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. 2023 May;11(3):733-738.
doi: 10.1007/s43390-023-00645-6. Epub 2023 Jan 23.

Low radius of curvature growth-friendly rib-based implants increase the risk of developing clinically significant proximal junctional kyphosis

Ellen Parker  1 , Mohammed Al Anazi  2 , Jennifer K Hurry  2 ; Pediatric Spine Study Group; Ron El-Hawary  3   4
Collaborators, Affiliations

Low radius of curvature growth-friendly rib-based implants increase the risk of developing clinically significant proximal junctional kyphosis

Ellen Parker et al. Spine Deform. 2023 May.

Abstract

Background: Clinically significant proximal junctional kyphosis (PJK) occurs in 20% of children with scoliosis treated with posterior distraction-based growth-friendly surgery. In an effort to identify modifiable risk factors, it has been theorized biomechanically that low radius of curvature (ROC) implants (i.e., more curved rods) may increase post-operative thoracic kyphosis, and thus may pose a higher risk of developing PJK. We sought to test the hypothesis that early onset scoliosis (EOS) patients treated with low ROC distraction-based implants will have a greater risk of developing clinically significant PJK as compared to those treated with high ROC (straighter) implants.

Methods: We conducted a retrospective review of prospectively collected data obtained from a multi-centre EOS database on children treated with rib-based distraction with a minimum 2-year follow-up. Variables of interest included: implant ROC at index (220 mm or 500 mm), participant age, pre-operative scoliosis, pre-operative kyphosis, and scoliosis etiology. PJK was defined as clinically significant if revision surgery with a superior extension of the upper instrumented vertebrae was performed.

Results: In 148 participants with scoliosis, there was a higher risk of clinically significant PJK with low ROC (more curved) rods (OR: 2.6 (95% CI 1.09-5.99), χ2 (1, n = 148) = 4.8, p = 0.03). Participants had a mean pre-operative age of 5.3 years (4.6y 220 mm vs 6.2y 500 mm, p = 0.002). A logistic regression model was created with age as a confounding variable, but it was determined to be not significant (p = 0.6). Scoliosis etiologies included 52 neuromuscular, 52 congenital, 27 idiopathic, 17 syndromic with no significant differences in PJK risk between etiologies (p = 0.07). Overall, participants had pre-op scoliosis of 69° (67° 220 mm vs 72° 500 mm, p = 0.2), and kyphosis of 48° (45° 220 mm vs 51° 500 mm, p = 0.1). The change in thoracic kyphosis pre-operatively to final follow-up (mean 4.0 ± 0.2 years) was higher in participants treated with 220 mm implants compared to 500 mm implants (220 mm: 7.5 ± 2.6° vs 500 mm: - 4.0 ± 3.0°, p = 0.004).

Conclusions: Use of low ROC (more curved) posterior distraction implants is associated with a significantly greater increase in thoracic kyphosis which likely led to a higher risk of developing clinically significant PJK in participants with EOS.

Level of evidence: Level III - retrospective comparative study.

Keywords: Early onset scoliosis (EOS); Proximal Junctional Kyphosis (PJK); Radius of curvature; Rod shape; Scoliosis.

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