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Medical Reports & Case Studies 2022, Vol.7, Issue 1, 003-004 Commentary Article
A Review of Knee Polyethylene Geometry Design - Progression to Constraining
Barrett C*, Barrett T, Testa EJ, Garcia D, Antoci V
Department of Orthopaedic Surgery, Warren Alpert School of Medicine, Brown University, Providence, RI, USA
Corresponding Author* on the cam-mechanism [9]. The ultracongruent insert is characterized by
a high anterior wall and a deeper trough which allows for posterior stability
Valentin Antoci without the cam-mechanism, ultimately reducing wear [10]. Decreased
Associate Professor of Orthopedics wear of ultracongruent inserts was also made possible with the creation
Department of Orthopaedic Surgery, Warren Alpert School of Medicine, of highly cross-linked polyethylene. Conventional polyethylene has been
Brown University, Providence, RI, USA credited as a common cause of revision TKA due to insert particle wear
Tell: 401-270-0105 [11]. Subsurface cracking of conventional polyethylene inserts due to
E-mail: valentin.antoci@gmail.com compressive and tensile loads release particles into the joint space
inciting periprosthetic inflammation. Over time this can lead to osteolysis
Copyright: 2022 Barrett C, et al. This is an open-access article distributed and ultimate implant failure [12,13] Studies have indicated that highly
under the terms of the Creative Commons Attribution License, which permits crosslinked polyethylene has greater wear resistance, making it ideal for
unrestricted use, distribution, and reproduction in any medium, provided the use in ultracongruent inserts [14].
original author and source are credited. The Sigma Curved Plus (Cvd+) insert became commercially available in
2004 and follows the design features of other ultracongruent inserts [15].
Our study looked at the difference in outcomes for patients who received
Received: 5 Jan 2022; Manuscript No. M-50370; Editor assigned: 19- Jan-2022, either the Sigma Cvd or Cvd+ polyethylene inserts during TKA. 68 patients
Pre QC No. mrcs-22-51656 (PQ); Reviewed: 23- Jan-2022, QC No. were retrospectively reviewed during the study with SF-12 MCS, SF-12
mrcs-22-51656; Revised: 28-Jan-2022, Manuscript No. mrcs-22-51656 (R); PCS, KOOS, KOOS-Pain and KOOS-ADL data assessed both pre-and post-
Published: 29-Jan-2022, DOI: 10.4172/2572-5130.1000177 operatively. For each outcome measure the absolute improvement (AI)
Introduction along with the percentage of maximal possible improvement (%MPI) were
calculated and the difference in primary outcomes, AI, and %MPI between
The ideal articulating surface in total joint design is difficult to CVD and CVD+ inserts determined using two-sample t-tests. The results
determine. In total hip arthroplasty, the variability of bearing surfaces of the study indicated that the only statistically significant difference
used and the grandiosity of their subsequent failures has generated between the CVD and CVD+ designs was that the CVD design had a greater
much discussion, press, litigation, and catastrophic patient impact. The improvement in KOOS-pain scores for both AI and %MPI. The increased
original hip designs used natural surfaces such as ivory. The Charnley level of pain for the ultracongruent design could indicate a kinematic
total hip arthroplasty started with the use of Teflon which failed rapidly disparity. Despite this finding, further investigation is required as the bias
due to erosion, failing mechanical properties, and associated granulomas of a single surgeon retrospective study could have led to ultracongruent
[1,2]. High density polyethylene was initially researched against Sir John insert designs being utilized for higher complexity cases [16].
Charnley’s wishes, who was then convinced after data showing wear of It is well documented in the literature that the use of ultracongruent
less than 1/2000 of an inch over the first two days, which was far less than polyethylene inserts in PCL-sacrificing TKA provides statistically similar
previously used Teflon [3]. Modern highly crosslinked polyethylene shows outcomes to patients who underwent PCL-sparing knee replacement.17
wear rates even better than that, with radio stereometric analysis showing The improved wear profile of the ultracongruent highly crosslinked
yearly wear of less than 0.06 and as low as 0.005 mm. Even though most polyethylene insert compared to the posterior stabilized insert indicates
wear studies are performed in the hip, some of the data extrapolates the that the prior is the preferred choice in PCL-sacrificing TKA.
findings for the knee.
