An Early Development of Force Distribution Sensor Using Pressure-Sensitive Conductive Rubber for Soft Tissue Balance in Total Knee Arthroplasty

Aims It is unknown whether gap laxities measured in robotic arm-assisted total knee arthroplasty (TKA) correlate to load sensor measurements. The aim of this study was to determine whether symmetry of the maximum medial and lateral gaps in extension and flexion was predictive of knee balance in extension and flexion respectively using different maximum thresholds of intercompartmental load difference (ICLD) to define balance. Methods A prospective cohort study of 165 patients undergoing functionally-aligned TKA was performed (176 TKAs). With trial components in situ, medial and lateral extension and flexion gaps were measured using robotic navigation while applying valgus and varus forces. The ICLD between medial and lateral compartments was measured in extension and flexion with the load sensor. The null hypothesis was that stressed gap symmetry would not correlate directly with sensor-defined soft tissue balance. Results In TKAs with a stressed medial-lateral gap difference of ≤1 mm, 147 (89%) had an ICLD of ≤15 lb in extension, and 112 (84%) had an ICLD of ≤ 15 lb in flexion; 157 (95%) had an ICLD ≤ 30 lb in extension, and 126 (94%) had an ICLD ≤ 30 lb in flexion; and 165 (100%) had an ICLD ≤ 60 lb in extension, and 133 (99%) had an ICLD ≤ 60 lb in flexion. With a 0 mm difference between the medial and lateral stressed gaps, 103 (91%) of TKA had an ICLD ≤ 15 lb in extension, decreasing to 155 (88%) when the difference between the medial and lateral stressed extension gaps increased to ± 3 mm. In flexion, 47 (77%) had an ICLD ≤ 15 lb with a medial-lateral gap difference of 0 mm, increasing to 147 (84%) at ± 3 mm. Conclusion This study found a strong relationship between intercompartmental loads and gap symmetry in extension and flexion measured with prostheses in situ. The results suggest that ICLD and medial-lateral gap difference provide similar assessment of soft-tissue balance in robotic arm-assisted TKA. Cite this article: Bone Jt Open 2021;2(11):974–980.

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Does Patella Position Influence Soft Tissue Balance and Clinical Outcome in Minimally Invasive Total Knee Arthroplasty?

10.21203/rs.3.rs-16382/v1 ◽

2020 ◽

Author(s):

Kaiyuan Liu ◽

Dong Yang ◽

Tianyang Xu ◽

Wenwei Jiang ◽

Lin Fan ◽

...

Keyword(s):

Total Knee Arthroplasty ◽

Soft Tissue ◽

Minimally Invasive ◽

Knee Arthroplasty ◽

Soft Tissue Balance ◽

Femoral Prosthesis ◽

Group A ◽

Total Knee ◽

Group B ◽

Varus Angle

Abstract Purpose: We hypothesized that patellar positioning during minimally invasive total knee arthroplasty (MIS-TKA) would affect soft tissue balance and postoperative outcome.Methods: From December 2018 to February 2019, 55 patients receiving primary MIS-TKA were enrolled. The gap-balance technique was used, with patients randomly assigned to undergo osteotomy and balance of soft tissue with the patella reduced (group A; n = 27) or with the patella subluxated (group B; n = 28). The soft tissue balance achieved with the patella reduced and subluxated were compared. Femoral prosthesis rotation, mechanical femoral axis–to–tibial axis angle, Knee Society Score (KSS), pain score, and range of flexion were compared between the groups. Follow-up was for 6 months.Results: The flexion gap and the varus angle were significantly greater after patella reduction than before reduction, but the extension joint gap and varus angle were comparable before and after patella reduction. The femoral prosthesis tended to be internally rotated in group B. Range of flexion was better in the group A than in group B at 1 month after surgery, but the differences were not significant at 3 and 6 months. KSS and pain score were comparable between the groups after surgery.Conclusion: During MIS-TKA, as far as possible, soft tissue balance should be achieved with the patella reduced; otherwise, the femoral prosthesis may be installed more internally and, after patella reduction, the flexion gap and varus would increase.

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