A novel instrument for ligament balancing: a biomechanical study in human cadaveric knees

Abstract

Purpose: Ligament balancing is a prerequisite for good function and survival in total knee arthroplasty (TKA). Various balancing techniques exist, but none have shown superior results. The pie-crusting technique by Bellemans of the medial collateral ligament is commonly utilized; however, it can be difficult to achieve repeatable ligament lengthening with this technique. Therefore, we invented a novel instrument to standardize the pie-crusting technique of the superficial and deep medial collateral ligament (hereafter MCL). The purpose was to examine if pie-crusting with the instrument could produce repeatable ligament lengthening.

Methods: The MCL was isolated in 16 human cadaveric knees, and subjected to axial tension. The instrument was composed of a specific grid of holes in rows, used to guide sequential pie-crusting puncturing of the MCL with a Ø1.6 mm end-cutting cannula. Ligament lengthening was measured after each row of punctures. Regression analysis was performed on the results.

Results: Mean lengthening ± SD in human cadaveric MCL for puncturing of row 1 in the instrument was 0.06 ± 0.09 mm, 0.06 ± 0.04 mm for row 2, 0.09 ± 0.08 mm for row 3, 0.06 ± 0.05 mm for row 4 and 0.06 ± 0.04 mm for row 5, giving a mean total lengthening of 0.33 ± 0.20 mm. Linear regression revealed that MCLs were repeatably lengthened by 0.07 mm per row when punctured using the instrument.

Conclusions: MCLs showed linear lengthening in human cadavers for subsequent use of the instrument. Our instrument shows promising results for repeatable ligament lengthening.

Keywords: Balancing; Bellemans; Knee arthroplasty; Ligament lengthening; MCL; Medial collateral ligament; Pie-crusting; Soft tissue balance; TKA; Whiteside.

Conflict of interest statement

The corresponding author and JG declare that a conflict of interest exists in respect of this work owing to the duties of the former as part owners of Compenso MedTech AS, and the potential subsequent financial ties arising from this position (including payment for current or future research, ownership of stock and stock options, fees for advice or public speaking, consulting, serving on advisory boards or for medical training companies, and receipt of patents or patents pending).

© 2023. European Society of Sports Traumatology, Knee Surgery, Arthroscopy (ESSKA).

Figures

Fig. 1

The novel instrument. Dimensions of the novel instrument for ligament balancing with the specific staggered puncturing grid. The rows are numbered 1–5 in a horizontal fashion starting from the top. Columns are numbered 1–7 from the left. An end-cutting cannula is passed through the holes to cut individual MCL-fibres

Fig. 2

Biomechanical setup. Biomechanical setup in the MTS® machine. The tibia is fixed with polymethylmethacrylate and screws to a steel tube and the femoral bone block to a metal clamp

Fig. 3

Total lengthening per human specimen. Human cadavers. Total cumulative lengthening in mm for each individual specimen (black lines) and the mean (red)

Fig. 4

Load-to-failure. Load-to-failure of MCL intrasubstance strength compared to pull-out strength

Fig. 5

Lengthening at different tensile forces. Lengthening of MCL in mm for increasing tensile forces after puncturing was completed. Tensile strength at intrasubstance MCL failure was 527 N with an SD of 131 N, and 307.6 ± 70.2 N for pull-out failure. The lengthening is approximately linear up to 200N, as seen in the figure, but from 200N to failure the scale is not proportional and therefore cannot be used to assess linearity (Fig. 6)

Fig. 6

Stiffness of human MCL. Stiffness measured in N/mm of the MCL, showing mean values and SD