- Email: [email protected]
(ii) Shoulder replacement—current problems
Current Orthopaedics (2002) 16, 15^20
c 2002 Published by Elsevier Science Ltd. doi:10.1054/ycuor.245, available online at http://www.idealibrary.com on
MINI SYMPOSIUM: SHOULDER PROBLEMS
(ii) Shoulder replacementFcurrent problems D. Limb Division of Surgery, Orthopaedic Surgery, Clinical Sciences Building, St James’s University Hospital Trust, Beckett Street, Leeds LS9 7 TF, UK
Summary Shoulder replacementis a successfulprocedure withresults comparable to hip and knee replacement surgery. As surgical technique and implant design evolve, the management of uncomplicated osteoarthritis and rheumatoid disease gives increasingly satisfying results.It has become apparent, however, thatthe best shoulder replacements are those that most accurately reproduce the normal anatomy and mechanics of the shoulder. Implants are quickly evolving to address the ¢ndings of basic science research, sometimes tothe detrimentofthe requirementforlong-termresults. Arguments have been made to alter the design of both humeral and glenoid components to allow more adaptability for the variable anatomy encountered. For fracture surgery, these changes also attempt to facilitate secure reattachment of the rotator cu¡, whilst more radical changes have been tried to substitute the absent rotator cu¡ in cu¡ arthropathy.
c 2002 Published by Elsevier Science Ltd.
INTRODUCTION Shoulder surgery in general, and joint replacement surgery speci¢cally, continues to enjoy a growth period worldwide. In 1990 ^1992, 5000 shoulder replacements were carried out in the USA. In 1999, more than 1000 shoulder replacements were carried out in New York State alone. As the number of procedures performed grows, more information becomes available on the performance of the prostheses. Both technique and implants can evolve more rapidly. Presently, this has created dilemmas in management more e¡ectively than it has resolved contentious issues. This article reviews areas of controversy in shoulder replacement and current thought processes, as evidenced by recent publications in the ¢eld.
THE HUMERAL COMPONENT With regard to the long-term results of shoulder replacement, the humeral component generates least worry. Loosening is unusual and certainly much less frequent than loosening of the glenoid component. Nevertheless, dissatisfaction has arisen because of the failure of earlier designs to accurately reproduce normal anatomy and because reconstruction of the humeral tuberosities around bulky prostheses in trauma cases can be unsatisfactory. Greater tuberosity migration after hemiarthroplasty for
fracture has a major negative in£uence on the functional outcome.
Anatomy It has become a widely upheld principle that successful humeral head replacement should be just that F a prosthesis that replaces the damaged articular surface and reproduces normal anatomy. Theoretically, this restores normal relationships within the joint and the biomechanical environment will be favourable to normal function. Early prostheses o¡ered few alternatives in terms of humeral head size, radius of curvature, o¡set from the long axis of the humeral shaft and head/neck angle. First generation prostheses o¡ered a monobloc humeral head replacement with only few alternative sizes. Although many successful replacements were carried out, di⁄culties were often met in balancing the soft tissues after surgery because the head was too large or small for the joint space available. Over-large components ‘overstu¡ing’ the joint were often sti¡ and painful. Components that were too small were prone to instability. Second-generation components provided modular systems for independent stem and head selection. This allows adequate ¢lling of the humeral shaft and metaphysis (particularly important in uncemented designs) and correct balancing of the rotator cu¡ by selection of a head size (radius of curvature and length) that is right for the joint space.
16
CURRENT ORTHOPAEDICS
Fracture prostheses
Figure 1 By rotating an eccentric ¢xation post the humeral head can be o¡set in relation to the axis of the stem.
Further anatomical studies have drawn attention to the variability that exists in other aspects of humeral anatomy. Thus, third-generation components introduce another level of modularity or selection by o¡ering a variety of neck/shaft angles and the ability to alter the o¡set of the head in relation to the stem.1 This latter variable is achieved usually by providing an eccentric coupling of the head to the stem that can be rotated until the head lies in the desirable position, usually the judged position of the excised natural humeral head, before locking the components together (Fig.1). The development of prostheses has been driven by basic science research and a desire to overcome commonly encountered di⁄culties during joint replacement surgery. Similar research has demonstrated that newer designs are better able to reproduce the 3D position of the centre of rotation, the contact point of the articulation and the radius of curvature of the articular surface.2 As yet, however, clinical studies have failed to demonstrate any e¡ect of these radiologically identi¢ed variables on functional outcome.3 Time will tell if the improved biomechanical environment will have any e¡ect on long-term survivorship of the humeral component. A parallel development has been the concept of humeral head surface replacement without the imposed restrictions of a stem. Stephen Copeland and co-workers discuss this in his article in this issue.
