Study of the Neurovascular Bundle in Tarsal Tunnel Region among Sudanese - 2020

Background : Tarsal tunnel is situated medial to the ankle lying deep to the flexor retinaculum. Within which lies the neurovascular bundle in separate compartments. This study examines the level of bifurcation points of tibial nerve and posterior tibial artery, and the location of medial and lateral plantar nerves in the tarsal tunnel. As well as the origin of the medial calcaneal nerves. Methods : This study was a descriptive observational cross sectional study. Step by step dissections of the tarsal tunnel were performed on 30 Sudanese cadavers, the contents of the tarsal tunnel were explored. Results : The tibial nerve was found to bifurcate before the the medial malleolus calcaneal axis (MMCA) in (n=4/30, 13.3%) specimens , and inside the tunnel (n=26/30, 86.7%). The branching point of the posterior tibialartery was found before the MMCA in (n=10/28, 35.7%) of specimens, at the MMCA in (n=16/28, 57.1%), and after the MMCA in (n= 2/28, 7.1%). Medial calcaneal nerves were found to be derived from the LPN plus the TN in (n=13/30, 43.3%), while in (n=6/30, 20%) were derived from LPN plus MPN plus TN. only (n=5/30, 16.7 %) were derived from LPN alone. Conclusion :


Introduction:
Tarsal tunnel is situated medial to the ankle lying deep to the flexor retinaculum. It is also termed as portapedis. It transmits the tendons of tibialis posterior, flexor digitorumlongus and flexor hallucislongus muscle along with the posterior tibial vessels, tibial nerve and their bifurcations.
The neurovascular bundle, as well as, other tendons lie in separate compartments deep to the flexor retinaculum (1) .
Compromise of the Tarsal tunnel space by any cause can lead to the development of Tarsal Tunnel Syndrome (TTS). This syndrome results from entrapment of tibial nerve in the tarsal tunnel.
Joshi et al (2) studied anatomy of the tarsal tunnel among Indian cadavers and its applied significant, and have shown the bifurcation of tibial nerve to be of type I in 85.2%, type II in 14.7% and type III in 0.89%. they also had shown that the arterial bifurcation was type I in 16.17%, type II in 72.04% and type III in 11.76%.
Bilge et al. (3) dissected the tarsal tunnel region in 60 cases and found types of arterial bifurcation to be type I in 10%, type II in 46% and type III in 44%.
Nīdaye et al (4) studied the tarsal tunnel and found the presence of "one" Medial Calcaneal Nerve (MCN) in 80% cases, where asDellon et al . (5) reported it in 37% and in the present series it was found to be 6.7%.
Dellon et al. (5) also described great variability in the number of MCNS, Davis &Schon (6) have also shown multiple MCN branches.
The purpose of the present study is to describe the bifurcation point of the tibial nerve and posterior tibial artery, and the location of the medial and lateral plantar nerves in the tarsal tunnel to establish an anatomical guide for safe interventions of some tarsal region diseases such as tarsal tunnel syndrome, fixations of fractures with external nailing, medial displacement osteotomy and nerve blocks in podiatric medicine.

Methodology:
This was a descriptive observational cross sectional cadaveric study conducted in the period from January 2020 to February 2020.Thirty lower limbs of formalin fixed embalmed cadavers were dissected in the dissection rooms of some medical schools in Khartoum State -Sudan.
Exclusion criteria: high bifurcation points.
The bifurcation of the tibial nerve and the posterior tibial artery were classified with respect to the medial malleolus calcaneal axis into type I, II and III with bifurcation proximal to the axis, at the axis and distal to the axis respectively. And the number and origin of medial calcaneal nerves were studied.

Results:
In all the specimens, the flexor retinaculum was not clearly demarcated at its superior and inferior borders and it was merged with deep fascia of leg and foot.Also fibrous septae were observed arise from deep surface of the flexor retinaculum and heading towards the bones giving rise to 4 osteofacial compartments. The contents of these compartments were found to be (from medial to lateral order): the tendon of the tibialis posterior muscle, the tendon of the flexor digitorumlongus muscle, the neurovascular bundle and the tendon of flexor hallucislongus muscle. The neurovascular bundle which was enclosed in a separate compartment was surrounded by a delicate fibro fatty cushion.         The neurovascular bundle being lodged in an independent compartment within the tarsal tunnel.
My findings during the dissections in this study are in agreement with the above researcher.
Within the tarsal tunnel, distinct superficial and deep relationship was observed between the vessels which are lying superficial and the nerve which is lying deeply. During the dissection of the tarsal tunnel the posterior tibial vessels were seen to form characteristic superficial strata which partially hides the terminal part of the tibial and the beginnings of the medial and lateral plantar nerves from view. This was seen in 90% of the specimens. Based on this observation I suggest more investigations to be done using more specimens to demonstrate the relation between the vessels and the nerve and to match the description giving in concern of such relation  gives origin to MCN in the above mentioned combinations is LPN and in all the specimens it gives at least one MCN (100 %).

Conclusion
1. Deep to the flexor retinaculum there is an independent compartment which lodges the neurovascular bundle.
2. The vascular plane is superficial to the plane of the nerves.
3. Bifurcation of the tibial nerve is at higher level (proximal) to that of the posterior tibial artery.
4. Most of the neurovascular bifurcation and branching occur between the tip of medial malleolus and the medial calcaneal tuberosity (MMCA).

5.
There are more than one medial calcaneal nerves which mainly arise from the lateral plantar nerve and the tibial nerve.