Iatrogenic instability of the lateral meniscus after partial meniscectomy.

BACKGROUND: Partial resection of the lateral meniscus can lead to iatrogenic instability of the remnant, resulting in recurrent locking episodes. Due to the innocuous appearance on MRI, the etiology of the locking episodes can be difficult to determine, leading to delays in diagnosis and treatment of this entity. CASE DESCRIPTION: We describe two cases of unstable lateral meniscus posterior horn remnants after previous partial meniscectomy for meniscal tear. Both patients initially presented with lateral pain without mechanical symptoms and were treated with partial meniscectomies. They developed new locking symptoms after initial arthroscopies, and worsened after repeat arthroscopy with removal of additional meniscal tissue. Both patients had their locking symptoms questioned and been accused of malingering by previous physicians due to the benign MRI findings. They were treated successfully by completion meniscectomy. LITERATURE REVIEW: Few studies investigate atypical locking symptoms secondary to undiagnosed lateral meniscus tears. No previous case reports have described knee locking after partial lateral meniscectomy secondary to iatrogenic posterior horn remnants instability. CLINICAL RELEVANCE: New onset mechanical symptoms after partial resection of the lateral meniscus body can be due to posterior horn instability with subluxation under the femoral condyle. This entity appears benign on MRI, requiring a high index of suspicion to make the diagnosis.