Biomedical subjects
Publications and source records attributed to W H Harris.
To elucidate the role of mechanical factors in the etiology of osteoarthritis, the detailed geometry of the weight-bearing cartilage layer over the human hip socket is compared with the corresponding pressure distribution. The shape of the pressure distribution is strongly correlated with the shape of the cartilage compression distribution.
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A programme consisting of 14 daily injections of progesterone (10 mg) followed by single injection of PMSG (500 i.u.) and oestradiol- 17 beta (30 micrograms), along with controlled temperature (18-20 degrees C) and lighting (10 h light/24 h), was applied to 60 anoestrous ewes between late May and early August to induce reproductive activity. Breeding started within 24 h of the oestradiol injection and 80.0% of the ewes conceived at the induced oestrus. Dorset ewes had higher conception (95.2 versus 71.8%) and prolificacy (1.74 versus 1.52 fetuses/ewe) rates than did crossbred Suffolk ewes. Plasma progesterone concentrations during progesterone administration were significantly higher than those found during anoestrus and were generally lower in ewes which did not conceive than in those which did. The plasma progesterone data indicated that ovulation had occurred in most of the ewes which were not pregnant at 90-100 days and that many may have been pregnant initially but then lost the conceptus.
The authors have studied the effects of a 20 microampere current applied to bone in rabbits and dogs. The results have been analysed according to the age of animal, whether mature or immature, and the nature of the electrode (whether steel or platinum). They found no different in the osteogenesis produced in the medullary canal which was constant. The authors further studied the effects of currents on osteotomies of the radius in dogs which generally led to non-union in the absence of electrical currents. They failed to demonstrate any stimulation of bone repair by the current. They conclude that bone formation in the medullary canal of intact bones and the repair of fractures are two different processes.
In eight patients with so-called idiopathic degenerative arthritis of the hip the acetabular labrum, at surgery, was found to lie in the articulation between the femoral head and the acetabulum. In none of the patients was there a history or roentgenographic evidence of congenital dysplasia or congenital dislocation. None of the patients had had a closed reduction or manipulation of the hip during infancy, childhood, or adolescence. No patient had had a traumatic dislocation. The findings suggest that the intra-articular labrum was a developmental abnormality and we postulate that this abnormality was the cause of the degenerative arthritis.
Serial blood, muscle, and bone concentrations of cephalothin following intravenous infusion were determined in forty-eight patients during total hip replacement. Thirty patients received hypotensive anesthesia and the remaining eighteen received anesthesia without induced hypotension. The concentrations of cephalothin were determined during the first (early) and second (late) hours of the operation. Late serum levels were lower in the patients who had induced hypotension. In all patients at least one bone specimen contained measurable amounts of cephalothin. When pentolinium (Ansolysen) was used to induce hypotension, the late serum and early bone cephalothin concentrations were lower, while use of trimethaphan (Arfonad) did not appear to result in lower cephalothin concentrations in serum, muscle, or bone compared with patients with normotensive anesthesia.
A study was made of thirty-nine traumatic posterior dislocations of the hip that had remained unreduced for from three days to nine years. The purpose of the review was to compare the results of closed and open reduction with those of primary reconstructive surgery. Three of the twenty hips that had closed or open reduction had good results as compared with ten of the thirteen hips that had primary reconstructive surgery. Six hips that were left dislocated had uniformly poor results.
The effects of dopamine on blood pressure and heart rate have been studied in continuously cannulated fetal lambs and adult sheep. Drugs were administered by direct intravenous injection into either the fetus or the adult sheep, and blood pressure was measured from an arterial cannula and heart rate was computed from the electrocardiogram (ECG). The magnitude of the fetal pressor response to dopamine increased slightly as the dose of dopamine (1, 10, 50, 100, and 200 mcg. per kilogram was increased, but the magnitude of the response did not increase with advancing gestation (112 to 145 days). However, in the adult sheep, the dose-response relationship was much steeper. In both cases the pressor response was accompanied by a reflex bradycardia that was blocked by atropine (1 mg. per kilogram). In the atropinized fetus, doses of 50 to 200 mcg. per kilogram of dopamine produced tachycardia (30 to 120 b.p.m) and a greater pressor response than that in the unatropinized fetus. Thus, the fetal cardiovascular system is capable of responding to relatively large amounts of dopamine injected as a bolus, suggesting that relatively large amounts of endogenous dopamine would have to be secreted by the mast cells to significantly alter fetal cardiovascular function.
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The cardiovascular effects of phenylephrine or ephedrine alone and after autonomic blockade was studied in the chronically cannulated fetal lamb (100-145 days), the newborn lamb, and adult sheep. As gestation advanced, phenylephrine and ephedrine produced an increasing pressor response before and after pretreatment with atropine (1 mg/kg). Compared with the fetus, the magnitudes of the pressor responses were somewhat greater in the newborn and much larger in the adult. Both drugs produced a reflex bradycardia in the unatropinized fetus which in the case of ephedrine was followed by a tachycardia. Pretreatment with atropine resulted in an immediate tachycardia after ephedrine but not after phenylephrine administration. Pretreatment with phentolamine (0.15 mg/kg) produced about a 55% inhibition of the phenylephrine pressor response in both the fetus and adult, suggesting a linear relationship between body weight and number of alpha-adrenergic receptors. Pretreatment with metoprolol blocked the tachycardia associated with ephedrine administration to unatropinized fetuses. In summary, the increase in the magnitude of the pressor response to phenylephrine suggested development of the receptor-effector system. The greater development of the response to ephedrine suggested that there was an increasing amount of noradrenaline being released with advancing gestation.
