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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.