Content area
Full text
Introduction
The traditional view of the muscle tendon unit involved a distinct delineation between the muscle belly and the tendon(s) at one or both ends of the muscle leading to its bony attachment. The musculotendinous junction has been described as the most common site of muscle injury, 1 yet both clinically and radiologically, it is clear that the majority of muscle injuries occur within the muscle belly.
Improved resolution via MRI and excellent anatomical dissection studies provide evidence that in many muscles, the tendon extends within the muscle belly, and these muscle belly injuries occur at an intramuscular myotendinous or myoaponeurotic junction. The intramuscular tendon (rachis or aponeurosis) acts as a central supporting strut to which the muscle fibres attach.
Failure of the myofibrillar attachments may occur along the intramuscular tendon (or aponeurosis). This is analogous to the failure of struts along a suspension bridge.
This failure often occurs in a zipper-like fashion with oedema and blood products tracking alongside the torn muscle fibres. The effect is a characteristic feather-like appearance on MRI ( figure 1 A,B) and ultrasound scans. Recently, injuries to the intramuscular tendon itself, often in association with a musculotendinous injury, have been identified.
The aim of this narrative review is to examine the evidence to support our clinical experience that muscle injuries involving damage to the tendon itself are more serious than those affecting the myotendinous junction only.
Imaging appearance
MRI of the disrupted intramuscular tendon demonstrates a wavy retracted appearance as opposed to the normal taut cord-like appearance ( figure 2 A). Sometimes, as the tendon fails, the tendon strands unravel and give way similar to a piece of intertwined rope. The tendon consequently loses its taut appearance, but there is no gap in the tendon, despite it losing its tensile strength ( figure 2 B). In some cases, there is longitudinal delamination and splitting of the intramuscular tendon ( figure 2 C), which otherwise appears continuous. In other cases, the tendon may retract and create a gap ( figure 2 D).
The role of intramuscular tendon tears
Two examples of the important role these intramuscular tendons play are in the hamstring and quadriceps muscles.
Hamstring muscle injuries
Hamstring injuries are a major cause of time loss injuries in sport...