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Failure of the hinge mechanism in total elbow arthroplasty
J Shoulder Elbow Surg (2010) 19, 368-375
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Failure of the hinge mechanism in total elbow arthroplasty William H. Seitz Jr., MDa,*, Hisham Bismar, DOb, Peter J. Evans, MD, PhDc a
Cleveland Orthopaedic and Spine Hospital at Lutheran, a Cleveland Clinic Hospital, and Cleveland Clinic Lerner College of Medicine, Cleveland, OH b Kaiser Permanente, Clackamas c Hand and Upper Extremity Center, Orthopaedic and Rheumatologic Institute, Cleveland Clinic, Cleveland, OH Hypothesis: Total elbow arthroplasty (TEA) has become an accepted means of dealing with intractable elbow arthritis. The Coonrad-Morrey elbow prosthesis has become the workhorse for management of elbow arthropathy. Its successful initial use in rheumatoid patients has evolved, as has its design, to allow use in osteoarthritic patients and patients with posttraumatic arthritis. More active patients with elbow arthropathy are also treated using TEA. Prior design flaws led to central bushing failure and resulted in a redesign of the implant. However, the newer design has been noted to demonstrate a new mode of failure that appears to be more prevalent in active patients with osteoarthritis and posttraumatic arthritis. The authors hypothesize that the mechanical properties of the second generation hinge mechanism are inadequate to resist the high stresses placed upon it by some active patients treated for osteo- and posttraumatic arthritis. Materials and methods: Since 2000, 2 senior surgeons at Cleveland Clinic performed 82 TEAs, 64 in osteoarthritic or posttraumatic patients. Outcomes are reviewed. Results: Five patients demonstrated failure of the central locking and bushing components, with instability and dissociation requiring revision surgery. Two of these patients had secondary failure and required repeat revision using a more substantial central axis with lock washer and set screw. Discussion: The mode of failure and radiographic and clinical findings demonstrate that younger patients with a more active lifestyle are at risk for central axis and bushing failure. It is recommended that younger, more active patients be monitored indefinitely at 6-month intervals and counseled about the risk of potential failure and the need to limit forces across the reconstructed elbow. Results: These failures indicate the need for alternative designs in younger, active patients. Level of evidence: Level IV, Case Series; Treatment Study Ó 2010 Journal of Shoulder and Elbow Surgery Board of Trustees. Keywords: Total elbow arthroplasty; osteoarthritis; posttraumatic arthritis; implant failure
Total elbow arthroplasty (TEA) has become an established procedure for a wide variety of degenerative elbow conditions, with a more predictable and improved outcome *Reprint requests: Dr William H. Seitz Jr, Lutheran Hospital, a Cleveland Clinic Hospital, 1730 W 25th St, 2C, Cleveland, OH 44113. E-mail address: [email protected] (W.H. Seitz Jr.).
in recent years. Its use in the past was predominantly indicated in patients with rheumatoid arthritis. More recently, a significant number of TEAs have been performed in patients with osteoarthritis and posttraumatic arthritis for painfully restricted range of motion, instability refractory to reconstructive procedures, or intractable pain.
1058-2746/2010/$36.00 - see front matter Ó 2010 Journal of Shoulder and Elbow Surgery Board of Trustees. doi:10.1016/j.jse.2009.11.004
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Figure 2 Mechanical failure of locking pin assembly is shown without dissociation of the humeral and ulnar components.
Figure 1 (A) The separate components of locking pin and the bushing assembly are shown. (B) Entire implant assembly is shown with the polyethylene bushings in place.
At present, the 2 broad categories for total elbow prostheses are semiconstrained linked designs and resurfacing unlinked designs. The Coonrad-Morrey total elbow prosthesis (Zimmer, Warsaw, Ind) is currently the most commonly used design and has one of the longest track records. It is a linked, semiconstrained design with a ‘‘sloppy hinge’’ that allows for some varus-valgus motion in the coronal plain.15,20 Despite its versatility, a number of
complications have been described that can lead to mechanical failure, most notably, polyethylene wear of the bushings and failure of the hinge locking mechanism. The design of the Coonrad-Morrey total elbow prosthesis has undergone several modifications since its introduction in 1978.15 Most recently, the central axis locking mechanism design was changed from a C-ring locking design to a 2-piece snap fit locking assembly. There have been several reports of polyethylene wear in this prosthesis7,10,17 and fewer reports of the older C-ring locking mechanism failure.20 To our knowledge, there are no reports on the failure of the new snap fit locking pin assembly. This article reports a small subset of patients in our institution with incidence of locking mechanism failure, the common characteristics associated with these failed cases, and the results of revisions performed.
