To the Editor:

The insertion of the patellar ligament on the tibial tuberosity is a frequent site of enthesitis in all forms of spondylarthritis (SpA) (1), including psoriatic arthritis (2). In adolescents with SpA, the tibial tuberosity enthesitis is often confused with Osgood-Schlatter disease, a traction apophysitis (1, 3, 4). This report emphasizes that enthesitis of SpA can masquerade as Osgood-Schlatter disease by radiographic findings.

A 17-year-old girl was referred to us in October 1998 for evaluation of arthritis involving her right elbow and knee begun one month before. Her family history was unremarkable. Her personal history revealed an episode of swelling of the left knee of three-months duration occurring at the age of three. At that time she was admitted to a pediatric unit where, on the basis of high acute-phase reactants, the diagnosis of juvenile onset oligoarthritis was made. At the age of 14, the patient exhibited pain and swelling over the right tibial tuberosity that persisted for 6 months. A lateral view of the knees showed swelling of the tibial insertion of the patellar tendon and the adjacent subcutaneous tissue, the distension of deep infrapatellar bursa together with findings similar to those of Osgood-Schlatter disease, i.e., enlargement and fragmentation of the tibial tubercle (Figure 1). A diagnosis of Osgood-Schlatter disease was made, in spite of elevated levels of acute-phase reactants, in the same pediatric unit in which she had been admitted 11 years before.

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Figure 1. Lateral view of the right knee emphasizing enlargement and fragmentation of the epiphysis of the tibial tuberosity.

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Physical examination disclosed swelling with effusion of the right knee without any clinical sign of adjacent enthesis involvement and a mild swelling of the right elbow. A large psoriatic plaque was present on her scalp. Laboratory evaluation revealed an erythrocyte sedimentation rate of 30 mm/hour and c-reactive protein level of 30.3 mg/L (normal <5). HLA typing showed A2, A3, B18, B35 Cw4, and Cw7. Arthrocentesis of the right knee yielded 40 ml of a yellow fluid with reduced viscosity, a fair mucin clot, and a white cell count of 2,000/mm3. Pelvis radiographs were normal; however, knee radiographs showed a bone proliferation into the tibial insertion of the right patellar tendon typical of enthesitis (Figure 2). Peripheral arthritis was successfully treated with injections of steroids.

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Figure 2. After 3 years, a bone proliferation into the tibial insertion of the right patellar ligament became evident.

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In February 2002, the girl developed a painful swelling over the base of the left fifth metatarsal bone and over the right lateral epicondyle, typical of enthesitis. Steroid injections were given in both sites with good results.

Osgood-Schlatter disease is a traction apophysitis occurring frequently in athletically active male adolescents, which has no association with SpA and the HLA-B27 (3). Its clinical manifestations (pain together with swelling over the tibial tuberosity) are similar to those of patellar ligament enthesitis of SpA. The disorder is self-limiting in most cases, but sometimes separated osseous fragments may persist and cause pain. Our patient had enthesitis of the tibial tuberosity with radiographic findings indistinguishable from Osgood-Schlatter disease in the erosive phase. The appearance of bone proliferation in the ligamentous insertion, which represents the normal evolution of SpA enthesitis, prompted us to make the correct diagnosis of patellar ligament enthesitis.

  • 1
    Olivieri I, Padula A, Barozzi L. The enthesiopathy: clinical manifestations, imaging and treatment. Bailliere's Clin Rheumatol 1998; 4: 66581.
  • 2
    Salvarani C, Cantini F, Olivieri I, Macchioni P, Niccoli L, Padula A, et al. Isolated peripheral enthesitis and/or dactylitis: a subset of psoriatic arthritis. J Rheumatol 1997; 24: 110610.
  • 3
    Sherry DD, Petty RE, Tredwell S, Shroder ML. Histocompatibility antigens in Osgood-Schlatter disease. J Pediatr Orthop 1985; 5: 3025.
  • 4
    Cassidy JT, Petty RE. Spondyloarthropathies. In: CassidyJT, PettyRE, editors. Textbook of pediatric rheumatology. New York: Churchill Livingstone; 1990. p. 2219.

Ignazio Olivieri MD*, Angela Padula MD*, Vincenzo Giasi MD*, Enrico Scarano MD†, * San Carlo Hospital, Potenza and Madonna delle Grazie Hospital, Matera, Italy, † San Carlo Hospital, Potenza, Italy.