00004623-200509000-00020

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BY
THE JOURNAL
OF
BONE
AND JOINT
SURGERY, INCORPORATED
Effects of Elbow Flexion and
Forearm Rotation on
Valgus Laxity of the Elbow
BY MARC R. SAFRAN, MD, MICHELLE H. MCGARRY, MS, STEVE SHIN, MD, STEVE HAN, BS, AND THAY Q. LEE, PHD
Investigation performed at Orthopaedic Biomechanics Laboratory, VA Long Beach Healthcare System (09/151)
and University of California, Irvine, Long Beach, California
Background: Clinical evaluation of valgus elbow laxity is difficult. The optimum position of elbow flexion and forearm
rotation with which to identify valgus laxity in a patient with an injury of the ulnar collateral ligament of the elbow has
not been determined. The purpose of the present study was to determine the effect of forearm rotation and elbow
flexion on valgus elbow laxity.
Methods: Twelve intact cadaveric upper extremities were studied with a custom elbow-testing device. Laxity was
measured with the forearm in pronation, supination, and neutral rotation at 30°, 50°, and 70° of elbow flexion with
use of 2 Nm of valgus torque. Testing was conducted with the ulnar collateral ligament intact, with the joint vented,
after cutting of the anterior half (six specimens) or posterior half (six specimens) of the anterior oblique ligament of
the ulnar collateral ligament, and after complete sectioning of the anterior oblique ligament. Laxity was measured in
degrees of valgus angulation in different positions of elbow flexion and forearm rotation.
Results: There were no significant differences in valgus laxity with respect to elbow flexion within each condition.
Overall, for both groups of specimens (i.e., specimens in which the anterior or posterior half of the anterior oblique
ligament was cut), neutral forearm rotation resulted in greater valgus laxity than pronation or supination did (p <
0.05). Transection of the anterior half of the anterior oblique ligament did not significantly increase valgus laxity; however, transection of the posterior half resulted in increased valgus laxity in some positions. Full transection of the anterior oblique ligament significantly increased valgus laxity in all positions (p < 0.05).
Conclusions: The results of this in vitro cadaveric study demonstrated that forearm rotation had a significant effect
on varus-valgus laxity. Laxity was always greatest in neutral forearm rotation throughout the ranges of elbow flexion
and the various surgical conditions.
Clinical Relevance: The information obtained from the present study suggests that forearm rotation affects varusvalgus elbow laxity. Additional investigation is warranted to determine if forearm rotation should be considered in the
evaluation and treatment of ulnar collateral ligament injuries of the elbow joint.
E
lbow instability is a challenging clinical problem. The
diagnosis of injury to the ulnar collateral ligament, especially the degree of laxity, is difficult, even for experienced clinicians1,2. Other than stress radiographs, which can be
misleading1,3, there are no objective tests or measures of valgus
laxity. The elbow is the second most commonly dislocated
major joint in the body, and the ulnar collateral ligament is
usually injured in association with elbow dislocation4-6. The
mechanism of injury occurs with a fall on an outstretched
hand, which applies both a valgus stress and an external rotatory moment on the elbow joint7,8. This is important because
long-term follow-up has shown that elbows with persistent
valgus laxity following dislocation have inferior overall clinical
and radiographic results compared with elbows without
increased valgus laxity following dislocation9. Furthermore,
persistent elbow instability, although uncommon, is being
recognized more frequently following elbow dislocation. The
ulnar collateral ligament also may be injured as a result of excessive or repetitive valgus loading associated with a throwingtype motion of the upper extremity3,10-12. This type of injury
has been seen in athletes who participate in baseball3,13, volleyball, tennis14, javelin15,16, water polo, and football17. Disruption
of the ulnar collateral ligament can result in loss of velocity
during baseball pitching, instability of the elbow, and excessive
stress and injury to other structures in and about the elbow,
such as the ulnar nerve, the flexor-pronator tendon group, or
the posteromedial or lateral elbow joint surfaces10,18,19.
