To analyze the effect of the arthroscopic meniscal procedure in adult discoid lateral meniscus (DLM) according to the age and meniscal preservation by making comparisons with the non-discoid lateral meniscus (N-DLM).
From March 2014 to October 2020, comparative analysis was performed in adult DLM who underwent arthroscopic meniscal procedures (Operative DLM:134 knees), non-operative treatment (Non-operative DLM: 56 knees), and adult N-DLM who underwent arthroscopic meniscal procedures (Operative N-DLM: 64 knees). Those were between 20 and 65 years old and completed a minimum follow-up of 2 years. DLM patients who underwent arthroscopic procedure were divided into subgroups according to age and extent of the meniscal preservation. The following parameters were assessed and compared between the groups: (1) coronal limb alignment, (2) osteoarthritis grade, and (3) clinical outcomes and the minimal clinically important difference (MCID).
The coronal limb alignment was significantly changed to valgus in the order of operative DLM, N-DLM, and non-operative DLM (Δ mechanical hip-knee-ankle angle (mHKA): 3.23 ± 1.85 versus 1.35 ± 1.03° versus -0.57 ± 1.88°; p < 0.05). Operative DLM showed most prominent osteoarthritic change in the lateral compartment, followed by the N-DLM and non-operative DLM groups (40.3 % versus 17.2 % versus 5.3 %; p < 0.05). These changes in operative DLM were more prominent in older adults who underwent meniscal sacrificing procedures and resulted less satisfactory clinical outcomes (all p < 0.05).
Arthroscopic surgery for adult DLM resulted in progression to valgus alignment and lateral compartment degeneration compared with non-operative treatment and arthroscopic surgery of the adult N-DLM. The old age and meniscal sacrificing procedure showed more rapid radiographic changes and lower clinical outcomes.

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