The inward rotation of the femur which occurs as the knee comes close to its locking position of extension is not large but very important to knee function, making the knee much more complex than a simple hinge joint. The small internal movements of the knee are limited in the knee joint and the joint cannot afford any losses of these motions without losing some of its function. These small movements are called accessory movements and are small gliding and sliding movements which occur within the joint during functional activity but which cannot be performed in isolation.

The knee has to satisfy the competing demands of stability and mobility, it has to be a powerful and reliable prop for the body weight and it has to move into varied positions with great speed. In the case of walking the knee must at one moment bear the entire body weight and then the next unlock so that the leg can be lifted to step forward. As the cycle progresses the knees lock and unlock regularly and reliably, enabling rapid walking and the covering of great distances without fear of falling. The slide that occurs during the knee lock and unlock is vital to this function and can give problems early on in knee pathology.

The knee has very strong muscles but can also respond to changes such as an uneven surface by finer controlled reactions. The knee is strong enough to achieve full squatting and then stand our body weight up again without pause. The knee’s accessory movements are small in distance with side to side more limited than front to back, both however contributing to coping with uneven ground. The inside of the knee joint can gap open more than the outside due to the natural angle of the lower leg to the knee.

The first article about the knee covered the idea that the knee moves backwards and forwards and tends to stick in that plane, so if an abnormal stress such as to the side is added this changes the balance in the joint. The kneecap and the main knee compartments can experience wear changes if the knee suffers from bow-leg or knock knee. The knee is divided into two compartments, the medial and the lateral side, both with their own meniscus, ligament, femoral and tibial condyles. The stresses which are transmitted across the compartments vary with changes in the sideways angle of the knee.

If the knee becomes bow-legged to some degree the quadriceps pulling on the patella levers it towards the inside and can cause the patella to be compressed against the inside of the femoral groove, with painful results. The lateral knee compartment then suffers increased forces and is subject to accelerated wear changes on that side. Typically people have a small degree of knock knee, and any exaggeration of this can make kneecap pain more likely on the outside and cause increased wear of the inside compartment.

Patellar problems can also occur if the knee does not typically extend fully, as the knee remains slightly flexed and the quadriceps has to maintain knee stability, pushing the patella strongly against the femoral groove. These increased forces can be a cause of patello-femoral pain which is a very common complaint. If the knee has some abnormal lateral alignment then a small wedge under one side of the heel can realign the foot and shin bone from below and thereby make a very small but important change to the stresses through the knee.

The patella can also give problems in response to abnormal changes in other joints. As we get older our foot arches can become less strong and so less pronounced, sometimes leading towards a degree of flat foot. As the feet rotate inwards on weight bearing the whole foot and shin move inwards to some extent, introducing an amount of knock knee effect at the knee. This can cause the kneecap to glide more outwards along the groove than normal and lead to patello-femoral pain. An effective treatment can be to wear orthotics in the shoes, which can combine restoration of the foot arches with the necessary level of medial wedging of the heel.

Jonathan Blood Smyth, editor of the Physiotherapy Site, writes articles about Physiotherapy, back pain, orthopaedic conditions, neck pain, injury management and physiotherapists in Leicester. Jonathan is a superintendant physiotherapist at an NHS hospital in the South-West of the UK.

Small movements which allow a glide and a slide inside a joint are essential for the normal use of the joint but cannot be done in isolation, occurring with other movements. These are called accessory movements and their presence is vital to joint function, a reduction in available range or a pain problem resulting if they are lost or reduced. The hip is a deep joint with significant stability so the accessory movements are rather subtle, with the main one being compression and distraction, the pushing in to and pulling out of the ball from the socket.

The health and well-being of the articular cartilage are related to the repeated cycles of compression and relaxation applied to the joint such as with weight bearing and walking. The cartilage is pressed downwards to a degree when pressure is applied and this indentation returns to normal once the pressure is relieved. This engages a fluid pumping system where it is squashed out of the cartilage under compression and pulled back in on relief of the pressure. This pumping of fluid from the deeper cartilage and underlying bone keeps the surface healthy.

