Radiology · Year 4 · from Radiology
Case 2: Anterior Cruciate Ligament (ACL) Tear
Patient Demographics
- Age: 24 years
- Sex: Female
Chief Complaint
Left knee pain and instability after basketball injury
Presenting Symptoms
The patient was playing recreational basketball when she landed awkwardly after a jump shot. She felt a "pop" in her left knee and experienced immediate pain and swelling. She was unable to continue playing and had difficulty bearing weight. She describes her knee as feeling "unstable" and "like it might give out." She iced the knee and took ibuprofen but presents the following day due to persistent symptoms.
Physical Exam Findings
- Vital Signs: Within normal limits
- Left Knee:
- Moderate effusion with loss of normal knee contour
- Tenderness along the medial and lateral joint lines
- Limited range of motion (20-90 degrees) due to pain and swelling
- Lachman Test: Positive with soft endpoint (Grade 2, 5-10mm translation)
- Anterior Drawer Test: Positive
- Pivot Shift Test: Unable to perform due to guarding
- McMurray Test: Equivocal due to pain
- No varus/valgus laxity at 0 or 30 degrees of flexion
- Neurovascular: Intact distally
Imaging Findings and Interpretation
Knee Radiographs (AP, Lateral, Sunrise):
- Lipohemarthrosis: Fat-fluid level visible on cross-table lateral view, indicating intra-articular fracture (likely Segond fracture or osteochondral injury)
- Segond Fracture: Small avulsion fracture of the lateral tibial plateau at the site of the lateral capsular ligament attachment - pathognomonic for ACL injury
- No other acute fractures
- Joint space maintained
MRI Knee without Contrast:
ACL Findings:
- Complete ACL tear: Discontinuity of ACL fibers with abnormal course
- Edema: T2 hyperintense signal within the residual ligament stump
- Location: Mid-substance tear (most common)
- "Empty notch sign": Absence of normal ACL in the intercondylar notch
Associated Findings:
- Bone Contusions (Kissing contusions):
- Lateral femoral condyle: Sulcus deepening and bone marrow edema (pivot shift mechanism)
- Posterolateral tibial plateau: Bone marrow edema
- This "kissing contusion" pattern is characteristic of ACL injury
- Segond Fracture: Small avulsion at anterolateral tibial plateau confirmed
- Medial Meniscus: Intact, no tear
- Lateral Meniscus: Posterior horn shows increased signal not reaching articular surface (Grade 2 signal, no tear)
- MCL: Intact
- PCL: Intact
O'Donoghue Triad Assessment: Classic "unhappy triad" (ACL + MCL + medial meniscus) NOT present. This is an isolated ACL tear with bone contusions.
Diagnosis
Complete ACL tear, mid-substance, with characteristic bone contusion pattern and Segond fracture
Management
- Acute Phase:
- RICE (Rest, Ice, Compression, Elevation)
- Hinged knee brace locked in extension
- Crutches, partial weight-bearing as tolerated
- NSAIDs for pain and inflammation
- Prehabilitation:
- Physical therapy focusing on:
- Quadriceps strengthening
- Range of motion restoration
- Reduction of swelling
- Goal: Restore full extension and reduce swelling before surgery
- Surgical Planning:
- ACL reconstruction recommended given:
- Young, active patient
- Desire to return to pivoting sports
- Symptomatic instability
- Graft options discussed: Bone-patellar tendon-bone autograft vs. hamstring autograft
- Surgery scheduled for 4-6 weeks post-injury (after "prehab")
- Post-operative Rehabilitation:
- Standardized ACL reconstruction protocol
- Return to sports at 9-12 months if criteria met
Radiological Image
Image Description: Sagittal T2-weighted MRI of the knee demonstrating a complete ACL tear. The normal taut band of the ACL is absent, with only edematous, discontinuous fibers visible. Associated bone marrow edema (bone contusions) is seen in the lateral femoral condyle and posterolateral tibial plateau.
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