New supports, new stimulation?

Professor Dr. med. Niels Hammer, from the Anatomy Department at the University of Otago, New Zealand, sees proprioception research – especially in neuromechanics – as a way to develop new approaches
for the treatment of musculoskeletal diseases.

Bauerfeind life: How would you describe proprioception?

Prof. Hammer: Proprioception can be described as the organism’s perception of sensory stimuli regarding its position and orientation in a space. In medical fields, particularly in orthopedics and rehabilitation, it primarily refers to the capacity to perceive the position of a joint or extremity, or the relative position of different body parts. Proprioception is primarily a protective function. It is also the most important stimulus for coordinating complex movement processes such as walking.

Can proprioception be measured?

Prof. Hammer: Until just a few years ago, there were few possibilities to do so. Now new methods such as functional MRIs and transcranial magnetic stimulation offer the prospect of interesting findings. There have also been promising developments in sensor technology that make it possible to determine the muscular response and subconscious positional reflexes quite precisely.

What does the situation look like for the knee?

Prof. Hammer: The knee has a very dense network of nerves. This primarily affects a specific type of receptor, namely mechanoreceptors. These are mostly concentrated at the bases and attachments of tendons and ligaments. In the knee, mechanoreceptors can be found in the cruciate ligaments and collateral ligaments as well as the surrounding tendons, along with the menisci and even in regions near the joint surfaces.

Are there differences in sensitivity here?

Prof. Hammer: Sensitivity is primarily dependent on the type of receptor. Free nerve endings as well as Pacini and Golgi receptors are mostly specialized in the perception of stronger forces and variations in length. Ruffini nerve endings and muscle spindles respond even to small changes in position and orientation. With the exception of tendon organs, all of these receptor types can be found in ligaments; Ruffini, Pacini and Golgi receptors can also be found in menisci, while free nerve endings are also found near the joint surfaces and in the Hoffa’s fat pads (see also page 18).

“Proprioception is the most important stimulus for coordinating complex movement processes such as walking.”
(Prof. Dr. med. Niels Hammer)

The complex neuronal situation in and around the knee.

Prof. Hammer: The complexity of the interconnections around the knee can be demonstrated by two principles. Three peripheral nerves on the knee joint , known as the nervi articulares, serve the knee joint exclusively. There are other nerves that serve the surrounding muscles as well as their terminals, which also draw on the joint capsules of the knee. This dense network of nerves means that the majority of tendons and ligaments are supplied with at least two different nerves, one attached at each end. However, if you consider the complexity of the knee joint as an organ with asymmetrical joint surfaces, two condyles of different sizes and the patella as an additional joint component , this dense and redundant supply also seems necessary. Neuromechanics becomes a crucial word in this context: the interface and interconnection between the nerve system and the posture system. In addition to new training approaches, various options are emerging for the treatment of musculoskeletal diseases.

“Supports also change the mobility of soft tissue and bring about modified patterns of movement.”
(Prof. Dr. med. Niels Hammer)

What role could supports play here?

Prof. Hammer: Clinical experimental research about supports is still relatively new in this context. It is evident that medically effective compression from supports performs a splinting function in addition to changing the pressure conditions on the joint , thereby influencing mechanoreceptors as well as chemoreceptors. The skin’s movability is changed in respect to the underlying muscle fascia and ligaments, which also generates new combinations of stimuli. Supports also change the mobility of soft tissue and bring about modified patterns of movement. It is highly likely that supports create new stimuli and offer new combinations of stimuli patterns.

Is it conceivable that the modification of stimuli using a support such as the new GenuTrain could eliminate possible habituation effects?

Prof. Hammer: This is also highly dependent on the type of receptor. For example, Ruffini nerve endings are very slow to adapt , which means that a habituation effect for a specific joint position will only be established after some time. On the other hand, Golgi receptors and muscle spindles react extremely quickly to stimuli. In addition to the receptor generating the stimulus, the spinal cord and control centers play an important role. For this complex system, habituation effects also exist at the level of the receptor, the spinal cord and the cerebral cortex. They can be disrupted by a temporary interruption of the stimulus or a modification in the type of stimulus. This means it is absolutely possible to eliminate such effects. 

Images: private, Source Skin Graphic: www.dasGehirn.info, Bauerfeind