Materials and methods The internal review boards of the institutions from the participating authors waived approval for the human protocol for this investigation. All investigations were conducted in conformity with ethical principles of research. Between 2000 and 2007, 2 senior surgeons at Cleveland Clinic performed Coonrad-Morrey TEAs in 82 patients, of which 64 procedures were because of osteoarthritis (n ¼ 28) or
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W.H. Seitz Jr. et al. pin. A 3-piece polyethylene bushing assembly interfaces between this locking assembly and the humeral and ulnar components of the prosthesis (Fig. 1).
Results The average time between the index procedure and the time failure of the locking mechanism was 25 months (range, 768 months). Before bushing and locking mechanism exchange, 4 of the 5 patients reported pain at the elbow, 3 also reported a squeaking noise with elbow flexion, and 2 reported gross instability, crepitus, and a decreased range of motion by the time of the revision surgery. None of the patients relayed any acute traumatic events associated with the onset of the initial symptoms; however, 3 patients admitted to performing some strenuous activities (eg, wood splitting, heavy lifting over 20 lbs) against medical advice .
Radiographic assessment
Figure 3 Anteroposterior and lateral of mechanical dissociation of the locking mechanism is shown with complete dissociation of the elbow ulnar and humeral components. The phalanges of the male locking components are broken and free in the soft tissue. posttraumatic arthritis (n ¼ 36), and 18 were performed in rheumatoid patients. There were 71 primary TEAs and 11 revision TEAs, 8 of whom underwent the primary procedure at an outside institution. The average age at the time of the arthroplasty was 63 years. Of these, 5 patients (4 men, 1 woman) underwent 8 revision surgeries due to failure of the central axis locking mechanism. These patients were a mean age of 45 years (range, 29-60 years) at the time of the primary arthroplasty. Three of these patients received primary elbow arthroplasties. Two patients who received revision arthroplasties underwent the primary procedure at another institution but had undergone revision surgery for periprosthetic fractures and loosening at our institution before the locking mechanism failed. There were 3 right and 2 left elbows, with the dominant side involved in 3 of the 5 elbows. One patient had the procedure secondary to ‘‘burnt out’’ juvenile rheumatoid arthritis, and the other 4 had the procedure for posttraumatic arthritis15 and osteoarthritis.15 Two patients had multiple incidents of the locking mechanism failure comprising 2 incidents in 1 patient and 3 incidences in another. Three patients were receiving disability secondary to medical conditions, 1 worked as a mailman, and 1 was retired. All the implants that failed were the latest generation Coonrad-Morrey total elbow implants, which were introduced in 2000. This generation of implants included a circumferential plasma spray surface of the proximal ulnar component, and all used the snap-fit pin assembly. This assembly consists of a ‘‘male’’ pin with four phalanges at its tip, which locks into a larger hollow ‘‘female’’
Plain anteroposterior (true AP of the humeral component) and lateral radiographs of the elbows were obtained at routine follow-up visits or when patients presented with complaints of pain before the revision surgery. Partial dissociation of the locking mechanism occurred in 7 of the 8 incidents; that is, the male and female locking pins were still partially engaged but had started to drift apart within the hinge cavity (Fig. 2). In 1 patient, the locking pins had completely dissociated from each other and from humeral and ulnar components (flail elbow; Fig. 3). Initial radiographs also revealed 4 incidents where there was visible evidence of breakage of the male pin phalanges. Two more incidents that had originally showed partial dissociation were found to have pin breakage at surgery (Fig. 4). Evaluation of prerevision radiographs for the alignment of the humeral stem within the medullary canal revealed 3 patients with a slight average varus alignment of 4 (range, 3 -5 ), 1 in 2 of valgus alignment, and 1 in neutral. Alignment of the ulnar component was difficult to assess due to the lack of true AP views of the ulna. Three patients had osteolysis of the distal humeral metaphysis along with prior complete or near complete loss of both medial and lateral condyles. Two of these patients also demonstrated partial olecranon resorption. The other 2 patients exhibited minor evidence of osteolysis near the metaphysis of the humerus adjacent to the hinge mechanism, and some evidence of osteolysis was found in 1 patient at the proximal ulnar component. There was no evidence of osteolysis or radiolucent lines (loosening) around the proximal humeral or the distal ulnar stem components in any of the patients.
