Sinding-Larsen-Johansson Syndrome

Sinding-Larsen-Johansson (SLJ) syndrome is a traction apophysitis of the inferior pole of the patella in active adolescents. It causes localised pain, swelling and tenderness at the origin of the patellar tendon, and it is less common than Osgood-Schlatter disease (OSD), which shares its mechanism.

Who. Peak incidence is 11-14 years in boys and 10-13 years in girls, slightly younger than OSD, with a male to female ratio of approximately 2:1. It is bilateral in 20-30%, often asymmetric in severity, and is most common in running, jumping and kicking sports: soccer, basketball, gymnastics and volleyball.

How firm those figures are. The peak ages, the 2:1 male predominance and the 20-30% bilaterality are the conventional textbook figures, inherited from the older descriptive literature, and have not been re-measured in a large cohort. The hardest modern number is imaging prevalence: SLJ features in 0.8% of adolescents on MRI, against 2.3% for OSD (Kemmeren 2024, Evidence Base).

Risk factors. The intrinsic factors belong to the growing child:

• Skeletal immaturity with an open patellar apophysis
• Male sex (puberty timing, sports participation)
• Rapid growth, which increases tension
• Quadriceps tightness, which increases the traction force
• Hamstring tightness, which adds load to the extensor mechanism

The extrinsic factors belong to the training:

• High-impact sport: running, jumping, kicking
• Intense practice schedules during growth
• Poor conditioning, with a sudden increase in activity level
• Hard playing surfaces, which increase impact loading
• Inadequate rest, with no recovery time between training sessions

The extensor mechanism. Quadriceps force passes through the quadriceps tendon, which inserts on the superior pole of the patella, then through the patella, which acts as a sesamoid and pulley, and then through the patellar tendon, which originates from the inferior pole and inserts on the tibial tubercle. The inferior pole is therefore the origin of the patellar tendon, and in the growing adolescent its apophysis takes high tensile stress at the tendon-bone junction.

The apophysis. The patella has a secondary ossification centre at its inferior pole that appears during childhood and fuses during adolescence.

Stage names follow the general scheme of apophyseal maturation (cartilaginous, apophyseal, epiphyseal, fusion); applied to the inferior patellar pole they are a descriptive convention with approximate ages, not a validated patella-specific staging system.

Why the inferior pole. The tendon-bone junction at the tendon's origin concentrates force, and the cartilaginous apophysis there is the weak link, biomechanically weaker than mature bone or the patellar tendon.

Why the growth spurt. Rapid bone growth increases muscle-tendon tension, and rapid femoral growth increases quadriceps tightness, while the apophysis has not yet fused. Repetitive traction from the powerful quadriceps then causes microtrauma, inflammation and sometimes fragmentation of the apophysis at the patellar tendon origin.

Relationship to Osgood-Schlatter. SLJ and OSD affect opposite ends of the patellar tendon: SLJ the origin at the inferior pole of the patella, OSD the insertion at the tibial tubercle. Both are traction apophysitides with the same mechanism, age group and treatment. They often coexist, representing stress at both ends of the extensor mechanism.

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Making the diagnosis. Point tenderness localised to the inferior pole of the patella is the key positive finding, but it is not unique to SLJ: jumper's knee and an inferior-pole avulsion are tender at the same spot. What makes it SLJ is that tenderness together with skeletal immaturity (an open apophysis) and an insidious, activity-related onset with no acute injury.

History. The pain is worsened by running, jumping, kneeling, squatting and stairs. Ask about:

• Sport: type, frequency and intensity
• Recent increase in training volume or intensity
• Pain location, timing and aggravating factors
• Symptoms in the other knee
• Previous injury, to rule out acute trauma
• Tibial tubercle symptoms of coexisting OSD

Red flags. Each points to something other than SLJ:

• Night pain or rest pain: tumour, infection
• Acute traumatic onset: avulsion fracture
• Knee effusion: unusual for SLJ, suggests other pathology
• Systemic symptoms such as fever or weight loss: infection, malignancy
• A very young child, under 8: SLJ is rare, so investigate
• Hip symptoms: SCFE, Perthes

Inspection. Visible swelling over the inferior pole is less common than the Osgood-Schlatter bump. Compare both sides, because bilateral SLJ may be asymmetric, look for an effusion, which suggests another diagnosis, and assess overall limb alignment and muscle bulk.

Palpation. Point tenderness over the inferior pole is the cardinal finding, though it localises the problem rather than making the diagnosis, and there may be palpable calcification. Then palpate the whole patellar tendon for tendinopathy, the tibial tubercle for coexisting OSD, the medial and lateral joint lines for meniscal pathology, and the patella and peripatellar tissues.

Movement. Knee range is usually full, with perhaps slight discomfort in flexion; passive flexion may be painful at end range because it compresses the inferior pole. Quadriceps and hamstring flexibility are often reduced. Examine hip range too, to rule out referred pain.

Special tests. Resisted knee extension reproduces the pain over the inferior pole. Patellar mobility is normal, unlike patellofemoral pain syndrome, the ligaments should be stable, meniscal tests should be negative, and the child can straight-leg raise.

Same pain, fused apophysis. Inferior-pole pain is age-determined at the same anatomical site. In the skeletally immature athlete with an open apophysis it is SLJ, a traction apophysitis; once the apophysis has fused, identical proximal-patellar-tendon pain in a jumping athlete is patellar tendinopathy (jumper's knee), an overload tendinopathy of the deep proximal tendon fibres rather than a bone-apophysis problem.

