An anatomic study on the overlap patterns of structural components in the keystone area in noses of koreans.

Abstract

The keystone area has critical importance in maintaining the stability of the nasal dorsum. However, overlap patterns between structural components in the keystone area have rarely been studied, especially in the noses of Koreans.
Dissections were performed on 18 cadaveric noses. The length and width of the structural components in the keystone area were measured. The shape of the caudal margin of the nasal bone and the overlap patterns between the upper lateral cartilage and the nasal bone were classified.
THE SHAPE OF THE CAUDAL MARGIN OF THE NASAL BONE WERE CLASSIFIED AS FOLLOWS: type A, curvilinear margin; type B, paramedian retractions or "M" shape; type C, elongated midline; and type D, retracted midline. The overlap area between the upper lateral cartilage and the nasal bone was classified as follows: type Ao, crescent shape; type Bo, short midline extension; and type Co, long midline extension. The cephalocaudal length of the overlap area between the upper lateral cartilage and the nasal bone was 4-10 mm (mean, 7 mm) in the midline, and 0-7 mm (mean, 3.1 mm) in the paramedian area. The overlap width of the upper lateral cartilage with the nasal bone was 8-14 mm (mean, 9.7 mm).
The overlap pattern of the structural components in the keystone area is variable. Therefore, a thorough understanding and a cautious evaluation of the relationships of these components before and during surgery is important in performing safe and effective nasal procedures.

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INTRODUCTION
The keystone area of the nose is critical for maintaining the struc-
tural stability of the nasal dorsum. The keystone area is comprised
of the nasal bone (NB), cartilaginous septum (CS), bony septum
(BS), and upper lateral cartilages (ULCs). Each component is firm-
ly connected with muco-periosteum, muco-perichondrium, and
dense fibrous articulations. When the stability of any component
in the keystone area is interrupted during rhinoplasty or septal
surgery, the stability of the remaining structures should be pre-
served.
Embryologically, the CS and ULCs have the same origin and
they can be considered as a single structural unit, the so-called
quadrilateral cartilage (QLC) (1-4). The QLC is overlapped by the
NB in variable lengths. The overlapped portion of the QLC and
the NB is covered by a continuation of the muco-periosteum and
muco-perichondrium, which extend to the entire nasal cavity on
both the dorsal and ventral surfaces. Therefore, it is practically
impossible to detach the ULCs from the NB with a cephalo-cau-
dal directed force. However, the connection between the QLC
and the NB is relatively weak to dorso-ventral forces, making the
connection vulnerable to trauma. The connection between the
QLC and NB is also easily damaged during rhinoplasty procedures,
such as hump resection and osteotomies.
Therefore, the strong connection of the components in the key-
stone area has been of primary interest for rhinoplasty surgeons.
Rorich et al. (5) reported the overlap length of the ULCs under
Objectives. The keystone area has critical importance in maintaining the stability of the nasal dorsum. However, overlap
patterns between structural components in the keystone area have rarely been studied, especially in the noses of
Koreans.
Methods. Dissections were performed on 18 cadaveric noses. The length and width of the structural components in the
keystone area were measured. The shape of the caudal margin of the nasal bone and the overlap patterns between
the upper lateral cartilage and the nasal bone were classified.
Results. The shape of the caudal margin of the nasal bone were classified as follows: type A, curvilinear margin; type B,
paramedian retractions or “M” shape; type C, elongated midline; and type D, retracted midline. The overlap area
between the upper lateral cartilage and the nasal bone was classified as follows: type Ao, crescent shape; type Bo,
short midline extension; and type Co, long midline extension. The cephalocaudal length of the overlap area between
the upper lateral cartilage and the nasal bone was 4-10 mm (mean, 7 mm) in the midline, and 0-7 mm (mean, 3.1
mm) in the paramedian area. The overlap width of the upper lateral cartilage with the nasal bone was 8-14 mm
(mean, 9.7 mm).
Conclusion. The overlap pattern of the structural components in the keystone area is variable. Therefore, a thorough under-
standing and a cautious evaluation of the relationships of these components before and during surgery is important
in performing safe and effective nasal procedures.
Key Words. Keystone area, Nasal septum, Nasal bone, Rhinoplasty
An Anatomic Study on the Overlap Patterns of
Structural Components in the Keystone Area in
Noses of Koreans
In-Sang Kim, MDYoung-Jun Chung, MDYoung Il Lee, MD1
Departments of Otorhinolaryngology-Head and Neck Surgery and 1Anatomy, College of Medicine, Dankook University, Cheonan, Korea
�Received August 5, 2008
Accepted after revision August 26, 2008
�Corresponding author : In-Sang Kim, MD
Department of Otorhinolaryngology-Head and Neck Surgery, College of
Medicine, Dankook University, Dankook University Hospital, 359
Manghyang-ro, Dongnam-gu, Cheonan 330-715, Korea
Tel : +82-41-550-3974, Fax : +82-41-556-1090
E-mail : codoctor@dreamwiz.com
DOI 10.3342/ceo.2008.1.3.158
Clinical and Experimental Otorhinolaryngology Vol. 1, No. 3: 158-160, September 2008
Original Article

