Immediate Effects of an External Rotation-Restricting Knee Brace on Knee Osteoarthritis: Evaluation Using AI-Based Motion Analysis

A total of 12 patients (12 knees) diagnosed with medial knee osteoarthritis (OA) were included in this study (9 females and 3 males). The mean age was 69.8 ± 5.4 years, with a mean height of 156.0 ± 5.4 cm and a mean body weight of 58.0 ± 8.9 kg. Radiographic evaluation showed a femorotibial angle (FTA) of 178.7 ± 1.8°. According to the Kellgren–Lawrence (KL) classification, 1 knee was graded as KL I, 6 knees as KL II, 3 knees as KL III, and 2 knees as KL IV. This study was conducted with the approval of the Ethics Committee of Saitama Prefectural University. All participants were fully informed of the purpose and methods of the study, and written informed consent was obtained prior to participation.

Structure of the Knee Brace

The newly developed knee brace was named the Clinical Balance for Motion (CBM) knee brace, reflecting its function of adjusting body alignment while maintaining the continuity of movement (Figure 1). The magnitude of the corrective force can be modified by altering three types of straps. The knee joint axis incorporates bilateral coil spring supports, which are removable. The use of coil springs minimizes misalignment with the knee joint axis and prevents distal slippage during brace wear. The strap system is designed to prevent excessive tibial external rotation by applying a force in the internal rotation direction. In addition, varus alignment of the knee is corrected by applying tension from the lateral aspect of the knee joint axis toward the medial aspect of the thigh (Figure 1).

Results

The knee adduction moment significantly decreased from 3.90 ± 1.69 Nm without the brace to 2.78 ± 1.12 Nm with the CBM knee brace, corresponding to a reduction of approximately 1.1 Nm. Similarly, the tibial external rotation moment significantly decreased from 2.43 ± 0.72 Nm without the brace to 1.29 ± 0.51 Nm with the CBM knee brace, also representing a reduction of approximately 1.1 Nm (Table 1).

Table 1: Knee adduction moment and Tibial external rotation moment (mean ± standard deviation).

Discussion

The tibia exhibits a physiological tendency to externally rotate during knee flexion. However, excessive external rotation moment may increase compressive and shear stress on the medial meniscus, elevate tension in the medial collateral ligament, and raise intraarticular pressure [3-5]. These factors are considered to increase the risk of knee pain by augmenting the mechanical load on medial knee structures. In the present study, the CBM knee brace demonstrated not only a reduction in the knee adduction moment but also a reduction in the tibial external rotation moment. These findings suggest that the external rotation–restraining mechanism of the brace may contribute to decreasing mechanical stress on the medial compartment of the knee. On the other hand, the observed reduction in the external rotation moment itself may have clinical significance. However, the optimal magnitude of reduction required to achieve pain relief remains unclear and should be investigated in future studies. Excessive restriction of external rotation may interfere with the natural rotational biomechanics of the knee and potentially increase the risk of joint overload or injury, such as medial displacement of the knee or increased dynamic valgus [7]. Therefore, consideration of rotational alignment is important in knee joint assessment, as external rotation may also contribute to individual differences in pain presentation. Furthermore, pain reduction is closely associated with improvements in gait ability and quality of life [8]. This study has several limitations, including the small sample size and the lack of comparison with other types of knee braces. Future studies with larger sample sizes are needed to clarify the relationship between rotational control, pain reduction, and functional outcomes.

Conclusion

The CBM knee brace may contribute not only to the reduction of the knee adduction moment but also to the suppression of the tibial external rotation moment. These findings suggest that rotational control could represent a novel therapeutic strategy for knee osteoarthritis.

Acknowledgements

The authors would like to thank the Orthotic Device Laboratory for providing the materials used in this study. We also express our sincere gratitude to all participants for their cooperation.

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