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The anatomy of the medial canthal ligament
THE ANATOMY OF THE MEDIAL CANTHAL LIGAMENT
By T. J. ROBINSON,M.D., L.M.C.C., D.A.N.B. and M. F. STRANC,L.R.C.P.&S.I., F.R.C.S. Mount Vernon Centre for Plastic Surgery, Mount Vernon Hospital, Northwood, Middlesex FOR many years medical schools have steadily reduced the time allotted to the teaching of anatomy in general, and gross anatomy in particular. While knowledge in other disciplines has expanded at an ever-increasing rate, there has been little recent study directed towards extending or revising our knowledge of gross anatomy. Work which has been done in this field has often derived its impetus from clinical observation. In severe naso-ethmoid injuries with canthal displacement, the standard approach to therapy has involved dosed lateral compression. This type of operation often fails to produce an acceptable correction of the deformity and may even damage the lacrimal apparatus in some cases. Recently, open exploration has produced very satisfactory results (Stranc, 197o). Since the principles underlying any operative procedure should take the regional anatomy into account, the world literature on the anatomy of the inner canthal region was reviewed. Although existing anatomical texts contain descriptions of the medial canthal ligament (MCL), they fail to emphasise important structural differences between its anterior and posterior limbs (Homer, 1824 ; Spalteholz, 19oo ; Testut, I911 ; Evans, I925 ; Whitnall, 1932 ; Wolff, 1954), while a recent surgical publication suggests that the posterior limb plays a major role in maintaining the normal relationships of the inner canthus (Converse and Smith, I966). As our operative findings did not wholly concur with the foregoing view, this study was undertaken to re-examine the structural differences between the anterior and posterior limbs and to reconsider their relative importance. Materials a n d M e t h o d s . w T h e following observations result from the study of the inner canthal region in fourteen surgical explorations and six dissections in cadavers. The clinical observations on the anatomy of the inner canthal region were made possible in some cases by exploring pre-existing lacerations across the region. Where no laceration was present, a vertical incision in the midline of the root of the nose was utilised as a means of exploring the area and accurately assessing the anatomy and the changes produced by trauma. The dissections on cadavers were all performed on formalinised specimens. The cadavers were all of Caucasian race with ages ranging from middle-aged to elderly. Two of the cadavers were male, and three were female. On one of the male cadavers, both inner canthal regions were dissected. All measurements are referable to the cadaver dissections. Measurements were obtained with calipers, except in the case of the anterior lacrimal ridge. In this particular case, the thickness was measured by passing a hooked wire with a sleeve on it through a small drill hole. The sleeve was fixed in place with a Spencer-Wells forcep, and the wire withdrawn for measurement. Lastly, the relationship of the lacrimal canaliculi to the palpebral extensions of the ligament was examined in detail histologically.
B R I T I S H JOURNAL OF PLASTIC SURGERY
Artist's impression of medial canthal ligament.
FIG. 2
Artist's impression : transverse section of the right orbit viewed from above. L Anterior limb of M C L . 2. Lacrimal sac. 3. Posterior limb of M C L (lacrimal fascia and H o m e r ' s muscle).
THE A N A T O M Y OF THE M E D I A L C A N T H A L L I G A M E N T
3
Results (Fig. I ) . - - T h e medial canthal ligament is a band of fibrous tissue which acts as a tendon of insertion for the orbicularis oculi muscle. It is situated between the medial borders of the eyelids and the bones of the medial orbital wall, viz. the lacrimal bone and the frontal process of maxilla. The most lateral parts of the medial canthal ligament are the upper and lower palpebral extensions which attach to the margins of the tarsal plates lateral to the caruncle, and delimit the inner canthus. Anterior Limb (Fig. 2).--Medial to the caruncle, the ligament bifurcates into a superficial anterior and a deep posterior limb. The anterior limb, which is the stronger
FIG. 3 Dissection o f M C L . I. A n t e r i o r limb o f M C L . 2. L a c r i m a l sac (opened). 3. Posterior l i m b o f M C L (retracted).
of the two, is palpable clinically and its lower border is sometimes visible through the skin. During dissection, all of this limb except its inferior border is usually obscured by the inserting fibres of the orbicularis oculi. Removal of these fibres reveals a shiny white band of considerable mass and strength (Fig. 3). Running medially, it becomes a direct anterior relation of the lacrimal sac. The most medial fibres are posterior to the angular vessels. As seen in the Table, the length of the anterior limb from the inner canthus to its most medial fibres of insertion averaged I I-7 ram., while its width in the A-P plane averaged 4"9 ram. Whereas the inferior border is well defined, the superior aspect merges gradually with the lacrimal fascia sweeping up and over the dome of the lacrimal sac.
