Download Lateral Epicondylitis Originates At The Anterior Side Of The Articular

Lateral Epicondylitis Originates At The Anterior Side Of The Articular Capsule
Underlying The Extensor Carpi Radialis Brevis
Akimoto Nimura, Keiichi Akita.
Graduate School, Tokyo Medical and Dental University, Tokyo, Japan.
Disclosures:
A. Nimura: None. K. Akita: None.
Introduction: Numerous causes and pathologies have been described for lateral epicondylitis of the humerus. Stenotic changes
in the annular ligament, chondromalacia of the capitellum or the radial head, and synovial fringe are considered to be attributed
to the pathology. While these are viable factors, the common extensor origin, in particular the extensor carpi radialis brevis
(ECRB), has been considered as the primary candidate for the pathologic origin. As a matter of fact, there have been few studies
regarding the differentiating characteristics of ECRB itself in comparison with other extensors.(1) We hypothesize that the ECRB
may have a unique anatomic character that differentiates itself from other extensors and causes the initiation of lateral
epicondylitis.
In regard to the causes of lateral epicondylitis, the capsuloligamentous structures of the radio-humeral joint, including the
synovial fringe and the annular ligament, have also been discussed in depth. However, though the attachment of the articular
capsule of the radio-humeral joint is the deepest structure underlying the ECRB origin, the relationship of the two has rarely
been discussed with respect to the etiology. We secondly hypothesize that there may be a specific relationship between the
ECRB origin and the underlying structures from the viewpoint of the etiology.
The first aim is to analyze the anatomic features of the ECRB origin that make it subjective to the pathology of lateral
epicondylitis in comparison with other extensors. The second aim is to identify relationships between the ECRB origin and other
deeper structures, such as the articular capsule of the radio-humeral joint and the supinator.
Methods: A total of 23 arms from 17 Japanese cadavers (10 male and 7 females; average age, 79.6 years old) were used in this
study. All cadavers were fixed in formalin. Three arms with capsular tears at their attachment under ECRB origins were excluded.
Of the 20 arms, 16 arms were used for macroscopic observations. First, each extensor was identified at the distal side and
flipped to proximal. To evaluate the composition of the muscular and tendinous parts, all muscular fibers were removed from
each tendon. In 8 arms, all extensors were removed and the complete origin of the extensor carpi radialis longus (ECRL), the
extensor digiti minimi (ED/EDM), and ECRB were exposed. Finally, the articular capsule and the supinator tendon were detached
together and reflected to lateral. In 8 arms, we examined and measured the size of the origin of ED/EDM and ECRL and the
width of the attachment of the articular capsule. The remaining 4 arms were sectioned and analyzed histologically with Masson
trichrome stainning.
Results: Brachioradialis (BR) and ECRL arose from the lateral supracondylar ridge of the humerus and contained a large muscular
part (Fig. 1A). ED/EDM originated from the lateral epicondyle just distal to ECRL. ECRL and ED/EDM were adjoined and
originated from the surface of the tendon of ECRB. The ECRB origin could be clearly separated from the overlying muscular part
of ECRL, ED/EDM and the underlying articular capsule and supinator. To evaluate the composition of the muscular and
tendinous portions of the extensors, muscular fibers were removed from each tendon. BR and ECRL were mostly composed of a
muscular part and only thin and short tendons (Fig. 1B). ED/EDM and extensor carpi ulnaris (ECU) were composed of a muscular
part and a thin membranous tendon. Note that only ECRB was simply composed of a thick tendinous part without any muscular
parts.
To understand the relationship between the ECRB origin and deeper structures, each tendon was detached. The origin of
ED/EDM (circle in Fig. 2A) was located distal to that of ECRL (star). The origin of ECRB (square) was located anterior to that of
ED/EDM. The anterior side of the origin of ECRB was surrounded by the articular capsule. The attachment of the articular
capsule at the anterior edge of the ECRB origin (Ca in Fig. 2C) was 3.3 mm (SD, 0.7 mm). In contrast, the tendinous slip of the
supinator originated in contact with the postero-distal side of the ECRB origin and intermingled with the articular capsule. The
attachment of the articular capsule at the distal edge of the ECRB origin (Cd) was 10.7 mm (SD, 1.0 mm).
