- Email: [email protected]
Cementless Prosthetic Fixation: When Less Is More—In the Affirmative
Cementless Prosthetic Fixation: When Less Is More—In the Affirmative Shadley C. Schiffern, MD, Donnis K. Harrison, MD, Wayne Z. Burkhead, Jr, MD, and Sumant G. Krishnan, MD Shoulder arthroplasty is a reliable treatment for pain relief and restoration of function in patients with degenerative conditions of the glenohumeral joint. The designs of shoulder prostheses has evolved since Neer first introduced his original press-fit humeral hemiarthroplasty component back in 1951. This was followed by the development of a glenoid prosthesis for resurfacing of arthritic glenoid surfaces. Use of cement for fixation of both humeral and glenoid components became the gold standard for many years in the treatment of glenohumeral degenerative conditions, such as osteoarthritis and rheumatoid arthritis. The trend toward performing shoulder arthroplasty in younger, more active patients has led to a transition back to cementless fixation to preserve bone stock and make revision surgery easier. In addition, the concept of cementless surface replacement has also been described for treatment of arthritic conditions in younger patients. Results have been equivocal with uncemented versus cemented prostheses used on the humeral side. However, there have been problems with metal backed, press-fit glenoid fixation. At the current time, cemented all-polyethylene glenoid components remain the choice for most shoulder surgeons. As the technology improves, the use of press-fit, bone in-growth designs may become a more reliable alternative. Semin Arthro 16:257-262 © 2005 Elsevier Inc. All rights reserved. KEYWORDS arthroplasty, total shoulder, cementless hemiarthroplasty
S
houlder arthroplasty has been evolving since its first reported use in 1893 by the French surgeon Pean for the treatment of tuberculous arthritis.1,2 Neer first reported on shoulder replacement for fracture-dislocation of the humeral head in 1955.3 His original hemiarthroplasty design was made of cast cobalt chrome alloy and was designed for pressfit insertion. This prosthesis was used successfully without problems with loosening of the humeral component in the early series. Given the early success, Neer expanded the indications for shoulder arthroplasty to include degenerative conditions such as osteoarthritis, rheumatoid arthritis, and osteonecrosis.4 In treating these conditions, the importance of an arthritic glenoid on patient symptoms was realized. This led to the design of the first total shoulder arthroplasty systems.5 At this same time, the use of polymethylmethacrylate (PMMA) cement for fixation of hip arthroplasty stems was gaining popularity, based on the early success of Charn-
ley. The Neer II total shoulder system introduced a cemented all-polyethylene glenoid component. In addition, the humeral stems were modified for insertion with cement. Since these early years, many shoulder arthroplasty designs have been developed. Difficulties with radiolucent lines around cemented glenoid components led to an interest in press-fit and tissue in-growth fixation methods. On the humeral side, loosening has not been a significant problem. However, as the trend toward arthroplasty in younger patients has occurred, a swing back to press-fit fixation with humeral components has also followed. The aim of this manuscript is to discuss the pros and cons of cementless fixation in shoulder arthroplasty. We will review the state of the art of cementless fixation, as well as offer guidelines for implant selection and fixation method used by orthopedic surgeons today.
Humeral Component Shoulder Service, W.B. Carrell Memorial Clinic, Dallas, TX. Address reprint requests to Wayne Z. Burkhead, Jr, MD, Shoulder Service, W.B. Carrell Memorial Clinic, 9301 N. Central Expressway, Suite 400, Dallas, TX 75231. E-mail:[email protected]
1045-4527/05/$-see front matter © 2005 Elsevier Inc. All rights reserved. doi:10.1053/j.sart.2005.10.009
The original humeral components were designed for use in hemiarthoplasty for treatment of proximal humeral fractures.3 These early components were press-fit designs, with 257
258
S.C. Schiffern et al. (Fig. 2) may allow for improved tuberosity fixation, with or without bone grafting (Fig. 3). Results with modern cementless humeral prostheses have been equivalent to cemented components, with a low incidence of humeral loosening in outcome studies.8,9 SanchezSotolo and colleagues followed 72 press-fit Neer II humeral components for a mean 4.1 years. They found a high percentage (55.6%, 40/72) to be at risk for loosening, based on presence of radiolucent lines or evidence of subsidence.10 Since that time, the development of in-growth technology has improved the stability of press-fit stem fixation. At this time, cementless humeral stems continue to evolve in their design. Options include different stem shapes: round, square, fluted; different types of in-growth surfaces: porous coating or fiber mesh surface; and extent of in-growth capa-
Figure 1 Original Neer humeral prosthesis, designed for press-fit fixation.
