October 2013

Investigating OA: Studies revisit underlying variables

In the moment: Knee

10ITMknee-iStock24183345smBy Jordana Bieze Foster

Knee osteoarthritis researchers are taking a closer look at the factors that influence knee adduction moment (KAM) and also considering the contributions of sagittal plane variables, as illustrated by studies presented in September at the American Society of Biomechanics (ASB) annual meeting in Omaha, NE.

The knee-ground reaction force (GRF) lever arm is a stronger predictor of KAM after arthroscopic partial meniscectomy (APM) than frontal plane GRF magnitude and therefore might be a desirable focus for interventions to prevent or delay the development of knee osteoarthritis in these patients, according to research from the University of Melbourne in Australia.

Investigators performed a secondary analysis of gait data from an earlier study in which 65 individuals with isolated medial APM demonstrated a statistically significant 9% increase in KAM two years after surgery. The secondary analysis revealed that the two-year change from baseline of the knee-GRF lever arm, calculated as the perpendicular distance between the frontal plane GRF vector and knee joint center of rotation, accounted for 29% of the variance in KAM increase. The change in frontal plane GRF magnitude accounted for 14% of the variance.

“We might have more of a chance to decrease knee adduction moment if we can decrease the lever arm,” said Michelle Hall, a graduate student in the Sports Medicine Research Program at the University of Melbourne, who presented her group’s findings at the ASB meeting.

Although the majority of knee osteoarthritis studies use KAM as a surrogate marker for knee loading, a study from Stanford University in Stanford, CA, suggests that knee flexion moment could also be a clinically important marker for osteo­arthritis progression.

Researchers analyzed the gait of 18 female patients with medial tibiofemoral compartment knee osteoarthritis (mean Kellgren-Lawrence grade of 2.3) at baseline; they also obtained magnetic resonance (MR) images of the affected knees at baseline and after five years.

They found that baseline knee flexion moment significantly predicted changes in medial tibial cartilage at five years, whereas baseline knee adduction moment did not.

“Knee adduction moment and knee flexion moment really should both be considered in patients with medial compartment knee osteoarthritis,” said Eric F. Chehab, a graduate student in the department of bioengineering at Stanford, who presented the findings at the ASB meeting.

Sagittal plane variables may also influence the effect of lateral wedging in patients with medial knee osteoarthritis, according to research from the Kessler Foundation Research Center in West Orange, NJ.

Investigators took weight-bearing MR images of the knee in 12 individuals with medial tibiofemoral knee osteoarthritis wearing custom shoes with external nylon heel wedges that could be rotated to provide 0° or 5° of lateral wedging.

At 20° of knee flexion, the wedge condition was associated with an anterior migration of the lateral compartment that approached significance when compared to the no-wedge condition; the same effect was not seen at 0° of flexion.

“Because ankle dorsiflexion accompanies knee flexion, that decrease in ankle mobility may have increased transmission of forces upward,” said Peter J. Barrance, PhD, an assistant professor in the Department of Physical Medicine & Rehabilitation at Rutgers New Jersey Medical School in Newark, who presented the findings at the ASB meeting.

Study participants were not screened for foot type or other variables associated with responsiveness to lateral wedging, which may have contributed to the variability and the lack of statistical significance in the results, Barrance noted.

Sources:

Hall M, Wrigley TV, Metcalf BR, et al. A longitudinal study of the knee adduction moment components post-arthroscopic partial meniscectomy. Presented at the American Society of Biomechanics 2013 Annual Meeting, Omaha, NE, September 2013.

Hall M, Wrigley TV, Metcalf BR, et al. A longitudinal study of strength and gait following arthroscopic partial meniscectomy. Med Sci Sports Exerc 2013 Jun 22. [Epub ahead of print]

Chehab EF, Favre J, Erhart-Hledik JC, Andriacchi TP. Knee flexion moment during walking influences medial compartment cartilage thickness in patients with knee osteoarthritis. Presented at the American Society of Biomechanics 2013 Annual Meeting, Omaha, NE, September 2013.

Barrance PJ, Gade V, Allen J, Cole JL. Tibiofemoral contact location changes associated with lateral heel wedging – a study using weightbearing MRI. Presented at the American Society of Biomechanics 2013 Annual Meeting, Omaha, NE, September 2013.

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6 Responses to Investigating OA: Studies revisit underlying variables

  1. Harvey Johnson says:

    Another lateral wedge study. When are researchers and clinicians going to realize that it’s internal rotation caused by pronation that is the driver of medial and lateral joint pain/DJD? Pronation also increases femoral hip adduction. Why did these researcher leave out the obvious? How about adding a 5 degree medial wedge to the study and see what happens? I’ll put my custom medial wedged motion control shock absorbent orthotics up against all medial and lateral knee compartment DJD/arthritis and bet the farm on the results. Lateral plantar wedges translate most of their energy and affect mostly the subtalar joint and ankle mortice which then translates up the closed chain via the GRF. When those forces hit the knee its game over and then adding the adduction moment to the hip and it just gets worse.

  2. Lucy Best says:

    When hip adduction is increased, assuming width of walking base remains constant, then the knee valgus force increases, i.e medial joint is off-loaded.

  3. tim witoski says:

    Harvey I agree that that the bulk of the altered GRF created by a lateral wedge is directed to the sub talar joint but just to be clear on your line of thought I ask you the following.
    Are you saying that your “custom medial wedged motion control shock absorbent orthotics” can reduce medial compartment OA pain? How does that work, a medially posted foot orthosis will induce a supinatory force or more realistically decrease pronation which by any measure will create a mild varus force at the knee level and therefore not at all aid in reducing medial compartment joint pain….

  4. Harvey Johnson says:

    Yes I am saying “custom medial wedged motion control shock absorbent orthotics” can reduce medial compartment OA pain”. I have been doing it for decades. I am not creating a “supinatory force”. I am reducing pronation, reducing internal rotation of the tibia/knee and femur, reducing adduction at the hip via pronation control and attenuation of shock in the GRF. If you want to effectively open the medial knee compartment, assuming you have the ligamentous laxity available,then use a knee orthosis with a 1st class lever arm. Pronation and subsequent internal rotation of the tibia/knee/femur (+hip adduction) is the problem in DJD. It is the reason the person got DJD in the first place.
    If you agree that the bulk of a lateral wedge is directed at the STJ then what is the biomechanical consequence of a lateral wedge?

  5. Harvey Johnson says:

    Lucy Best says “When hip adduction is increased, assuming width of walking base remains constant, then the knee valgus force increases, i.e medial joint is off-loaded”.
    1. Not necessary as you need joint laxity (MCL) to allow the joint to open.
    2. Increased hip adduction further increases internal rotation through the condylar surface of the knee. Rotational forces through the knee joint are destructive.

  6. Harvey Johnson says:

    From the study which proves my point “At 20° of knee flexion, the wedge condition was associated with an anterior migration of the lateral compartment that approached significance when compared to the no-wedge condition; the same effect was not seen at 0° of flexion.
    “Because ankle dorsiflexion accompanies knee flexion, that decrease in ankle mobility may have increased transmission of forces upward,”
    What do you get with increased pronation? Dorsiflexion of the ankle with internal rotation. Actually there is an increase moment/lever arm when you laterally wedge the STJ . What happens here is that the ankle/tibia maximally internally rotates both in total motion as well as velocity with the lateral wedge.
    What do you get with increased hip adduction? Increase of knee flexion.
    The greater the knee flexion the more anterior migration (internal rotation) of the lateral compartment. Without the lateral wedge they did not see the excessive migration of the lateral knee compartment.

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