Former clinical studies have reported the superiority of the landmark guided paramedian approach above the classical landmark guided midline approach for the continuous spinal anesthesia especially in the elderly. On the other hand, more recent clinical trials have suggested that the use of ultrasound to guide spinal anesthesia will be safer and more effective than the conventional palpation-guided technique.

The aim of this study will be to compare the conventional "blind" landmark paramedian approach to the ultrasound "modern" guided midline approach for the continuous spinal anesthesia in the elderly with hip fractures.

Patients will randomly divided into two groups:

Group(PML): will undergo conventional landmark guided paramedian continuous spinal anesthesia Group (MUS): will undergo ultrasound guided midline continuous spinal anesthesia

All elderly patients above 65 years old scheduled for elective surgery for hip fracture under continuous spinal anesthesia will be included in the study.

Patients will randomly divided into two groups by using random number generating software (Research Randomizer Version 4.0) Group(PML): will undergo conventional landmark guided paramedian continuous spinal anesthesia Group(MUS) : will undergo ultrasound guided midline continuous spinal anesthesia A written informed consent will be obtained from all participants, who will be blinded as to their allocated group.

After establishing a baseline monitoring (3 lead ECG, pulse oximetry and non-invasive blood pressure) and an intravenous access, a fascia-iliaca ultrasound guided block at the fractured hip will be performed for all patients by the injection of 20 ml of 1.5 % lidocaine.

15 minutes later with the aid of an assistant, the patient will be positioned at the edge of the operating table in an arched back posture.

In both groups the continuous spinal anesthesia(CSA) will be performed with one of three anesthesiologists (two residents in their fourth year of training anesthesia and one associate professor), each have sufficient experience in performing neuraxial ultrasound scans prior to the study. To fulfill this they will use an 18 gauge Tuohy needle with a 22 gauge intrathecal catheter.

In group PML:

The anesthesiologist will star by drawing the 10th rib line then he will by palpation identify the most prominent spinous process beneath. At this level he will mark on the patient skin the point of injection which will be1 cm lateral and 1 cm caudal to the caudal edge of the spinous process chosen.

After infiltration of the skin with 3 ml of 1% lidocaine at the marked site, the anesthesiologist will introduce the tuohy needle in a cephalomedial direction 10 to 15° off the sagittal plane.

when cerebrospinal fluid will be obtained, the CSA (continuous spinal anesthesia) catheter will be advanced 3 cm cephalad to the intrathecal space and taped to the skin.

The patient will be then returned to dorsal position and a volume of 30 ug of fentanyl and 3 ml of 0.1% isobar bupivacaine will be injected intrathecally via the catheter.

The intervertebral level at which the injection will be done,will be scanned with ultrasound at the end of the surgery, before CSA catheter withdrawal.

In group MUS:

The anesthesiologist will use a portable ultrasonography with a curved 2-5 MHz (Mega Hertz) probe to detect the sacrum in the paramedian sagittal oblique view (PSO) of the neuroaxis.

Than the transducer will be moved cephalad to scan the quality of interspinous spaces from L5/S1 to L2/L3. The interlaminar space that will have the best PSO quality i.e the clearest and largest ultrasound image of the posterior complex ( ligamentum flavum and posterior dura) and anterior complex ( posterior longitudinal ligament and anterior dura) will be chosen as the interspace for injection.

At this level a skin marker will be used to mark the midpoint of the short borders of the probe. Following this the probe will be rotated by 90° to obtain the transverse median view (TM) and by the same way the midpoint of the short borders of the probe will be marked.

The intersection of these two marks will be used as the point of injection. Similarly skin will be infiltrated with lidocaine and the tuohy needle will be inserted in the cephalomedial plane with a cephalad angle estimated by the probe inclination in the TM view.In this group, the anesthesiologist will not palpate the landmarks except he changing technique.For the rest of the procedure, the same steps will be followed.

In both groups, an alternative technique would be used if unsuccessful after 3 attempts( landmark/ultrasound guided paramedian approach for MUS Group ; landmark/ultrasound midline approach for PML Group).

For all participants strict asepsis will be respected throughout all the procedure, The distance needed to reach the intrathecal space from the skin will be recorded and the quality of the interspinous spaces chosen will be noted in the PSO and TM ultrasound views using a predefined scale (good = both posterior and anterior complex visible ; intermediate = posterior or anterior complex visible ; poor = neither complex visible)

Inclusion Criteria:

• all consented patients aged over 65 years old scheduled to undergo surgery for hip fracture under continuous spinal anesthesia with American Society of Anesthesiologists ASA physical status classification from I to III

Exclusion Criteria:

• contraindications to spinal anesthesia ( allergy to local anesthetic, coagulopathy, infection at the site of injection)
• previous history of lumbar spine surgery
• per operative severe complication with conversion to general anesthesia