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Continuing Medical Education No. 18
doi: 10.1054/ cuor.2000.0143, available online at http://www.idealibrary.com on
Bonsell S et al. The relationship of age, gender and degenerative changes observed on radiographs of the shoulder in asymptomatic individuals JBJS 82–B: 1135–1139 Papers such as this are needed to put other research findings into context. What use is work on the incidence of degenerative change after shoulder injuries if we do not know how common such changes are without trauma? The glenohumeral joint is not investigated, only the AC joint and subacromial region (which are, after all, the areas commonly assessed for signs of degenerative change) This study evaluates X rays of 84 asymptomatic individuals between 40 and 83 years of age. We do not know how the patients were selected for screening, other than that they were paid volunteers. Three views were evaluated – AP and supraspinatus outlet views and an AC joint view. Gender didn’t predict degenerative change but, unsurprisingly, age did. In particular the following findings were commoner with advancing age – medial acromial and lateral clavicle sclerosis, acromial subchondral cysts, inferior acromioclavicular osteophytes and narrowing of the AC joint. Sample size constraints mean that the incidence of these various factors could not be discussed, only odds ratios. However we are sufficiently alerted to avoid jumping to conclusions when assessing patients with shoulder pain
FOLD HERE
Hintermann B, Trouillier HH & Schafer D Rigid internal fixation of fractures of the proximal humerus in older patients. JBJS 82–B: 1107–1112 Papers such as this are so easy to pick apart that they make good fuel for journal clubs and possibly even exams. The question addressed is also so controversial that the paper may impact on one’s practise simply because the evidence available on management of these fractures is so inconclusive. The classification of shoulder fractures is fraught with intra-and interobserver error, exemplified by the illustrated ‘4 part’ fracture in this paper. We are to accept that bone quality in ‘older’ patients is poor yet the same illustrated case is 58 years old and the definition of ‘older’ in this paper is 50 years age. The implant used is a hip plate especially shortened, though of course specifically designed plates are now available. Fixation is recommended for 4 part fractures but only 7 are studied. Why should we then take away anything from this paper? The value of this work hinges on the same points as it’s downfall. Proximal humeral fractures are poorly understood. We cannot reliably classify them and the literature is replete with small studies of poorly described techniques that we cannot reliably reproduce. The generic technique here is easy to understand and the results at least as good as has been obtained with any other technique. Nevertheless the management of 3 and 4 part fractures (if that is what we should call them) requires much fundamental work before we can produce an acceptable and generalisable plan for their management.
Govender S, Maharaj JF & Haffajee MR Fractures of the odontoid process. JBJS 82–B: 1143–1147 This South African team has treated 196 patients with odontoid peg fractures over a 5-year period and insight into the incidence and causes of non union is presented. Only 13 patients were excluded because of inadequate follow-up and data collection was prospective. Eighteen patients — 8 with acute type 2 fractures, 10 with type 2 nonunions — had selective angiography. We do not know how these patients were selected, though the cohort had separate ethical approval for angiography. Angiography showed that the blood supply to the peg was not disrupted. Non-union occurred in 29% of type II fractures with fibrous union in 17%. The incidence of non-union was strongly related to age > 40 and late presenters. Posterior displacement, or anterior displacement over 4 mm contributed. All type III fractures united and had significantly greater exposed fracture surface area. The clinical (crude pain and stiffness) and radiological outcomes were not related This is really two studies. There are faults with the design of each component but nevertheless this is an enormous experience and represents best evidence on the incidence of non-union and some aspects of aetiology.