Shoulder replacement as we know it, came into being through e¡orts to replace the humeral head in cases of severe fractures and fracture dislocations of the proximal humerus.4 Shoulder replacement systems have evolved, as described above, and the same modular components have been used for replacement of arthritic and fractured heads.The proximal bulk of the prostheses and its metaphyseal ¢ns (originally used to provide holes for suture attachment of the tuberosities) give good contact between the component and the intact proximal humerus. This allows rotational stability and often it is not necessary to cement humeral components, even perhaps those with no bioactive coating to facilitate ¢xation. In proximal humeral fractures the tuberosities are usually detached. There is no rotational stability of a round stem in a roundish humeral shaft and cement or bioactive coatings are essential.The bulk of the prosthesis proximally now becomes a disadvantage. Although ¢ns allow the provision of suture holes, which are good for initial ¢xation, the aim of fracture surgery is to get the tuberosities to unite to each other and to the humeral shaft around a correctly positioned humeral prosthesis. This is achieved by tension band ¢xation of the tuberosities to each other and to the shaft over bone graft from the excised humeral head. A bulky prosthesis limits the volume of bone graft that can be used. The main problem identi¢ed in tuberosity ¢xation after fracture is secure ¢xation of the greater tuberosity. Insecure ¢xation with a posterior and/or superior drift after surgery is associated with poor function. This has been addressed by a tendency to use tension band sutures more readily and to pass a circumferential suture medial to the shaft and around both greater and lesser tuberosities.5 Many manufacturers are now also o¡ering a ‘fracture kit’, which is a modi¢ed prosthesis allowing more space beneath the head for containment of bone graft. Examples are the De Puy Global Fxs and the Tornier (Forth Medical) Aequaliss fracture prostheses seen in Fig 2(a) and (b). Both are speci¢cally designed now for trauma cases, though as yet no long-term studies are available to demonstrate a de¢nite advantage over standard components with known de¢ciencies. As can be seen, instrumentation systems are becoming more complex to assist in correct component positioning and this in itself may a¡ect the outcomes.
THE GLENOID COMPONENT Neer’s prosthesis employed a keel of polyethylene that could be cemented into a vertical slot cut into the glenoid fossa. This design has withstood the test of time and, decades later, is still in use. It has been recognized, however, that the keel design results in greater contact
SHOULDER REPLACEMENTFCURRENT PROBLEMS
17
Figure 3 Finned (upper) and pegged (lower) glenoid components.
Figure 2
stress than pegged designs, which support the glenoid articular plate at multiple points (Fig. 3).Glenoid components became available that o¡ered multiple pegs for ce-
mentation into the glenoid rather than a single, central column. If there is insu⁄cient bone to allow an adequate hole to be drilled in the glenoid without perforation of the scapular cortex, then the appropriate peg can be removed or shortened before implantation, permitting proper cement containment. Again this seems a neat response to the identi¢ed problem, but may not be an ideal solution in the real world. Unfortunately, when a pegged component does loosen it takes with it bone adjacent to each peg. Since the pegs are multiple, large cavitary defects can result, making revision to a new glenoid component impossible. A biomechanical study investigating multiple possible contributors to glenoid component stability identi¢ed not only that pegs (threaded more so than cylindrical) were better than keels, but that the following design features provided better resistance to loosening in vitro F rough, curved back wall to component, less constrained articulation with humerus and an all polythene rather than metal-mesh-backed construction.6 Another study demonstrated that although a pegged component gave better ¢xation in normal bone, a keeled component was better in rheumatoid bone.7
18
Uncemented glenoid components may avert the problems of lucent lines around keeled or pegged cemented components. Initial ¢xation, for example with screws, is necessary since the small glenoid component cannot otherwise be ¢xed in a stable fashion in the initial phase before osseointegration of its active coating.This in turn demands that the component is metal-backed and therefore bulkier. Anatomic studies of the scapula become important in deciding how to position the initial screws in order to obtain the most secure ¢xation of metal-backing plate to prepared glenoid fossa. It seems that the strong lateral column of the scapula and the base of the coracoid o¡er the best bone for ¢xation. Access may be di⁄cult to place screws into these areas, however, and mechanisms for locking the screws into the metal plate may impose the needs for left/right components, increasing an inventory already burgeoning since the introduction of modular humeral components. As yet, we have no good evidence base on which to base our decisions about glenoid component ¢xation. Unfortunately, we are unlikely to obtain any good evidence in the near future.Taking shoulder replacement as a whole, it has been pointed out that 20 di¡erent arthroplasty systems were available in the UK in 2000. Twelve of these had been introduced in the previous 8 years and only eight had results for perusal in peer review journals (not necessarily long-term results). These eight prostheses accounted for less than 40% of the prostheses being implanted annually at the time of the study.8
INDICATIONS FOR SURGERY It is more or less accepted that shoulder replacement gives excellent pain relief and increased function in rheumatoid disease (see the article by lan Kelly in this issue) and osteoarthrosis. There has been considerable recent interest in the place of shoulder replacement for the more di⁄cult indications, particularly rotator cu¡ arthropathy, fracture malunions and instability arthropathy.
