Summary

This study clarified that, in an open-wedge osteotomy of the proximal tibia with hemicallotasis for medial knee osteoarthritis, with the correction angle more than 15 degrees, the postoperative upward translocation of fibular head might cause the degenerative change in the articular cartilage of the proximal tibiofibular joint as evidenced by MRI T1-rho mapping.

Abstract

[Backgroud]
Medial opening-wedge osteotomy has gained popularity for medial knee osteoarthritis with a varus deformity. An open-wedge osteotomy of the proximal tibia with hemicallotasis (HCO) was described as a new technique with an external fixator using a gradual distraction. In the previous prospective trial, we reported good clinical outcomes and radiological alignment maintenance at the averaged 14 years following HCO. HCO needs no fibular osteotomy, however, it is not yet clear how the postoperative articular cartilage changes in the proximal tibiofibular joint (PTFj) of the involved knee underwent HCO. The purpose of this study is to clarify those changes using MRI 3D T1-weighted fast field echo with water-selective excitation (3D WATS) and T1-rho mapping.
[Patients and Methods]
A total of 20 patients were underwent HCO without fibulectomy for their unilateral medial knee osteoarthritis. The correction angle was planned so that the Mikulicz line would pass through a point approximately 65 % of the distance from the medial edge of the proximal tibial plateau on the AP radiograph of whole leg. The radiographs, and the 3D WATS and T1-rho mapping MRI were obtained from all patients pre-operatively and at one year after surgery. On the radiograph, we measured the correction angle (CA), the distance of fibular head from the lateral tibial plateau (d-FH), and the distance of distal fibular tip from the distal tibial plafond (d-DFT). In addition, on those coronal 3D WATS MRIs, we set the region of interest (ROI) on the full-thickness cartilage of the PTFj. After that, we measured the T1-rho relaxation time (ms) of the ROI. Statistical analysis of time-dependent changes in the d-FH, d-DDT, and the T1-rho relaxation time was performed using the Student's t-test. A correlation between those parameters and CA were also examined. A p-value less than 0.05 was considered as significant. We obtained approval from the IRB of our institution, and all patients provided their informed consent to participate in this study.

Results

The mean correction angle at one year after surgery was 16º. Seven out of 13 patients had the CA more than 15º. There was a significant negative correlation between CA and d-FH (r=0.54, p=0.03) while the d-DDT had no changes postoperatively. In addition, there was also a significant correlation between CA and the amount of postoperative change of T1-rho value (r=0.78, p<0.01). The pre-and post-operative mean T1-rho values in the seven patients with the CA more than 15º were 38.4 ms and 41.4 ms, respectively, showing the postoperative significant higher relaxation time (p=0.02). On the other hand, those values in the remaining patients were 40.1ms and 40.3 ms, respectively, showing no postoperative change.

Discussion

HCO has several attractive advantages compared to conventional procedures, including the simplicity of the surgical procedure without fibulectomy, easier acquisition of accurate correction, and the great correction angle. On the other hand, we reported that T1-rho relaxation time of PTFj cartilage showed a constant value ranged from 35 ms to 40ms, and its value was not affected by aging or cartilage degeneration in the femorotibial joint in knee osteoarthritis. In addition, we also reported that T1-rho values more than 40 ms could indicate the degenerative change of articular cartilage. There are some limitations of the MRI analysis only up to one year after surgery and no histological examination by biopsy.

Conclusion

This study clarified that, within the CA more than 15º in HCO, the degenerative change of articular cartilage in the PTFj occurred due to the upward translocation of the fibular fead postoperatively as evidenced by MRI T1-rho mapping. This result suggests that the fibular osteotomy may be needed with the valgus correction more than 15º in HCO.