A 40-year-old male patient was referred for magnetic resonance imaging (MRI) of the right knee after a knife attack. On physical examination, two-incision scars were observed on the anterior aspect of the knee. Both active and passive joint extensions were restricted.
Radiographic examination showed thickening of prepatellar soft tissue, partially obliterated infrapatellar bursal fat pad just above the tibial tuberosity and an incomplete fracture line at the dorsal cortex of patella (Figure 1). On the sagittal T1-weighted MR image complete transection of the patellar tendon is observed (Figure 2). Additionally, the sagittal T2-weighted fat-saturated(fs) MR image shows edematous signal changes in the Hoffa’s fat pad, subcortical patellar bone marrow edema and periosteal oedema corresponding to the radiographic findings at respective locations (Figure 3). Micrometalic artifacts, anterior of the patella, and the patellar tendon were seen on sagittal fs-T2-weighted gradient-echo images (Figure 4).
Although the patellar tendon with its bone to bone attachment classifies this structure as a ligament, it is commonly referred to like the patellar tendon. It constrains patellar motion together with the patellotibial ligament, and the retinacula. Primary supporting muscles of the patellofemoral joint are rectus femoris, vastus-lateralis, vastus-medialis, and vastus-intermedius which join caudally to form the quadriceps tendon [1].
The most common cause of patellar tendon tear is a weakened patellar tendon due to overuse traumas, chronic diseases, steroid use, and tendinopathy [2]. Patellar tendon tear due to penetrating sharp object trauma is rare.
The most common site for a tear is avulsion of the tendon from the inferior pole of the patella. Other particular sites include midsubstance tear and avulsion from the tibial tubercle [1].
In this case, two separate incisions were present, one at the patellar level and the other in the infrapatellar area. Trauma at the patellar level caused damage to the quadriceps tendon, patellar cortex, and dorsal periosteum, trauma at the infrapatellar level caused mid-substance patellar tendon discontinuity and incomplete fracture of the proximal tibia.
Findings of complete tear on radiographs include high riding patella, blurring of the posterior margin of the patellar tendon into Hoffa's fat pad and an avulsion fracture [3].
Ultrasonography is a cost-effective and highly sensitive method that is used as a first-line diagnostic modality for patellar tendon pathologies. High-frequency linear transducers provide high spatial resolution [3,4].
MRI can further demonstrate the whole extent of the patellar tendon, peritendinous soft tissue, bone injuries and outlines possible co-existing intraarticular lesions [5]. Due to the presence of an open wound in the prepatellar area, MRI was preferred as the first-line diagnostic modality in the presented case.
Magic angle artifact which is most pronounced in the proximal patellar tendon on MR should be distinguished from true tendon disorders. True pathologic signal changes due to degeneration or partial tears require a close comparison between T1 and T2-weighted images. Findings of tendon thickening and associated fluid may secondarily help to discriminate true tendon disorders from magic angle artifact [6].
Complete patellar tendon tears require surgical treatment, either by primary repair or tendon reconstruction based on the type of tear. With complete tears, primary repair is performed. The end-to-end repair is preferred for midsubstance tears, as in our case. The prognosis is better with prompt surgical repair [1].
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Patellar tendon transection
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Based on the X-ray and MRI images of the patient’s right knee, the following main characteristics can be observed:
Considering the patient’s history of sharp-object trauma, clinical symptoms (limited range of motion, pain), and imaging findings, the following potential diagnoses are proposed:
Taking into consideration the patient’s age (40, male), history of sharp injury, clinical presentation (restricted knee extension), and the detailed visualization of soft tissue and bone structures on MRI, the most likely final diagnoses are:
The traumatic mechanism and the involvement of multiple injury sites are consistent with sharp-object trauma, and the imaging findings correlate with the clinical presentation.
(1) Treatment Plan
For a complete or near-complete patellar tendon tear, surgical repair is generally necessary. If the soft tissues at both ends of the tear are in good condition, a direct end-to-end suture repair can be performed; if there is a significant tissue defect, a tendon graft or ligament reconstruction might be required. For an incomplete fracture of the proximal tibia without significant involvement of the articular surface, conservative management (immobilization/brace) may be considered, but should be planned in conjunction with the surgical approach and postoperative rehabilitation. If the quadriceps tendon is severely damaged, it must also be repaired or reinforced during surgery.
(2) Rehabilitation/Exercise Prescription
Rehabilitation should follow a gradual and individualized approach, adjusted according to the surgical technique and the status of soft tissue healing. The following stages can be considered:
When creating a specific exercise prescription, the FITT-VP principle (frequency, intensity, time, type, volume and progression) should be adhered to, ensuring that each stage’s training intensity aligns with the patient’s recovery status.
Precautions: For patients with relatively lower capacity for bone or soft tissue healing, closely monitor the surgical site and fracture healing. If there is a significant increase in pain, notable swelling, or a marked restriction of movement, prompt medical consultation and repeat imaging are advised.
Disclaimer: This report is for reference only and does not replace an in-person consultation or professional medical advice. Specific treatment plans must be determined in conjunction with clinical findings and a physician’s comprehensive evaluation.
Patellar tendon transection