Rotator cu¡ disease Massive tears of the rotator cu¡ that cannot be repaired, such as are found in cases of rotator cu¡ arthropathy, present a particular problem for the shoulder surgeon. By de¢nition reconstruction of the cu¡ is not possible. A shoulder arthrodesis may resolve issues of pain, but at the sacri¢ce of all glenohumeral movement. Any attempt at conventional shoulder replacement will leave the prosthesis just as de¢cient of the centring action of the rotator cu¡ in the glenoid fossa as was the natural humeral head. Thus, attempts to move the shoulder will inevitably be accompanied by anterosuperior migration of the prosthesis. If the coracohumeral arch has been
CURRENT ORTHOPAEDICS
rendered de¢cient by a substantial acromioplasty (often carried out for pain relief or in attempts to repair the cu¡) then actual dislocation can occur, the prosthesis subluxing out to lie under the deltoid with attempted arm use. The translation that occurs across the glenoid in these cu¡-de¢cient shoulders loosens any implanted glenoid component rapidly by edge loading (rocking horse phenomenon). Despite this, hemiarthroplasty does o¡er pain relief and modest gains in motion and function9 and patients are satis¢ed overall with the procedure. Patient selection is paramount, however, and expectations have to be made clear. Hemiarthroplasty cannot be expected to restore pain-free overhead range and strength, though many activities of daily living can be rendered comfortable.These results lag far behind what can be achieved otherwise with shoulder replacement and the search is on for acceptable alternatives. Currently, there seems to be a vogue for ¢xed fulcrum prostheses. These have designed-in stability that maintains the humeral and glenoid components in articulation without the need for an intact rotator cu¡.Clearly, however, the shear forces generated by deltoid will have to be resisted within the system and this usually means at the glenoid component/bone interface, even if the centre of rotation is medialized to minimize this. Good short-term results have been reported at meetings concerning the functional improvements patients experience after such implants are used. By restoring a stable fulcrum for the shoulder muscle couples to act upon high overhead elevation and function can be restored. Only time will tell how the mechanical environment of the glenoid-sided component will fare. It is very unlikely that the results will even approach what can be achieved in osteoarthrosis with an intact cu¡, but if the bene¢ts are 5-years worth of dramatic functional improvement then in this a price worth paying?
Fracture malunion As the supply of shoulder surgeons increases more patients are referred for treatment of late problems. Typical of these is the 3- or- 4 -part fracture that has been treated non-operatively and has resulted in a malunion. If the patient has good range and function there is no need for further action, but what of the patient with painful restriction of function? If shoulder hemiarthroplasty is a satisfactory treatment for the original fracture, is it a viable alternative for managing the late complications? Certainly, shoulder replacement in the presence of malunion is technically more demanding. In the case of surgical neck malunion, it may be impossible to pass a stem down the medullary canal. In these cases, either an osteotomy of the neck or surface-replacement hemiarthroplasty, such as the Copeland prosthesis, can now
SHOULDER REPLACEMENTFCURRENT PROBLEMS
19
be considered. More commonly, the problem is malunion of the tuberosities. In general, the reports on osteotomy of malunited tuberosities followed by reconstruction around a prosthesis have not been encouraging. There is a higher risk of dehiscence of the reattached tuberosities and early surgical complications.The largest case series on the subject10 demonstrated inferior results to hemiarthroplasty for acute fractures in all respects. Nevertheless, patients are overall improved and this is currently the best reconstructive option for these patients provided that they understand the limited goals of the procedure. The real question that needs to be answered here is ‘what patient population should be considered for immediate hemiarthroplasty?’ The best results are obtained if the procedure is carried out as soon as possible after injury, so a policy of ‘see how it goes F we can always do a shoulder replacement later’ is far from satisfactory.
Figure 4 Glenoid augmentation with bone graft.
