Advancements in cruciate retaining total knee arthroplasty

When it comes to cruciate retaining (CR) total knee arthroplasty, the majority of tibial resections result in at least partial compromise of the posterior cruciate ligament (PCL), despite the best efforts of experienced orthopaedic surgeons¹. To retain the function of the PCL, one must pay close attention to preserving its anatomy and avoid releasing PCL fibers - either directly by surgical releases or indirectly by increasing the slope of the tibial resection.

A fundamental shift in approach to CR knees
Optetrak CR Slope® is an advanced technique and implant system that enables surgeons to plan and perform a cruciate retaining total knee replacement based on the anatomical integrity of the posterior cruciate ligament. There has been much discussion about the theoretical advantages of retaining the PCL, and the orthopaedic community has recognised that consistently achieving PCL retention is not always possible. Optetrak CR Slope is redefining PCL retention, by allowing surgeons to:²

• Identify and protect anatomical integrity of the PCL
• Balance the flexion and extension gaps independently
• Improve predictability and consistency of knee kinematics through Posterior Cruciate Referencing Technique
• Preserve bone and soft tissue with no additional resections necessary
• Perform consistent and reproducible tibial bone cuts
• Accommodate variability in patients' anatomies with a selection of implant geometries.

Identify the PCL
To address the clinical challenges CR surgeons face, the Optetrak CR Slope design team conducted an MRI study with two goals in mind: (1) to consistently identify the origins of the PCL in both the femur and the tibia and (2) to define the resulting “joint space” depending on the posterior slope of the proximal tibial cut^3,4.

The study revealed that a reference point at the base of the ligament's tibial attachment could be consistently identified and measured over a variety of knee sizes and geometries. Additionally, the vertical distance between the PCL femoral insertion and the planned proximal tibial cuts was measured. The data revealed that if the surgeon performed the proximal tibial cut according to the natural posterior slope with the PCL tibial insertion as a reference, the resultant tibial cut could be insufficient (less than 9mm) joint space for the implant components. If the surgeon needed to increase the slope and depth of the proximal tibial resection to open up the flexion space, the PCL integrity was most often compromised.

The results of the study led to the development of an advanced operative technique and instrumentation through which the PCL is used as the reference point and a tibial cut is made according to a neutral slope.

Posterior Cruciate Referencing Technique
Traditional CR operative techniques reference the tibial plateaus and often try to recreate the natural slope of the tibia. This approach can lead to a compromise of the PCL in the process^5-9.

By referencing the PCL and using it as a landmark to guide the tibial resection, Optetrak's advanced operative technique and unique instrumentation enable you to consistently protect the PCL and preserve bone.

Unique instruments, including the Adjustable PCL Stylus and No-Touch PCL Retractor, facilitate the technique. The No-Touch PCL Retractor protects both the PCL and resected surface of the distal femur. The Adjustable PCL Stylus is placed at the tibial insertion point of the PCL. The Adjustable PCL Stylus allows surgeons to set their tibial resection level so that they may also ensure that PCL fibers are not damaged during tibia resection.

How to make the balancing act easy
The space between the flexion and extension gaps is often compromised during total knee arthroplasty and must be balanced when trialing the implants.

To achieve a well-balanced knee, Optetrak CR Slope enables surgeons to accommodate the variability in the angle of the tibial surface resulting from resection of the tibia. Optetrak CR Slope provides a selection of tibial inserts with varying posterior tibial slopes, in addition to choices in size and thickness.

Trials and inserts with increased posterior angulation, including a standard slope, CR Slope+ and CR Slope++ allow you to balance the flexion gap, reducing the need for soft tissue releases, partial PCL releases or additional tibial bone cuts. The Optetrak CR Slope tibial inserts allow surgeons to adjust and titrate the tension of the PCL so that the system performs in conjunction with the articular geometry of the Optetrak CR femoral component. CR Slope has been designed to aid surgeons in balancing the flexion and extension gaps in scenarios such as these:

• In instances where the tension of the PCL is adequate or loose in extension yet tight in flexion, a CR Slope+ or CR Slope++ insert should be used during trialing to balance the gaps.
• In instances where the tension of the PCL is loose in both extension and flexion, the poly insert should be exchanged for one of a thicker dimension.
• In instances where the tension of the PCL is adequate in flexion yet loose in extension, a thicker CR Slope+ or CR Slope++ insert should be used to balance the gaps.

A comprehensive knee system
While advancing the art of cruciate retention, Optetrak CR Slope retains all the proven design elements of the Optetrak comprehensive knee system, which has been evolving for more than a quarter of a century. Its lineage began with a concept developed at Hospital for Special Surgery in New York, USA. Successive designs, guided by clinical and laboratory data, demonstrated 91-99 percent long-term implant survival rates^10-17.

The Optetrak comprehensive knee system addresses surgeons' concerns for contact stress, patellar tracking, polyethylene wear, joint stability and bone preservation. The advantage of evolving the cruciate retaining design within the Optetrak family is that we retain all of the qualities of the Optetrak system.

References

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2. Covall DJ, Stulberg BN, Mabrev J, Burstein AH, Angibaud LD, Smith K, Zadzilka JD. Introducing a new technique for improving predictability in cruciate-retaining total knee arthroplasty: the posterior cruciate referencing technique. Techniques in Knee Surgery. 2009 Dec; 8(4):271-5.
3. Mabrey J, Covall D, Stulberg B, Burstein A, Angibaud L. Vertical separation distance of the bony insertions of the posterior cruciate ligament as a function of the posterior tibial slope - an MRI study, Deutscher Kongress fur Orthopadie and Unfallchirurgie (DKOU), Berlin. Oct 2009.
4. Data on file at Exactech, Inc.
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