Polyethylene has been the gold standard for the articulating surface Despite the annual number of total knee replacements predicted to
in total knee arthroplasty implants since their original design in the 1970s increase 40% by 2040, roughly 20% of patients are not satisfied with their
following principles outlined by Freeman et al [4]. Unlike the hip where a lot surgical outcome [18,19]. While the design and kinematic movement of
of attention has been focused on the mechanical properties of polyethylene, implants have improved with innovations like the ultracongruent insert,
the geometry of the articulation is of significant importance in the total these statistics demonstrate a need for continued development of
knee arthroplasty design. From its conception to the modern day, there has implants which better mimic the native knee. Instability of the knee joint
been significant evolution in the geometry of the polyethylene insert. In and reduced range of motion are common complaints following TKA and
the late 20th century early stages of design such as the duocondylar and most likely stem from a difference in kinematics between the implant and
geometric prosthesis, polyethylene was used as a flat tibial component patient’s native knee [20]. Studies have indicated that posterior stabilized
[5]. The introduction of anterior and posterior lips of the polyethylene tibial inserts are associated with a “paradoxical motion” during active motion
component came about with the design of the total condylar implant, and and this phenomenon has been linked to post-surgical complications
the basic mechanics of this early prosthetic are now utilized in modern including instability, pain, and poor range of motion [21].
implants [6]. Current attempts to address this “paradoxical motion” and better mimic
Continued optimization of the polyethylene insert seeks to better the native physiology in implant design have focused on the anatomy of the
replicate native knee kinematics as well as provide constraint. The use medial and lateral compartments. Medial pivot polyethylene inserts have
of posterior stabilized symmetric inserts, such as the Sigma Curved (Cvd) been designed with a more concave and congruent medial compartment
design, have been successful in mimicking native knee movement for and a shallower lateral compartment that displays less conformity [22].
patient’s retaining their posterior cruciate ligament (PCL). These symmetric The deeper medial compartment transfers a greater percentage of the
inserts have shown high patient satisfaction and longevity following total patient’s body weight to the medial side, improving stability between full
knee arthroplasty (TKA) [7]. Despite the success of these symmetric extension and deep flexion. While some research has indicated that medial
inserts, increasing revision numbers have prompted further research pivot inserts provide patients with improved post-surgical outcomes,
of alternate insert designs to address instability and range of motion further investigation comparing medial pivot polyethylene inserts with
issues. Asymmetric inserts, which differ geometrically from symmetric other designs is needed to provide significant evidence [23,24].
inserts in their proximal surface came about with the development of the With over one hundred and fifty total knee implants on the market
mobile bearing TKA implant. These asymmetric polyethylene inserts were today, companies and surgeons continue to optimize implant design for
introduced to improve stability for patients following TKA [8]. better functional outcomes following surgery. There is strong interest
To address issues of instability in patients with deficient or focused on modifications to the polyethylene insert of the implant, with
deteriorated PCLs, the development of the ultracongruent insert occurred. recent advancements in wear properties (highly cross-linked polyethylene)
Originally posterior stabilized implants were utilized in these cases, but and geometric design (ultracongruent and medial pivot inserts). Ultimately
due to the nature of their design there was a high risk of polyethylene wear as developments are made, the focus will remain on creating a total knee
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Medical Reports & Case Studies 2022, Vol.7, Issue 1, 003-004 Barrett, et al.
implant which best replicates the kinematics of a patient’s native knee Polyethylene Tibial Inserts at Short-term."
joint. Clin Orthop Relat Res. 474.1
(2016):107-116.
References 14. Thiele, K., et al. "Current failure mechanisms after knee arthroplasty
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Cite this article: Barrett C, Barrett T, Testa EJ, et al. A Review of Knee Polyethylene Geometry Design - Progression to Constraining. Med Rep
Case Stud. 2022, 07 (1), 003-004.
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