In this study, we identified a 36.2% rate of developing a postoperative radiculitis following anterior lumbar surgery. There was a mild correlation between change in discal height and the development of a postoperative radiculitis, however, between groups differences did not reach statistical significance. Additionally, patients treated with rhBMP-2 appeared to have a higher rate of developing postoperative radiculitis compared to other graft sources (36.5% vs 17%), unfortunately the number of patients not treated with rhBMP-2 were too few to make a statistical comparison. This number, however, is similar to what Lee reported in patients undergoing anterior lumbar surgeries . We also found that all of the symptoms resolved by the 3 month postoperative appointment.
There are multiple studies in the literature discussing transient leg pain or radiculitis in patients undergoing interbody fusion with the use of rhBMP-2. In 2009, Mindea et al published the first study looking at this phenomenon showing a rate of 11% postoperative nonstructural radiculitis in patients when using rhBMP-2 during TLIF procedures. All symptoms were on the side of the TLIF procedure, and in their study, all resolved within 6 weeks . Likewise, in 2012, Rowan et al showed there was a 2.33 odds ratio of developing postoperative radiculitis in patients having a posterolateral or posterior fusion with the use of rhBMP-2. They also found that patients treated with rhBMP-2 filled interbody cages were twice as likely to have non-structural radiculitis compared to those treated without . In 2016 Villavicencio et al looked at a dose dependent rate of postoperative radiculitis with the use of rhBMP-2. They found an overall rate of 11.3% of postoperative radiculitis in patients undergoing TLIF surgery. They did not find a correlation with the dose of rhBMP-2 used. A majority of their symptoms resolved by 6 months postoperatively . Finally, in 2017 Lee et al evaluated postoperative radiculitis in patients undergoing ALIF procedures. They found 40% of patients developed radiculitis when rhBMP-2 was used compared to 9.52% of patients when allograft was used .
In contrast to the above listed studies, and the current study, Sebastian et al, prospectively evaluated patients undergoing TLIF procedures with the use of rhBMP-2 and compared them to patients undergoing TLIF without the use of BMP. They found no difference in the rate of postoperative radiculitis. Additionally, they found a similar improvement in preoperative leg symptoms in both groups .
The results of this study also suggest that these symptoms may be related to an acute stretch phenomenon on the nerve root. There have been multiple animal models investigating the development of nerve changes following acute stretch. Ming et al showed that sciatic nerve blood flow and somatosensensory evoked potentials both decreased significantly after lengthening of the femur 24% and 32%, and this corresponded to decreased neurologic function . Additionally, there have been multiple reports of motor, sensory and mixed motor/sensory neuropathies following limb lengthening procedures, valgus knee injuries and limb lengthening after total hip arthroplasty [13, 14, 15, 16]. Finally, a study by Kershner et al used a cadaveric model to show the effects of spinal column lengthening on exiting nerve roots. They found that lengthening of the spinal column by 4 cm caused proximal migration of the spinal cord by 2.8 mm. They found a significant increase in dorsal nerve roots being tethered by intrathecal ligaments during lengthening. They speculated that this is a cause of lumbar back pain in astronauts during space flight .
To date two studies list post-operative radiculitis as complications in patients undergoing ALIF procedures. Lee et al reviewed 41 patients undergoing ALIF procedures. They treated 20 patients with allograft and 21 patients with rhBMP-2. They found that overall 10 patients experienced a postoperative “radiculitis,” 2 in the allograft group and 8 in the rhBMP-2 group . There was a trend towards more complications in the rhBMP-2 group. Similarly, Hirabalek et al compared their results in patients undergoing anterior versus lateral interbody fusions. They found a rate of 8.3% radiculitis in their ALIF patients, 6 of which were groin numbness, while 4 complained of pain. They did not discuss time to resolution or possible causes of the symptoms .
The results of this study, however, should be viewed in the light of its limitations. First, this is a retrospective study, relying on review of postoperative notes to identify patients with neurologic symptoms. The number of patients affected may be under-reported in this study if the symptoms were not disclosed during their follow up visit. Likewise, the number of patients included in this study is relatively small. Additionally, the number of patients not treated with rhBMP-2 for their fusion were too few to develop a statistical comparison. Finally, the follow up in this study is short, but with the primary outcome being resolution of post-operative radiculitis, and all patients with these symptoms resolved within 3 months, our primary outcome was achieved in all patients. Future prospective research is needed to assess the development of a postoperative radiculitis following anterior lumbar surgery.
In conclusion, this study identified a 36.2% rate of postoperative radiculitis following anterior lumbar surgery, with 100% of patients demonstrating spontaneous symptom resolution within 3 months of surgery. There was a significant correlation between postoperative radiculitis and change in disc height following surgery. There also appeared to be an increased rate when rhBMP-2 was used, with 36.5% of patients developing postoperative radiculitis when rhBMP-2 was used when compared to 17% when rhBMP-2 was not used. This information can aid in the preoperative and postoperative counseling for patients undergoing anterior lumbar surgery.