Meyers–McKeever (± Zaricznyj) — Tibial Spine (ACL Avulsion)

Overview — Tibial Spine (Eminence) Fractures

Tibial spine (tibial eminence) fractures are avulsion injuries of the anterior cruciate ligament (ACL) tibial attachment from the intercondylar eminence of the tibia. They occur predominantly in children and adolescents (typically aged 8–14 years) and represent the paediatric equivalent of a mid-substance ACL tear — the ACL itself remains intact, but its bony attachment avulses from the tibial epiphysis. The Meyers-McKeever classification (later modified by Zaricznyj) is the universal system for grading these fractures, guiding surgical decision-making based on the degree of displacement and rotational malalignment of the avulsed fragment.

Epidemiology: peak incidence 8–14 years; male predominance; most commonly caused by a hyperflexion injury of the knee — a fall from a bicycle (the most classic mechanism), landing from a jump, or a sporting collision; the ACL is attached to the anterior tibial eminence; when a hyperflexion or hyperextension force is applied, the ACL pulls the avascular cartilaginous tibial eminence attachment off the epiphysis rather than rupturing the ligament substance; in adults, the same mechanism produces a mid-substance ACL tear
Why avulsion rather than ligament rupture in children: the relative strength of the ACL ligament versus the bone-cartilage attachment is reversed in children vs adults; in the skeletally immature, the bone-cartilage interface at the tibial eminence is the `weak link` — it fails before the collagen fibres of the ligament; as the child approaches skeletal maturity, the ossification of the tibial eminence increases bony strength, and the failure mode shifts from avulsion to intraligamentous tear (mid-substance ACL rupture); this transition occurs around puberty (12–16 years); in pre-pubertal children, isolated tibial eminence avulsion is the rule; in late adolescence (16+), ACL mid-substance tears become more common

Meyers-McKeever Classification (Modified by Zaricznyj)

Type	Description	X-Ray/Arthroscopic Appearance	Treatment
Type I — Undisplaced	Minimal displacement of the fragment; the anterior tibial spine is avulsed but remains in an essentially anatomical position; the fracture gap is minimal (<2 mm); the fragment is undisplaced or only minimally elevated anteriorly	On lateral X-ray: the tibial eminence fragment may show a subtle radiolucency at its base (the fracture line); the fragment position appears normal	Non-operative — above-knee cylinder cast or hinged knee brace in extension (30° or full extension — maintains the ACL under minimal tension; closes the fracture gap by relaxing the ACL); 4–6 weeks immobilisation; good outcomes expected; close radiological follow-up to ensure fragment remains undisplaced
Type II — Partial displacement (anterior hinge)	The anterior portion of the tibial eminence fragment is elevated (displaced anteriorly) but the posterior portion of the fragment remains hinged to the intact tibial bone; the fragment has a `beak` or `flap` appearance — the posterior cortex is intact, creating an anterior displacement with posterior hinge; the fragment is tilted but not completely freed	Lateral X-ray: the anterior tibial eminence fragment appears elevated — the anterior lip of the eminence is raised anteriorly while the posterior portion remains in contact with the tibial epiphysis; the `anterior hinge` appearance	Attempt closed reduction under sedation or GA: extension of the knee (the ACL slackens, allowing the fragment to drop back) → if successful, cylinder cast in extension for 4–6 weeks; follow-up X-ray at 1–2 weeks to confirm maintenance; if closed reduction fails (soft tissue interposition — meniscus, fat pad, transverse ligament) → operative reduction; borderline between non-operative and operative
Type III — Complete displacement	The tibial eminence fragment is completely elevated and displaced from the tibial bed; the fragment is free-floating (not hinged); it may be rotated (Type III A = no rotation; Zaricznyj`s Type IIIB addition = fragment is rotated — the inferior cortical surface faces superiorly due to a 90–180° rotation)	Lateral X-ray: the fragment is visibly displaced superiorly (floating anteriorly within the knee joint); the `empty tibial plateau bed` is visible; the ACL is intact but under tension on the displaced fragment	Surgical fixation — arthroscopic reduction and fixation is the preferred modern approach; open reduction and fixation is also effective; fixation options: suture fixation (sutures passed through tunnels in the fragment and tied over the bony bridge); cannulated screws (for fragments with adequate bony fragment size); suture anchors; bioabsorbable implants; the fragment must be anatomically reduced before fixation (restoration of exact tibial eminence position); post-operative rehabilitation with progressive knee ROM
Type IV (Zaricznyj addition) — Comminuted	Comminuted fracture of the tibial eminence — the avulsed fragment is broken into multiple pieces; added by Zaricznyj in 1977 to acknowledge the comminuted variant; the ACL attachment is fragmented rather than a single displaced piece	Multiple fragment pieces visible on X-ray or CT/MRI; the tibial eminence is shattered rather than cleanly avulsed	Surgical fixation — suture fixation is often preferred (screws may not provide purchase in comminuted fragments); mattress sutures passed through the ACL fibres and through drill holes in the tibia; the ACL is effectively re-attached to the tibia through sutures rather than screw fixation of the bony fragment; difficult to achieve anatomical reduction; residual laxity is more common after comminuted repairs