Instability
INFECTION
Repeated anterior dislocation of the glenohumeral joint enlarges the Hill Sachs lesion on the posterior surface of the humeral head and erodes away the anterior glenoid rim. In chronic cases, a situation is reached where the entire front half of the glenoid is eroded away and the humeral head articulates, via its enlarged Hill Sachs lesion, perched on the glenoid de¢cit in a position of anterior subluxation not amenable to reduction (the glenoid socket is largely missing). This di⁄cult situation can be seen as one of the few indications for arthrodesis, though many patients would prefer to keep their painful false joint than to lose the glenohumeral joint completely (often expecting a sti¡er shoulder than they get after arthrodesis, since the scapulothoracic joint is very mobile). More experience is now published on the management of this, and similar cases of glenoid de¢ciency. Essentially, the bone defect is managed in instability just as it would be for arthropathy of other cases. Minor defects can sometimes be dealt with by reaming down the glenoid to the level of the defect, thus realigning it normally. This only works for shallow defects, however, not the deep de¢ciencies seen in instability. These large defects require structural bone grafts, securely ¢xed with 3.5 mm lag screws. A glenoid fossa can thus be recreated onto which a component can be cemented, so careful planning of screw positioning is required (Fig. 4). Hemiarthroplasty is not precluded but, needless to say, careful attention has to be paid to soft tissue balance to reduce the incidence of recurrence. Only small series of cases have been reported for this rare operation, and even in the best of hands a 10% redislocation rate is expected.
As the number of shoulder joints replaced increases there is an inevitable increase in the volume of revision surgery for infection, just as has been witnessed over the past three decades in hip and knee surgery.The infection rate after shoulder arthroplasty is approximately 0.5%.11 Since the rate of shoulder replacement is much lower than that of hip and knee replacement, experience of the operation and its outcomes have been slower to accumulate. The approach to the infected prosthesis has been developed from lessons learned in lower limb revision surgery. An outline approach is to consider early aggressive debridement for ‘early’ infections and to follow this up with 6 weeks of focussed antibiotic treatment. Cases presenting later can be investigated to identify the organism by biopsy (? Needle or open) and managed by prosthetic removal either as de¢nitive treatment or followed by immediate or delayed reimplantation. What limited experience there is in respect of the shoulder suggests that patients fare better symptomatically if prosthesis can be successfully reimplanted and retained. The reinfection rate and risk of further surgery are high, however.12 Shoulder arthrodesis after removal of a shoulder prosthesis is very much less reliable than when carried out with good bone stock, such as might exist in a case of brachial plexus injury. The results of arthrodesis should not be confused when counselling patients beforehand. It is recommended that if arthrodesis is contemplated as a treatment for infected prosthesis, then the components are removed and antibiotic treatment continued for 6 weeks to reduce the risk of reinfection at arthrodesis.This rather goes against the grain of using stability as
20
a weapon against bacterial infection and as yet there is no strong evidence to back this recommendation.
CONCLUSION The challenges facing shoulder replacement are being addressed by modi¢cations of prosthetic design and surgical technique. Care needs to be taken to ensure that these‘improvements’ are not simply short-term solutions to perceived problems that in the long term detract from the improving results we have enjoyed over the past three decades. A foundation of reliable prostheses is available and newer designs may be useful for the speci¢c conditions that suggest scope for improvement, for example, rotator cu¡ arthropathy, fracture surgery, instability and revision surgery.
REFERENCES 1. Walch G, Boileau P. Prosthetic adaptability: a new concept for shoulder arthroplasty. J Shoulder Elbow Surg 1999; 8: 443–451. 2. Ehnes D L, Stone J J, Cofield R H. Analysis of the shoulder implant. Biomed Sci Instrum 2000; 36: 129–134. 3. Gartsman G M, Hasan S S. What’s new in shoulder surgery. J Bone Jt Surg Am Vol 2001; 83A: 145–151.
CURRENT ORTHOPAEDICS
4. Neer C S. 2nd Displaced proximal humeral fractures. II Treatment of three-part and four-part displacement. J Bone Jt Surg Am Vol 1970; 52:1090–103. 5. Bioleau P. Indications and important features of primary prosthetic replacement in acute fractures. Presented at F European Shoulder and Elbow Society Annual Meeting, The Hague. September 1999. 6. Anglin C, Wyss U P, Nyffeler R W, Gerber C. Loosening performance of cemented glenoid prostheses design pairs. Clin Biomech 2001; 16: 144–150. 7. LaCroix D, Murphy L A, Prendergast P J. Three-dimensional finite element analysis of glenoid replacement prostheses: a comparison of keeled and pegged anchorage systems. J Biomech Eng 2000; 122: 430–436. 8. Mackay D C, Hudson B, Williams J P. Which primary shoulder and elbow replacement? A review of the results of prosthesis available in the UK. Ann R Coll Surg Eng 2001; 83: 258–265. 9. DiGiovanni J, Marra G, Park J K, Bigliani L U. Hemiarthroplasty for glenohumeral arthritis with massive rotator cuff tears. Orth clin N Am 1998; 29: 477–489. 10. Norris T R, Green A, McGuigan F x. Late prosthetic arthroplasty for displaced proximal humerus fractures. Clin Orth Rel Res 2001; 382: 206–216. 11. Cofield R H. Should arthrodesis and resection arthroplasty. Instruct Course Lect 1988; 34: 268. 12. Sperling J W, Kozak T K, Hanssen A D, Cofield R H. Infection after shoulder arthroplasty. J Shoulder Elbow Surg 1995; 4: 271–280.
