Subsidence of the femoral component related to long-term outcome of hip replacement.

We compared the clinical outcome with femoral subsidence and radiographic changes in 102 patients at 9 to 13 years after low friction arthroplasty. In 92 cases with a satisfactory outcome there was an average of 2.3 radiological signs and mean subsidence of less than 5 mm. An unsatisfactory outcome was associated with 3.4 signs per film and with subsidence of more than 5 mm. The radiological signs we describe are often the hallmark of successful load transmission, but if they increase with time or are associated with subsidence of over 5 mm, then clinical failure is likely. Fracture of the cement tip is associated with increased subsidence and adversely affects the long-term clinical outcome.

Hydroxychloroquine and postoperative thromboembolism after total hip replacement.

Evidence for the usefulness of hydroxychloroquine as prophylaxis against thromboembolism after total hip replacement is examined. This agent causes reduction in red blood cell aggregation without prolonging the bleeding time in humans and, experimentally, reduces the size of the thrombus. There is a variably demonstrable reduction in platelet aggregation and blood viscosity in humans. After hip replacement, the venographic incidence of deep vein thrombosis is not influenced by hydroxychloroquine. The incidence of fatal pulmonary embolism appears to be reduced, but a controlled trial against placebo does not exist. There are no serious or irreversible side effects, and wound healing is not affected by the administration of this drug. Hydroxychloroquine remains the prophylaxis of choice in use at the Hip Center, Wrightington Hospital, England, 13 years after its introduction.

Hydroxychloroquine sulfate prophylaxis for pulmonary embolism for patients with low-friction arthroplasty.

Hydroxycholoroquine sulfate has been administered for prophylaxis against pulmonary embolism following total hip arthroplasty. A significant reduction was observed in the rate of fatal emboli, with relatively few and minor side effects, on daily doses of 1200 mg.

Femoral prosthetic subsidence after low-friction arthroplasty.

A quantitative method has been used to measure femoral prosthetic subsidence after insertion. Increased amounts of subsidence are associated with the development of radiologic signs by one year after surgery. The most marked effect occurs with fractures of the cement tip. Follow-up examination up to five years shows that the rate of subsidence usually stabilizes, or stops at about 5 mm. Less commonly, subsidence is progressive, averaging up to 2 cm at five years. Demonstrable subsidence is also associated with prostheses that subsequently go on to break. The implications are that the nonflanged femoral prostheses are end bearing, with eccentric loading of the distal cement column, which leads to radiologic signs around the cement tip, demarcation, and, eventually, fracture of the cement tip. There may also be resorptive changes in the proximal femur, characteristically demonstrated in the medial femoral neck. It is suggested that the recent improvements in cement technique and the addition of the prosthetic dorsal flange may increase the success of low-friction arthroplasty.

Subsidence of the femoral prosthesis in total hip replacement in relation to the design of the stem.

A method is described of measuring radiological subsidence of a femoral prosthesis in relation to the femur after total hip arthroplasty. The method depends on measuring the distance from the tip of the femoral prosthesis to a fixed point in the bone. Subsidence after the use of a conventional design of femoral stem is compared with that after the use of a stem with a dorsal flange (Cobra). A significant reduction in the incidence and amount of subsidence was found when using the dorsal flange. There was also a notable absence of transverse fractures involving the cement near the tip of the stem, which occurred in 26 per cent of the cases using a conventional prosthesis.

The fibrinogen uptake test after hip surgery.

The fibrinogen uptake test has been used to detect deep vein thrombosis after total hip replacement in 90 patients. The upper third of the thigh in each leg was ignored and peripheral leg counting carried out distal to this. The results were directly compared with the findings of venography in the 170 legs of the 90 patients. There was a high false positive rate (30 per cent) with the fibrinogen uptake test which was associated with the presence of the knee joint effusion or varicose veins, but not with the site of operation. There was a low false negative rate (less than 5 per cent), and the fibrinogen uptake test, used in this way, may fail to detect a percentage of small thrombi in the wound area that are probably produced by the local trauma of operation. It is considered that the fibrinogen uptake test has a clinical use as a screening test for deep vein thrombosis after hip replacement, but venography is required in the interests of accuracy.

The antagonistic actions of calcium and magnesium on the superfused ventricle of the snail Helix pomatia.

1. The isolated, superfused half-ventricle of the snail (Helix pomatia) maintains a degree of tonic activity even when not beating, since the membrane is depolarized beyond the tension threshold. Beating may be initiated by lateral stretch of the ventricle and by 5-hydroxytryptamine.2. Ca and Mn each have a hyperpolarizing action, while K and to a lesser extent Na cause depolarization: the tonic activity of the ventricle is affected accordingly.3. An increase in the extracellular concentration of Mg also causes the tension to fall, but without change in membrane potential. It can also initiate beating.4. Contractures induced by 30 mM-K are steadily maintained, but start with a more-or-less distinct twitch-like contraction. A contracture induced by a concentration of K above about 50 mM is poorly sustained and is followed by a further brief contracture when the K concentration is reduced to normal.5. Relations between contracture tension and the concentrations of Ca and Mg accord with the hypothesis that the two ions compete for attachment to a binding site on the cell surface and that tension is proportional to the amount of bound Ca. On this hypothesis, the apparent dissociation constant of the Mg complex is 11.4 mM and that of the Ca complex 0.15 mM or less.6. This effect of Mg is like that of Na on frog ventricle and some of the differences in the behaviour of snail and frog ventricles are abolished by appropriate adjustment of the extracellular concentrations of these ions.