The employee appeals from the compensation judge’s findings that the employee’s February 22, 2006, work injury was temporary in nature and that the employee was not entitled to wage loss, medical, and rehabilitation benefits after May 22, 2006.  We affirm.

BACKGROUND

The employee, Lona Burgin, began working for the employer,  Metro Transit, as a bus driver in 1999.  The employee claimed to have sustained a work-related injury on February 22, 2006, after the air-cushioned driving seat in her bus “bottomed out” when the bus struck a pothole.  She testified that she started to experience a headache, muscle spasms into her neck, back and buttocks, and a cramp in the arch of her right foot.  The employee reported the injury to her supervisor and made an appointment to see a chiropractor, Dr. Shannon J. Score.

The employee completed intake forms for Dr. Score on February 27, 2006, and Dr. Score immediately took her off work pending evaluation.  Chiropractic treatment began the next day, February 28, 2006, on which date Dr. Score authorized the employee to return to work with restrictions, including a prohibition on bus driving.  Dr. Score recommended 8-12 weeks of chiropractic manipulation, passive therapy, exercise therapy, and a lumbar support belt. He estimated that treatment would require 24 sessions.

On March 1, 2006, the employee was seen by an occupational medicine specialist, Dr. Constance Pries, at the Park Nicollet Clinic.  She reported aching in her low back, stiffness in the neck and a dull headache.  She had no radicular pain into the arms or legs.  On examination, she had full range of motion in the neck and no objective spasm in the paracervical or trapezius muscles.  She exhibited some discomfort in the low back bilaterally on forward flexion.  Straight leg raising was negative.  The employee told the doctor she had started chiropractic treatment and that x-rays taken by the chiropractor showed disc space narrowing.  Dr. Pries diagnosed probable lumbar degenerative disk disease, with any work-relatedness being unclear.  She thought that it would be reasonable for the employee to continue chiropractic treatment for the next two weeks and return at that time.  In her opinion, the employee could work full time but should avoid bus driving for the time being.

The employer gave the employee various non driving jobs including cleaning buses. On March 7, 2006, Dr. Score issued a work status report noting that the employee’s restrictions would not permit her to clean or dust buses because of the bending and repetitive motions involved.  On March 8, 2006, Dr. Score noted that the employee was now working only two hours per day until the employer could find more work she could do.

The employee returned to Dr. Pries on March 15, 2006.   There were no radicular symptoms and straight leg raising was negative.  She exhibited pain behaviors of facial grimacing with bending and extending.  The employee had brought her x-rays along, and Dr. Pries concluded from them that she had longstanding preexisting degenerative disc disease at L4-5.  The doctor saw no reason why the employee could not return to bus driving work on a half day basis.  The employee stated that she disagreed and would follow only the recommendations of her chiropractor.

The employer gave the employee light duty delivery work driving a Ford Taurus to deliver small items.  The employee testified that she was able to do this work.

In response to an inquiry from the employer about the employee’s status, Dr. Score wrote on April 4, 2006, that he believed the employee could not tolerate bus driving without continued worsening of her condition, and would need employment rehabilitation to facilitate a change of jobs.  Dr. Score’s working diagnosis was of a repetitive soft tissue injury complicated by severe degenerative disc disease.  She reported that the employee was currently undergoing active rehabilitation and would require ongoing home exercises and possibly ongoing periodic chiropractic care to prevent deterioration of her condition.  She stated that the employee was continuing to recover as expected.

The employee underwent a fitness for duty evaluation at the employer’s request by Dr. Michael Goertz at the Park Nicollet Clinic on April 25, 2006.  The employee described a gradual onset of symptoms without a specific precipitating cause but felt that the symptoms were work related in the sense that her bus had a seat that bottomed out and there was a lot of bouncing and vibration.  The employee’s history included multiple prior work injuries, including bursitis of both hips and low back symptoms with treatment in 2003.  She had tenderness at about the L4 level in the paraspinal muscles.  Flexion was limited to 60 degrees and extension to 30 degrees.  Dr. Goertz diagnosed mechanical low back pain.  He agreed with Dr. Pries that the employee could return to bus driving at four hours per day, noting that she was currently driving a vehicle and tolerating it well.

The following day, April 26, 2006, Dr. Score authorized the employee to return to driving a bus for two hours per day.  The employee did return to bus driving for two hours on May 1, 2006.  When she saw Dr. Score that day, she reported that her seat had bottomed out again and that she was having soreness around her tail bone.  In a letter dated May 8, 2006, Dr. Score wrote that the employee had sustained a flare-up of low back pain and headache.  She took the employee back off bus driving on May 10, 2006.

