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Biomedical subjects

J Kenwright

Publications and source records attributed to J Kenwright.

At least 55 records · Page 3Linked to original sources
PubMed1991

Axial movement and tibial fractures. A controlled randomised trial of treatment.

Diaphyseal fractures of the tibia in 80 patients were treated by external skeletal fixation using a unilateral frame, either in a fixed mode or in a mode which allowed the application of a small amount of predominantly axial micromovement. Patients were allocated to each regime by random selection. Fracture healing was assessed clinically, radiologically and by measurement of the mechanical stiffness of the fracture. Both clinical and mechanical healing were enhanced in the group subjected to micromovement, compared to those treated with frames in a fixed mode possessing an overall stiffness similar to that of others in common clinical use. The differences in healing time were statistically significant and independently related to the treatment method. There was no difference in complication rates between treatment groups.

Adolescent↗
PubMed1991

Problems encountered in leg shortening.

We reviewed 46 leg-shortening operations (37 femoral and nine tibial), performed by different methods, to assess the incidence of complications and permanent disability. Shortening of as much as 7.5 cm in the femur and 5 cm in the tibia was achieved in men of normal height without any loss of function. Complications were seen with all surgical techniques despite the use of modern implants. Most problems arose from inadequate stabilisation of the osteotomy. The most reliable method of femoral shortening was open subtrochanteric osteotomy with preservation of the isthmus, and fixation with an intramedullary nail locked at its proximal end. In tibial shortening, bone excision should be at the level of the flare in the lower diaphysis in order to achieve reliable bone healing. Simple intramedullary nail fixation should be supplemented with a long-leg cast for six weeks or the nail should be locked at both ends to prevent postoperative distraction or rotation.

Adolescent↗
PubMed1991

The importance of delay in distraction of osteotomies.

The factor of timing of the commencement of distraction of an osteotomy is evaluated. Experimental osteotomies subjected to immediate distraction result in the production of a small volume of callus with deficient vascularity. Delay alters this response, and there is a more cellular osteogenic reaction with proliferative vascularization during lengthening. A delay is advocated in all gradual leg lengthening procedures, in progressive correction of deformity controlled by external skeletal fixation following osteotomy, and in bone transport procedures. The period of delay should be carefully determined according to each individual case.

Animals↗
PubMed1990

The timing of distraction of an osteotomy.

New methods of limb lengthening are being adopted in the hope of overcoming the poor osteogenic responses characteristic of distraction. Delay between the osteotomy and starting distraction is said to be important but there is little experimental evidence. We have compared immediate with delayed distraction in the rabbit tibia and shown that delay is an important factor in promoting osteogenesis. It seems that its effects are partly mediated by an improvement in the extra-osseous blood supply.

Animals↗
PubMed1990

Response of the growth plate to distraction close to skeletal maturity. Is fracture necessary?

Axial force applied during epiphyseal distraction has been measured close to skeletal maturity in patients having leg lengthening, in a rabbit model, and in vitro from an amputation specimen. In the patient study, both slow distraction rates and low constant distraction loads were applied. For all the distraction regimens, it was not possible to lengthen the limb significantly without evidence of fracture as demonstrated by a sudden decrease in distraction force. Growth plate failure was observed from 600 to 800 N, these levels being lower than those recorded from the in vitro tests. In the animal study, three distraction regimens (0.13, 0.26, and 0.53 mm/day) were applied across the upper tibial growth plate of New Zealand white rabbits close to skeletal maturity. Distraction was applied and force measured using a strain-gauge dual-frame external fixator. The force-time results revealed two distinct patterns. One pattern, in which the forces rapidly increased to maximum values of approximately 25 N and then suddenly decreased, indicated fracture of the growth plate, which was confirmed histologically. In the other pattern, forces increased steadily throughout distraction, reaching maximum values at the end of distraction of approximately 16 N. Histologic observations indicated hyperplasia of the growth plate without fracture, however, only a small increase in limb length was detectable. Hence, if a significant increase in leg length is required close to skeletal maturity, then fracture of the growth plate must occur.

Adolescent↗
PubMed1989

Measurement of fracture movement in patients treated with unilateral external skeletal fixation.

Axial movement occurring at the fracture site has been determined in a group of healing tibial fractures treated by external skeletal fixation. Fracture movement was determined via a strain gauge transducer which was attached to the column of the external fixator and measured the deflection of the bone screw adjacent to the fracture site and the active loading or weight bearing given by the patient to the fractured limb was monitored using a force platform. The results for 27 subjects show that, with a rigid unilateral fixator, the axial movement occurring at the fracture site was initially small (mean = 0.28 mm at 5 weeks post fracture). This movement increases to reach a mean maximum value of 0.43 mm at 11 weeks post-fracture and then decreases, despite increased weight bearing, as fracture healing progresses. In the early stages of healing, the movement can be increased slightly if the fixator is fitted with a module which permits additional fracture site movement, although the resultant increase in movement is only a small proportion of the potential available with this module.

Bone Screws↗
PubMed1989

Biomechanical aspects of pelvic and hip injuries in road traffic accidents.

The mechanism of pelvic fractures has been well documented from radiographs but little is known of the forces required to produce these injuries. We examined 40 cases of pelvic injury sustained in road traffic accidents where the direction of impact and the velocity differential was known. In frontal impacts, indirect shear injuries of the pelvis were prominent, while in side impacts, lateral compressive injuries occurred. With increasing velocity differentials and vehicle deformation and intrusion, more severe pelvic injury occurred, often in association with significant head, chest, and lower limb injuries. Side impacts were noted to produce more severe injuries at lower velocity differentials when compared with frontal crashes.

