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Massive Osteolysis Due to Failure of a Unipolar Endoprosthesis
The Journal of Arthroplasty Vol. 23 No. 8 2008
Case Report
Massive Osteolysis Due to Failure of a Unipolar Endoprosthesis Amalia M. Decomas, MD, and John L. Ochsner, MD
Abstract: Unipolar endoprostheses are commonly used for the treatment of displaced femoral neck fractures in the elderly. Failure due to polyethylene wear, which has been well documented in bipolar endoprostheses, is not a commonly reported problem with unipolar prostheses. We present 2 cases of a particular unipolar design that failed due to polyethylene wear. We report these cases to promote awareness of this particular reason for failure in this design. We also question the need for polyethylene in any prosthetic, when it is not indicated for the bearing surface. Key words: unipolar hip endoprosthesis, osteolysis, endoprosthesis failure. © 2008 Elsevier Inc. All rights reserved.
Hemiarthroplasty has been well established as a treatment of femoral neck fractures in the elderly. At our institution, unipolar endoprostheses are used almost universally for elderly patients with displaced femoral neck fractures. Many reports have been published to demonstrate osteolysis from bipolar designs, mostly consisting of wear polyethylene debris [1-3]. We present 2 case reports of massive osteolysis in a particular unipolar endoprosthesis, which are unique.
Materials Osteonics (Stryker Orthopedics, Mahwah, NJ) endo head and femoral hemihip prosthesis: catalog no. 22-0046 and 22-0048 (46 mm and 48 mm,
From the Department of Orthopaedics, Ochsner Health System, New Orleans, Louisiana. Submitted August 31, 2006; accepted October 16, 2007. There are no conflicts of interest in regards to this manuscript. Reprint requests: John L. Ochsner, MD, Ochsner Health System, New Orleans, LA 70121. © 2008 Elsevier Inc. All rights reserved. 0883-5403/08/2308-0027$34.00/0 doi:10.1016/j.arth.2007.10.024
respectively). The materials include a cobalt-chrome alloy and ultrahigh-molecular-weight polyethylene.
Case Report The first case is a 69-year-old-woman with a left displaced femoral neck fracture that was treated using an Osteonics unipolar endoprosthesis with a 46-mm head. This particular Osteonics endo head design has a polyethylene core in the head. This could be described as a “poly sandwich”–bearing surface. In this design, there was no intended motion between the polyethylene and metallic unipolar “cap.” Less than 9 years later, she had progressive and significant pain, requiring a revision to a total hip arthroplasty, with trabecular metal and bone grafting of the acetabulum. Her prerevision radiographs showed a crack through the endoprosthetic coupling between the head and stem, with erosions into the rami, ischium, and the medial femoral cortex (Fig. 1). During the case, the findings were confirmed, showing massive osteolysis of the proximal femur with cystic changes and erosion of both the anterior and posterior columns. The distal stem was not loose. Pathologic findings showed fibrosis with polarizable foreign material and a
1240.e5
1240.e6 The Journal of Arthroplasty Vol. 23 No. 8 December 2008
Fig. 2. Sixty-four-year old female with osteolysis, loosening, and wear of the acetabulum, which occurred 9 years after her original surgery for a displaced femoral neck fracture.
Fig. 1. Seventy-seven-year-old female with massive osteolysis and failure of a unipolar endoprosthesis less than 9 years after her original surgery.
foreign body giant cell reaction. The patient has been pain-free for 1 year after revision. The second case is a 55-year-old female with a right displaced femoral neck fracture also treated with an Osteonics unipolar endoprosthesis with a 48-mm head. This patient started to have pain and signs of osteolysis as soon as 5 years after her original surgery, which progressed with time (Fig. 2). She underwent 2 surgeries before her revision, for biopsy and irrigation and debridement, due to history of cancer. She finally had a revision, 9½ years after her original surgery, for a tumor prosthesis with an articulating bipolar component. This case also was found to have massive osteolysis of the proximal femur and acetabulum. Pathologic findings showed fragments of bone and fibroconnective tissue with reactive changes. Five years out from her revision, she is functioning well with minimal pain. Both of these cases showed a dislodged polyethylene core with grossly visible wear. I reiterate that the polyethylene was never intended to be a part of the bearing surface, which leads us to question the need for it in the first place.
