In this section
Many children and adolescents present to Emergency Departments after an acute knee injury, e.g. from a twisting injury during sports, a sudden change in direction, landing a jump, or from a direct blow to the knee.
The challenge for the treating clinician is to differentiate between serious knee injuries and self-limiting conditions in the acute presentation, determining which of these children have a significant internal joint derangement. The most important of these are ligamentous injuries, meniscal tears, and osteochondral fractures. (
Patella Dislocations are covered in a separate guideline, but be aware they may not be appreciated if they have spontaneously reduced).
Pain and swelling associated with the injury can mean it is often not possible to adequately examine the knee, even with good analgesia. Thus, making an accurate diagnosis may be difficult on that day. Excluding a fracture requiring urgent intervention needs to be done but arranging appropriate discharge advice and follow-up is more important than establishing a precise diagnosis.
Decisions about operative intervention are usually best delayed until the acute phase/haemarthrosis has settled, with a few important exceptions discussed below.
Please note that penetrating or open wounds involving the knee are beyond the scope of this guideline
Anterior cruciate ligament tear (partial or complete)
Most important in the adolescent age group.
Uncommon under age 10.
“Pop” heard and giving way of the knee associated with a pivoting movementor knee hyperextension.
Tibial spine avulsion
Most common in ages 8-15
As with ACL, but the ligament remains intact with avulsion of bone at its tibial insertion
(+/- associated osteochondral fracture)
See separate guideline
Valgus force with some femur rotation or direct blow to the medial patella
Meniscus injury (lateral or medial)
Frequently associated with ligamentous injuries. Anatomic predisposition in some children
Twisting/Pivoting injury on a weight-bearing, semi-flexed knee.
True Knee Dislocation
Invariably involves multi-ligamentous injury, often with associated vascular and neurological injury
Major trauma, eg motor vehicle accident or skiing
Posterior Cruciate Ligament tear
High force to anterior proximal tibia with the knee flexed; eg from dashboard during a motor-vehicle accident, landing on a flexed knee e.g. rugby
Medial Collateral Ligament injury
Rare in children
(May be associated with medial meniscus injury)
Impact causing valgus stress on knee eg being fallen on by another player
Lateral Collateral Ligament
Rare in children
Impact causing varus stress on knee.
The knee examination is best performed after adequate analgesia has been arranged – which may include opioids or nitrous. The joint should be examined for deformity, swelling (in particular, the presence of an effusion), and focal tenderness.
When a patient is able to tolerate an examination (which may be several days later), the characteristic findings are as follows:
Posterior Cruciate Ligament injury: Posterior sag of the tibia in relation to the femur at 90° of flexion. Loss of “hard” endpoint with posterior draw of the knee.
True Knee Dislocation: Gross deformity, often with co-existing vascular or neurological injuries. Represents a surgical emergency that requires prompt investigation and stabilisation.
X-rays should be ordered in all patients with a haemarthrosis, or an inability to weightbear. Not all knee injuries need an x-ray.
In an isolated anterior cruciate or meniscus injury, often the only X-ray finding is a haemarthrosis in the knee joint.
Figure 1. Moderate haemarthrosis as only radiographic finding in ACL tear
A Segond fracture is an avulsion off the lateral aspect of the tibia. Whilst appearing innocuous to the untrained eye, it represents a menisco-capsular injury that is almost always associated with an ACL injury.
Figure 2 : Coexisting Segond fracture and tibial spine avulsion.
Tibial spine fractures represent avulsion injuries of the Anterior Cruciate Ligament and can be thought of as the paediatric equivalent of an Adult ACL rupture. This fracture can be missed on an AP film and only visible on the lateral Xray
Figure 3: AP and lateral views showing tibial spine avulsion
Figure 4: Acute osteochondral defect – requires admission and arthoscopic removal
Early Analgesia provision
Any high-force injuries (eg. Motor Vehicle Accident, water-skiing) require a full
trauma survey for co-existing injuries
Admission on day of presentation for management of any of these injuries:
(Other injuries where internal joint derangement is suspected are suitable for outpatient management so long as the importance of appropriate follow-up (see below) is understood.)
Injuries requiring same day admission are listed in point 5 above.
Follow-up is highly important for knee injuries with a significant effusion or where internal joint derangement cannot be excluded at first encounter. This is best done with the family’s GP in the next 1-2 weeks after a period of rest/elevation/intermittent ice.
Re-examination at this appointment is the core aim, as the findings listed in section 3 above will become more apparent once the acute swelling has settled.
The GP will be able to arrange further investigations (including an outpatient MRI (medicare rebate applicable) if there are any persisting signs suggestive of internal joint derangement.
Referral to outpatient orthopaedics and/or physiotherapy can occur depending on the clinical exam and MRI findings.
Tibial spine fractures may require early surgical fixation in order to prevent malunion of the fragment
True Knee Dislocation will require emergent reduction and treatment of any vascular injuries, with delayed definitive ligamentous repair
ACL Tears: Decisions around reconstruction of these should only be made after expert orthopaedic assessment, often following a period of prehabilitation with physiotherapy. Most partial tears respond to non-operative management through physiotherapy guided injury rehabilitation. Complete ACL tears in skeletally immature patients require special techniques to avoid injuries to the physes and may best be treated when nearing skeletal maturity.
Meniscal tears may require operative treatment, depending on the location and pattern of the injury. Surgical treatment is more likely to be necessary where the knee is locking, catching or giving way.
ACL injury: possibility of ongoing knee stability without treatment; possibility of osteoarthritis in the long term (whether reconstruction undertaken or not)
Meniscus injury: ongoing instability and pain
True knee dislocation: associated neurovascular injuries and/or compartment syndrome
All injuries: possibility of significant muscle atrophy (particularly VMO) if early physiotherapy/mobilisation is not undertaken, flexion contractures
Fabricant, P. & Kocher, M. Management of ACL Injuries in Children and Adolescents, J Bone Joint Surg Am, 2017;99:600-612
Ardern C et al, International Olympic Committee consensus statement on prevention, diagnosis and management of paediatric anterior cruciate ligament (ACL) injuries. Knee Surg Sports Traumatol Arthrosc. 2018;26(4):989-1010
Shieh, Meniscus Tear Patterns in relation to skeletal immaturity: Children vs Adolescents Am J Sports Med 2013;41(12)2779-83
Mathison D. & Teach S. Approach to Knee Effusions, Pediatric Emergency Care 2009;25(11):773-86