Knee injuries in adolescents need special consideration given the immature ligamentous, bony structures and growth plates. This case describes a common type of adolescent knee injury involving the tibial spine.
Tibial Eminence Injuries
Tibial Eminence Fractures, also known as a Tibial Spine Fracture, is an intra-articular fracture of the bony attachment of the ACL on the tibia. It is most commonly seen in children from age 8 to 14 years during athletic activity.
The knee has lots of ligamentous attachments which are susceptible to injury. In the immature skeleton the bony attachment site of a ligament usually has less tensile strength than the ligament itself. This can lead to an avulsion fracture of the bone rather than ligament disruption. Note, these injuries are different to apophyseal pathology (e.g Osgood Schlatters) as there is no growth plate at the ligament attachment site.
The ligamentous attachments for the knee are shown in the diagram below with the ACL insertion higlighted in blue.
Figure 1. Ligamentous attachments for the knee.
The intercondylar area is located between the proximal articular surfaces of the medial and lateral tibial condyles. It is non-articular. In the middle of the intercondylar area are:
- Intercondylar eminence – narrow, raised central part of the intercondylar area
- Medial and lateral intercondylar tubercles or spines – arise from the central aspect of the intercondylar eminence
Six facets are present althougher for the attachment of the cruciate ligaments and menisci in the intercondylar area. With regards to the cruciate ligaments and their attachments:
- The anterior cruciate ligament attaches slightly anterior to the medial tibial spine (not directly on it) highlighted in Figure 1.
- The posterior cruciate ligament attaches to the the posterior margin of the intercondylar area (not on the spines).
Clinical History
- 14-year-old boy has hyperextension right knee injury on the rugby pitch with player landing on knee during tackle
- Immediate pain and swelling, extricated of pitch
- Went to local A+E department who performed X-ray which came back as normal
- No locking or instability symptoms in knee but still swollen
- Past Medical Hx – nil
- Exercise Hx – very active sport participation at school, football, rugby and cricket
- Development Hx – Pre growth spurt, but 60th centile for height and weight
Examination
- Presents to clinic 1 week later with knee still swollen and able to walk but only partial weight bear
- Moderate size effusion on sweep
- Lachman’s testing, mildly painful but firm end point
- No real medial or lateral joint line tenderness
Bedside Ultrasound
- Quads and Patella tendon normal
- ++ fluid in suprapatellar pouch, PFJ and medial meniscocapsular recess
- MCL and LCL attachment site normal
- No meniscal extrusion and no obvious tears (given limitations of US)
Differential Diagnosis and clinical reasoning
- ACL injury/rupture – This should always be at the forefront of the clinician’s mind in the adolescent. However, in this case the isolated hyperextension mechanism with no valgus or cutting motion, as well as firm end point of anterior translation testing makes this less likely.
- Tibial Plateau/Tibial spine fracture/Growth plate fracture – This must be considered in the adolescent knee particular as there was a high impact force transmission. However, a quality x-ray with an experienced reader can rule out most significant fractures. However, more subtle fracture lines and bony bruising may require further investigation such as MRI.
- Anterior horn meniscal injury – Extreme hyperextension mechanisms can trap the anterior horns of the menisci (more commonly medial). This cannot be ruled out on x-ray so needs further consideration. This may also present with joint effusion although unlikely to be as severe.
- Fat pad impingement – This commonly occurs during hyperextension injuries of the knee and can be very painful, but does not cause gross swelling. An intra-articular knee effusion would indicate damaged to an intra-articular structure (Hoffa’s fat pad is extra-articular).
Imaging
X-ray (taken same day as injury at A+E). No tibial spine, growth plate or tibial plateau fracture or widening. No ligamentous avulsion injury.
MRI (taken 2 weeks after injury)
T1 weighted image (left) shows subchondral tibial intercondyle fracture at site of ACL insertion (not extending into articular surface).
T2 weighted image (right) shows subchondral tibial intercondyle bone brusing with ACL sprain but no tear.
Diagnosis
Subchondral bone injury from ACL traction (Meyer and McKeevers Classification Type 1)
Management
- Patient placed in hinged knee brace for 2 weeks 5-60 degrees lock
- Progressive return to strength training with lower limb open chain exercise 2-8 weeks
- Repeat MRI at 8 weeks to confirm bony healing
- Return to closed chain exercises 8-10 weeks
- Return to impact training 10-12 weeks
- Return to sport 12 > weeks
Discussion And Key Points
ACL injuries in adolescents lie on a spectrum of bony to ligamentous injury and can also be a mixture of both. It is helpful to categories them as:
- Isolated ACL ligament injury – with no bony injury
- Tibial eminence (spine) avulsion – with or without ACL injury (usually without, as the avulsion of the spine has “spared” the ACL). This makes up the vast majority of “ACL injuries” in the adolescent.
- Tibial eminence subchondral injury without avulsion – with or without ACL injury. This is often a missed minority due to normal appearances of X-ray.
When describing ACL injuries that have an associated tibial eminence fracture, the Meyers and McKeever classification can be useful.
| Type 1 | Nondisplaced (<3mm) |
| Type 2 | Anterior elevation of the fragment |
| Type 3 | Complete separation of the fragment |
| Type 4 | Comminuted avulsion or rotation of fragment |
Type 1 can usually be managed with a hinged brace for 2-4 weeks and then a progressive rehab programme.
Type 2 also can be managed with a hinged brace for 6-8 weeks and then a progressive rehab programme. Ideally the knee brace will bias extension to allow anatomical alignment of the avulsed fragment.
Type 3-4 require surgical consideration to fix the tibial eminence.
Key Learning Points
- ACL injuries in adolescents often occur with bony disruption from ligamentous avulsions due to the immature skeleton
- The most common of these are tibial eminence avulsions and Segond fractures
- Most tibial spine fractures can be managed with a hinged brace. We recommend the Acute Knee Ossur Brace as a useful brace for all acute knee injuries (expect PCL)
- X-ray is a useful first line investigation. MRI is required to look at soft tissue components (e.g. ACL) but also subtle bone injury that is not detected on X-ray
- Grading the injury is important when considering further management