In both cases, the patients had a history of cancer, which lead to confusion, as at first, the osteolysis was thought to have possibly been a metastasis to bone. In both cases, there was no tumor or infection involved.
Discussion Displaced femoral neck fractures in the elderly, have long been treated with hemiarthroplasty. They were found to be very stable constructs, especially with the use of larger diameter bearings. Larger femoral heads provide good range of motion, with
Fig. 3. The polyethylene core removed from our first case, which was dislocated from the head, with gross wear.
Massive Osteolysis Due to Failure of a Unipolar Endoprosthesis Decomas and Ochsner
less risk of dislocation [4]. Arthroplasty has been shown to significantly reduce the risk of revision surgery, compared to fixation, while at the same time showing better function and less pain [5-8]. Arthroplasty carries its own set of complications, including greater blood loss, longer operative time, and an increase in infection [5-8]. Osteolysis and aseptic loosening are known risks that have been studied with the use of arthroplasty, resulting from wear and material fatigue [9,10]. Unipolar designs were historically shown to cause acetabular erosion, and although bipolar designs came about to attempt to reduce the wear by forming a second interface, findings have not shown much difference between the two [11-13]. Dalldorf et al [14] reviewed histology of failed hemiarthroplasties and found no difference in metallic acetabular erosion between unipolar and bipolar prostheses. Other studies have suggested that bipolar cup design, with the introduction of ultrahigh-molecular-weight polyethylene and a second bearing surface, is in itself a reason to promote osteolysis [1,2]. Polyethylene wear is a very commonly reported reason for osteolysis in bipolar endoprostheses. Maloney et al [15] reported a study suggesting that there were twice as many particles generated than in a standard total hip. All this being said, to our knowledge, there have been no cases of failure of a unipolar endoprosthesis from polyethylene wear, as it is not used for articulation. This prosthesis is unique in that a traditional Morris taper stem (Osteonics, Stryker, Orthopedics) is coupled with a cobalt-chrome head filled with a polyethylene core. In both of these case reports, failure of the prosthesis lead to the core being dislodged from the metal cap and created an articulating surface. On visualization, as can be seen in the photographs, the polyethylene had large areas that had basically been carved out from direct wear (Figs. 3 and 4). This caused a large amount of polyethylene debris, which we believe was responsible for this massive osteolysis that was encountered. In a unipolar endoprosthesis, most physicians would not have polyethylene wear on the top of the differential, when presented with a case of massive osteolysis. The articulating surface is meant to be the native acetabulum with a metallic head. This may lead to a delay in diagnosis and prompt the surgeon to place more weight on a preliminary diagnosis of infection or tumor. We felt it was important to report these cases for the very reason of heightening the awareness that there is a polyethylene component in this particular Osteonics endoprosthetic head. We also questioned the need for implanting polyethylene in any prosthetic in which it is not
1240.e7
Fig. 4. All of the original components of the Osteonics endoprosthesis after being removed from our first patient.
being directly used for the bearing surface and questioned the rationale for the design. We used this particular design at our institution because it was part of our hospital contract and at the time did not realize the problems that would arise. Subsequently, Osteonics has not responded to our requests for information, and therefore, we cannot explain the reasoning for the design. We believe that these particular types of failures would have been significantly decreased in a comparable prosthesis with a purely metallic head. We feel there is an added risk of failure with the use of this prosthesis and plan on further investigating retrospectively within our patient population. This will help us to determine if there are more cases of failure with this particular prosthesis, as well as help delineate how significant these findings are. We no longer use this design and question its appropriateness.
