An Adaptive Drumming Device for a Bilateral Above-Knee Amputee
Judd E. Lundt, B.S., A.E.
Introduction
As prosthetists we are occasionally called
upon by a patient to help solve a problem that
goes beyond our training and usual experience.
Because of his impairment, the patient is unable to either perform or to achieve a degree of
proficiency in an important activity. The answer is usually a straightforward adaptive device that can be quickly and easily fabricated.
At the other extreme, the problem may appear
so perplexing that we may be inclined to dismiss the patient's goal as foolish or unrealistic.
Our level of interest in the patient's total rehabilitation, our own perceived limitations, and
our ingenuity all play a major part in how we
handle such a request. It is certainly easier to
avoid what might appear to be a hopeless situation, especially where the solution is not obvious. However, with a little thought, these
seemingly difficult challenges can often be
worked out simply and economically. The case
cited here represents one such example (Figure 1)
.
The patient, a 23 year old male, sustained
severe injuries in March 1984, which resulted
in bilateral mid-thigh amputations and functional loss of his right thumb. Prior to his injury, he had become interested in music and
had taken up the drums. He wished to continue
this avocation, combine it with formal education, and ultimately develop a career in the
field of music.
Clearly, the greatest physical demands in
drumming are on the arms and upper body.
Despite the limitations from his hand injury,
the patient's upper body motion and agility
were relatively unimpaired. However, a full
drum set includes bass drums and high hat
cymbals connected to foot pedals which, in this case, obviously could not be operated by the
patient. Yet, he was eager to find an alternate
way to regain this function.
The author was approached by the patient in
February 1985 after several well-intentioned
individuals had generated enthusiasm by offering to attempt a solution, but then had failed
to follow-through. Because of this, he was becoming discouraged and frustrated and had
fading hopes that he would ever again reach an
acceptable level of drumming proficiency.
The patient had previously been fit with endoskeletal bilateral above-knee prostheses, as
well as stubbies, but was uncomfortable in
them primarily as a result of weight gain. Consequently, at the outset of this project, he had a
diminished interest in therapy with little motivation towards learning to walk. Since it appeared that this trend would likely continue, a
non-prosthetic approach was decided upon.
The patient had a vague idea of adding rigid
extensions to his standard drum pedals to bring
them to sitting height where he would operate
them with his residual limbs.
The patient's elaborate drum set-up includes
two bass drums and high hat cymbals, one bass
drum played normally with the right foot and
the other along with the high hat selectively
played with the left foot. It was decided that a
cable-operated pedal device with an adjustablelever rocker arm would be the best solution. By
following such a course, the optimum balance
between the patient's available range of motion
and residual limb hip extension forces could be
easily developed by varying the force and cable
attachment point lever arms with respect to the
rocker arm fulcrum. In the final analysis, this
adjustability was unnecessary as a fixed 1:1
ratio proved to be the most effective.
In an effort to keep costs down, the devices
were constructed of wood and readily-available
commercial hardware (Figure 2)
. The system
had a heavy-duty 3/16" upper extremity cable
running over a series of pulley assemblies made
from steel angle braces and nylon wheels (commonly used on sliding patio doors). The cable
was attached to a commercial drum pedal
beater unit from which the foot plate had been
removed. Some cable length adjustability was
included in the design to allow for optimum
positioning of the drum beater when in the rest
position.
The downward force of the residual limb
against the pad was reversed via the rocker arm
and transferred by cable pull through the
pulleys to the beater unit. The pad was hinged
and held in place with an adjustable elastic
strap which allowed it to remain flush against
the posterior surface of the residual limb
through the range of hip extension needed for
effective operation. The beater unit had a builtin adjustable spring for beater return after pressure on the pad was released. However, there was
not enough spring adjustment available to balance the weight of the patient's residual limbs
on the pads, so an additional spring was added
to the rocker arm for this purpose. This was
later replaced with a double elastic strap when
we found that the elastic produced a more
lively action.
With proper spring and elastic strap adjustments, the patient could rest his residual limb
on the pad and, with only slight exertion, was
able to drive the beater against the drum head.
