Lumbar Total Disc Replacement: 9th after the Operation, is it the Breakpoint for Clinical Deterioration and Spontaneous Fusion?
Authors: Štastná Daniela , Chrobok Jirí , Kučera Roman , Prokop Ludek , Klener Jan 
Published: April 2016

Introduction Total disc replacement (TDR) is one of the treatment options in the degenerative disc disease (DDD), presuming to preserve segmental range of motion and prevent development of ASD. There are many arguments arising against TDR's benefits, mostly in long-term period. We performed a single-center retrospective clinical–radiological study to evaluate the long-term results and safety of TDR operation. Materials and Methods Our cohort included 222 patients treated for moderate or severe DDD by single or two-level implantation of TDR between January 2002 and January 2011. An average follow-up was 8.2 ± 3.1 years. Clinical evaluation constisted of visual analog scale and postoperative Odom's outcome score. We analyzed the progress of radiologic adjacent segment degeneration (rASD) and heterotopic ossifications (HO). Results We found that Odom's scores for low back pain and leg pain both decrease lineary in time, with with cut-off and rapid deterioration of low back pain after the 9th year from surgery(p=.00001). We assume that this might be related to natural progression of initial DDD or development of ASD favored by HO and spontaneous fusion in TDR level. In agreement with this assumption, we have found that heterotopic ossifications have a triphasic course of progression, with plateau between 4th and 8th year after TDR( p = 0.00001). After the 9th year we observed an accelerated progression to bridging HO, resulting in the loss of movement. We demonstrated that our patients with fusion in TDR level had significantly higher incidence of rASD and significantly worse clinical outcome, for both low back pain and leg pain ( p = 0.000324). Similarly to other authors we conclude that dynamic TDR might prevent or delay rASD. We found interesting that using two independent measurements, clinical outcome and HO/range of movement, we determined the same approximate cut-off deterioration by the 9th year after the TDR operation. We didn't find significant effect of HO on clinical outcome. Implantation of TDR resulted in a 15.8.% of spontaneous fusion in our series. We found quite important rate of radiologic adjacent degeneration, 23.85%,still within the range of literature. Incidence of delayed reoperations was 12.2%, mostly because of adjacent-segment disease, with the mean time 4.1 years after TDR. These patients were significantly less satisfied. According to risk factors, we found previous discectomy is significantly related with higher incidence of leg pain, which might be explained due to nerve root traction within preexisting scar tissue. Patients with higher initial BMI had significantly higher incidence of segmental fusion. We found worse outcome for bisegmental and L5/S1 TDR, both nonsignificant. At last follow-up (5–14 years postsurgery), excellent and good outcomes were achieved in 66.9% patients for low back pain, and 72.4% for leg pain. Conclusions According to our results, we estimate that approximately after the 9th year after TDR, loss of segmental movement due to bridging ossifications might accelerate naturally occurring adjacent segment degeneration and leads to worse clinical outcome, mostly low back pain. We are still persuaded that despite technical difficulty, TDR has its place in lumbar DDD surgery. Reasonable indication and optimal placement of TDR are crucial. We need more prospective studies of long-term to understand.