femur. The rounded end of the femur contacts the flat upper part of the tibia, and the two menisci or cartilages lie between them. The menisci are deeper around the edge and so provide a slight depression on the flat tibia for the rounded femur but even then the basic stability of the joint is almost nil. Its strength depends upon its capsule and ligaments together with the muscles acting across the joint.
The knee has always been considered a simple joint but over the last decade the whole concept of the functional anatomy of the knee has changed and the exact functions of each ligament are still open to argument. The joint is surrounded by a capsule, the posterior part of which is only taut in full extension of the knee and provides some stability even in medial and lateral directions. The anterior part of the capsule is only taut in full flexion and is extended as a pouch above and behind the patella. The only structures within the capsule are one small tendon and two menisci.
The medial ligament of the knee passes from the femoral condyle to the upper margin of the tibia. It is composed of a superficial layer which is attached to the tibia several inches below the joint line and a deep layer which is attached to the medial meniscus and the upper margin of the tibia. The whole ligament forms a wide fan-like structure.
The lateral ligament of the knee is a narrow band passing from the femoral condyle to the head of the fibula and should not be considered the major support on the lateral aspect; this function is performed by the ilio-tibial tract. There are also thickened areas in the capsule which are sometimes described as ligaments.
There are also two major ligaments which are situated centrally, deep within the joint and because of a fold in the capsule are actually outside the joint capsule. These are (1) the anterior cruciate ligament which runs upwards and backwards from its origin on the anterior lip in the mid-line of the upper tibia to the femur and (2) the posterior cruciate ligament, the key to stability of the joint, which arises just medial to the mid-line of the femur and runs downwards and backwards to the tibia. These ligaments are important in the antero-posterior plane.
A major stabilising factor for the knee joint are the muscles . Anteriorly, the powerful quadriceps muscle is inserted into the patella and then through the patellar tendon into the upper part of the tibia. Posteriorly, there are not only the hamstring muscles from the thigh but also the gastrocnemius muscle from the calf. This stabilising factor is important in sport because we can only strengthen the ligaments in a minor way but we can ensure maximum help from the muscles.
A previously unreported series of 8899 sports injuries seen in the sports medicine clinic of St James’ Hospital, Leeds over a four year period and in an accident and emergency department over a three year period show that ligamentous injuries of the knee comprised nine per cent (803 patients) and of the ankle 11.4 per cent (1014 patients), these being the two most frequent diagnoses.
Injury to the knee may damage skin and subcutaneous tissue, muscle, tendon, ligament, capsule, cartilage or bone. Initial examination of an injured player has to decide only three things. 1. Is there a possibility of a fracture? 2. Is there severe ligamentous injury? 3. Is there a torn cartilage?
These are the three serious problems which have to be considered at first.
It is important to have some idea of what happened to the athlete or player at the time of injury as well as any history of previous trouble with the knee joint before proceeding to an examination. The mechanism of injury is important in diagnosis and this is best recalled immediately. Did the patient have the weight on the leg? Was the leg bent or straight when injured? Was the patient turning and if so, in what direction? When laid on the ground could the patient bend and straighten the leg? If unable to straighten the leg, what position was the best he could manage? Was the patient aware of any snapping or tearing sensation? How soon after injury did any swelling occur? If there was contact with an opponent where was the patient struck and from which direction? In many cases it is a precise history of the mechanics of injury and of the symptoms upon which a diagnosis is made.
Examination should start with observation for the presence of any deformity or swelling. Obvious deformity, severe pain, tenderness over bone and loss of power raise the possibility of fracture and the patient should be moved as carefully as possible to hospital. Can the patient fully flex the knee and, more particularly, can he fully extend the joint? If there is any loss of movement this must be recorded. Carefully palpate the joint for swelling and localised tenderness. It is important to localise accurately any tenderness and in particular to say whether this tenderness was over bone or over the joint line.
Examine the knee for stability, testing in full extension when instability implies damage to the posterior cruciate, the posterior capsule and the medial ligament. Also check for stability in approximately 30° of flexion when the posterior capsule and the posterior cruciate ligament are relaxed; instability in this position implies a possible rupture of the medial or lateral ligament which will not show when the joint is in full extension if the posterior cruciate ligament is intact. Considerable swelling developing within 30 minutes of injury means there has been bleeding into the joint, I.e. haemarthrosis, and this implies serious injury. On some occasions, however, the absence of this sign may be misleading in that if the injury is sufficiently severe then the capsule itself will be torn and the blood will leak into the subcutaneous tissues, particularly at the back of the knee. Similarly, it is important to remember that a complete tear of the ligament may be less painful than a partial tear but this type of injury can almost always be differentiated from the minor injury by the fact that there has been significant violence, the patient is usually aware that something has torn or given way and, in the more serious injury, there is gross instability when the patient attempts to bear weight.
