- Email: [email protected]
The posterior-stabilized knee—No post required
Author's Accepted Manuscript
The Posterior Stabilized Knee-No Post Required Brian P. Dahl M.D., FAWM, Aaron A. Hofmann M.D.
www.elsevier.com/locate/sart
PII: DOI: Reference:
S1045-4527(15)00085-1 http://dx.doi.org/10.1053/j.sart.2015.08.007 YSART50648
To appear in: ĆSeminars in Arthroplasty
Cite this article as: Brian P. Dahl M.D., FAWM, Aaron A. Hofmann M.D., The Posterior Stabilized Knee-No Post Required, ĆSeminars in Arthroplasty , http://dx.doi.org/10.1053/j.sart.2015.08.007 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
The Posterior Stabilized Knee-No Post Required
Brian P. Dahl M.D., FAWM Orthopaedic Fellow Hofmann Arthritis Institute 24 So. 1100 E, Suite 101 Salt Lake City, UT 84102 (801) 355-6468
Aaron A. Hofmann M.D. Hofmann Arthritis Institute Director – Center for Precision Joint Replacement 24 So. 1100 E, Suite 101 Salt Lake City, UT 84102 (801) 355-6468
Contact Author Brian P. Dahl, M.D., FAWM Hofmann Arthritis Institute 24 S 1100 E Suite 101 Salt Lake City, UT 84102 (801)355-6468 – phone (801)355-3450 – fax [email protected]
Abstract: The goal of total knee arthroplasty is to provide the patient with a stable, painless knee. The modern total joint orthopaedist has many options to help achieve stability through cruciate retaining and posterior stabilized implants. Over the lifespan of the implant eventual posterior cruciate ligament instability can make an otherwise well-functioning cruciate retaining implant fail. The drawback of many posterior stabilized implants include the need for more bone resection and the noisy clunk of the polyethylene post contacting the femoral component. The use of an ultracongruent polyethylene liner is an effective way to achieve stability with a cruciate sacrificing method.
Keywords: Total Knee Arthroplasty, TKA, Ultracongruent, Cruciate Substituting
Introduction: The total knee arthroplasty (TKA) is one of the most successful surgeries performed in orthopaedics today. Advances in their design and the materials used such as highly cross-linked polyethylene has prolonged the life of the bearing surface and allowed younger patients to enjoy a pain free TKA. Despite much progress, there is room for improvement in the complications associated with both cruciateretaining and posterior stabilized knee designs. Early posterior cruciate ligament (PCL) incompetence after placement of cruciate retaining prosthesis likely occurs more frequently than it is reported in the literature1. This complication associated exclusively with cruciate retaining designs can lead to pain, persistent effusions, and incapacitating flexion instability1. Dislocation of the posterior stabilized TKA and dissatisfaction with posterior stabilized implants due to the noise associated with the post are also concerns. Anterior-lipped, deep dish styled polyethylene inserts have remedied these problems with great success. For the purpose of this paper we will refer to them as ultracongruent. It has been
suggested that the ultracongruent design may avoid the complications observed with the posterior stabilized design2.
Discussion: The senior author began using ultracongruent inserts in the early 90s. At that time, many surgeons were making a switch to posterior stabilized TKA components regardless of the integrity of the PCL. Though the literature has not indicated a superiority of either design, it enabled surgeons to open fewer trays at the start of each case if the PCL was insufficient. The improved consistency of using one type of femoral component has the advantage of familiarity for those surgeons who perform fewer total knees. Unfortunately, posterior stabilization components have specific disadvantages. The prevalence of post fracture, patellar clunk, and intercondylar fracture are known to those surgeons already utilizing a posterior stabilized component. The impingement of the post and cam mechanism in a posterior stabilized design creates a point of increased stress that can lead to catastrophic failure years after implantation3. The advent of highly cross linked polyethylene in the last decade has increased the theoretical risk of tibial post fracture due to the increased stiffness of the polyethylene4. The ultracongruent insert has no additional point of articulation when compared to conventional cruciate retaining design, reducing additional sources of wear as well as mechanisms for failure. Its stability is based on the increased height of the anterior aspect of the insert, as well as the increased conformity with respect to the femoral component. Post noise is another annoying associated with the posterior stabilized design. Although not necessarily a complication some patients are distracted and concerned about the metal-on-plastic clicking caused by contact between the post and the cam mechanism. This is most often pronounced when firing the hamstrings as the patient attempts to rise from a seated position. There is no treatment for this, requiring frustrated patients to live with the annoyance.
