Answer to the letter of Allard J. F. Hosman regarding “Scheuermann’s kyphosis: surgical management (V. Arlet, D. Schlenzka)”

Abstract

We are glad that you have appreciated our paper on Scheuermann (‘s) Kyphosis. Your first concern is about correct spelling: In your letter to the editor we could notice that you used the French expression “mis en place”. This should in reality be written “mise en place” and it appears that we all can make small typo mistakes. Following your observation whether we should query Scheuermann or Scheuermann’s, we went in Pubmed and retrieved 527 articles indexed when we entered Scheuermann and only 500 when we added “‘s”. However most of the citations were identical. This became far more of a concern when we queried for Scheuermann kyphosis that led to only 175 papers as opposed to Scheuermann’s kyphosis that led to 480 answers. We should thank you for bringing this serious flaw in our Pubmed queries, and we will definitively remember to add an’s to any of my similar queries. We do apologize for a typo mistake in the text where your name has been misspelled once with an s at the end, yet being correctly typed in the reference list and elsewhere in the text. Your main concern is our lack of emphasis on your research: “Scheuermann Kyphosis: the importance of tight Hamstrings in the surgical correction [1]”. We agree with your paradigm “that the sagittal correction of the Kyphosis will shift the sagittal balance posteriorly and compensation to regain balance can be provided according to the three ways you describe”. Reducing the lordosis of the spine, increasing the sacral slope (or rotating the pelvis on the hip) or a combination of both”. We would however, like to emphasize that to regain their sagittal balance the apparition of a junctional kyphosis either proximal or distal can be the fourth way these patients regain their sagittal balance, even though not the most desirable way to maintain balance. In your study you reported that the tight hamstring group (group 1) that you called lumbar compensators had a greater risk of postoperative imbalance [1]. Your tight hamstring group had increased lumbar lordosis (82° average). On the other hand the non tight Hamstring group had less lumbar lordosis (average 72°) and a lesser chance for postoperative imbalance. It is well known now that patients with increased pelvic incidence (PI) have increased lumbar lordosis [2]. Therefore patients with an increased pelvic incidence should fall into your group 1 category, yet this was not investigated in your paper. Recently Loner looking at the pelvic incidence of the patient and the frequency of junctional kyphosis has reported that proximal junctional kyphosis was associated with increased pelvic incidence in the surgical treatment of Scheuermann’s kyphosis [3]. However, Loner did not find any relationship between pelvic incidence and Scheuermann’s disease. As the pelvic incidence is the only sagittal parameter that is invariable, one should think about the patients who have an increased pelvic incidence, rather than patients who have tight hamstrings. Patient with increased PI will have an increased lumbar lordosis, therefore surgical correction of a thoracic kyphotic will project them more posteriorly (than patient with less lumbar lordosis). To regain their sagittal balance they will have to adapt according to the four different mechanisms you and I described and to a larger extent than their counterpart with less pelvic incidence and less lumbar lordosis. If stiff hamstrings are present (the pelvis will not rotate around the hip), if the unfused discs above or below the instrumentation are kyphotic, if the lumbar spine does not compensate by decreasing its kyphosis patient are at risks of junctional kyphosis. With the current knowledge available today we can therefore recommend to be careful with patients with Scheuermann’s and increased Pelvic Incidence and or Stiff Hamstrings. Probably this group should be considered for less surgical correction. Further studies on the relationship between pelvic incidence and tight Hamstrings in Scheuermann’s Kyphosis may shed further light in postoperative proximal or distal junctional kyphosis.