Pediatric Patella Sleeve Fractures

A patella sleeve fracture is an avulsion of the inferior or superior pole of the patella in which the bony fragment pulls off a "sleeve" of articular and periarticular cartilage. The cartilage injury is much larger than the visible bone fragment.

Who. Children aged 8-12 years, before skeletal maturity, and males more often than females. The sports are basketball, soccer and gymnastics.

Why this age. In a child the cartilage at the patellar poles is weaker than the bone or the tendon. In an adult the bone or the tendon fails instead, as a transverse fracture or a tendon rupture.

The patella. The largest sesamoid bone, embedded in the extensor mechanism between the quadriceps tendon, which attaches to the superior pole, and the patellar tendon, which attaches to the inferior pole. Its articular surface carries thick hyaline cartilage.

Mechanism. An eccentric quadriceps contraction, on landing from a jump or in forceful extension. In the child the cartilaginous pole is the weak link, so the bony pole avulses and takes a sleeve of articular cartilage with it. The result is disruption of the extensor mechanism and loss of active knee extension.

Why the radiograph underestimates it. Only the small ossified fragment is visible. The large cartilage sleeve attached to it is radiolucent.

Sleeve fractures are described by the pole involved and by displacement.

• Inferior pole, at the patellar tendon attachment. The more common site.
• Superior pole, at the quadriceps tendon attachment. Less common.

Displacement. A non-displaced sleeve (less than 2mm) has an intact extensor mechanism and is treated conservatively. A displaced sleeve (greater than 2mm) has disrupted it and needs surgical repair.

History. The mechanism is jumping or landing; a direct blow is rare. The child has anterior knee pain with immediate swelling. Ask whether they can straighten the knee and whether they can walk.

Examination. The knee is swollen with a haemarthrosis and tender over the inferior (or superior) pole, and a defect may be palpable at the inferior pole. Then test the extensor mechanism:

• Active extension, the key test. Can the child actively extend the knee against gravity? If not, the mechanism is disrupted and surgery is needed.
• Straight-leg raise. Can they lift the leg off the bed with the knee extended? An intact raise is less reassuring than it looks (see the differential diagnosis below).

Radiographs. AP and lateral views, of which the lateral is the key film. Look for:

• A small shell of bone at the inferior pole
• Patella alta, the patella sitting high because the patellar tendon has pulled the fragment distally
• A joint effusion, the haemarthrosis

Read the film knowing that it severely underestimates the injury: a small bone chip means a large cartilage avulsion.

MRI and ultrasound. MRI is used if the diagnosis is unclear, and shows the full extent of the cartilage avulsion. Ultrasound can assess the extensor mechanism if it is available.

Patella alta is the single best plain-film clue, and the differential diagnosis leans on the Insall-Salvati ratio. A viva will ask you to define it, and in a child the standard adult index can mislead.

The Insall-Salvati ratio is patellar tendon length divided by 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 caveat in a child. In a young child the patella is incompletely ossified, so the measured patellar bone length is short and variable and the standard Insall-Salvati ratio becomes unreliable. Two practical moves get round this:

• Compare with the contralateral, uninjured knee. The child is their own best control. An asymmetric high-riding patella on the injured side means the patellar tendon has avulsed the pole and pulled it, with its cartilage sleeve, distally.
• Use an index based on the articular surface rather than the ossific nucleus, such as Caton-Deschamps or the modified Insall-Salvati, which are less distorted by incomplete ossification.

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. The figures below are from the 125-patient comparative cohort of Devana et al (Am J Sports Med 2022).

The straight-leg raise trap. Read the table in the other direction: 38% of the sleeve fractures had an intact straight-leg raise. The reassuring sign clinicians reach for was present in more than a third of the injuries you must not miss, while in the same cohort no sleeve fracture could weight-bear. The two functional signs are not interchangeable.

How to use them. Inability to weight-bear is the more sensitive screen and loss of the straight-leg raise the more specific confirmation; a preserved raise narrows nothing on its own. When the child cannot weight-bear and the lateral film shows asymmetric alta, the diagnosis stands whatever the straight-leg raise does.

Other diagnoses. Also consider:

• Acute patellar dislocation with an osteochondral fragment
• Bipartite patella: smooth corticated margin, usually superolateral, often bilateral and asymptomatic
• Patellar or quadriceps tendon avulsion in older adolescents

The decision. It rests on displacement and extensor function, and surgery is indicated by any of:

• Displacement greater than 2mm
• Loss of active extension
• Patella alta on the lateral radiograph

The 2mm figure is pragmatic rather than trial-derived, and the functional test arguably matters more than any millimetre (see Controversies).