The employee was seen at the North Clinic on May 9, 2006, by a physician’s assistant, Amy Olson.  She stated that she was planning to transfer her primary care to this clinic.  She reported having an onset of pain and spasms in her back and left buttock when her bus seat bottomed out on February 22.  She stated she also had pain radiating down her leg into her foot, but that it had resolved.  She had since started to have stiffness and tightness in her neck and shoulders and was experiencing headaches.  The employee reported that her symptoms had been getting better with chiropractic treatment and light duty work limitations, but after having returned to bus driving two hours per day, she felt her symptoms were getting worse again.  She stated that the employer’s physician had authorized her to drive a bus four hours per day, and requested that Ms. Olson provide her with a medical workability report limiting her to light duty work with no bus driving.  Examination showed the employee to be tender over the bilateral SI joints and in the lumbar musculature, and there was some limitation in her forward flexion and side bending.  Ms. Olson provided the employee with the requested light duty limitations through May 22, 2006, after which she was authorized to try to return to bus driving.

On May 12, 2006, Dr. Score wrote a letter reiterating that she had restricted the employee from all bus driving through June 10, 2006, because driving two hours per day had caused her condition to flare up.  Dr. Score opined that the employee’s lumbar spine did not have the stability required to tolerate the constant vibration and jarring associated with driving a bus, and that this caused inflamation and irritation of the nerve roots due to the employee’s degenerative disc condition.  She offered the opinion that the employee would never be able to resume bus driving “without the proper chiropractic treatment.”  Dr. Score opined that the employee had not yet reached maximum chiropractic improvement and that the treatment to date had been reasonable, necessary, and “causally related to driving the bus.”  Dr. Score thereafter continued to keep the employee off bus driving.  As the employer had no further light duty work for the employee, she has been off work through the date of the hearing below.

The employee returned to the North Clinic on June 5, 2006, where she was seen by Dr. Matthew Barnes on a one-time basis.  She told Dr. Barnes that she had recently awakened with tingling in her right arm and leg, and a feeling that her right side was “disconnected.”  She was also concerned about her neck pain and headaches, and reported that she had been having trouble with speaking, in that the words “just do not want to come out right.”  The employee’s exam showed a decreased range of neck motion, and x-rays showed a lack of normal curvature of the neck.  Dr. Barnes noted that the employee’s symptoms were “somewhat unusual.”  He was concerned about the employee working as a bus driver “if she has something going on in her head as well.”  He ordered an MRI of the employee’s head and neck, recommended that she establish a treatment relationship with another provider at the clinic, and referred the employee for neurosurgical evaluation.

The employee underwent MRI studies of the brain, cervical spine and lumbar spine on the same day, June 5, 2006, at Minneapolis Radiology.  The brain MRI was normal.  In the cervical spine, diffuse degenerative changes were noted at several levels, most severe at C6-7 where there was a right-sided herniation narrowing the intervertebral foramen.  At C3-4 and C4-5, there was left neural foraminal stenosis, and at C5-6 mild left foraminal narrowing was present.  The lumbar spine showed mid to lower lumbar disc degeneration and facet osteoarthritis, without significant narrowing of the spinal canal.  There was mild to moderate stenosis of the left neural foramen at L5-S1 and lesser degrees of stenosis elsewhere.

On June 12, 2006, the employee was evaluated by Dr. Gregory Harrison at Millennium Neurosurgery at the request of Dr. Barnes.  Her principal complaints were headaches, neck pain, bilateral hand numbness, and right leg numbness.  She related these problems to “bouncing in her seat on the bus” and “bottoming out” of the seat.  Dr. Harrison’s neurological examination of the employee gave normal findings in motor, sensory and range of motion testing other than the presence of some numbness in a left C6 distribution.  Dr. Harrison’s assessment was of headaches and mechanical back pain without any strong radicular component.  He noted that the recent MRI of the employee’s cervical spine showed modest foraminal stenosis on the left at multiple levels, but opined that this condition was not particularly symptomatic and did not then require treatment.  Dr. Harrison suggested a neurologic evaluation.

The employee was seen by Dr. Richard A. Peterson at the Minneapolis Clinic of Neurology on June 28, 2006.  Her chief complaint was headaches, which were associated with a sensation of a stiff neck, light and sound sensitivity, and occasional nausea.  Dr. Peterson noted that the employee gave no clear cut history of head or neck trauma, but described her bus seat “falling out” and hitting the bus floor.  The employee also reported sensations of tingling on the right side of her body and again noted a feeling that her right side was “disconnected.”  The employee’s findings were normal on neurologic examination.  Dr. Peterson noted that it was not clear to him that the employee’s headaches were caused by her driver’s seat “falling out.”  He recommended that the employee start Nortriptyline as a preventive medication for her headaches, to watch her diet for potential headache triggers, and to exercise.  The employee was advised to return in about a month.

