Sinding–Larsen–Johansson Disease

Sinding-Larsen-Johansson (SLJ) disease is a traction apophysitis affecting the inferior pole of the patella at the proximal attachment of the patellar tendon. It is an overuse condition of the growing skeleton, characterised by pain, tenderness, and sometimes ossification or fragmentation at the inferior patellar pole. It shares the same pathophysiological mechanism as Osgood-Schlatter disease (distal patellar tendon at the tibial tubercle) — repetitive tensile stress across an open apophysis during periods of rapid skeletal growth leading to microtears, periosteal reaction, and secondary ossification.

• Age: typically affects children aged 10–14 years; slightly younger than Osgood-Schlatter disease (which affects 10–15 years); male predominance (3:1); bilateral in approximately 10–15% of cases; associated with periods of rapid growth (growth spurts) and high physical activity (running sports, jumping, football, gymnastics); the extensor mechanism is placed under greatest stress during the growth spurt when muscle strength increases faster than bone maturation
• The inferior patellar pole is the site of the proximal patellar tendon attachment; during vigorous quadriceps contraction (jumping, running), the patellar tendon exerts repetitive tensile stress on the inferior pole apophysis; this causes microtrauma at the tendon-bone interface, periosteal irritation, and reactive bone changes
• Not a true avascular necrosis — unlike Perthes disease or Köhler disease, SLJ is a traction apophysitis (not osteochondrosis of epiphyseal bone); the prognosis is invariably excellent and the condition resolves with skeletal maturity

• Pain: activity-related anterior knee pain localised to the inferior pole of the patella; pain is exacerbated by running, jumping, kneeling, and stair climbing; relieved by rest; typically insidious onset over weeks
• Examination: point tenderness precisely at the inferior pole of the patella (the proximal patellar tendon attachment); this is the key distinguishing feature from Osgood-Schlatter disease (tibial tubercle tenderness) and patellofemoral pain syndrome (peripatellar pain without a single tender point); soft tissue swelling may be present at the inferior pole; pain reproduced by resisted knee extension, single-leg squat, or squatting
• Differentiating SLJ from Osgood-Schlatter: SLJ — inferior patellar pole tenderness; Osgood-Schlatter — tibial tubercle tenderness; both are traction apophysitides of the extensor mechanism; both are activity-related in the adolescent; both are self-limiting; may coexist in the same patient
• Differentiating from patellar sleeve fracture: in the skeletally immature patient, a sudden forceful contraction can avulse the cartilaginous sleeve at the inferior patellar pole (patellar sleeve fracture) — this presents acutely with inability to extend the knee and a high-riding patella (patella alta); SLJ is a chronic overuse condition; an acute event with inability to extend should prompt X-ray assessment for a sleeve fracture

• Clinical diagnosis in most cases — investigations are not routinely required for a straightforward presentation in the correct age group
• Plain radiographs (lateral view of the knee): may show irregular ossification, fragmentation, or calcification at the inferior patellar pole; a small ossicle at the inferior pole may persist into adulthood; the X-ray finding of inferior pole calcification supports the diagnosis but the diagnosis is primarily clinical; X-ray is indicated if the diagnosis is uncertain, if the history is acute (to exclude sleeve fracture), or if symptoms fail to resolve
• MRI: rarely required; may be used in atypical presentations or to exclude patellar sleeve fracture; shows oedema and signal change at the inferior pole; thickening of the proximal patellar tendon; differentiates from patellar tendinopathy (which occurs at the same site in adults)
• Ultrasound: can demonstrate thickening of the proximal patellar tendon and irregular inferior pole morphology; useful in specialist sports medicine settings