Effusion which is due to damage or irritation of the synovial lining of the capsule will show several hours later. This might be caused by a direct blow or in response to an internal injury of the knee.
When there is a possibility of serious injury to the knee joint then this must be adequately examined in proper surroundings and examination may include x-rays, arthrography (when dye is injected into the joint) or arthroscopy (when a small telescope is placed into the joint for direct vision). All methods of examination have advantages and disadvantages.
Routine x-rays do not show soft tissue such as the menisci so a radio-opaque dye may be injected into the joint in an attempt to show these tissues. However, there is a risk of infection; the x-rays may still not show the area of interest; and the interpretation of the films requires considerable skill. Arthroscopy allows a direct view of the majority, but not all, of the articular surfaces of the knee joint and the menisci but carries the risk of a general anaesthetic and of infection.
PRINCIPLES OF TREATMENT
The basic principles in the treatment of knee injuries are those applicable to other injuries. Initially, check for possible fracture or severe ligament injury both of which should be seen at hospital. Other injuries should be treated by ice followed by compression for 36 hours after which definitive treatment usually begins. Contrast bathing is most helpful in reducing swelling with more complicated forms of electrotherapy being only marginally better.
For the athlete it is essential that exercises be carried out from an early stage but these must be exactly performed and their severity frequently adjusted to the capability of the injured limb. Speed of rehabilitation is important in the athlete but the maximal rate of progress through an exercise routine is very close to that which will exacerbate the condition or cause another injury so great skill is required.
Initially, simply lifting the leg with the knee fully extended may be carried out and then with increasing weight strapped to the ankle or using a lead boot, progressing to at least 201b (9kg) in the adult. When flexion of the knee to 90° is pain-free, extension from this position may be started, using a De Lorme boot for increasing resistance. An adult must be able to fully extend 301b (13.5kg) ten times in 45 seconds before starting to run. This is necessary to provide joint stability. The adult should similarly lift 401b (18kg) before returning to sports other than rugby when the weight should be 451b (20kg). This may appear a lot but it is required to protect the joint against body contact forces.
It is important to ensure that there is muscular balance between the two legs, a difference of greater than five per cent statistically increases the chance of further injury. This balance should be between the strength of the two quadriceps muscle groups and also between the hamstrings and the quadriceps of the same limb when the hamstrings should have at least 60 per cent of the strength of the quadriceps (Klein and All-man, 1969).
In order to protect a joint it is essential to have strength applied very quickly to counteract potentially damaging forces so ‘power’ is required. Power or explosive strength may be improved by activities such as hopping which should only be attempted late in the rehabilitation phase. Hopping may be carried out for distance or height or up a slope, all methods being useful.
Fitness testing should be carried out before the player returns to competition and this must be related to the requirements of the athlete’s own sport. Can he sprint, check, twist, jump, stretch as required? If there is any discomfort it is better to have a further week of rehabilitation rather than have a possible recurrence or endure the remainder of the season performing below par with a minor chronic injury.
Contusions of the knee
Contusion of the knee is common in many sports but particularly football. There is a history of a direct blow and on examination there may be localised swelling, tenderness, possibly bruising and slight limitation of movement. Initial treatment is ice, that is to say, ice, compression and elevation. An ice pack is applied to the injured area and held in place for at least 30 minutes by an elasticated bandage, the leg being elevated. The player has a quick shower, not a leisurely bath, and a compression dressing is applied. This may consist of a layer of cotton wool over which is a crepe or elastic bandage and the compression should extend for a hand’s breadth above and below the joint. This should stay in place for 36 hours after which the patient should be encouraged to move the joint. The player usually returns to full activity within the week.
Ligamentous injury, usually known as a sprain, of the knee is less common than the similar injury to the ankle joint but is often more serious. The injury may range from the trivial to the most severe and could keep the athlete permanently from competition. The severe injuries typically occur when the whole bodyweight of the opponent is against the joint when the leg itself is carrying weight and therefore fixed to the ground, for example, in a rugby tackle.
Minor ligamentous injury with tenderness over the attachment of the ligament to bone, pain on stressing the ligament and without effusion, may be treated as a contusion but with a definite rehabilitation phase in which increasingly severe turning movements are incorporated.
Moderate sprains show considerable pain, swelling which is localised at first but may become generalised, tenderness, pain and some apprehension on movement, pain and possibly some laxity on stressing the ligament. In this injury a variable proportion of the ligament has been torn and the important aspect of treatment is to prevent the patient accidentally stressing the ligament, thereby converting a partial into a complete tear. The initial treatment with ice must be followed by a firm bandage which gives great support to the joint and prevents movement but allows the initial swelling to take place. A Robert Jones bandage, which consists of three alternating layers of cotton wool and domette bandage, is the most usual form of firm bandage. Three or four days later this should be removed for re-examination of the knee in case the initial examination, obscured by pain and muscle spasm, led to the wrong diagnosis. Depending upon the severity of the condition a decision is then made regarding further treatment. This will vary from some support with periodic exercise to immobilisation in a plaster cast.
