Arthritis & Rheumatism, Volume 62,
November 2010 Abstract Supplement

Abstracts of the American College of
Rheumatology/Association of Rheumatology Health Professionals
Annual Scientific Meeting
Atlanta, Georgia November 6-11, 2010.


Lateral Compartment Unloading in People with Medial Knee Osteoarthritis.

Kumar,  Deepak, S. Rudolph,  Katherine, Manal,  Kurt

Background:

It is well known that people with medial knee osteoarthritis (MKOA) exhibit high knee adduction moments (KAM) during walking. Investigators have speculated that a failure to generate sufficient muscle force to counter high external loads could result in the lateral femoral condyle lifting off the tibia. Lateral condular lift-off has not been confirmed by modeling techniques that account for subject specific EMG patterns, kinematics and kinetics. The aims of this study are (1) to estimate articular loads in people with MKOA using an EMG-driven model and, (2) to examine the relationship between passive laxity, varus malalignment, functional knee instability (FKI) and loading patterns.

Methods:

16 MKOA and 12 control (C) subjects walked while kinematic, kinetic and EMG data were collected. Muscle forces and moments were calculated from an EMG-driven model previously described. Loading of the medial and lateral compartments were calculated by balancing the internal/external moments at the knee. One walking trial was used to optimize the model parameters and the average of 3 separate trials was used to predict articular loading during stance. Functional Knee Instability (FKI) was assessed from the Knee Outcome Survey. Stress radiographs were used to assess frontal laxity and long cassette radiographs were used to assess alignment. ANOVAs and Pearson's correlation coefficients comprised the statistical analyses.

Results:

MKOA subjects walked more slowly and had greater laxity, static and dynamic varus alignment, less flexion and greater KAM than controls. Loading, when normalized to BW was no different between the groups but MKOA subjects had greater absolute medial load than C and maintained a greater %total load on the medial compartment. Lateral compartment unloading during mid-late stance was observed in 50% of OA subjects which was related to greater KAM, dynamic varus alignment and FKI but not to laxity or static malalignment. MKOA subjects with lateral joint unloading had lower hamstring force and lower force in the lateral muscles.

Discussion:

Loading for C subjects matched that measured from instrumented knee prostheses, supporting the veracity of the model. Speculations about greater medial loading in people with MKOA are confirmed with our data, as well as, the phenomenon of lateral condylar lift-off. It was interesting that the unloading did not occur during weight acceptance phase when the loads are greatest but rather occurred during mid-late stance when the knee experiences its greatest varus angulation. The relations between unloading to FKI rather than laxity or malalignment suggest that it is due to a failure of neuromuscular strategies and not only mechanical factors. This was confirmed by the muscle force data where we found that MKOA subjects who showed unloading, had poor quadriceps-hamstring and medial-lateral muscle force balance resulting from lower hamstring and lateral muscle forces. These data support the need for neuromuscular retraining interventions for people with MKOA that address loading and FKI rather than quadriceps strengthening alone.

To cite this abstract, please use the following information:
Kumar, Deepak, S. Rudolph, Katherine, Manal, Kurt; Lateral Compartment Unloading in People with Medial Knee Osteoarthritis. [abstract]. Arthritis Rheum 2010;62 Suppl 10 :190
DOI: 10.1002/art.27959

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