Frans Van den Berg

Connective tissue of the locomotor apparatus

In this chapter we will restrict ourselves primarily to the connective tissue of the locomotor apparatus. The types of connective tissue relevant to manual therapy are hyaline joint cartilage and the unformed, taut, fibrous connective tissue. The latter can be found in the joint capsule, the fascia, and in the intramuscular and intraneural connective tissue. Networks are built by the collagen fibers and these can move and unfold in different directions. These networks occur because the tissue is strained and distorted in different directions. This gives rise to the mobility, which is typical for these structures.

Additional connections (pathological cross links) can arise under pathophysiological circumstances between the intercrossing collagen fibers in the network. These reduce mobility in the network and lead to capsule shrinkage and muscle shortening (see also Chapter 4.3) (Akeson et al. 1973, 1977, 1987, 1992; Grodzinsky 1983; Videman 1987; Brennan 1989; Currier & Nelson 1992).

The unformed, taut, fibrous connective tissue is definitely different from formed connective tissue which is found in tendons, ligaments, retinaculae, aponeuroses, etc. As this tissue is always stressed in the same direction, the collagen fibers tend to run parallel to each other. The therapeutic options are limited here, predominantly to deep frictions (performed after injury), with the aim of promoting circulation and optimizing healing (Van den Berg 2010).

Collagen has a tensile strength of about 500 to 1000 kg/cm². This extremely high stability explains why collagen and connective tissue – whether a joint capsule or a ligament – cannot be significantly extended (Leadbetter et al. 1990; Currier & Nelson 1992; Aaron & Bolander 2005). The original joint mobility is the maximum that can be achieved by using joint mobilization and/or muscle stretching. In adults, it is virtually impossible to achieve greater mobility than was originally there. The reason lies once more in the physiology: Connective tissue can only become longer by the deposit of collagen molecules strung sequentially together. This usually happens under the influence of growth hormones; the optimum influence occurs in the first eight years of life. Think of gymnasts or ballet dancers who begin in childhood and train to achieve the required mobility. Appropriate mobility and extension stimuli are also applied far more often among top athletes than in manual therapy treatment or even in a patient’s home exercise program.

After periods of longer immobilization it is usually very difficult to regain the former level of mobility. The majority of patients invest too little time in performing the necessary exercises and think that two visits a week to the manual therapist are sufficient (Van den Berg 2007).

Paoletti (2001) describe the whole connective tissue of the locomotor apparatus as fascia. It is certainly true that the fascia apparatus holds together all the structures in our body, from our head to the tips of our fingers and toes. You could say that the joint capsule is a specialized fascia and that the ligaments are functional adaptations or swellings of the fascia.

Construction and function

Connective tissue consists of cells and extracellular matrix. We differentiate between fibroblasts, chondroblasts, and osteoblasts. Sometimes we talk of fibrocytes, chondrocytes, and osteocytes. The difference lies in the synthesis activity: Blasts have a higher synthesis activity than cytes, which are characterized by more mitochondria and a larger endoplasmic reticulum (Leadbetter et al. 1990; Currier & Nelson 1992; Finerman & Noyes 1992; Aaron & Bolander 2005).

In the embryo, all connective tissue cells stem from mesenchymal cells. The type of connective tissue cell into which the mesenchymal cells will develop is predominantly determined by the mechanical stress to which the cells and their cell membrane are subjected. As the cell membrane does not possess any great mechanical stability, the cell forms an extracellular matrix to protect against mechanical stress. The construction and composition of the extracellular matrix again depends on the form of the mechanical demands (Van den Berg 2010).

Traction or tensile load versus pressure

If the force on the tissue is predominantly traction, the fibroblasts formed as a result produce predominantly type I collagen fibers and only a few elastic fibers and a small quantity of ground substance. For example, the matrix of a tendon or a ligament is constructed of up to 97% collagen fibers. Only about 1% to 2% of the dry weight are elastic fibers and about 0.5% to 1% are ground substance. Ground substance serves here to reduce the friction during movement between the collagen fibers and allow diffusion in the tissue by deposit of water (Van den Berg 2010).

On the other hand, if pressure is the dominant force, as in hyaline cartilage and nucleus pulposus, the chondroblasts formed here produce almost entirely ground substance. The nucleus pulposus therefore consists of about 98% to 99% ground substance and up to about 1% to 2% very thin type II collagen. The collagen here has the task of mechanically protecting and stabilizing the ground substance (see also Chapter 4.2) (Buckwalter et al. 1988; Eyre et al. 1989; Currier & Nelson 1992).

The physiological construction of the connective tissue determines the required treatment, depending on the injuries: If there is an injury to the joint capsule, gradually increased extension (frequent movement without pain) should be applied to the tissue or cells, so that the original construction and stability of the joint capsule can be achieved.

However, if there is injury or degeneration of the joint cartilage, treatment should consist of the application of physiological force by compression. Accordingly, the joint should be regularly treated with gradually increased application and relief of axial force.

Physiological stimuli

It is therefore questionable that manual therapists frequently treat patients with problems in the area of the joint cartilage with traction. It is often advised that strain (axial loading) should also be minimized. It is obvious that this cannot lead to repair of the cartilage structures – there are no physiological stimuli.

Even after injuries to the intervertebral disc – this is usually a lesion of the annulus fibrosus which lends itself to traction – physiological stress should be included in the treatment. This means that flexion and rotation movements must be made. (In reality, however, this important stimulus to regeneration is very often forbidden to patients.)

Similar considerations should be taken into account for injuries to the meniscus as well: Although it repeatedly says in the literature that the meniscus has a weight-bearing function, this is very doubtful if you look at its histologic construction. The meniscus consists largely of type I collagen and has only 1–2% type II collagen and hardly any ground substance. It follows that the meniscus is primarily designed for traction. As a result, therapy should include traction exercises for the meniscus. This is achieved by gradually increasing rotation with the knee joint flexed (Van den Berg 2010).