Studies have been performed to assess the contributions
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of the osseous architecture, ligaments, and capsule about the
elbow to varus-valgus and anterior-posterior stability in varying degrees of flexion-extension20-31. Research has shown that
stability of the elbow is provided by osseous, ligamentous, and
capsular structures as well as by muscles20-31. Some controversy
exists with regard to the contribution of forearm musculature
to valgus stability to the elbow; however, joint compression
due to the anterior and posterior muscle contractions about
the elbow do appear to contribute to elbow stability32-35.
The main structure that resists valgus loading, especially
in the middle part of the range of elbow motion, is the ulnar
collateral ligament complex (also known as the medial collateral ligament or medial ulnar collateral ligament)20-26,36-42. The
ulnar collateral ligament is comprised of three ligaments: the
anterior oblique ligament (the most important ligament in
throwing athletes, also known as the anterior band or anterior
bundle), the posterior oblique ligament (also known as the
posterior band or posterior bundle), and the transverse ligament (also known as Cooper’s ligament)20-26,37,40,41,43. The transverse ligament is considered to be unimportant with regard to
valgus loading. The anterior oblique ligament may be further
subdivided into two functional components: the anterior and
posterior bands (although in some studies, these structures
are referred to as the anterior and posterior bundles). These
bands become selectively tensioned throughout the range of
elbow motion21,26,37,40.
Between 20° and 120° of elbow flexion, the soft tissues,
particularly the ulnar collateral ligament complex, are the
main elbow stabilizers that resist valgus loading20-22,24-27,37,40-42.
The anterior band of the anterior oblique ligament has been
shown to be the most important ligamentous structure to resist valgus loading22. Biomechanical studies of elbow stability
have revealed that valgus laxity is most evident at 70° of elbow
flexion when the ulnar collateral ligament is cut21,41. Thus, valgus laxity of the elbow has been shown to be affected by the
degree of elbow flexion.
However, the elbow predominantly participates in two
planes of motion: flexion-extension and pronation-supination.
The effect of forearm rotation on valgus laxity and stability of
the elbow is not well understood. In our review of the literature, it was notable that many investigators neglected to mention the position of the forearm when testing valgus stability
of the elbow. The few researchers who did mention forearm
rotation noted that the contribution of forearm rotation was
negligible; however, no data were provided to support this
statement20,40. In fact, while studies have revealed that the forces
across the radiocapitellar joint depend on forearm rotation27,
the effect of forearm pronation on the degree of valgus elbow
laxity has received only limited attention28,44-47.
The hypothesis of the present study was that forearm
rotation affects valgus laxity at different degrees of elbow flexion when the origins and insertions of the muscles that cross
the elbow joint are left intact. It was also hypothesized that
this effect persists with valgus loading when the ulnar collateral ligament is intact, partially cut, and completely sectioned.
Therefore, the objective of the present study was to quantify
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the effects of forearm rotation and elbow flexion on valgus
laxity of the elbow in a human cadaveric model that involved
use of the entire upper extremity with intact musculature.
Materials and Methods
he number of specimens needed for the present study
was determined with use of an analysis-of-variancebased power analysis (JMP 3.2 statistics software package;
SAS Institute, Cary, North Carolina) and the mean and standard deviation ranges from preliminary tests performed on
three specimens. A minimum of six specimens was needed to
show a significant difference between different ligamentsectioning conditions and between different degrees of elbow
flexion, and a minimum of two specimens was needed to
show a significant difference between different forearm rotation positions. Therefore, six specimens were chosen for each
ligament-sectioning group (one group in which the anterior
half of the anterior oblique ligament was transected first and
one group in which the posterior half was transected first),
for a total of twelve specimens. Seven right and five left specimens were obtained from nine female and three male donors.
The mean age of the donors at the time of death had been
73 ± 9 years (range, forty-nine to eighty-three years). All
specimens were examined radiographically and macroscopically prior to dissection. Specimens with pathological changes
(such as arthritis), a previous fracture, and/or previous operative treatment were not included in the study. The cadaveric
upper extremities were stored at –20°C and were thawed
overnight prior to study.