The anterior limb has a broad insertion to the frontal process of maxilla with some fibres extending medially towards the nasal bones. In some individuals, these fibres may actually reach the nasal bones. The area of insertion averages 2 5.3 sq. mm. The bone (or bones) into which the anterior limb of the ligament is inserted forms a strong buttress for its attachment.
4
B R I T I S H JOURNAL OF PLASTIC SURGERY TABLE
FINDINGS AVERA6E MEASUREMENTS .~.
, ~.'-:..~ . . , "
-
,,.~,.'.~" '
- I , MEDIAL
BONY ATTA(~HME81" -.T.O S q . m n t
IN SUBJECT:
$#X
CA
DAVE
R S
2r~MfiMa/e iS.Female J g . F e m ~ e ] 4 5 . F e m a l e [ 51 Male u~tE~e giqhr~¢e giqht~e ] gichrE~e ]~iqht~'e ] Left~¢e...
and 91isf'eninq ANTERIOR HEAD $ r r o n g , . _ f _ i b r o u s 11-4 II '5 I1.0 II "7 II "8 Length : __,~-~5 _ 5.1 .... 4.9 5-3 4.2 Width : ~ n q Affachmen|" 4"5 5.0 .4 t 5.0 6.0 - anterior ro ridge: -area:
5"5
5 "5
~O'25S#m. 25".50sgm ~3"OOam, 26"50~,~ ?2.~.20y¢~ 30"2~mn
POSTER/OR HEAD i
All measurementsare in milllmefres.
13"0
LacrimalfAs6a. Homer's muscle. Weak and p o o r h I de]-'Jned Areolarand ligamentousti.ue.
FIG. 4 Transilluminated skull. I. Thick anterior lacrimal crest, z. T h i n posterior lacrimal crest.
See text,
THE ANATOMY OF THE MEDIAL CANTHAL L I G A M E N T
5
Examination of the medial orbital wall on a skull (Fig. 4) reveals considerable thickening of the fronto-nasal process of maxilla along the anterior lacrimal crest. In a transilluminated skull this is seen as a darkened region which allows relatively little light to pass through it. By measuring the depth of a small drill hole, this thickening was found to average 1.5 mm. By virtue of the inherent strength of the anterior limb, the breadth of its insertion, and the strength of the bones to which it attaches, the anterior limb of the M C L provides solid anchorage for the medial end of the palpebral fissure. In all of these anatomical features the anterior limb presents a striking contrast to the posterior limb. Posterior Limb (Fig. 2 ) . ~ T h e posterior limb is difficult to define. It consists of lacrimal fascia (which is its strongest component), Horner's muscle and areolar tissue. Its thickness varied from I.O to 3"3 mm. In only one dissection were there any fibres
FIG. 5 Artist's impression of lacrimal apparatus. Arrow indicates dome of lacrimal sac.
comparable to those of the anterior limb, and these were few in number. The small extension of orbicularis oculi found in the posterior limb is known as Homer's muscle. Together, the lacrimal fascia and Horner's muscle insert into the posterior lacrimal crest. The site of insertion of Horner's muscle is the more posterior of the two. Although the vertical extent of this insertion is considerable, the crest is very fine and the total area of the attachment could not be accurately measured. In contrast with the bones to which the anterior limb is attached, the entire lacrimal bone and crest are paper-thin and allow much light to pass through them when the skull is transilluminated. Thus the insertion of the posterior limb lacks strength not only because of its weak fibres and small area of insertion, but also because the underlying bone is incapable of providing solid anchorage. Lacrimal Apparatus.--By opening the lacrimal sac it was possible to measure how far its dome extended above the anterior limb of the MCL. With minor variations the distance was I.O mm. in all cases. The palpebral extensions together with the main body of the ligament form a letter " Y "placed on its side. These extensions appeared on gross examination to contain the lacrimal canaliculi, as demonstrated in Figure 5. Certainly, the two structures, i.e. the palpebral extensions ~nd the canaliculi, were intimately associated in all dissections. To confirm this, sagittal sections were prepared and examined histologically from the lacrimal puncta to the sac.
