Commentary & Perspective

Commentary & Perspective on
"Harrington and Cotrel-Dubousset Instrumentation in Adolescent Idiopathic Scoliosis: Long-Term Functional and Radiographic Outcomes"
by Ilkka Helenius, MD, PhD, et al.

Commentary & Perspective by
George H. Thompson, MD*,
Rainbow Babies and Children's Hospital, Case Western Reserve University, Cleveland, Ohio

The goals of surgical treatment in adolescent idiopathic scoliosis are to prevent further curve progression, obtain satisfactory correction, restore or maintain balance in the sagittal plane, improve cosmesis, achieve a solid arthrodesis, have a low incidence of complications, and prevent back pain and functional impairment for the patient as an adult. However, it has been documented that radiographic results do not always correlate with the long-term clinical results^1-5. In this study, the authors compared the results of two traditional instrumentation systems. Harrington instrumentation was widely utilized until the early 1980s. It consisted of a single rod with a proximal and distal hook. Distraction force applied across the concavity of the thoracic curvature produced relatively good correction but provided very little control in the sagittal plane. One of the major problems when using the Harrington instrumentation was a flattening of lumbar lordosis, producing the so-called flat-back syndrome^1,3,6. This is a common cause of back pain for the patient as an adult. Also, the Harrington construct is relatively weak and requires postoperative immobilization of the patient either in a Risser localizer or an orthosis until adequate healing has occurred (six to nine months).

Cotrel-Dubousset instrumentation provides segmental spinal instrumentation with dual rods and multiple anchor points (hooks, wires, and pedicle screws) per construct. There is increased load sharing, increased correction forces, and improved three-dimensional correction, particularly in the sagittal plane. This type of instrumentation decreases the risk for so-called flat-back syndrome⁵. The strength of the constructs is such that no postoperative immobilization is necessary. Patients are restricted in their activities for four to five months postoperatively.

This is the first study to compare in a systematic manner the functional and radiographic results between these two common forms of instrumentation. Seventy-eight consecutive patients with adolescent idiopathic scoliosis who were treated with Harrington rod instrumentation were compared with fifty-seven consecutive patients with the same diagnosis who were treated with Cotrel-Dubousset instrumentation. The two treatment groups were clinically and radiographically similar preoperatively, but the lengths of follow-up were different. The Harrington instrumentation group had a longer mean follow-up (20.8 years) compared with the Cotrel-Dubousset instrumentation group (13.0 years).

The operative technique for Harrington instrumentation was different than the one that is usually performed in North America. Most patients underwent a two-stage procedure with a two-week interval between the insertion of the Harrington rod and the posterior spinal fusion. The bone grafting technique was also different, as most of the patients had an osteoperiosteal tibial autograft. A Milwaukee orthosis was used for six to nine months postoperatively. The Harrington rod was routinely removed two years postoperatively. The Cotrel-Dubousset instrumentation was applied in a standard manner. The instrumentation was not removed and there was no postoperative immobilization. Interestingly, no patients in either group received perioperative prophylactic antibiotics.

At the final follow-up examination, all patients underwent a systematic physical examination and radiographic evaluation. They also received the Scoliosis Research Society questionnaire. This questionnaire has twenty-four questions, yielding a maximum score of 120 points (indicating a highly satisfied and asymptomatic patient). Previously validated spinal mobility and non-dynamometric trunk performance tests were also performed. All patients underwent standing anteroposterior and lateral standing radiography of the entire spine.

Clinical results were relatively similar in both groups. The total score on the Scoliosis Research Society questionnaire averaged 97 points in both groups. The magnitude of the thoracic or lumbar curve correction at the final follow-up did not correlate with the total scores. There was a significant inverse correlation between the magnitude of the thoracic curve and the score for appearance in clothes at the final follow-up examination.

