Edinburgh Napier University

  Background
Definition and clinical diagnosis of instability in TKA is challenging. Sensitive and objective biomechanical tools to aid diagnosis are currently lacking. This proof-of-concept study evaluates the use of pressure mat analyses to identify abnormal biomechanical loading patterns associated with TKA instability within an outpatient clinical setting.

Methods
Twenty participants were examined: 10 patients with suspected unilateral TKA instability and 10 healthy controls. Participants underwent bilateral stance and gait tests measuring time and limb loading pressure parameters. Gait was divided into three phases: heel strike, mid-foot and toe off. Pressure recordings are expressed relative to bodyweight. Between-limb loading discrepancies were calculated in TKA patients and controls, and these differences were then compared between groups. Statistical significance was accepted at p < 0.05.

Results
TKA patients consistently offloaded pressure away from the operated limb, whereas healthy controls exhibited more even limb loading throughout bilateral stance ( p < 0.05). TKA patients exhibited greater discrepancy in overall step contact time between limbs (−0.09 s ± 0.16 s; p = 0.016) compared to controls (0.06 s ± 0.08 s; p = 0.04). Post-hoc tests showed significant between-group differences during midfoot (−0.04 s ± 0.07 s; p = 0.03) and toe-off (0.05 s ± 0.14 s; p = 0.013). Between-group differences in limb loading discrepancy were evident at heel strike (−9.24% ± 2.11%; p = 0.0166) and toe-off (−10.34% ± 5.51%; p = 0.0496).

Discussion
Pedobarographic measurements demonstrated differences in mechanical loading patterns in patients with TKA instability compared to healthy controls during functional tasks and warrants further investigation. This may prove to be a useful clinical diagnostic tool in identifying patients that would benefit from revision surgery or physical therapy.