6
BRITISH JOURNAL OF PLASTIC SURGERY
Figure 6, an example of the sections prepared, clearly demonstrates that each canaliculus runs completely encased in a fibrous tissue sheath. Although only one section is shown out of the twenty-four prepared, examination of all sections reveals that the sheath is present along the entire length of both upper and lower canaliculi. Medial to
FIG. 6 Sagittal section of the canaliculi at the level of the caruncle ( × 7"5 magnification). I. Epithelial lining of the canaliculi. 2. Fibrous sheath surrounding the canaliculus. This sheath constitutes the palpebral extensions of the M C L .
the caruncle, the canaliculi run within the anterior limb of the M C L for the greater part of their course. In three cases the canaliculi entered the sac separately, and in the remaining three they joined before entering. Where entry was separate, the two sites of entry were in close proximity to each other. In all dissections the entry was at or near the level at which the anterior limb crossed the front of the sac.
THE ANATOMY OF THE MEDIAL CANTHAL LIGAMENT
7
DISCUSSION
While it is true that the inner canthus is a rather fixed point, the anatomical structures that hold it " i n the depth of the naso-orbital valley " (Blair et al., I93I) have been the subject of much controversy. Although the orbicularis oculi muscle causes marked lateral displacement of the inner canthus when the M C L is detached, the same muscle provides a dynamic force tending towards lateral displacement of the undisturbed inner canthus (Jones, I967). The force of this muscular pull must be counteracted by 9ne or more sturdy structures that are well anchored medially. From the foregoing description it is clear that the anterior limb of the medial canthal ligament and its bony attachment provide such an anchor, while the posterior limb is incapable of such ff task. What then is the function or purpose of the posterior limb ? The muscular portion has previously been termed t h e " tensor tarsi ", but the bulk of the muscle is so small that the function implied by this term seems unlikely. It will be recalled that the muscle insertion is posterolateral to the lacrimal sac. Thus its contraction may facilitate sac emptying and tear drainage either by expansion of the sac in a manner analogous to the action of the diaphragm on inspiration, or by direct compression of the sac. SUMMARY
This paper presents results of study of the anatomy of the medial canthal ligament. The authors feel that existing texts have failed to emphasise the important structural differences between the anterior and posterior limbs of this ligament. Particular note was taken of the intimate relationship of the lacrimal apparatus and the ligament. The function of Homer's muscle as reflected in the term " tensor tarsi" has been questioned. The authors wish to acknowledge with gratitude the invaluable artistic skill of Miss K. Ockendon who spent many hours preparing drawings for this paper. We also wish to thank Dr A. Knudson of the West Middlesex Hospital for preparing histological sections, Mr P. R. Runnicles for his excellent photography, and Professor E. IF. Walls of the Anatomy Department at The Middlesex Hospital Medical School for the use of his dissection facilities. REFERENCES BLAIR, V. P., BROWN, J. B. and HAMM, W. G. (1931). Am..7. Ophthal. 15, 498. CONVERSE,J. M . and SMITH,B. (1966). Plastic reconstr. Surg. 38, !47. EVANS, J. H. (1925). Am. ft. phys. Anthrop. 8, 411. HORNER, W. E. (1824). Philad. ft., p. 70. JoNEs, L. T . (1967). Proc. 2nd int. Symp. plast, reconstr. Surg. Eye and Adnex~, p. 3 o. St Louis : Mosby. SPALTI~HOLTZ~W. (19OO). " H a n d Atlas of H u m a n Anatomy ", 3rd ed. Philadelphia : Saunders. STRANC,i . F. (1970). Br. ft. plast. Surg., 23, 8. TESTUT, L. (1911). " Trait6 d'Anatomie Humaine ", 6th ed. Paris : Doin. WHITNALL,S. E. (1932). " A n a t o m y of the H u m a n Orbit ", 2nd ed. London : Oxford University Press. WOLFF, E. (1954). " T h e Anatomy of the Eye and Orbit ", 4th ed. London : Lewis.
