Histological Cross Sectional Area Analysis of Tibial Nerves Following Stretch Injury

Monica MuthaiyaThe Biomechanics Research Laboratory

University of Illinois at Chicago

Farid Amirouche, Ph.D.

Background

Nerve injury occurs in 1-2% of patients who undergo

total joint arthroplasty [1]. Injury to the peroneal division of

the sciatic nerve is most common, being involved in

nearly 80% of the cases [2].

Since most injuries involve the peroneal division of the

sciatic nerve, it is important to be familiar with the gross

anatomy. The common peroneal nerve is derived from L4,

L5, S1, S2 as a part of the sciatic nerve. It travels to the

posterior component, supplies the short head of the

biceps femoris in the thigh, crosses posterior to the lateral

head of the gastrocnemius, and becomes subcutaneous

behind the fibular head.

The tibial nerve also originates from the sciatic nerve,

with contributions from L4, L5, S1, S2, and S3. It splits in

the distal thigh and then passes through the popliteal

fossa. It then runs under the arch of the soleus and

continues distally on its undersurface [3]. With damage of

the tibial nerve, you have loss of plantar flexion of the

foot, loss of flexion of the toes and weakened inversion of

the foot. The tibial nerve is considerably larger than the

peroneal nerve and has a more distal distribution in the

extremity with fewer points of connective tissue tethering.

Hypothesis/Purpose

- The purpose of this study is to compare the histological

differences between the peroneal and tibial divisions of

the sciatic nerve with or without manual stretching using

fresh cadaver material. My experiment focused on the

cross-sectional areas of the tibial nerve, in order to be

able to compare my data to that of Dr. Amirouche’s.

- If tibial and peroneal divisions of the sciatic nerve are

histologically compared, there will be histological

differences between the two since the peroneal nerve is

less protected and more prone to injury.

References

1. DeHart et al. Nerve Injuries in Total Hip Arthroplasty. Am Acad Orthop Surg March 1999 vol. 7 no. 2 101-111.

2. Schmalzried et al. Update on nerve palsy associated with total hip replacement. Clin Orthop Rel Res 1997 Nov;(344):188-206.

3. Wood et al. Peroneal nerve repair. Surgical results. Clin Orthop Rel Res 1991 Jun;(267):206-10.

Procedure

1. Peroneal and tibial nerves harvested bilaterally from 10

adult cadavers from a prone position.

2. Sciatic nerve dissected free from surrounding tissue,

including the peroneal and tibial nerves.

3. Peroneal and tibial nerves sectioned into 2 samples,

each 60 mm in length.

4. 25mm section in middle was isolated, also distal and

proximal control samples taken.

5. Proximal was stretched, embedded in paraffin, stained

w/Masson’s trichrome stain (distinguishes connective

tissue from other components).

6. Nerves examined under light microscopy and digital

images were collected.

7. These images were calibrated and uploaded to ImageJ

software.

8. Nerves analyzed for overall and individual fascicular

cross sectional area and extent of roundness

(4xarea/pi(dsquared))

9. If value of roundness approaches zero, more of an oval

shape.

10. Thickness of perineurium was measured at these 3

locations of the fascicle in the subsample and compared to

their areas (by dividing 2 values)

11. Statistical analysis performed using SPSS software

according to Friedman test, keeping right and left samples

separate (sample was small and data did not have a

normal distribution so non-parametric analysis was used)

Results

Conclusion

In conclusion, by examining the areas of the fascicles in each division of the sciatic nerve of fresh human cadaver nerves,

there seems to be a pattern developing. Based on Dr. Amirouche’s current research paper and my findings, there seems to be

several histological differences between the tibial and the peroneal nerves. As already mentioned, the tibial nerve is much larger

than the peroneal nerve, meaning that there are more fascicles in the tibial nerve. This numerical difference in fascicles and the

excess amount of extra fascicular connective tissue explains why the area of fascicles in the tibial nerves were higher than in

comparison to the area of fascicles in the peroneal nerves. We can conclude that the elliptical shape of the tibial nerves following

stretch offers protection, but from this study, we cannot conclude why. This is not fully clear, but Dr. Amirouche’s study and my study

do offer some understanding as to the differences between the two main nerves, their connective tissue similarities and differences,

and other aspects which may eventually help to explain why the peroneal nerve is more at risk than the tibial nerve following the

moderate stretch associated with hip surgery.

Safety

Safety concerns during these experiments primarily revolved around

the use of the human cadavers, and precautions taken included

wearing of gloves, and lab coats when handling the nerves and tissues.

For my part in the experiment, there were no safety concerns since I

simply used a computer program to examine the histological slides. In

no way was I ever in contact with the human cadaver nerves or tissues.