The use of adhesive dressing dressings following orthopaedic surgery.

During recent years the SMTL, which is the defect reporting center for medical devices and dressings in Wales, has received a number of complaints concerning the problem of blister formation following orthopaedic surgery.

The problem seems to be associated with the use of self-adhesive island dressings backed with apertured non-woven fabric and it has been suggested that this might be due to a change in supplier for these materials.

A laboratory examination of the products concerned has revealed no significant difference between the different brands of dressings which would support this view.

A review of the literature, however, indicated that blister formation is not a new phenomenon and that blisters occurring lateral to the surgical incision of patients following orthopaedic surgery have been observed for many years.

The papers concerned suggest that blisters occur as a result of continued friction applied to the skin causing damage to the finger-like projections within the dermis that hold the epidermis and dermis together allowing the two major components of the skin to separate.

In one small study [1] involving 20 patients undergoing total hip replacements, seven (35%) developed painful blisters that appeared to be linked to dressing usage, most of these (85%) occurred in patients dressed with a non-woven fabric backed dressing.

In a larger study [2] involving 169 patients, 22 (13%) developed blisters. Whilst a number of different types of dressings were found to be associated with blister formation the greatest problem related to the use of a non-woven-fabric backed dressing. It was reported that 4 of 28 patients dressed with this material developed blisters compared with 8 of 88 patients dressed with an island dressing backed with a polyurethane membrane.

Following this study it was proposed that the relative lack of extensibility in the fabric product was responsible for this apparent increase in blister formation.

It is therefore strongly recommended that fabric backed dressings of all types should not be used to dress orthopaedic wounds particularly when swelling is occurring or is anticipated. A more extensible product or a simple dressing pad held in place with tape should be considered for these applications particularly in the early stages of treatment.

S. Thomas

  1. Wright M. 1994 Hip Blisters, Nursing Times 90 (16), 86-88.


  2. Jester R et al. 2000 A one hospital study of the effect of wound dressings and other related factors on skin blistering following total hip and knee athroplasty, Journal of Orthopaedic Nursing 4 (7), 71-77.


CSSD Clean Room Monitoring and the New ISO Standard

Many CSSD or HSDU departments in Wales are now accredited, and can affix the CE mark to the products they reprocess in accordance with the Medical Device Directive. As part of their accreditation, they must have their clean rooms monitored on a regular basis to satisfy the notified bodies that the environment in which they are packing and handling the devices is acceptable.

SMTL have provided advice and testing of clean rooms for pharmacy departments for many years, and recently these services have been extended to CSSD departments in Wales and other parts of the UK.

Prior to August 1999 the maximum particulate concentration acceptable to the accreditation bodies was specified by Class L of BS 5295 Part 1. This provided limits for the number of particles at sizes of 5 micron, 10 micron and 25 micron. In addition to the particle concentrations, BS 5295 also required that there be pressure differentials between classified rooms and the external world. Part 4 of the same standard specified the frequency of monitoring required to ensure that the location in question complied with the stated room class at all times.

This all changed in August 1999 with the publication of BS EN ISO 14644-1 and the simultaneous withdrawal of BS 5295 Parts 1 & 4. This appeared to merely replace one system of classification with another. Unfortunately the withdrawal of Part 4 of the BS meant that no frequency of monitoring was specified until the publication of Part 2 of the ISO in December 2000.

The ISO standard differs in several ways from the old BS.

  • The ISO standard sets up a new classification system for clean rooms which is based exclusively on the concentration of airborne particles - there is no requirement for pressure differentials.
  • The way a particular location may be classified is left more to the discretion of the user - a room may be classified with single or multiple particle sizes unlike the rigid requirements of the BS.
  • The range of particle sizes which may be considered for classification purposes is much reduced, covering only 0.1micron to 5 micron.

These changes may at first sight appear to make things easier and more flexible - for example, there is no requirement for balanced air systems, but as usual there are pitfalls for the unwary.

The decision as to which particle size range to use to classify a clean room is one which requires detailed knowledge and experience of clean room monitoring. The range of particle sizes covered by the ISO only just impinges on those of interest to the CSSD manager. Process generated particles (those produced by the handling of paper and fabrics) are usually in the macro particle range, i.e. larger than 5 micron and not directly covered by the ISO classification.

The publication of BS EN ISO 14644 need not lead to any changes in regard of the monitoring of CSSD packing rooms. For example, BS 5295 Class L is almost equivalent to:

ISO Class 8.8, 5 micron 185,000 particles/m3 [1], M(45,000;>10micron);laser light scattering [2], M(5,000;>25micron);laser light scattering [3].

