Calf implants offer assured and a permanent muscle enhancing effect for the lower legs. They are specifically used to enhance the size of the gastrocnemius muscles. They are most commonly placed in the subfascial pocket on top of the muscle through incisions on the back of the knee. While a relatively straightforward procedure for those surgeons experienced in performing it, there are several important anatomic considerations that are key steps in their surgical placement.
The best way to understand these key steps in calf implant surgery is through cadaveric dissections. In the cadaveric pictures shown calf implant sizers which are colored blue are used and the overlying skin is removed to show the pertinent anatomic points.
SUBFASCIAL PLACEMENT The most common location for calf implants is subfascial on top of the muscle. The implant pocket is dissected out through incisions placed on the back of the knee. (popliteal fossa) While a layer of fascia is found soon after the incision is made, this is not the gastrocnemius muscle fascia. Rather it is the hamstring muscle fascia from the back of the thighs. The dissection needs to continue lower below the hamstring fascia which is where the muscle is located. It is here that the gastrocnemius muscle fascia needs to be incised and entered. In essence a stair step approach is needed from the incision to be able to enter the correct subfascial plane. This is usually 3 to 5 cm down from the incision.
The gastrocnemius muscle fascia is incredibly thin. For a tight compact muscle that is incredibly strong its fascia covering is surprising thin. It is easy to inadvertently be above it and have a subcutaneous implant placement.
AVOIDING NERVE INJURIES
The sensory sural nerve runs right down the middle in the fascia between the two muscle heads. With both subfascial pocket dissections it is important to not cross the midline to avoid injuring the nerve. On the inner or medial muscle pocket dissection it should curve around the side of the leg so the implant augmentation can show frontally. This will keep the dissection well away from the nerve. On the lateral or outer muscle the dissection is down the middle of the muscle but avoiding closing the midline.
inadvertently being above the fascia increases the risk of sural nerve injury as well.
The nerve that is the most important to avoid injuring is the common perineal nerve. Injuring this nerve causes a foot drop which can take 3 or 4 months to fully recover…if recovery is to occur at all. This motor nerve wraps around the head of the fibula and is near the side of the outer knee area where the incision for the outer muscle implant is placed. To avoid even seeing the nerve the incision should not be too lateral. Keeping the lateral skin incision closer to the midline and away from the sides of the knee is the method that will avoid the common peroneal nerve. The nerve moves laterally immediately below the knee and then is well away from the subfascial pocket dissection.
There is a relationship between being in the correct subfascial pocket and decreasing the risk of nerve injuries in calf implants. There is nothing to injure once inside the pocket as long as the midline is not crossed. Keeping the lateral skin incision closer to the midline and away from the sides of the knee is the method that will avoid the common peroneal nerve.
Dr. Barry Eppley