Roposch A, Saraph V & Linhart WE Flexible intramedullary nailing for the treatment of Unicameral bone cysts in long bones. JBJS 82–A 1447–1453 The management of pathological fracture through a unicameral bone cyst is problematic. We hope that the fracture will induce healing of the cyst but this does not always occur and management in the interim can be difficult. We are recommended a technique of flexible nailing that has been used by the authors in 32 patients. It is not clear if this is a consecutive series of all patients with significant cysts or if others were managed by other techniques. The summary of the authors is that this technique provides early stability allowing mobilisation without a cast and avoiding further pathological fracture. A literature review is provided to illustrate that all available treatments are fraught with failures. Fortunately the authors do not stretch their conclusions too far. Even with this technique healing took up to almost 8 years! Exchange nailing was therefore required in 9/32 simply because growth left the nails too short. Only 14 cysts healed completely and 16 healed with residual radiolucent areas. Clearly there are advantages to this technique but it certainly is not the panacea one would hope for.
POLYETHYLENE
Manufacture Ethylene monomers are polymerised over Titanium chloride catalyst with a cocatalyst that can vary. A powder is produced that must meet stringent quality criteria to be used in medical applications. Calcium Stearate is added as a lubricant, anticorrosive agent and whitener. Recent speculation of it’s possible contribution to the wear process has led some manufacturers to make available polyethylene without this additive. Polyethylene components for replacement joints are fabricated from polyethylene powder, which is either— ● Compressed directly into a mould ● Ram extruded into bar stock ● Compressed into sheets
Oxidation can occur both in storage and in vivo after gamma sterilisation. Oxidized polymer is more brittle. A long storage period before implantation, allowing preimplantation oxidization, is thought to make the polyethylene more vulnerable to in vivo oxidation. The mechanical properties of the polyethylene are changed and theoretically wear processes can be enhanced. The first 2 mm of the exposed surface are at particular risk It is thought that Ethylene oxide and gas plasma sterilization avert this
Possible adverse effects Gamma irradiation causes chain scission, cross-linking and oxidation in polymers. Intermolecular bonds are broken down, creating free radicals that can— ● Reattach and restore the molecule ● Bond adjacent polymer at a new site, causing cross linking ● React with oxygen (if available)
2 mm
Depth Fig. 2 Radiation produces free radicals and the potential for oxidation at depths of up to 2 mm
collision g
ray
em radiation
chain
Fig. 1
free radical
oxidation effect entirely and that components sterilized in this way maintain their properties indefinitely.
Newer developments Special processes have been developed to manipulate the mechanical properties of polyethylene in an attempt to control it’s wear characteristics. As yet no clinical trials have proven that these enhanced polyethylenes have any advantage over standard product (although the properties of this are very dependent on manufacturing conditions so ‘standard’ is perhaps not a good description). Examples of the processes include a, isostatic compression to increase the crystallinity of the product b, compression in an argon environment, which is said to increase the ultimate tensile strength, and c, heating after gamma irradiation to promote recombination and cross-linking leaving fewer free radicals available for oxidation after implantation. Newer techniques have been developed to increase cross-linking between polymer chains. This is promoted by peroxide and has been commercially successful. However, concern remains that residual peroxide may enhance later oxidation so this method has not been used for joint replacement components. An alternative to chemically induced cross-linking is radiation-induced change and this avenue is being explored. Certainly, highly cross-linked polyethylenes have already been shown to have greatly improved wear characteristics in wear simulators.
POLYETHYLENE
In the latter two instances, bar stock or sheet is machined to produce the final component. In all cases the essential process is compression, but control of temperature, pressure, atmosphere, rates of heating and cooling and time factors all influence the physical properties.
Sterilization Components can be sterilized by gamma irradiation or by ethylene oxide or gas plasma contact. Gamma irradiation passes throughout the component and is effective at all levels. Ethylene oxide and gas plasma are active only at the areas of surface contact so are not suitable if the component is assembled from several parts. Components are packaged for protection against mechanical damage and to maintain sterility. Historically the parts were packaged in air but currently vacuum packing or packing in an inert atmosphere such as nitrogen or argon is preferred to discourage oxidation.
C.M.E. No 18
Ultrahigh Molecular Weight Polyethylene (UHMWPE) has been used successfully as a bearing surface in joint replacement surgery for around four decades. It is not to be confused with High Density Polyethylene from which supermarket carrier bags are fabricated. Only a small proportion of the world output of UHMWPE ends up in joints, most of the rest facilitates our passage down the ski slopes as the low friction base of skis and snowboards.