References 1. Coleman SH. Failure of bipolar hemiarthroplasty: a retrospective review. Am J Orthop 2001;30:313. 2. Nishii TN. Bipolar cup design may lead to osteolysis around the uncemented femoral component. Clin Orthop 1995;316:112. 3. Rizzo M. Premature failure of a hip hemiarthroplasty secondary to osteolysis and aseptic loosening. Am J Orthop 2003;32:206. 4. Burroughs BR. Range of motion and stability in total hip arthroplasty with 28-, 32-, 38-, and 44-mm femoral head sizes. J Arthroplasty 2005;20:11. 5. Bhandari M. Internal fixation compared with arthroplasty for displaced fractures of the femoral neck. A meta-analysis. J Bone Joint Surg Am 2003; 85-A:1673. 6. Bray TJ. The displaced femoral neck fracture. Internal fixation versus bipolar endoprosthesis. Results of a prospective, randomized comparison. Clin Orthop 1988;230:127.
1240.e8 The Journal of Arthroplasty Vol. 23 No. 8 December 2008 7. Bjorgul K. Hemiarthroplasty in worst cases is better than internal fixation in best cases of displaced femoral neck fractures. Acta Orthop 2006;77:368. 8. Rogmark C. Primary arthroplasty is better than internal fixation of displaced femoral neck fractures: a meta-analysis of 14 randomized studies with 2,289 patients. Acta Orthop 2006;77:359. 9. Willert HG. The significance of wear and material fatigue in loosening of hip prostheses. Orthopade 1989;18:350. 10. Calton TF. Failure of the polyethylene after bipolar hemiarthroplasty of the hip: A report of five cases. J Bone Joint Surg Am 1998;80:420. 11. Ong BC. Unipolar versus bipolar hemiarthroplasty: functional outcome after femoral neck fracture at a
12.
13.
14.
15.
minimum of thirty-six months of follow-up. J Orthop Trauma 2002;16:317. Cornell CN. Unipolar versus bipolar hemiarthroplasty for the treatment of femoral neck fractures in the elderly. Clin Orthop 1998;348:67. Raia FJ. Unipolar or bipolar hemiarthroplasty for femoral neck fractures in the elderly? Clin Orthop 2003;414:259. Dalldorf PG. Rate of degeneration of human acetabular cartilage after hemiarthroplasty. J Bone Joint Surg Am 1995;77:877. Maloney WJ. Isolation and characterization of wear particles generated in patients who have had failure of a hip arthroplasty without cement. J Bone Joint Surg 1995;77:1301.
Case Report
Massive Osteolysis Due to Failure of a Unipolar Endoprosthesis Amalia M. Decomas, MD, and John L. Ochsner, MD
Abstract: Unipolar endoprostheses are commonly used for the treatment of displaced femoral neck fractures in the elderly. Failure due to polyethylene wear, which has been well documented in bipolar endoprostheses, is not a commonly reported problem with unipolar prostheses. We present 2 cases of a particular unipolar design that failed due to polyethylene wear. We report these cases to promote awareness of this particular reason for failure in this design. We also question the need for polyethylene in any prosthetic, when it is not indicated for the bearing surface. Key words: unipolar hip endoprosthesis, osteolysis, endoprosthesis failure. © 2008 Elsevier Inc. All rights reserved.
Hemiarthroplasty has been well established as a treatment of femoral neck fractures in the elderly. At our institution, unipolar endoprostheses are used almost universally for elderly patients with displaced femoral neck fractures. Many reports have been published to demonstrate osteolysis from bipolar designs, mostly consisting of wear polyethylene debris [1-3]. We present 2 case reports of massive osteolysis in a particular unipolar endoprosthesis, which are unique.
Materials Osteonics (Stryker Orthopedics, Mahwah, NJ) endo head and femoral hemihip prosthesis: catalog no. 22-0046 and 22-0048 (46 mm and 48 mm,
From the Department of Orthopaedics, Ochsner Health System, New Orleans, Louisiana. Submitted August 31, 2006; accepted October 16, 2007. There are no conflicts of interest in regards to this manuscript. Reprint requests: John L. Ochsner, MD, Ochsner Health System, New Orleans, LA 70121. © 2008 Elsevier Inc. All rights reserved. 0883-5403/08/2308-0027$34.00/0 doi:10.1016/j.arth.2007.10.024
respectively). The materials include a cobalt-chrome alloy and ultrahigh-molecular-weight polyethylene.