Surgical findings All revision surgeries were performed using a posterior approach or a modified posterior approach. Metallosis (dark
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Figure 4 (A) Backing out of the locking pin is shown. (B) Complete dissociation of the elbow components few weeks later is shown, with evidence of male pin breakage.
metallic debris staining) was present within the pseudocapsule in 3 patients (Fig. 5). All cases demonstrated some degree of polyethylene wear, but 3 patients had evidence of significant polyethylene component deformity and breakage. Most polyethylene wear occurred at the ulnar polyethylene bushing (Fig. 6). Two ulnar bushings demonstrated asymmetrical wear and distortion patterns peripherally at opposing sides of the medial and lateral edges. The retrieved humeral polyethylene bushings showed minimal deformation and wear. The locking mechanism was retrieved and was broken in 6 of the 8 cases. Failure of the locking mechanism occurred through breakage at the base of the 4 locking phalanges on the male component (Fig. 7). In 2 cases, the locking mechanism had disengaged without breakage. Upon retrieval of these components at revision surgery, it was apparent that the phalanges of the male locking pin had failed to completely spread and engage the female pin rim (Fig. 8). This occurred even though all locking mechanisms were confirmed to be fully engaged at the time of original
surgery through visual inspection and by the auditory feedback obtained after snapping the pin assembly. The humeral and ulnar components were checked for instability at the revision surgery. All components were well fixed and none required revision. Only the locking pin assembly and the polyethylene bushings were exchanged. In the cases with multiple locking mechanism failure or dissociation, a more durable custom-made locking mechanism was installed. This locking mechanism consisted of a central pin with a matching nut locked by a set-screw (Fig. 9).
Discussion The sloppy-hinge Coonrad-Morrey total elbow prosthesis is one of the most commonly used linked total elbow designs. Its use in low-demand rheumatoid arthritis patients has been established with a lengthy track record.1,2,6,8,12,14,16,19 The use of the implant in younger posttraumatic arthritis
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Figure 5 ‘‘Metallosis’’ and polyethylene debris are seen at revision surgery after locking mechanic failure.
Figure 6
Asymmetrical wear of the ulnar bushing.
and osteoarthritic patients (<60 years old) with higher physical demand has demonstrated a less satisfactory survival outcome.2,14,16,19 Revision surgery for mechanical failure or bushing wear in this implant has been reported,7,10,20 and most of these were related to fracture of the ulnar component in younger more active patients.
The ulnar component was modified in 2000 with the addition of circumferential plasma spray surface on the proximal part of ulnar component. Failure of the hinge locking mechanism has been reported in this implant and other semiconstrained hinged elbow prostheses.4,9,13,18,20 Figgie et al5 reported the failure of the locking mechanism in 9 Osteonics (Allendale, NJ) hinged elbow implants. The failure rate in that series was 5.3%, with most failures occurring in women with rheumatoid arthritis at an average of 5.5 years after the index procedure. Similarly, locking mechanism failure has been reported in the triaxial elbow design (Johnson & Johnson, Warsaw, IN), and the Pritchard elbow (Smith & Nephew, Memphis, TN).3,5,11,13,18 Very few reports have specifically addressed the failure of the locking mechanism in the Coonrad-Morrey elbow. Wright et al20 reported failure of the locking mechanism in 7 elbows. All of the failures in that series occurred with the older generation of locking mechanism, which consisted of a central axis pin with a C ring to lock it in place. Several factors were associated with C-ring failure, including a diagnosis of posttraumatic arthritis, male sex, high physical demand, deficient humeral condyles or olecranon, and young age. Our study showed similar factors and patient demographics were associated with the locking mechanism failure. Of 5 patients in the failure group, 4 had TEA for posttraumatic arthritis or osteoarthritis. The patient with ‘‘burnt-out’’ rheumatoid arthritis had undergone the initial procedure at a young age and had a relatively active life style. Young age at the time of the index procedure and male sex were also predominant in the failure group. All patients had an active life style and had admitted to using the elbow beyond the recommended 5-lb weight limit. Several surgical factors might have contributed to locking mechanism failure in this group. First is the issue of malalignment or malpositioning of the prosthesis. Malalignment of the humeral component was minimal in this group, and we do not believe it contributed to mechanical failure here. On the other hand, we were not able to measure ulnar malalignment; therefore, we do not know if there was a torsional malalignment that could have contributed to increased loading on the locking mechanism. The second issue is related to periarticular bone deficiency. Three of the 5 patients in the failure group had significant deficiency of the condyles and or the olecranon. Both patients with multiple episodes of locking mechanism failure had deficient condyles. Significant distal humeral or proximal ulnar bone deficiency, or both, makes determination of the true center of rotation of the elbow more difficult during surgery. Accurate reconstruction of the anatomic center of rotation of the elbow and accurate humeral and ulnar stem alignment have been correlated with improved durability and decreased complications.3 This might have been a factor contributing to increased load on the locking mechanism.
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Figure 7
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Locking pin assembly and bushing retrieved after revision.