Complete tear of the ligament constitutes a severe injury. The history is one ofsevere violence, the patient usually being aware of a tearing sensation and instability of the joint. Pain may be variable. Swelling within the joint or in the subcutaneous tissues rapidly appears. Laxity in full extension implies rupture of the posterior cruciate ligament. Laxity of more than 10° greater than in the uninjured knee, when the joint is examined in part flexion, implies damage to the medial or lateral ligament. Antero-posterior instability of the tibia in relation to the femur may be misleading; examination of this with the foot in a neutral position may be positive but in the minor injury this should be abolished when the foot is internally rotated. A posterior sag of the tibia in relation to the femur is always significant.
The presence of a ruptured knee ligament in an athlete requires surgical repair to all the torn structures. This should be carried out within ten days of injury and this is why moderate sprains should be re-assessed after three or four days in case the initial diagnosis is wrong. Care must also be taken in this type of injury to look for the presence of ‘O’Donoghue’s triad’ – tears of the medial ligament, the anterior cruciate ligament and the medial meniscus (O’Donoghue, 1970). This is also called the ‘unhappy triad’ because unhappily the full extent of the injury is often not appreciated.
Cartilage injuries ‘You have a torn cartilage’ are words of impending doom to the athlete which are not inevitable; troubles arise not from surgical technique but through inadequate rehabilitation. There is a covering of articular cartilage over the weight-bearing surfaces of the bones within the joint and there are also two C-shaped menisci – it is these latter structures which the athlete calls cartilages. They are avascular and may develop, within their substance, cysts or tears which do not heal. Once torn, there is the choice of leading an inactive life with possible occasional trouble or having the cartilage removed surgically. After removal, the space occupied by the meniscus is filled by a replacement but not of the same material or quality so the joint is marginally worse than previously. Therefore, the operation should not be undertaken lightly and also, it may be very difficult to decide whether the symptoms are truly from a torn meniscus or from which of the two menisci.
A meniscus usually tears when the knee joint is carrying bodyweight, the foot being fixed as may happen with a studded shoe and the body is rotated in relation to the foot. The patient usually complains of pain on one side of the joint and often of inability to fully extend the knee, so called ‘locking’. This occurs about 30° short of full extension and typically, full extension suddenly returns minutes or days later. Momentary difficulty in extension with the knee more fully flexed is not locking and not due to a torn cartilage. Generalised swelling of the joint may occur later that day or next morning. An athlete with this type of history requires a medical opinion and the initial treatment of simply ice.
Other knee injuries
Less common causes of knee pain include patellar tendinitis known as ‘jumper’s knee’ because it is often associated with sports such as basketball which demand take-off and landing on hard surfaces (Blazina et al, 1973). It is characterised by pain in front of the knee, below the patella and precipitated by forceful knee extension. There is localised tenderness in or around the patellar tendon, usually near its proximal attachment. The condition comes on gradually over several matches and may be very persistent. Treatment is, initially, rest – a dreadful word to the athlete! – for about two weeks. The condition is helped by ultrasound, anti-inflammatory drugs, injection of hydrocortisone and more rarely, operation.
A condition peculiar to the early teenage, enthusiastic athlete is Osgood Schlatter’s disease. This affects the tibial tuberosity- the prominence on the upper part of the anterior surface of the tibia into which is attached the patellar tendon. Comparative overstrain of the quadriceps muscle acting upon a delicate area of growing bone can produce a painful reaction. It usually involves boys aged 12 to 16 years; there is an aching pain over the tuberosity which is worse during or commonly after exercise, and there is local swelling and tenderness. The condition may be diagnosed clinically, although the x-ray has a characteristic appearance of fragmentation. Treatment is very definitely rest until the bone settles down. I merely prohibit organised physical activity for several months but some orthopaedic surgeons place the joint in a full leg plaster for six to eight weeks followed by a gradual return to full activity. Usually the condition settles satisfactorily but may recur during the growth phase of adolescence.
Injury to the knee joint is common and may be very difficult to manage. The most important single factor is to ensure that the athlete does not cause further damage by returning to sport without adequate, balanced strength. It is neglectful to allow an athlete to participate with a weak leg or swollen knee.
Blazina, M. E., Kerlin, R. K., Jobe, F. W., Carter,
V. S. and Carlson, G. J. (1973). Orthopaedic Clinics of North America, 4, 665-678. Klein, K. K. and Allman, F. L. (1969). The knee in sports. Pemberton Press, New York. O’Donoghue, D. H. (1970). Treatment of injuries to athletes. W. B. Saunders, Philadelphia.