Case Report The first case is a 69-year-old-woman with a left displaced femoral neck fracture that was treated using an Osteonics unipolar endoprosthesis with a 46-mm head. This particular Osteonics endo head design has a polyethylene core in the head. This could be described as a “poly sandwich”–bearing surface. In this design, there was no intended motion between the polyethylene and metallic unipolar “cap.” Less than 9 years later, she had progressive and significant pain, requiring a revision to a total hip arthroplasty, with trabecular metal and bone grafting of the acetabulum. Her prerevision radiographs showed a crack through the endoprosthetic coupling between the head and stem, with erosions into the rami, ischium, and the medial femoral cortex (Fig. 1). During the case, the findings were confirmed, showing massive osteolysis of the proximal femur with cystic changes and erosion of both the anterior and posterior columns. The distal stem was not loose. Pathologic findings showed fibrosis with polarizable foreign material and a
1240.e5
1240.e6 The Journal of Arthroplasty Vol. 23 No. 8 December 2008
Fig. 2. Sixty-four-year old female with osteolysis, loosening, and wear of the acetabulum, which occurred 9 years after her original surgery for a displaced femoral neck fracture.
Fig. 1. Seventy-seven-year-old female with massive osteolysis and failure of a unipolar endoprosthesis less than 9 years after her original surgery.
foreign body giant cell reaction. The patient has been pain-free for 1 year after revision. The second case is a 55-year-old female with a right displaced femoral neck fracture also treated with an Osteonics unipolar endoprosthesis with a 48-mm head. This patient started to have pain and signs of osteolysis as soon as 5 years after her original surgery, which progressed with time (Fig. 2). She underwent 2 surgeries before her revision, for biopsy and irrigation and debridement, due to history of cancer. She finally had a revision, 9½ years after her original surgery, for a tumor prosthesis with an articulating bipolar component. This case also was found to have massive osteolysis of the proximal femur and acetabulum. Pathologic findings showed fragments of bone and fibroconnective tissue with reactive changes. Five years out from her revision, she is functioning well with minimal pain. Both of these cases showed a dislodged polyethylene core with grossly visible wear. I reiterate that the polyethylene was never intended to be a part of the bearing surface, which leads us to question the need for it in the first place.
In both cases, the patients had a history of cancer, which lead to confusion, as at first, the osteolysis was thought to have possibly been a metastasis to bone. In both cases, there was no tumor or infection involved.
Discussion Displaced femoral neck fractures in the elderly, have long been treated with hemiarthroplasty. They were found to be very stable constructs, especially with the use of larger diameter bearings. Larger femoral heads provide good range of motion, with
Fig. 3. The polyethylene core removed from our first case, which was dislocated from the head, with gross wear.
Massive Osteolysis Due to Failure of a Unipolar Endoprosthesis Decomas and Ochsner
less risk of dislocation [4]. Arthroplasty has been shown to significantly reduce the risk of revision surgery, compared to fixation, while at the same time showing better function and less pain [5-8]. Arthroplasty carries its own set of complications, including greater blood loss, longer operative time, and an increase in infection [5-8]. Osteolysis and aseptic loosening are known risks that have been studied with the use of arthroplasty, resulting from wear and material fatigue [9,10]. Unipolar designs were historically shown to cause acetabular erosion, and although bipolar designs came about to attempt to reduce the wear by forming a second interface, findings have not shown much difference between the two [11-13]. Dalldorf et al [14] reviewed histology of failed hemiarthroplasties and found no difference in metallic acetabular erosion between unipolar and bipolar prostheses. Other studies have suggested that bipolar cup design, with the introduction of ultrahigh-molecular-weight polyethylene and a second bearing surface, is in itself a reason to promote osteolysis [1,2]. Polyethylene wear is a very commonly reported reason for osteolysis in bipolar endoprostheses. Maloney et al [15] reported a study suggesting that there were twice as many particles generated than in a standard total hip. All this being said, to our knowledge, there have been no cases of failure of a unipolar endoprosthesis from polyethylene wear, as it is not used for articulation. This prosthesis is unique in that a traditional Morris taper stem (Osteonics, Stryker, Orthopedics) is coupled with a cobalt-chrome head filled with a polyethylene core. In both of these case reports, failure of the prosthesis lead to the core being dislodged from the metal cap and created an articulating surface. On visualization, as can be seen in the photographs, the polyethylene had large areas that had basically been carved out from direct wear (Figs. 3 and 4). This caused a large amount of polyethylene debris, which we believe was responsible for this massive osteolysis that was encountered. In a unipolar endoprosthesis, most physicians would not have polyethylene wear on the top of the differential, when presented with a case of massive osteolysis. The articulating surface is meant to be the native acetabulum with a metallic head. This may lead to a delay in diagnosis and prompt the surgeon to place more weight on a preliminary diagnosis of infection or tumor. We felt it was important to report these cases for the very reason of heightening the awareness that there is a polyethylene component in this particular Osteonics endoprosthetic head. We also questioned the need for implanting polyethylene in any prosthetic in which it is not
1240.e7
Fig. 4. All of the original components of the Osteonics endoprosthesis after being removed from our first patient.
