Tibial Spine Avulsion — Pediatrics

Tibial spine (intercondylar eminence) avulsion fractures are the paediatric equivalent of anterior cruciate ligament (ACL) rupture. Rather than tearing the ligament substance — which is stronger than the bone-ligament interface in children — the ACL avulses the tibial attachment along with a fragment of the intercondylar eminence. These injuries must be recognised early and managed appropriately to restore knee stability and prevent long-term functional deficit.

• Peak incidence: 8–14 years; boys more commonly affected; associated with bicycle accidents, sports injuries, and pedestrian trauma
• The ACL is stronger than the developing bone in children — avulsion fracture occurs instead of midsubstance ligament tear
• Mechanism: hyperextension or valgus force with tibial internal rotation — same mechanism as adult ACL injury
• Haemarthrosis universally present — tense haemarthrosis in a child after a twisting knee injury = tibial spine avulsion until proven otherwise
• Associated injuries: medial collateral ligament sprain (25–50%), meniscal tears (particularly posterior horn medial meniscus entrapment beneath the fragment — 26–65% in surgical series), lateral meniscus tears
• Adults can also sustain tibial spine avulsions — more commonly in middle-aged patients after high-energy trauma; management principles similar

The Meyers and McKeever classification (1959), as modified by Zaricznyj (1977), is universally used and directly guides treatment.

• Type I and reducible Type II: non-operative; Type III and IV and irreducible Type II: surgical fixation
• Type II reduction: aspirate haemarthrosis, extend knee to approximately 20° — anterior fragment descends under gravity and ligamentotaxis; apply cylinder cast in extension
• If closed reduction of Type II fails to restore fragment to anatomic position on fluoroscopy or radiograph — proceed to surgical fixation

• History: twisting injury or hyperextension; immediate swelling; pain limiting weight bearing; pop not always reported in children
• Examination: tense haemarthrosis; limited range of motion due to swelling and pain; Lachman test and anterior drawer positive but difficult to interpret in acute setting with pain; assess MCL, LCL, and posterolateral corner
• Plain radiographs (AP and lateral): lateral view most diagnostic — fragment visible as avulsed bony piece from intercondylar eminence; the fragment may be small and only visible on true lateral — always obtain a true lateral view; notch view (tunnel view) may help define fragment size
• MRI: indicated in all cases — defines fragment size (cartilaginous component often larger than bony fragment on X-ray), identifies entrapped meniscus (posterior horn of medial or lateral meniscus beneath fragment), assesses ACL continuity, and identifies associated ligamentous injuries
• Intermeniscal ligament or anterior horn of medial meniscus may be interposed beneath the fragment — prevents reduction; must be identified on MRI and addressed at surgery
• CT: rarely required; useful for defining comminution in Type IV fractures preoperatively

• Aspiration of haemarthrosis: reduces pain and facilitates reduction in Type II injuries; performed under sterile conditions before application of cast
• Type I: cylinder cast or hinged knee brace in full extension for 4–6 weeks; followed by supervised physiotherapy
• Type II (reducible): knee aspiration; gentle extension to reduce fragment; cylinder cast in extension (10–20°) for 4–6 weeks; confirm reduction on radiograph or fluoroscopy before casting
• Non-weight bearing for first 2–3 weeks; gradual progression to full weight bearing in cast
• After cast removal: supervised physiotherapy for quadriceps and hamstring rehabilitation; return to sport at 3–4 months when strength symmetric and full ROM restored
• Failure of non-operative management: residual laxity (positive Lachman), recurrent instability episodes, or radiographic non-union — reassess for surgical intervention

Arthroscopic fixation is now the gold standard for displaced tibial spine avulsion fractures (Type III and IV) and irreducible Type II injuries. Open fixation is reserved for cases where arthroscopic access is inadequate.

Arthroscopic Technique:

• Standard anterolateral and anteromedial portals; accessory portals as needed
• Assess for and address entrapped meniscus or intermeniscal ligament before reducing fragment — failure to identify and remove interposed tissue is the most common cause of failed reduction
• Irrigate and debride fracture bed of haematoma; curette to bleeding cancellous bone if chronic
• Reduce fragment with probe or blunt instrument; confirm anatomic seating

Fixation Options:

• Suture fixation is preferred in young children with open physes and comminuted fragments — avoids physeal damage from screws
• After fixation: hinged knee brace locked in extension for 4–6 weeks; progressive range of motion introduced at 2–3 weeks; full weight bearing progressed as tolerated
• Return to sport: 3–6 months depending on sport and rehabilitation progress; confirm strength symmetry and full ROM before clearance

• Residual laxity: most common complication; occurs in 10–30% even after anatomic reduction and fixation — due to plastic deformation of ACL fibres at time of injury; Lachman may remain positive despite healed fracture
• Residual Lachman laxity does not necessarily correlate with functional instability — many children are clinically stable despite radiographic laxity
• Extension deficit (extension block): malunion of fragment in elevated position blocks full knee extension — common with inadequate reduction; symptomatic extension block requires arthroscopic fragment revision or partial notchplasty
• Non-union: rare; more common in older adolescents and adults; treated with bone grafting and repeat fixation
• Arthrofibrosis: complication of prolonged immobilisation — emphasises importance of early protected motion after fixation
• Recurrent instability: if residual laxity is symptomatic after skeletal maturity — standard ACL reconstruction may be required
• Long-term outcomes: good to excellent in most patients with anatomic reduction; worse outcomes with Type III/IV injuries, missed meniscal entrapment, and inadequate reduction

• Meniscal entrapment is underdiagnosed: routine MRI before any surgical intervention is strongly recommended — posterior horn of medial meniscus is the most commonly trapped structure; intermeniscal ligament entrapment is also well-documented; failure to remove interposed tissue leads to malreduction and non-union
• Cartilaginous fragment size underestimated on plain X-ray: MRI or arthroscopy reveals the true fragment is much larger than the bony component visible radiographically — important for implant sizing and reduction technique
• Physeal considerations: large cannulated screws crossing the tibial physis risk iatrogenic growth disturbance — suture fixation is biomechanically adequate and physis-sparing in young children; in adolescents near skeletal maturity, screws are acceptable
• Chronic tibial spine avulsion (missed or late presentation): fibrous union forms within 4–6 weeks; mobilisation and bone grafting required; outcomes less predictable than acute fixation; consider ACL reconstruction if laxity is the primary complaint after skeletal maturity
• Extension block after malunion: prominent healed fragment impinges in the notch during extension; arthroscopic notchplasty or fragment excision with ACL repair/augmentation required; emphasises need for accurate reduction at index surgery

• Tibial spine avulsion = paediatric ACL equivalent — ACL stronger than bone in children
• Meyers-McKeever: Type I = undisplaced; Type II = partial hinge; Type III = complete displacement; Type IV = comminuted
• Type I and reducible II = non-operative; Type III, IV and irreducible II = surgical fixation
• MRI mandatory — identifies meniscal entrapment (26–65%), cartilaginous fragment size, and associated injuries
• Interposed meniscus or intermeniscal ligament prevents reduction — must identify and remove before fixation
• Suture fixation preferred in young children and comminuted fragments — avoids physeal injury
• Residual Lachman laxity common after healed fracture — does not always equal functional instability
• Extension block after malunion = healed fragment impinging in notch — arthroscopic notchplasty or revision
• Tense haemarthrosis in child after twisting injury = tibial spine avulsion until proven otherwise
• True lateral X-ray essential — fragment may be invisible on AP view alone