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n Feature Article
Anatomy and Histology of the Transverse
Humeral Ligament
Brian J. Snow, MD; Steven J. Narvy, MD; Reza Omid, MD; Roscoe D. Atkinson, MD†;
C. Thomas Vangsness Jr, MD
abstract
Full article available online at Healio.com/Orthopedics. Search: 20130920-23
The classic literature describes the transverse humeral ligament (THL) as a distinct
anatomic structure with a role in biceps tendon stability; however, recent literature
suggests that it is not a distinct anatomic structure. The purpose of this study was to
evaluate the gross and microscopic anatomy of the THL, including a specific investigation of the histology of this ligament.
Thirty frozen, embalmed cadaveric specimens were dissected to determine the gross
anatomy of the THL. Seven specimens were evaluated histologically for the presence
of mechanoreceptors and free nerve endings. Two tissue layers were identified in the
area described as the THL. In the deep layer, fibers of the subscapularis tendon were
found to span the bicipital groove with contributions from the coracohumeral ligament
and the supraspinatus tendon. Superficial to this layer was a fibrous fascial covering
consisting of distinct bands of tissue. Neurohistology staining revealed the presence of
free nerve endings but no mechanoreceptors.
This study’s findings demonstrate that the THL is a distinct structure continuous with
the rotator cuff tendons and the coracohumeral ligament. The finding of free nerve
endings in the THL suggests a potential role as a shoulder pain generator.
Figure: Photograph of dissection showing the
transverse humeral ligament spanning the intertubercular groove. The superficial layer in distinct
bundles is visible.
The authors are from the Department of Orthopaedic Surgery (BJS, SJN, RO, CTV) and the Department of Pathology (RDA), Keck School of Medicine, University of Southern California, Los Angeles,
California.
The authors have no relevant financial relationships to disclose.
†Deceased.
Correspondence should be addressed to: C. Thomas Vangsness Jr, MD, Department of Orthopaedic
Surgery, Keck School of Medicine, University of Southern California, 1520 San Pablo St, #2000, Los
Angeles, CA 90089 ([email protected]).
doi: 10.3928/01477447-20130920-23
OCTOBER 2013 | Volume 36 • Number 10
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n Feature Article
T
he rotator interval of the shoulder
is a triangular space in the shoulder capsule bordered by the base
of the coracoid medially, the anterior margin of the supraspinatus tendon superiorly, the superior border of the subscapularis
tendon inferiorly, and the transverse ligament laterally. Aspects of the interval region have been the topic of controversy in
the literature in both anatomic and functional aspects.1-8
The transverse humeral ligament
(THL) was first described in 1889 by Brodie9 as a broad band of trapezoidal fibrous
tissue between the greater and lesser tuberosities of the humerus. It has been described in similar fashion by other early
works, including in Anatomy: Descriptive and Surgical by Gray10 and Applied
Anatomy by Davis.11 Its described function was to help retain the long head of
the biceps tendon within the intertubercular groove as it emerges from beneath the
coracohumeral ligament.
Although the insertional anatomy and
function of the rotator cuff have been
studied extensively, little attention has
been given to the THL. Few precise anatomic or functional descriptions of the
THL exist, and no consensus has been
reached regarding its lateral insertion and
exact structure.6,12-17 Magnetic resonance
imaging evidence suggests that the structure classically described as the THL may
be a direct continuation of the tendon of
the subscapularis.18
The purposes of this study were to
provide an accurate anatomic description
of the THL and to define the neural structures it contains.
Materials and Methods
Thirty frozen, embalmed cadaver
shoulders of uncertain age were dissected under loupe magnification. The skin
and subcutaneous tissue were removed.
The deltoid muscle was sharply released
from its origins and reflected distally. The
short head of the biceps and the pectoralis major muscles were also released and
e1296
reflected. Blunt dissection was used to
reach the long head of the biceps tendon
on the surface of the humerus and free it
below the level where the THL has been
described. The superior and inferior borders of the fibrous tissue overlying the intertubercular groove were then demarcated, and all connective and adipose tissue
were removed to aid in visualization. The
origin, insertion, and nature of the fibers
composing the ligament were defined and
described. A standard caliper was then
used to measure the height and width of
the ligament.
Seven specimens were subsequently
removed, frozen, and sectioned with a
25-µm-wide sliding microtome, which
produced 240 continuous tissue sections
mounted on 100 slides per specimen. A
modified Zimny gold chloride technique
consisting of 90% formic acid, 1% aqueous
gold chloride, and lemon juice was then
used to identify the neural tissue within
each section.19 The slides were reviewed
by a single neuropathologist (R.D.A.).
