ZygomaticoMaxillary Complex osteology and clinical aspects

details about the osteology of zmc

1. Seminar 2 – Osteology of Zygomatico-Maxillary Complex
ZMC is a major midfacial support structure and important component of facial contour line. It is also called
as zygoma, zygomatic bone, cheekbone, malar bone. It is small and quadrangular or diamond – shaped body
with its longer diagonal lying in an almost horizontal plane. It is a paired bone i.e. present bilaterally in skull
and is considered to be one of the most irregular shaped bones of the skull as it consists of three different
processes, varying in size and shape. It is seen in human skull when viewing it from front as well as from side
i.e. in norma frontalis and lateralis.

DEVELOPMENT / OSSIFICATION
The zygomatic bone ossifies from three centers—one for the malar and two for the orbital portion; these
appear about the 8th week and fuse in about 5th month of fetal life. After birth, the bone is sometimes
divided by a horizontal suture into an upper larger, and a lower smaller division. The entire zygoma matures
through a process known as intramembranous ossification.

EVOLUTION OF THE ZYGOMATIC ARCH
In comparative anatomy, the zygomatic bone is also called the jugal bone, which is found in all tetrapods
(amphibians, reptiles, birds, and mammals). In the ancestors of mammals, the synapsid reptiles, a single
opening was present in the skull behind the eye socket. The jugal (zygomatic) bone stretched from the
bottom of the eye socket to the bottom of this opening. Around the time the first mammals evolved, the
vertical separation between this opening and the orbit disappeared, leaving the zygomatic arch formed from
the zygomatic bone and temporal bone. A vertical connection between the zygomatic bone and frontal bone
is again present in humans, but the zygomatic arch remains.

ARTICULATIONS AND SUTURES
Several bones surround the zygoma including the frontal bone, zygomatic process of temporal bone,
zygomatic process of maxillary bone and sphenoid bone. These bones articulates with zygoma by similarly
named sutures i.e. frontal bone via the zygomatico-frontal suture which creates the rounded form of
the bony orbit, zygomatic process of the temporal bone via zygomatico-temporal suture, zygomatic process
of the maxillary bone, articulated by the zygomatico-maxillary suture, which again, forms another aspect of
the bony orbit and sphenoid bone via zygomatico-sphenoidal suture.

It is situated at the upper and lateral part of the skull, under each eye and forms the prominence of the
cheek, part of the lateral wall and floor of the orbit (orbital socket), and parts of the temporal and
infratemporal fossae.

SURFACES - It presents 3 surfaces:
 Malar surface
 Temporal surface
 Orbital surface

The malar surface is convex, directed foreward and is perforated by a small aperture near its center which is
called as zygomaticofacial foramen. Through this foramen, passes the zygomaticofacial nerve and vessels.
Below this foramen there is a slight elevation, which gives origin to the Zygomaticus major and Zygomaticus
minor muscle.
The temporal surface is concave, directed backward and medially. Medially, it presents a rough, triangular
area that articulates with the maxilla, and Laterally, it presents a smooth surface having a upper part and
lower part. The upper part forms the anterior boundary of the temporal fossa and the lower part forms the
anterior boundary of infratemporal fossa. Temporal surface is perforated by a small aperture near its center
which is called as zygomaticotemporal foramen through which zygomaticotemporal nerve passes.
The orbital surface is concave and forms the lateral part and some of the inferior part of the bony orbit.
There is a foremen on this surface called zygomatic-orbital foramen through which zygomatic nerve passes.

