Although rare, mucoid degeneration of the PCL can be a source of activity-related pain in athletes. As a point of reference, Bergin
et al. [
1] reported that the incidence of mucoid degeneration in ACL is 1.0% (44/4221), and McMonagle
et al. [
7] reported that the incidence of PCL mucoid degeneration is 0.1% (14/12,972). To our knowledge, only five cases of symptomatic mucoid degeneration of the PCL have been previously reported. A review of these five cases indicated that mucoid degeneration of the PCL generally affects middle-aged patients with ages ranging from 36 to 65 years, in contrast to the present patient, who was 18 [
2‐
6]. Mucoid degeneration of the cruciate ligaments is usually asymptomatic, and is often hard to diagnose clinically owing to the lack of specific symptoms and signs. However, MRI findings in sagittal plane show longitudinal layers of increased signal intensity on T2-weighted images within the ligament substance with an adjacent well-defined intact rim of hypointense PCL fibers that give the PCL a “tram-track” appearance [
7]. Its clinical symptoms were characterized by posterior knee pain on deep knee flexion without causative or preceding injuries. To date, the mechanism underlying knee pain in mucoid degeneration of the PCL is controversial. According to previous studies, increased volume of the PCL and resultant increases in internal pressure within the notch have been considered a cause of knee pain during terminal flexion [
6]. Several possible etiologies have been suggested, including structural variations of the intercondylar notch and microtrauma leading to the release of a mucin substance [
8]. In this case, there was no abnormality in the morphology of the intercondylar notch. Therefore, we considered that excessive stress on the knee associated with repetitive minor injuries during the sports activity may have caused mucoid degeneration. For treatment of mucoid degeneration of the cruciate ligament, partial excision or debridement is usually performed. Most authors have reported satisfactory results after these procedures without instability [
2‐
6]. In our case, we excised the PCL in part, and it resulted in complete relief of pain and full range of motion without instability. Mucoid degeneration of the PCL can be a source of activity-related pain in young athletes. Its clinical symptoms were characterized by posterior knee pain on deep knee flexion without causative or preceding injuries.