Document Title: Yoshimura-AJSM-Nov03.shtml
Article Title: The Effect of Wedged Insoles on the Lateral Thrust of Anterior Cruciate Ligament-Insufficient Knees
Authors: Ichiro Yoshimura, MD, Masatoshi Naito, MD, Michiya Hara, MD and Jingfan Zhang, MD
Publication: American Journal of Sports Medicine, Baltimore, Maryland
Date: November 2003
Volume 31, pages 999-1002
Keywords: knee biomechanics, valgus thrusting, osteoarthritis, degeneration, shoe-insert wedges.

(Reference-denoting numbers appear in the same font and point size as the document text. As with all Knee Library documents, this article is provided in full-text form, complete with all figures and tables.)

Comments: This article describes an intriguing concept: instead of costly OA braces, simply put a wedge-shaped insole (in this case, a lateral-wedge one) in the shoe. The Discussion section of this article is absolutely superb and very insightful, since it describes the effect of ACL rupture on knee biomechanics -- and thus it enunciates points which are highly relevant to anyone with any ACL-injury history (irrespective of whether accompanied by osteoarthritic changes). The authors note that, when the ACL is fully torn, the tensile stresses in the lateral structures increase five-fold. This causes them to stretch out, and is a major reason why prompt reconstruction of a fully torn ACL is very wise. The abnormal stress distribution also means osteoarthritic changes in the articular cartilage can be expected, particularly if meniscal damage is also present. Keep in mind that ACL-tearing incidents are almost invariably accompanied by ancillary damage such as meniscal tearing, articular-cartilage damage via bone-bruising, or both. So, clearly, delaying the reconstruction means more long-term problems. The authors also note that the ACL functions as a secondary restraint to varus-valgus torque, and thus assists the collateral ligaments (MCL and LCL), especially at full extension. With all these aspects in mind, using lateral-wedge-shaped insoles to redistribute these loadings in an ACL-deficient-and-subsequently-osteoarthritic knee intuitively makes sense, and the authors describe their findings. Note that similar biomechanical advantages can be obtained by using a sideways-forcing osteoarthritis-type knee brace. Additionally, such a brace, if well-designed, would provide protection against injurious sideways forcing and hyperextension (just like a standard functional brace does). Such protection is extremely desirable for an ACL-deficient knees in particular, but is not available with shoe-insert wedges. Also, keep in mind that shoe-insert wedges must act through the ankle; such forcing could eventually result in problems in the ankle joints. Keep in mind that shoe-insert wedges might increase the risk of ankle injuries. These wedges would also cause accelerated wear at the edges of one's shoe soles, which could result in the user having to repair or replace his/her shoes frequently.

ABSTRACT

Background: Patients with untreated anterior cruciate ligament insufficiency often develop osteoarthritis. In Japan, laterally or medially elevated insoles have been widely used for the relief of symptoms associated with unicompartmental osteoarthritis of the knee.

Hypothesis: The use of a valgus wedge in the shoe of a patient with anterior cruciate ligament insufficiency will decrease lateral thrust.

Study Design: Controlled laboratory study.

Methods: An accelerometer was used to measure thrust force in 60 control knees and 35 knees with anterior cruciate ligament insufficiency. The sensor was attached to the affected and the control anterior tibial tubercles to record motion in the medial-lateral and perpendicular directions. The lateral thrust immediately after heel strike was measured continuously by a telemeter under stabilized walking conditions. Measurements were made both with and without wedged insoles.

Results: When compared with the control knee, the peak value of lateral acceleration immediately after heel strike was significantly greater in the anterior cruciate ligament-insufficient knees. However, lateral thrust decreased significantly in the anterior cruciate ligament-insufficient knees when a wedged insole was used.

Conclusions: Use of an insole resulted in a significant decrease in lateral thrust, even in anterior cruciate ligament-insufficient knees.

Clinical Relevance: Use of an insole is one possible prophylaxis for osteoarthritis for an anterior cruciate ligament-insufficient knee.

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