Class selected from ISO.
M=macro, so this means less than 45,000 particles at the 10 micron size or greater, measured with a laser light scattering particle detector.
Same as [2], but the limit is less than 5,000 particles greater than 25 microns.

Clearly, the new ISO classification is quite complex. Therefore, as the old Class L is almost identical, SMTL believe that continuing with Class L should be acceptable to notified bodies.

Bruce Fisher,

Quality Manager,


Latex Labelling

In June 2000, the European Commission Scientific Committee on Medicinal Products and Medical Devices published a report entitled ``Opinion on Natural rubber latex allergy'' (available on the Internet at

Sixteen questions were formulated on various aspects of latex allergy, and the expert group provided answers.

Some of the interesting facts that emerged from the paper were:

  • The lowest dose (or threshold level) of proteins for inducing sensitisation and/or elicitation of an allergic response has still not yet been established. This means that it is not yet possible to test for safe levels of proteins in medical devices.
  • With regard to the presence of glove powder, although it has been established that latex proteins bind to powder particles present on cornstarch powdered gloves, it has not been demonstrated that powdered gloves are more likely to induce sensitisation than powder-free gloves, provided the protein content of the gloves is identical.
  • The presence of chemicals in latex gloves known to induce sensitisation (such as accelerators) can be demonstrated by various methods. There seems to be no agreement on the best applicable method, and this may be dependent on the chemical to be determined.
  • The report concludes by noting that the risk groups for latex allergy are atopics, and subjects frequently in contact with latex medical gloves, including the medical profession and patients needing multiple surgery. Particularly interesting is their statement that ``Information on the package of medical devices on the presence of natural rubber latex is therefore essential.''

P. Phillips

Wound Management Quiz

The next few issues of SMTL news will contain a series of questions designed to help you test your own knowledge of wound management. The answers are provided belowso no prizes for getting them all right! The first part of the quiz covers some of the basic terms and concepts that are used to describe the healing process. Future editions of the SMTL News will cover dressings and other aspects of this important topic.

  1. A wound which is to heal by primary intention;
    1. Has the edges drawn together with sutures, clips or tapes
    2. Is covered with a dressing and allowed to heal by granulation
    3. Is left exposed to the air to form a scab


  2. Most experts agree that for a wound to heal at the optimum rate it should be kept;
    1. Dry
    2. Moist
    3. Wet


  3. Which of the following cells are responsible for removing bacteria and debris from a wound ?
    1. Macrophages
    2. Platelets
    3. Keratinocytes
    4. Fibroblasts
    5. Erythrocytes


  4. Which of the following are responsible for the production of granulation tissue ?
    1. Macrophages
    2. Platelets
    3. Keratinocytes
    4. Fibroblasts
    5. Erythrocytes


  5. Which of the following are responsible for forming a new layer of epithelium ?
    1. Macrophages
    2. Platelets
    3. Keratinocytes
    4. Fibroblasts
    5. Erythrocytes


  6. Granulation tissue consists principally of;
    1. A mass of red blood cells held together in chains
    2. A collagen matrix containing protein and polysaccharides
    3. A network of fibrinous tissue


  7. Angiogenesis is;
    1. The formation of new blood vessels in a wound
    2. The control of wound temperature
    3. A mechanism for controlling wound


  8. Collagen is a major structural component of the skin. It is composed of;
    1. A protein helix
    2. A polysaccharide containing glucose and fructose
    3. A complex mixture of polysaccharides and lipids



Just why do luers sometimes stick together?

``I can't get it undone - pass me the Spencer Wells!''

``Why won't these connections stay together?''

These are fairly common problems and show that, since their introduction in 1925, and despite a widely accepted international standard or two, there are still compatibility problems between some male and female luers.

With few exceptions, it can be assumed that all luers meet the sizing requirements of the International Standard ISO 594 - ``Conical fittings with a 6% (Luer) taper for syringes, needles and certain other medical equipment'', parts 1 (General Requirements) and 2 (Lock fittings). With this assumption, we know that they will certainly come together and fit, and usually do, but we also know that some will come apart and others will stick fast.

The reasons why luers stick or slip can be related, and requires a brief look at the surfaces of plastics, some very broad generalisations and some over simplification.

Plastic Properties

Some plastics are relatively soft (such as polyethylene and polypropylene) while others are very hard (such as polycarbonate (PC) and Acrylonitrile Butadiene Styrene (ABS)). Normally the hard plastics will (or can) be very clear and the soft plastics more opaque and this is related to the way the plastic behaves at the molecular level when it is molten going into the mould.

