What’s the cause of this woman’s right knee x-ray abnormality?
Vol.20, No.03, April 2012

A 52-year-old woman presents with intermittent right knee pain 1 year following a valgus right knee injury. A previous right knee x-ray from 3 years earlier was normal. Past medical history is otherwise non-contributory.

What’s the cause of the abnormality on this woman’s knee x-ray and the condition associated with it?

a) exostosis of femur, “Multiple hereditary exostoses”

b) healed prior MCL origin tear, “Pellegrini-Stieda disease”

c) regional bone infarct, “SONK; Spontaneous OsteoNecrosis of the Knee”

d) chronic regional osteomyelitis, “Majeed syndrome”

e) enchondroma, “Ollier’s disease”

Solution to Analyze This!

b) healed prior MCL origin tear, “Pellegrini-Stieda disease”

Pellegrini-Stieda disease is a post-traumatic condition of the knee represented by dystrophic soft tissue calcification, and occasionally ossification, at the site of the medical collateral ligament (MCL) origin, secondary to partial or complete MCL strain or tear. It’s thought that the local hematoma and subsequent inflammatory response to the MCL injury incites a foreign-body-type reaction by the body, resulting in heterotopic calcification, similar to myositis ossificans from local muscle trauma. Augusto Pellegrini first described the condition in 1905 followed by Alban Köhler in the same year and subsequently by Alfred Stieda in 1908, unaware of Pellegrini’s and Köhler’s article. The condition over the years embraced a few eponyms including “Köhler-Pellegrini shadow,” “Köhler-Pellegrini-Stieda syndrome,” and “Stieda’s fracture” but it’s best recognized as Pellegrini-Stieda disease.

The dystrophic soft tissue calcification may be visible on radiographs within 2 weeks of the knee injury. Clinically, there may be local swelling, pain, erythema, and some limitation of range of motion. Occasionally, the calcific mass may become palpable along the upper inner knee aspect. The condition may occur at any age and in either sex. It’s usually self-limited and can be treated conservatively with local ice and/or heat, rest and anti-inflammatory medication. The calcification/ossification may never resolve but the symptoms typically will, over time.

An exostosis is a benign bony growth projecting outward from the external bone cortex, typically arising near joints and characteristically growing away from the joint surface (likely related to local muscle traction forces). These lesions can become symptomatic depending on size and location and may require surgical removal. When found in multiple locations on the body (and they can develop on virtually any bone but long bones are most common), the condition is known as Multiple hereditary exostoses syndrome. The lesions have a very small (1%) risk of malignant transformation, typically to chondrosarcoma. SONK, or spontaneous osteonecrosis of the knee, is now thought to represent a form of subchondral insufficiency fracture. The lesion in the knee typically occurs in older patients (> 60 years), pathologically is similar to osteochondritis dessicans (OCD) in younger patients, although the location within the joint is different. Within the knee, OCD develops most commonly along the lateral aspect of the medial femoral condyle in a non-weight-bearing portion of the condyle. Alternatively, SONK typically develops along the subchondral bone in the mid-aspect of the weight-bearing portion of the condyle. Majeed syndrome is a rare genetically-linked disease characterized by intermittent recurring episodes of osteomyelitis, often associated with congenital dyserythropoietic anemia. Osteomyelitis causes bone destruction along with local soft tissue swelling, erythema and marked discomfort. The case presented is not in keeping with that rare disease. An enchondroma is a benign, often asymptomatic cartilaginous tumour of bone residing within the central marrow component of the bone. They may become large enough to thin the cortex and lead to pathologic fractures, depending on location. When seen in multiple bones throughout the body, the problem is known as Ollier’s disease. In those patients there’s an increased risk of chondrosarcoma transformation of up to 20-25% by age 40. Maffucci’s syndrome is characterized by multiple enchondromas and numerous dermal hemangiomas or angiomas. The lesion in our case is along the outer cortex of the bone, which can’t be an enchondroma.


  1. Mulligan SA et al. Am J Roentgenol 2000;175;1099-102.
  2. Kogon PL, Tchoryk J, Fleming O. J Can Chiropr Assoc 1987;31:191-2.
  3. Callen HS. Radiology 1937;29:158-65.
  4. Stieda A. Archiv für klinische Chirurgie 1908;85:815-26.
  5. Köhler A. Die normale und pathologische Anatomie des Hüftgelenkes und Oberschenkels in röntgenographische Darstellung. Hamburg, 1905:140.
  6. Pellegrini A.
Clin Moderne Firenze 1905:11:433-9.

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Clinical challenge image
Figure 1: a PA upright right knee radiograph, revealing a minimal curvilinear focus of soft tissue calcification over the supero-medial aspect of the medial femoral condyle, at the adductor tubercle. The underlying medial femoral condyle is normal. No periosteal reaction, cortical break, or soft tissue mass is evident.
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