Contact forces in the tibiofemoral joint from soft tissue tensions: Implications to soft tissue balancing in total knee arthroplasty
Introduction
Total knee arthroplasty involves critical interaction with the soft tissues surrounding the knee to obtain a stable, well-functioning joint following surgery. The tension in these soft tissues controls the boundaries of laxity. At any angle of flexion, the soft tissues’ effect is determined by their initial tensions and their stiffnesses. After a total knee arthroplasty (TKA), achieving normal laxity and stability during function is an important consideration, made more difficult due to the resection of one or both cruciate ligaments in most total knee designs. This problem is evident because instability can lead to increased polyethylene wear (Kretzer et al., 2010) and remains an important reason for early failure after TKA surgery, responsible for 17–26% of the early revision surgeries (Dalury et al., 2013, Lee et al., 2014). These numbers are not surprising, given the complexity in compensating for the alteration and loss of stabilizing structures during insertion of the implant. Simultaneously, a correct component alignment needs to be assured (whether kinematic or mechanical is still under debate (Cherian et al., 2014)), taking into account cartilage wear and potential deformity in the bone morphology. A large number of variables are thus involved in this process: implant design, surgical technique, soft tissue tensioning and component positioning (Walker et al., 2014). This paper focuses on the soft tissues surrounding the articulating surfaces, consisting of purely passive structures (e.g. capsule and ligaments) and combined active-passive restraints (e.g. tendons and muscles).
Dominated by the ligaments, the soft tissues control the passive stability of the knee joint (Blankevoort et al., 1991, Halewood and Amis, 2015). As a result, the degree of (in)stability can be assessed at the time of surgery by evaluating the tension in and/or strain of the ligaments. Although results have been published in the literature, a direct evaluation of the ligament strain remains impractical in a surgical setting (Fleming et al., 2003). Alternatively, the ligament tension can be indirectly assessed by evaluating the contact loads in the tibiofemoral joint. More specifically, the load transferred through the medial and lateral compartment can be quantified using sensors that quantify the forces exerted by the femur at the level of the tibia. In the remainder of this paper, these loads are referred to as compartmental loads. Such approach has the advantage of additionally accounting for the tension created by other structures (e.g. capsule) and not narrowing down to tension in a (discrete) number of ligaments.
Nowadays, these compartmental loads can be assessed intra-operatively, for instance by using instrumented tibial trial components that quantify the tibiofemoral contact forces at the level of the tibia. Use of these sensors has the potential to restore physiological load balance and increase patient satisfaction following TKA surgery (Gustke et al., 2014a, Gustke et al., 2014b). Literature recommends compartmental load levels in the range of 90–180 N (20–40 lbs), with a constant magnitude through the flexion-extension range (Asano et al., 2004) and a limited load difference between the medial and lateral compartment (<67 N/15 lbs) (Gustke et al., 2014a, Gustke et al., 2014b). However, a fundamental basis for the identification of these target load levels is missing. In an attempt to identify loads that are representative of the native anatomical situation, this study presents a quantitative assessment of the compartmental load levels in a series of cadaveric non-arthritic knees.
Section snippets
Test specimens
A total of eight fresh frozen cadaveric specimens was used. The specimens consisted of full lower limbs including a hemi-pelvis. Prior to inclusion, the knees were assessed for osteoarthritis using X-rays. Only specimens with a Kellgren-Lawrence score below grade 2 were selected (Table 1). Three additional specimens were used for method development and data from a forth additional specimen was discarded because the sensor described below failed during testing.
Test setup
The full lower limb specimens, from
Varus/valgus alignment of the knee specimens
For each specimen, the coronal alignment was assessed during a thigh pull test. One specimen is in valgus (specimen 11) and two specimens are in pronounced varus (specimen 5 and 6). The other specimens are in near-neutral alignment (Table 2).
Absolute forces transmitted through medial and lateral compartment
The absolute forces transferred through the medial and lateral compartment are first evaluated. The average data and associated standard deviation for both the heel push and thigh pull experiments are presented in Fig. 3a and b. For the heel push test,
Discussion
The main objective of this paper was to identify target intra-articular loads that may serve as reference for restoration of compartmental loads in TKA surgery. The magnitude of these loads highly depend on how knee flexion was imposed. Furthermore, these loads are non-constant through the range of motion. Eventually, the clinical importance with respect to TKA surgery along with the main limitations of the study are addressed.