In addition, the loss of epicondyles with the origin of wrist flexor and extensor muscle groups might decrease dynamic stabilization of the elbow and therefore increase the load seen by the locking mechanism. Wright el al20 hypothesized that the flexor pronator mass and the extensor origin muscles may act to dampen the end range varusvalgus loading of the implant, and therefore, the loss of the condyle might subject the locking mechanism to higher loads leading to failure. The overall failure rate of locking mechanism in our series was 6.1%. This rate, which was calculated without including the multiple episodes of locking mechanism failure, is similar to those described in other implants. The average time to revision surgery, excluding the 3 recurrences, was 25 months. In 2 cases in this series, the locking pin mechanism had disengaged without breakage of the locking phalanges. One of these cases appeared related to a failure of the locking pin to engage properly within the female component and might have been related to a defective pin. In addition, there were 2 other cases where the locking mechanism was noticed to be disengaging on follow-up radiographs without evidence of pin breakage. A few months later, both of these demonstrated pin breakage as evidenced on radiographs. It is unclear whether this same scenario (ie, locking mechanism dissociation before pin breakage) occurred in the cases with significant polyethylene wear and later revision time. In these cases, it is evident from the asymmetrical wear patterns on the ulnar polyethylene that it was caused by excessive valgus load at the elbow. This repetitive high load on the locking pin could have caused the phalanges on the male pin to break in a manner similar to the dissociation of the old C ring as described by Wright and Hastings.20
Figure 8 Deformed locking assembly that disengaged a few months after placement without breakage (upper arrow). Notice the deformity of the phalanges, which failed to completely spread and catch the female rim (lower arrow) compared with a normal coupling system.
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Figure 9 (A) Radiograph of a 50-year-old woman whose locking mechanism failed 4 years after total elbow implantation after fracture and repair required extensive de´bridement. (B) ‘‘Metallosis’’ and failed components are seen intraoperatively at revision. (C) Failure of all bushing and locking components was found. (D and E) A special custom heavy-duty central bolt with locked washer and set-screw were fabricated for revision.
Conclusions Our experience demonstrates ongoing potential problems with the use of the current Coonrad-Morrey total elbow prosthesis in patients with higher physical demands. Failure of the locking mechanism still occurred despite a change in the locking mechanism assembly from a Cring design to the new snap-pin design. At this time we recommend that younger patients with higher physical
demand who have received the Coonrad-Morrey total elbow be monitored regularly at 6- to 12-month interval for radiographic signs of locking mechanism dissociation or bushing wear. If caught early, exchange of the locking assembly and the bushing to a custom-made locking pin assembly can be performed through a limited exposure. For new patients with higher physical demand in need of TEA, we have started exploring other designs with more durable wear characteristics.
Failure of the elbow hinge mechanism
Disclaimer The authors, their immediate families, and any research foundations with which they are affiliated have not received any financial payments or other benefits from any commercial entity related to the subject of this article.
References 1. Aldridge JM 3rd, Lightdale NR, Mallon WJ, Coonrad RW. Total elbow arthroplasty with the Coonrad/Coonrad-Morrey prosthesis. A 10- to 31-year survival analysis. J Bone Joint Surg Br 2006;88:509-14. 2. Connor PM, Morrey BF. Total elbow arthroplasty in patients who have juvenile rheumatoid arthritis. J Bone Joint Surg Am 1998;80:678-88. 3. Figgie HE 3rd, Inglis AE, Mow C. A critical analysis of alignment factors affecting functional outcome in total elbow arthroplasty. J Arthroplasty 1986;1:169-73. 4. Figgie HE, Inglis AE, Ranawat CS, Rosenberg GM. Results of total elbow arthroplasty as a salvage procedure for failed elbow reconstructive operations. Clin Orthop 1987;219:185-93. 5. Figgie MP, Su EP, Kahn B, Lipman J. Locking mechanism failure in semiconstrained total elbow arthroplasty. J Shoulder Elbow Surg 2006; 15:88-93. 6. Gill DR, Morrey BF. The Coonrad-Morrey total elbow arthroplasty in patients who have rheumatoid arthritis. A ten to fifteen-year follow-up study. J Bone Joint Surg Am 1998;80:1327-35. 7. Goldberg SH, Urban RM, Jacobs JJ, King GJ, O’Driscoll SW, Cohen MS. Modes of wear after semiconstrained total elbow arthroplasty. J Bone Joint Surg Am 2008;90:609-19.