being directly used for the bearing surface and questioned the rationale for the design. We used this particular design at our institution because it was part of our hospital contract and at the time did not realize the problems that would arise. Subsequently, Osteonics has not responded to our requests for information, and therefore, we cannot explain the reasoning for the design. We believe that these particular types of failures would have been significantly decreased in a comparable prosthesis with a purely metallic head. We feel there is an added risk of failure with the use of this prosthesis and plan on further investigating retrospectively within our patient population. This will help us to determine if there are more cases of failure with this particular prosthesis, as well as help delineate how significant these findings are. We no longer use this design and question its appropriateness.
References 1. Coleman SH. Failure of bipolar hemiarthroplasty: a retrospective review. Am J Orthop 2001;30:313. 2. Nishii TN. Bipolar cup design may lead to osteolysis around the uncemented femoral component. Clin Orthop 1995;316:112. 3. Rizzo M. Premature failure of a hip hemiarthroplasty secondary to osteolysis and aseptic loosening. Am J Orthop 2003;32:206. 4. Burroughs BR. Range of motion and stability in total hip arthroplasty with 28-, 32-, 38-, and 44-mm femoral head sizes. J Arthroplasty 2005;20:11. 5. Bhandari M. Internal fixation compared with arthroplasty for displaced fractures of the femoral neck. A meta-analysis. J Bone Joint Surg Am 2003; 85-A:1673. 6. Bray TJ. The displaced femoral neck fracture. Internal fixation versus bipolar endoprosthesis. Results of a prospective, randomized comparison. Clin Orthop 1988;230:127.
1240.e8 The Journal of Arthroplasty Vol. 23 No. 8 December 2008 7. Bjorgul K. Hemiarthroplasty in worst cases is better than internal fixation in best cases of displaced femoral neck fractures. Acta Orthop 2006;77:368. 8. Rogmark C. Primary arthroplasty is better than internal fixation of displaced femoral neck fractures: a meta-analysis of 14 randomized studies with 2,289 patients. Acta Orthop 2006;77:359. 9. Willert HG. The significance of wear and material fatigue in loosening of hip prostheses. Orthopade 1989;18:350. 10. Calton TF. Failure of the polyethylene after bipolar hemiarthroplasty of the hip: A report of five cases. J Bone Joint Surg Am 1998;80:420. 11. Ong BC. Unipolar versus bipolar hemiarthroplasty: functional outcome after femoral neck fracture at a
12.
13.
14.
15.
minimum of thirty-six months of follow-up. J Orthop Trauma 2002;16:317. Cornell CN. Unipolar versus bipolar hemiarthroplasty for the treatment of femoral neck fractures in the elderly. Clin Orthop 1998;348:67. Raia FJ. Unipolar or bipolar hemiarthroplasty for femoral neck fractures in the elderly? Clin Orthop 2003;414:259. Dalldorf PG. Rate of degeneration of human acetabular cartilage after hemiarthroplasty. J Bone Joint Surg Am 1995;77:877. Maloney WJ. Isolation and characterization of wear particles generated in patients who have had failure of a hip arthroplasty without cement. J Bone Joint Surg 1995;77:1301.