Introduction
The lack of full active external rotation of the shoulder joint is presented in many
publications as an indication for neuro-reconstructive surgery (specifically, transfer
of the accessory nerve to the suprascapular nerve) in cases of obstetric brachial
plexus palsy [[1]]. Thus the correctness of the measurement of the external rotation and the interpretation
of the results is crucial. Although the infraspinatus muscle innervated by the suprascapular
nerve, is regarded as the main external rotator of the shoulder joint, external rotation
can also be achieved by thoraco-scapular movements. The Mallet score [[2]], in particular the modification by Tassin [[3]], is (one of several methods) often used to express the degree of external rotation.
This method scores range of motion and composite movement and not individual muscular
motion, so that even in cases of complete ankylosis of the gleno-humeral joint, it
is possible to obtain a satisfying score because of sufficient thoraco-scapular motion.
Another aspect of using scores is the possibility of divergence of opinion between
observers, due to misinterpretation of the measurement results.
This problem is not new as illustrated by the following citation. In 1920, Clark [[4]] from the Mayo Clinic remarked: “When an angle is specifically stated in degrees
the reader is sometimes at a loss to know which angle is meant, whether it is the
angle included between the two bones concerned in deformity or movement, or the angle
between one of the bones and an imaginary line projected into space from the bones”.
Measuring and recording joint motion is a matter of agreement. If the measurement
results are regarded as absolute facts, this may lead to an incorrect decision on
treatment. Thus measurement results must be converted to simple muscular movements
and distinguished from global movements.
In 1936, Cave and Roberts [[5]], from the Committee on Joint Measurement, presented a standard system for measuring
and recording joint function. It was the result of a ten years’ trial, plus suggestions
from members of the American College of Surgeons. The first of five general principles
was “all motions should be measured by degrees from a neutral point of zero” and the
second: “the neutral point from which the motion is measured must be defined”. Their
definition of the zero neutral point differed considerably from Clark’s system. The
internationally approved publication: Joint Motion. Method of measuring and recording published in 1965 [[6]], was based on the principles of Cave and Roberts’ Neutral Zero Method. This contains
the same problem as sketched above: joint motion does not usually reflect movement
caused by one muscle and is usually the result of several muscles acting, and in the
case of the shoulder, of action in more than one joint.
Rotation of the shoulder
When investigating the limits of rotation in the shoulder articulation, one must realize
that the scapula moves, to greater or lesser extent, with all the movements of the
humerus. It is, therefore, necessary to try to immobilize the scapula while determining
the range of rotation of the shoulder. In this way, gleno-humeral external rotation
([Figure 1]a and b) can be distinguished from functional external rotation ([Figure 2]), which is executed by combined thoraco-scapular and gleno-humeral movements. Thus
external rotation with the arm held in stable adduction reflects gleno-humeral external
rotation which is mainly exerted by the infraspinatus muscle. If stable adduction
is not created, external rotation is achieved by a combination of muscles and joints
and is thus called functional external rotation.
Figure 1 External rotation with the scapula not participating: glenohumeral rotation,
1b External rotation with the scapula not participating: glenohumeral rotation.
Figure 2 External rotation with glenohumeral movement complemented by thoraco-scapular
movement: functional external rotation.
Passive and active rotation can be measured in adduction or abduction. First with
the arm in adduction (arm at the side of the body) with the elbow flexed 90° and the
forearm pointing forward. This is called the neutral position: the 0° position ([Figure 3]a and b). Secondly the rotation can be measured with the arm in 90° abduction, 90°
elbow flexion: de arm is held horizontally. This position is then also called the
neutral or 0° position ([Figure 4]). The advantage of the second neutral position is that rotation in this position
is pure gleno-humeral in a more restricted sense; the disadvantage is that the muscles
holding the shoulder, in particular the scapula, must function normally. Thus for
the measurement of active and passive rotation in patients with brachial plexus lesions,
measurement in adduction is usually chosen; on the other hand, guidelines from the
American Medical Association for evaluating impairment recommend measuring with the
shoulder in 90° abduction [[7],[8]]. Furthermore, the limits of rotation in abduction and adduction differ inter- and
intra-individually. Testing extreme internal rotation is performed with the arm behind
the back ([Figure 5]).
Figure 3 Rotation with arm at side (from: Joint Motion). 3b External rotation with the arm at side to the neutral zero position in an individual.
Figure 4 Rotation in abduction (from: Joint Motion).
Figure 5 Internal rotation posteriorly (from: Joint Motion).
Expressing the range of active rotation must be performed with caution. While testing
the passive mobility, the examiner tries to put the arm against the patient’s abdomen.
This is the −70° position. Secondly, the examiner rotates the arm with fixed scapula
as far externally as possible, which is normally +70°. This means that with this test
the passive mobility is 140°. When we test the active motion by asking the patient
to rotate from the position hand–to-abdomen to the neutral 0° position, he has actually
externally rotated 70°; when he then is able to rotate to, for example, the +20° position,
his total range of external rotation is 90° and not 20°. Vice versa, when rotating
his arm from the +20° position to the −70° position, he has rotated 90° internally.
Thus the number of degrees indicates the limit of motion in relation to the neutral zero point and not the amount of the motion.