375 8. Hildebrand KA, Patterson SD, Regan WD, MacDermid JC, King GJ. Functional outcome of semiconstrained total elbow arthroplasty. J Bone Joint Surg Am 2000;82:1379-86. 9. Kraay MJ, Figgie MP, Inglis AE, Wolfe SW, Ranawat CS. Primary semiconstrained total elbow arthroplasty. Survival analysis of 113 consecutive cases. J Bone Joint Surg Br 1994;76:636-40. 10. Lee BP, Adams RA, Morrey BF. Polyethylene wear after total elbow arthroplasty. J Bone Joint Surg Am 2005;87:1080-7. 11. Little CP, Graham AJ, Carr AJ. Total elbow arthroplasty: a systematic review of the literature in the English language until the end of 2003. J Bone Joint Surg Br 2005;87:437-44. 12. Little CP, Graham AJ, Karatzas G, Woods DA, Carr AJ. Outcomes of total elbow arthroplasty for rheumatoid arthritis: comparative study of three implants. J Bone Joint Surg Am 2005;87:2439-48. 13. Matarese W, Stuchin SA, Kummer FJ, Zuckerman JD. Polyethylene bearing component failure and dislocation in the triaxial elbow. A report of two cases. J Arthroplasty 1990;5:365-7. 14. Morrey BF. Fractures of the distal humerus: role of elbow replacement. Orthop Clin North Am 2000;31:145-54. 15. Morrey BF, Adams RA. Semiconstrained elbow replacement for distal humeral nonunion. J Bone Joint Surg Br 1995;77:67-72. 16. Morrey BF, Adams RA. Semiconstrained arthroplasty for the treatment of rheumatoid arthritis of the elbow. J Bone Joint Surg Am 1992; 74:479-90. 17. O’Driscoll SW, King GJ. Treatment of instability after total elbow arthroplasty. Orthop Clin North Am 2001;32:679-95. ix. 18. Pritchard RW. Long-term follow-up study: semiconstrained elbow prosthesis. Orthopedics 1981;4:151-5. 19. Schneeberger AG, Adams R, Morrey BF. Semiconstrained total elbow replacement for the treatment of post-traumatic osteoarthrosis. J Bone Joint Surg Am 1997;79:1211-22. 20. Wright TW, Hastings H. Total elbow arthroplasty failure due to overuse, C-ring failure, and/or bushing wear. J Shoulder Elbow Surg 2005;14:65-72.
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Failure of the hinge mechanism in total elbow arthroplasty William H. Seitz Jr., MDa,*, Hisham Bismar, DOb, Peter J. Evans, MD, PhDc a
Cleveland Orthopaedic and Spine Hospital at Lutheran, a Cleveland Clinic Hospital, and Cleveland Clinic Lerner College of Medicine, Cleveland, OH b Kaiser Permanente, Clackamas c Hand and Upper Extremity Center, Orthopaedic and Rheumatologic Institute, Cleveland Clinic, Cleveland, OH Hypothesis: Total elbow arthroplasty (TEA) has become an accepted means of dealing with intractable elbow arthritis. The Coonrad-Morrey elbow prosthesis has become the workhorse for management of elbow arthropathy. Its successful initial use in rheumatoid patients has evolved, as has its design, to allow use in osteoarthritic patients and patients with posttraumatic arthritis. More active patients with elbow arthropathy are also treated using TEA. Prior design flaws led to central bushing failure and resulted in a redesign of the implant. However, the newer design has been noted to demonstrate a new mode of failure that appears to be more prevalent in active patients with osteoarthritis and posttraumatic arthritis. The authors hypothesize that the mechanical properties of the second generation hinge mechanism are inadequate to resist the high stresses placed upon it by some active patients treated for osteo- and posttraumatic arthritis. Materials and methods: Since 2000, 2 senior surgeons at Cleveland Clinic performed 82 TEAs, 64 in osteoarthritic or posttraumatic patients. Outcomes are reviewed. Results: Five patients demonstrated failure of the central locking and bushing components, with instability and dissociation requiring revision surgery. Two of these patients had secondary failure and required repeat revision using a more substantial central axis with lock washer and set screw. Discussion: The mode of failure and radiographic and clinical findings demonstrate that younger patients with a more active lifestyle are at risk for central axis and bushing failure. It is recommended that younger, more active patients be monitored indefinitely at 6-month intervals and counseled about the risk of potential failure and the need to limit forces across the reconstructed elbow. Results: These failures indicate the need for alternative designs in younger, active patients. Level of evidence: Level IV, Case Series; Treatment Study Ó 2010 Journal of Shoulder and Elbow Surgery Board of Trustees. Keywords: Total elbow arthroplasty; osteoarthritis; posttraumatic arthritis; implant failure
Total elbow arthroplasty (TEA) has become an established procedure for a wide variety of degenerative elbow conditions, with a more predictable and improved outcome *Reprint requests: Dr William H. Seitz Jr, Lutheran Hospital, a Cleveland Clinic Hospital, 1730 W 25th St, 2C, Cleveland, OH 44113. E-mail address: [email protected] (W.H. Seitz Jr.).
in recent years. Its use in the past was predominantly indicated in patients with rheumatoid arthritis. More recently, a significant number of TEAs have been performed in patients with osteoarthritis and posttraumatic arthritis for painfully restricted range of motion, instability refractory to reconstructive procedures, or intractable pain.
