Pressure on the patient.

The primary cause of pressure sores is the interference with the blood supply of the tissues which, if prolonged, will result in their death. In most cases, the prolonged pressure which occludes vessels is caused by the inability of the patient to feel pain and/or move. Fortunately the surface area of the body available for the support of the patient is such that it is possible to design patient-support systems which will prevent the pressure per unit area exceeding the critical value. The criteria for an ideal patient-support system are given.

A new method of assessing the mechanical properties of patient support systems (PSS) using a phantom. A preliminary communication.

Pressure ulcers are a major problem worldwide believed to affect over 5% of all hospital in-patients, and countless others in the community at large. Many types of Patient Support Systems (PSS) are sold as pressure ulcer prevention equipment, but no consensus exists as to their mechanical efficacy. The use of human volunteers to assess the mechanical properties of PSS introduces non-repeatability and variability in results which cannot give a statistically significant difference in performance between systems. Mechanical testing without human volunteers provides faster evaluations of PSS, with improved precision and repeatability. An instrumented articulated anthropometric phantom has been developed to investigate the distortion of simulated soft body "tissues" of the buttock and sacral areas due to precise and repeatable static loading on a PSS. The weight of the phantom can be adjusted to 50, 70 and 90 kg and can be applied with the torso inclined at 0 degrees, 45 degrees and 80 degrees. Validation of the phantom by measuring interface pressure using a force sensing array mat indicates that the phantom represents realistic physiological loading conditions. The new method of measuring the distortion of the "artificial tissues" provides a highly selective ranking of PSS.

A method for determining the heat transfer and water vapour permeability of patient support systems.

The formation of pressure ulcers can be exacerbated by a breakdown in the integrity of the patient's skin caused by poor maintenance of the skin microclimate. Patient support systems (PSSs-specialised beds, mattresses, chairs, cushions and pads) play an important role in the dissipation of heat and moisture away from the skin/support interface which is necessary in order to maintain the physiological skin microclimate. This paper reports a laboratory method and theory for the simultaneous measurement of the heat and water vapour dissipating properties of PSSs. The results demonstrate that the method is extremely selective, exhibiting very significant differences between the PSSs tested. It also shows that assessing PSS covers independently does not necessarily indicate the overall performance of the complete PSS.

Uncemented intramedullary fixation of implants using polyethylene sleeves. A roentgenographic study.

Forty-three prostheses with noncemented, high-molecular-weight, polyethylene-sleeved components were used in the treatment of bone tumors around the knee in growing children. The average age of the patients was 11 years. There were 27 boys and 16 girls. There were 17 sleeved components in the distal femur and 26 in the proximal tibia. The average follow-up time was 27 months. The roentgenograms were nominally obtained at three, six, 12, 18, and 24 months, and irregularly thereafter, and were assessed using a zonal evaluation scheme. A sclerotic interface around the polyethylene sleeves invariably developed and progressed in density up to 28 months postoperatively. There were significant zonal differences in sclerosis, particularly between the plateau and the mid-sleeve zone. Only in one patient did a sleeve become loose and require revision.

Prosthetic replacement of the distal femur for primary bone tumours.

Over a 16-year period, 135 custom-made distal femoral prostheses, based on a fully constrained Stanmore-type knee replacement, were used in the treatment of primary malignant or aggressive benign tumours. Survivorship analysis showed a cumulative success rate of 72% at five years and 64% at seven years. Intact prostheses in 91% of the surviving patients gave good or excellent functional results. Deep infection was the major complication, occurring in 6.8% of cases; clinical aseptic loosening occurred in 6.0%. Revision surgery was carried out for loosening and infection, and the early results are encouraging. We conclude that prosthetic replacement of the distal femur can meet the objectives of limb salvage surgery.

Endoprosthetic replacement of the humerus and elbow joint.

Between 1969 and 1985 26 patients with destructive lesions of the distal humerus were treated by endoprosthetic replacement; each implant was custom-made and incorporated part of the distal humerus or the entire bone as well as a hinged total elbow replacement. Recurrence occurred in three of the patients with tumours, and three prostheses were removed because of deep infection in patients with previously compound injuries of the elbow. Another three loosened without infection, but none needed revision or removal and no amputations resulted. Other complications included nerve palsies, but the only deaths were from metastases. A useful range of elbow movement, with a stable arm and good hand function, was achieved in every patient.

Endoprosthetic replacement of the proximal humerus.