Prior to testing, the specimens were disarticulated from
the cadaver at the scapulothoracic joint. All structures, including muscles and tendons from the scapula to the hand, were left
intact. The skin and the subcutaneous tissue were removed for
the study, and all of the other tissues were maintained. The specimens were kept moist with intermittent irrigation with physiologic saline solution throughout the entire period of study.
The entire upper extremity was tested with a custom elbow valgus laxity-testing system (Fig. 1). After removal of the
skin and the subcutaneous fat, both the humerus and the forearm were centered and fixed in two cylinders that were used to
secure the specimen to the testing system. A muscle-splitting
approach was used to attach the humerus to the humeral cylinder with use of screws. The length of the radius was measured from the radial head to the distal styloid process with
the arm in pronation. Two 1.6-mm fixation screws were then
placed in the radius, one at the middle part of the forearm and
the other 3 in (7.6 cm) distal to the screw in the middle part of
the radius, to fix the radius to the metal cylinder. The specimen was then mounted onto the testing system, which allowed six degrees of freedom of both the humerus and the
forearm.
Once the specimen was mounted onto the testing system, the elbow was flexed and extended for several cycles to allow the humerus to reach an anatomic neutral position, with
the epicondyles aligned parallel to the baseplate of the testing
system in the medial-lateral plane. The humeral rotation was
T
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TABLE I Valgus Laxity with the Application of 2 Nm of Valgus Torque in the Group of Six Elbows in Which the Anterior Band
Was Transected Prior to Full Transection of the Anterior Oblique Ligament
Elbow Flexion
Angle (deg)
Forearm
Rotation
30
Pronation
30
Neutral
30
Supination
50
Pronation
50
Neutral
50
70
70
Neutral
70
Supination
Valgus Laxity (deg)
Intact
Vented
Demarcated
5.5 ± 2.8
6.5 ± 3.0
6.5 ± 2.9
Anterior Band Cut
10.7 ± 3.9
11.5 ± 3.9
11.0 ± 4.4
12.9 ± 5.3
16.1 ± 7.1
9.6 ± 3.6
9.6 ± 3.9
9.8 ± 3.9
10.8 ± 5.3
12.6 ± 4.8
8.2 ± 5.0
Full Cut
11.2 ± 7.0
6.0 ± 3.0
6.4 ± 3.4
6.9 ± 2.9
8.3 ± 5.0
12.3 ± 6.7
10.6 ± 3.5
11.3 ± 4.1
11.2 ± 4.0
13.6 ± 6.4
16.6 ± 6.8
Supination
9.0 ± 3.9
9.3 ± 4.4
9.4 ± 4.4
10.7 ± 6.0
12.6 ± 4.9
Pronation
6.1 ± 4.0
7.2 ± 3.2
7.8 ± 3.7
8.5 ± 4.0
11.8 ± 4.4
11.1 ± 4.5
11.0 ± 3.8
11.0 ± 3.4
12.0 ± 5.2
14.9 ± 4.5
7.9 ± 3.9
7.8 ± 3.4
8.0 ± 3.8
8.9 ± 4.9
10.9 ± 4.0
then locked at this position throughout each phase of testing.
The forearm cylinder was placed in 30° of flexion (as measured with a goniometer) and was secured at this position for
all tests. The elbow flexion angle could then be adjusted by
changing the humeral height. Once the humerus was adjusted
for each flexion angle, each degree of freedom of the humerus
was locked at this position. The forearm was aligned in neutral
rotation by aligning the distal radioulnar plane perpendicular
to the base of the testing device or epicondylar axis while observing hand position. Pronation was then defined as 90° of
internal rotation from this position, and supination was defined as 90° of external rotation from this position. All forearm rotation positions were marked on the forearm cylinder
and mounting device so that the forearm could be returned to
the exact rotation position throughout each testing phase. The
distance from the medial epicondyle to the varus-valgus
torque application point (center of rotation) was measured to
determine the amount of load needed for torque application.
