Orthopaedic Surgeon

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Nerve Supply

Nerves

The nerves around the knee are motor (move muscles) and sensory (allow you to feel what is happening). The sensory nerves supply the joint itself as well as the skin over the knee. Many muscles have both motor and sensory functions.

While there is a great deal of variation in the nerves, essentially there are the nerves at the back of the knee and the nerves at the front of the knee. The nerves that supply sensation to the back of the knee joint itself are the posterior (back) articular (joint) branches of the tibial and obturator nerves.  The equivalent nerves in the front are the articular branches of the femoral, common peroneal and saphenous nerves. This is different to the pattern of skin sensation nerve supply.

The obturator nerve

(L2,3,4)  supplies the adductor muscles on the inner side of the thigh. These are the muscles that squeeze the knees together. This nerve also supplies the hip and sometimes pain from the hip can be felt as pain on the inner side of the knee. For this reason the hip must always be examined if the cause of the pain in the knee is not obvious.

The femoral nerve (L2,3,4) supplies the main muscles at the front of the thigh (motor) as well as the knee joint (sensory). Damage to the femoral nerve results in weakness of the quadriceps muscles (which straighten the knee). The saphenous nerve is a sensory continuation of the femoral nerve (supplies feeling to the inner aspect of the foot).

The sciatic nerve

(L4,5, S1,2,3) is a large nerve which runs down the back of the leg. It is made up of the tibial and common peroneal nerves which branch at different levels of the leg in different people. The sciatic nerve splits into the tibial and common peroneal nerves above the knee.  The tibial nerve supplies the hamstring muscles (which bend the knee). It also supplies the muscles in the back if the calf (gastrocnemius and soleus).  The common peroneal nerve supplies the front compartments of the leg including the peroneal muscles.

The tibial nerve

is the larger of the two branches of the sciatic nerve and runs down the back of the knee. The common peroneal nerve separates from the tibial portion of the sciatic nerve just above the knee and then follows behind the hamstring on the outer side of the leg to top part of the smaller done in the leg called the fibula.  The nerve then goes past the head of the fibula, winds round the neck of the fibula and dives deep into the muscles to divide into the superficial (closer to the surface) and deep (further inside) peroneal nerves.

Any nerve that goes past the knee joint gives off a sensory branch to the knee joint.

Nerve injury around the knee is rare compared to meniscal, chondral or ligamentous injuries. Nerve releases are occasionally needed but are rare compared to arthroscopic and reconstructive surgery of the knee.