In order to histologically analyze these relationships, coronal sections of the radio-humeral joint were made. At the anterior part
of the ECRB origin, the very thin articular capsule was found to underlie the ECRB tendon with a distinct border and distally it
combined with the annular ligament (asterisk)(Fig. 3AB). However, at the posterior portion, the articular capsule, annular
ligament, and supinator intermingled and attached to the humerus with a substantial area(Fig. 3CD).
Measurement of the origin of the extensors and the attachment of the articular capsule
The location of the measurement
Average and standard deviation (mm)
Origin of extensor digitorum and extensor digiti minimi (ED/EDM)
Craniocaudal length (L1)
7.7±2.1
Anteroposterior width (W1)
4.6±7.2
Origin of extensor carpi radialis brevis (ECRB)
Craniocaudal length (L2)
7.2±2.0
Anteroposterior width (W2)
5.5±0.5
Attachment of the articular capsule
Width at the anterior edge of the origin of ECRB (Ca)
3.3±0.7
Width at the distal edge of the origin of ECRB (Cd)
10.7±1.0
Discussion: While the origin of ECRB has been described as an initiation of lateral epicondylitis, the differentiating characteristics
of ECRB itself have rarely been discussed in comparison with other extensors including ECRL, ED/EDM, and ECU. The reason may
be that they form a tight structure of conjoined tendon and they were not considered to be clearly differentiated. In the current
study, however, based on the composition of the muscular and tendinous parts of each extensor, the anatomic characteristic of
ECRB could be clearly identified. ECRB simply originated as a rigid and long tendinous portion without any muscular portions.
Meanwhile, other extensors in the common extensor tendon including ED/EDM and ECU originated as a mixture of thin tendon
and muscular portions. Similar to the mechanism of hamstring injury(2), the origin of ECRB could be speculated to be subject to
repetitive traction force during elbow motions for sports and daily activities based on the anatomic feature of the composition
of the tendinous and muscular portions. Meanwhile, the other extensors of the common extensor are adjoined to the tendon of
ECRB and might support its function as a unit of the common extensor.
The attachment of the articular capsule at the anterior side of the origin of ECRB was thin and completely separated from the
tendon of ECRB. On the contrary, that under the postero-distal side of the ECRB origin was merged with the supinator, and
formed a robust attachment. Thus, it could be shown that the proximal attachment of the articular capsule was not consistent
but rather altered according to the location. In the superior shoulder joint, Nimura et al.(3) showed the attachment of the
articular capsule was relatively thin at the border of the insertion of the supraspinatus and the infraspinatus, while that at the
posterior edge of the infraspinatus insertion was very thick and >9mm. Additionally, they speculated that the initiation of a
rotator cuff tear might be related to the thinnest point of the capsule attachment. By taking the above findings into
consideration, the thin attachment of the articular capsule at the anterior side of the origin of ECRB could be a factor causing
initiation of the pathology of lateral epicondylitis, rather than the robust attachment mixed with the capsule and the supinator
at the postero-distal side.
In conclusion, ECRB simply originated as a rigid and long tendinous portion without any muscular portions, whereas other
extensors in the common extensor tendon originated as a mixture of thin tendon and muscular portions. At the anterior side of
the ECRB origin, the attachment of the articular capsule was thinner than that of postero-distal side. The thin attachment of the
articular capsule could be a factor causing initiation of the pathology of lateral epicondylitis.
Significance: The results of the current study will lead to identification of the cause of lateral epicondylitis and will result in
better treatment.
Acknowledgments:
References: 1Bunata RE. J Bone Joint Surg Am. 2007
2Sato K. J Orthop Sci. 2012
3Nimura A. J Shoulder Elbow Surg. 2012
ORS 2014 Annual Meeting
Poster No: 1008