The beater assembly was attached to the rim of
the drum, forming a rigid unit of the entire
drum and mechanical linkage complex, but
only on the downbeat. By using flexible cable
instead of a rigid "push rod" to operate the
pedals, an unexpected and decidedly positive
advantage was gained. Because of the spring
and elastic returns and the slack induced in the
cable when the pedal is released, the entire
system becomes non-rigid during the upbeat.
This gives the player the "bounce" that
drummers normally achieve with the flexibility, rapid movement, and subtle action of the
ankle. Certainly, neither this nor any other design can totally duplicate that action, and some
time is needed to develop a proficiency in its
use, but the results achieved have far exceeded
all expectations.
The initial device was built as a prototype
and included several features which proved unnecessary, reinforcing the wisdom of simplicity
in design. These were primarily the inclusion
of height, distance, and positioning adjustments of the device with respect to the patient
and the drum. These concerns were best resolved by moving either the drum or the patient
to the optimum position with respect to the device. Accordingly, these features were eliminated in the final design. Because of the heavy
pounding the devices sustain, the final versions
were constructed of hardwood (Figure 3)
.
Operations and effectiveness of the devices,
particularly the right side, exceeded all expectations. The demands of the left side presented
a different problem. The patient's developed
pattern of playing dictated that the high hat be
placed to the left and played alternately with
the left bass drum. Unfortunately, his left residual limb is about 2" shorter than the right
(6 3/4" versus 8 3/4"), yet he must be able to play
both the bass drum and high hat.
A device similar to that developed for the
bass drums was fabricated for high hat operation, with the pad placed adjacent to the left
bass drum actuator pad. The patient, who
straddles the snare drum, subtends an angle of
roughly 50°with his thighs, and they are positioned on the two bass drum pads. When he
wants to play the high hat, he must first slightly
flex his left hip to lift the limb from the drum
pad and then abduct an additional 25° to 30° to
reach the high hat pad (Figure 4)
. The change
proved slow, awkward, and tiring, largely due
to extensor muscle loss and atrophy. Exacerbating this problem was the patient's increasing
weight gain manifested in the increasing tissue
bulk of this residual limbs. This in turn limited
his range of motion, his effective reach, and his
ability to quickly and easily differentiate between the two adjacent pedals.
Primarily because of his limitations in rapidly changing from the left side drum to high
hat pedal, a new high hat device was built
which used onlv minimal hip abduction. rather than extension, to operate. With his residual
limb resting on the left bass drum pad, the patient could, by a slight sideways motion, actuate an adjacent vertical pad which, through a
cable pulley arrangement similar to the bass
drum design, operated the high hat. The result
was a disaster! Because the motion required
(abduction) was both unnatural and 90° from
the patient's normal rhythm beat direction, it
was totally unacceptable. Possibly this method
could be developed through practice; however,
it was not considered worth the struggle.
With the failure of the vertical high hat device, it was agreed that a return to the side-byside system for the left side was the only reasonable solution. The patient would work to
develop proficiency through exercise and practice with this earlier arrangement. Since he had
lost the powerful hip extension capability of the
hamstring muscles, he was, by his own admission, in poor condition to effectively play with
the underdeveloped remaining musculature.
Several years have passed since this project
was started. During that period, some minor
modifications have been necessary to increase
device strength. Occasional broken cables have
also needed replacement. Nevertheless, the
basic design has stood the test of time and the
user is satisfied with the results. He has since
entered college, pursuing a course of study in
music as was his initial goal. He continues to
effectively use the devices within their limitations. Of necessity, the high hat has to some
extent become subordinate in his playing style;
however, as he continues to refine this technique, he envisions it will assume a greater
role. Perhaps some additional modifications
with the left side actuator pads will be required
before the drum set-up is finally optimized.
Whatever the case, the current result of this
challenge has clearly set the patient on the road
to a more meaningful and positive recovery.
Judd E. Lundt, B.S., A.E.,is with UCLA, Division
of Orthopedic Surgery, 1000 Veteran Avenue, 22-56
Rehab Center, Los Angeles, California 90024; (213) 825-6341.
|
|