Bonsell S et al. The relationship of age, gender and degenerative changes observed on radiographs of the shoulder in asymptomatic individuals JBJS 82–B: 1135–1139 Papers such as this are needed to put other research findings into context. What use is work on the incidence of degenerative change after shoulder injuries if we do not know how common such changes are without trauma? The glenohumeral joint is not investigated, only the AC joint and subacromial region (which are, after all, the areas commonly assessed for signs of degenerative change) This study evaluates X rays of 84 asymptomatic individuals between 40 and 83 years of age. We do not know how the patients were selected for screening, other than that they were paid volunteers. Three views were evaluated – AP and supraspinatus outlet views and an AC joint view. Gender didn’t predict degenerative change but, unsurprisingly, age did. In particular the following findings were commoner with advancing age – medial acromial and lateral clavicle sclerosis, acromial subchondral cysts, inferior acromioclavicular osteophytes and narrowing of the AC joint. Sample size constraints mean that the incidence of these various factors could not be discussed, only odds ratios. However we are sufficiently alerted to avoid jumping to conclusions when assessing patients with shoulder pain
FOLD HERE
Hintermann B, Trouillier HH & Schafer D Rigid internal fixation of fractures of the proximal humerus in older patients. JBJS 82–B: 1107–1112 Papers such as this are so easy to pick apart that they make good fuel for journal clubs and possibly even exams. The question addressed is also so controversial that the paper may impact on one’s practise simply because the evidence available on management of these fractures is so inconclusive. The classification of shoulder fractures is fraught with intra-and interobserver error, exemplified by the illustrated ‘4 part’ fracture in this paper. We are to accept that bone quality in ‘older’ patients is poor yet the same illustrated case is 58 years old and the definition of ‘older’ in this paper is 50 years age. The implant used is a hip plate especially shortened, though of course specifically designed plates are now available. Fixation is recommended for 4 part fractures but only 7 are studied. Why should we then take away anything from this paper? The value of this work hinges on the same points as it’s downfall. Proximal humeral fractures are poorly understood. We cannot reliably classify them and the literature is replete with small studies of poorly described techniques that we cannot reliably reproduce. The generic technique here is easy to understand and the results at least as good as has been obtained with any other technique. Nevertheless the management of 3 and 4 part fractures (if that is what we should call them) requires much fundamental work before we can produce an acceptable and generalisable plan for their management.
Govender S, Maharaj JF & Haffajee MR Fractures of the odontoid process. JBJS 82–B: 1143–1147 This South African team has treated 196 patients with odontoid peg fractures over a 5-year period and insight into the incidence and causes of non union is presented. Only 13 patients were excluded because of inadequate follow-up and data collection was prospective. Eighteen patients — 8 with acute type 2 fractures, 10 with type 2 nonunions — had selective angiography. We do not know how these patients were selected, though the cohort had separate ethical approval for angiography. Angiography showed that the blood supply to the peg was not disrupted. Non-union occurred in 29% of type II fractures with fibrous union in 17%. The incidence of non-union was strongly related to age > 40 and late presenters. Posterior displacement, or anterior displacement over 4 mm contributed. All type III fractures united and had significantly greater exposed fracture surface area. The clinical (crude pain and stiffness) and radiological outcomes were not related This is really two studies. There are faults with the design of each component but nevertheless this is an enormous experience and represents best evidence on the incidence of non-union and some aspects of aetiology.
Roposch A, Saraph V & Linhart WE Flexible intramedullary nailing for the treatment of Unicameral bone cysts in long bones. JBJS 82–A 1447–1453 The management of pathological fracture through a unicameral bone cyst is problematic. We hope that the fracture will induce healing of the cyst but this does not always occur and management in the interim can be difficult. We are recommended a technique of flexible nailing that has been used by the authors in 32 patients. It is not clear if this is a consecutive series of all patients with significant cysts or if others were managed by other techniques. The summary of the authors is that this technique provides early stability allowing mobilisation without a cast and avoiding further pathological fracture. A literature review is provided to illustrate that all available treatments are fraught with failures. Fortunately the authors do not stretch their conclusions too far. Even with this technique healing took up to almost 8 years! Exchange nailing was therefore required in 9/32 simply because growth left the nails too short. Only 14 cysts healed completely and 16 healed with residual radiolucent areas. Clearly there are advantages to this technique but it certainly is not the panacea one would hope for.