1058-2746/2010/$36.00 - see front matter Ó 2010 Journal of Shoulder and Elbow Surgery Board of Trustees. doi:10.1016/j.jse.2009.11.004
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Figure 2 Mechanical failure of locking pin assembly is shown without dissociation of the humeral and ulnar components.
Figure 1 (A) The separate components of locking pin and the bushing assembly are shown. (B) Entire implant assembly is shown with the polyethylene bushings in place.
At present, the 2 broad categories for total elbow prostheses are semiconstrained linked designs and resurfacing unlinked designs. The Coonrad-Morrey total elbow prosthesis (Zimmer, Warsaw, Ind) is currently the most commonly used design and has one of the longest track records. It is a linked, semiconstrained design with a ‘‘sloppy hinge’’ that allows for some varus-valgus motion in the coronal plain.15,20 Despite its versatility, a number of
complications have been described that can lead to mechanical failure, most notably, polyethylene wear of the bushings and failure of the hinge locking mechanism. The design of the Coonrad-Morrey total elbow prosthesis has undergone several modifications since its introduction in 1978.15 Most recently, the central axis locking mechanism design was changed from a C-ring locking design to a 2-piece snap fit locking assembly. There have been several reports of polyethylene wear in this prosthesis7,10,17 and fewer reports of the older C-ring locking mechanism failure.20 To our knowledge, there are no reports on the failure of the new snap fit locking pin assembly. This article reports a small subset of patients in our institution with incidence of locking mechanism failure, the common characteristics associated with these failed cases, and the results of revisions performed.
Materials and methods The internal review boards of the institutions from the participating authors waived approval for the human protocol for this investigation. All investigations were conducted in conformity with ethical principles of research. Between 2000 and 2007, 2 senior surgeons at Cleveland Clinic performed Coonrad-Morrey TEAs in 82 patients, of which 64 procedures were because of osteoarthritis (n ¼ 28) or
370
W.H. Seitz Jr. et al. pin. A 3-piece polyethylene bushing assembly interfaces between this locking assembly and the humeral and ulnar components of the prosthesis (Fig. 1).
Results The average time between the index procedure and the time failure of the locking mechanism was 25 months (range, 768 months). Before bushing and locking mechanism exchange, 4 of the 5 patients reported pain at the elbow, 3 also reported a squeaking noise with elbow flexion, and 2 reported gross instability, crepitus, and a decreased range of motion by the time of the revision surgery. None of the patients relayed any acute traumatic events associated with the onset of the initial symptoms; however, 3 patients admitted to performing some strenuous activities (eg, wood splitting, heavy lifting over 20 lbs) against medical advice .
Radiographic assessment
Figure 3 Anteroposterior and lateral of mechanical dissociation of the locking mechanism is shown with complete dissociation of the elbow ulnar and humeral components. The phalanges of the male locking components are broken and free in the soft tissue. posttraumatic arthritis (n ¼ 36), and 18 were performed in rheumatoid patients. There were 71 primary TEAs and 11 revision TEAs, 8 of whom underwent the primary procedure at an outside institution. The average age at the time of the arthroplasty was 63 years. Of these, 5 patients (4 men, 1 woman) underwent 8 revision surgeries due to failure of the central axis locking mechanism. These patients were a mean age of 45 years (range, 29-60 years) at the time of the primary arthroplasty. Three of these patients received primary elbow arthroplasties. Two patients who received revision arthroplasties underwent the primary procedure at another institution but had undergone revision surgery for periprosthetic fractures and loosening at our institution before the locking mechanism failed. There were 3 right and 2 left elbows, with the dominant side involved in 3 of the 5 elbows. One patient had the procedure secondary to ‘‘burnt out’’ juvenile rheumatoid arthritis, and the other 4 had the procedure for posttraumatic arthritis15 and osteoarthritis.15 Two patients had multiple incidents of the locking mechanism failure comprising 2 incidents in 1 patient and 3 incidences in another. Three patients were receiving disability secondary to medical conditions, 1 worked as a mailman, and 1 was retired. All the implants that failed were the latest generation Coonrad-Morrey total elbow implants, which were introduced in 2000. This generation of implants included a circumferential plasma spray surface of the proximal ulnar component, and all used the snap-fit pin assembly. This assembly consists of a ‘‘male’’ pin with four phalanges at its tip, which locks into a larger hollow ‘‘female’’
Plain anteroposterior (true AP of the humeral component) and lateral radiographs of the elbows were obtained at routine follow-up visits or when patients presented with complaints of pain before the revision surgery. Partial dissociation of the locking mechanism occurred in 7 of the 8 incidents; that is, the male and female locking pins were still partially engaged but had started to drift apart within the hinge cavity (Fig. 2). In 1 patient, the locking pins had completely dissociated from each other and from humeral and ulnar components (flail elbow; Fig. 3). Initial radiographs also revealed 4 incidents where there was visible evidence of breakage of the male pin phalanges. Two more incidents that had originally showed partial dissociation were found to have pin breakage at surgery (Fig. 4). Evaluation of prerevision radiographs for the alignment of the humeral stem within the medullary canal revealed 3 patients with a slight average varus alignment of 4 (range, 3 -5 ), 1 in 2 of valgus alignment, and 1 in neutral. Alignment of the ulnar component was difficult to assess due to the lack of true AP views of the ulna. Three patients had osteolysis of the distal humeral metaphysis along with prior complete or near complete loss of both medial and lateral condyles. Two of these patients also demonstrated partial olecranon resorption. The other 2 patients exhibited minor evidence of osteolysis near the metaphysis of the humerus adjacent to the hinge mechanism, and some evidence of osteolysis was found in 1 patient at the proximal ulnar component. There was no evidence of osteolysis or radiolucent lines (loosening) around the proximal humeral or the distal ulnar stem components in any of the patients.