large flutes to interface with the diaphyseal bone, and were designed to sit flush on the metaphyseal bone (Fig. 1). These early humeral stems achieved excellent early fixation and were durable, with very few reports of loosening. As the success of cement fixation with PMMA in total hip arthroplasty was gaining popularity, humeral component designs were modified for use with cement in the 1970s. Cemented humeral stem fixation continued to be successful, with long-term results showing very infrequent loosening or failures. Torchia and co-workers reviewed results of total shoulder arthroplasty with the Neer prosthesis from 1975 to 1981 and found a higher incidence of loosening of stems that were press-fit, compared with cemented stems.6 Cemented humeral stems became the gold standard in shoulder replacement, and are still indicated today for total shoulder arthroplasty in older patients and osteoporotic bone. Third generation cementation techniques have continued to improve the quality of cement fixation in with current implants. However, the use of cement fixation is not without its downsides. As the number of shoulder replacements performed in younger, active patient’s increases, the number of revision surgeries will inevitably increase. Revision of cemented shoulder arthroplasty is a much more technically difficult procedure.7 Removal of cemented humeral stems risk the destruction of significant proximal metaphyseal bone, making salvage of the tuberosity, and rotator cuff integrity, difficult. Press-fit humeral components with designs to allow biologic in-growth may be a better option for initial fixation in these younger patients with good bone quality. Another reason for cementless fixation is in reconstruction after comminuted proximal humeral fractures. Among the goals of proximal humeral arthroplasty for fractures is restoration of the tuberosity fragments and creation of a favorable milieu for healing. Placement of PMMA cement around the tuberosity fragments may prevent biologic healing and lead to failure. Use of streamlined, fracture-specific humeral stems
Figure 2 Aequalis-Fracture shoulder prosthesis (Tornier, Inc., Grenoble, France). Note open neck for placement of autogenous bone graft from the humeral head. Also note low profile design to allow for anatomic reconstruction of tuberosity fragments. (Color version of figure is available online.)
Cementless prosthetic fixation: in the affirmative
Figure 3 Intraoperative photograph of Aequalis-Fracture prosthesis with autogenous bone graft in position in open neck slot. (Color version of figure is available online.)
bilities: fully coated or proximally coated stems. The use of porous coating only in the proximal metaphyseal region provides adequate fixation, while preventing significant bone loss from stress shielding, seen in fully coated stem designs. When used with an implanted polyethylene glenoid component, it is important to use circumferential porous coating, preventing progression of wear debris along the prosthesis and limiting osteolysis. Additional techniques such as use of impaction bone grafting can augment initial stability of pressfit components.11 As the indications for use of press-fit humeral component increase, we will undoubtedly see further improvements in the cementless designs and technique.
259
Figure 4 Axial CT image showing significant bone loss and lucency around a cemented glenoid component.
metal backed polyethylene glenoids. These components rely on bony in-growth for stability. Regardless of the type of porous coating or mesh backing available for in-growth, the initial implant fixation must be solid enough to allow time for in-growth to occur. In addition, the strength of initial fixation must be adequate to allow early passive motion for functional rehabilitation after shoulder arthroplasty. With the introduction of metal backed polyethylene, there were some additional complications reported, including accelerated polyethylene wear, dissociation of the polyethylene from the metal
Glenoid Components Loosening of the glenoid component continues to be the major factor affecting the long-term survivorship in total shoulder arthroplasty. There are multiple factors associated with glenoid component stability, including: glenoid vault preparation, quality of glenoid bone stock for implantation, adequate soft-tissue balancing, and polyethylene wear debris.12 However, the design and fixation method of the glenoid component may be the most important factor. Neer’s original glenoid design was an all-polyethylene, keeled component fixed with cement.5 The early clinical results were good, however, several series reported an alarmingly high incidence of radiolucent lines surrounding the cement prosthesis interface, ranging from 30% to 90%.8,13,14 Recent study by Yian and co-workers reported use of CT imaging to evaluate glenoid lucencies. They concluded that it may be a more sensitive tool for assessing glenoid radiolucency (Figs. 4 and 5).15 Although there is concern about the correlation between these lucent lines and clinical glenoid loosening, the-long term consequences are not known at this time.7,13,16,17 Pressfit and bone in-growth glenoid components were designed to avoid these difficulties. Among the first cementless glenoid components used were
Figure 5 Sagittal CT image showing significant bone loss and lucency around a cemented glenoid component.