The torque was applied with use of a pulley-and-weight sys-
tem that was attached to the medial-lateral forearm translator. Once the forearm was placed in the appropriate rotation,
the cylinder could be locked in this position. During varusvalgus load application, three degrees of freedom of the elbow
(medial-lateral translation, superior-inferior translation, and
varus-valgus rotation) were free. Prior to each measurement
of valgus laxity, the specimen was preconditioned for five cycles with 2 Nm of valgus torque. Valgus laxity was measured
with use of a Microscribe 3DLX digitizing system (Immersion,
San Jose, California) by digitizing two points along an extension plate that was attached to measure varus-valgus rotation.
The two points along the plate were digitized at the position of
the forearm with the application of 1 Nm of varus torque (the
starting position). These two points lie on the proximal-distal
axis of the forearm (Fig. 1). The same two points were digitized again after the application of 1 Nm of counterbalance
and an additional 2 Nm of valgus torque (Fig. 1). Valgus laxity
was then calculated with use of the four digitized points and
the formula:
Fig. 1
Illustration depicting the upper extremity
mounted on custom testing device, showing
the six degrees of freedom. Valgus laxity was
measured by digitizing two points on a plate
that was attached to the forearm-mounting
device.
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TABLE II Valgus Laxity with the Application of 2 Nm of Valgus Torque in the Group of Six Elbows in Which the Posterior Band
Was Transected Prior to Full Transection of the Anterior Oblique Ligament
Elbow Flexion
Angle (deg)
Forearm
Rotation
30
Pronation
30
Neutral
30
Supination
50
Pronation
50
Neutral
50
70
70
Neutral
70
Supination
Valgus Laxity = cos
Valgus Laxity (deg)
Intact
Vented
Demarcated
Posterior Band Cut
Full Cut
8.8 ± 2.9
9.4 ± 2.8
9.9 ± 2.9
10.8 ± 2.5
13.3 ± 2.9
12.0 ± 2.7
12.5 ± 2.8
12.6 ± 2.6
13.7 ± 2.5
15.7 ± 2.5
9.3 ± 2.9
9.9 ± 2.7
10.1 ± 2.2
10.8 ± 2.2
12.8 ± 1.8
8.3 ± 2.0
9.1 ± 2.5
9.6 ± 2.9
11.0 ± 2.5
12.8 ± 2.4
10.0 ± 1.9
10.7 ± 1.8
10.5 ± 2.2
12.1 ± 1.3
14.9 ± 1.9
Supination
9.3 ± 2.3
9.5 ± 2.1
10.2 ± 1.7
11.1 ± 2.0
13.1 ± 2.3
Pronation
9.6 ± 4.1
9.6 ± 2.7
10.0 ± 2.5
11.9 ± 2.0
14.0 ± 3.5
–1
10.8 ± 2.7
11.7 ± 2.6
11.7 ± 2.0
13.1 ± 1.6
15.7 ± 2.3
9.9 ± 2.8
10.0 ± 2.6
10.8 ± 2.2
11.8 ± 2.4
13.9 ± 3.0
varus 1 varus 2 • valgus 1 valgus 2
-----------------------------------------------------------------varus 1 varus 2 valgus 1 valgus 2
Valgus laxity was directly measured with 2 Nm of valgus torque with use of the custom testing system with the
forearm in pronation, supination, and neutral rotation and
with the elbow in 30°, 50°, and 70° of flexion. This resulted in
nine elbow positions (30° of flexion with pronation, 30° of
flexion with neutral rotation, 30° of flexion with supination,
50° of flexion with pronation, 50° of flexion with neutral rotation, 50° of flexion with supination, 70° of flexion with pronation, 70° of flexion with neutral rotation, and 70° of flexion
with supination). Testing was performed for five ligament
conditions: (1) with the specimen intact, (2) after venting of
the joint with a 19-gauge needle, (3) after demarcation of the
anterior oblique ligament, (4) after transection of the anterior half (six specimens) or posterior half (six specimens) of
the anterior oblique ligament, and (5) after complete transection of the anterior oblique ligament (Fig. 2). The degrees of
elbow flexion that were tested were based on currently used
clinical tests, in which the elbow is placed in approximately
30° of flexion3,11,12,17,48-54 and 45° of flexion55, and on biomechanical data suggesting that the greatest medial joint laxity is
near 70° of flexion21,22,36,41,42. The applied loads were based on
previous load-displacement studies25 and on studies that have
shown that valgus torques of >2.5 Nm may result in ulnar
collateral ligament avulsion fractures21.