2. PROCESSES – It has 4 processes / angles:
 Frontal / frontosphenoidal process (superior anlge)
 Temporal process (posterior angle)
 Orbital process
 Maxillary process (anteroinferior angle)

Superior angle / frontosphenoidal process is drawn out superiorly and inwardly as a strong process that is
triangular in cross section and it connects zygomatic bone with frontal and sphenoidal bones forming
frontosphenoidal process.
The frontosphenoidal process is thick and serrated, and articulates with the zygomatic process of the frontal
bone on its orbital surface.
Posterior angle is elongated as temporal process of zygomatic bone which is long, narrow and serrated and
articulates with the zygomatic process of temporal bone to complete the zygomatic arch and has a paired
zygomaticotemporal foramen present on the medial deep surface of the bone.
The orbital process is a thick, strong plate, projecting backward and medially from the orbital margin. Just
within the orbital margin, there is a protuberance of varying size and form and about 11mm below the
zygomaticofrontal suture called as orbital tubercle/whitnalls tubercle to which lateral palpebral ligament is
attached.
Antero-medial surface of orbital process forms part of the floor and lateral wall of the orbit by its junction
with the orbital surface of the maxilla and with the great wing of the sphenoid. On this anteromedial surface
zygomaticoorbital foramina is present and transmits zygomatic nerve. Foramen connects with
zygomaticotemporal and zygomaticofacial foramen so zygomatic nerve emerges out as zygomaticotemporal
and zygomaticofacial nerve on temporal and malar surface respectively.
Postero-lateral surface of orbital process is smooth and convex, forms parts of the temporal and
infratemporal fossa. Its anterior margin, smooth and rounded, is part of the circumference of the orbit.
Its superior margin,rough, and directed horizontally, articulates with the frontal bone behind the zygomatic
process. Its posterior margin is serrated for articulation, with the great wing of the sphenoid and the orbital
surface of the maxilla. At the angle of junction of the sphenoidal and maxillary portions, a short, concave,
non-articular part is generally seen; this forms the anterior boundary of the inferior orbital fissure.
The maxillary process presents a rough, triangular surface which articulates with the maxilla. The orbital
surface of the maxillary process forms a part of the infraorbital rim and a small part of the anterior part of
the lateral orbital wall.

BORDERS – It has four borders :
 Anterosuperior
 Anteroinferior
 Posterosuperior
 Posteroinferior

Antero-superior or orbital border is smooth, concave, and forms a considerable part of the circumference of
the orbit.
Antero-inferior or maxillary border is rough, and bevelled at the expense of its inner table, to articulate with
the maxilla. Near the orbital margin it gives origin to the Quadratus labii superioris.
Postero-superior or temporal border is curved like an italic letter ‘f’. It ascends from the zygomatic arch
behind the orbit and forms anterior boundary of temporal fossa and is continues above with the
commencement of the temporal line.
Postero-inferior or zygomatic border is free and affords attachment by its rough edge to the Masseter, so it
is also called as massetric border.
FORAMINA – It has three foramina :

3.  Zygomatico-facial foramen
 Zygomatico-temporal foramen
 Zygomatico-orbital foramen

FUNCTIONS
There are four main physiological functions of zygomatic bone with zygomatic arch :
 Protective function – As they are located on both sides of face, they protect maxillary sinus,
temporalis muscle and skull against the force coming from lateral side of face.
 Appearance – They constitute the outline of middle face contour which is influenced by its shape and
size to a larger extent.
 They separates the skin from temporalis muscle so muscle movement is seen only in temporal area
but not in area of zygomatic bone and arch while chewing.
 They provide attachment to facial muscles responsible for facial expressions and other functions.

SOFT TISSUE ATTACHMENTS
It provides attachment to various muscles:
1. Masseter – Lower border of zygomatic arch and adjoining zygomatic process of maxilla provides
origin to the Masseter by its rough edge. Masseter elevates mandible to close the mouth to bite.
2. Temporalis – Inner and outer lips of upper border of zygomatic arch gives origin to temporal fascia.
3. Quadratus labii superioris – Maxillary border gives origin to the zygomatic head of Quadratus labii
superioris near the orbital margin.
4. Zygomaticus – Below the zygomatico-facial foramen, there is a slight elevation which gives origin
to Zygomaticus muscle.
 Zygomaticus major – responsible for the expression of smile and laugh.
 Zygomaticus minor – brings about the expression of contempt.

Ligament – It provides attachment to lateral palpebral ligament over orbital / whitnalls tubercle.

