SPORTS INJURIES REFRESHER KNEE JOINT

THE KNEE JOINT – AN INTRODUCTION TO ASSESSMENT AND DIAGNOSIS

BY DR SIMON KAY, GP

ANATOMY OVERVIEW The knee consists of two joints: 1. the main joint - the tibio-femoral joint which consists of the facets of the tibia which articulate with the two congruent surfaces on the femur, cushioned and stabilised by two avascular structures, the mensici

2. the patella-femoral joint - a joint between shallow V-shaped facets on the back of the patella 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. Note that the fibula pays no part in the articulation of the knee. The tibia is linked to the femur by

two 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 (see Online extras panel at the end of the article for videos).

The neutral and the anatomical positions of the knee are the same with the leg fully extended in a straight line.

MOVEMENTS OF THE KNEE Movement of the knee occurs in two main directions: n Flexion and extension (sagittal plane) n A small amount of rotation or twist. This rotation is to allow the knee to ‘unlock’ before flexion can occur.

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The knee 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, propulsion, plus allowing positioning of the torso near the ground as in 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.

Femur ©2010 Primal Pictures

Patello- femoral joint

(behind patella)

Tibio- femoral joint

Menisci Fibula Tibia

The gastrocnemius muscles also aid knee flexion when the foot is fixed. Man can stand straight upright on his legs because the facets of the tibia and femur lock to stabilise the joint in full extension, minimising muscle activity. Please note that hamstring injuries are not be addressed by this article (please refer to previous articles published in sportEX for this topic). Usually the pain from the muscle injury is more significant than the effect on knee flexion.

The stability of the knee joint is a due to the array of ligaments connecting the tibia and femur and the very strong muscles surrounding the joint which are activated in response to tensions within the ligaments. It is the ligaments which not only

Figure 1: The joints of the knee

MUSCLE MOVEMENTS Different muscle groups are involved in movement of the knee.

1. Knee flexion - hamstring muscles ie. semi-tendinosus, semi-membranosus and biceps femoris with some help from the accessory muscle, popliteus, which unlocks the knee prior to flexion. 2. Knee extension - quadriceps muscles ie. rectus femoris, vastus lateralis, vastus medialis and vastus intermedialis.

hold the two bones together, but also tighten when they are stretched, firing off stretch receptors which allows the spinal reflexes to contract the appropriate muscle to avoid excess movement. This is the main reason why arthritis occurs if a patient has a deficient ACL ligament after injury because the disarticulation and excess movement within the knee leads to minor trauma and ultimately osteoarthritis.

As in the shoulder, eccentric movements of the prime movers slow 7