Functional instability of the foot (a term used in this paper to designate the disability to which patients refer when they say that their foot tends to " give way ") follows about 40 per cent of injuries to the lateral ligament of the ankle (Bosien, Staples and Russell 1955 ; Freeman THE JOURNAL OF BONE AND JOINT SURGERY THE ETIOLOGY AND PREVENTION OF FUNCTIONAL INSTABILITY OF THE FOOT 679 MATERIAL (Tables I and II) Eighty-five patients presenting consecutively at the Casualty Department of Westminster Hospital with recent sprains of the foot and ankle were studied. Every patient was examined radiographically to exclude bone injury. ETIOLOGY AND PREVENTION OF FUNCTIONAL INSTABILITY OF THE FOOT ThE JOURNAL OF BONE AND JOINT SURGERY THE ETIOLOGY AND PREVENTION OF FUNCTIONAL INSTABILITY OF THE FOOT We wish to express our gratitude to Mr D. L. Evans for permission to study his patients and to Dr D. A. Brewerton and the staff of the Physiotherapy Department of Westminster Hospital for treating the patients on our behalf.

1. Forty-two previously asymptomatic patients presenting with a recent rupture of the lateral ligament of the ankle, and twenty similar patients with a simple sprain of this ligament, have been followed for one year. The physical and radiological findings upon the completion of treatment have been related to functional instability of the foot one year later. 2. Persistent mechanical varus instability of the talus in the ankle mortise was a possible cause of functional instability one year after injury in four (or perhaps six) patients. 3. Adhesion formation was a possible cause of functional instability in one patient. 4. Seventeen patients finally displayed no clinical or radiological abnormality after injury, but noted functional instability of the foot one year later. 5. It is concluded that the pathological process which is usually responsible for functional instability of the foot after a lateral ligament injury is at present unknown.

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Tissues from five patients who underwent revision operations for failed total hip replacements were found to contain large quantities of particulate titanium. In four cases this metal must have come from titanium alloy screws used to fix the acetabular component; in the fifth case it may also have originated from a titanium alloy femoral head. Monoclonal antibody labelling showed abundant macrophages and T-lymphocytes, in the absence of B-lymphocytes, suggesting sensitisation to titanium. Skin patch testing with dilute solutions of titanium salts gave negative results in all five patients. However, two of them had a positive skin test to a titanium-containing ointment.

1. We have shown that the permeability of cartilage is the same in necropsy specimens as in the living animal. We have concluded that studies of material transport into cartilage carried out on necropsy specimens validly reflect in vivo conditions. 2. We have studied the effect of agitation of the fluid in which cartilage is immersed upon the rate of diffusion of substances into cartilage and have found that agitation increases the rate of penetration up to three or four fold. We believe that it may be inferred from this fact that the nutrition of cartilage is partly dependent on joint movement. 3. We have examined the permeability of the bone-cartilage interface to water and solutes and have found that in the adult no detectable material transfer occurs across this zone. In the child on the other hand the bone-cartilage interface appears to be permeable to water and solutes. 4. We have measured the diffusion coefficient of glucose in cartilage and have hence estimated the depth of cartilage which can be adequately supplied with glucose from the synovial fluid in the presence and absence of agitation. 5. We have examined both experimentally and theoretically the possible effect of intermittent loading on the rate of penetration of substances into cartilage. We have concluded that at low pressures intermittent loading contributes little to the material transfer into cartilage. At high pressures intermittent loading does lead to the transport of solutes into cartilage but it cannot significantly increase the rate of transfer above that attributable to normal diffusion. Loading cartilage surfaces for prolonged periods of time without allowing intermittent relaxation would be expected to lead to decreased diffusion, without any absorption of fresh fluid attributable to the action of a pump, and would thus result in an overall decrease in the rate of penetration of substances into cartilage.

The vertical migration of four configurations of a proximal femoral prosthesis, followed for up to nine years, was measured on standard radiographs. The same implant was used without cement (group 1) and with cement (group 2). The migration of both groups was linear from six months onwards. The mean migration rate and the incidence of late aseptic loosening were both greater in group 1. Survival analysis of the two groups, however, showed no statistically significant difference. In both groups, hips later destined for revision migrated more rapidly from the initial postoperative period onwards, than did the remainder. A threshold migration of 1.2 mm/year during the first two years after implantation detected hips likely to fail with a specificity of 86% and a sensitivity of 78%. This 'migration test' was applied to the results in two further groups of patients in which a modified femoral prosthesis had been implanted without hydroxyapatite coating (group 3) and with hydroxyapatite coating (group 4). The test distinguished between the four groups and suggested that at least two fixation procedures should be abandoned. We conclude that vertical migration measured on standard radiographs in the first two years after implantation can be used to predict late aseptic loosening. New prosthetic configurations should be evaluated by migration measurements before their general release. Our observations support the view that one cause of late aseptic loosening is imperfect initial fixation.