The Mallet score
This is a score with tests for five functions: 1. shoulder abduction, 2. external
rotation with the arm against the side of the body, 3. putting the hand to the nape
of the neck, 4. putting the hand on the back as high up as possible and 5. hand touching
the mouth. This is not a sliding scale, as 5 grades are recognized: from function
not possible (grade 1) to normal function (grade 5). Usually only grades 2, 3 and
4 are depicted in publications ([Figure 6]). The functions 2, 3 and 5 are tests of external rotation of the shoulder, but only
the second function can, if strictly applied, provide the best score for gleno-humeral
external rotation. It is important to note that also in this score, the neutral point
for the second test is with the hand pointing forward so that grade 2 will give 0°
as the result, often interpreted as: “there is no external rotation possible”, which,
of course, is not correct as illustrated above.
Figure 6 The Mallet score.
How we do it
Measuring active external rotation or any function in the arm may be difficult in
a young child who has been pestered because of his brachial plexus lesion by doctors,
physiotherapists and other helpful people. It sometimes demands patience from the
examiner.
As pointed out in the previous paragraph, the second, third and fifth functions from
the Mallet scale are functional tests of external rotation. The second function evaluates
external rotation without touching the child and produces an assessment expressed
in degrees. Then we examine the third Mallet function. When the child is not able
(or only with great difficulty) to put the hand of the affected side in the nape of
the neck, we can be sure that the active external rotation is diminished. The same
holds true for the fifth Mallet function. When the child in the effort to reach his
mouth with his hand, can only succeed by abduction of the arm (the trumpet sign),
this also illustrates diminished external rotation (or insufficient strength of the
biceps).
We then try to obtain a more accurate measurement expressed in degrees. The patient
is asked to stand straight, that is, curvature of the spine to compensate for a lack
of external rotation is prevented by the examiner. Additionally, the upper arm is
held in adduction by the examiner. Then the patient is asked to rotate his arm externally
as far as possible, evoking pure gleno-humeral external rotation, avoiding scapulo-thoracic
muscular assistance. Sometimes it is advisable to evoke this movement first in the
unaffected arm to familiarize the child with the movement.
In younger children, external rotation is graded by observation of play in three positions:
supine, lying on their side and sitting. Attention is attracted using bright toys
with rattles and bells with the examiner standing on the affected side. Offering a
tit-bit may be helpful. It is evident that accurate measurement is often not possible,
because external rotation is examined functionally.
We wish to point out that the insidious problem of fixed deformity, even to a minor
degree, will contribute to the problem of loss of active functional movement. The
risk of developing a fixed glenohumeral deformity is high whenever the passive external
rotation diminishes to under 30° (with the arm held in neutral adduction position).
Discussion
The positioning of the neutral zero point, more or less in the middle of the range
of active external rotation of the shoulder joint, has produced confusing conclusions
concerning the gravity of the restriction of active external rotation in case of weakness
of the infraspinatus muscle. This has influenced the indications for surgery. Pondaag
e.a. [[9]] reported results on recovery of external rotation after brachial plexus surgery,
whether by grafting from C5 or by nerve transfer of the accessory nerve, as disappointingly
low, but they did not mention the preoperative results. In our view, their conclusion
is based on a misinterpretation of the measurement of external rotation as illustrated
above. In their paper, they correctly considered the normal range of external rotation
to be −70° to +80 degrees, but they did not specify why they regarded recovery of
external rotation as unsatisfactory in their patients. Van Ouwerkerk e.a. [[10]] showed satisfactory spontaneous recovery of shoulder and hand function in patients
with obstetric brachial plexus palsy except for active shoulder external rotation.
They thought that a central issue, whether due to defective central learning or due
to co-contraction, might be responsible for a disappointing result.
Preoperative electromyographic investigations may often show good voluntary muscle
contractions in the infraspinatus muscle. Also many surgeons have found that intraoperative
electrical stimulation of the suprascapular nerve shows a good response in the infraspinatus
muscle in spite of unsatisfactory function. A central issue may be the cause of co-contraction.
Schaakxs e.a. [[11]], in a series of 65 children who underwent an accessory nerve neurotization, reported
that all the patients presented an active external rotation close to 0° (i.e. to the
neutral position, meaning 70° only) preoperatively, which they called lack of recovery,
disregarding the presence of external rotation from hand–to-abdomen to the neutral
zero position. They took samples from the suprascapular nerve from 13 patients for
histopathological examination. One patient had a neuroma; the others showed signs
of good endoneural regeneration and no signs of degeneration.
Conclusion
Literature reports of measurements of active joint motion must be regarded with caution.
So-called lack of recovery of active rotational movements of the shoulder may not
be caused by lack of innervation of the infraspinatus muscle, but by misinterpretation
of measurement results. Also, co-contraction or defective central learning may cause
insufficient external rotation in spite of sufficient reinnervation of the infraspinatus
muscle. Co-contraction causing defective external rotation can be registered with
multi-channel electromyography and it can (possibly) be treated by Botox-injection
into the subscapularis muscle.
Cite this article as: Blaauw and Muhlig: Measurement of external rotation of the shoulder in patients with obstetric brachial
plexus palsy. Journal of Brachial Plexus and Peripheral Nerve Injury 2012 7:8.
