Purpose

It is important to retain sufficient hinge from the standpoint of bone healing and mechanical stability after open wedge high tibial osteotomy (OWHTO). However, no method has been established to quantitatively evaluate the amount of remaining hinge. The purpose of this study was to develop a new method to quantitatively evaluate the amount of residual hinge after OWHTO and to examine its inter-examiner reliability.

Method

Fifteen patients who underwent OWHTO at our hospital (5 males, 10 females; mean age 60.7 years old; mean height 161.8 cm; mean weight 71.6 kg; mean BMI 27.3) were included in the study, and measurements were made using CT images taken 2 weeks after surgery. A 3D bone model was created using image processing software (Mimics, Materialise), and cancellous and cortical bone remaining as a hinge in the osteotomy plane was depicted using image processing software (3-matic, Materialise). The area of the cancellous bone was measured as the hinge area, and the surface length of the lateral cortical bone was measured as the hinge length. Each measurement was performed by two examiners, and the inter-examiner reliability was examined. The intraclass correlation coefficient (ICC) was used to analyze inter-examiner reliability for the hinge area and the hinge length.
Result: The hinge area of the two examiners averaged 169.8 ± 90.6 mm2 and 185.6 ± 101.9 mm2, respectively. The inter-examiner reliability for the hinge area was 0.96 (95% confidence interval 0.89-0.99). The hinge length of the two examiners averaged 36.4 ± 8.8 mm and 37.8 ± 9.7 mm2, respectively. The inter-examiner reliability for the hinge length was 0.94 (95% confidence interval 0.84-0.98).

Discussion

Although there have been a few reports on the evaluation of hinge position using 3DCT, no method has been established to measure the amount of hinge remaining after surgery. In this study, we quantitatively evaluated the hinge area and hinge length using 3DCT. High inter-examiner reliability was obtained between two examiners, and the method was considered to be useful as a quantitative evaluation method for the amount of hinge remaining after surgery. In the future, this method could be used to examine the relationship between the amount of residual hinge and clinical outcomes such as bone healing time, hinge fracture after OWHTO, and patient-reported outcome measures.

Conclusion

We developed a new quantitative evaluation method to measure the residual hinge amount as hinge area and hinge length after OWHTO. An acceptable high inter-examiner reliability was confirmed and the method could be useful for further analyses.