Elsevier

Clinical Biomechanics

Volume 28, Issue 3, March 2013, Pages 285-290
Clinical Biomechanics

Increasing posterior tibial slope does not raise anterior cruciate ligament strain but decreases tibial rotation ability

https://doi.org/10.1016/j.clinbiomech.2013.01.011Get rights and content

Abstract

Background

It was investigated whether the strain of the anterior cruciate ligament and tibial kinematics are affected by increasing posterior tibial slope.

Methods

9 human cadaveric knee joints were passively moved between full extension and 120° flexion in a motion and loading simulator under various loading conditions and at 0°, 5°, 10° and 15° posterior tibial slope angles. The anterior cruciate ligament strain and the tibial rotation angle were registered. To assess the influence of posterior tibial slope on the anterior cruciate ligament strain at a fixed flexion angle the anterior cruciate ligament strain was recorded at three different flexion angles of 0°, 30° and 90° while continuously increasing the osteotomy angle from 5° to 15°.

Findings

The anterior cruciate ligament strain was either not affected by the posterior tibial slope angle or, in some load cases, was decreased for increasing posterior tibial slope (P < 0.05). There was a significant decrease of tibial rotation when the posterior tibial slope was increased to 15° for many of the load cases tested (P < 0.05). The mean maximum decrease was from 17.4° (SD 5.7°) to 11.2° (SD 4.7°) observed for flexion-extension motion under 30 N axial load in combination with an internal rotation moment.

Interpretation

The hypothesis that increasing posterior tibial slope results in higher anterior cruciate ligament strain was not confirmed. However, knee kinematics were affected in terms of a reduced tibial rotation. From a biomechanical point of view the data do not support the efficacy of sagittal osteotomies as performed to stabilize anterior cruciate ligament deficient knees.

Introduction

High tibial osteotomy has been performed as a treatment for knee osteoarthritis to correct varus deformity for many years. The long term success of the traditionally performed closed-wedge osteotomy has been proven by different authors (Akizuki et al., 2008, Amendola and Bonasia, 2010, Benzakour et al., 2010, Koshino, 2010). As major advantages of the open-wedge osteotomy compared to the closed-wedge osteotomy have been described medial open-wedge osteotomy has become the treatment of choice to correct varus deformity. The open-wedge technique avoids fibular osteotomy with the risk of malunion, dissection of the peroneal nerve and detachment of the tibialis anterior muscle (Lobenhoffer et al., 2004, Luites et al., 2009, Song et al., 2010).

Additionally, open-wedge osteotomy allows the correction of knee deformity in the sagittal plane as well. On lateral radiographs the mean tibial slope of the knee is 10° (SD 3°) (Dejour and Bonnin, 1994, Genin et al., 1993). It has been postulated by different authors that the posterior tibial slope (PTS) is a major factor affecting anterior–posterior knee stability (Dejour et al., 1994, Giffin et al., 2004, Giffin et al., 2007, Hernigou et al., 1987, Kostogiannis et al., 2011, Rodner et al., 2006, Terauchi et al., 2011, Todd et al., 2010). This is supported by radiographic studies that showed a linear relationship between PTS and tibial translation (Bonnin and Chambat, 2004, Dejour and Bonnin, 1994). Liu and Maitland found a relation between anterior tibial translation and posterior tibial slope in anterior cruciate ligament (ACL) deficient knees. Anterior tibial displacement increased from 9.1 mm for a tibial slope angle of 4° to 15.2 mm for a tibial slope angle of 12° (Liu and Maitland, 2003).

Several biomechanical studies have shown that increasing the posterior slope of the tibial plateau shifts the resting position of the tibia anteriorly and therefore causes a change in knee kinematics and thus affecting the distribution of contact pressure (Agneskirchner et al., 2004, Fening et al., 2008, Giffin et al., 2004). Rodner et al. described similar findings in ACL deficient knee joints (Rodner et al., 2006).

Giffin et al. found an anterior shift in the resting position, which was accentuated under axial loads, but no increased translation under anterior tibial shear loads after increasing the tibial slope (Giffin et al., 2004). From these results they concluded that decreasing slope may be protective in an ACL-deficient knee.

Brandon et al. found in a radiographic study an association between increased PTS and anterior translation and tensioning of the ACL. This may cause ACL laxity and rupture (Brandon et al., 2006).