The production of new cartilage is in response to the daily expected mechanical stresses put on a joint, and with the high forces involved in heel strike the cycle of stresses and relaxation are important to counter this. Encouraging larger movements in greater ranges may be useful to encourage growth of cartilage, however if loads are static or significantly reduced the opposite may occur. Loss of cartilage may occur with continued static loading, high bodyweight and allowing the joint forces to reduce by using a walking aid.

When a joint is painful it may not always be the best idea to rest it although pain will be reduced at least initially. Without normal forces the cartilage regrowth stimulation does not occur and there may be a tightening of the joint capsule and a loss of the full movement of the joint. The joint may then become more painful as the tightness increases compressive forces. Respecting a painful joint is important but overall it is better to keep an arthritic joint moving than to keep it static. The normal cyclical rhythm of gait is very important in maintaining movement and good blood supply to the upper hip area.

In the inside of the hip, leading from the acetabulum to the femoral head, is the band like ligamentum teres which carries blood vessels that can be stimulated by the typical cycle of gait and allow a fluid pump. The may give an improved blood supply to the femoral head and maintain bone health. The normal forces which walking places on the upper femoral region are vital to keeping the bone composition and density within normal ranges. Resting in bed or using a walking aid can both contribute to a reduction in mineralisation and density in bone, making it less flexible and so less able to counter strains and jars.

In western societies we typically use little of the relatively large available ranges of movement of the hip joint. We walk in a limited, repetitive range and when we sit we typically do so at a mostly high level so our hips don’t go beyond 90 degrees flexion. We seldom push our hips to the extremes of movement of which they are capable and this tendency increases greatly with age. Overall the hip will benefit from maintaining a variety of its movements and from placing it at the ends of its ranges at times. Eastern peoples typically squat or sit cross legged, even to iron, and seem to have lower levels of hip arthritis.

An increased tightness in the joint capsule can result from a person not taking advantage of their full joint ranges over a time period, elevating the tendency for the head to be compressed into the socket. If there is a discrepancy in leg length this can primarily affect hip extension as the hip and knee are maintained in slight flexion to keep the eyes and head level. This fixed flexion deformity of the hip limits extension excursion of the joint in walking and changes the pattern of gait.

Jonathan Blood Smyth, editor of the Physiotherapy Site, writes articles about Physiotherapists, physiotherapy, Physiotherapists in Windsor, back pain, orthopaedic conditions, neck pain and injury management. Jonathan is a superintendant physiotherapist at an NHS hospital in the South-West of the UK.

Like the elbow, the knee joint is an example of a hinge joint with added complexity. The condyles of the femur are enlarged rounded areas at the base of the femur and they make up the knee joint with the enlarged flattened area of the upper end of the tibia. On the outer side of the shin lies the fibula, a thin, long bone which does not make up part of the knee nor bear much weight, mainly acting as an area of muscle origin for the muscles which move the foot, ankle and toes. The hinge joint of the knee splits the leg in two, allowing tidy folding in resting or active positions, the necessary shortening of the leg to allow effective walking and the large levels of of propulsive power required.

As the knee approaches full extension or straightening the main thigh muscles (the quadriceps) engage to achieve full active extension and guide the knee into its locking position. Apes are unable to straighten their knee in standing, whilst humans can extend their knees fully in standing which allows very low energy usage. As the knee gets closer to full extension the thigh muscle rotates the knee inwards to allow it to reach the locking point. Humans can stand with their knees straight for long periods with little activity in the quadriceps and hip muscles, combining stability and low effort.

Inside the joint are two crescent-shaped structures made of cartilage, looking a little like banked tracks, accommodating the large rounded femoral condyles. Their exact function is not clear but they may contribute to guiding the knee towards locking, stabilise the knee by centring the condyles during bending and straightening and evening out any potential unwanted small movements during joint motion. The kneecap is the other part of the knee joint and is a small bone with an inner lining of articular cartilage which is suspended in front of the knee joint.

