Injuries of the posteromedial bundle of the posterior cruciate ligament after knee hyperextension trauma: A new clinical entity based on an original case series.

ABSTRACT

Purpose: This original case series aims to describe an uncommon triad of clinical signs in patients presenting with persistent pain and inability to resume physical activities after knee hyperextension trauma. Methods: Patient history, clinical examination, arthroscopic findings and investigations of 12 patients who consulted with the senior author are presented. Results: Twelve patients (seven males/five females) presented with persistent pain after knee hyperextension trauma either in sport or a traffic accident. They had a median age of 18.5 and a median body mass index of 23 kg/m2. All had medical visits and at least one magnetic resonance imaging (MRI) before visiting the senior author's institution but the cause of their problems could not be explained. The clinical examination of the injured knee appeared normal except for an uncommon triad of clinical signs with the knee close to extension (1) a grade 1+ anterior-posterior laxity around 10-20° of knee flexion with a firm end-point (pseudo-Lachman sign), (2) a grade 1+ tibiofemoral step-off sign with a posterior drawer at 10-20° of knee flexion and (3) an increased knee hyperextension compared to the contralateral side. Arthroscopy of eight patients confirmed the pseudo-Lachman sign with a grade I posterior drawer close to knee extension, normal posterior laxity at 90° of knee flexion and an intact anterior cruciate ligament. Conclusion: Patients displayed an increased hyperextension and posterior laxity close to knee extension which normalised at 90° of knee flexion. In patients with a history of knee hyperextension trauma associated with persistent pain, inability to resume physical activities, inconclusive MRIs and a standard clinical examination, clinicians should consider extending their investigations with the knee close to extension to identify this clinical triad consistent with a lesion to the posteromedial bundle of the posterior cruciate ligament. Level of evidence Level IV.