Demarcation of the anterior oblique ligament was performed with use of a muscle-splitting approach56 to limit injury to other structures and to maintain soft-tissue integrity.
The anterior border of the ligament was palpated with the elbow in 30° of flexion, and a 10-mm longitudinal cut was made
along the ligament fibers with use of a scalpel. The posterior
border of the ligament was then palpated with the elbow in
70° of flexion, and a 10-mm longitudinal cut was made along
Fig. 2
Flowchart showing the experimental design and the independent and dependent variables.
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Fig. 3
Photographs illustrating the experimental conditions of the anterior oblique ligament, showing
the humerus (H), the forearm (FA) with the ligament demarcated (A), with the anterior half cut (B),
with the posterior half cut (C), and with the ligament fully cut (D).
the posterior border (Fig. 3, A). The width of the anterior oblique ligament was measured with use of digital calipers. The
width of the ligament was then divided in half to demarcate
the anterior half and the posterior half because it is difficult to
determine the exact functional division between the anterior
and posterior bands. After demarcation, the ligament could be
divided reliably into two equal halves (the anterior band and
the posterior band) for testing. For six specimens the anterior
half was transected first, followed by complete sectioning of
the ligament, and for the remaining six specimens the posterior half was transected first, followed by complete sectioning
of the ligament (Fig. 3, B, C, and D).
The sequence for forearm rotation, elbow flexion, and
varus-valgus loading was randomized throughout the testing
protocol to minimize bias related to the viscoelastic effects of
the soft tissues. Three trials were recorded for each position,
and the average of the three trials was used for analysis. A
multifactorial repeated-measures analysis of variance was
performed for statistical analysis, followed by a univariate
repeated-measures analysis of variance with a Tukey post hoc
test for individual comparisons, with the level of significance
set at p < 0.05. All data are reported as the mean and the standard deviation, in degrees of valgus laxity.
Results
Effect of Order of Ligament Sectioning
he valgus laxity associated with sectioning either the anterior half or the posterior half of the anterior oblique liga-
T
ment was compared with that associated with the other
ligamentous conditions (intact, vented, demarcated, and fully
transected) (Tables I and II). The average width of the anterior
oblique ligament was 7.2 mm (standard deviation, 1.7; standard error, 0.5). Among the specimens in which the anterior
half of the anterior oblique ligament was transected prior to
full transection, the valgus laxity after full transection was significantly greater than the valgus laxity associated with the intact, vented, and demarcated conditions at each of the nine
positions (Table I) (p = 0.0001 to 0.006). Valgus laxity following full sectioning of the anterior oblique ligament was significantly greater than that associated with sectioning of only the
anterior half of the ligament at four positions: 30° of flexion
with neutral rotation (p = 0.04), 50° of flexion with pronation
(p = 0.04), 70° of flexion with pronation (p = 0.006), and 70°
of flexion with neutral rotation (p = 0.04). There were no significant differences in valgus laxity when sectioning of the
anterior band was compared with the intact, vented, and demarcated conditions.
Among the specimens in which the posterior band was
transected prior to full transection of the anterior oblique ligament, valgus laxity following full transection was significantly greater than that associated with the intact, vented,
and demarcated conditions at all nine positions (Table II)
(p = 0.0001 to 0.03). Valgus laxity after full transection was
significantly greater than that after sectioning of only the posterior band at six positions: 30° of flexion with pronation
(p = 0.002), 30° of flexion with neutral rotation (p = 0.01),
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30° of flexion with supination (p = 0.008), 50° of flexion with
neutral rotation (p = 0.02), 50° of flexion with supination
(p = 0.03), and 70° of flexion with supination (p = 0.02). Valgus laxity following transection of the posterior band of the
anterior oblique ligament was significantly greater than that
associated with the intact condition at four positions: 30° of
flexion with pronation (p = 0.007), 30° of flexion with neu-
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tral rotation (p = 0.03), 50° of flexion with pronation (p =
0.004), and 50° of flexion with supination (p = 0.04).
