IMAST 2022: Use of low radius of curvature implants increases the risk of developing clinically significant proximal junctional kyphosis

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Ron El-Hawary

In patients with early onset scoliosis (EOS), implants with a lower radius of curvature (ROC) are associated with an increased risk of clinically significant proximal junctional kyphosis (PJK). This is the key finding from new research which was presented by Ron El-Hawary (IWK Health Centre, Halifax, Canada) at the Scoliosis Research Society’s 29th International Meeting on Advanced Spine Techniques (IMAST 2022; 6–9 April; Miami, USA).

El-Hawary et al sought to test the hypothesis that EOS patients treated with low ROC (more curved rods) distraction-based treatment will have a greater risk of developing PJK compared to those with high ROC (straighter) implants.

The researchers state that “clinically significant PJK occurs in 20% of children treated with posterior distraction-based growth friendly surgery. In an effort to identify modifiable risk factors, it has been theorised biomechanically that low ROC implants may increase postoperative thoracic kyphosis, and thus may pose a higher risk of developing PJK”.

A retrospective review of prospectively collected data was conducted. Data was obtained from a multicentre EOS database on children treated with rib-based distraction with minimum two-year follow-up.

Variables of interest included: implant ROC at index (220mm or 500mm), patient age, preoperative scoliosis, preoperative kyphosis, and scoliosis aetiology. In the literature, PJK has been defined as clinically significant if revision surgery with superior extension of the upper instrumented vertebrae was performed.

Out of 148 scoliosis patients, there was shown to be a higher risk of clinically significant PJK with low ROC rods (odds ration [OR]: 2.6 (95% confidence interval [CI] 1.09-5.99), χ2 (1, n=148) =4.8, p=0.03). Patients had a mean preoperative age of 5.3 years (4.6 years, 220mm vs. 6.2 years, 500mm, p=0.002). A logistic regression model was created with age as a confounding variable, but it was not found to be significant (p=0.6). Scoliosis aetiologies included 52 neuromuscular, 52 congenital, 27 idiopathic and 17 syndromic with no significant differences in PJK risk between aetiologies (p=0.07).

Overall, patients had preoperative scoliosis of 69° (67°, 220mm vs. 72°, 500mm, p=0.2), and kyphosis of 48° (45°, 220mm vs. 51°, 500mm, p=0.1). The change in thoracic kyphosis preoperatively to final follow-up (mean 4 ± 0.2 years) was higher in patients treated with 220mm implants compared to 500mm implants (220mm: 7.5 ± 2.6° vs. 500mm: -4 ± 3°, p=0.004).

Speaking to Spinal News International, El-Hawary said: “This research highlights one of the few modifiable risk factors in the prevention of proximal junctional kyphosis in early onset scoliosis. PJK is a common problem encountered in the treatment of early onset scoliosis.

“By using this information to help guide rod contour of current surgical devices, the risk of PJK should diminish over time. It is the first step towards evaluating the contour of magnetically controlled growing rods and how best to decrease the risk of PJK.”


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