Patellar clunk is a painful and palpable shift of the patella during extension of the knee from a flexed position greater than 45 degrees. It is caused by a supra-patellar soft tissue nodule that impinges in the elongated P.S. intracondylar notch of the femoral component5,6. This phenomenon is almost exclusively associated with posterior stabilized knees. Ultracongruent inserts have not been implicated in this particular complication. Surgical ablation of the painful nodule results in resolution of symptoms. Occasionally, revision of the patellar component may be necessary. Changing the polyethylene from a posterior stabilized to ultracongruent design is not currently a recommended treatment for this complication. A more serious complication related to the posterior stabilized design is an intracondylar fracture. Although this is a potential complication with any total knee design, the box cut necessary for a posterior stabilized implant removes more bone than conventional implants and increases the risk for iatrogenic fracture7. Bone preservation is a tenant of joint arthroplasty and bony cuts should be kept to a minimum unless increased constraint or stability is required. In cases of revision TKA, the femoral stem necessitates the box cut for added stability and is recommended in these cases. As more of these complications have become associated with the posterior stabilized design, the popularity of ultracongruent polyethylene inserts has begun to rise. Though there are many potential benefits associated with the use of ultracongruent inserts in the form of avoidance of complications, most literature has been focused on functional and clinical outcome comparisons between ultracongruent and posterior stabilized designs. Intraoperative kinematics differ between the two groups due to the fundamental difference in design. The post articulation with the femoral component in posterior stabilized TKAs creates a forced femoral roll back mechanism in order to substitute the natural PCL. The ultracongruent insert has been found to create paradoxical anterior translation of the femur during flexion by as much as 10.8 degrees8. Despite differences in kinematics, the functional outcomes, range of motion, and patient satisfaction have been found to be the same in multiple
studies8,9,10. Long term stability is seen in both designs without the risk of early PCL insufficiency from cruciate retaining implants10. A recent publication noted an increase in revision rates with cruciate retaining designs when compared to ultracongruent components11.There has been no evidence of superiority of posterior stabilized over ultracongruent TKAs in multiple studies12. A theoretical decrease in complications is not the only reason to use ultracongruent inserts. Intraoperative efficiency is very important and every reasonable chance to decrease blood loss, operative time, and cost will benefit the patient and the community as a whole. Switching from a posterior stabilized design to an ultracongruent insert on a conventional TKA has been shown to improve all three parameters by eliminating the necessary box cut13.
Conclusion: Ultracongruent polyethylene inserts provide cruciate substituting stability without many of the drawbacks of conventional posterior stabilized inserts. Outcomes based on function have been shown to be equivalent to the posterior stabilized inserts and may reduce blood lose and operative time. Most implant companies offer ultracongruent polyethylene inserts with their modern TKA designs. The use of an ultracongruent design is well suited for most patients in need of a primary TKA. No post is required.
Disclosure: Consultant: Zimmer Inc.