First, the focus is on how knee flexion was imposed. It was clearly
Conflict of interest
As mentioned in the acknowledgement section, the research department at which the research took place received an unrestricted research grant from: OrthoSensor Inc. To the authors’ opinion, the impact of this financial support to the results presented in this paper is negligible.
Acknowledgements
The research department at which the research took place received an unrestricted research grant from OrthoSensor Inc. To the authors’ opinion, the impact of this financial support to the results presented in this paper is negligible. The international mobility of the first author was supported the Fonds Wetenschappelijk Onderzoek (FWO – grant n° V444415N). The authors also wish to thank Daniel Hennessy, for the well appreciated help and suggestions in constructing the test setup.
References (28)
- et al.
Soft-tissue tension total knee arthroplasty
J. Arthroplasty
(2004) - et al.
Why are total knee arthroplasties being revised?
J. Arthroplasty
(2013) - et al.
Collateral ligament strains during knee joint laxity evaluation before and after TKA
Clin. Biomech.
(2013) - et al.
A new method for defining balance: promising short-term clinical outcomes
J. Arthroplasty
(2014) - et al.
Effect of joint laxity on polyethylene wear in total knee replacement
J. Biomech.
(2010) - et al.
Function of the medial meniscus in force transmission and stability
J. Biomech.
(2015) - et al.
Effects of surgical variables in balancing of total knee replacements using an instrumented tibial trial
Knee
(2014) - et al.
Recruitment of knee joint ligaments
J. Biomech. Eng. – Trans. ASME
(1991) - et al.
Mechanical, anatomical and kinematic axis in TKA: concepts and practical applications
Curr. Rev. Musculoskelet. Med.
(2014) - et al.
Gap balancing versus measured resection technique in total knee arthroplasty
Clin. Orthop. Surg.
(2014)
The effects of compressive load an knee joint toruqe on peak anterior cruciate ligament strains
Am. J. Sports Med.
Increased satisfaction after total knee replacement using sensor-guided technology
Bone Joint J.
Clinically relevant biomechanics of the knee capsule and ligaments
J. Knee Surgery Sports Traumatol. Arthrosc.
Tibiofemoral movement 1: the shapes and relative movements of the femur and tibia in the unloaded cadaver knee
J. Bone Joint Surg. Brit.
Cited by (48)
Functional knee apparatus for the evaluation of ligamentous tensions on contact loads
2022, KneeCitation Excerpt :Historically and conventionally, the characterization of the soft tissue coronal envelope is conducted without the use of sensing systems [8], indicating that the surgeon is unable to accurately quantify the effects of the soft tissue releases on either the value of the ligamentous tensions or the resulting contact knee loads. In recent years, instrumented tibial trial components have allowed for the indirect assessment of intraoperative ligamentous tensions through contact loads [3,8,17,18,23,24,25]. These sensors measure medial and lateral compartmental loads at the joint surface, providing surgeons with an approximation of “balance” of the surrounding soft tissues.
Extra-articular factors of the femur and tibia affecting knee balance in mechanically aligned total knee arthroplasty
2022, Orthopaedics and Traumatology: Surgery and ResearchThe medial gap is a reliable indicator for intraoperative soft tissue balancing in posterior-stabilized total knee arthroplasty
2021, KneeCitation Excerpt :Although the appropriate soft tissue balance is important, the extensive medial release to obtain a perfect rectangular gap in extension and flexion sometimes leads to irremediable medial instability, resulting in poor outcome [33,37]. The normal knee is medial tight and lateral lax [38,39] and the medial soft tissue length showed an isometric pattern [30]. Therefore, it is reasonable to maintain a constant medial gap throughout the whole arc of motion to keep the medial constraint and conformity.
Calipered Kinematically Aligned Total Knee Arthroplasty Closely Restores the Tibial Compartment Forces of the Native Knee
2021, Calipered Kinematically aligned Total Knee Arthroplasty: Theory, Surgical Techniques and PerspectivesIt Is Time to Consider a Philosophical Change From Mechanical to Kinematic Alignment
2021, Calipered Kinematically aligned Total Knee Arthroplasty: Theory, Surgical Techniques and Perspectives