Effect of Elbow Flexion
Among the six specimens in which the anterior band was cut
prior to full transection, no significant differences in valgus
laxity were noted in association with the flexion angle when
Fig. 4
Bar graph illustrating the effect of the flexion angle on valgus laxity, with the forearm in neutral
rotation and with the application of 2 Nm of valgus torque, for the specimens in which the anterior half of the anterior oblique ligament was transected prior to full transection (p > 0.05 for all
comparisons).
Fig. 5
Bar graph illustrating the effect of the flexion angle on valgus laxity, with the forearm in neutral forearm rotation and with the application of 2 Nm of valgus torque, for the specimens in which the posterior half of the anterior oblique ligament was transected prior to full transection. *p < 0.05.
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Fig. 6
Bar graph illustrating the effect of forearm rotation on valgus laxity, with the elbow in 30° of flexion and with the application of 2 Nm valgus torque, for the specimens in which the anterior half
of the anterior oblique ligament was transected prior to full transection. *p < 0.05.
the values for each ligamentous condition and forearm rotation were compared (p = 0.07 to 0.99). There was a trend toward decreasing laxity at 70° compared with 30° and 50° for
the anterior-cut and full-cut conditions, but the differences
were not significant (Fig. 4).
With only the posterior band cut, no significant differences in valgus laxity were noted in association with the flexion angle (p = 0.99 to 0.11) under any of the conditions except
for one. With the posterior band demarcated and the forearm
in neutral rotation, the valgus laxity at 30° was significantly
greater than that at 50° (12.6° ± 2.6° compared with 10.5° ±
2.2°; p = 0.04) (Fig. 5).
Effect of Forearm Rotation
Among the specimens in which the anterior band was
transected prior to full transection of the anterior oblique ligament, the valgus laxity with the forearm in neutral rotation
was significantly greater than that with the forearm in pronation for all flexion angles and conditions (p = 0.0003 to 0.01)
(Fig. 6). Similar trends were seen at each flexion angle. At 30°
and 50° of elbow flexion, valgus laxity with the forearm in
pronation was significantly greater than that with the forearm
in supination under the intact condition (p = 0.0009 for 30° of
elbow flexion and p = 0.03 for 50° of elbow flexion), the
vented condition (p = 0.01 for 30° of elbow flexion and p =
0.03 for 50° of elbow flexion), and the demarcated condition
(p = 0.01 for 30° of elbow flexion and p = 0.03 for 50° of elbow
flexion). Valgus laxity with the forearm in neutral rotation was
greater than that with the forearm in supination at 30° of flexion with the ligament fully cut (p = 0.02), at 50° of flexion
with the anterior band transected (p = 0.03) and with the ligament fully cut (p = 0.02), and at 70° of flexion for all conditions (p = 0.0005 to 0.03).
Among the specimens in which the posterior band was
transected prior to full sectioning of the anterior oblique ligament, a similar trend of increased valgus laxity was noted
with the forearm in neutral rotation as compared with pronation and supination. Specifically, at 30° of elbow flexion,
valgus laxity with the forearm in neutral rotation was greater
than with the forearm in pronation (p = 0.0002 to 0.009) and
supination (p = 0.0003 to 0.003) for all conditions (Fig. 7).
At 50° of elbow flexion, valgus laxity with the forearm in
neutral rotation was significantly greater than that with the
forearm in pronation only with the anterior oblique ligament
fully cut (p = 0.03). At 70° of elbow flexion, valgus laxity with
the forearm in neutral rotation was significantly greater than
that with the forearm in pronation for the vented (p = 0.02)
and demarcated (p = 0.04) conditions and was greater than
that with the forearm in supination with the posterior band
transected (p = 0.04).