c 2002 Published by Elsevier Science Ltd. doi:10.1054/ycuor.245, available online at http://www.idealibrary.com on
MINI SYMPOSIUM: SHOULDER PROBLEMS
(ii) Shoulder replacementFcurrent problems D. Limb Division of Surgery, Orthopaedic Surgery, Clinical Sciences Building, St James’s University Hospital Trust, Beckett Street, Leeds LS9 7 TF, UK
Summary Shoulder replacementis a successfulprocedure withresults comparable to hip and knee replacement surgery. As surgical technique and implant design evolve, the management of uncomplicated osteoarthritis and rheumatoid disease gives increasingly satisfying results.It has become apparent, however, thatthe best shoulder replacements are those that most accurately reproduce the normal anatomy and mechanics of the shoulder. Implants are quickly evolving to address the ¢ndings of basic science research, sometimes tothe detrimentofthe requirementforlong-termresults. Arguments have been made to alter the design of both humeral and glenoid components to allow more adaptability for the variable anatomy encountered. For fracture surgery, these changes also attempt to facilitate secure reattachment of the rotator cu¡, whilst more radical changes have been tried to substitute the absent rotator cu¡ in cu¡ arthropathy.
c 2002 Published by Elsevier Science Ltd.
INTRODUCTION Shoulder surgery in general, and joint replacement surgery speci¢cally, continues to enjoy a growth period worldwide. In 1990 ^1992, 5000 shoulder replacements were carried out in the USA. In 1999, more than 1000 shoulder replacements were carried out in New York State alone. As the number of procedures performed grows, more information becomes available on the performance of the prostheses. Both technique and implants can evolve more rapidly. Presently, this has created dilemmas in management more e¡ectively than it has resolved contentious issues. This article reviews areas of controversy in shoulder replacement and current thought processes, as evidenced by recent publications in the ¢eld.
THE HUMERAL COMPONENT With regard to the long-term results of shoulder replacement, the humeral component generates least worry. Loosening is unusual and certainly much less frequent than loosening of the glenoid component. Nevertheless, dissatisfaction has arisen because of the failure of earlier designs to accurately reproduce normal anatomy and because reconstruction of the humeral tuberosities around bulky prostheses in trauma cases can be unsatisfactory. Greater tuberosity migration after hemiarthroplasty for
fracture has a major negative in£uence on the functional outcome.
Anatomy It has become a widely upheld principle that successful humeral head replacement should be just that F a prosthesis that replaces the damaged articular surface and reproduces normal anatomy. Theoretically, this restores normal relationships within the joint and the biomechanical environment will be favourable to normal function. Early prostheses o¡ered few alternatives in terms of humeral head size, radius of curvature, o¡set from the long axis of the humeral shaft and head/neck angle. First generation prostheses o¡ered a monobloc humeral head replacement with only few alternative sizes. Although many successful replacements were carried out, di⁄culties were often met in balancing the soft tissues after surgery because the head was too large or small for the joint space available. Over-large components ‘overstu¡ing’ the joint were often sti¡ and painful. Components that were too small were prone to instability. Second-generation components provided modular systems for independent stem and head selection. This allows adequate ¢lling of the humeral shaft and metaphysis (particularly important in uncemented designs) and correct balancing of the rotator cu¡ by selection of a head size (radius of curvature and length) that is right for the joint space.
16
CURRENT ORTHOPAEDICS
Fracture prostheses
Figure 1 By rotating an eccentric ¢xation post the humeral head can be o¡set in relation to the axis of the stem.
Further anatomical studies have drawn attention to the variability that exists in other aspects of humeral anatomy. Thus, third-generation components introduce another level of modularity or selection by o¡ering a variety of neck/shaft angles and the ability to alter the o¡set of the head in relation to the stem.1 This latter variable is achieved usually by providing an eccentric coupling of the head to the stem that can be rotated until the head lies in the desirable position, usually the judged position of the excised natural humeral head, before locking the components together (Fig.1). The development of prostheses has been driven by basic science research and a desire to overcome commonly encountered di⁄culties during joint replacement surgery. Similar research has demonstrated that newer designs are better able to reproduce the 3D position of the centre of rotation, the contact point of the articulation and the radius of curvature of the articular surface.2 As yet, however, clinical studies have failed to demonstrate any e¡ect of these radiologically identi¢ed variables on functional outcome.3 Time will tell if the improved biomechanical environment will have any e¡ect on long-term survivorship of the humeral component. A parallel development has been the concept of humeral head surface replacement without the imposed restrictions of a stem. Stephen Copeland and co-workers discuss this in his article in this issue.