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Kim I-S et al.: Overlap Patterns in Keystone Area
159
the NB was 6-8 mm, while Daniel (4) reported the overlap length
to be 11 mm in the midline and 4 mm at the lateral sides.
Asians tend to have a shorter nasal length, shorter nasal bones,
and smaller cartilages compared to Caucasians. However, the over-
lappatterns of the structural components in the keystone area have
rarely been studied in the noses of Asians.
Therefore, we identified the overlap patterns and anatomic
variations in the keystone area in noses of Koreans in an effort
to ensure safe nasal procedures involving this anatomic area.
MATERIALS AND METHODS
Eighteen cadavers (12 males and 6 females) were used for dissec-
tion. The ages at death ranged from 55-70 yr. There were no
identifiable nasal or facial deformities or evidence of previous
sinonasal surgical procedures in the cadavers. The soft tissues
were dissected along the entire nasal dorsum, exposing the NB,
ULCs, CS, and lower lateral cartilages. After meticulous removal
of the periosteum on the NB, the caudal margin of the NB was
inspected and photographed. The caudal margin of the NB was
marked on the CS with a marking pen. Then, the caudal portion
of the NB was carefully removed using sphenoid punch forceps
in a piecemeal fashion until the entire ULC under the NB was
exposed. The bony-cartilaginous junction of the nasal septum was
identified under the NB and the distance from the most caudal
point of the NB to the bony-cartilaginous junction was measured.
RESULTS
The midline cephalocaudal length of the overlap area between
the NB and ULCs was 4-10 mm (average, 7.0 mm), which near-
ly coincided with the distance from the most caudal point of the
NB to the bony-cartilaginous junction of the septum. On the line
bisecting the width of the NB on each side, the cephalocaudal
overlap length of the NB with the ULCs was 0-7 mm (average,
3.1 mm).
The overlap width of the NB and ULCs was widest at the
caudal margin of the NB (range, 8-14 mm; average, 9.7 mm).
The shape of the caudal margin of the NB was classified into
four types, as follows: type A, curvilinear margins; type B, “M”
shape with paramedian retractions; type C, a caudal extension of
the midline over the cartilaginous dorsum; and type D, a cephalic
retraction on the midline (Fig. 1, 2). Types A, B, C, and D exist-
ed in eight, two, four, and two cadavers respectively, and there
were combined patterns in two cadavers (types A+B and A+D).
The combined patterns had different types on each side showing
asymmetry in the paired NBs.
The shape of the overlap area was classified into three types,
as follows: type Ao, a crescent shape with a curvilinear cephalic
margin; and types Bo and Co, midline extensions. The types were
easily discerned by the average overlap length of 7 mm for all
types. Type Bo had a short midline extension, in which the mid-
line was elongated in the cephalic direction by <7 mm. Type Co
had a long midline extension in which the midline portion was
markedly elongated by >7 mm (Fig. 3). The number of cadavers
with types Ao, Bo, and Co was three, four, and nine, respective-
ly, and the combined patterns existed in two cadavers (types Ao+
Co and Bo+Co). In the combined patterns, the overlap types were
different on the right and left sides.
Fig. 1. Classification of the caudal margin of the nasal bone.
Type A, curvilinear margin; type B, paramedian retractions or “M”
shape; type C, a caudal extension of the midline over the cartilaginous
dorsum; andtype D, a cephalic retraction on the midline.
ABCD
Fig. 2. Types of caudal margin of the nasal bone in cadaver dissections. (A) Type A. (B) Type B. (C) Type C. (D) Type D.
ABCD

