Unloader Knee Brace Increases Medial Compartment Joint Space During Gait In Knee Osteoarthritis Patients

Abstract

Objectives:

Clinical outcome measures suggest the unloader brace provides small-to-moderate improvements in pain and function in varus knee osteoarthritis (OA) patients. However, controversy still exists as to whether the brace has the real effect of increasing tibiofemoral joint space in the medial compartment during functional activity. As a limitation, the previous studies did not report ground reaction forces (GRF) with and without the brace, which could be a confounding factor affecting joint space. Therefore, the purpose of the present study was to investigate the effect of an unloader brace on dynamic joint space in medial compartment in OA patients while simultaneously recording GRF during gait. The hypotheses were (1) dynamic joint space in the medial compartment would be greater with the unloader brace than without the brace during gait, and (2) GRF during gait would be smaller with the brace than without the brace.

Methods:

Ten varus knee OA patients were enrolled (Age: 52±8 years). After minimum 2-week daily use of the unloader brace, subjects walked (1.0 m/s) on an instrumented treadmill while biplane radiographs of the OA knees were acquired at 100 Hz. Tibiofemoral motion was determined from the biplane radiographs from initial contact to terminal stance phase (gait cycle: 0-40%) using a previously validated model-based tracking process. Dynamic joint space measurement in the medial compartment was performed using previously reported method. Briefly, the medial tibial plateau was divided into 9 sub-regions (Figure 1A) and the average minimum distance between femur and tibia subchondral bone was calculated in each region. The region with the smallest joint space over the three walking trials was selected for the analysis. GRF during gait were collected at 1000 Hz and normalized by each subject’s body weight. Output parameters were averaged over 10% intervals of the gait cycle. Two-way repeated measures ANOVA (gait cycle x brace condition) was used to explore differences in medial compartment dynamic joint space and GRF between the 2 conditions (unbraced and braced). Post-hoc paired t-tests identified the differences between the 2 conditions during the same gait cycle period. Significance level was set as P < 0.05. A subjective questionnaire for the brace usage was collected at the time of the test.

Results:

The dynamic joint space in the medial compartment was significantly greater with the unloader brace than without the brace during gait (P = 0.004) (Table 1, Figure 1B). The average difference between the 2 conditions was 0.27 mm (95% confidential interval: 0.12-0.43). No significant difference was observed in terms of GRF between unbraced and braced conditions. The questionnaire showed participants felt reduced pain (4.1±0.7 out of 5 scale) and were comfortable (3.8±0.8 out of 5) when wearing the brace.

Conclusion:

The unloader knee brace induced a small but significant increase in medial dynamic joint space during gait. Furthermore, no differences in GRF during gait were found between unbraced and braced conditions, indicating that the increase of medial joint space with bracing was not due to decreased limb-loading during gait, but instead due to the brace use itself. These results suggest that the OA unloader brace may reduce medial compartment joint loading during dynamic loading activities.

Figure 1.

(A) Medial compartment regions used to calculate dynamic joint space. The medial tibial plateau was divided into 9 sub-regions, and the average joint space in each region was obtained over every 10% of gait cycle. The regions with the smallest joint space (region 5 in 9/10 subjects) was selected for the analysis. (B) The instantaneous dynamic joint space during gait at 15% of the gait cycle for one subject, demonstrating increased medial compartment joint space in the braced condition.

Table 1.

Results of medial compartment dynamic joint space and ground reaction forces during gait. *Statistically significant difference (vs unbraced condition)

Gait cycle	Medial compartment dynamic Joint space (mm)			Ground reaction forces / Body weight
	Unbraced	Braced	P-value	Unbraced	Braced	P-value
0-10%	2.8 ± 0.9	3.2 ± 1.0*	0.007	0.55 ± 0.11*	0.56 ± 0.12*	N/A
10-20%	2.4 ± 0.8	2.6 ±0.8*	0.001	0.94± 0.11*	0.94 ± 0.08*
20-30%	2.4 ± 0.8	2.6 ±0.7*	0.028	0.87 ± 0.09*	0.92 ± 0.08*
30-40%	2.3± 0.7	2.6 ±0.6*	0.017	0.90 ± 0.08*	0.91 ± 0.09*
Overall	2.5 ± 0.8	2.8 ±0.7*	0.004	0.81 ± 0.04*	0.83 ± 0.04*	0.15