The employee returned to Dr. Peterson on July 24, 2006.  Her headache medications were giving good results and she had experienced only one headache since attaining her current dosage.  The employee was accompanied by her QRC, who wanted guidance on whether the employee could perform a job requiring occasional lifting to 60 pounds.  Dr. Peterson saw no reason why this would affect her headaches.  The employee reported that she had stopped going to her chiropractor.  Dr. Peterson authorized a course of physical therapy, to address the possibility that there was a musculoskeletal component to the employee’s headaches.

As of the end of August 2006, Dr. Score was still restricting the employee from bus driving, as well as from lifting more than 35 pounds or repetitive bending/lifting.  The records of Dr. Score show no further dates of treatment after mid-September.  The employee testified that she stopped going to Dr. Score when the self-insured employer refused to continue paying for the chiropractic treatment.

The employee was seen for an orthopedic examination by Dr. Paul T. Wicklund on behalf of the employer on September 12, 2006.  Her symptoms on that date included stiffness in the neck and soreness in the rhomboid muscles, without pain, numbness or tingling into either arm.  The employee stated that her low back pain had improved and that she only had occasional stiffness and soreness, with no pain, numbness or tingling in either leg and no muscle spasms in the buttocks.  Dr. Wicklund noted that he had previously seen the employee in 2001, at which time she had low back pain, tail bone pain, and pain radiating into her upper back and shoulders.  Her x-rays then showed disc narrowing at L4-5 and mild scoliosis.

Dr. Wicklund’s current diagnosis was degenerative disk disease in the cervical and lumbar spine, and headaches.  He opined that the work incident on February 22, 2006 would not have resulted in more than a temporary manifestation of low back pain consistent with her degenerative disk disease, and that this temporary manifestation of symptoms would not have lasted more than six to eight weeks.  He found no objective findings to indicate any permanent injury as a result of the work injury, and further concluded that the employee had no permanent partial disability in light of her normal examination with normal neurologic findings in the upper and lower extremities.  He stated that maximum medical improvement following the February 22, 2006, work injury would have been reached within three months.  In his view, she was not disabled from work and could return to work as a bus driver with no increased risk of acceleration of her age-related degenerative problems of the low back or neck.  He did not believe any medical care or treatment after three months was reasonable and necessary or related to the temporary manifestation of symptoms she had in February.  He further concluded that there was no causal relationship between ongoing treatment and the alleged injury of February 22, 2006.

The employee was also seen for a neurologic evaluation on behalf of the self-insured employer by Dr. James R. Allen, on September 18, 2006.  The employee told Dr. Allen that around the end of January 2006, she began having continuing problems with headaches, and on February 22, 2006, she also began to have low back pain and spasms in the buttocks after her seat bottomed out.   She had subsequently developed a stiff neck.  The employee’s current symptoms were low back stiffness with occasional tingling into the toes, and occasional tingling in the distal phalanx of the left ring and little fingers and the distal right thumb and all right fingers.  The right foot had bothered her on two occasions.   She denied having these symptoms prior to February 22, 2006.  Examination of the neck and back showed good range of motion without spasm or tenderness.  Thoracic outlet testing was negative bilaterally.  Straight leg raising was negative.  Sensation, strength, coordination and reflexes were normal, and the remainder of the examination was within normal limits.  Dr. Allen noted that her MRI scan had revealed degenerative changes in the spine with arthritic spurring, particularly in the low back.

Dr. Allen diagnosed pre-existing chronic degenerative disc disease with secondary arthritic spurring.   He noted that the employee’s longstanding history of chronic headaches had been documented as early as October 31, 2000, and that she had a history of low back spasms and treatment of the neck, mid back and lower back for which she had started to received chiropractic treatment in 1998 and 1999.  He found no evidence of any neurologic problem or permanent injury from the reported “bottoming out” incident of February 22, 2006.  He did not feel that the employee needed work restrictions as a result of the alleged injury and considered her to be fully capable of working as a bus driver.

The employee was seen by Dr. John L. Kipp at the Park Nicollet clinic for another fitness for duty examination on September 22, 2006.  The employee had no clear radicular symptoms from her neck or low back conditions.  Dr. Kipp diagnosed degenerative cervical and lumbar disc disease with a significantly decreased range of motion.  He characterized the employee’s headaches as migraine in nature with no origin in work-related activity.  He found nothing in the employee’s medical records to establish any credible causation between her work as a bus driver and her degenerative cervical condition, specifically rejecting that either the employee’s seat “bottoming out” or vibration from bus driving could have aggravated a degenerative condition of the cervical spine.  However, he did feel that the employee should be completely restricted from bus driving at that time because her active cervical range of motion precluded the safe operation of a commercial motor vehicle.

