A Study on Bilateral Ossified Pterygospinous Ligament and Its Clinical Significance

Associate Professor, Department of Anatomy, Vijayanagar Institute of Medical Sciences, Bellary, Karnataka, India. Professor and Head of the Department , Department of Anatomy, Vijayanagar Institute of Medical Sciences, Bellary, Karnataka, India. Professor, Department of Anatomy, Vijayanagar Institute of Medical Sciences, Bellary, Karnataka, India. Post graduate student, Department of Anatomy, Vijayanagar Institute of Medical Sciences, Bellary, Karnataka, India.


Introduction
The pterygospinous ligament extends from lateral pterygoid plate to spine of sphenoid bone. This ligament is ossified sometimes, forming a foramen, which can be traversed by mandibular nerve branches to supply temporalis, masseter and lateral pterygoid muscle 1 . In 1837, Civinini described the pterygospinous ligament and found that this ligament ossified in 2% to 3% of his specimen 2 . The pterygospinous ligament and ossified foramen formed is named after Civinini 3 .
Nayak et al found Civinini ligament fully ossified in 5.76% and incompletely ossified in 3.84% of their specimen 4 . The complete ossification of pterygospinous ligament is known as the pterygospinous bar 5 . Partial or complete ossification of pterygospinous ligament seems to be a major cause of trigeminal neuralgia 4 , causing lingual numbness and pain associated with speech impairment 6 .

Discussion
The ossification of pterygospinous ligament is very rare 8,9 . The presence of an osseous bar between the lateral pterygoid plate and the spine of sphenoid has been considered as a phylogenetic remnant in human beings 10 .
The pterygospinous ligament located close to foramen ovale and of anatomical, clinical and surgical importance because ossified ligaments may compress neurovascular structures present in region of foramen ovale causing trigeminal neuralgia 11 . The ossified pterygospinous ligaments can produce difficulty in accessing the foramen ovale in therapeutic approach 12 .
An unusual course of lingual nerve with entrapment of nerve between ossified pterygospinous ligament and medial pterygoid pla te was found 13 . The lingual nerve and the inferior alveolar branch of mandibular nerve in the region of the infratemporal fossa are forced to take a long curved course in presence of a large pterygoid plate and during contraction of pterygoid muscles, these nerves are subjected to compression 14 . The pterygospinous bony bridge can also pass among the fibers of the lingual nerve and divide it into anterior and posterior parts. Anterior part passes medially and lies between Tensor veli palatini muscle and the bony bridge, so these fibers are vulnerable to the risk of compressio n 15 . In view of close relationship of the chordatympani nerve, it may also be compressed by anomalous bar of bone and its involvement would result in impairment taste sensation in anterior 2/3 rd of the tongue 16 . The presence of ossified pterygospinous ligament means that there would be less accessible space to gain entry into the para and retro pharyngeal space 10 .
Lateral pterygoid plate forms an important landmark for mandibular anaesthesia and any anomalies in lateral pteryoid plate is bound to confuse anaesthetists and also cause difficulty during thermocoagulation of trigeminal ganglion due to pterygospinous ligament ossification 17 .
According to Newton and Potts an ossified pterygospinous ligament can be an obstacle in a radiograpically guided trigeminal ganglion blockage 18 . While applying conductive anaesthesia on mandibular nerve by lateral subzygomatic route may encounter obstacle to high quality conductive anaesthesia due to ossified pterygospinous ligament at lateral pterygoid plate 18 . A research study had also advocated that a distance of approximate 0.25cm beyond the distance to the lateral pterygoid plate be taken while performing maxillary nerve block by lateral extraoral approach 19 .
Incidence of ossified pterygospinous ligament has been reported by different authors with different results. Wood reported an 8% pterygospinous ligament ossification in Hawaiian skulls 20  Complete ossification of pterygospinous ligament was found in 3.6% skulls-1.31%bilaterally as well as 1.31%on the right side and 0.98% on the left side. Incomplete type was found in 14.7% skulls-bilaterally in 12 skulls and unilaterally in 33 skulls. They emphasized that the presence of such an ossified Pterygospinous ligament may prevent anaesthesia of mandibular nerve at the l ateral subzygomatic approach 18 . Yadav et al 24 studied 500 skulls reported 10.2% of total incidence of pterygospinous bar incompletely ossified in 6.2% (unilateral -5%, Bilateral-1.2%) and completely ossified in 4% (unilateral -4%, Bilateral-nil) 24 . Bilateral presence of complete Pterygospinous bars/bridges has not been reported by Yadav et al or in the study by Verma et al or Thomson et al 25 . Rafaela et al reported higher frequency of partial ossification of pterygospinous ligament -19.36% when compared to complete ossification 8.61% 26 . Agarwal et al studied 67 adult human skulls of Punjab region and revealed the incidence of pterygospinous bar as 9.7%-complete pterygospinous bridges in 2.99% and incomplete ones in 6.72% of skulls 27 . The present study reports an incidence of 0.95% complete ossification of pterygospinous ligament bilaterally resulting in a well formed pterygospinous foramen.
In most of the above studies the incomplete variety was more common than complete one and unilateral variety was more common than the bilateral variety. The present study analysed morphologicaly exposed the presence of bilateral ossified pterygospinous ligament and civinini's for amen which may involved in multiple complication involving both vascular and nervous compression. The present observation ( fig.1 a nd fig.2) on bilateral presence of pterygospinous bar in 1 skull out of 105 Skull bones makes the study clinically important with an incidence 0.95% .

Conclusion
Different authors have reported with different results, though and this difference is probably regional. The ossification of pterygospinous ligament is very rare 8,9 . In the present study, the bilateral complete ossified pterygospinous ligament incidence 0.95% found 1 out of 105 dried human adult s kull bones of either sex.
In most of the above studies the complete bilateral ossified pterygospinous ligament very rare. Whether complete or incomplete ossified pterygospinous ligament can produce various symptoms depending upon the dimensions of the pterygospinous foramina and grades of neurovascular compression.
Pterygospinous bar leads to difficulty while performing surgical operation on pterygoid region by leaving little space due to increase in width and flattening of lateral pterygoid plate causes less accessible space to gain entry into para and retropharyngeal space 10 . Thus, the knowledge of the ossified pterygospinous ligament is important for surgeons for planning surgical procedures and who perform invasive procedures in/near infratemporal fossa would IJBR (2014) 05 (09) www.ssjournals.com increases the success rate of the surgical procedures 25 . Also important for anaesthetists and neurosurgeons since anomalous bony obstructions could interfere positioning the needle during transfacial needle approaches to foramen ovale 3 . Therefore, the knowledge of Anatomical variation of the pterygospinous ligament-ossification is clinically important to radiologists and neurosurgeons, maxillofacial and dental surgeons, and anaesthetists along with academically for anatomists and anthropologists.