Distinctions of introarticular force distribution between genesis-II posterior stabilized and cruciate retaining total knee arthroplasty: An intraoperative comparative study of 45 patients

Highlights

• Total force was similar in the two common types of total knee arthroplasty.

• Force distribution differed in the two types of total knee arthroplasty.

• Force in posterior stabilized knees was concentrated in the medial compartment.

• Force in cruciate retaining knees was well balanced at mid-flexion.

• Force in cruciate retaining knees shifted to the lateral side at end flexion.

Abstract

Background

Although both the posterior stabilized and cruciate retaining total knee arthroplasty have been proven to effectively relieve pain and restore basic functions, the joint gap width during flexion was reported to be different due to the presence or absence of posterior cruciate ligament, which may lead to different intra-articular force distribution. In this study, we investigated the distinctions in intra-articular force distribution between the two types of TKA designs in patients with varus knee osteoarthritis.

Methods

Forty five patients (50 knees) with varus knee osteoarthritis were prospectively included, with each 25 knees receiving cruciate retaining and posterior stabilized total knee arthroplasty, respectively. With an intra-articular force measurement system, the intra-articular force distribution with knee flexion at 0°, 30°, 45°, 60°, 90°, and 120° were recorded in all patients.

Findings

The total force was similar for posterior stabilized and cruciate retaining knees at all flexion degrees. However, force in the medial compartment accounted for 59.8% –84.0% of total force in posterior stabilized knees, while 27.4% –65.7% in cruciate retaining knees. In cruciate retaining knees, no significant difference was found between forces in the two compartments at 30° flexion (P = 0.444), but force was significantly concentrated in the lateral side during 45° –120° flexion (P = 0.000– 0.028).

Interpretation

Although the entire intra-articular forces were similar between CR and PS knees at different flexion angles, medial part had higher force than lateral part when PS knee was used. The posterior cruciate ligament do a role in soft balance, and make the force more evenly distributed.

Introduction

Total knee arthroplasty has achieved great success in the treatment of end-stage knee joint disease (Berger et al., 2001, Keating et al., 2002, Kurtz et al., 2007). Accurate alignment and soft tissue balance are both prerequisites to satisfactory postoperative outcome (Sharkey et al., 2002). Although computer assisted surgery has achieved accurate intraoperative control of implant position, soft tissue imbalance remains to be one of the major reasons for early revisions after TKA (Fehring et al., 2001, Lonner et al., 1999, Sharkey et al., 2002). However, traditional methods of evaluating soft tissue balance mainly rely on surgeon's subjective judgment and personal experience, limiting the mathematical accuracy of soft tissue balancing (In et al., 2009, Lau et al., 2012, Mihalko et al., 2009).

Recently, there have been increasing interests in computer assisted soft tissue balancing techniques. Intra-articular sensing devices have been proven to effectively improve soft tissue balance, indicating that intra-articular force distribution sensitively reflects soft tissue tension surrounding the knee joint (Camarata, 2014, Gustke et al., 2014, Roche et al., 2014). A recent study reported that patients balanced with the orthosensor system were significantly more likely to obtain meaningful postoperative improvements in activity levels and satisfaction than unbalanced patients (Gustke et al., 2014).

Both the Posterior Stabilized (PS) TKA and the Cruciate Retaining (CR) TKA have been testified by long term follow-up studies for their effectiveness of reliving pain and restoring function (Berger et al., 2001, Keating et al., 2002, Kurtz et al., 2007). However, it has been pointed out that they were different in joint gap width during flexion (Asano et al., 2008, K. Hino et al., 2013, Matsumoto et al., 2011). It is still unknown whether these differences may lead to distinctions in force distribution.

In order to determine the differences in soft tissue balance of PS and CR-TKA, we asked two major questions: (1) In what patterns does the intra-articular force distribute in PS and CR total knee joints throughout flexion? (2) Are there any distinctions in the patterns of force distribution between the two designs of TKA?