260
Figure 6 Fluted, pegged all-polyethylene glenoid component, designed for cementless application.
tray, subsequent metal on metal wear, baseplate fracture, or screw breakage.18 The accelerated wear is proposed to secondary to backside wear, similar to the tibial component in total knee arthroplasty. Improvements in the locking mechanism in these implants and better fixation methods may be able to prevent these complications. Another option for cementless fixation of the glenoid component is the use of an all-polyethylene component modified for use without cement. Wirth and co-workers studied a pegged glenoid component with additional flutes on the central peg to enhance bony in-growth and stability (Fig. 6). They compared this design to a standard keeled glenoid in a dog model and noted superior stability and bony integration in the fluted peg component.19 They have subsequently shown acceptable results in human subjects with use of the fluted, pegged glenoid component, mated with a traditional porous coated humeral component.20 There are limited studies documenting the outcomes after cementless glenoid fixation. Cofield reviewed his experience with uncemented glenoid components between 1989 and 1993, with 180 in-growth glenoids implanted, with variable follow-up. The functional results were very similar to standard cemented glenoid components. He reported a notable decrease in the appearance of radiolucent lines around the press-fit components, with only 6 of 180 having lucency between the implant and bone. Only one component had loosened at the time of his report.7 Boileau and co-workers randomized 40 shoulders with primary osteoarthritis to receive either a cemented, all-polyethylene glenoid component or a cementless, metal backed component at the time of total shoulder arthroplasty. They reported a higher incidence of radiolucent lines in the polyethylene group (85% versus 25%, P ⬍ 0.01). How-
S.C. Schiffern et al. ever, no significant correlation between radiolucent lines and functional outcomes with cemented, polyethylene components were observed. By contrast, radiolucent lines seen in metal backed components were progressive, with four cases (20%) having significant loosening.13 Another recent study by Martin and co-workers reviewed 147 consecutive total shoulder arthroplasties with use of an uncemented glenoid component fixed with screws between 1988 and 1996. There were 140 shoulders available for follow up at mean of 7.5 years. Radiolucency around the glenoid component was present in 53 of the 140 shoulders. The mean ASES scores improved from 15.6 to 75.8 at the time of follow up. However, 15 (11%) of the glenoids failed clinically, and 10 of them had radiographic signs of failure. Eleven other shoulders had signs of loosening on radiographs, but no symptoms at the time of publication.21 At the International Symposium on Shoulder Arthroplasty in 2005, Hertel reported better results, with no difference between cemented and cementless glenoid component loosening rates or functional results when treating proximal humerus fractures. The increased use of reverse ball in socket shoulder arthroplasty for treatment of rotator cuff tear arthropathy and in revision surgery has expanded the indication for press-fit fixation of the glenoid. The glenoid baseplate used in reverse shoulder arthroplasty is subjected to significant shear forces and requires secure initial fixation. These baseplate designs utilize a combination of in-growth technology as well as com-
Figure 7 Postoperative AP radiograph showing a reverse ball-andsocket prosthesis (Aequalis-Reversed shoulder prosthesis, Tornier, Inc.). Note central peg that has porous coating, and four screws providing initial stability of the glenoid baseplate.
