Ossification of the posterior longitudinal ligament (OPLL) is a relatively common cause of myelopathy in Asian populations. While relatively rare in Western countries, it can be encountered in non-Asian patients as well. Given the higher incidence of OPLL in Asia, most of the literature on this topic is from Japan. The pathology is located anterior to the cord, however, the ossified PLL frequently becomes adherent to the dura, making resection difficult and associated with a relatively high rate of spinal fluid leak. Posterior surgery is oftentimes preferred for this reason, though a posterior approach is generally associated with a higher infection rate, higher blood loss, and more post-operative pain. In order to gain a better understanding of how anterior and posterior surgery for OPLL compare, Dr. Yoshii and colleagues from Tokyo used a Japanese administrative database to compare outcomes between OPLL patients treated with anterior and posterior decompression and fusion. They identified over 2,300 patients who underwent anterior (n=1,333) or posterior (n=1,020) decompression and fusion between 2010 and 2016. The posterior patients tended to be somewhat older and had a greater comorbidity burden. They propensity-score matched 854 pairs of patients in order to limit the effects of selection bias. After matching, there were no significant baseline differences between the two groups. They found that the anterior surgery group had a higher rate of dysphagia (2.5% vs. 0.8%), respiratory failure (1.1% vs. 0.2%), and experiencing at least one medical complication (14.5% vs. 10%). The anterior group also had a higher rate of spinal fluid leak (2.7% vs. 0.1%). The posterior group had a higher transfusion rate (12.5% vs. 7.5%), longer length of stay (33 days vs. 29 days) and a higher hospital cost ($30,700 vs. $22,800).
The authors have used a national database to create what is likely the largest cohort of OPLL patients ever assembled. Their findings that anterior surgery was associated with a higher durotomy rate is not surprising. The fact that anterior surgery was associated with a higher rate of medical complications is somewhat surprising as posterior surgery is generally considered more invasive. Higher rates of dysphagia, respiratory failure and pneumonia in the anterior group drove the differences. It is not clear how dysphagia was defined, and it is surprising that only 2.5% of anterior surgery patients were classified as having dysphagia. Given that some degree of dysphagia is essentially universal after anterior surgery, this implies that dysphagia was only coded for severe cases or that it was coded inconsistently. The in-hospital infection rate was nearly as high for the anterior group (2.7%) as for the posterior group (2.9%). In general, infection after anterior cervical surgery is very rare, less than 1% in most series. Infection after posterior surgery occurs much more commonly in most series. It is not clear why the infection rate after anterior surgery was so high in this cohort, and the authors do not comment on that. One of the drawbacks of administrative database studies is that the investigators have to accept the data on face value and cannot dig deeper into it to try to better understand unexpected findings. The findings are only as good as the quality of the coding. While some of the exact numbers are hard to reconcile and likely represent heterogeneity in coding practices across Japan, the finding of higher complication rates, especially spinal fluid leak, in the anterior surgery group is consistent with prior literature. The authors attempted to address selection bias with propensity score matching, however, the database did not contain detailed information on myelopathy severity, number of levels involved, or the presence of kyphosis. It seems as though a posterior approach is favored in most cases with neutral or lordotic alignment that can be sufficiently decompressed with a laminectomy. For kyphotic patients or those with severe anterior compression that cannot be addressed with a posterior decompression, surgeons likely need to use an anterior approach despite the risks.
Please read Dr. Yoshii's article on this topic in the August 15 issue. Does this change how you consider your approach for OPLL?
Adam Pearson, MD, MS
Associate Web Editor