Shoulder replacement as we know it, came into being through e¡orts to replace the humeral head in cases of severe fractures and fracture dislocations of the proximal humerus.4 Shoulder replacement systems have evolved, as described above, and the same modular components have been used for replacement of arthritic and fractured heads.The proximal bulk of the prostheses and its metaphyseal ¢ns (originally used to provide holes for suture attachment of the tuberosities) give good contact between the component and the intact proximal humerus. This allows rotational stability and often it is not necessary to cement humeral components, even perhaps those with no bioactive coating to facilitate ¢xation. In proximal humeral fractures the tuberosities are usually detached. There is no rotational stability of a round stem in a roundish humeral shaft and cement or bioactive coatings are essential.The bulk of the prosthesis proximally now becomes a disadvantage. Although ¢ns allow the provision of suture holes, which are good for initial ¢xation, the aim of fracture surgery is to get the tuberosities to unite to each other and to the humeral shaft around a correctly positioned humeral prosthesis. This is achieved by tension band ¢xation of the tuberosities to each other and to the shaft over bone graft from the excised humeral head. A bulky prosthesis limits the volume of bone graft that can be used. The main problem identi¢ed in tuberosity ¢xation after fracture is secure ¢xation of the greater tuberosity. Insecure ¢xation with a posterior and/or superior drift after surgery is associated with poor function. This has been addressed by a tendency to use tension band sutures more readily and to pass a circumferential suture medial to the shaft and around both greater and lesser tuberosities.5 Many manufacturers are now also o¡ering a ‘fracture kit’, which is a modi¢ed prosthesis allowing more space beneath the head for containment of bone graft. Examples are the De Puy Global Fxs and the Tornier (Forth Medical) Aequaliss fracture prostheses seen in Fig 2(a) and (b). Both are speci¢cally designed now for trauma cases, though as yet no long-term studies are available to demonstrate a de¢nite advantage over standard components with known de¢ciencies. As can be seen, instrumentation systems are becoming more complex to assist in correct component positioning and this in itself may a¡ect the outcomes.
THE GLENOID COMPONENT Neer’s prosthesis employed a keel of polyethylene that could be cemented into a vertical slot cut into the glenoid fossa. This design has withstood the test of time and, decades later, is still in use. It has been recognized, however, that the keel design results in greater contact
SHOULDER REPLACEMENTFCURRENT PROBLEMS
17
Figure 3 Finned (upper) and pegged (lower) glenoid components.
Figure 2
stress than pegged designs, which support the glenoid articular plate at multiple points (Fig. 3).Glenoid components became available that o¡ered multiple pegs for ce-
mentation into the glenoid rather than a single, central column. If there is insu⁄cient bone to allow an adequate hole to be drilled in the glenoid without perforation of the scapular cortex, then the appropriate peg can be removed or shortened before implantation, permitting proper cement containment. Again this seems a neat response to the identi¢ed problem, but may not be an ideal solution in the real world. Unfortunately, when a pegged component does loosen it takes with it bone adjacent to each peg. Since the pegs are multiple, large cavitary defects can result, making revision to a new glenoid component impossible. A biomechanical study investigating multiple possible contributors to glenoid component stability identi¢ed not only that pegs (threaded more so than cylindrical) were better than keels, but that the following design features provided better resistance to loosening in vitro F rough, curved back wall to component, less constrained articulation with humerus and an all polythene rather than metal-mesh-backed construction.6 Another study demonstrated that although a pegged component gave better ¢xation in normal bone, a keeled component was better in rheumatoid bone.7
18
Uncemented glenoid components may avert the problems of lucent lines around keeled or pegged cemented components. Initial ¢xation, for example with screws, is necessary since the small glenoid component cannot otherwise be ¢xed in a stable fashion in the initial phase before osseointegration of its active coating.This in turn demands that the component is metal-backed and therefore bulkier. Anatomic studies of the scapula become important in deciding how to position the initial screws in order to obtain the most secure ¢xation of metal-backing plate to prepared glenoid fossa. It seems that the strong lateral column of the scapula and the base of the coracoid o¡er the best bone for ¢xation. Access may be di⁄cult to place screws into these areas, however, and mechanisms for locking the screws into the metal plate may impose the needs for left/right components, increasing an inventory already burgeoning since the introduction of modular humeral components. As yet, we have no good evidence base on which to base our decisions about glenoid component ¢xation. Unfortunately, we are unlikely to obtain any good evidence in the near future.Taking shoulder replacement as a whole, it has been pointed out that 20 di¡erent arthroplasty systems were available in the UK in 2000. Twelve of these had been introduced in the previous 8 years and only eight had results for perusal in peer review journals (not necessarily long-term results). These eight prostheses accounted for less than 40% of the prostheses being implanted annually at the time of the study.8
INDICATIONS FOR SURGERY It is more or less accepted that shoulder replacement gives excellent pain relief and increased function in rheumatoid disease (see the article by lan Kelly in this issue) and osteoarthrosis. There has been considerable recent interest in the place of shoulder replacement for the more di⁄cult indications, particularly rotator cu¡ arthropathy, fracture malunions and instability arthropathy.