Surgical findings All revision surgeries were performed using a posterior approach or a modified posterior approach. Metallosis (dark
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Figure 4 (A) Backing out of the locking pin is shown. (B) Complete dissociation of the elbow components few weeks later is shown, with evidence of male pin breakage.
metallic debris staining) was present within the pseudocapsule in 3 patients (Fig. 5). All cases demonstrated some degree of polyethylene wear, but 3 patients had evidence of significant polyethylene component deformity and breakage. Most polyethylene wear occurred at the ulnar polyethylene bushing (Fig. 6). Two ulnar bushings demonstrated asymmetrical wear and distortion patterns peripherally at opposing sides of the medial and lateral edges. The retrieved humeral polyethylene bushings showed minimal deformation and wear. The locking mechanism was retrieved and was broken in 6 of the 8 cases. Failure of the locking mechanism occurred through breakage at the base of the 4 locking phalanges on the male component (Fig. 7). In 2 cases, the locking mechanism had disengaged without breakage. Upon retrieval of these components at revision surgery, it was apparent that the phalanges of the male locking pin had failed to completely spread and engage the female pin rim (Fig. 8). This occurred even though all locking mechanisms were confirmed to be fully engaged at the time of original
surgery through visual inspection and by the auditory feedback obtained after snapping the pin assembly. The humeral and ulnar components were checked for instability at the revision surgery. All components were well fixed and none required revision. Only the locking pin assembly and the polyethylene bushings were exchanged. In the cases with multiple locking mechanism failure or dissociation, a more durable custom-made locking mechanism was installed. This locking mechanism consisted of a central pin with a matching nut locked by a set-screw (Fig. 9).
Discussion The sloppy-hinge Coonrad-Morrey total elbow prosthesis is one of the most commonly used linked total elbow designs. Its use in low-demand rheumatoid arthritis patients has been established with a lengthy track record.1,2,6,8,12,14,16,19 The use of the implant in younger posttraumatic arthritis
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W.H. Seitz Jr. et al.
Figure 5 ‘‘Metallosis’’ and polyethylene debris are seen at revision surgery after locking mechanic failure.
Figure 6
Asymmetrical wear of the ulnar bushing.
and osteoarthritic patients (<60 years old) with higher physical demand has demonstrated a less satisfactory survival outcome.2,14,16,19 Revision surgery for mechanical failure or bushing wear in this implant has been reported,7,10,20 and most of these were related to fracture of the ulnar component in younger more active patients.
