Medial knee pain after trauma

Clinical History

Fifteen days after being struck by a bus, a 76 year old woman was referred to our department for CT (Figure 1) due to persisting, exquisite pain along the medial compartment of her right knee.
Based on her imaging findings, she then underwent a knee MRI (Figure 2).

Imaging Findings

CT showed an avulsion fracture ("reverse Segond fracture") at the superomedial angle of the medial tibial plateau, a large joint effusion, and soft tissue swelling along the course of the posterior cruciate ligament (PCL). Fracture margins along the medial tibial plateau and avulsed fragment appeared non-corticalized.

MRI confirmed the large suprapatellar effusion and avulsion fracture, and showed the associated partial rupture of the medial collateral ligament (deep layer) at its tibial insertion site (best seen on the coronal view). Bone marrow oedema is seen in the medial tibial plateau near the small avulsed bone fragment. The PCL appeared swollen, heterogeneous, and diffusely hyperintense, consistent with partial, incomplete rupture (sagittal view). The anterior cruciate ligament (ACL) and medial meniscus were intact. There was a longitudinal fissure of the medial meniscus (not shown).

Discussion

Background:
A reverse (or 'medial') Segond fracture designates an avulsion fracture at the superomedial angle of the medial tibial plateau associated with disruption of the corresponding insertion of the deep layer of the medial collateral ligament of the knee [1].

Clinical Perspective:
Reverse Segond fractures are rare, having been reported in a few cases only [1-4], and, in a large Finnish retrospective study at a large trauma centre, represented less than 1% (10 cases) of "emergency room acute knee trauma MDCT examinations" [3].
The affected knee may demonstrate a variety of associated injuries, which makes the radiologist's role important to guide further therapy. These injuries may include lesions of the posterior cruciate ligament and medial meniscus [2, 3, 5]. Anterior cruciate ligament (ACL) tears, depression fracture of the medial tibial plateau [2], and lateral meniscal tears [3] have also been described.
Despite the potential for neuromuscular complications in associated knee dislocation [2], such complications have not been described yet in the context of reverse Segond fractures.

Imaging Perspective:
The mechanism of injury is, unsurprisingly, opposite to that seen in original Segond fractures [5]. In the latter, the avulsion fracture at the lateral (fibular) collateral ligament insertion site and the associated ACL injury typically result from an injury sustained during combined varus and internal rotation. In reverse Segond fractures, the lesions stem from a valgus and external rotation mechanism [1, 2, 5].
These lesions typically result from high speed trauma such as being struck in a motor vehicle accident (instead of sport activities, as in true Segond fractures).

Outcome:
Prognosis depends on associated ligamental and/or meniscal injuries. Imaging is important to guide subsequent management, by determining what structure(s) may require surgical repair, and for pre-operative planning, by warning in advance the surgeon of co-existing lesions that may be difficult to see during arthroscopy.

Take home messages:
The discovery of a reverse Segond fracture should alert physicians to the possibility of associated knee injuries.
Pellegrini-Stieda post-traumatic lesions also affect the medial side of the knee, but the avulsion fracture involves the medial collateral ligament at its femoral condyle attachment site.
A true Segond fracture is the mirror image of this case but on the lateral side of the knee: it consists of an avulsion fracture from the lateral tibial plateau. It is 4 times more common than reverse Segond fractures [3], results from internal rotation and varus stress, and is often (75% of cases) associated with an ACL tear.

Differential Diagnosis List

Final Diagnosis

Reverse Segond fracture.

URL:	https://www.eurorad.org/case/12929
DOI:	10.1594/EURORAD/CASE.12929
ISSN:	1563-4086