The clear plastics flow easily and cleanly, fully covering the surfaces of the mould, whereas the softer plastics do not flow as well and will ``sit on top'' of the mould surface. The hard plastics will take on the form of the mould right down to the microscopic polishing scratches, and it is these that can contribute to the problem.

When two hard plastics are brought together, these microscopic scratches will overlap and settle in grooves and valleys. Enough of these will make turning or moving the two plastic components apart very difficult. In the case of soft plastics, the scratches are not present on the surface and a smooth undulating surface is formed. This allows fewer contact points and no ridges to stop movement, thus disconnection is very easy, sometimes too much so.

So, why don't manufacturers make their luers from materials that allow reasonably easy disconnection? One of the main reasons relates to the ability to join materials. The softer materials are very difficult to bond, whereas hard materials are relatively easy. The technology to join soft materials is available, but does involve considerable expense which would be reflected in the final product cost - in the current climate a significant factor.

Luer Cracking

Some luers will join and disconnect easily when dry or when an aqueous solution is running, yet will become stuck later or may even crack when a different fluid is passed through. The term used in the plastics industry is `Environmental Stress Degradation', in other words an external factor is causing a change in the nature of the materials. This is a problem most commonly associated with the ``hard plastics''.

Two of the most common influencing factors in the medical world are alcohol (or alcohol based fluids) and lipid. In essence we can say that their effect is the same - both are oleophilic (oil loving), and the plastic (which was once an oil) is very keen to absorb the oleophilic fluid and does so very quickly (which is where the problem starts).

To absorb the liquid, it must expand quickly, and initially this expansion takes place only at the surface. Unfortunately, the female luer is also trying to hold it in place so a large amount of stress is built up. If the female luer is strong enough, it will absorb the stress of the expanding male luer and the male luer will become stuck. If not, it will crack and a different set of problems arises. When alcoholic solutions are used, they are often in contact with the outside of the luers, but the swelling effect will still be the same.

With the increased use of drugs carried by lipids and the increased use of alcohol based antiseptic solutions, these problems are becoming more common place. The manufacturers of medical devices are incorporating the latest generation of plastics that resist oleophilic attack into their devices but have to make changes sensibly and safely whilst meeting the customers requirements of cost efficient devices manufactured to a high quality.

The common sense approach to using all devices does not change. Ensure that everything being used is right for the job, read the instructions for use on devices (especially the cautions) and do the same with any medications being used with the devices. If in doubt, ask the device or the drug manufacturer. Graham Milward Manager

Technical Support Services

Vygon (UK) Ltd

Wound Management Quiz - Answers

  1. The correct answer is (a). Open wounds that are exposed to the air or covered with a dressing and allowed to heal by granulation and epithelialisation are said to heal by secondary intention.


  2. The answer is (b). It is now generally accepted that a moist wound heals more rapidly than a comparable wound that is kept dry. This is because epidermal (skin) cells can migrate faster across the surface of a moist wound than a dry one. If a wound becomes too wet the surrounding skin may become macerated an infection may become a problem.


  3. The correct answer is (a). Macrophages, together with polymorphonucleocytes (neutrophils) produce proteinases and other enzymes that break down clots and debris. They are also believed to produce factors that stimulate the formation of new vascular tissue and play a role in the control of fibroblasts, (see below).


  4. The correct answer is (d). Fibroblasts are responsible for the synthesis of collagen a major component of granulation tissue


  5. The correct answer is (c). Keratinocytes, or epidermal cells, are produced in the basal layer of the epidermis. Normally these cells gradually migrate upward from this region and become keratinised and flattened to form the stratum corneum, the outer layer of the skin. In the vicinity of a wound, however, the cells migrate sideways across the surface of defect to form a new layer of skin.


  6. The correct answer is (b). Granulation tissue consists of a complex mixture of proteins and polysaccharides which form a gel-like matrix contained within a fibrous collagen network.


  7. The correct answer is (a).


  8. The correct answer is (a). Collagen consists of a mass of protein fibrils that are formed extra-cellularly from precursors (building blocks) produced by fibroblasts.



The Medical
Disposables and
Dressings Newsletter
Vol. 2 No. 2
February 2001
Published by:
The Surgical Materials
Testing Laboratory
Edited by:
Dr Stephen Thomas
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Peter Phillips
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Contact Information
Tel: 01656-752820
Fax: 01656-752830
Princess of Wales Hospital
Coity Road
CF31 1RQ
©2001 by SMTL.
All rights reserved. No permission necessary to copy, reprint and distribute unaltered within the NHS as required.
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