Shear Wave Speeds Track Axial Stress in Porcine Collateral Ligaments

Abstract

Ligament tension is an important factor that can affect the success of total knee arthroplasty (TKA) procedures. However, surgeons currently lack objective approaches for assessing tension in a particular ligament intraoperatively. The purpose of this study was to investigate the use of noninvasive shear wave tensiometry to characterize stress in medial and lateral collateral ligaments (MCLs and LCLs) ex vivo. Nine porcine MCL and LCL specimens were subjected to cyclic axial loading while wave speeds were measured using laser vibrometry. We found that squared shear wave speed increased linearly with stress in both the MCL (r2avg = 0.94) and LCL (r2avg = 0.98). Wave speeds were slightly lower in the MCL than the LCL when subjected to comparable axial stress (p < 0.001). Ligament-specific wave speeds may arise from differences in geometry and stress distributions between ligaments. These observations suggest it may be feasible to use noninvasive shear wave speed measures as a proxy of ligament loading during orthopedic procedures such as TKA.

Shear wave tensiometry tracks reductions in collateral ligament tension due to incremental releases

“…30 In the present study, the shear wave speeds ranged from 14.3 to 46.5 m/s, whereas Blank et al measured shear wave speeds in intact ligaments to be 32.5 to 160.3 m/s for the same load range. 30 The primary difference between the two studies is the sensors used to track shear wave propagation. Blank et al tracked shear wave propagation with laser Doppler vibrometers, 30 a non-contact measurement technique.…”

“…Regarding the first key finding, we demonstrated that the tensioned beam model, 29 shown previously to hold in intact ligaments, 30 also applies to ligaments damaged by iterative releases.…”

“…First, we axially loaded each ligament with 50 cycles from 25 to 250 N at 1 Hz followed by a static hold at 250 N for 30 minutes to minimize viscoelastic effects. 30 We limited the maximum load to 250 N based on pilot studies that showed failures at the bony attachments of some porcine ligaments when applied loads exceeded 250 N. We recorded the maximum stretch during the 30-minute static hold at 250 N, referred to subsequently as δ 250 .…”

“…One promising method to measure the tension in individual ligaments during TKA directly and objectively is shear wave tensiometry. 29,30 Prior studies have shown that shear wave speed squared is proportional to the axial stress in tendons 29 and ligaments. 30 This relationship between shear wave speed squared and axial stress is consistent with the analytical relationship predicted by a tensioned beam model.…”

“…29,30 Prior studies have shown that shear wave speed squared is proportional to the axial stress in tendons 29 and ligaments. 30 This relationship between shear wave speed squared and axial stress is consistent with the analytical relationship predicted by a tensioned beam model. 29 However, it is unknown whether reductions in tension due to releases alter shear wave propagation speed differently than reductions in tension due to changes in the axial stretch of an intact ligament.…”