case_images: PMC11711688_01
case_images: Evolution of the passive range of motion (flexion) of both knees (squares) in degrees assessed with a goniometer, and pain intensity (triangles) assessed with a Numeric Rating Scale ranging from 0 to 10.
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case_images: F0001
case_images: Clinical examination of the lower limbs showed a bilateral limitation of passive knee flexion at 65  and active flexion of the knees was almost unobtainable (Fig. 1). As a result, passive knee flexion marginally improved to 80  (Fig. 1). Despite satisfactory pain control and intensive mobilization, the range of motion of both knees decreased to 30  active flexion and 50  passive flexion (Fig. 1). An intensive in-patient physical therapy program was continued in the rehabilitation department and knee flexion was measured at 90  on both sides 1 week after surgery (Fig. 1). Assessment Tool improved from 21/28 to a maximal score of 28/28 and the Functional Independence Measure (FIM) scale increased from 86/126 to 103/126. At the same timepoint and following continuing outpatient physical therapy, passive flexion was measured at 90  on the right knee and 120  on the left knee (Fig. 1) and standard knee radiographs showed stability of the HO (Fig. 2C). Thirteen months after the start of the symptoms and 9 months after surgery, both knees reached a normal range of motion of 140  (Fig. 1).
case_images: Sequential anteroposterior radiographical images showing bilateral extra-articular calcifications on the anteromedial side of the knees (white arrows). (A) Radiological diagnosis of heterotopic ossification. (B) Three weeks after surgery. (C) Two months after surgery.
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case_images: PMC11711688_01_JRMCC-8-41323-g002.jpg
case_images: F0002
case_images: Standard knee X-rays showed extensive bilateral extra-articular HO on the anteromedial side of both knees without joint abnormalities (Fig. 2A). The HO was still partially visible on postoperative X-rays, but showed a significant decrease in density and size (Fig. 2B).
case_images: Magnetic resonance imaging of the left knee in a 26-year-old woman without previous relevant medical history, showing extensive heterotopic ossification in the medial femoro-patellar recess with a slight extension to the vastus medius muscle (white arrows). (A) Transversal T2-weighted fast spin echo and (B) Coronal PD-weighted fast spin echo with fat-saturation.
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case_images: F0003
case_images: MRI showed bilateral HO in the medial femoro-patellar recess with a slight extension to the vastus medialis muscle (Fig. 3).
case_images: (A) Transversal SPECT-CT of the knees with fused images showing active bilateral heterotopic ossifications 6 weeks after first symptoms. (B) 3D reconstructed image showing the localization of heterotopic ossifications with regard to the knee joint.
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case_images: PMC11711688_01_JRMCC-8-41323-g004.jpg
case_images: F0004
case_images: Bone scintigraphy showed actively inflammatory HO's 6 weeks after the start of symptoms (Fig. 4A). The SPECT-CT images allowed creation of a 3D-modeling image reconstruction, which showed the extent of the HO's (Fig. 4B).
case_images: Serum alkaline phosphatase levels during hospitalization showing a peak at 23 days after admission to intensive care unit.
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case_images: PMC11711688_01_JRMCC-8-41323-g005.jpg
case_images: F0005
case_images: In retrospect, it was noticed that during the ICU stay, serum alkaline phosphatase (AP) reached a peak at day 23 (751 U/L; normal values 35-104 U/L) (Fig. 5).