Lower limb Degeneration
The foot is the part of the body generally in contact with the ground and, in essence, acts as a platform to support the mass of the body above it. The bones of the foot are fashioned in such a way as to form two arches – a ‘longitudinal’ arch between the heel bone and the heads of the metatarsals, and a ‘transverse’ arch. It is these structural arches which give it strength and aid in its dynamic functions.
The foot bears the brunt of the forces which are generated while carrying the body over the ground during activities, such as walking and running. Because of its arch-like construction, the forces pass between the ground and the normal foot foot in two main areas; at the heel of the foot and across its ‘ball’. These arches, nevertheless, give the foot great strength and aid in its dynamic action by imparting a certain amount of ‘spring’ to the steps.
In addition to the arch-like configuration of the bones in the foot they meet together at synovial joints which allow for some movement between them. Some of these joints are quite mobile, allowing the foot to adapt to variations in the texture and direction of the ground during walking and running; and some of these joints are quite stiff, which allows for conduction of the forces between different regions of the foot which aids its function, especially when pushing off as the foot can act as a lever arm increasing the action of the muscles of the leg..
The foot may be malformed from birth or the large forces, which constantly pass through it, may injure it, or lead to degeneration of one or more of its components. It is because the foot is such a precise and highly specialised structure that any abnormality in its structure will have a significant and detrimental affect its function, usually in the form of pain. It often takes only a very minor change in the shape of the foot, or one of its bones, to make walking very uncomfortable for the affected individual.
A bunion is a firm swelling on the inner side of the foot at the base of the big toe. It often found in association with an outward deviation of the big toe, a condition termed ‘hallux valgus’ and with a ‘cocking up’ of the second toe because this is pushed up by the migrating big toe.
Several factors are considered to contribute to the development of a bunion. The condition frequently runs in families. Tight footwear has been blamed as the cause, as has wearing ‘high heeled’ shoes.
It is also often found in association with a ‘flat’ or ‘pronating’ foot. Hypermobility of the first ray of the foot, causes the foot to splay when standing (metatarsus primus varus) and is particularly associated with hallux valgus and a bunion.The ‘bunion’ is said to be a response of the foot to excessive pressure at the side of the foot from the toecap of the shoe but may also result from the abnormal mechanics in a pronated foot while walking. The first response to the pressure is a thickening of the skin and the formation of a ‘bursa’ between the skin and the underlying bone. As the condition progresses this bursa becomes thickened and swollen and the bone enlarges to form a hard swelling which may be painful. During its development the bunion sets up a vicious circle. As it grows it causes the forefoot to enlarge as a whole. This, in turn, increases the pressure when the foot is within the shoe, leading to a greater reaction from the bunion. Although small bunions generally do not cause much trouble the final result in many instances is a painful, swollen foot which is difficult to get into a shoe and uncomfortable to walk on.
Because bunions in the early stages of its development generally do not cause much of a problem people often do not seek attention when they first appear. However, the bunion is frequently progressive and may slowly increases in size over the years. Eventually pain and deformity force the affected individual to seek advice when, in some cases, the use of a compensatory support within the shoe may have offset the progression for a number of years.
Once it has grown to a significant size and the affected person is more aware of its presence, various measures may still be taken to improve the comfort of the foot. Wearing broad toed, low heeled shoes is important. The use of a custom made, supporting orthosis in the shoe can go a long way to relieving any discomfort. The disadvantage of these orthoses is that they can make the shoe feel a bit tight. The use of soft ‘bunion’ shoes or custom made ‘surgical’ shoes may then also be of assistance.
If these relatively simple measures do not work the only recourse is to surgery. There are many different types of operations which can be utilised in the treatment of bunions. The exact procedure performed will therefore depend on the exact form and size of the bunion, and the personal preference of the surgeon. The operation generally includes excision of the bunion itself along with some other associated procedure. These include soft tissue releases and transfers, division of the metatarsal bone (osteotomy), and sometimes excision of part of the bone of the toe. The metatarsal bone is cut in order to realign the foot. This ‘osteotomy’ of the 1st metatarsal bone is performed either at its proximal end or, more commonly, at its distal end adjacent to the bunion. The aim of these operations is to remove the bunion and, if possible, to rebalance any associated deformity of the foot.