Associated Injuries & Diagnostic Workup

Associated injuries: tibial eminence fractures may be associated with: medial collateral ligament (MCL) sprain or rupture (in valgus-loading injuries); medial or lateral meniscal tears; posterior cruciate ligament injury (less common); chondral injuries; the medial or lateral meniscus may become interposed between the fragment and the tibial bed — meniscal interposition is the most common cause of failed closed reduction (particularly for Type II injuries); MRI is valuable for identifying associated soft tissue injuries and meniscal interposition
Imaging: plain AP and lateral knee X-rays are the initial investigation; the lateral view is most informative for assessing fragment displacement; MRI is recommended for all tibial spine fractures to: (1) confirm the diagnosis and assess fracture anatomy; (2) identify associated soft tissue injuries; (3) detect meniscal interposition; (4) assess ACL substance integrity (a combined intrasubstance ACL tear + tibial eminence avulsion is rare but reported in high-energy injuries)
Examination under anaesthesia (EUA): before fixation, test the ACL and collateral ligaments under anaesthesia; a Lachman test should be performed at the beginning of arthroscopy to document preoperative laxity; in successfully fixed Type III injuries, some residual laxity may persist due to the cartilaginous component of the fragment and ACL elongation during injury

Surgical Technique — Arthroscopic Reduction & Fixation

Arthroscopic approach: the arthroscope is inserted via the anterolateral portal; the fragment is visualised within the intercondylar notch; the fracture bed on the tibial eminence is débrided of haematoma and loose fibrocartilage; the fragment is assessed for size, viability, and rotation (rotated fragments must be de-rotated before reduction); any interposed meniscus or fat pad is mobilised from beneath the fragment; the fragment is then reduced with probes or an ACL tibial guide; fixation is performed under arthroscopic visualisation
Fixation options: (1) Suture fixation — a suture retriever is used to pass sutures through the ACL tibres at the base of the fragment; the sutures are then retrieved through two tibial tunnels drilled through the tibial epiphysis (below the fragment bed); the sutures are tied over a bone bridge on the anterior tibia, pulling the fragment down into its bed; particularly useful for small or comminuted fragments; (2) Cannulated screw fixation — for large, solid fragments; a guidewire is placed into the fragment under arthroscopic and fluoroscopic guidance; a partially threaded cannulated screw provides compression across the fracture; MUST avoid the proximal tibial physis; the screw tip should not penetrate the posterior tibial cortex; (3) Bioabsorbable implants — absorbable suture anchors or bioabsorbable screws/pins; avoid hardware removal in growing skeletons

Outcomes & Complications

Residual laxity: even after anatomical reduction and fixation, 40–70% of patients have some degree of residual ACL laxity (positive Lachman test) at long-term follow-up; the laxity is usually mild and asymptomatic (positive Lachman without pivot shift); clinically significant instability (functional instability, symptomatic pivot shift) is less common (~10–20%); the residual laxity is thought to be due to: (1) elongation of the ACL ligament at the time of injury (the ACL stretches before the bone avulses); (2) the cartilaginous component of the avulsed fragment not fully restoring the exact anatomical ACL attachment position; despite the radiological laxity, functional outcomes are generally good in children
Arthrofibrosis: loss of knee extension is the most common complication, particularly after prolonged immobilisation in flexion; immobilisation in extension (not flexion) reduces this risk; early physiotherapy after fixation; cyclops lesion (anterior fibroproliferative nodule) can form if fragment healing is incomplete and causes a block to full extension
Growth disturbance: tibial spine fractures generally do NOT cause significant growth disturbance because the fracture is of the epiphysis (not crossing the physis); however, fixation devices (particularly screws) that cross the proximal tibial physis can cause growth arrest → always direct fixation away from the physis in children

Exam Pearls

Tibial eminence fracture = paediatric ACL avulsion; the ACL itself is intact but its bony attachment avulses; children fail at the bone-cartilage interface before the ligament; adults fail the ligament substance; transition occurs around puberty
Meyers-McKeever classification: Type I (undisplaced — cast in extension); Type II (partial displacement/anterior hinge — attempt closed reduction, cast in extension; operate if fails); Type III (complete displacement — operative); Zaricznyj added Type IV (comminuted — operative, suture fixation)
Most common mechanism: fall from bicycle (hyperflexion); haemarthrosis; positive Lachman; inability to fully extend the knee (the elevated fragment blocks extension); the fragment can block full extension mechanically
Cast position for Type I and successful Type II: full extension or 30° flexion — relaxes ACL tension, allows fragment to sit back in its bed; immobilise in extension NOT flexion to prevent arthrofibrosis
Meniscal interposition: the most common cause of failed closed reduction in Type II; the anterior horn of the medial meniscus or the fat pad becomes trapped under the fragment; MRI pre-operatively identifies this; must be mobilised arthroscopically before fragment reduction
Arthroscopic fixation: suture fixation (through ACL fibres + tibial tunnels) for small/comminuted fragments; cannulated screw for large fragments; avoid crossing the proximal tibial physis with any fixation; bioabsorbable implants avoid hardware removal
Residual laxity: positive Lachman in 40–70% at long-term follow-up; usually asymptomatic or mild; functional outcomes generally good; ACL elongation at time of injury is likely responsible; pivot shift without symptoms = acceptable outcome in children
Cyclops lesion: fibroproliferative nodule in the intercondylar notch from incomplete fragment healing; causes block to full extension; treat with arthroscopic excision

Meyers–McKeever (± Zaricznyj) — Tibial Spine (ACL Avulsion)

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