Introduction:

Idiopathic fibrosis of the quadriceps muscles is not a common entity. Early presentation is not usual as well. Few cases were reported in the literature describing the Magnetic Resonance Imaging which is considered the modality of choice for diagnosis and some of them added the histopathological correlation as well.

Case report:

We report a 27 months old boy that was referred to the rheumatologist by the orthopaedic surgeon from another institution with possible underlying juvenile idiopathic arthritis in the left knee. This patient presented with complaints of gradually progressing loss of flexion of the left knee and limping gait. No history of recent trauma or previous injection to that limb. No history of joint swelling or other joint involvement. Mental and motor development was otherwise normal

Physical examination revealed full extension in both knees but significant loss of flexion of the left knee was seen. The patient was able to do a total of 15 degrees of flexion before he started complaining of severe pain and inability to flex further on the left side. He walked with a significant limp. The rest of the joints exam were unremarkable including his hips and ankles joint which had full range of motion and no evidence of any effusion or arthritis. No evidence of lesions or rash was seen in the overlying skin.

Radiographs and ultrasound of knees and the bone scan were normal. No bony abnormality was detected neither was joint effusion (Figure 1). The Magnetic Resonance Imaging demonstrated atrophy with intra-substance T2 and T1 hyper intense foci suggestive of fatty atrophy with fibrosis (Figure 2 and 3) compared to the normal side.

Figure 1

AP and lateral radiograph of the left knee show normal bones and soft tissue.

Figure 2

Axial STIR show small size left vastus lateralis and intermedius muscles and hypo-intense signal of the left vastus intermedius muscle compared to the right side.

Figure 3

Axial T1 FS post gadolinium show hypo-intense signal of the left vastus intermedius muscle with no enhancement in keeping with fibrosis.

Discussion:

In the literature, quadriceps muscle contractures have been reported as either congenital [1–3] or acquired (mainly due to injections or trauma) [4-5]. Herewith, congenital cases generally display bilateral involvement and acquired ones show unilateral involvement.

Quadriceps contractures have been classified into three types: rectus femoris type, vastus type and mixed type [6]. Vastus type is the most common form and rectus type has been reported as quite rare.

The exact cause is still unknown (8). The pathophysiology of the progressive fibrosis is unclear but was suggested that causes includes compression of the muscles bundle and capillaries by the volume of the medication injected and the toxicity of the drugs (9-11).

MRI findings of this entity include decreased side of the affected quadriceps muscles, fatty atrophy and fibrosis of the muscles. The fatty atrophy appears as hyper-intense signal on T1WI and T2W images with suppression on STIR sequences. Fibrosis appears as hypo-intense in all of the above sequences. 

Conclusion:

This rare disease should be kept in mind by the general practitioners and the orthopaedic surgeon in cases of loss of flexion of the knee and abnormal gain. Magnetic Resonance Imaging is the modality of choice for diagnosis of this entity. Early diagnosis and treatment can help to prevent and decrease disability.