Introduction: Functional assessment of lumbar disc herniation (LDH) patients can provide valuable information on postoperative recovery rate and physical performance level following discectomy surgery. "Cone of Economy" (COE) balance measures have been used to evaluate balance following lumbar surgery, but it is unclear whether they are applicable to more demanding balance situations. The y-balance test (YBT) is another clinical balance test which poses greater demands on postural coordination and may be more indicative to changes in balance during more strenuous activity. The purpose of this study was to compare COE and YBT balance measures among LDH discectomy patients and to determine whether YBT provides better insight into overall balance capacity. We hypothesized that YBT would show greater sensitivity to changes in dynamic balance when compared to COE range-of-sway (ROS) and total sway distance (TSD) measures following lumbar discectomy.

Methods: This was a preliminary non-randomized retrospective review of LDH patients treated with single-level discectomies and healthy (H) controls who underwent functional balance assessments. LDH patients were evaluated four times: before (P0), 2 weeks after (P2w), 6 weeks after (P6w) and 3 months after (P3m) surgery. Subjects completed patient-reported outcome measures (PROMs) for pain (VAS low back, leg) and disability (ODI), a COE balance test, and YBT. COE balance measures included coronal and sagittal ROS and TSD at the center-of-mass (COM) and head. YBT measures the forward (F), back lateral (BL), and back medial (BM) leg reach distance of the dominant leg normalized by leg length. Kinematic data was collected during all balance tests using three-dimensional motion tracking.

Results: 26 LDH (4F/11M, 43±14yr, 93±20kg, 1.8±0.1m, 30±6kg/m²) and 15 H (11F/4M, 29±14yr, 66±10kg, 1.7±0.1m, 24±3kg/m²) subjects were included. Patients reported significant improvements in VAS low back, VAS leg, and ODI at all follow-ups compared to P0 (VAS low back=3.5±2.7; VAS leg= 5.8±2.7; ODI= 40.2±16.3) with the exception of VAS low back at P3: P2w (VAS low back=0.9±1.1, p=0.001; VAS leg=1.2±1.9, p<0.001; ODI=16.1±13.3, p<0.001), P6w (VAS low back=0.5±0.8, p=0.002; VAS leg=0.6±1.3, p<0.001; ODI= 7.8±13.3, p<0.001), and P3m (VAS low back=0.9±1.7, p=0.067; VAS leg=1.5±3.0, p=0.007; ODI=9.0±18.0, p=0.001). All LDH COE measures showed no significant differences at follow-ups compared to P0 or H (all p>0.05). All LDH YBT reach distances showed significant improvements at all follow-ups relative to P0 (F=55±10%; BL=76±10%; BM=55±13%) with the exception of BL at P3m: P2w (F=61±10%, p=0.046; BL=83±12%, p=0.044; BM=67±17%, p=0.020), P6w (F=67±8%, p=0.001; BL=85±11%, p=0.024; BM=73±19%, p=0.005), P3m (F=65±5%, p=0.043; BL=84±14%, p=0.147; BM=72±16%, p=0.033). Compared to H (F=72±7%, BL=100±7%, BM=89±8%), LDH YBT reach distances showed recovery of F at P6w (p=0.141) and P3m (p=0.075), however all other directions remained significantly shorter at all other follow-ups (all p<0.05).

Discussion: LDH discectomy patients showed greater improvement in the more demanding YBT than during the quiescent COE balance test. This suggests YBT has greater sensitivity to dynamic balance among active LDH patients which may already have elevated COE balance compared to other spinal pathologies. YBT may be a valuable assessment for patients who seek accelerated return to work or sporting activity.