Cementless prosthetic fixation: in the affirmative
261
pression screw fixation to ensure primary stability (Fig. 7).22-24
Cementless Surface Replacement Arthroplasty Another option available for surgeons in the treatment of glenohumeral arthritis in younger patients is the concept of surface replacement with minimal bone resection. Levy and Copeland initially reported their results using a cementless surface replacement hemiarthroplasty for arthritic conditions including osteoarthritis, rheumatoid arthritis, and avascular necrosis in 2001 (Figs. 8 and 9).25 They have also developed a cementless glenoid component, to enable total shoulder replacement with this system. The outcomes after cementless surface replacement for osteoarthritis were reported in 2004.26 They performed 79 surface replacement procedures (42 total shoulder replacements, 37 hemiarthroplasties) for osteoarthritis between 1986 and 1997. The mean follow up was 7.6 years for total shoulders, and 4.4 years for hemiarthroplasty, respectively. Age-adjusted Constant scores improved from mean preoperation 33.8% (20 points) to 94% (61.9 points) for total shoulder replacement, and from 40.0% (25.3 points) to 91% (58.1 points) for hemiarthroplasty. Active elevation improved by a mean of 59.9 degrees to a mean of 128 degrees for total shoulder replacement and to a mean of 124 degrees for hemiarthroplasty. Radiographically, one humeral implant and three glenoid implants had evidence of loosening. Four revisions were performed in the total shoulder replacement group. No revision surgery was needed in the hemiarthroplasty group. The authors concluded that surface replacement were at least comparable to stemmed prostheses for treatment of glenohumeral osteoarthritis. The benefits of surface replacement arthroplasty are preservation of bone stock, with minimal resection of proximal humerus. This makes revision surgery easier if necessary in the future. The cementless surface replacement humeral component has shown excellent stability, without problems
Figure 9 Postoperative AP radiograph of the above patient after treatment with cementless surface replacement hemiarthroplasty (Copeland CSRA, Biomet, Inc., Warsaw, IN).
with loosening. However, there have been some difficulties with glenoid component failure. This may be related to difficulties with glenoid exposure, because of the smaller resection of proximal humeral bone, leading to problems with glenoid preparation. At this time, we would consider the use of surface replacement arthroplasty for limited indications, such as younger patients with degenerative changes limited to the humeral side.
Conclusions The designs of prostheses for shoulder replacement have come a long way since Neer first introduced his original press-fit humeral hemiarthroplasty component back in 1951. Use of PMMA cement for fixation of both humeral and glenoid components became the gold standard for many years in the treatment of glenohumeral degenerative conditions, such as osteoarthritis and rheumatoid arthritis. The trend toward performing shoulder arthroplasty in younger, more active patients has led to a transition back to cementless fixation to preserve bone stock and make revision surgery easier. Results have been equivocal when used on the humeral side. However, there have been problems with metal backed, press-fit glenoid fixation. At the current time, cemented all-polyethylene glenoid components remain the choice for most shoulder surgeons. As the technology improves, the use of pressfit, bone in-growth designs may become a more reliable alternative.
References
Figure 8 Preoperative AP radiograph of a patient with severe avascular necrosis of the proximal humerus.
1. Lugli T: Artificial shoulder joint by Pean (1893). The facts of an exceptional intervention and the prosthetic method. Clin Orthop 133:215218, 1978 2. Matsen FA III, Rockwood CA, Wirth MA, et al: Glenohumeral arthritis and its management, in Rockwood CA, Matsen FA III, Wirth MA, et al (eds): The Shoulder, vol 2 (ed 3). Philadelphia, PA, Saunders, 2004, pp 879-1000 3. Neer CS II: Articular replacement for the humeral head. J Bone Joint Surg Am 37:215-228, 1955
S.C. Schiffern et al.
262 4. Neer CS II: Replacement arthroplasty for glenohumeral osteoarthritis. J Bone Joint Surg Am 56:1-13, 1974 5. Neer CS II, Watson KC, Stanton FJ: Recent experience in total shoulder replacement. J Bone Joint Surg Am 64:319-337, 1982 6. Torchia ME, Cofield RH, Settergren CR: Total shoulder arthroplasty with Neer prosthesis: Long term results. J Shoulder Elbow Surg 6:495505,1997 7. Cofield RH: Uncemented total shoulder arthroplasty: A review. Clin Orthop 307:86-93, 1994 8. Bauer GS, Murthi AM, Bigliani LU: Fixation for the millennium: The shoulder. J Arthroplasty 17(suppl 1):9-10, 2002 9. Matsen FA III, Iannotti JP, Rockwood CA Jr: Humeral fixation by pressfitting of a tapered metaphyseal stem: A prospective radiographic study. J Bone Joint Surg Am 85:304-308, 2003 10. Sanchez-Sotelo J, Wright TW, O’Driscoll SW, et al: Radiographic assessment of uncemented humeral components in total shoulder arthroplasty. J Arthroplasty 16:180-187, 2001 11. Hacker SA, Boorman RS, Lippitt SB, et al: Impaction grafting improves the fit of uncemented humeral arthroplasty. J Shoulder Elbow Surg 12:431-435, 2003 12. Williams GR, Abboud JA: Total shoulder arthroplasty: Glenoid component design. J Shoulder Elbow Surg 14(suppl S):122S-128S, 2005 13. Boileau P, Avidor C, Krishnan SG, et al: Cemented polyethylene versus uncemented metal-backed glenoid components in total shoulder arthroplasty: A prospective, double-blinded, randomized study. J Shoulder Elbow Surg 11:351-359, 2002 14. Wirth MA, Rockwood CA Jr: Complications of shoulder arthroplasty. Clin Orthop 307:47-69, 1994 15. Yian EH, Werner CML, Nyffeler RW, et al: Radiographic and computed tomography analysis of cemented pegged polyethylene glenoid components in total shoulder replacement. J Bone Joint Surg Am 87:19281936, 2005 16. Lazarus MD, Jensen KL, Southworth C, et al: The radiographic evalu-
17.
