Anatomy
Lower Limb
A 34 year old farmer has sustained a deep laceration to the popliteal fossa and damaged the nerve which lies more medially. Which of the following clinical features are you mostly likely to see on examination:
Answer:
The tibial nerve and the common fibular nerve both lie in the popliteal fossa, but the tibial nerve lies more medially. The tibial nerve innervates the muscles in the posterior compartment of the leg, which act primarily to produce plantarflexion of the foot at the ankle, but also assist in flexion of the leg at the knee and inversion of the foot. You would not expect loss of flexion of the leg at the knee because this is mainly produced by the hamstrings, but you might see weakness of this movement.Tibial Nerve
Anatomy / Lower Limb / Innervation of Lower Limb / Posterior Leg
Last Updated: 10th April 2019
The tibial nerve is a branch of the sciatic nerve receiving nerve fibres from L4 - S3.
Table: Anatomical Overview of the Tibial Nerve
| Nerve | Tibial |
|---|---|
| Nerve roots | L4 – S3 |
| Motor supply | All muscles in the posterior compartment of the leg and the intrinsic muscles in the sole of the foot |
| Sensory supply | Skin on the posterolateral side of the lower leg, the lateral side of the ankle, foot and little toe, the medial side of the heel and the sole of the heel, foot and toes |
| Injury | Motor Loss: Weakness of flexion at knee, loss of plantarflexion at ankle and flexion of toes, weakness of foot inversion
Sensory Loss: Loss of sensation to the skin on the posterolateral side of the lower leg, the lateral side of the ankle, foot and little toe, the medial side of the heel and the sole of the heel, foot and toes |
Anatomical Course
It arises at the apex of the popliteal fossa before descending in the leg to enter the popliteal fossa posterior to the knee. The tibial nerve then passes under the tendinous arch formed by the two heads of the soleus muscle and then descends through the deep region of the posterior compartment of the leg. The tibial nerve passes through the tarsal tunnel, posterior to the medial malleolus to enter to foot.
![By Henry Vandyke Carter [Public domain], via Wikimedia Commons](https://mrcemsuccess.com/wp-content/uploads/2017/01/Sciatic-Nerve.png)
Tibial Nerve. (Image by Henry Vandyke Carter [Public domain], via Wikimedia Commons)
Branches
Table: Branches of the Tibial Nerve
| Branch | Supply |
|---|---|
| Muscular branches | Posterior compartment of leg |
| Sural nerve | Skin on lower posterolateral leg, lateral side of ankle, foot and little toe |
| Medial calcaneal nerve | Skin on medial surface and sole of heel |
| Plantar nerves | Intrinsic muscles in sole of foot, skin over sole of foot and toes |
Through its muscular branches, the tibial nerve innervates all of the muscles in the posterior compartment of the leg.
The tibial nerve gives rise to the sural nerve in the proximal leg which supplies skin on the lower posterolateral surface of the leg, and the lateral side of the ankle, foot and little toe, and the medial calcaneal nerve in the distal leg which supplies skin on the medial surface and sole of the heel.
In the foot the tibial nerve divides into the medial and lateral plantar nerves which innervate all of the intrinsic muscles of the sole of the foot and supply skin over the medial and lateral sole of foot and toes respectively.
Function
The table below details the motor function of the tibial nerve.
Table: Motor Supply of the Tibial Nerve
| Muscle | Function |
|---|---|
| Gastrocnemius | Plantarflexion of foot and flexion of leg |
| Plantaris | Plantarflexion of foot and flexion of leg |
| Soleus | Plantarflexion of foot |
| Flexor digitorum longus | Flexion of lateral four toes |
| Flexor hallucis longus | Flexion of great toe and plantarflexion of foot |
| Tibialis posterior | Plantarflexion and inversion of foot, support of medial arch |
![Modified by FRCEM Success. Original by Henry Vandyke Carter [Public domain], via Wikimedia Commons](https://mrcemsuccess.com/wp-content/uploads/2017/01/Cutaneous-Innervation-Leg.png)
Cutaneous Innervation of Lower Limb. (Image modified by FRCEM Success. Original by Henry Vandyke Carter [Public domain], via Wikimedia Commons)
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- Biochemistry
- Blood Gases
- Haematology
| Biochemistry | Normal Value |
|---|---|
| Sodium | 135 – 145 mmol/l |
| Potassium | 3.0 – 4.5 mmol/l |
| Urea | 2.5 – 7.5 mmol/l |
| Glucose | 3.5 – 5.0 mmol/l |
| Creatinine | 35 – 135 μmol/l |
| Alanine Aminotransferase (ALT) | 5 – 35 U/l |
| Gamma-glutamyl Transferase (GGT) | < 65 U/l |
| Alkaline Phosphatase (ALP) | 30 – 135 U/l |
| Aspartate Aminotransferase (AST) | < 40 U/l |
| Total Protein | 60 – 80 g/l |
| Albumin | 35 – 50 g/l |
| Globulin | 2.4 – 3.5 g/dl |
| Amylase | < 70 U/l |
| Total Bilirubin | 3 – 17 μmol/l |
| Calcium | 2.1 – 2.5 mmol/l |
| Chloride | 95 – 105 mmol/l |
| Phosphate | 0.8 – 1.4 mmol/l |
| Haematology | Normal Value |
|---|---|
| Haemoglobin | 11.5 – 16.6 g/dl |
| White Blood Cells | 4.0 – 11.0 x 109/l |
| Platelets | 150 – 450 x 109/l |
| MCV | 80 – 96 fl |
| MCHC | 32 – 36 g/dl |
| Neutrophils | 2.0 – 7.5 x 109/l |
| Lymphocytes | 1.5 – 4.0 x 109/l |
| Monocytes | 0.3 – 1.0 x 109/l |
| Eosinophils | 0.1 – 0.5 x 109/l |
| Basophils | < 0.2 x 109/l |
| Reticulocytes | < 2% |
| Haematocrit | 0.35 – 0.49 |
| Red Cell Distribution Width | 11 – 15% |
| Blood Gases | Normal Value |
|---|---|
| pH | 7.35 – 7.45 |
| pO2 | 11 – 14 kPa |
| pCO2 | 4.5 – 6.0 kPa |
| Base Excess | -2 – +2 mmol/l |
| Bicarbonate | 24 – 30 mmol/l |
| Lactate | < 2 mmol/l |
