Stephen W. Spencer and Joseph M. Barron of Peddicord, Wharton, Spencer, Hook, Barron & Wegman, LLP, West Des Moines, for appellants.
Martin Ozga of Neifert, Byrne & Ozga, P.C., West Des Moines, for appellee.
The court of appeals concluded a workers' compensation award of permanent total disability benefits was not supported by sufficient medical evidence providing a causal link between the claimant's injury and his employment. Upon further review, we conclude the commissioner's factual finding on causation was supported by substantial evidence. We therefore vacate the decision of the court of appeals and affirm the district court ruling affirming the commissioner's award of permanent total disability benefits.
I. Background Facts and Proceedings.
The following facts are supported by substantial evidence in the agency record. James David House is forty-eight years old and has had a career as a commercial truck driver. In 2002, he was involved in a motor vehicle accident resulting in injuries to his shoulder, neck, fibula, and cheek bone. In January 2004, while driving for C & C Distribution, House injured his neck again while trying to push a truck tire onto a rack. He underwent a cervical spine fusion and entered into a workers' compensation settlement of the 2004 injury claim based upon a 26.2% industrial disability.
House began working as a commercial truck driver for Mike Brooks, Inc.,  on July 26, 2005. On March 7, 2007, House sustained a back injury when he slipped and fell in an icy parking lot while retrieving cargo. The safety director for Brooks directed House to have his injury evaluated by Lori Bailey, ARNP-FNPC. On March 14, Bailey noted House was experiencing pain at a " 9 on a 0-10 pain scale," loss of sleep " due to the back discomfort," and an inability " to stand up straight secondary to the pain." Bailey initially diagnosed House's symptoms as " [l]ow back spasms," prescribed medications and physical therapy, ordered an MRI, and released House to return to work with certain restrictions. The MRI report " indicat[ed] a L4, L5 disc herniation with a protrusion of the disc material left paracentral extending to the margins of the nerve roots that exit at L5, L6 on the left." Based on these findings, Bailey recommended House discontinue physical therapy and referred him to Dr. David Hatfield, an orthopedic surgeon.
Dr. Hatfield evaluated House on April 6, 2007. At that time, House reported " pain in his back and down the right lower extremity" as a result of " a slip on the ice." Dr. Hatfield confirmed Bailey's diagnosis of muscle spasms and a disc protrusion at the L4-5 level, administered an epidural injection, prescribed physical therapy, and released House to return to work with significant restrictions.
On May 4, House again saw Dr. Hatfield who noted House's buttock and leg symptoms had dramatically improved but the pain and stiffness in his back had persisted. A second epidural injection scheduled for that day was postponed by Dr. Hatfield because House reported symptomatic improvement. Dr. Hatfield released House to return to work without restrictions, as House was very eager to get back to his
full activities. On August 6, Dr. Hatfield opined House had achieved maximum medical improvement (MMI) as of May 4 and assigned a five percent permanent physical impairment rating as a consequence of House's March 7 injury.
House passed an Iowa Department of Transportation (IDOT) physical examination and returned to work. He continued to experience regular back pain after doing so. In early January 2008, House told his supervisors at Brooks that his back pain had become so severe it " was tearing [him] up," and that he needed pain medications. House was again directed to see Bailey. While working in the course of his employment on January 4, House pushed open a heavy door and experienced an increase in pain and a burning sensation in the area of his March 7, 2007 back injury, which he described as feeling like " somebody stuck a red hot poker in [his] back." 
Bailey examined House again on January 16, 2008. Bailey gave House an injection that day for pain management, prescribed other medications, scheduled another MRI study, and referred House back to Dr. Hatfield. The new MRI report showed " [p]rogressing left paracentral and lateral disc protrusion at L4-5 disc space causing moderate spinal stenosis and encroachment of the non exited L5 nerve roots, left greater than the right from the previous exam of [March 22, 2007]."
On January 31, 2008, Dr. Hatfield performed a L4-5 bilateral discectomy on House. Following the discectomy, House reported persisting back pain and stiffness on three occasions to Dr. Hatfield in February and March. House was released to return to work and he passed another IDOT physical examination on April 1. The examination report noted House was experiencing " [i]ntermittent discomfort" and swelling at and near the incision cite. Still taking over-the-counter and ...