Because the bone is cut and the fragments moved in relation to one another it is usually necessary to hold the osteotomy in position until it has healed. This can occasionally be done sutures but, more often, it is done with wires or pins which may have to be removed after about 6 weeks. Depending on the exact nature of the operation, the surgeon may wish to support the foot in a plaster cast for a few weeks.
Usually these operations work reasonably well but occasionally they do not relieve the problem. Like all other operations, infection of the operation site is always a risk. Sometimes the osteotomy of the metatarsal bone does not heal and this can lead to localised pain. Further, it is possible for the operation to upset the imbalance of the foot which had initially lead to the formation of the bunion. If this occurs the hallux valgus of the big toe can recur and pain in the foot can be exacerbated.
A fairly frequent deformity of the foot, which can arise either by itself or in association with a bunion, is the cocking-up of one or more of the toes. The small muscles within the foot are responsible for balancing the action of the long tendons which pull on the toes and a cock-up deformity can occur as a result of weakness of these muscles. This often occurs as people get older, or if they suffer from some neurological complaint. Another cause for the toes cocking up is if they are ,too long, for the shoe. Some people have excessively long second and third toes. In this case they are pushed up from their normal position by the narrow toecaps of modern shoes.
The toe has an important function in the action of the foot. It helps to support the front of the foot when standing and the weight of the body is distributed between the toes and the heads of the metatarsal bones. If the toe ‘cocks up’ this supporting action is lost and the full weight is concentrated on the metatarsal head. This increase in pressure on the sole of the foot is indicated by the development of a callosity in the skin underlying the metatarsal head. The constant pressure localised to this region when the affected individual stands causes a distressing pain in the metatarsal head (metatarsalgia) which makes walking very uncomfortable.
If the deformity of the toe occurs as a result of an intrinsic weakness of the foot a specialised, custom support within the shoe relieves the pressure on the metatarsal head and (hopefully) reduces the pain. If, however, the cock-up deformity is due to an excessively long toe it is usually necessary to shorten this toe to obtain adequate relief.
This condition is relatively uncommon but occurs when there is severe loss of the longitudinal arch and the normal supporting mechanism of the foot is lost. The affected person then walks on a flattened foot which bends slightly backward with every step. The result of this chronic, abnormal strain is that the joints in middle of the foot react, initially to form a painful, bony lump over their upper surface and may later become arthritic.
Customised supports within the shoes are often enough to relieve the pain in the foot arising from this condition,but if the discomfort becomes too severe it may be necessary to fuse the affected joints.
Arthritis of the Big Toe (Hallux Rigidus)
Like other synovial joints of the body, the big toe is also susceptible to developing arthritis of the joint at its base (the metatarso-phalangeal joint). This arthritis usually begins slowly with increasing pain in the joint, which often gradually becomes swollen and develops a deformity by bending to the side. At the same time there may be swelling of the joint itself due to a ring of osteophytes (reaction of bone) which can form around it. An x-ray of the foot will show marked narrowing of the joint space. With time the joint becomes stiff and very painful and, as this is discomfort is aggravated by movement of the toe, it may make fitting shoes and walking extremely difficult.
The cause of hallux rigidus is not clear but it may arise as a result of an injury to the toe, or to overuse of the foot. Wearing high heel shoes has long been implicated as a cause. It is also frequently associated with hyperpronation of the foot, which puts an excessive strain on the joint.
Initial treatment is usually conservative, consisting of wearing flat shoes, physiotherapy and exercises to the foot. Self mobilisation of the joint to maintain movement is also advocated, as is anti-inflammatory pain medication. An anti-pronation orthosis within the shoes can also be helpful.
If the condition does not respond to these conservative measures there are surgical options available. Removing the osteophytes from the joint edges (a chielectomy) will often free the joint, reducing the pain and allowing a greater range of motion of the toe. There is also the option of fusing the joint, although this makes the stiffness permanent and this can limit the types of shoes which can be worn. Finally there are different types of artificial joints which can be inserted into the toe which can reduce the discomfort as well as allowing a reasonable range of movement.