Accidents, Traffic↗
PubMed1989

Distraction physiolysis in the rabbit.

Axial forces across the growth plate of the upper tibia during controlled distraction were studied in 24 rabbits close to skeletal maturity. Distraction rates of 0.13, 0.26, and 0.53 mm every 24 hours were applied through a dual-frame external fixator. Strain gauges were bonded to the fixator, and axial forces were estimated prior to and following distraction. The results demonstrate two distinct patterns. In one group, forces increased to maximum values of 20-32 newtons and then suddenly decreased on subsequent distraction. This force pattern indicated fracture of the growth plate with associated hyperplasia. In the other group, lower maximum forces of 6-18 newtons were produced at the end of the distraction period, which were associated with physeal hyperplasia without fracture. These results showed that response to controlled distraction was dependent upon both the level of force acting across the growth plate and the rate of distraction; hyperplasia was achieved with lower rates of distraction up to a critical peak force above which fracture occurred.

Animals↗
PubMed1989

A mechanical assessment of applied compression and healing in knee arthrodesis.

The applied compression and stiffness of a knee arthrodesis treated with unilateral external fixation can be mechanically assessed. Of ten patients in whom arthrodesis bending stiffness measurements were obtained during healing, nine had a minimum bending stiffness of 5 Nm/degree and sound clinical fusion. In seven of these nine patients, a bending stiffness of at least 10 Nm/degree was obtained, suggesting that this stiffness value is a safe and reliable indicator for successful arthrodesis. Arthrodesis compression declined rapidly; daily adjustments were required to maintain a compression of 500 Newtons. A small but significant loss of length was associated with this high value of compression. On reduction of the compression to 200 Newtons, the rate of decrease of compression and the loss of length across the arthrodesis were simultaneously reduced.

Arthrodesis↗
PubMed1989

Controlled mechanical stimulation in the treatment of tibial fractures.

Although it is known that the mechanical environment affects the fracture healing process, the optimal conditions for the different stages of healing have not been defined. In the present studies, the influence of applying a very short period of axial micromovement with defined characteristics to healing fractures has been studied both in simulated and clinical tibial fractures. The fracture healing process is seen to be acutely sensitive to small periods of daily strain applied axially within two weeks of fracture. There are boundaries of strain magnitude and force of application of applied movement that, if exceeded, inhibit the healing process. The application of appropriate applied strain to clinical tibial fractures at a time shortly after injury, when most patients would be very inactive, appears to enhance the healing process when using external skeletal fixation.

Animals↗
PubMed1988

Design and performance of a fracture monitoring transducer.

The answer to the question, 'when is a fracture healed?' is not simple, since the healing process is progressive and it is not possible to specify a time when the fracture can be said to have healed. In the past the assessment of fracture healing has, in the main, been subjective, relying upon the skill of the interpreter. A more objective method would be an advantage for many reasons, and since the bone is intended to be load bearing it is reasonable to assess healing by measuring the mechanical integrity of the bone. To do this a 'clamp on' transducer has been developed which, when fitted to the support column of an external fixator, enables the stiffness of a fracture to be determined during the healing process. Over the past 6 years this system has been used for both clinical and research work. It has enabled various forms of treatment to be evaluated in terms of 'rate of healing' and it also indicates the safe point at which the fixator can be removed.

Biomechanical Phenomena↗
PubMed1987

Leg-length inequality in children treated by Syme's amputation.

We have reviewed the results of amputation through the ankle in the management of 37 children with congenital leg-length discrepancy, followed up for a mean of 7.6 years after operation. In general good function was achieved and 18 patients considered their activities to be unrestricted. The main factor affecting the functional result was the underlying condition for which operation had been performed. Although heel pad migration, scar rotation and os calcis remnants were seen, these could be accommodated by the prosthesis. Syme's amputation is tolerated well in the younger child and, in patients with a predicted leg-length discrepancy of over 15 cm associated with an abnormal foot, we recommend the operation as a primary procedure between the ages of 18 months and two years.

Activities of Daily Living↗
PubMed1986

Effect of controlled axial micromovement on healing of tibial fractures.

The preliminary results are presented from a study in which 85 serious tibial fractures were treated with external skeletal fixation. In group I patients were treated with highly rigid fixation. In group II the same fixation was used but axial micromovement was applied across the fracture site for 30 min per day, starting 1-3 weeks after injury and continuing until partial weight-bearing, which leads to self-induced movement. The overall mean time to independent weight-bearing was longer in group I than group II (p = 0.02); delayed union occurred in more group I patients. Objective measurement of fracture stiffness was made by means of strain gauges placed on the fixation frame for 49 fractures treated consecutively. The time to reach stiffness levels equivalent to clinical union was significantly longer in group I than in group II. The fractures in the treatment groups were of comparable severity. It seems that the fracture healing process is susceptible to small changes in mechanical environment.

Fracture Fixation↗
PubMed1985

Effect of seat belts on injuries to front and rear seat passengers.

Data on 2520 occupants of cars involved in accidents were analysed in relation to injury and the severity of the crash to investigate the effect of rear seat passengers on injury to restrained and unrestrained front seat occupants and vice versa. Unrestrained front seat occupants showed a higher incidence of serious injury when there were rear seat passengers. The presence of a rear seat passenger did not affect significantly the overall incidence of injury among restrained front seat occupants within the range of crash severity considered. Unrestrained rear seat passengers behind unrestrained front seat occupants showed a higher incidence of moderate injury and a lower incidence of no injury than those behind restrained front seat occupants. It is concluded that legislation on seat belts has not greatly increased the risk of person to person injury.

Accidents, Traffic↗