The kneecap or patella is placed within the tendon the main thigh muscle or quadriceps, the muscle which enables us to move our body weight up and down stairs and up from a chair. The patella is shaped on its inner surface with two facets, fitting into the groove formed between the condyles of the femur, sliding along the groove as the knee moves. The kneecap is present to allow the muscular forces developed by the quadriceps to be amplified across the knee and so enable application of high levels of power.

When a knee continues to bend and straighten in a forward and backwards direction the alignment is good and problems are less likely to arise. When a sideways misalignment is added however, the knee can develop painful conditions. A sideways alignment (knock knee or bow leg type conditions) throws the stresses onto one side of the knee by compressing that side of the joint, exposing it to increased wear. A misalignment also changes the angles of function of the patella and causes it to track off to one side, increasing joint friction and causing pain.

The high mechanical forces transmitted through the knee are responsible for a variety of knee conditions, often affecting the kneecap or the knee cartilages (more properly called menisci). The knee typically has a range of motion from full extension (stated as zero) to full flexion at around one hundred and forty degrees, depending to some extent on body size and bodily mobility. There is an important degree of internal glide and slide of the femoral condyles as they move on the reciprocally moving tibial surfaces.

The forward and backward gliding of the condyles of the femur ensure that they will not slide off the back of the shin bone during motion. In motion one bone does not move in isolation, rather one bone moves in a complicated manner on a complementary bone which is also moving to complete the overall function. This permits a much larger range of motion than would be achievable without such a technique. The femur exhibits an amount of rotation also at the knee which is most discernible as the knee approaches fully straight and the thigh rotates inwards to lock the knee safely.

Jonathan Blood Smyth is the Superintendent of Physiotherapists at an NHS hospital in the South-West of the UK. He writes articles about back pain, neck pain, and injury management. If you are looking for Winchester physiotherapy visit his website.

The effect on the function of the hip joint of a difference in the length of the legs has been mentioned previously in an article in this series. The longer of the two legs will attempt to keep the head level by flexing slightly at the hip and knee, leading to a lack of movement into extension of the hip as we walk. Rotation of the hip and pelvis is required to achieve a more normal gait pattern if extension is not fully achievable. This may be a small change in joint movement, but on repetition thousands of times per day this can set up difficulties in joint movement and over time a painful joint condition.

The hip can give problems and deteriorate into a severely painful joint very quickly after a traumatic event such as a fall, strain or jar. However, this is less common on average as hip problems usually come on slowly over a long period. A small event can set off a painful process which starts with some muscle spasm and a reduction in the extension range typically used in walking. The hip joint is at its tightest and most pressured when it is put into extension, and when we have a painful joint we avoid this kind of joint position in order to avoid pain.

A limp is a normal development when one has a painful hip and this is commonly observed with arthritic hips and knees. Once a limp has been present for some time it is difficult to get rid of it. The stresses which occur across the hip joint are greatly altered by a limp, with abnormal muscle use and a gradual tightening of the ranges of movement. The capsule of the hip can be progressively tightened by this process and this is why a normal gait is the aim of all physiotherapists who are assessing and managing a lower limb condition.

The major weight bearing joints of the knee and hip are mostly affected by osteoarthritic changes, osteoarthritis being the most common degenerative joint condition in the world. Many factors contribute to the incidence and severity of arthritis, with a family history being important to some degree. Osteoarthritis becomes much more prevalent with increasing age and is almost universal in some joints in older people. As the arthritis worsens the joint can gradually lose movement as the capsule tightens, with a slow healing due to the lack of good blood supply.

The steady loss of the articular surface of the hip goes on with an increased limp and consequent spasm of the hip muscles. There can be a rapid deterioration of an arthritic joint without much of a mechanical insult and it is not understood exactly why, but elevated levels of muscle spasm and pain may contribute. Pain from a hip joint refers to the anterior thigh region, the groin, the side of the hip or the lower buttock. Patients may attend a medical consultation with what they expect is a leg or knee condition and are surprised with a diagnosis of an arthritic hip.

Little useful information may come from x-rays of the hip in the early stages of osteoarthritis and the patients disability or pain is not easily connected with x-ray findings overall. A worsening joint will show clear x-ray changes such as narrowing of the joint space caused by loss of thickness of the articular cartilage. Abnormal shaping of the femoral head and the formation of marginal joint bone outgrowths called osteophytes will occur in severe cases. On bearing weight or movement a severely osteoarthritic joint will shudder and grate audibly.

