Myotendinous Junction

Original Editor - Lucinda hampton

Top Contributors - Lucinda hampton  

Introduction

MTJ structure

Myotendinous junction (MTJ) is a part of the myotendinous unit, which connects muscle and tendon, and transmits forces between them.

The MTJ has a unique morphology with a highly folded muscle membrane filled with invaginations of collagen fibrils from the tendon. This creates an increased area of force transmission between muscle and tendon and, as a result, disperses the energy of a contracting muscle decreasing focal stress.

During muscle activity and mainly during high effort exercise, large forces are transmitted from muscle fibers to the tendon through the MTJ. It is a common location for strain injuries in sports. Most of these can be prevented by heavy eccentric exercise.

The surface area between muscle and tendon is enlarged by foldings of tendon into muscle, and this reduces stress between the tissues.

• In animals, the size and number of foldings are increased as a response to heavy training and reduced during inactivity.
• In humans, the muscle fibers near the MTJ show very high rates of remodeling compared to other regions of the muscle.

Physiotherapy Implications

Dissection of the gastrocnemius–soleus MTJ

In a healthy adult, the MTJ is the weakest region of the myotendinous unit and for that reason it is its most commonly injured part (the myotendinous unit consisting usually of bone, enthesis, tendon, myotendinous junction and muscle).

• The highest risk of strain occurs in large pennate muscles that cross two joints and produce large tensile forces e.g. biceps femoris, quadratus femoris, biceps brachii.
• With aging there is shortening of the interdigitations with a resulting decrease in contact area between the sarcolemma and extracellular components.

US and MRI

For correct diagnosis and prognosis a grading system of MTJ injuries was created

1. Mild strain: feathery interstitial edema and fluid/hemorrhage around the MTJ
2. Moderate strain: intramuscular hematoma and perifascial fluid/hemorrhage
3. Severe strain: MTJ tear with laxity/discontinuity of the tendon and muscle ends, sometimes with retraction

Scar tissue, old blood products and atrophy/fatty degeneration of the muscle are indicative of an old strain.