More than 10% of patients observed that their phantom knee sometimes moved spontaneously as much as 90 degrees "just automatically." These automatic changes could not be voluntarily initiated or prevented. 

Johns Hopkins University

- Statistics from the Study
- Natural Phantoms
- Telescoping
- Course of the Phantom
- Impression of Voluntary Movement
- Automatic Knee Movements
- Factors that Affect Phantom Perception
- Relationship of Phantom to Solid Structures

Henderson and Smyth "Phantom Limbs" Study (1940)

HENDERSON, W. R., & SMYTH, G. E. (1948). Phantom limbs. Journal of neurology, neurosurgery, and psychiatry, 11(2), 88–112. https://doi.org/10.1136/jnnp.11.2.88

HENDERSON, W. R., & SMYTH, G. E. (1948). Phantom limbs. 

Whether or not a patient can, and the degree to which they can, "move" certain components of the phantom depends on two factors:
1. The level of the amputation
2. Degree of sensory awareness of the various joints
In forearm amputations, the digits can at first be moved in every phantom. However with lower limbs, the phantom is weaker and "movements" are more difficult to produce. 

"Voluntary Movement" of Phantom Limbs

Automatic Knee Movements in Phantoms

In total, "some three hundred major and many minor amputations" were observed in this longitudinal study. A minority of of men (~10%) could identify "well-marked" phantoms, had made original observations, and could describe their impressions clearly. The majority of men (~80%) had a typical phantom that "had been so mild and unobtrusive" and had given "little thought to it" prior to the study (dubbed the "average phantom"). The remaining men (~10%) felt vague tingling, did not perceive a phantom.  

Statistics from the Henderson & Smyth Study (1948)

The "natural phantom" is defined as the almost invariable appearance in consciousness of the missing limb/part. As observed by Henderson and Smyth, it is usually associated with a positive sensation described as tingling or numbness. In the context of the study, this "tingling" sensation was always stronger than any vague awareness of an intact limb. 

The "Natural Phantom"

Telescoping refers to the phenomenon observed in the phantom limb patients where patients perceived digits gradually approaching the stump and almost becoming "attached" it. This presumably resulted from the weakening of the phantom, or specific parts of it. The time at which shortening begins is variable, though the rate of telescoping appears to be related to the strength of the phantoms.

Telescoping

There are a number of factors that may impact the degree to which a patient detects the tingling, or phantom-like, sensation.
- Pain in the Stump
- Sedatives
- Climatic Conditions
- Thinking of Phantom
- Urinating and other Visceral Reflexes
- Loss of Balance
- Instinctive Actions
- Fright
- Emotion
- Attachment of Artificial Limb

Factors that Affect Phantom Perception

Phantoms are often perceived when the patient awakens from the anesthetic and there is nothing unusual detected about the sensation. At first, the phantom is felt continuously. After a few weeks, the tingling becomes weaker and recurs less frequently. During the next six to twelve months, the phantom weakens considerably. The average phantom is mild and rapidly subsided, however.
- Relation Between Cerebral Structures and Phantom

Course of Natural Phantom

Patients perceived phantom to pass through solid structures unimpeded and without arousing any feeling of obstruction or unpleasant sensation; mostly observed in upper limbs; only exception is when strong phantom digits (attached to stump through telescoping) appear to occupy a space that "does not exist"

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