ANATOMY REFRESHER Written by Dr Simon Kay, GP

and sports physician - adapted from an article which appeared in sportEX medicine magazine

Introduction

Although the knee appears to be fairly simple in having only one plane of movement, it is the most commonly severely injured joint in the lower limb, like the shoulder mostly due to its relative instability.

The function of the knee is to allow support of the body, particularly during propulsion, as well as to allow positioning of the torso near the ground, for example during squatting and sitting. Propulsion can either be moving the body, as in walking and running, or moving the foot allowing rapid acceleration of the foot as in kicking. So while it may seem to be a simple joint, the knee is responsible for a number of key and complex functions.

In this article we review the anatomy of the knee and the roles of the key structures. The online version which can be found at http://bit.ly/ REPsJournalDec10 - is brought to life by a series of animations taken from the award-winning 3D anatomy software produced by Primal Pictures.

Anatomy overview Bones and joints of the knee The knee consists of two joints: 1. The tibio-femoral joint which consists of the facets of the tibia which articulate with the femur. The joint is cushioned and stabilised by two avascular structures called the menisci. (See video 1 for an animation showing the movement of the tibia and femur) 2. The patella-femoral joint - a joint between shallow V-shaped facets on the back of the patella bone which articulate only with the femoral trough. The patella essentially acts as a fulcrum for the quadriceps muscle, travelling in front of the knee and inserting into the tibia, making it mechanically more efficient. (See video 2 for an animation showing the movement of the patella on the femur).

Note that the fibula pays no part in the articulation of the knee.

Ligaments The tibia is linked to the femur by two

www.exerciseregister.org The knee

Often the last time we studied anatomy was during our training. So we thought an animated refresher every now and again wouldn’t go amiss. Here is the knee, brought to life!

©2010 Primal Pictures Femur

Patello- femoral joint

Tibio- femoral joint

(behind patella)

Fibula

Menisci

Figure 1: Bones of knee (source Primal Pictures) Tibia

strong crossing ligaments – the anterior cruciate ligament (ACL) and the posterior cruciate ligament (PCL). Uncommonly for ligaments they have a good vascular supply. They are contained within the joint and covered by synovium. The ACL stops twist between the two bones and anterior glide of the tibia on the femur. The PCL also stops twist along with posterior glide of the tibia on the femur. Videos 3 and 4 show the stabalising role of the ACL and PCL.

In addition, the ACL and PCL are given additional support by the two lateral collateral ligaments. The medial collateral ligament connects the tibia to the femur and runs down the inside of the knee.

The lateral collateral ligament runs down the outside of the knee and originates from the tibia but attaches to the smaller fibular bone.

The neutral and the anatomical positions of the knee are the same, with the leg fully

Video 2: Patellofemoral tracking (animation from Primal Pictures)

extended in a straight line.

Movements of the knee Movement of the knee occurs in two main directions: l Flexion and extension (sagittal plane) l A small amount of rotation or twist.

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Video 1: Tibio-femoral joint motion (animation from Primal Pictures)