Is a dual pivot bearing more effective than a medial pivot bearing in TKA?
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Dual pivot is best
Total knee replacement attempts to alleviate pain and improve function. Despite advances in surgical techniques and biomaterials, there continue to be multiple studies reporting patient dissatisfaction rates of 10% to 25%.
It is generally assumed that the surgical target of TKR is to replicate the kinematics of the native non-diseased knee. The traditional belief of knee kinematics was that the knee pivoted along the medial aspect of the tibia, while the lateral side demonstrated more sliding motion. While this is may be true in activities of deep knee flexion, this is not the case in activities of early flexion, such as running and walking. In these high-demand activities, the center of rotation is based along the lateral compartment of the knee. The dual pivot knee is an articulation that provides conformity in the lateral compartment during early flexion with a transition to a medial pivot in deeper knee flexion. The goal of this design is to allow early posterior translation along the medial aspect of the knee in early flexion with conformity of the lateral compartment. This kinematic pattern has been shown to occur in the non-diseased knee and offers the potential advantage to replicate more normal kinematics following TKR.
Alternatives to a dual pivot knee, outside of the historic posterior stabilized and cruciate-retaining knee, include an “ultracongruent” design or a “medial pivot” design. While both of these articulations may assist with sagittal plane stability, these do not consistently replicate normal knee kinematics. Ultracongruent designs demonstrate medial and lateral compartment conformity throughout the entire range of motion. While this conformity may decrease polyethylene stress, the conformity can also result in the failure of femoral external rotation in deep flexion and result in subsequent decreased motion. The medial pivot designs are effectively a ball-in-socket design that result in a medial pivot during the entire range of motion. The downside to this design is that this does not allow the early posterior translation of the medial femoral condyle during early flexion as observed in the native knee. Clinically, the kinematic pattern of early lateral pivot followed by medial pivot in deeper flexion have been shown to result in the greatest patient satisfaction and functional scores.
- References:
- Hoshino Y, et al. Knee Surg Sports Traumatol Arthrosc. 2012;doi:10.1007/s00167-011-1731-6.
- Meneghini RM, et al. J Arthroplasty. 2017;doi:10.1016/j.arth.2017.04.050.
Scott M. Sporer, MD, is a professor of orthopedic surgery at Rush University Medical Center in Chicago.
Medial pivot is more effective
Medial pivot bearing is significantly more effective than an ultracongruent bearing. Dual pivot is not a bearing design concept, in my opinion. It is more of a single manufacturer’s attempt to stand apart in a relatively homogenous market. Outside of designer’s series and theoretical models, dual pivot has not been shown to be a more effective bearing in TKA. Medial pivot is, by definition, a medial ball-in-socket articulation. Without having a spherical medial condyle, any other design is simply medially congruent, and these are not the same. It is important to understand that the ultracongruent bearing was designed nearly 40 years ago by Aaron A. Hofmann, MD, to address anterior posterior instability in an otherwise cruciate-retaining, J-curve femoral design. The use of ultracongruent now 40 years later still has the same goal: To provide better anterior posterior stability without the use of a cam and post. This is, however, not anatomic. The results of ultracongruent in many series, including our own, show superiority over posterior stabilized and cruciate-retaining bearing types. The actual stability is not the same as with a true medial pivot or medial sphere. The medial pivot has shown improved outcomes when compared with cruciate-retaining and posterior stabilized knees, particularly when performed with kinematic alignment. These improved results are a direct result of improved stability through the ball-in-socket and resultant improved kinematics. A dual pivot bearing is simply a different way to think about medial congruent and better than ultracongruent in stair climbing, but significantly worse getting up from a chair and zero overall difference in patient-reported outcome measures. Simply put, a true medial pivot or sphere, meaning ball-in-socket, when placed using kinematic alignment techniques, is more effective than ultracongruent or dual pivot bearings in TKA. We have shown a significant reduction in the need for manipulation, and faster and greater improvement in range of motion with medial sphere compared with ultracongruent.
- References:
- Alexander JS, et al. Surg Technol Int. 2022;doi:10.52198/22.STI.41.OS1641.
- Kaneda K, et al. Arthoplast Today. 2021;doi:10.1016/j.artd.2021.10.004.
- Kulshrestha V, et al. Clin Orthop Surg. 2022;doi:10.4055/cios21091.
- Scott DF, et al. J Bone Joint Surg Am. 2023;doi:10.2106/JBJS.22.00549.
- Pastolka B, et al. Clin BioMech. 2022;doi:10.1016/j.clinbiomech.2022.105667.
Keith R. Berend, MD, is a senior partner at JIS Orthopedics and chief medical development officer at OrthoAlliance.
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