For both groups (the group in which the anterior half
of the ligament was transected prior to full transection and
the group in which the posterior half of the ligment was
transected prior to full transection), the valgus laxity with the
forearm in neutral rotation with the ligament intact was generally larger than that with the forearm in pronation and supination with the anterior or posterior half of the ligament cut
(Tables I and II). However, the only significant difference was
observed in the group in which the posterior half of the ligament was transected first; specifically, at 30° of elbow flexion,
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Fig. 7
Bar graph illustrating the effect of forearm rotation on valgus laxity, with the elbow in 30° of flexion and with the application of 2 Nm valgus torque, for the specimens in which the posterior half
of the anterior oblique ligament was transected prior to full transection. *p < 0.05.
the valgus laxity with the ligament intact and the forearm in
neutral rotation was significantly greater than that with the
posterior half of the ligament cut and the forearm in supination (12.0° ± 2.7° compared with 10.8° ± 2.2°; p = 0.02).
Discussion
everal studies have been performed to evaluate the contribution of different structures about the elbow to the stability of the joint. We identified only one study that specifically
investigated the effects of forearm rotation on elbow stability46,
although a few reports in the literature have discounted the effect of rotation on stability of the elbow20,44,57. Unfortunately,
those studies evaluated stability with an incomplete upper extremity specimen and most of the studies involved specimens
that were devoid of muscles and noncapsuloligamentous soft
tissues crossing the joints20-22,24-27,37,40-42. To our knowledge, the
present report describes the first study in which valgus stability of the elbow has been evaluated in completely intact upper extremity specimens that included all muscles that cross
the joint.
Our findings confirm the importance of forearm rotation on elbow stability and laxity. Our review of the literature
showed that the reports on several major studies of elbow stability did not mention the position of forearm rotation in the
description of testing methods23,24,26,37. Thus, it is not possible to
directly assess the effect of forearm rotation on elbow stability
on the basis of those studies. Other authors have specifically
mentioned that forearm rotation does not influence the stability and laxity of the elbow joint20,40.
Most investigators who have investigated elbow valgus
stability and laxity have fixed the forearm in one position of
rotation, although this position has varied among studies.
S
Callaway et al.21 studied valgus laxity with the muscles crossing the elbow joint detached and the forearm fixed in neutral
rotation. Those authors identified the anterior band of the
anterior oblique ligament as the primary restraint to valgus
loading and stated that valgus laxity was not affected by elbow flexion when the ulnar collateral ligament was intact.
Hotchkiss and Weiland22 tested valgus laxity with the forearm
maintained in full pronation and with all soft tissues, except
the capsule and ligaments, being excised prior to testing.
Those authors also noted that the anterior oblique ligament
was the primary stabilizer to valgus stability and that the radial head was a secondary stabilizer. Morrey and An25 studied
elbow stability with all muscles detached while the forearm
was held in neutral rotation. Later, Morrey et al.20 studied valgus laxity with the forearm in supination. In a pilot study assessing the contributions of the ulnar collateral ligament and
radial head to valgus stability during dynamic flexion of the
elbow, those investigators identified no change in motion
patterns in association with differing degrees of forearm rotation. Sojbjerg et al.41,58 maintained the forearm in neutral
rotation in their studies of elbow stability. Tanaka et al.59 studied
the three-dimensional kinematics of the ulnohumeral joint
with the forearm in neutral rotation.
Only a couple of reports have mentioned testing in different degrees of forearm rotation. King et al.44 used a dynamic
model that simulated active elbow motion to study the stabilizing effects of radial head arthroplasty in ulnar collateral
ligament-deficient cadaveric elbows. The varus-valgus laxities
were similar with the forearm in pronation and supination in
all positions of elbow flexion under each condition. Pribyl et
al.57, in a study of five cadaveric elbows that were tested for resistance to valgus stress under various conditions (with the
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radial head intact, with the radial head resected, and with insertion of a radial head implant), reported that forearm rotation had no effect on valgus stability when the ligments were
intact.