References: 1. Waslewski GL, Marson BM, Benjamin JB: Early, incapacitating instability of posterior cruciate ligament-retaining total knee arthroplasty. 7:763-767, 1998 2. Chaidez-Rosales PA, Briseno-Estrada CA, Aguilera-Zepeda JM, et al: Total knee arthroplasty with ultracongruent tibial insert. Two-year follow-up. Acta Ortop Mex. 1:17-20, 2011 3. Clarke HD, Math KM, Scuderi GR: Polyethylene post failure in posterior stabilized total knee arthroplasty. J Arthroplasty 19:652–657, 2004 4. Chakrabarty G, Vashishtha M, Leeder D: Polyethylene in knee arthroplasty: A review. J Clin Orthop Trauma 2:108-12, 2015 5. Yau WP, Wong JW, Chiu KY, et al: Patellar clunk syndrome after posterior stabilized total knee arthroplasty. J Arthroplasty 18:1023-8, 2003 6. Hozack WJ, Rothman RJ, Booth RE, Balderston RA: The patellar clunk syndrome: a complication of posterior stabilized total knee arthroplasty. Clin Orthop Relat Res 241:203–208, 1989 7. Lombardi AV, Mallory T, Waterman R, Eberle R: Intercondylar distal femoral fracture: an unreported complication of posterior-stabilized total knee arthroplasty. J Arthroplasty 10:643– 650, 1995 8. Kim TW, Lee SM, Seong SC, et al: Different intraoperative kinematics with comparable clinical outcomes of ultracongruent and posterior stabilized mobile-bearing total knee arthroplasty. Knee Surg Sports Traumatol Arthrosc; Jan 8:(Epub ahead of print), 2015 9. Lützner J, Firmbach FP, Lützner C, et al: Similar stability and range of motion between cruciateretaining and cruciate-substituting ultracongruent insert total knee arthroplasty. Knee Surg Sports Traumatol Arthrosc 6:1638-1643, 2015 10. Hofmann AA, Tkach TK, Evanich CJ, et al. Posterior stabilization in total knee arthroplasty with use of an ultracongruent polyethylene insert. J Arthroplasty 5:576-583, 2000
11. Peters C, Mulkey P, Erickson J, et al. Comparison of Total Knee Arthroplasty with Highly Congruent Anterior-stabilized Bearing versus a Cruciate-retaining Design. CORR 472(1):175-80, 2014 12. Parsley BS, Conditt MA, Bertolusso R, et al: Posterior cruciate ligament substitution is not essential for excellent postoperative outcomes in total knee arthroplasty. J Arthroplasty 21:127131, 2006 (suppl) 13. Scott DF, Smith RR: A prospective, randomized comparison of posterior stabilized versus cruciate-substituting total knee arthroplasty: A preliminary report with minimum 2-year results. J Arthroplasty 29:179-81, 2014 (suppl)
The Posterior Stabilized Knee-No Post Required Brian P. Dahl M.D., FAWM, Aaron A. Hofmann M.D.
www.elsevier.com/locate/sart
PII: DOI: Reference:
S1045-4527(15)00085-1 http://dx.doi.org/10.1053/j.sart.2015.08.007 YSART50648
To appear in: ĆSeminars in Arthroplasty
Cite this article as: Brian P. Dahl M.D., FAWM, Aaron A. Hofmann M.D., The Posterior Stabilized Knee-No Post Required, ĆSeminars in Arthroplasty , http://dx.doi.org/10.1053/j.sart.2015.08.007 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
The Posterior Stabilized Knee-No Post Required
Brian P. Dahl M.D., FAWM Orthopaedic Fellow Hofmann Arthritis Institute 24 So. 1100 E, Suite 101 Salt Lake City, UT 84102 (801) 355-6468
Aaron A. Hofmann M.D. Hofmann Arthritis Institute Director – Center for Precision Joint Replacement 24 So. 1100 E, Suite 101 Salt Lake City, UT 84102 (801) 355-6468
Contact Author Brian P. Dahl, M.D., FAWM Hofmann Arthritis Institute 24 S 1100 E Suite 101 Salt Lake City, UT 84102 (801)355-6468 – phone (801)355-3450 – fax [email protected]
Abstract: The goal of total knee arthroplasty is to provide the patient with a stable, painless knee. The modern total joint orthopaedist has many options to help achieve stability through cruciate retaining and posterior stabilized implants. Over the lifespan of the implant eventual posterior cruciate ligament instability can make an otherwise well-functioning cruciate retaining implant fail. The drawback of many posterior stabilized implants include the need for more bone resection and the noisy clunk of the polyethylene post contacting the femoral component. The use of an ultracongruent polyethylene liner is an effective way to achieve stability with a cruciate sacrificing method.
