Pediatric Patella Sleeve Fractures

Why This Age?

• In children, the cartilage at the patellar poles is weaker than the bone or tendon.
• In adults, the bone or tendon fails (transverse fracture or tendon rupture).

Patella alta is the single best plain-film clue and the differential table leans on the Insall-Salvati ratio throughout — yet a viva will ask you to define it, and the standard adult index can mislead in a child. This section closes that loop.

The Insall-Salvati ratio is the patellar tendon length divided by the patellar (bone) length on a lateral radiograph in roughly 30 degrees of flexion; the normal range is about 0.8 to 1.2, and a value greater than 1.2 indicates patella alta. (The full catalogue of patellar-height indices — Caton-Deschamps, Blackburne-Peel, patellotrochlear — is developed in the patellar-height-abnormalities topic.)

The three inferior-pole pathologies of the immature knee are frequently confused. Clinical function (straight-leg raise, weight-bearing) and patellar height discriminate them far better than fragment size. Figures below are from the 125-patient comparative cohort of Devana et al (Am J Sports Med 2022).

Also consider: acute patellar dislocation with osteochondral fragment, bipartite patella (smooth corticated margin, usually superolateral, often bilateral and asymptomatic), and patellar/quadriceps tendon avulsion in older adolescents.

• Immobilization: Cylinder cast or Knee Immobilizer in extension 4-6 weeks.
• Weight-Bearing: WBAT in brace.
• ROM: Start at 4-6 weeks. Gentle.
• Strengthening: Quad strengthening after 6 weeks.
• Return to Sport: 4-6 months (when full strength and ROM).

• Good Outcomes: Expected with early diagnosis and anatomic repair.
• Poor Outcomes: Delayed diagnosis, Articular incongruity, Missed injury.

"Missed diagnosis → poor outcome" is repeated throughout this topic and the controversies section flags the bone-forming "neglected sleeve," but the entity itself deserves to be developed — because the radiograph underestimates the injury, the sleeve fracture is classically dismissed as a "sprain" and presents late.

Global epidemiology

• Patella fractures are rare in children (roughly 1% of paediatric fractures), but among them the sleeve fracture is the most common pattern (Hunt & Somashekar, Knee 2005).
• Peak age 8–12 years, strongly male-predominant (82% male in the Devana et al cohort), reflecting the window of chondro-osseous transformation at the patellar poles.
• Mechanism is consistent worldwide: forceful eccentric quadriceps contraction during jumping/landing sports (basketball, football/soccer, gymnastics).

Side-by-side guidance

Registry note: Paediatric patella sleeve fractures are not tracked by arthroplasty/implant registries (NJR, AJRR, AOANJRR, SHAR) because no implant is registered — evidence remains single-centre cohorts and reviews rather than registry data.

High- vs limited-resource practice

• Well-resourced settings: ready access to MRI/ultrasound to confirm the cartilage sleeve and intra-articular extension; suture-anchor fixation common.
• Limited-resource settings: diagnosis is clinical (patella alta on lateral film, loss of straight-leg raise, tense effusion); transosseous sutures through drill holes are reliable and low-cost. Awareness of the entity is the single biggest determinant of outcome everywhere.

• Operative threshold. The widely quoted "greater than 2mm displacement" cut-off is pragmatic rather than trial-derived. The functional test (loss of active extension / straight-leg raise) arguably matters more than any millimetre figure, and current-concept reviews list the non-operative versus operative threshold as genuinely unresolved (Turati et al, J Child Orthop 2025).
• Imaging strategy. Ultrasound (Hunt & Somashekar) and MRI (Bates et al) both reveal the radiolucent cartilage sleeve, but neither is universally available acutely. Whether every suspected case needs cross-sectional imaging, or whether clinical extensor-mechanism failure alone justifies surgery, varies by centre and resources.
• Fixation construct. Transosseous non-absorbable sutures, suture anchors and (in larger ossified fragments) tension-band or screw constructs are all reported; no comparative trial establishes superiority. Choice is guided by fragment ossification and surgeon preference.
• The neglected sleeve. Because the periosteal sleeve continues to ossify, a missed injury can enlarge or duplicate the patella, complicating late reconstruction — a strong argument for early recognition but based on case-level evidence only.
• Evidence ceiling. The entire literature is Level III–V (small retrospective cohorts and reviews); there are no randomised data, so most "rules" are consensus and mechanism-based.