1
Figure 1: Photograph of dissection showing the
transverse humeral ligament spanning the intertubercular groove. The superficial layer in distinct
bundles is visible.
Results
The anatomic region described as the
THL consisted of 2 layers of tissue: a
thin, superficial layer consisting of fibers
in distinct bundles and a deeper layer of
fibrous tissue spanning the intertubercular
groove (Figure 1). Proximally, this deep
layer was a continuance of fibers from the
rotator cuff tendons and the coracohumeral ligament. Fibers of the subscapularis
continued from the superomedial side,
whereas the supraspinatus tendon contributed fibers laterally. The coracohumeral
ligament fibers blended with the rotator
cuff tendons at the proximal superior edge
of the groove. Distally, the fibers of the
subscapularis muscle were predominant.
Average width of the bicipital groove
was 10 mm. The tissue spanning the groove
averaged 14 mm wide and 14 mm high.
Histologic staining revealed flat sheets of
collagen consisting of dense regular connective tissue centrally and dense irregular connective tissue at the periphery near
2
Figure 2: Photograph showing an unmyelinated
free nerve ending (arrow) in the periphery of the
ligament near the greater tuberosity.
the humeral tuberosities. No mechanoreceptors were noted after the modified gold
chloride stain was applied. Free nerve
endings were noted in both tissue layers,
particularly in the areas of dense irregular
connective tissue (Figure 2). Both myelinated and unmyelinated nerves were present in all specimens examined.
Discussion
Much anatomic variation exists within
the rotator interval, and the literature is
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Transverse Humeral Ligament | Snow et al
controversial regarding the existence of
the THL as a discrete anatomic structure
traversing the intertubercular groove.
Gleason et al20 performed anatomic,
magnetic resonance imaging, and histology studies on 7 matched pairs of freshfrozen cadaveric shoulders. Two layers
of distinct tissue were noted, as were
observed in the current study, but the authors determined that the fibers covering
the intertubercular groove were composed
of a sling formed mainly by fibers of the
subscapularis, with contributions from the
supraspinatus tendon and coracohumeral
ligament. No separate ligamentous structure, consistent with the described THL,
was identified traversing the bicipital
groove.20
MacDonald et al21 performed a similar
dissection study involving 85 embalmed
cadaver shoulders. In all specimens, a fibrous expansion was found arising from
the posterior lamina of the tendon of the
pectoralis major; however, a discrete THL
could not be identified within this fibrous
tissue in any specimen. Significant variation in the insertion of the subscapularis
was again noted, leading the authors to
conclude that the structure overlying the
intertubercular groove consists of tendinous fibers of subscapularis rather than a
separate THL.21
Regarding the neural anatomy of the
shoulder, Soifer et al22 evaluated the
neural elements within the subacromial
space in 14 cadaveric shoulders. Neurofilaments and peripheral nerves were
identified within the subacromial bursa,
rotator cuff tendon, biceps tendon and
tendon sheath, and THL; a significantly
richer supply of free nerve fibers was
found in the bursa compared with other
tissues. Previously, Vangsness et al23
studied the sensory innervations of the
superior, middle, and inferior glenohumeral ligaments in 8 fresh, unembalmed
cadavers and found that the ligaments
contained proprioceptive mechanoreceptors, such as Ruffini and Pacinian corpuscles, as well as free nerve endings. These
OCTOBER 2013 | Volume 36 • Number 10
results were compared with the current
study’s finding of only free nerve endings of the THL.
The current study is an anatomic descriptive basic science study that adds
to the body of evidence about the true
nature of the THL. Prior work has cast
doubt on the existence of the THL, instead describing contributions of the
subscapularis tendon across the intertubercular groove. In a magnetic resonance
imaging study of 58 shoulders, Cash et
al18 noted significant variability in this
region and found a discrete THL in only
36% of specimens. The current study
identifies a distinct structure with contributions from the rotator cuff and the
coracohumeral ligament to the THL. The
reasons for these contrasting findings
are unclear; however, the smaller sample
size in the current study is a significant
limitation given the extensive variability
within this anatomic region.
The THL identified in the current
study lacks the pressure and proprioceptive mechanoreceptors that are present in
other stabilizing shoulder structures,
such as the superior, middle, inferior, and
posterior glenohumeral ligaments. However, the presence of myelinated and unmyelinated free nerve endings suggests a
potential role of the THL as a pain generator in the clinical situations of impingement, biceps tendonitis, hypertrophy or subluxation, rotator cuff tears or
tendonitis, and rotator interval lesions.
Further study of the anatomy of the rotator interval using a larger number of
study specimens could provide more
conclusive data regarding the existence
and clinical relevance of the THL.
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