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DISCUSSION
In a study using 60 adult cadavers, Godley et al. (6) in reported the
cartilaginous dorsum of the nose was 21±5 mm long, and it was
shorter in females by 5±4 mm. It was also reported that the car-
tilaginous dorsum was overlapped by the NB by 4±2 mm (6).
In our previous study using magnetic resonance imaging, the
length of the cartilaginous dorsum was 26±4 mm in adults, and
there was no significant difference between genders (7). The over-
laplength between the NB and CS was 7±2 mm in adults, which
decreased with age, possibly due to calcification of CS. In the cur-
rent study, the midline overlap length of the NB and ULC was
7.0 mm on average, which was similar to the radiologic findings.
In consideration of these findings, if the NB in the rhinion area
is removed during hump resection >7 mm from the caudal mar-
gin, the overlap between the NB and QLC could be damaged for
the most part. In that case, other components of the keystone area
should be secured, such as the stability of the septal cartilage itself,
the strong connection between the CS and the perpendicular plate
of the ethmoid, the overlap between the ULC and the pyriform
aperture, and the surrounding soft tissue connections. Even if the
overlap between the NB and QLC is severely damaged, a saddle
nose would not result if these supports are carefully preserved.
The overlap length between and the NB and QLC decreases
with age, possibly due to calcification of the septal cartilage. The
overlap length also decreases with a decrease in the overall nasal
length (7). Rorich et al. (8) reported that elderly people have weak-
er strength and support of the nasal bone and cartilages. Lam and
Williams (9) also reported that in those with short NBs, there is
a higher risk of instability in the keystone area during rhinoplasty.
Therefore, for the elderly and the patients with the short nose,
very cautious manipulation is necessary in the keystone area be-
cause they tend to have a shorter and weaker overlap between
the NB and QLC.
In the current study, we determined that ULCs are overlapped
under the NB in variable length, width, and shape. This variability
of the connection between the ULC, SC, and NB is also increased
by the variable shape of the caudal margin of the NB. Therefore,
there might be weaker or stronger combinations of connections.
For example, an overlap of a type Ao and a caudal margin of type
D would be the weakest form of a connection. In contrast, an over-
lap involving a type Co and the caudal margin of a type C would
be the strongest combination of connections with the largest over-
laparea.
These anatomic variations may be the cause of different results
after aggressive nasal procedures, such as hump resection, osteo-
tomies, and wide septal resection resulting in certain degrees of
saddle nose in some patients, while not in other patients.
Therefore, the relationships and overlap patterns of the struc-
tural components in the keystone area should be thoroughly
evaluated pre- or intra-operatively in individual patients. Preo-
peratively, the shape of the NB should be examined because the
patients with a short nasal bone are known to have a weaker key-
stone area. Intraoperatively, fine dissection in the proper supraperi-
chondrial plane should be performed to identify the shape of the
caudal margin of the NB. The overlap length of the NB with the
CS can be evaluated by carefully comparing the position of the
caudal end of the NB on the cartilaginous dorsum with the bony-
cartilaginous junction of the nasal septum inside.
If there is a risk of weakness or instability, proper management
should be performed to secure the structural stability of the com-
ponents.
CONFLICTS OF INTEREST STATEMENT
The authors had no conflicts of interest with this study.
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Clinical and Experimental Otorhinolaryngology Vol. 1, No. 3: 158-160, September 2008
Fig. 3. Classification of the overlap area between the upper lateral car-
tilages and the nasal bone.
Type Ao, crescent shape; type Bo, short midline extension; and type
Co, long midline extension.
Ao
Bo
Co