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ation of keeled and pegged glenoid component insertion. J Bone Joint Surg Am 84:1174-1182, 2002 Mileti J, Boardman ND 3rd, Sperling JW et al: Radiographic analysis of polyethylene glenoid components using modern cementing techniques. J Shoulder Elbow Surg 13:492-498, 2004 Cofield RH, Daly PJ: Total shoulder arthroplasty with a tissue-ingrowth glenoid component. J Shoulder Elbow Surg 1:77-85, 1992 Wirth MA, Korvick DL, Basamania CJ, et al: Radiologic, mechanical, and histologic evaluation of 2 glenoid prosthesis designs in a canine model. J Shoulder Elbow Surg 10:140-148, 2001 Wirth MA, et al: Radiographic evaluation of an innovative pegged glenoid component. Presented at the American Shoulder and Elbow Surgeons meeting, Washington, DC, February 26, 2005 Martin SD, Zurakowski D, Thornhill TS: Uncemented glenoid component in total shoulder arthroplasty: Survivorship and outcomes. J Bone Joint Surg Am 87:1284-1292, 2005 Boileau P, Watkinson DJ, Hatzidakis AM, et al: Grammont reverse prosthesis: Design, rationale, and biomechanics. J Shoulder Elbow Surg 14(suppl S):147S-161S, 2005 Frankle M, Siegal S, Pupello D, et al: The reverse shoulder prosthesis for glenohumeral arthritis associated with severe rotator cuff deficiency: A minimum two-year follow up study of sixty patients. J Bone Joint Surg Am 87:1697-1705, 2005 Werner CML, Steinmann PA, Gilbart M, et al: Treatment of painful pseudoparesis due to irreparable rotator cuff dysfunction with the Delta III reverse-ball-and-socket total shoulder prosthesis. J Bone Joint Surg Am 87:1476-1486, 2005 Levy O, Copeland SA: Cementless surface replacement of the shoulder: 5- to 10-year results with the Copeland mark-2 prosthesis. J Bone Joint Surg Br 83:213-221, 2001 Levy O, Copeland SA: Cementless surface replacement arthroplasty (Copeland CSRA) for osteoarthritis of the shoulder. J Shoulder Elbow Surg 13:266-271, 2004
S
houlder arthroplasty has been evolving since its first reported use in 1893 by the French surgeon Pean for the treatment of tuberculous arthritis.1,2 Neer first reported on shoulder replacement for fracture-dislocation of the humeral head in 1955.3 His original hemiarthroplasty design was made of cast cobalt chrome alloy and was designed for pressfit insertion. This prosthesis was used successfully without problems with loosening of the humeral component in the early series. Given the early success, Neer expanded the indications for shoulder arthroplasty to include degenerative conditions such as osteoarthritis, rheumatoid arthritis, and osteonecrosis.4 In treating these conditions, the importance of an arthritic glenoid on patient symptoms was realized. This led to the design of the first total shoulder arthroplasty systems.5 At this same time, the use of polymethylmethacrylate (PMMA) cement for fixation of hip arthroplasty stems was gaining popularity, based on the early success of Charn-
ley. The Neer II total shoulder system introduced a cemented all-polyethylene glenoid component. In addition, the humeral stems were modified for insertion with cement. Since these early years, many shoulder arthroplasty designs have been developed. Difficulties with radiolucent lines around cemented glenoid components led to an interest in press-fit and tissue in-growth fixation methods. On the humeral side, loosening has not been a significant problem. However, as the trend toward arthroplasty in younger patients has occurred, a swing back to press-fit fixation with humeral components has also followed. The aim of this manuscript is to discuss the pros and cons of cementless fixation in shoulder arthroplasty. We will review the state of the art of cementless fixation, as well as offer guidelines for implant selection and fixation method used by orthopedic surgeons today.