Keywords: Total Knee Arthroplasty, TKA, Ultracongruent, Cruciate Substituting
Introduction: The total knee arthroplasty (TKA) is one of the most successful surgeries performed in orthopaedics today. Advances in their design and the materials used such as highly cross-linked polyethylene has prolonged the life of the bearing surface and allowed younger patients to enjoy a pain free TKA. Despite much progress, there is room for improvement in the complications associated with both cruciateretaining and posterior stabilized knee designs. Early posterior cruciate ligament (PCL) incompetence after placement of cruciate retaining prosthesis likely occurs more frequently than it is reported in the literature1. This complication associated exclusively with cruciate retaining designs can lead to pain, persistent effusions, and incapacitating flexion instability1. Dislocation of the posterior stabilized TKA and dissatisfaction with posterior stabilized implants due to the noise associated with the post are also concerns. Anterior-lipped, deep dish styled polyethylene inserts have remedied these problems with great success. For the purpose of this paper we will refer to them as ultracongruent. It has been
suggested that the ultracongruent design may avoid the complications observed with the posterior stabilized design2.
Discussion: The senior author began using ultracongruent inserts in the early 90s. At that time, many surgeons were making a switch to posterior stabilized TKA components regardless of the integrity of the PCL. Though the literature has not indicated a superiority of either design, it enabled surgeons to open fewer trays at the start of each case if the PCL was insufficient. The improved consistency of using one type of femoral component has the advantage of familiarity for those surgeons who perform fewer total knees. Unfortunately, posterior stabilization components have specific disadvantages. The prevalence of post fracture, patellar clunk, and intercondylar fracture are known to those surgeons already utilizing a posterior stabilized component. The impingement of the post and cam mechanism in a posterior stabilized design creates a point of increased stress that can lead to catastrophic failure years after implantation3. The advent of highly cross linked polyethylene in the last decade has increased the theoretical risk of tibial post fracture due to the increased stiffness of the polyethylene4. The ultracongruent insert has no additional point of articulation when compared to conventional cruciate retaining design, reducing additional sources of wear as well as mechanisms for failure. Its stability is based on the increased height of the anterior aspect of the insert, as well as the increased conformity with respect to the femoral component. Post noise is another annoying associated with the posterior stabilized design. Although not necessarily a complication some patients are distracted and concerned about the metal-on-plastic clicking caused by contact between the post and the cam mechanism. This is most often pronounced when firing the hamstrings as the patient attempts to rise from a seated position. There is no treatment for this, requiring frustrated patients to live with the annoyance.
Patellar clunk is a painful and palpable shift of the patella during extension of the knee from a flexed position greater than 45 degrees. It is caused by a supra-patellar soft tissue nodule that impinges in the elongated P.S. intracondylar notch of the femoral component5,6. This phenomenon is almost exclusively associated with posterior stabilized knees. Ultracongruent inserts have not been implicated in this particular complication. Surgical ablation of the painful nodule results in resolution of symptoms. Occasionally, revision of the patellar component may be necessary. Changing the polyethylene from a posterior stabilized to ultracongruent design is not currently a recommended treatment for this complication. A more serious complication related to the posterior stabilized design is an intracondylar fracture. Although this is a potential complication with any total knee design, the box cut necessary for a posterior stabilized implant removes more bone than conventional implants and increases the risk for iatrogenic fracture7. Bone preservation is a tenant of joint arthroplasty and bony cuts should be kept to a minimum unless increased constraint or stability is required. In cases of revision TKA, the femoral stem necessitates the box cut for added stability and is recommended in these cases. As more of these complications have become associated with the posterior stabilized design, the popularity of ultracongruent polyethylene inserts has begun to rise. Though there are many potential benefits associated with the use of ultracongruent inserts in the form of avoidance of complications, most literature has been focused on functional and clinical outcome comparisons between ultracongruent and posterior stabilized designs. Intraoperative kinematics differ between the two groups due to the fundamental difference in design. The post articulation with the femoral component in posterior stabilized TKAs creates a forced femoral roll back mechanism in order to substitute the natural PCL. The ultracongruent insert has been found to create paradoxical anterior translation of the femur during flexion by as much as 10.8 degrees8. Despite differences in kinematics, the functional outcomes, range of motion, and patient satisfaction have been found to be the same in multiple
studies8,9,10. Long term stability is seen in both designs without the risk of early PCL insufficiency from cruciate retaining implants10. A recent publication noted an increase in revision rates with cruciate retaining designs when compared to ultracongruent components11.There has been no evidence of superiority of posterior stabilized over ultracongruent TKAs in multiple studies12. A theoretical decrease in complications is not the only reason to use ultracongruent inserts. Intraoperative efficiency is very important and every reasonable chance to decrease blood loss, operative time, and cost will benefit the patient and the community as a whole. Switching from a posterior stabilized design to an ultracongruent insert on a conventional TKA has been shown to improve all three parameters by eliminating the necessary box cut13.
