posterior Lumbar

The posterior approach to the lumbar spine requires a thorough understanding of back muscles.

The Erector Spinae are large superficial muscles below the deep lumbodorsal fascia arising from the iliac crest, the thoracolumbar processes, and the aponeurosis on the sacrum. This muscle makes a confluent mass in the lower lumbar region but can be discerned into three muscles in the upper lumbar region: the Illiocostalis, the longissimus, and the spinalis. The multifidus are a series of the small muscles seen prominently only in the lumbar spine. These originate from the mamillary process of the superior facet and insert of spinous processes medially about two segments higher. The most lateral muscle is the Quadratus lumborum originating from the iliac crest and illio lumbar ligament, it runs obliquely and inserts into the 12th rib and the transverse process of upper four lumbar vertebrae. The Interspinalis muscle is a pair of deep muscles that is present between the two spinous processes. Similarly the inter transversii are present bilaterally between the transverse process.

The pressure on the abdomen leads to an increase in spinal venous pressure and bleeding intraoperatively so it is necessary to ensure that abdomen hangs free, this may be ensured by using bolsters or horse shoe shaped pheasants.

Pad the knees with foam rubber and shin and anterior border with pillow.

Free chest expansion and no pressure on abdomen is the key to a good exposure.

Exposure:

Incision: A midline longitudinal incision centered over the vertebrae intended to be exposed is made. The length of incision can be increased depending on the number of vertebrae that need to be exposed.

Adrenaline infiltration: Depends on surgeon’s preference, as the duration of action is limited. A 1: 500,000 epinephrine solution in saline can be injected into subcutaneous tissue.

The incision is carried down to the spinous process.

Para spinal muscles are then stripped subperiosteally using a cobbs elevator. The elevator is directed with cutting edge dorsally so as to go under the bulbous tip of spine process. The cutting edge may then be turned ventrally to clear the tissue from the lamina as far laterally as needed.

This side is then packed with roller gauze to control bleeding.

Similar steps are then repeated on other side and that side too is packed with roller gauze.

After few minutes the packing is removed and the area is irrigated with saline solution to remove all the blood clots, and two self-retaining mastoid retractors are put at both ends of the wound.

Cut the intervening soft tissue between the spinous process using a cautery.

The level can now be reconfirmed either by sacral sounding or taking an intraoperative marker X ray.

Deep Surgical dissection: The ligamentum flavum has two layers superficial and deep. The lateral edge of the superficial ligament flavum is cut with a knife. The superficial portion in the interlaminar space is removed laterally to medially using a curet. A forward can be used to make laminotomy in the superior lamina. An incision made medially in the ligametum flavum where it is thinnest exposes the epidural fat and blue white dura. A small cottoniod can be inserted under the ligamentum flavum laterally, over which the ligamentum flavum can be cut from medial to lateral on both sides.

A blunt dissection lateral to dura is continued down the floor of spinal canal, retracting the dura and nerve root medially.

Potential Complication:

Postoperative infections.

Post laminectomy kyphosis.

Adhesive arachoniditis.

Neural root damage.

Cerebrospinal fluid leakage