The results of the comparison of functional tests, mobility measurements, and non-dynamometric trunk performances were unique to this study. Although the results were relatively similar, abnormal lumbar extension and trunk side bending were significantly more common in the Harrington instrumentation group. There was no correlation between the magnitudes of the thoracic or lumbar curves and the spinal mobility measurements. The mean squatting score was higher in the Cotrel-Dubousset instrumentation group. This was probably due to the shorter follow-up and the fact that the lowest instrumented vertebra was at a higher level in this group, thus allowing for more distal mobile segments.

The magnitude of the preoperative curve and the immediate postoperative correction were similar as measured radiographically in the two groups, but there was a progressive loss of correction in the Harrington instrumentation group at two years postoperatively and at the final follow-up examination. This was attributed to the removal of the instrumentation at two years, which allowed bending of the fusion mass. Thus, at the final follow-up examination, there was statistically better correction with Cotrel-Dubousset instrumentation. Postoperative alignment in the sagittal plane was relatively normal in both groups. There was greater radiographic evidence of spinal imbalance in the Harrington instrumentation group, as well as an increased incidence of lumbar disc-space narrowing and degenerative osteoarthritis.

Surprisingly, complications were higher in the Cotrel-Dubousset group. Fifteen patients (26%) in the Cotrel-Dubousset group had complications compared with nine patients (12%) in the Harrington instrumentation group. There was a high prevalence of caudad hook dislodgment in both groups. One early and three late deep infections occurred in the Cotrel-Dubousset group compared with none in the Harrington rod group. Lenke et al. reported no infections in seventy-six patients with adolescent idiopathic scoliosis who received Cotrel-Dubousset instrumentation⁵. All of the patients in that study received a first-generation cephalosporin prophylactically before the operation. The lack of perioperative antibiotics undoubtedly was a contributing factor in the study by Helenius et al.

Although the two patient cohorts are not exactly identical with respect to surgical techniques and postoperative follow-up, the authors note that when sagittal-plane alignment is maintained, the long-term results with Harrington instrumentation are similar to those achieved with Cotrel-Dubousset instrumentation. While coronal-plane correction is important, sagittal-plane alignment is probably the key to a successful long-term result. Also, maintaining distal mobile lumbar segments is critically important. This is easier to achieve with Cotrel-Dubousset instrumentation and other forms of segmental spinal implants. More mobile distal lumbar segments and normalized sagittal-plane alignment appear to yield the best long-term results⁵. However, it is important, in view of these factors, that junctional changes not be allowed to occur, as these can result in back pain for the patient as an adult¹.

*The author did not receive grants or outside funding in support of his research or preparation of this manuscript. He did not receive payments or other benefits or a commitment or agreement to provide such benefits from a commercial entity. No commercial entity paid or directed, or agreed to pay or direct, any benefits to any research fund, foundation, educational institution, or other charitable or nonprofit organization with which the author is affiliated or associated.

References

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2. D'Andrea LP, Betz RR, Lenke LG, Clements DH, Lowe TG, Merola A, Haher T, Harms J, Huss GK, Blanke K, McGlothlen S. Do radiographic parameters correlate with clinical outcomes in adolescent idiopathic scoliosis. Spine. 2000;25:1795-802.
3. Dickson JH, Erwin WD, Rossi D. Harrington instrumentation and arthrodesis for idiopathic scoliosis. A twenty-one-year follow-up. J Bone Joint Surg Am. 1990;72:678-83.
4. Helenius I, Remes V, Yrjönen, T, Ylikoski M, Schlenzka D, Helenius M, Poussa M. Comparison of long-term functional and radiologic outcomes after Harrington instrumentation and spondylodesis in adolescent idiopathic scoliosis: a review of 78 patients. Spine. 2002;27:176-80.
5. Lenke LG, Bridwell KH, Blanke K, Baldus C, Weston J. Radiographic results of arthrodesis with Cotrel-Dubousset instrumentation for the treatment of adolescent idiopathic scoliosis. A five to ten-year follow-up study. J Bone Joint Surg Am. 1998;80:807-14.
6. Willers U, Hedlund R, Aaro S, Normelli H, Westman L. Long-term results of Harrington instrumentation in idiopathic scoliosis. Spine. 1993;18:713-17.