Surgeons’ procedural choices and patient malalignment are the strongest predictors of distal junctional kyphosis in the first year following surgery. This was the conclusion presented by Peter Passias (Department of Orthopaedic Surgery, NYU Langone Orthopedic Hospital, New York, USA) at the 18th annual conference of the International Society for the Advancement of Spine Surgery (ISASS; 11–13 April 2018, Toronto, Canada). The findings were first published in Spine.
Six percent of patients in the study were diagnosed with clinical distal junctional kyphosis within two years of surgery. However, a total of 23.8% of patients met the radiographic definition of distal junctional kyphosis.
Passias and colleagues comment, “Distal junctional kyphosis is a primary concern of surgeons correcting cervical deformity. Identifying patients and procedures at higher risk for developing this condition is paramount to improving patient selection and care. The aim of this study was to develop a risk index for distal junctional kyphosis development in the first year after surgery.”
Developing a risk index for distal junctional kyphosis
To develop this risk index, Passias and his team used Conditional Inference Decision Trees to identify factors predictive of distal junctional kyphosis incidence, and the cutoff points at which they have an effect. Twelve influencing factors were found. The following baseline radiographic malalignments were the most numerous and strong predictors for distal junctional kyphosis:
- C2–T1 tilt > 5.33 (OR: 6.94, CI: 2.99–16.14)
- Kyphosis < -50.6° (OR: 5.89, CI: 0.07–0.43)
- C2–C7 lordosis < -12° (OR: 5.7, CI: 0.08–0.41)
- T1 slope minus cervical lordosis > 36.4 (OR: 5.6, CI: 2.28–13.57)
- C2–C7 SVA > 56.3° (OR: 5.4, CI: 2.20–13.23)
- C4 tilt > 56.7 (OR: 5.0, CI: 1.90–13.1)
Clinically, combined approaches (OR: 2.67, CI: 1.21–5.89) and useage of Smith Petersen osteotomy (OR: 2.55, CI: 1.02–6.34) were the most important predictors for distal junctional kyphosis.
“Knowledge of these factors will potentially help direct future study and strategy aimed at minimising this potentially dramatic occurrence”, Passias et al conclude.
Patients with neurological symptoms were also at risk for distal junctional kyphosis (OR: 3.71, CI: 0.11–0.63). However, no significant relationship was found between osteoporosis, age, or ambulatory status with incidence of distal junctional kyphosis.
The study involved a retrospective review of a prospective, multicentre cervical deformity database. Patients over the age of 18 meeting certain deformity requirements were included in the analysis. They had to have either: a cervical kyphosis with a C2–C7 Cobb angle greater than 10°; cervical stenosis with a coronal Cobb angle greater than 10°; a positive cervical sagittal imbalance where the C2–C7 sagittal vertical axis was greater than four centimetres, or T1–C6 angle greater than 10°; or a horizontal gaze impairment where the chin–brow vertical angle is greater than 25°.
The statistical analysis included 101 surgical patients undergoing long cervical deformity correction: 58.3% female, with an overall average age of 60.1 years, and an average BMI of 30.2. During surgical practice, the mean number of levels fused was 7.1, an osteotomy was performed on 49.5% of cases, and the surgical approach was split thus: 46.5% posterior, 17.8% anterior, and 35.7% combined. Distal junctional kyphosis was defined by both clinical diagnosis (by the enrolling surgeon) and posthoc identification of development of an angle less than -10 from baseline.
Passias and colleagues were awarded the Charles Ray award for best clinical paper at ISASS for this work. In addition to New York University Langone Orthopaedic Hospital (New York, USA), study authors are affiliated with ten other US institutions.
These are the: SUNY Downstate Medical Center (New York); University of California, (Davis); University of Virginia (Charlottesville); Hospital for Special Surgery (New York); University of California (San Francisco); University of Virginia (Charlottesville); San Diego Center for Spinal Disorders (La Jolla); Johns Hopkins University (Baltimore); Swedish Neuroscience Institute (Seattle); University of Kansas Medical Center (Kansas City).