Rotator cu¡ disease Massive tears of the rotator cu¡ that cannot be repaired, such as are found in cases of rotator cu¡ arthropathy, present a particular problem for the shoulder surgeon. By de¢nition reconstruction of the cu¡ is not possible. A shoulder arthrodesis may resolve issues of pain, but at the sacri¢ce of all glenohumeral movement. Any attempt at conventional shoulder replacement will leave the prosthesis just as de¢cient of the centring action of the rotator cu¡ in the glenoid fossa as was the natural humeral head. Thus, attempts to move the shoulder will inevitably be accompanied by anterosuperior migration of the prosthesis. If the coracohumeral arch has been
CURRENT ORTHOPAEDICS
rendered de¢cient by a substantial acromioplasty (often carried out for pain relief or in attempts to repair the cu¡) then actual dislocation can occur, the prosthesis subluxing out to lie under the deltoid with attempted arm use. The translation that occurs across the glenoid in these cu¡-de¢cient shoulders loosens any implanted glenoid component rapidly by edge loading (rocking horse phenomenon). Despite this, hemiarthroplasty does o¡er pain relief and modest gains in motion and function9 and patients are satis¢ed overall with the procedure. Patient selection is paramount, however, and expectations have to be made clear. Hemiarthroplasty cannot be expected to restore pain-free overhead range and strength, though many activities of daily living can be rendered comfortable.These results lag far behind what can be achieved otherwise with shoulder replacement and the search is on for acceptable alternatives. Currently, there seems to be a vogue for ¢xed fulcrum prostheses. These have designed-in stability that maintains the humeral and glenoid components in articulation without the need for an intact rotator cu¡.Clearly, however, the shear forces generated by deltoid will have to be resisted within the system and this usually means at the glenoid component/bone interface, even if the centre of rotation is medialized to minimize this. Good short-term results have been reported at meetings concerning the functional improvements patients experience after such implants are used. By restoring a stable fulcrum for the shoulder muscle couples to act upon high overhead elevation and function can be restored. Only time will tell how the mechanical environment of the glenoid-sided component will fare. It is very unlikely that the results will even approach what can be achieved in osteoarthrosis with an intact cu¡, but if the bene¢ts are 5-years worth of dramatic functional improvement then in this a price worth paying?
Fracture malunion As the supply of shoulder surgeons increases more patients are referred for treatment of late problems. Typical of these is the 3- or- 4 -part fracture that has been treated non-operatively and has resulted in a malunion. If the patient has good range and function there is no need for further action, but what of the patient with painful restriction of function? If shoulder hemiarthroplasty is a satisfactory treatment for the original fracture, is it a viable alternative for managing the late complications? Certainly, shoulder replacement in the presence of malunion is technically more demanding. In the case of surgical neck malunion, it may be impossible to pass a stem down the medullary canal. In these cases, either an osteotomy of the neck or surface-replacement hemiarthroplasty, such as the Copeland prosthesis, can now
SHOULDER REPLACEMENTFCURRENT PROBLEMS
19
be considered. More commonly, the problem is malunion of the tuberosities. In general, the reports on osteotomy of malunited tuberosities followed by reconstruction around a prosthesis have not been encouraging. There is a higher risk of dehiscence of the reattached tuberosities and early surgical complications.The largest case series on the subject10 demonstrated inferior results to hemiarthroplasty for acute fractures in all respects. Nevertheless, patients are overall improved and this is currently the best reconstructive option for these patients provided that they understand the limited goals of the procedure. The real question that needs to be answered here is ‘what patient population should be considered for immediate hemiarthroplasty?’ The best results are obtained if the procedure is carried out as soon as possible after injury, so a policy of ‘see how it goes F we can always do a shoulder replacement later’ is far from satisfactory.
Figure 4 Glenoid augmentation with bone graft.
Instability
INFECTION
Repeated anterior dislocation of the glenohumeral joint enlarges the Hill Sachs lesion on the posterior surface of the humeral head and erodes away the anterior glenoid rim. In chronic cases, a situation is reached where the entire front half of the glenoid is eroded away and the humeral head articulates, via its enlarged Hill Sachs lesion, perched on the glenoid de¢cit in a position of anterior subluxation not amenable to reduction (the glenoid socket is largely missing). This di⁄cult situation can be seen as one of the few indications for arthrodesis, though many patients would prefer to keep their painful false joint than to lose the glenohumeral joint completely (often expecting a sti¡er shoulder than they get after arthrodesis, since the scapulothoracic joint is very mobile). More experience is now published on the management of this, and similar cases of glenoid de¢ciency. Essentially, the bone defect is managed in instability just as it would be for arthropathy of other cases. Minor defects can sometimes be dealt with by reaming down the glenoid to the level of the defect, thus realigning it normally. This only works for shallow defects, however, not the deep de¢ciencies seen in instability. These large defects require structural bone grafts, securely ¢xed with 3.5 mm lag screws. A glenoid fossa can thus be recreated onto which a component can be cemented, so careful planning of screw positioning is required (Fig. 4). Hemiarthroplasty is not precluded but, needless to say, careful attention has to be paid to soft tissue balance to reduce the incidence of recurrence. Only small series of cases have been reported for this rare operation, and even in the best of hands a 10% redislocation rate is expected.
