These figures show a clear superiority of Artificial Disc Replacement as compared to Spinal Fusion Surgery.

There are several reasons for this. First, Artificial Disc Replacement surgery of the lumbar spine is dependent on the availability of surgeons with appropriate experience and knowledge of the surgical approach required. Unfortunately, very few surgeons worldwide have the required experience in the field of surgical access to the spine. In addition, experience in determining the appropriate intervention, surgery, or implant also plays a significant role. If the procedure is not routinely performed, experience in making these determinations is also lacking. In addition, the assessment of postoperative results is enormously dependent on experience. Spine surgery patients are usually chronic back pain patients with histories of several years. As a rule, all of these patients will have postoperative complaints, regardless of whether they underwent fusion or Artificial Disc Replacement surgery. However, the assessment of fused patients seems to be easier, after all, fusion is the last resort surgery and what has been fused, or fixed and no longer in motion, can then no longer cause any complaints. In contrast, the Artificial Disc Replacement surgery offers the chance of preserving motion, and if the patients continue to have complaints postoperatively, the implants or the facet joints are quickly determined to be the "culprits".  This regularly ignores the fact that complications also occur after spinal fusion surgery.

Stenum Orthopaedic Clinic Results

The following statistics are based on cases at the Stenum Orthopaedic Clinic from 2014 to 2022, and thus represent approximately 20% of the cases provided by my team over the past 20 years.

Between 2014 and 2022, we provided disc prosthetics to 2614 patients in the cervical and lumbar spine, and we fused 2417 patients during the same period. Pre-operations and revisions were performed on 1643 patients. This means that minus our own revisions, every third patient who reached the clinic had already been pre-operated on.

In this paper, I would like to focus on the patients who underwent Artificial Disc Replacement surgery and try to determine the root cause of any complications.

In the context of the 2614 patients treated with Artificial Disc Replacement, we had 169 patients with revision operations after Artificial Disc Replacement in the same period.  This means that the revision rate is 2.75%. In relation to the number of implanted devices (4265), the revision rate is 1.69%.

But what were the reasons for the revisions? Here, of course, several considerations must be made:

1. Patients who were fitted by us or elswhere prior to revision
2. Analysis of the reasons for revision
3. Analysis of the implant types involved.

Only this overall view can help us to recognize certain patterns and this in turn is helpful to avoid errors in the future.

The following errors could be systematically identified:
- Hematoma early/postoperatively
- subsidence
- migration
- Root irritation early
- Early complication SPL
- Paresis early
- early infection
- Defect of the prosthesis
- low grade infection
- Spondylolisthesis aquisata
- osteolysis
- Stick-slip friction
- hypermobility
- instability
- Rotational Slippage
- loosening
- persistent stenosis
- Late acute infection

Here again, a distinction must be made between early and late complications. The early complications were postoperative hematoma, nerve root irritation, and paresis, followed by subsidence, migration, and the early complication spondylolisthesis aquisata as immediate postoperative instability. Only one early infection was noted.

Late complications were prosthesis defects and low grade infections followed by spondylolisthesis aquisata, osteolysis of unclear cause, stick-slip friction, hypermobility, instability, rotational slippage, loosening, persistent stenosis and, in distinction from low grade infections, acute late infection.

If the reasons for revision are further differentiated, it becomes apparent that, as a rule, early complications are not implant-associated.

In the case of late complications, there are clear indications of implant-associated and non-implant-associated complications.

Thus, all cases of prosthesis defects are exclusive to Cadisk-C and -L, which has been withdrawn from the market.

Low-grade infections occur with different prosthesis types, but in our group there is a high incidence with the M6-C, although it must be emphasized that we also have very high numbers of implants here. In the context of the scientific literature, however, it should be noted that the affinity of bacteria for plastics is significantly higher than for metals. If bacteria enter the bloodstream (hematogenous infection pathway), the probability of bacterial colonization of a plastic surface is greater than with a metallic surface. Nevertheless, the numbers are in the absolute per mille range.

We have seen osteolyses of unclear cause exclusively in ESP-L prostheses, usually occurring 4-5 years after implantation and again leading to increasing complaints. The reason for their occurrence is unclear, but it must be assumed that they only occur with one type of prosthesis, so that there is a clear implant association here.

The same applies to the stick slip friction. We have observed this effect exclusively with the Triadyme prosthesis. The spherical design of the surface can lead to overloading of the articulating surfaces with perceptible crepitation during rotational movements of the head.

Subsidence, in turn, affects different types of prosthesis and is not causally implant-associated; rather, due to the force distribution occurring immediately after surgery, occasional weakening of the cover plate of the caudal vertebra occurs with sinking of the prosthesis.

In the migrations that have occurred, the L5/S1 segments are usually affected. In this case, it is not the implant that is the cause, but rather the implantation technique.

The complex of hypermobility, instability and rotational slippage can essentially be summarized as increasing instability of the affected segment, which the prosthesis must follow due to its design. Intervertebral disc prostheses are not designed to compensate for segmental instabilities that occur, which is why primary implantation is contraindicated in cases of known instability. However, it cannot be ruled out that instabilities may develop over time even in supplied segments, which then overtax the lying implant.

The situation is similar with spondylolisthesis aquisata; this pathology is already known after fusion surgery. The present cases almost exclusively involve the L5/S1 segment and almost without exception the M6-L. Since the prosthesis, in contrast to classical ball and socket prostheses, has all the movement qualities of a normal healthy intervertebral disc, the possibility of translation is given and thus the prosthesis will passively follow a sliding of the respective cranial vertebra and thus be damaged.

Persistent stenoses are the result of insufficient primary decompression or arise on the basis of secondary hypersostotic bone formation postoperatively. In either case, they are not implant associated.

Acute late infections must be distinguished from low grade infections. These arise as acute, clinically imposing infections with accompanying abscess formation and are also known from other areas of orthopedic surgery. As with low grade infections, the pathway of origin is also hematogenous. Again, there is no implant-associated origin.

In summary, the present analysis shows that 87 of 172 cases are implant associated. Except for 10 cases, all other cases were pretreated in other hospitals.

No implant-associated complication was found in any case involving the M6 prosthesis.

During the same period, a total of 4265 prostheses were implanted in the cervical and lumbar spine in 2614 patients. Related to these numbers, 72 revision surgeries were necessary for various reasons. Thus, the number of necessary revisions is 2.75% in relation to the number of patients and 1.69% in relation to the number of implants.

Overall, our revision rate is thus about half of the German average. Only 0.38% of the revisions were implant associated. All other revisions showed no implant associated causes.

The present analysis considers cases that were surgically treated between 2014 and 2022. However, in total, the number of patients we cared for is much higher and is likely to approximate 10,000 cases. Thus, further workup will  continue, but is time-consuming given the large number.

Dr. Karsten Ritter-Lang - Stenum Orthopedic Clinic