Conclusion: Ultracongruent polyethylene inserts provide cruciate substituting stability without many of the drawbacks of conventional posterior stabilized inserts. Outcomes based on function have been shown to be equivalent to the posterior stabilized inserts and may reduce blood lose and operative time. Most implant companies offer ultracongruent polyethylene inserts with their modern TKA designs. The use of an ultracongruent design is well suited for most patients in need of a primary TKA. No post is required.
Disclosure: Consultant: Zimmer Inc.
References: 1. Waslewski GL, Marson BM, Benjamin JB: Early, incapacitating instability of posterior cruciate ligament-retaining total knee arthroplasty. 7:763-767, 1998 2. Chaidez-Rosales PA, Briseno-Estrada CA, Aguilera-Zepeda JM, et al: Total knee arthroplasty with ultracongruent tibial insert. Two-year follow-up. Acta Ortop Mex. 1:17-20, 2011 3. Clarke HD, Math KM, Scuderi GR: Polyethylene post failure in posterior stabilized total knee arthroplasty. J Arthroplasty 19:652–657, 2004 4. Chakrabarty G, Vashishtha M, Leeder D: Polyethylene in knee arthroplasty: A review. J Clin Orthop Trauma 2:108-12, 2015 5. Yau WP, Wong JW, Chiu KY, et al: Patellar clunk syndrome after posterior stabilized total knee arthroplasty. J Arthroplasty 18:1023-8, 2003 6. Hozack WJ, Rothman RJ, Booth RE, Balderston RA: The patellar clunk syndrome: a complication of posterior stabilized total knee arthroplasty. Clin Orthop Relat Res 241:203–208, 1989 7. Lombardi AV, Mallory T, Waterman R, Eberle R: Intercondylar distal femoral fracture: an unreported complication of posterior-stabilized total knee arthroplasty. J Arthroplasty 10:643– 650, 1995 8. Kim TW, Lee SM, Seong SC, et al: Different intraoperative kinematics with comparable clinical outcomes of ultracongruent and posterior stabilized mobile-bearing total knee arthroplasty. Knee Surg Sports Traumatol Arthrosc; Jan 8:(Epub ahead of print), 2015 9. Lützner J, Firmbach FP, Lützner C, et al: Similar stability and range of motion between cruciateretaining and cruciate-substituting ultracongruent insert total knee arthroplasty. Knee Surg Sports Traumatol Arthrosc 6:1638-1643, 2015 10. Hofmann AA, Tkach TK, Evanich CJ, et al. Posterior stabilization in total knee arthroplasty with use of an ultracongruent polyethylene insert. J Arthroplasty 5:576-583, 2000
11. Peters C, Mulkey P, Erickson J, et al. Comparison of Total Knee Arthroplasty with Highly Congruent Anterior-stabilized Bearing versus a Cruciate-retaining Design. CORR 472(1):175-80, 2014 12. Parsley BS, Conditt MA, Bertolusso R, et al: Posterior cruciate ligament substitution is not essential for excellent postoperative outcomes in total knee arthroplasty. J Arthroplasty 21:127131, 2006 (suppl) 13. Scott DF, Smith RR: A prospective, randomized comparison of posterior stabilized versus cruciate-substituting total knee arthroplasty: A preliminary report with minimum 2-year results. J Arthroplasty 29:179-81, 2014 (suppl)