Previous studies have investigated the effect of forearm
rotation on varus stability of the elbow. Jensen et al.28, in a
study of two elbow specimens, reported that pronation and
supination had no effect on varus or external rotation stability. In another study of varus instability, Olsen et al.45 found
that varying rotations of the forearm did not affect the stability of elbows with all ligaments intact or with transection of
the lateral collateral ligament, lateral ulnar collateral ligament,
and annular ligament.
In what we believe to be the only study that has formally
assessed the effect of forearm rotation on elbow stability and
laxity, Pomianowski et al.46 concluded that forearm rotation
does affect valgus elbow stability. Those authors used upper
extremity specimens with the wrist disarticulated. They made
no mention about tension on the forearm muscles that cross
the elbow joint, despite the use of weights to stimulate muscle
forces to the tendons of the biceps, brachialis, and triceps. The
authors concluded that valgus laxity is more evident with the
forearm in pronation, regardless of the status of the ulnar collateral ligament and elbow flexion. Using a similar testing scenario, the same authors tested different radial head prostheses
for valgus stability47. Again, they found that forearm pronation
resulted in the greatest amount of valgus laxity as compared
with supination or neutral rotation.
One of the main differences between the present study
and the study by Pomianowski et al.46 was that in our model all
of the muscles that cross the elbow had intact origins and insertions, whereas in the study by Pomianowski et al.46 the insertions of several muscles that cross the elbow were not
intact. Another difference was the number of positions of elbow flexion and forearm rotation. Leaving the muscles that
cross the elbow joint completely intact allows passive tension
to accumulate within the musculotendinous unit, which may
result in an increase in joint compression force and thereby
provide some stability to the elbow and some resistance to varusvalgus loading. We believe that experiments in which the musculature is completely intact more closely replicate the clinical
scenario with regard to evaluation of the elbow.
In the present study, neutral rotation resulted in the
greatest degree of valgus laxity, regardless of the ligamentous
E F F E C T S O F E L B OW F L E X I O N A N D F O RE A R M
R O T A T I O N O N VA L G U S L A X I T Y O F T H E E L B OW
condition. With pronation, this finding may be due to the fact
that radiocapitellar joint-compression forces increase as a result of proximal migration of the radius, possibly because of
increased passive tension within the supinator and/or distal
biceps musculotendinous units and/or the interosseous membrane, thereby increasing the contribution of the osseous articulation in valgus elbow stability25. With supination, this
finding may be due to the intact flexor-pronator muscles. In
supination, there is an increase in passive tension in the pronator muscles, which may provide added passive stability to
the medial part of the elbow.
The findings of the present in vitro cadaveric study support the concept that valgus laxity of the elbow is affected by
forearm rotation. Clinically, these findings may help with the
clinical examination of the elbow in patients with an injury of
the the ulnar collateral ligament. Our results suggest that ulnar collateral ligament laxity should be tested clinically, and
possibly evaluated with stress radiographs or ultrasound, with
the forearm in neutral rotation. Furthermore, positioning of
the forearm may need to be considered during tensioning of a
graft at the time of ulnar collateral ligament reconstruction,
although this issue still needs to be studied. Marc R. Safran, MD
Department of Orthopaedic Surgery, University of California, San Francisco, 500 Parnassus Avenue, MU 320W, San Francisco, CA 94143. E-mail
address: safranm@orthosurg.ucsf.edu
Michelle H. McGarry, MS
Steve Shin, MD
Steve Han, BS
Thay Q. Lee, PhD
Orthopaedic Biomechanics Laboratory, VA Long Beach Healthcare System (09/151), and University of California, Irvine, 5901 East 7th Street,
Long Beach, CA 90822. E-mail addresses for T.Q. Lee: tqlee@med.va.gov;
tqlee@uci.edu
The authors did not receive grants or outside funding in support of their
research or preparation of this manuscript. They did not receive payments or other benefits or a commitment or agreement to provide such
benefits from a commercial entity. No commercial entity paid or
directed, or agreed to pay or direct, any benefits to any research fund,
foundation, educational institution, or other charitable or nonprofit
organization with which the authors are affiliated or associated.
doi:10.2106/JBJS.D.02045
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