Is there a correlation between the change in the interscrew angle of the eight-plate and the delta joint orientation angles?

Objectives: It is known that the screws of the eight-plate hemiepiphysiodesis construct diverge as growth occurs through the physis. Our objective was to investigate whether there is a correlation between the amount of change of the joint orientation angle (JOA) and that of the interscrew angle (ISA) of the eight-plate hemiepiphysiodesis construct before and after correction. Patients and methods: After the institutional review board approval, medical charts and X-rays of all patients operated for either genu valgum or genu varum with eight-plate hemiepiphysiodesis were analyzed retrospectively. All consecutive patients at various ages with miscellaneous diagnoses were included. JOA and ISA were measured before and after correction. After review of the X-rays, statistical analyses were performed which included Pearson correlation coefficient and regression analyses. Results: There were 53 segments of 30 patients included in the study. Eighteen were males, and 12 were females. Mean age at surgery was 9.1 (range 3–17). Mean follow-up time was 21.5 (range, 7–46) months. The diagnoses were diverse. A strong correlation was found between the delta JOA (d-JOA) and delta ISA (d-ISA) of the eight-plate hemiepiphysiodesis construct (r = 0.759 (0.615–0.854, 95%CI), p < 0.001). This correlation was independent of the age and gender of the patient. Conclusions: There is a strong correlation between the d-ISA and the d-JOA. The d-ISA follows the d-JOA at a predictable amount through formulas which regression analysis yielded. This study confirms the clinical observation of the diverging angle between the screws is in correlation with the correction of the JOA. Level of evidence: Level IV, Therapeutic study.