POLYETHYLENE
Manufacture Ethylene monomers are polymerised over Titanium chloride catalyst with a cocatalyst that can vary. A powder is produced that must meet stringent quality criteria to be used in medical applications. Calcium Stearate is added as a lubricant, anticorrosive agent and whitener. Recent speculation of it’s possible contribution to the wear process has led some manufacturers to make available polyethylene without this additive. Polyethylene components for replacement joints are fabricated from polyethylene powder, which is either— ● Compressed directly into a mould ● Ram extruded into bar stock ● Compressed into sheets
Oxidation can occur both in storage and in vivo after gamma sterilisation. Oxidized polymer is more brittle. A long storage period before implantation, allowing preimplantation oxidization, is thought to make the polyethylene more vulnerable to in vivo oxidation. The mechanical properties of the polyethylene are changed and theoretically wear processes can be enhanced. The first 2 mm of the exposed surface are at particular risk It is thought that Ethylene oxide and gas plasma sterilization avert this
Possible adverse effects Gamma irradiation causes chain scission, cross-linking and oxidation in polymers. Intermolecular bonds are broken down, creating free radicals that can— ● Reattach and restore the molecule ● Bond adjacent polymer at a new site, causing cross linking ● React with oxygen (if available)
2 mm
Depth Fig. 2 Radiation produces free radicals and the potential for oxidation at depths of up to 2 mm
collision g
ray
em radiation
chain
Fig. 1
free radical
oxidation effect entirely and that components sterilized in this way maintain their properties indefinitely.
Newer developments Special processes have been developed to manipulate the mechanical properties of polyethylene in an attempt to control it’s wear characteristics. As yet no clinical trials have proven that these enhanced polyethylenes have any advantage over standard product (although the properties of this are very dependent on manufacturing conditions so ‘standard’ is perhaps not a good description). Examples of the processes include a, isostatic compression to increase the crystallinity of the product b, compression in an argon environment, which is said to increase the ultimate tensile strength, and c, heating after gamma irradiation to promote recombination and cross-linking leaving fewer free radicals available for oxidation after implantation. Newer techniques have been developed to increase cross-linking between polymer chains. This is promoted by peroxide and has been commercially successful. However, concern remains that residual peroxide may enhance later oxidation so this method has not been used for joint replacement components. An alternative to chemically induced cross-linking is radiation-induced change and this avenue is being explored. Certainly, highly cross-linked polyethylenes have already been shown to have greatly improved wear characteristics in wear simulators.
POLYETHYLENE
In the latter two instances, bar stock or sheet is machined to produce the final component. In all cases the essential process is compression, but control of temperature, pressure, atmosphere, rates of heating and cooling and time factors all influence the physical properties.
Sterilization Components can be sterilized by gamma irradiation or by ethylene oxide or gas plasma contact. Gamma irradiation passes throughout the component and is effective at all levels. Ethylene oxide and gas plasma are active only at the areas of surface contact so are not suitable if the component is assembled from several parts. Components are packaged for protection against mechanical damage and to maintain sterility. Historically the parts were packaged in air but currently vacuum packing or packing in an inert atmosphere such as nitrogen or argon is preferred to discourage oxidation.
C.M.E. No 18
Ultrahigh Molecular Weight Polyethylene (UHMWPE) has been used successfully as a bearing surface in joint replacement surgery for around four decades. It is not to be confused with High Density Polyethylene from which supermarket carrier bags are fabricated. Only a small proportion of the world output of UHMWPE ends up in joints, most of the rest facilitates our passage down the ski slopes as the low friction base of skis and snowboards.