In the literature there is conflicting evidence whether an increased tibial slope is a risk factor for noncontact injury of the ACL (Todd et al., 2010). Whereas the results of the study of McLean et al. supported the concept that the PTS is an important risk factor, Meister et al. did not find an increased slope to be a risk factor for noncontact injury of the ACL (McLean et al., 2011, Meister et al., 1998).

As a higher PTS can potentially result in an anterior shift of the tibia this can possibly influence in situ forces on the anterior cruciate ligament. Different authors have therefore recommended operative correction of the PTS to improve joint stability (Agneskirchner et al., 2004, Giffin et al., 2004, Giffin and Shannon, 2007, Imhoff et al., 2004). But the relation between tibial slope and ACL strain and its influence on joint stability is still poorly understood.

Although there are several studies evaluating the effect of PTS on sagittal stability, the role of the PTS on rotational stability has not been studied to the same extent. A positive pivot shift is clinically used to assess rotational instability, Brandon et al. and Voos et al. showed an association between increased PTS and higher pivot shift grades (Brandon et al., 2006, Voos et al., 2012).

The hypothesis of this biomechanical in vitro study was that increasing tibial slope would result in increased strain of the ACL and hence increased risk of failure. We additionally hypothesized that increasing tibial slope would influence knee kinematics.

Section snippets

Methods

Posterior slope angles of 5°, 10° and 15° were created in 9 human cadaveric knee joints (South East Tissue Alliance, Gainesville, Florida) by osteotomizing the tibiae proximally of the tuberositas tibiae and fixing the osteotomy in the respective slope angle with an external fixator. Based on results of a study on the influence of tibial slope on anterior tibial translation (Dejour et al., 1994) an a-priori power analysis (d = 3.3, α = 0.05; 1-β = 0.8; ∂ = 4.04; t = 2.78) was performed to calculate the

Results

The mean ACL strain amplitude defined as difference between maximally and minimally occurring strain during flexion–extension cycles, ranged between 2.8 and 6.1% depending on the load case (Fig. 4). Increasing the posterior tibial slope up to 15° did not lead to statistically significant alteration of ACL strain in most of the load case. However, the ACL strain amplitude significantly decreased under an external rotation moment, when stepwise increasing the slope angle from 0° to 15° (Fig. 4).

Discussion

In contrast to the first postulated hypothesis of this study, increasing the posterior tibial slope by up to 15° did not increase anterior cruciate ligament strain under none of the tested loading conditions. Increasing the posterior tibial slope, however, affected knee kinematics in terms of a reduced extent of tibial rotation during flexion–extension cycles in most of the load cases tested, which confirmed the second hypothesis of this study.

Giffin et al. examined knee kinematics in ten

Conclusion

The results of the present study suggest that an increased posterior tibial slope does not result in increased strain of the ACL. Therefore, from a biomechanical point of view, osteotomies performed to correct the tibial slope as carried out by some clinicians to stabilize ACL deficient knees might not be effective. In addition, increasing tibial slope can reduce the extent of tibial rotation up to 5° during a knee joint flexion exercise, which may not be desirable and at this time is of

Acknowledgement

We kindly acknowledge the assistance of Patrizia Horny in preparing the illustrations.

References (35)

  • H. Dejour et al.

    Tibial translation after anterior cruciate ligament rupture. Two radiological tests compared

    J. Bone Joint Surg. Br.

    (1994)
  • H. Dejour et al.

    Anterior cruciate reconstruction combined with valgus tibial osteotomy

    Clin. Orthop. Relat. Res.

    (1994)
  • L. Dürselen et al.

    The influence of muscle forces and external loads on cruciate ligament strain

    Am. J. Sports Med.

    (1995)
  • L. Dürselen et al.

    Anterior knee laxity increases gapping of posterior horn medial meniscal tears

    Am. J. Sports Med.

    (2011)
  • S.D. Fening et al.

    The effects of modified posterior tibial slope on anterior cruciate ligament strain and knee kinematics: a human cadaveric study

    J. Knee Surg.

    (2008)
  • P. Genin et al.

    The tibial slope. Proposal for a measurement method

    J. Radiol.

    (1993)
  • J.R. Giffin et al.

    The role of the high tibial osteotomy in the unstable knee

    Sports Med. Arthrosc.

    (2007)
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