As the number of shoulder joints replaced increases there is an inevitable increase in the volume of revision surgery for infection, just as has been witnessed over the past three decades in hip and knee surgery.The infection rate after shoulder arthroplasty is approximately 0.5%.11 Since the rate of shoulder replacement is much lower than that of hip and knee replacement, experience of the operation and its outcomes have been slower to accumulate. The approach to the infected prosthesis has been developed from lessons learned in lower limb revision surgery. An outline approach is to consider early aggressive debridement for ‘early’ infections and to follow this up with 6 weeks of focussed antibiotic treatment. Cases presenting later can be investigated to identify the organism by biopsy (? Needle or open) and managed by prosthetic removal either as de¢nitive treatment or followed by immediate or delayed reimplantation. What limited experience there is in respect of the shoulder suggests that patients fare better symptomatically if prosthesis can be successfully reimplanted and retained. The reinfection rate and risk of further surgery are high, however.12 Shoulder arthrodesis after removal of a shoulder prosthesis is very much less reliable than when carried out with good bone stock, such as might exist in a case of brachial plexus injury. The results of arthrodesis should not be confused when counselling patients beforehand. It is recommended that if arthrodesis is contemplated as a treatment for infected prosthesis, then the components are removed and antibiotic treatment continued for 6 weeks to reduce the risk of reinfection at arthrodesis.This rather goes against the grain of using stability as
20
a weapon against bacterial infection and as yet there is no strong evidence to back this recommendation.
CONCLUSION The challenges facing shoulder replacement are being addressed by modi¢cations of prosthetic design and surgical technique. Care needs to be taken to ensure that these‘improvements’ are not simply short-term solutions to perceived problems that in the long term detract from the improving results we have enjoyed over the past three decades. A foundation of reliable prostheses is available and newer designs may be useful for the speci¢c conditions that suggest scope for improvement, for example, rotator cu¡ arthropathy, fracture surgery, instability and revision surgery.
REFERENCES 1. Walch G, Boileau P. Prosthetic adaptability: a new concept for shoulder arthroplasty. J Shoulder Elbow Surg 1999; 8: 443–451. 2. Ehnes D L, Stone J J, Cofield R H. Analysis of the shoulder implant. Biomed Sci Instrum 2000; 36: 129–134. 3. Gartsman G M, Hasan S S. What’s new in shoulder surgery. J Bone Jt Surg Am Vol 2001; 83A: 145–151.
CURRENT ORTHOPAEDICS
4. Neer C S. 2nd Displaced proximal humeral fractures. II Treatment of three-part and four-part displacement. J Bone Jt Surg Am Vol 1970; 52:1090–103. 5. Bioleau P. Indications and important features of primary prosthetic replacement in acute fractures. Presented at F European Shoulder and Elbow Society Annual Meeting, The Hague. September 1999. 6. Anglin C, Wyss U P, Nyffeler R W, Gerber C. Loosening performance of cemented glenoid prostheses design pairs. Clin Biomech 2001; 16: 144–150. 7. LaCroix D, Murphy L A, Prendergast P J. Three-dimensional finite element analysis of glenoid replacement prostheses: a comparison of keeled and pegged anchorage systems. J Biomech Eng 2000; 122: 430–436. 8. Mackay D C, Hudson B, Williams J P. Which primary shoulder and elbow replacement? A review of the results of prosthesis available in the UK. Ann R Coll Surg Eng 2001; 83: 258–265. 9. DiGiovanni J, Marra G, Park J K, Bigliani L U. Hemiarthroplasty for glenohumeral arthritis with massive rotator cuff tears. Orth clin N Am 1998; 29: 477–489. 10. Norris T R, Green A, McGuigan F x. Late prosthetic arthroplasty for displaced proximal humerus fractures. Clin Orth Rel Res 2001; 382: 206–216. 11. Cofield R H. Should arthrodesis and resection arthroplasty. Instruct Course Lect 1988; 34: 268. 12. Sperling J W, Kozak T K, Hanssen A D, Cofield R H. Infection after shoulder arthroplasty. J Shoulder Elbow Surg 1995; 4: 271–280.