Spinal anesthesia is the technique of choice in patients undergoing total joint arthroplasty at Toronto Western Hospital (UHN). The most significant predictor of the ease of performance of spinal anesthesia is the quality of palpable surface landmarks (the spinous processes of the lumbar vertebrae). These surface landmarks may be absent, indistinct or distorted in many of the patients presenting for total joint arthroplasty. This is because of obesity, previous spinal surgery, scoliosis and degenerative changes of aging. The investigators have shown in a previous study that a pre-procedural ultrasound scan of the spine can reliably identify an appropriate site for needle insertion in spinal anesthesia, and that this results in a high success rate on the first needle insertion attempt (84% vs 61-64% in published studies). The investigators therefore believe that this ultrasound-assisted technique of spinal anesthesia is extremely useful, especially in patients with poor-quality surface landmarks. However there are no published randomized controlled trials to date that compare the efficacy of the ultrasound-assisted technique with the traditional surface landmark-guided technique of spinal anesthesia.