Humeral Component Shoulder Service, W.B. Carrell Memorial Clinic, Dallas, TX. Address reprint requests to Wayne Z. Burkhead, Jr, MD, Shoulder Service, W.B. Carrell Memorial Clinic, 9301 N. Central Expressway, Suite 400, Dallas, TX 75231. E-mail:[email protected]
1045-4527/05/$-see front matter © 2005 Elsevier Inc. All rights reserved. doi:10.1053/j.sart.2005.10.009
The original humeral components were designed for use in hemiarthoplasty for treatment of proximal humeral fractures.3 These early components were press-fit designs, with 257
258
S.C. Schiffern et al. (Fig. 2) may allow for improved tuberosity fixation, with or without bone grafting (Fig. 3). Results with modern cementless humeral prostheses have been equivalent to cemented components, with a low incidence of humeral loosening in outcome studies.8,9 SanchezSotolo and colleagues followed 72 press-fit Neer II humeral components for a mean 4.1 years. They found a high percentage (55.6%, 40/72) to be at risk for loosening, based on presence of radiolucent lines or evidence of subsidence.10 Since that time, the development of in-growth technology has improved the stability of press-fit stem fixation. At this time, cementless humeral stems continue to evolve in their design. Options include different stem shapes: round, square, fluted; different types of in-growth surfaces: porous coating or fiber mesh surface; and extent of in-growth capa-
Figure 1 Original Neer humeral prosthesis, designed for press-fit fixation.
large flutes to interface with the diaphyseal bone, and were designed to sit flush on the metaphyseal bone (Fig. 1). These early humeral stems achieved excellent early fixation and were durable, with very few reports of loosening. As the success of cement fixation with PMMA in total hip arthroplasty was gaining popularity, humeral component designs were modified for use with cement in the 1970s. Cemented humeral stem fixation continued to be successful, with long-term results showing very infrequent loosening or failures. Torchia and co-workers reviewed results of total shoulder arthroplasty with the Neer prosthesis from 1975 to 1981 and found a higher incidence of loosening of stems that were press-fit, compared with cemented stems.6 Cemented humeral stems became the gold standard in shoulder replacement, and are still indicated today for total shoulder arthroplasty in older patients and osteoporotic bone. Third generation cementation techniques have continued to improve the quality of cement fixation in with current implants. However, the use of cement fixation is not without its downsides. As the number of shoulder replacements performed in younger, active patient’s increases, the number of revision surgeries will inevitably increase. Revision of cemented shoulder arthroplasty is a much more technically difficult procedure.7 Removal of cemented humeral stems risk the destruction of significant proximal metaphyseal bone, making salvage of the tuberosity, and rotator cuff integrity, difficult. Press-fit humeral components with designs to allow biologic in-growth may be a better option for initial fixation in these younger patients with good bone quality. Another reason for cementless fixation is in reconstruction after comminuted proximal humeral fractures. Among the goals of proximal humeral arthroplasty for fractures is restoration of the tuberosity fragments and creation of a favorable milieu for healing. Placement of PMMA cement around the tuberosity fragments may prevent biologic healing and lead to failure. Use of streamlined, fracture-specific humeral stems
Figure 2 Aequalis-Fracture shoulder prosthesis (Tornier, Inc., Grenoble, France). Note open neck for placement of autogenous bone graft from the humeral head. Also note low profile design to allow for anatomic reconstruction of tuberosity fragments. (Color version of figure is available online.)