The distinction matters because management changes with maturity. SLJ is self-limiting and treated with activity modification, stretching and reassurance, whereas jumper's knee is driven by a structured progressive loading programme, eccentric decline-squat or heavy-slow-resistance training, with imaging-guided injection or surgery reserved for refractory cases. So in the 16-18-year-old with the "same" history, confirm skeletal maturity and shift both the diagnosis and the rehabilitation accordingly rather than labelling it persistent SLJ.

A clinical diagnosis. Typical SLJ needs no imaging: point tenderness over the inferior pole in an athletic adolescent during the growth spurt is sufficient. Imaging is reserved for atypical presentations or to exclude other pathology.

When to X-ray. Any of these justifies a film:

• Acute traumatic event, to rule out avulsion fracture
• Atypical age, too young or too old for SLJ
• Night pain or rest pain, to rule out tumour or infection
• Effusion
• Failure to improve with 3-6 months of conservative treatment
• Suspected loose ossicle in a symptomatic adult

What the lateral film shows. It may show soft tissue swelling anterior to the inferior pole, fragmentation or irregular ossification of the inferior pole ossification centre, or a separate ossicle that may persist. After fusion, calcification may remain at the inferior pole.

Adults only. Surgery for SLJ is extremely rare. It is reserved for the adult, after skeletal maturity, with persistent symptoms from a loose ossicle at the inferior pole or persistent pain from calcification, and it is not indicated for active SLJ, or for acute symptoms, in adolescents.

Indications. Patient selection is key:

• Skeletal maturity, with a closed patellar apophysis
• Persistent focal pain over the ossicle
• Failed conservative management of 6 months or more
• Imaging confirming a symptomatic ossicle at the inferior pole

Technique. Ossicle excision is a straightforward procedure, arthroscopic or open. The open steps:

• Longitudinal or transverse incision over the inferior pole
• Identify the ossicle at the patellar tendon origin
• Excise the ossicle and debride the tendon edges
• Repair the tendon if needed
• Some surgeons also smooth a prominent inferior pole

Results. Good or excellent results with pain relief in the large majority of appropriately selected patients. The evidence is small retrospective series of carefully selected patients, not trial data, so quote it as a favourable expectation rather than a precise success rate. The main complication is recurrent pain; extensor weakness is rare.

The incidence figures in this table are conventional estimates from clinical experience and small retrospective series, not measurements from cohort studies - no prospective SLJ cohort has quantified them. Medlar & Lyne (Evidence Base) found residual calcification was common and asymptomatic, which is the basis for the "30-50%" convention.

Avulsion is a different injury. The cartilaginous apophysis is the weak link, and during the epiphyseal stage the inferior pole may avulse with acute trauma in jumping sports or on landing. SLJ is chronic overuse, with a gradual onset and preserved extension; avulsion is acute, with sudden pain, inability to extend the knee and a visible or palpable deformity.

Rehabilitation for Ossicle Excision (Adults)

Prognosis. The prognosis is good: the great majority resolve completely with skeletal maturity and without surgery, and most athletes return to full sport without long-term issues. Symptoms are conventionally said to settle within 1-2 years, as the patellar apophysis fuses.

Do not promise the timescale. The best prospective prognostic data on this family of apophysitis come from Osgood-Schlatter: of 51 adolescents followed for 24 months, 37% still had apophysitis-related knee pain at 2 years, the median symptom duration in that subgroup was 42 months, and more than 1 in 5 had stopped their sport (Evidence Base). Counsel families that recovery is usually complete but can take years.

Into adulthood. A minority have symptoms persisting into adulthood, usually as patellar tendinopathy at the same site. 5-10% have some adult symptoms, usually mild or related to an ossicle. The rare complications are inferior pole avulsion fracture and persistent symptomatic calcification.

A prolonged course is predicted by:

• Severe initial presentation
• Delay in activity modification
• Ongoing intense sports participation without modification
• Bilateral involvement
• Coexisting Osgood-Schlatter disease

Global epidemiology. Sinding-Larsen-Johansson syndrome is a worldwide condition of the skeletally immature, jumping/running athlete and is consistently reported as less common than its sister apophysitis, Osgood-Schlatter disease. As girls' participation in jumping and running sports has grown internationally, female incidence is rising and the historical male predominance is narrowing. In an unselected population-based Dutch adolescent cohort (3800 knees, ages 12-15), MRI features of SLJ were present in 0.8% versus 2.3% for OSD (DOI). Accessory-ossicle prevalence rises markedly in high-load youth sport: elite male soccer players show roughly 3-fold higher apophyseal ossicle rates than controls (DOI). There is no dedicated SLJ registry; surveillance comes from sports-medicine cohorts and imaging-prevalence studies rather than arthroplasty-style national registries.

Guideline landscape. No major society publishes an SLJ-specific guideline; recommendations are extrapolated from paediatric overuse-injury and apophysitis guidance, which is strikingly consistent across systems:

Medicolegal Considerations:

Prevention Strategies:

• Training-load management during growth spurts (volume progression before intensity)
• School and club programmes increasingly aware of growth-spurt overuse risk
• Pre-season flexibility screening may identify at-risk athletes (tight quadriceps/hamstrings)