In a letter dated October 6, 2006, Dr. Score stated that she disagreed with the opinions of Drs. Allen and Wicklund regarding causation and the reasonableness and necessity of medical services since February 22.  She agreed that the employee had not sustained a specific injury, but opined that the employee’s preexisting degenerative disk disease could have been permanently aggravated and accelerated by cumulative microtrauma over the course of more than six years of bus driving related to the effects of vibration and to seats that sometimes would bottom out.

A hearing was held before Compensation Judge Gary Mesna to determine, among other things, whether the employee had sustained a work-related injury on February 22, 2006, and whether the effects of the alleged injury were permanent or temporary.  Following the hearing, the compensation judge found that the employee sustained a work injury on February 22, 2006, resulting in a temporary aggravation to her prior low back and neck condition. The compensation judge determined  that the employee had reached maximum medical improvement on May 22, 2006, after which the February 22, 2006, work injury was no longer a substantial contributing cause of her low back, neck or headache complaints.  The employee appeals from the finding that the work injury was temporary, rather than permanent, and from the consequent denial of wage loss benefits, medical benefits, and rehabilitation after May 22, 2006.

The employee argues on appeal that the judge’s finding of a temporary, rather than permanent, injury is unsupported by substantial evidence.

First, while she does not dispute that she had pre-existing degenerative disc disease and a long prior history of headaches, the employee points to her testimony that her headaches were different in character and much worse in degree after the work injury.  She argues that no evidence refutes this testimony.  We note, however, that an employee’s testimony regarding the nature and extent of symptoms, whether or not unopposed, is still subject to the compensation judge’s assessment of credibility, a matter which this  court will not disturb unless clearly erroneous.  The compensation judge was not required to find that the employee’s headaches were different from those she had been having for many years prior to the date of injury.

The employee argues that there is, in any event, a marked contrast before and after the work injury with respect to her neck symptoms, which largely developed subsequent to the work injury, and have not resolved.  She also points out that she is still undergoing treatment for her back, neck and headaches.

With respect to the employee’s neck condition, we note that neck complaints do not significantly figure in the employee’s medical records until considerably after she stopped driving a bus.  The employee had stopped driving a bus on February 27, 2006, and other than for a few days in late April and early May when she drove two hours per day, she never went back to bus driving.  She had a full range of motion of the neck on March 1, 2006, when she was seen by Dr. Pries, and none of her medical examinations show decreased motion of the neck until June 5, 2006.  Given that several physicians expressed opinions denying that the employee’s pre-existing cervical degenerative disc condition could have been significantly aggravated by bus driving or by her seat “bottoming out,” and in light of the length of time before her neck symptoms became significant, the compensation judge’s failure to give great weight to the employee’s neck symptoms was not clearly erroneous.  With respect to the employee’s low back, we note that the medical records reasonably support that her low back symptoms had returned to their pre-injury baseline by May 22, 2006.

The employee also argues that there has been a significant change in her ongoing restrictions and ability to work, in that she was able to drive a bus prior to the injury but is now disabled from bus driving by her physicians.  Here also, the compensation judge did not make specific findings as to the employee’s restrictions or ability to work.  However, before May 22, 2006, several physicians had authorized the employee to return to such work on a part time basis, and after that date several other physicians have offered the opinion that she could drive a bus without limitation.  While Dr. Kipp and Dr. Score both restricted the employee from bus driving after that date, Dr. Kipp explicitly noted that, in his opinion, the employee’s inability to return to driving a bus was then unrelated to either her alleged February 22, 2006, work injury, or any effects of the employee’s work activities.  Thus the compensation judge could reasonably have concluded either that the employee was able to return to bus driving after May 22, 2006, or that her inability to do so was unrelated to her work injury.

Ultimately, this case was determined on the basis of the compensation judge’s choice of expert opinion.  This court will generally uphold a compensation judge’s choice between conflicting expert opinions unless the factual basis for the expert’s opinion is not supported by the record.  Nord v. City of Cook, 360 N.W.2d 337, 37 W.C.D. 364 (Minn. 1985).  The employee has not alleged any foundational defect in the expert opinions on which the compensation judge relied.

We conclude that the compensation judge’s determination in this case is supported by substantial evidence, and that the result is not clearly erroneous.  We therefore affirm.