Cementless prosthetic fixation: in the affirmative
Figure 3 Intraoperative photograph of Aequalis-Fracture prosthesis with autogenous bone graft in position in open neck slot. (Color version of figure is available online.)
bilities: fully coated or proximally coated stems. The use of porous coating only in the proximal metaphyseal region provides adequate fixation, while preventing significant bone loss from stress shielding, seen in fully coated stem designs. When used with an implanted polyethylene glenoid component, it is important to use circumferential porous coating, preventing progression of wear debris along the prosthesis and limiting osteolysis. Additional techniques such as use of impaction bone grafting can augment initial stability of pressfit components.11 As the indications for use of press-fit humeral component increase, we will undoubtedly see further improvements in the cementless designs and technique.
259
Figure 4 Axial CT image showing significant bone loss and lucency around a cemented glenoid component.
metal backed polyethylene glenoids. These components rely on bony in-growth for stability. Regardless of the type of porous coating or mesh backing available for in-growth, the initial implant fixation must be solid enough to allow time for in-growth to occur. In addition, the strength of initial fixation must be adequate to allow early passive motion for functional rehabilitation after shoulder arthroplasty. With the introduction of metal backed polyethylene, there were some additional complications reported, including accelerated polyethylene wear, dissociation of the polyethylene from the metal
Glenoid Components Loosening of the glenoid component continues to be the major factor affecting the long-term survivorship in total shoulder arthroplasty. There are multiple factors associated with glenoid component stability, including: glenoid vault preparation, quality of glenoid bone stock for implantation, adequate soft-tissue balancing, and polyethylene wear debris.12 However, the design and fixation method of the glenoid component may be the most important factor. Neer’s original glenoid design was an all-polyethylene, keeled component fixed with cement.5 The early clinical results were good, however, several series reported an alarmingly high incidence of radiolucent lines surrounding the cement prosthesis interface, ranging from 30% to 90%.8,13,14 Recent study by Yian and co-workers reported use of CT imaging to evaluate glenoid lucencies. They concluded that it may be a more sensitive tool for assessing glenoid radiolucency (Figs. 4 and 5).15 Although there is concern about the correlation between these lucent lines and clinical glenoid loosening, the-long term consequences are not known at this time.7,13,16,17 Pressfit and bone in-growth glenoid components were designed to avoid these difficulties. Among the first cementless glenoid components used were
Figure 5 Sagittal CT image showing significant bone loss and lucency around a cemented glenoid component.
260
Figure 6 Fluted, pegged all-polyethylene glenoid component, designed for cementless application.
tray, subsequent metal on metal wear, baseplate fracture, or screw breakage.18 The accelerated wear is proposed to secondary to backside wear, similar to the tibial component in total knee arthroplasty. Improvements in the locking mechanism in these implants and better fixation methods may be able to prevent these complications. Another option for cementless fixation of the glenoid component is the use of an all-polyethylene component modified for use without cement. Wirth and co-workers studied a pegged glenoid component with additional flutes on the central peg to enhance bony in-growth and stability (Fig. 6). They compared this design to a standard keeled glenoid in a dog model and noted superior stability and bony integration in the fluted peg component.19 They have subsequently shown acceptable results in human subjects with use of the fluted, pegged glenoid component, mated with a traditional porous coated humeral component.20 There are limited studies documenting the outcomes after cementless glenoid fixation. Cofield reviewed his experience with uncemented glenoid components between 1989 and 1993, with 180 in-growth glenoids implanted, with variable follow-up. The functional results were very similar to standard cemented glenoid components. He reported a notable decrease in the appearance of radiolucent lines around the press-fit components, with only 6 of 180 having lucency between the implant and bone. Only one component had loosened at the time of his report.7 Boileau and co-workers randomized 40 shoulders with primary osteoarthritis to receive either a cemented, all-polyethylene glenoid component or a cementless, metal backed component at the time of total shoulder arthroplasty. They reported a higher incidence of radiolucent lines in the polyethylene group (85% versus 25%, P ⬍ 0.01). How-
S.C. Schiffern et al. ever, no significant correlation between radiolucent lines and functional outcomes with cemented, polyethylene components were observed. By contrast, radiolucent lines seen in metal backed components were progressive, with four cases (20%) having significant loosening.13 Another recent study by Martin and co-workers reviewed 147 consecutive total shoulder arthroplasties with use of an uncemented glenoid component fixed with screws between 1988 and 1996. There were 140 shoulders available for follow up at mean of 7.5 years. Radiolucency around the glenoid component was present in 53 of the 140 shoulders. The mean ASES scores improved from 15.6 to 75.8 at the time of follow up. However, 15 (11%) of the glenoids failed clinically, and 10 of them had radiographic signs of failure. Eleven other shoulders had signs of loosening on radiographs, but no symptoms at the time of publication.21 At the International Symposium on Shoulder Arthroplasty in 2005, Hertel reported better results, with no difference between cemented and cementless glenoid component loosening rates or functional results when treating proximal humerus fractures. The increased use of reverse ball in socket shoulder arthroplasty for treatment of rotator cuff tear arthropathy and in revision surgery has expanded the indication for press-fit fixation of the glenoid. The glenoid baseplate used in reverse shoulder arthroplasty is subjected to significant shear forces and requires secure initial fixation. These baseplate designs utilize a combination of in-growth technology as well as com-
Figure 7 Postoperative AP radiograph showing a reverse ball-andsocket prosthesis (Aequalis-Reversed shoulder prosthesis, Tornier, Inc.). Note central peg that has porous coating, and four screws providing initial stability of the glenoid baseplate.