By T. J. ROBINSON,M.D., L.M.C.C., D.A.N.B. and M. F. STRANC,L.R.C.P.&S.I., F.R.C.S. Mount Vernon Centre for Plastic Surgery, Mount Vernon Hospital, Northwood, Middlesex FOR many years medical schools have steadily reduced the time allotted to the teaching of anatomy in general, and gross anatomy in particular. While knowledge in other disciplines has expanded at an ever-increasing rate, there has been little recent study directed towards extending or revising our knowledge of gross anatomy. Work which has been done in this field has often derived its impetus from clinical observation. In severe naso-ethmoid injuries with canthal displacement, the standard approach to therapy has involved dosed lateral compression. This type of operation often fails to produce an acceptable correction of the deformity and may even damage the lacrimal apparatus in some cases. Recently, open exploration has produced very satisfactory results (Stranc, 197o). Since the principles underlying any operative procedure should take the regional anatomy into account, the world literature on the anatomy of the inner canthal region was reviewed. Although existing anatomical texts contain descriptions of the medial canthal ligament (MCL), they fail to emphasise important structural differences between its anterior and posterior limbs (Homer, 1824 ; Spalteholz, 19oo ; Testut, I911 ; Evans, I925 ; Whitnall, 1932 ; Wolff, 1954), while a recent surgical publication suggests that the posterior limb plays a major role in maintaining the normal relationships of the inner canthus (Converse and Smith, I966). As our operative findings did not wholly concur with the foregoing view, this study was undertaken to re-examine the structural differences between the anterior and posterior limbs and to reconsider their relative importance. Materials a n d M e t h o d s . w T h e following observations result from the study of the inner canthal region in fourteen surgical explorations and six dissections in cadavers. The clinical observations on the anatomy of the inner canthal region were made possible in some cases by exploring pre-existing lacerations across the region. Where no laceration was present, a vertical incision in the midline of the root of the nose was utilised as a means of exploring the area and accurately assessing the anatomy and the changes produced by trauma. The dissections on cadavers were all performed on formalinised specimens. The cadavers were all of Caucasian race with ages ranging from middle-aged to elderly. Two of the cadavers were male, and three were female. On one of the male cadavers, both inner canthal regions were dissected. All measurements are referable to the cadaver dissections. Measurements were obtained with calipers, except in the case of the anterior lacrimal ridge. In this particular case, the thickness was measured by passing a hooked wire with a sleeve on it through a small drill hole. The sleeve was fixed in place with a Spencer-Wells forcep, and the wire withdrawn for measurement. Lastly, the relationship of the lacrimal canaliculi to the palpebral extensions of the ligament was examined in detail histologically.
B R I T I S H JOURNAL OF PLASTIC SURGERY
Artist's impression of medial canthal ligament.
FIG. 2
Artist's impression : transverse section of the right orbit viewed from above. L Anterior limb of M C L . 2. Lacrimal sac. 3. Posterior limb of M C L (lacrimal fascia and H o m e r ' s muscle).
THE A N A T O M Y OF THE M E D I A L C A N T H A L L I G A M E N T
3
Results (Fig. I ) . - - T h e medial canthal ligament is a band of fibrous tissue which acts as a tendon of insertion for the orbicularis oculi muscle. It is situated between the medial borders of the eyelids and the bones of the medial orbital wall, viz. the lacrimal bone and the frontal process of maxilla. The most lateral parts of the medial canthal ligament are the upper and lower palpebral extensions which attach to the margins of the tarsal plates lateral to the caruncle, and delimit the inner canthus. Anterior Limb (Fig. 2).--Medial to the caruncle, the ligament bifurcates into a superficial anterior and a deep posterior limb. The anterior limb, which is the stronger
FIG. 3 Dissection o f M C L . I. A n t e r i o r limb o f M C L . 2. L a c r i m a l sac (opened). 3. Posterior l i m b o f M C L (retracted).
of the two, is palpable clinically and its lower border is sometimes visible through the skin. During dissection, all of this limb except its inferior border is usually obscured by the inserting fibres of the orbicularis oculi. Removal of these fibres reveals a shiny white band of considerable mass and strength (Fig. 3). Running medially, it becomes a direct anterior relation of the lacrimal sac. The most medial fibres are posterior to the angular vessels. As seen in the Table, the length of the anterior limb from the inner canthus to its most medial fibres of insertion averaged I I-7 ram., while its width in the A-P plane averaged 4"9 ram. Whereas the inferior border is well defined, the superior aspect merges gradually with the lacrimal fascia sweeping up and over the dome of the lacrimal sac.
