Neuromuscular Control of Abnormal Shear Forces in Patients with Early Osteoarthritis of the Knee

Gary Sutton, DPT, MS, SCS, OCS, ATC, CSCS; Susan Blair, MS, PT; Katherine E. Webb MEd, ATC; Leah Taylor, DPT, CSCS; George Masiello, BSEET; William Nordt, MD

Introduction

Osteoarthritis (OA) of the knee is a common diagnosis affecting a large and growing portion of the population. The medial compartment of the knee is a site recognized for initial deterioration of articular cartilage defining the diagnosis of OA.  (Sharma, et al, 2010)  Uncontrolled shear forces across the knee either causing, or in the presence of faulty alignment of the knee and hip speed the progression of the disease.  (Sharma, et al, 2008)  Hip abductor muscle weakness has been cited as a factor in increased external knee adduction moment, an indirect measure of medial knee compartment loading.  (Chang, et al, 2005)  Data show that as little as a one-unit increase in external knee adduction moment is associated with up to a 6.5-fold increase in the risk of disease progression.  ( Miyazaki, et al, 2002)

Few studies have looked at a supervised exercise program focused on controlling hip and knee alignment in an effort to reduce forces on the medial compartment of the knee.  (Bennell, et al, 2010)

The purpose of this research is to examine the influence of a novel exercise program emphasizing hip and knee alignment in neutralizing excessive shear forces at the knee in patients with early osteoarthritis.  The authors hypothesize that patients completing this novel exercise program will demonstrate decreased knee symptoms as well as reduced shear forces at the knee while performing selected functional activities.  While traditional rehabilitation programs have demonstrated success in decreasing symptoms associated with OA of the knee this pilot study as part of  a larger cohort research design will examine the influence of knee and hip motor control strategies on improving alignment and decreasing shear forces as these factors relate to disease progression.

Methods

Seven subjects with either unilateral or bilateral early knee degeneration (Kellgren-Lawrence grade I or II) with or without patello-femoral pain for a total of ten knees were included in the study. Informed consent as well as descriptive data including age, sex, height, weight, and focused medical history were obtained on the initial visit. The subjects’ ages ranged from 40 to 66 years. Subjects were evaluated twice in the Motion Analysis Laboratory (baseline and post-treatment following 12 physical therapy sessions over an 8 week period). Three-dimensional kinematics and kinetics were measured at the hip and knee while the subjects walked at self-determined speeds across a force plate, performed a modified Star Excursion Balance test (Kinzey, 1998), and ascended/descended an eighteen centimeter step. Subjects completed the Knee Injury and Osteoarthritis Outcome Score (KOOS) and SF-36 inventories at baseline and post-treatment.

Physical therapy evaluation involved measures of knee PROM, AROM, MMT via strap-stabilized dynamometry of bilateral lower extremity muscles, standing Q angles, and graded performance of a movement screen.  The movement screen included bilateral comparisons of single leg stance, holding a “warrior II” yoga pose, hip hinge, full squat, and bench skip on a ten centimeter step.