Cementless prosthetic fixation: in the affirmative
261
pression screw fixation to ensure primary stability (Fig. 7).22-24
Cementless Surface Replacement Arthroplasty Another option available for surgeons in the treatment of glenohumeral arthritis in younger patients is the concept of surface replacement with minimal bone resection. Levy and Copeland initially reported their results using a cementless surface replacement hemiarthroplasty for arthritic conditions including osteoarthritis, rheumatoid arthritis, and avascular necrosis in 2001 (Figs. 8 and 9).25 They have also developed a cementless glenoid component, to enable total shoulder replacement with this system. The outcomes after cementless surface replacement for osteoarthritis were reported in 2004.26 They performed 79 surface replacement procedures (42 total shoulder replacements, 37 hemiarthroplasties) for osteoarthritis between 1986 and 1997. The mean follow up was 7.6 years for total shoulders, and 4.4 years for hemiarthroplasty, respectively. Age-adjusted Constant scores improved from mean preoperation 33.8% (20 points) to 94% (61.9 points) for total shoulder replacement, and from 40.0% (25.3 points) to 91% (58.1 points) for hemiarthroplasty. Active elevation improved by a mean of 59.9 degrees to a mean of 128 degrees for total shoulder replacement and to a mean of 124 degrees for hemiarthroplasty. Radiographically, one humeral implant and three glenoid implants had evidence of loosening. Four revisions were performed in the total shoulder replacement group. No revision surgery was needed in the hemiarthroplasty group. The authors concluded that surface replacement were at least comparable to stemmed prostheses for treatment of glenohumeral osteoarthritis. The benefits of surface replacement arthroplasty are preservation of bone stock, with minimal resection of proximal humerus. This makes revision surgery easier if necessary in the future. The cementless surface replacement humeral component has shown excellent stability, without problems
Figure 9 Postoperative AP radiograph of the above patient after treatment with cementless surface replacement hemiarthroplasty (Copeland CSRA, Biomet, Inc., Warsaw, IN).
with loosening. However, there have been some difficulties with glenoid component failure. This may be related to difficulties with glenoid exposure, because of the smaller resection of proximal humeral bone, leading to problems with glenoid preparation. At this time, we would consider the use of surface replacement arthroplasty for limited indications, such as younger patients with degenerative changes limited to the humeral side.
Conclusions The designs of prostheses for shoulder replacement have come a long way since Neer first introduced his original press-fit humeral hemiarthroplasty component back in 1951. Use of PMMA cement for fixation of both humeral and glenoid components became the gold standard for many years in the treatment of glenohumeral degenerative conditions, such as osteoarthritis and rheumatoid arthritis. The trend toward performing shoulder arthroplasty in younger, more active patients has led to a transition back to cementless fixation to preserve bone stock and make revision surgery easier. Results have been equivocal when used on the humeral side. However, there have been problems with metal backed, press-fit glenoid fixation. At the current time, cemented all-polyethylene glenoid components remain the choice for most shoulder surgeons. As the technology improves, the use of pressfit, bone in-growth designs may become a more reliable alternative.
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Figure 8 Preoperative AP radiograph of a patient with severe avascular necrosis of the proximal humerus.
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