Background Hallux valgus is a prevalent foot deformity characterized by lateral deviation of the great toe and medial deviation of the first metatarsal. Traditional corrective surgeries often involve osteotomies and soft tissue procedures, which may not fully address the underlying structural instability, particularly at the tarsometatarsal (TMT) joint. The Lapiplasty procedure has emerged as an innovative surgical approach that corrects the hallux valgus deformity by realigning the metatarsal in three planes and fusing the first TMT joint. While this technique has shown promising results in deformity correction and stability, it can introduce new challenges, such as intercuneiform instability. In this paper, we will discuss the case report of a patient who underwent Triplanar TMT Arthrodesis (Lapiplasty) and developed an uncommon complication known as intercuneiform instability. Case Presentation Our patient was a 78-year-old male (body mass index 26.91 kg/m2) with a history of osteoarthritis, BPH, and HLD who presented with right foot pain and deformity. He complained of foot pain for many years elicited by activities. He had previously undergone conservative treatment, including NSAIDS and toe spacers. Clinical examination and radiographs revealed a significant hallux valgus deformity with an HVA of 37 degrees and an IMA of 17.7 degrees. Given the patient’s persistent pain and evidence of deformity, the patient was indicated for surgery. Triplanar 1st TMT arthrodesis was performed using the Lapiplasty system as directed by the system. An akin osteotomy and exostectomy of the first metatarsal head were also performed. The patient was compliant with all post-surgical instructions. At twelve weeks postop, the patient presented with a minimal return of the hallux valgus deformity. Slight soreness and moderate swelling were noted with a bulging vein over the midfoot. Standard radiographs of the right foot showed a slight increase in the 1st intermetatarsal space indicative of the gap sign. Six and twelve-month radiographs showed a continuing slight increase in the space. Discussion The Lapiplasty procedure, while innovative in addressing tri-planar deformities in hallux valgus correction, has presented a notable but rare complication in the form of intercuneiform instability, as illustrated by the case of our 78-year-old male patient. Intercuneiform instability may manifest clinically as persistent pain, inflammation, and a recurrence of deformity, as seen in our patient. Further research is needed to refine surgical techniques and develop preventative measures to mitigate the risk of intercuneiform instability following Lapiplasty.