Imaging of the knee injuries in children should include AP and lateral radiographs. Add special views and MRI studies if ligament or meniscal injury is suspected. MRI is less reliable in the young child because congenital abnormalities are more common. When multiple injuries are present, MRI is also less reliable.
Foreign bodies may be imbedded when the child falls. The body may be readily imaged or require special imaging by ultrasound or MRI to demonstrate radiolucent objects. Remove all foreign material from within the joint.
Diaphyseal femoral or tibial fractures may be associated with ligamentous injuries or physeal injury. Examine the knee as part of the evaluation of shaft fractures.
Hemarthrosis is often an indication of a significant knee injury. The presence of fat in the aspirate is consistent with a fracture. A hemarthrosis or severe knee injury may be an indication for an arthroscopic evaluation. Its routine use for all hemarthrosis is controversial.
Arthroscopy is indicated when following a hemarthrosis if knee symptoms persist. Common arthrographic findings include meniscal and ligament injury, evidence of patellar dislocation, and osteochondral fractures.
Meniscal injuries are becoming more common as more children participate in sports. Also, demonstration of these injuries is more likely now because of improved diagnostic skills and expanded use of arthroscopy and MRI. Meniscal injuries increase with increasing age. In young children, tears are usually associated with discoid meniscus.
Collateral Ligament Injuries
Localized tenderness and swelling over the medial collateral ligament and instability suggest this diagnosis. Rule out a physeal fracture as the cause of the instability. An AP radiograph is usually diagnostic. Other imaging studies are less reliable than for meniscal or ACL injuries. medial collateral ligament, ACL, and meniscal injuries may occur together.
Manage acute grade 1 and 2 injuries by immobilization. Manage-ment of grade 3 injuries is controversial. Consider repair of the ligament when injuries are multiple, when very severe, and if a return to demanding activities is planned.
Cruciate injuries in the immature athlete are becoming more common, especially among girls. Suspect this injury if symptoms persist and physical signs are consistent. Be aware that coexisting meniscal injuries are common. Conservative management is often unsuccessful, and reconstruction is necessary if the patient is to return to preinjury activities.
Anterior Tibial Spine Fracture
This injury is common in late childhood, and a fall from a bicycle is a typical history. The ACL may stretch and finally fail through the bone, causing the avulsion fracture.
Evaluation From the lateral radiograph, classify by severity to guide management.
Management Manage type 1 injuries by cast immobilization in slight flexion for 4 weeks to allow healing. Start isometric quadriceps exercises in the cast. Allow a return to full activities after complete rehabilitation.
Manage type 2 injuries with the knee in extension if required to reduce the fragment. If reduction is incomplete, consider open repair.
Manage type 3 injuries by reduction and fixation. This may be performed open or by arthroscopy. Make certain that reduction is complete to avoid a residual step-off and add to the ACL laxity. Fix the fragment with suture, pins, or screws. Avoid traversing the physis. Consider fixation with heavy absorbable sutures through the fragment and into the epiphysis. Manage postoperatively as with type 1 and 2 injuries.
Prognosis About 80–90% of cases do well. About 40% will show abnormal ACL laxity.
Acute dislocation of the patella occurs with valgus flexion injuries and is common in individuals with anatomic features that make the patella less stable. These features include shallow sulcus, knee valgus, or rotational malalignment. Individuals with ligamentous laxity may be more likely to dislocate but less likely to sustain osteochondral fractures.
Evaluate Osteochondral fractures occur in about 40% of acute dislocations of the patella. The site of fracture varies. AP, lateral, and sulcus views often show the lesions. MRI usually shows an effusion, bone bruising of the femoral condyle, and medial retinacular tears. Arthroscopy will demonstrate lesions and make early treatment possible.
Risk of recurrence About one-third to one-half of patellar dislocations will recur. Recurrence is most likely in those cases that dislocated with minimal trauma, reduced spontaneously, and were associated with minimal swelling.
Treatment Options include early arthroscopy, aspiration, or immobilization.
Arthroscopy is most invasive, but appropriate if an osteochondral fragment is seen or suspected. Remove small osteochondral fragments. Replace and fix large fragments.
Aspiration provides pain relief. The finding of fat in the bloody aspirate suggests a fracture. Effusions often recur rapidly.
Immobilization is the final option. Apply a knee immobilizer for 7–10 days. Start isometric exercises early. If symptoms persist, consider additional studies.
Advise the family of the risks of recurrence. Reestablish range of motion and quadriceps strength before allowing return to full activity.
Stress Physeal Injuries
These injuries are common in myelodysplasia. Manage by prolonged immobilization with weight-bearing activities.
Proximal Tibial Physeal Fractures
If these rare injuries extend posteriorly, they may damage the popliteal artery. They are often classified with tibial tubercle fractures. This separation is useful to alert one to the risk of this injury. These injuries can be associated with severe polytrauma.
Tibial Tubercle Fractures
Tibial tubercle fractures occur at the end of growth when the physis is unable to withstand the tensile loading imposed by the adolescent. Classification includes the traditional Grade 1–3 with the addition of a fourth category—rupture of the patellar tendon. Manage most type 1 and 2 fractures with cast immobilization. Severely displaced fractures may require reduction and fixation to prevent a disabling residual prominence. Type 3 fractures require open reduction. Type 4 may require tendon repair.
Patellar fractures take a variety of forms.
Transverse fractures If these fractures are displaced, reduce anatomically and fix with tension-band wires, as done in adults.
Marginal fractures may occur from the medial, superior, or lateral side of the patella. Often only a small rim of bone is displaced, but the cartilage fragment is often large. Manage most by cast immobilization.
Sleeve fractures are characterized by avulsions of the patellar ligament. Because the fragment includes cartilage, it is usually considerably larger than the radiographic defect. Sometimes MRI is necessary to show the extent of the injury. Reduce widely displaced sleeve fractures and fix by suture repair.