Studies of flexible plates made of plastic have shown that less osteoporosis develops beneath them than beneath rigid metal plates. However, to date plastic plates of appropriate physical properties and biocompatibility are not available for use in humans. To determine if a similar beneficial effect could be obtained using metal plates, the effects of thick chromium cobalt plates were contrasted in experiments in dogs with the effects of thinner plates of similar design made of titanium, 6-aluminum, 4-vandium. A significant reduction in the osteoporosis was obtained by use of the more flexible plates. Following plate application a delayed, massive, transient stimulus to bone formation occurred endosteally, periosteally, and intracortically. Despite this, a substantial decrease in bone mass occurred, primarily mediated by endosteal bone resorption. Intracortical porosity played little or no role in net bone loss. The major effects subsided by six months. Recovery after plate removal was predominantly the result of endosteal new-bone formation.
Certain special problems in reconstruction of the arthritis hip in the adult require the use of a femoral component that has a long stem. A long stem component is essential if a major defect exists in the cortex of the proximal portion of the femur. Examples of such defects are windows cut in the femur to remove cement or to remove a broken femoral stem. Another example is the hole made by penetration of a femoral stem through the cortex. Standard long stem components are used for these cases. A new device in the long stem family, called the calcar replacement long stem component, is designed to restore leg length in those cases in which the femoral calcar has been removed or resorbed. It is also being used in certain cases of heterotopic ossification. In certain cases of primary or secondary malignant disease the entire proximal portion of the femur is excised and the proximal femoral replacement long stem component is inserted. The use of these long stem femoral components is illustrated and the limitations and pitfalls are discussed.
The three topical hemostatic agents--gelatin paste, microfibrillar collagen, and gelatin sponge soaked in thrombin--individually were effective in reducing bleeding from cancellous bone, as tested on the femoral surface of trochanteric osteotomies during total hip replacement. During a three-minute interval, the spontaneous reduction in bleeding in eight control hips to which no agent was applied was 11 per cent. Gelatin paste gave a reduction of 85 per cent; gelatin sponge soaked in thrombin, a reduction of 75 per cent; and microfibrillar collagen, a reduction of 47 per cent. None of these agents interfered with healing of the trochanteric osteotomy.
The distribution of strain in the proximal part of loaded cadaver femora was measured in vitro using strain gauges applied to the cortex. The loading conditions simulated single-limb stance and the strains were recorded first with the femora intact and then with the femoral components of six different designs inserted. Each femur served as its own control. After insertion of a femoral component, the pattern of strain in the proximal part of the femur was reversed compared with that in the intact femur, in that the maximum strain occurred around the tip of the prosthesis rather than at the calcar femorale. A massive decrease in stress in the region of the calcar femorale was found when the implants were in place, and it was concluded that this decrease could contribute substantially to the calcar femorale resorption sometimes observed in patients after total hip replacement. Transfer of load directly to the calcar femorale through a larger collar in direct contact with the cortical bone restored 30 to 40 per cent of the normal strain to the calcar femorale and shifted the strain pattern toward normal. Compared with the less stiff stems tested, the larger, stiffer stems, which provide more protection against fatigue failure, did not affect the strain pattern adversely.
For certian total hip-replacement operations osteotomy of the greater trochanter is essential, and for others it is advantageous. A system of management of trochanter reattachment is described that takes into account multiple factors, such as the need to remove large or small amounts of the trochanter depending on the patient's anatomy and on the style of the femoral component used, the need in some cases to advance the trochanter to lie against the cortex of the femur, the need in other instances to deal with markedly porotic trochanters, and the fact that a small number of the wires will fatigue, regardless of the technique used. The basic technique has one horizontal and two separate vertical wires, all passing medial to the femoral stem and each tied to itself in a square knot; All wires pass through the trochanter to prevent rotation. Wire mesh is used prophylactically if the trochanter is porotic. All patients use two crutches for two months postoperatively; In a consecutive series of 136 total hip replacements in which the trochanter was reattached using this technique, none of the trochanters migrated and all united.
An air turbine drill will remove methylmethacrylate from the medullary canal of the proximal femur in cases of failed total hip replacement and from the distal femur in cases of failed long stem total knee replacement. This power tool is expensive, but the high cost is partially offset by multiple other uses: cutting burr holes in the skull, doing osteotomies, cutting bone grafts and making windows in the femur. The power of the instrument and effectiveness of the burrs make it important to have instruction and direct experience in its proper use prior to use in the operating room.
When the distal part of the medullary canal of the femur was plugged with a bolus of methylmethacrylate prior to the insertion of cement and femoral component, fixation of the prosthesis was improved in vitro. A special syringe was devised to introduce the plug at the desired level. When the plug was used, the penetration of the cement into the trabecular bone lining the canal was increased, and subsequent push-out tests showed that the force necessary to disrupt the methacrylate from the bone was significantly greater. Casts of the methacrylate from femora with and without plugged canals showed that the surfaces of the casts made with the canal plugged conformed much more completely with the irregularities of the bone and provided more intimate contact at the cement-bone interface.