Drainage of the Lateral (Thenar) Space

Incision

Make a curved incision about 4 cm long, just on the ulnar side of the thenar crease (Fig. 5-84).

Internervous Plane

There is no internervous plane in this approach.

Superficial Surgical Dissection

Deepen the dissection in line with the skin incision, taking care to identify and preserve the digital nerves to the index finger. Identify the flexor digitorum superficialis tendon to the index finger (Figs. 5-85 and 5-86). Deep to these tendons is the lateral space; enter it by blunt dissection (Fig. 5-87).

Dang

Nerves

The digital nerves to the index finger are directly in line with the skin incision. Take care not to damage them during incision of the palmar aponeurosis.

The motor branch to the thenar muscles emerges from the deep surface of the median nerve as the median nerve leaves the carpal tunnel. Note, however, that the location of its division from the median nerve is quite variable. This nerve hooks around the distal end of the flexor retinaculum to supply the muscles. Make sure to identify the branch at the proximal end of the incision so as to avoid damaging it (see Fig. 5-39).

Figure 5-84 Incision for drainage of the lateral space (thenar space). The incision is made just to the ulnar side of the thenar crease.

Figure 5-85 Identify the palmar fascia and spread it in line with its fibers over the flexor tendon to the index finger.

Figure 5-86 Identify the flexor tendon to the index finger. The neurovascular bundles lie to each side. The lumbrical is seen on the radial side.

Figure 5-87 Retract the tendon and lumbrical radially, and enter the space beneath them by blunt dissection.