The losses of joint movement in the hip occur in a characteristic order, with extension being lost first, followed by abduction, the ability to move the hip out to the side and finally of internal rotation of the joint. On examination of a hip with an osteoarthritic joint the hip will be held forwards and lack extension, the leg will be rotated outwards and can be held close to the other leg as it cannot easily be moved away. The lack of extension and shortening of the leg due to the arthritis can force the trunk to twist in gait and the person to go up on their toes slightly to compensate for the shortening.

Jonathan Blood Smyth, editor of the Physiotherapy Site, writes articles about Physiotherapists, physiotherapy, Physiotherapists in Coventry, back pain, orthopaedic conditions, neck pain and injury management. Jonathan is a superintendant physiotherapist at an NHS hospital in the South-West of the UK.

The shoulder is a particularly interesting joint which is designed to allow a considerable degree of joint movement to occur between the arm and the trunk. The shoulder is classified as a ball and socket joint but the name is less appropriate than the hip joint. The upper end of the humerus or arm bone is formed into a large rounded structure which does resemble the ball of the hip joint to some extent. The socket however is not the deep one of the hip but a shallow and much smaller one than expected from this type of joint.

The shoulder blade or scapula is a flat bony structure which is placed over the upper posterior ribs on each side, and its outer ends are modified into the shoulder socket or glenoid cavity. There is a fibrous bag around the shoulder as in all synovial joints, called the capsule and in the shoulder this is less supportive than commonly and is baggy and slack to allow movement. The origin of the rotator cuff muscles is on the scapula and they run laterally from there to insert (stick onto) just lateral to the ball of the joint in an area called the lesser tuberosity.

Directly above the head of the humerus is a strut of bone made up of two parts, the acromion process which is part of the shoulder blade and the outer end of the collar bone. Where these two bones meet is called the acromioclavicular joint which is a joint without much movement and which stabilises the arm like a suspension arm on a car. This allows the shoulder to cope with force without it falling in towards the centre of the chest. A direct fall on the shoulder, the elbow or the hand can rupture the ligaments of this joint, an extremely painful injury and a difficult one to manage as the joint may not be restored.

The stabilising muscles and the joint capsule join the arm bone to the scapula but we must recognise that the scapula itself is not fixed to the thorax but lies over the ribs with only a muscular attachment to the trunk. The shoulder is more precisely called the glenohumeral joint and the movements which the shoulder blade is able to perform add to the already considerable movements of the glenohumeral joint. This permits us to place our arms and thereby our hands, the tools we use to manipulate objects, in a huge range of positions. The arm is a long lever and develops significant forces in use and its muscles do not seem particularly large.

There are several functions which the rotator cuff performs in the shoulder girdle. Firstly the cuff centres the large ball on the small socket by compression while the bigger shoulder muscles exert the power to move the arm. Secondly the cuff holds the ball up and stops it sagging down towards the edge of the small socket. Thirdly the cuff performs a degree of lifting of the arm and rotates it when required. Shoulder pathology may be related to stiffness and pain, usually with poor scapular control, or to increased mobility and pain with similar problems with scapular control. Pain and loss of movement is the commonest presentation.

If the rotator cuff is of sufficient strength it will help reduce the chance of suffering from a couple of shoulder problems. Lifting the arm above the head pulls the ball of the arm bone upwards towards the acromion and can cause impingement, which is prevented by the cuff muscles pulling the ball down and keeping it centred on the small socket. Subluxation of the joint, a part dislocation where one surface slips off the other to a degree, is also guarded against by the rotator cuff. Trauma is always necessary for full dislocation unless the person has abnormal collagen and so abnormal joint mobility.

The scapula moves around on the posterior chest wall and is the mobile base of support for the upper limbs, contributing significant mobility by itself before we start thinking about the large range of movement of the glenohumeral joint. Loss of shoulder power and movement begin to occur with shoulder joint stiffness and loss of scapular stability.