• Non-operative treatment: the mainstay of management; the condition is self-limiting and resolves with skeletal maturity in almost all cases; relative rest (reduce high-impact activities — no jumping, sprinting, or high-load squatting during flares); NSAIDs for pain relief; ice after activity; stretching of the quadriceps and hamstrings; patellar tendon strap or infrapatellar strap to redirect patellar tendon tension away from the inferior pole; physiotherapy-guided progressive loading of the extensor mechanism
• Return to sport: symptom-guided return; most children can continue low-impact activity (swimming, cycling); high-impact activities (jumping, sprinting) should be restricted during painful periods; full return to sport is expected with skeletal maturity
• Prognosis: excellent — virtually all cases resolve completely with skeletal maturity (growth plate closure); residual inferior pole ossicle may be visible on X-ray in adulthood but is rarely symptomatic; surgical intervention is virtually never required
• Patellar tendon strap: a circumferential strap worn just below the patella; applies pressure to the proximal patellar tendon, changing the angle of pull on the inferior pole; reduces pain during activity; widely used and effective for symptomatic relief; does not accelerate resolution but allows continued activity with less pain

• Patellar sleeve fracture — the important differential: in children, the inferior pole of the patella consists largely of cartilage (the ossification centre of the patella is incomplete); a forceful quadriceps contraction can avulse a large cartilaginous sleeve from the inferior pole, dragging the patellar tendon with it; the osseous fragment visible on X-ray may appear small but the cartilaginous sleeve is much larger; the hallmarks are acute onset, inability to perform straight leg raise (extensor mechanism disruption), patella alta on lateral X-ray (superior migration of the patella relative to the femur), and haemarthrosis; MRI confirms the extent of cartilaginous avulsion; surgical repair (reattachment of the cartilaginous sleeve) is required urgently to restore the extensor mechanism
• Posterior tibial slope and patellar tendon mechanics: increased posterior tibial slope increases anterior tibial translation and tibial external rotation, modifying the patellar tendon angle and increasing inferior pole stress; this relationship is of relevance in the adolescent knee with structural contributors to extensor mechanism overload; tibial slope measurement on the lateral X-ray is useful background knowledge for the consultant, though it is not routinely assessed in SLJ management
• Activity management in elite young athletes: the dilemma between rest and maintained training in a competitive young athlete with SLJ is common; complete rest is rarely necessary; a graded activity reduction programme (modifying sport type and volume rather than complete cessation) is preferred; swimming and cycling are low-impact alternatives; the athlete should understand the self-limiting nature of the condition and that it will resolve with skeletal maturity; prolonged complete rest increases deconditioning and may be more harmful than moderated activity

• SLJ disease: traction apophysitis of the inferior patellar pole; age 10–14 years; male predominance; activity-related anterior knee pain; inferior pole point tenderness
• Mechanism: repetitive patellar tendon tension on the inferior pole apophysis during growth spurt; same principle as Osgood-Schlatter at the tibial tubercle
• SLJ vs Osgood-Schlatter: SLJ — inferior patellar pole (proximal patellar tendon); Osgood-Schlatter — tibial tubercle (distal patellar tendon); both are traction apophysitides; both self-limiting
• SLJ vs patellar sleeve fracture: SLJ is chronic/overuse; sleeve fracture is acute + extensor mechanism disruption + patella alta + inability to straight leg raise; sleeve fracture needs urgent surgery
• X-ray: irregular ossification or fragmentation at inferior patellar pole; lateral view; diagnosis is clinical — X-ray supports but not required in typical cases
• Treatment: relative rest + NSAIDs + stretching + patellar tendon strap; self-limiting; resolves with skeletal maturity; surgery virtually never required
• Patellar tendon strap: worn just below patella; redirects tendon pull; symptom relief during activity
• Prognosis: virtually universally excellent; residual inferior pole ossicle in adulthood is common on X-ray but usually asymptomatic
• Patellar sleeve fracture repair: urgent surgical reattachment of cartilaginous sleeve; osseous fragment on X-ray underestimates the extent of cartilaginous avulsion — MRI for full assessment
• Adult equivalent: patellar tendinopathy (jumper`s knee) — same site, same mechanism, but degenerative tendinosis in an adult; NOT self-limiting; requires active management