The anterior limb has a broad insertion to the frontal process of maxilla with some fibres extending medially towards the nasal bones. In some individuals, these fibres may actually reach the nasal bones. The area of insertion averages 2 5.3 sq. mm. The bone (or bones) into which the anterior limb of the ligament is inserted forms a strong buttress for its attachment.
4
B R I T I S H JOURNAL OF PLASTIC SURGERY TABLE
FINDINGS AVERA6E MEASUREMENTS .~.
, ~.'-:..~ . . , "
-
,,.~,.'.~" '
- I , MEDIAL
BONY ATTA(~HME81" -.T.O S q . m n t
IN SUBJECT:
$#X
CA
DAVE
R S
2r~MfiMa/e iS.Female J g . F e m ~ e ] 4 5 . F e m a l e [ 51 Male u~tE~e giqhr~¢e giqht~e ] gichrE~e ]~iqht~'e ] Left~¢e...
and 91isf'eninq ANTERIOR HEAD $ r r o n g , . _ f _ i b r o u s 11-4 II '5 I1.0 II "7 II "8 Length : __,~-~5 _ 5.1 .... 4.9 5-3 4.2 Width : ~ n q Affachmen|" 4"5 5.0 .4 t 5.0 6.0 - anterior ro ridge: -area:
5"5
5 "5
~O'25S#m. 25".50sgm ~3"OOam, 26"50~,~ ?2.~.20y¢~ 30"2~mn
POSTER/OR HEAD i
All measurementsare in milllmefres.
13"0
LacrimalfAs6a. Homer's muscle. Weak and p o o r h I de]-'Jned Areolarand ligamentousti.ue.
FIG. 4 Transilluminated skull. I. Thick anterior lacrimal crest, z. T h i n posterior lacrimal crest.
See text,
THE ANATOMY OF THE MEDIAL CANTHAL L I G A M E N T
5
Examination of the medial orbital wall on a skull (Fig. 4) reveals considerable thickening of the fronto-nasal process of maxilla along the anterior lacrimal crest. In a transilluminated skull this is seen as a darkened region which allows relatively little light to pass through it. By measuring the depth of a small drill hole, this thickening was found to average 1.5 mm. By virtue of the inherent strength of the anterior limb, the breadth of its insertion, and the strength of the bones to which it attaches, the anterior limb of the M C L provides solid anchorage for the medial end of the palpebral fissure. In all of these anatomical features the anterior limb presents a striking contrast to the posterior limb. Posterior Limb (Fig. 2 ) . ~ T h e posterior limb is difficult to define. It consists of lacrimal fascia (which is its strongest component), Horner's muscle and areolar tissue. Its thickness varied from I.O to 3"3 mm. In only one dissection were there any fibres
FIG. 5 Artist's impression of lacrimal apparatus. Arrow indicates dome of lacrimal sac.
comparable to those of the anterior limb, and these were few in number. The small extension of orbicularis oculi found in the posterior limb is known as Homer's muscle. Together, the lacrimal fascia and Horner's muscle insert into the posterior lacrimal crest. The site of insertion of Horner's muscle is the more posterior of the two. Although the vertical extent of this insertion is considerable, the crest is very fine and the total area of the attachment could not be accurately measured. In contrast with the bones to which the anterior limb is attached, the entire lacrimal bone and crest are paper-thin and allow much light to pass through them when the skull is transilluminated. Thus the insertion of the posterior limb lacks strength not only because of its weak fibres and small area of insertion, but also because the underlying bone is incapable of providing solid anchorage. Lacrimal Apparatus.--By opening the lacrimal sac it was possible to measure how far its dome extended above the anterior limb of the MCL. With minor variations the distance was I.O mm. in all cases. The palpebral extensions together with the main body of the ligament form a letter " Y "placed on its side. These extensions appeared on gross examination to contain the lacrimal canaliculi, as demonstrated in Figure 5. Certainly, the two structures, i.e. the palpebral extensions ~nd the canaliculi, were intimately associated in all dissections. To confirm this, sagittal sections were prepared and examined histologically from the lacrimal puncta to the sac.