Endoprosthetic replacement of the proximal humerus has been performed in our unit on 25 occasions between 1950 and 1982. The indication for surgery was destruction of the proximal half of the humerus so extensive that the only alternatives were reconstruction or amputation. Of the patients with tumours two died from metastases, and three from unrelated causes; local recurrence necessitated amputation in two patients. Minor complications were frequent, but there were no deep infections and, after 1964, no prosthesis became loose. Active shoulder movement after operation was considerably limited, but passive movement was good and function of the elbow and hand were preserved.

Distal femoral replacement by custom-made prostheses. Clinical follow-up and survivorship analysis.

We report the long-term clinical follow-up and survivorship analysis of 40 distal femoral replacements performed between 1964 and 1980 for traumatic, locally aggressive and malignant conditions. Custom-made prostheses with fully-constrained knee joints were used to replace a mean of 42% of the length of the femur. Survivorship analysis showed a cumulative success rate of 80% at eight years, with no subsequent deterioration at 18 years. Clinical assessment revealed 78% excellent or good results. Failure was due to infection in three cases, and in two to fracture of a now-outmoded femoral stem.

Resection of a peri-acetabular chondrosarcoma and reconstruction of the pelvis. A case report.

We report a patient with a peri-acetabular chondrosarcoma which was treated by resection of part of the pelvis and the femoral head. This was followed by replacement with a custom-made titanium alloy pelvic portion and a conventional total hip prosthesis. The operation was carried out in two stages, and yielded a good functional and cosmetic result.

The long-term results of Stanmore total knee replacements.

Between 1969 and 1971 20 prototypes of the Stanmore total knee prosthesis were used to replace severely arthritic knees in 18 patients. Seven patients died before the final follow-up and one had to have her leg amputated because of deep infection; in none of these patients had the prosthesis become loose. Ten patients (11 knees) were reviewed at least 10 years after operation. There was no significant clinical deterioration in 7 of these 11 surviving knees when the results at one year were compared with those at 10 years.

Assessment of the survival and the clinical results of Stanmore total knee replacements.

We review 210 Stanmore knee replacements in 163 patients to assess the survival of the prostheses and the long-term results. The annual rate of failure reached a maximum of 4.6% in the fourth year after operation; thereafter it declined to reach zero by the eighth year. Between two and eight years after operation, 66.3% of the surviving knees were completely free of pain and 30.2% had mild retropatellar pain. Fixed flexion deformities present before operation were completely corrected in 73% of the knees, and varus or valgus deformities were invariably corrected. Stability was always restored to unstable knees and 80.8% of knees flexed to 90 degrees or more after replacement. Aseptic loosening (8.1%), prosthetic infection (4.3%) and femoral fracture (2.9%) led to 8.5% of the prostheses being revised or removed over eight years. Modifications in prosthetic design and operative techniques have been introduced to minimise such complications in the future.

Wear studies on prosthetic materials using the pin-on-disc machine.

The wear of ultra high molecular weight polyethylene in combination with cobalt-chromium-molybdenum alloy was investigated by pin-on-disc experiments in which the alloy pin was loaded against the rotating polyethylene disc. In some experiments the pin was stationary, but in others it rotated about its axis. The effect of lubricant type, pin rotation, magnitude of the applied load, magnitude of the relative surface velocity, and disc storage in various environments was investigated. Wear of the polyethylene was assessed at 100 h intervals by both volumetric and gravimetric methods. Each experiment lasted 1000 h. It was concluded that of the lubricants tested bovine serum was the most suitable and that pin rotation produced more suitable polyethylene surfaces than did the stationary pin. The wear rate increased slightly with load (possibly owing to creep), was insensitive to speed, and was not affected by disc storage. The dynamic coefficient of friction increased with running tme. Results obtained by the two wear assessment methods were comparable and the reproducibility of the results was good.

Endoprosthetic replacement of the proximal femur and acetabulum. A survival analysis.

A series of 81 patients has been reviewed to determine the value of endoprosthetic replacement of the proximal femur and hip in the treatment of bone tumours. Standard statistical methods were used to evaluate the survival of the replacements and the patients. Taking removal of the prosthesis, irrespective of the cause, as the criterion for failure the survival of the replacements was found to be 63 per cent after 10 years. If deaths are regarded as failures, then the survival value falls to 48 per cent. The survival of patients with chondrosarcoma and osteoclastoma treated by endoprosthetic replacement compares favourably with survival after amputation or excision of the tumour.