The ulnar component was modified in 2000 with the addition of circumferential plasma spray surface on the proximal part of ulnar component. Failure of the hinge locking mechanism has been reported in this implant and other semiconstrained hinged elbow prostheses.4,9,13,18,20 Figgie et al5 reported the failure of the locking mechanism in 9 Osteonics (Allendale, NJ) hinged elbow implants. The failure rate in that series was 5.3%, with most failures occurring in women with rheumatoid arthritis at an average of 5.5 years after the index procedure. Similarly, locking mechanism failure has been reported in the triaxial elbow design (Johnson & Johnson, Warsaw, IN), and the Pritchard elbow (Smith & Nephew, Memphis, TN).3,5,11,13,18 Very few reports have specifically addressed the failure of the locking mechanism in the Coonrad-Morrey elbow. Wright et al20 reported failure of the locking mechanism in 7 elbows. All of the failures in that series occurred with the older generation of locking mechanism, which consisted of a central axis pin with a C ring to lock it in place. Several factors were associated with C-ring failure, including a diagnosis of posttraumatic arthritis, male sex, high physical demand, deficient humeral condyles or olecranon, and young age. Our study showed similar factors and patient demographics were associated with the locking mechanism failure. Of 5 patients in the failure group, 4 had TEA for posttraumatic arthritis or osteoarthritis. The patient with ‘‘burnt-out’’ rheumatoid arthritis had undergone the initial procedure at a young age and had a relatively active life style. Young age at the time of the index procedure and male sex were also predominant in the failure group. All patients had an active life style and had admitted to using the elbow beyond the recommended 5-lb weight limit. Several surgical factors might have contributed to locking mechanism failure in this group. First is the issue of malalignment or malpositioning of the prosthesis. Malalignment of the humeral component was minimal in this group, and we do not believe it contributed to mechanical failure here. On the other hand, we were not able to measure ulnar malalignment; therefore, we do not know if there was a torsional malalignment that could have contributed to increased loading on the locking mechanism. The second issue is related to periarticular bone deficiency. Three of the 5 patients in the failure group had significant deficiency of the condyles and or the olecranon. Both patients with multiple episodes of locking mechanism failure had deficient condyles. Significant distal humeral or proximal ulnar bone deficiency, or both, makes determination of the true center of rotation of the elbow more difficult during surgery. Accurate reconstruction of the anatomic center of rotation of the elbow and accurate humeral and ulnar stem alignment have been correlated with improved durability and decreased complications.3 This might have been a factor contributing to increased load on the locking mechanism.
Failure of the elbow hinge mechanism
Figure 7
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Locking pin assembly and bushing retrieved after revision.
In addition, the loss of epicondyles with the origin of wrist flexor and extensor muscle groups might decrease dynamic stabilization of the elbow and therefore increase the load seen by the locking mechanism. Wright el al20 hypothesized that the flexor pronator mass and the extensor origin muscles may act to dampen the end range varusvalgus loading of the implant, and therefore, the loss of the condyle might subject the locking mechanism to higher loads leading to failure. The overall failure rate of locking mechanism in our series was 6.1%. This rate, which was calculated without including the multiple episodes of locking mechanism failure, is similar to those described in other implants. The average time to revision surgery, excluding the 3 recurrences, was 25 months. In 2 cases in this series, the locking pin mechanism had disengaged without breakage of the locking phalanges. One of these cases appeared related to a failure of the locking pin to engage properly within the female component and might have been related to a defective pin. In addition, there were 2 other cases where the locking mechanism was noticed to be disengaging on follow-up radiographs without evidence of pin breakage. A few months later, both of these demonstrated pin breakage as evidenced on radiographs. It is unclear whether this same scenario (ie, locking mechanism dissociation before pin breakage) occurred in the cases with significant polyethylene wear and later revision time. In these cases, it is evident from the asymmetrical wear patterns on the ulnar polyethylene that it was caused by excessive valgus load at the elbow. This repetitive high load on the locking pin could have caused the phalanges on the male pin to break in a manner similar to the dissociation of the old C ring as described by Wright and Hastings.20
Figure 8 Deformed locking assembly that disengaged a few months after placement without breakage (upper arrow). Notice the deformity of the phalanges, which failed to completely spread and catch the female rim (lower arrow) compared with a normal coupling system.
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W.H. Seitz Jr. et al.
Figure 9 (A) Radiograph of a 50-year-old woman whose locking mechanism failed 4 years after total elbow implantation after fracture and repair required extensive de´bridement. (B) ‘‘Metallosis’’ and failed components are seen intraoperatively at revision. (C) Failure of all bushing and locking components was found. (D and E) A special custom heavy-duty central bolt with locked washer and set-screw were fabricated for revision.
Conclusions Our experience demonstrates ongoing potential problems with the use of the current Coonrad-Morrey total elbow prosthesis in patients with higher physical demands. Failure of the locking mechanism still occurred despite a change in the locking mechanism assembly from a Cring design to the new snap-pin design. At this time we recommend that younger patients with higher physical
demand who have received the Coonrad-Morrey total elbow be monitored regularly at 6- to 12-month interval for radiographic signs of locking mechanism dissociation or bushing wear. If caught early, exchange of the locking assembly and the bushing to a custom-made locking pin assembly can be performed through a limited exposure. For new patients with higher physical demand in need of TEA, we have started exploring other designs with more durable wear characteristics.
Failure of the elbow hinge mechanism
Disclaimer The authors, their immediate families, and any research foundations with which they are affiliated have not received any financial payments or other benefits from any commercial entity related to the subject of this article.
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