6
BRITISH JOURNAL OF PLASTIC SURGERY
Figure 6, an example of the sections prepared, clearly demonstrates that each canaliculus runs completely encased in a fibrous tissue sheath. Although only one section is shown out of the twenty-four prepared, examination of all sections reveals that the sheath is present along the entire length of both upper and lower canaliculi. Medial to
FIG. 6 Sagittal section of the canaliculi at the level of the caruncle ( × 7"5 magnification). I. Epithelial lining of the canaliculi. 2. Fibrous sheath surrounding the canaliculus. This sheath constitutes the palpebral extensions of the M C L .
the caruncle, the canaliculi run within the anterior limb of the M C L for the greater part of their course. In three cases the canaliculi entered the sac separately, and in the remaining three they joined before entering. Where entry was separate, the two sites of entry were in close proximity to each other. In all dissections the entry was at or near the level at which the anterior limb crossed the front of the sac.
THE ANATOMY OF THE MEDIAL CANTHAL LIGAMENT
7
DISCUSSION
While it is true that the inner canthus is a rather fixed point, the anatomical structures that hold it " i n the depth of the naso-orbital valley " (Blair et al., I93I) have been the subject of much controversy. Although the orbicularis oculi muscle causes marked lateral displacement of the inner canthus when the M C L is detached, the same muscle provides a dynamic force tending towards lateral displacement of the undisturbed inner canthus (Jones, I967). The force of this muscular pull must be counteracted by 9ne or more sturdy structures that are well anchored medially. From the foregoing description it is clear that the anterior limb of the medial canthal ligament and its bony attachment provide such an anchor, while the posterior limb is incapable of such ff task. What then is the function or purpose of the posterior limb ? The muscular portion has previously been termed t h e " tensor tarsi ", but the bulk of the muscle is so small that the function implied by this term seems unlikely. It will be recalled that the muscle insertion is posterolateral to the lacrimal sac. Thus its contraction may facilitate sac emptying and tear drainage either by expansion of the sac in a manner analogous to the action of the diaphragm on inspiration, or by direct compression of the sac. SUMMARY
This paper presents results of study of the anatomy of the medial canthal ligament. The authors feel that existing texts have failed to emphasise the important structural differences between the anterior and posterior limbs of this ligament. Particular note was taken of the intimate relationship of the lacrimal apparatus and the ligament. The function of Homer's muscle as reflected in the term " tensor tarsi" has been questioned. The authors wish to acknowledge with gratitude the invaluable artistic skill of Miss K. Ockendon who spent many hours preparing drawings for this paper. We also wish to thank Dr A. Knudson of the West Middlesex Hospital for preparing histological sections, Mr P. R. Runnicles for his excellent photography, and Professor E. IF. Walls of the Anatomy Department at The Middlesex Hospital Medical School for the use of his dissection facilities. REFERENCES BLAIR, V. P., BROWN, J. B. and HAMM, W. G. (1931). Am..7. Ophthal. 15, 498. CONVERSE,J. M . and SMITH,B. (1966). Plastic reconstr. Surg. 38, !47. EVANS, J. H. (1925). Am. ft. phys. Anthrop. 8, 411. HORNER, W. E. (1824). Philad. ft., p. 70. JoNEs, L. T . (1967). Proc. 2nd int. Symp. plast, reconstr. Surg. Eye and Adnex~, p. 3 o. St Louis : Mosby. SPALTI~HOLTZ~W. (19OO). " H a n d Atlas of H u m a n Anatomy ", 3rd ed. Philadelphia : Saunders. STRANC,i . F. (1970). Br. ft. plast. Surg., 23, 8. TESTUT, L. (1911). " Trait6 d'Anatomie Humaine ", 6th ed. Paris : Doin. WHITNALL,S. E. (1932). " A n a t o m y of the H u m a n Orbit ", 2nd ed. London : Oxford University Press. WOLFF, E. (1954). " T h e Anatomy of the Eye and Orbit ", 4th ed. London : Lewis.