Non-operative care. Reserved for the non-displaced sleeve (less than 2mm) with an intact extensor mechanism, and active extension must be confirmed before choosing it.

1. Cylinder cast or knee immobiliser in extension for 4-6 weeks
2. Weight-bearing as tolerated in the brace
3. Radiograph at 2 weeks to ensure no displacement
4. After cast removal, range of motion and quadriceps strengthening

Operative care. ORIF is required for the displaced sleeve or the child without active extension. The principles are anatomic reduction of the cartilage to the patellar surface, restoration of articular congruity, and repair of the retinacular tears.

Set-up. Supine, with a bump under the knee for slight flexion and a tourniquet on the thigh. A midline longitudinal incision or a medial parapatellar approach, the standard paediatric knee approach, gives excellent access.

1. Find the fragments. Identify the retracted proximal fragment, often flipped superiorly, and the avulsed bone and cartilage sleeve, often flipped 180 degrees. Irrigate the haematoma to see the fracture bed.
2. Prepare the bed. Freshen bleeding bone at the inferior pole of the patella.
3. Reduce. Reduce the fragment anatomically, with the cartilage surface flush with the patellar articular surface.
4. Fix. With transosseous sutures, suture anchors, or both (below).
5. Repair the retinaculum. Identify the medial and lateral retinacular tears and close them with interrupted absorbable sutures. Complete retinacular repair prevents late extension lag.
6. Check and close. Confirm full knee extension before closure, then close in layers, over a drain if needed.

Fixation. For transosseous sutures, drill bone tunnels in the patella and pass non-absorbable sutures (Ethibond) through the tunnels and the fragment. For suture anchors, place the anchors in the patellar pole and pass their sutures through the avulsed cartilage and periosteum. The anchor technique is faster and equally effective.

Physiotherapy follows the repair, on this timetable:

• Cylinder cast or knee immobiliser in full extension for 4-6 weeks
• Weight-bearing as tolerated in the brace from day 1
• Gentle range of motion from 4-6 weeks
• Quadriceps strengthening after 6 weeks
• Return to sport at 4-6 months, when full strength and range of motion are achieved

Good outcomes are expected with early diagnosis and anatomic repair. Delayed diagnosis, articular incongruity and a missed injury lead to poor ones.

Because the radiograph underestimates the injury, the sleeve fracture is classically dismissed as a "sprain" and presents late, weeks to months after the injury.

Presentation. The late case shows some combination of:

• A persistent extensor lag, or inability to fully and actively extend the knee
• Quadriceps wasting, in a child who "got better" but never regained a normal knee
• Persistent patella alta
• A palpable gap at the inferior pole or, conversely, a firm mass there

The bone-forming sleeve. The avulsed periosteal sleeve keeps making bone, so on serial films it ossifies. It produces an elongated inferior pole, a bony bridge along the patellar tendon, an accessory ossicle, or a duplicated or enlarged patella (patella magna). This evolving ossification is the radiographic hallmark of a missed sleeve fracture, and is itself an argument for early treatment.

Why the late case is harder. By now the quadriceps is retracted and contracted and the fragment bed has remodelled. Reconstruction aims to restore patellar height and the extensor mechanism rather than simply re-fix a fragment, and may require:

• Quadriceps mobilisation or lengthening, e.g. a V-Y quadricepsplasty
• Excision of the heterotopic or ossified sleeve bone
• Reconstruction or reattachment of the extensor mechanism

The general technique of chronic extensor-mechanism reconstruction is developed in the extensor-mechanism-ruptures topic. Every one of these problems is prevented by recognising the injury acutely, which is why the functional examination (active extension, straight-leg raise) and the contralateral patellar-height comparison matter so much.

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.

Related pages: Patella Fractures for the adult injury this is repeatedly mistaken for, and for the tension-band principles that do not transfer to a mostly cartilaginous patella; Patellar Height Abnormalities for the full catalogue of height indices and why the ossific nucleus makes Insall-Salvati unreliable here; Extensor Mechanism Ruptures for the umbrella injury of which this is the paediatric form; Patellar Tendon Rupture and Quadriceps Tendon Rupture for the adult failure points - the sleeve exists because in a child the bone-cartilage junction fails before the tendon does; Bipartite Patella for the smooth corticated superolateral fragment that is the commonest false positive on the lateral film; Osgood-Schlatter Disease and Tibial Tubercle Fractures for the same forceful-quadriceps mechanism failing at the other end of the extensor mechanism; Patellar Instability in Children for the dislocation that produces an osteochondral fragment and a haemarthrosis in the same age group; and Physeal Injuries and the Salter-Harris Classification for the general principle that in the immature skeleton the radiograph shows only the ossified part of the injury.

• 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.