Various nerves and vessels passes through foramina present in ZMC:
1. Zygomatic nerve
2. Zygomatico-facial nerve and vessels
3. Zygomatico-temporal nerve and vessels

NERVE SUPPLY
ZMC is supplied by:
1. Zygomatic nerve
2. Infraorbital nerve

APPLIED / CLINICAL ASPECTS
A. ZMC FRACTURES
They are the second most common fractures of face. The level of protrusion from rest of skull makes
zygomatic bone more prone to fractures. It can be caused by RTA, assault, gunshot injuries etc.

FRACTURE SITES
 F-Z suture
 Infraorbital rim
 Junction of zygomatic arch and temporal bone
 Orbital floor
 Buttress

4. CLINICAL FEATURES OF ZMC # :-
Most common – Pain, circumorbital ecchymosis, a flattened cheek bone / malar depression, swelling, a sub-
conjunctival hemorrhage, step deformity at infraorbital margin, buttress and F-Z suture, paresthesia,
infraorbital nerve paraesthesia.
Less common – Enopthalmos, diplopia, lowered lateral portion of the palpebral fissure due to the downward
displacement of the lateral canthal ligament, decreased mobility of extraocular muscles.
Limitation of mandibular movements secondary to zygomatic arch impingement on coronoid process,
unequal papillary level.

EXAMINATION :-
Zygoma is palpated with fingers extraorally and buttress is palpated intraorally through labial vestibule.
RADIOGRAPHIC INVESTIGATIONS :-
It can be seen in
 CT scans –
o Coronal sections
o Axial sections
o 3D CT
 Water’s / Occipitomental view
 Jug-handle / Submentovertex view
 Caldwell / PA oblique view

SURGICAL APPROACHES :-
1. Indirect
 Extraoral
o Temporal / Gille’s
o Percutaneous
 Intraoral
o Keen
o Quin
2. Direct
 Extraoral
o Supraorbital eyebrow / Dingman’s
o Upper eyelid
o Lower eyelid
i. Sub tarsal
ii. Sub cilliary
iii. Infra orbital
iv. Trans cunjuctival
o Coronal / Bi-temporal
 Intraoral
o Maxillary vestibular
In temporal / Gille’s approach, 2-3 cm incision is given in hairline to and through temporal fascia and bristow
elevator is passed medial to zygomatic arch for elevation in a sweeping upward and outward direction.

In percutaneous approach, stab incision is given at the intersection point of ala-tragal line and line coming
from lateral corner of eye and bone hook is fitted at postero-inferior border of zygomatic bone and it is lifted
upward and outward. Malar hook or Carrol Girard bone screw is used.

B. PARAESTHESIA / INFRAORBITAL ANESTHESIA
Zygomatico-maxillary suture lies just lateral to infraorbital foramen so whenever there is impact on face from front
over cheeks or fracture through orbital floor and or anterior maxilla, it causes tearing, shearing or compression of
infraorbital nerve along its canal or foramen leading to infraorbital anesthesia. Accidental injury to nerve during
surgery may also induce paraesthesia.

5. C. ZYGOMATIC TRISMUS
There may be inability to open mouth and changes in occlusion following ZMC # due to impingement of
coronoid process of mandible on displaced zygomatic arch and also there is spasm of secondary to this
impingement on temporalis muscle as a result of which mandible is deviated towards fractured side when
mouth is opened. Zygomatic trismus is suggestive of ZMC #.

D. ZYGOMATIC IMPLANTS
Zygomatic implants are long screw shaped implants that can be used as an alternative to bone grafting and
sinus augmentation. Patients with loss of large amounts of supporting bone needs zygomatic implants, this
can make a huge amount of difference to appearance.
OTHER POINTS TO BE REMEMBERED
 Step deformity can be noticed by running a finger along the bone.
 The fixation of bone fragment should be solid, if not, then masseter muscle may drag the ZMC
downward resulting midface sag, nasolabial fold bloating, compromise of facial expressions, jaw
movement dysfunction.
 Surgical repair of ZMC # may be complex if it involves orbital floor because it has the potential for
damage to eyeball.