Introduction

A tibial insert with choices in size, thickness, and posterior slope is proposed to improve ligament balancing in total knee arthroplasty. However, increasing posterior slope, or the angle between the distal and proximal insert surfaces, will redistribute ultra-high molecular weight polyethylene (UHMWPE) thickness in the sagittal plane, potentially affecting wear. This study used in-vitro testing to compare wear for a standard cruciate-retaining tibial insert (STD) and a corresponding 6° sloped insert (SLP), both manufactured from direct-compression molded (DCM) UHMWPE. Our hypothesis was slope variation would have no significant effect on wear.

Introduction

While clinically successful for decades, CR TKA is persistently compromised by inconsistent PCL function. Problems of mid-flexion instability, incomplete knee flexion, erratic kinematic behavior and posterior instability, not seen with PS devices, raise concerns about the consistency of the technique, and the devices used. Most TKA systems offer at least 2 different geometries of tibial inserts to address this clinical problem.

We hypothesize these problems are a result of compromise of PCL anatomy. To avoid compromise to the PCL 3 steps are required: 1) The slope of tibial resection must be less than 5°; 2) the depth of tibial resection must be based off the insertion footprint of the PCL, not the deficiencies of the tibial articular surface; and 3) the tibial insert must be modified to allow intraoperative balancing of the PCL.

We introduce a new technique called the “Posterior Cruciate Referencing Technique” (PCRT), a specific combination of surgical technique, devices and instrumentation. Careful anatomic preservation of the posterior cruciate ligament (PCL) based upon a specific reference point off the tibia allows for use of sloped tibial components to achieve consistent functional behavior of the PCL. We discuss the preclinical design and development leading to availability of this device, and subsequent early clinical experience with this approach.

Posterior cruciate ligament (PCL) retention in total knee arthroplasty (CR-TKA) has been a feature of certain styles of TKA since the inception of predictable TKA in the early 1970s. It has been adapted and promoted as advantageous for a number of real and theoretical benefits. In reality, however, PCL retention has proven inconsistent when applied across a broad range of surgical environments. A number of adaptations in surgical technique, device modification and instrumentation have been developed to try to improve the predictability of the surgical intervention and subsequent postoperative performance. It is our belief that currently recommended surgical techniques can lead to inconsistencies in surgical judgment and consequently performance of CR devices because they inadvertently compromise the anatomy and hence functional performance of the PCL. A study by Shannon et al showed that, during CR-TKA, the PCL was either partially or completely removed as a result of the tibial cut in two out of three cases [1]. Unlike the long held and validated approach of ligament releases for fixed New Technique for Functional Posterior Cruciate Retention in TKA varus and valgus deformity that, along with alignment, allow successful long 45 term outcomes, ligament release of the PCL to balance the knee in flexion, whether by bone cuts or physical release, may compromise its overall function and explain kinematic differences in expected versus observed performance. Our hypothesis is that devices, surgical techniques and instruments designed around anatomical and functional preservation of the PCL would promote a reproducible surgical approach and consistent clinical performance of a CR-TKA. This manuscript provides the rationale for development of a new technique called the “Posterior Cruciate Referencing Technique” (PCRT), a combination of technique, instruments and devices specifically designed to preserve the PCL anatomy and take advantage of the functional performance of the PCL. We discuss the anatomical, radiographic, kinematic and mechanical testing approach that suggests that this is a safe and effective approach for primary CR-TKA.

Conclusion: This manuscript presents a body of work that elucidates specific issues of implant design and technical implantation that may have led to inadvertent compromise of function of the PCL during CR-TKA. We believe that such compromises may explain the inconsistent kinematic behavior of these devices in the hands of surgeons who use them, and may result in clinical outcomes that were unintended. We have provided the rationale for a new technique of implantation the Posterior-Cruciate Referencing Technique (PCRT) -which mates specific referencing approaches of the PCL and tibial resection, with implants, to address PCL functional New Technique for Functional Posterior Cruciate Retention in TKA behavior. We have provided laboratory, pre-clinical and early clinical evaluations that suggest that this will prove a safe and effective approach to CR-TKA.

The aim of the study was to look at the concentrations of pro-inflammatory cytokines and soluble cell surface receptors including tissue factor (TF) in the drainage fluid and in the serum after retransfusion. TF is a membranous glycoprotein from the surface of fibroblasts or smooth muscle cells of vessels that functions as a receptor for the coagulation factor VII/VIIa (Kobayashi 1998)

ELISAs were used in twelfve patients to measure the concentrations of interleukins (IL-1β, IL-2, IL-6, IL-8), tumor necrosis factor-a as well as of soluble cell surface receptors (sIL-2Ra, sHLA-DR) and of TF.

All pro-inflammatory cytokines were released into the drainage fluid at increasing concentrations, IL-6 and IL-8 thereby exceeding postoperative systemic blood levels by 200-fold or 80-fold, respectively. Reinfusion of the collected shed blood led to a further increase in both the IL-6 and IL-8 serum concentrations, which were found to be elevated already postoperatively. sHLA-DR was found in an about 100-fold excess vs. serum. The concentration of TF in the drainage fluid was five times higher (158±71 pg/ml) than in serum. There was no increase of the serum of sHLA-DR or TF levels following the retransfusion.

IL-6 and IL-8 seem to be responsible for potential febrile reactions. The 100-fold elevated concentration of sHLA-DR in shed blood could therefore represent a physiological tissue level. The high TF-levels in the shed blood could be related to a local tissue damage. Dilution effects of fluid retransfused may be responsible for minor or no changes of cytokines, soluble cell surface receptors and TF in the circulation