Which is your diagnosis?

EDITORIAL

Which is your diagnosis?

Rafael Burgomeister Lourenço^I; Marcelo Bordalo Rodrigues^II

^IMD, Resident at Instituto de Radiologia

^IIChief for Service of Radiology at Instituto de Ortopedia e Traumatologia

^{Mailing address}

Clinical cases

Case 1 (Figures 1 to 3): Four-year old patient presenting shortening of left lower limb with a history of neonatal septic arthritis surgically approached for drainage. A history of trauma is denied.

Case 2 (Figure 4): Five-year old patient, presenting right lower limb shortening, with knee varus deformity. History of neonatal septic arthritis surgically approached for drainage. A history of trauma is denied.

Imaging findings

Figure 1: Scanometry demonstrating shortening of left lower limb.

Figure 2: Anteroposterior plain X-ray view – an osteocondensation focus with star aspect at the distal femoral interface between metaphysis and epiphysis in the most central portion of the lateral compartment.

Figure 3: Magnetic resonance imaging T1-weighted image – transphyseal bone bridge between epiphysis and metaphysis, demonstrating fat signal intensity similar to that of the adjacent epiphysis.

Figure 4: Multidetector computed tomography (coronal oblique reconstruction image) – ossified transphyseal bone bridge at the most central portion of the lateral femoral condyle and on the medial aspect of the tibial metaphysis, the latest resulting in varus angular deformity of the tibial metaphysis.

Diagnosis: Transphyseal bone bridges.

COMMENTS

Transphyseal bone bridges are late complications resulting from injuries to the growth plate (physis). Epiphyseal fractures are amongst the most frequent causes of this complication and are classified by means of Salter-Harris classification. However, other kinds of injuries to the physis such as infections (especially perinatal pyoarthritis), therapeutic irradiation, metabolic or hematological diseases, tumors, burns, freezing lesions, electric shocks, sensory neuropathies, microvascular ischemia or lesions caused by metal instrumentation, also are etiologies described⁽¹⁾.

One estimates that 1%–2% of epiphyseal fractures evolve with formation of bone⁽²⁾. There is no statistical data regarding the frequency of these complications related to other etiologies such as pyoarthritis, like in the present cases. However, the higher the degree of injury to the growth plate cartilage, the higher the likelihood of alterations development⁽³⁾.

Sites most frequently affected are distal femur, proximal tibia and distal tibia, in decreasing order⁽²⁾.

When centrally located in the physis, bone bridges result in metaphysis cup deformities, consequently causing growth cessation and limb shortening (Figure 1). Peripheral lesions typically result in angular deformity⁽²⁾ (Figure 4).

Bone bridges physiopathology is related to the physis cartilage repair. After the injury, the development of transphyseal vascularity occurs, allowing osteoprogenitor cells penetration and consequent bone bridge formation⁽³⁾. Identification of vessels inside the physis is not frequent, since it is nourished by diffusion through the epiphysis.

Radiographic evaluation may demonstrate bone bridges as indentation, osteocondensation focus with star aspect or even conspicuous osseous bars at the metaepiphyseal interface (Figure 2). Bone bridges also may be indirectly observed through the loss of parallelism between physis and growth cessation lines⁽⁴⁾. However, since the radiographic evaluation does not directly demonstrate cartilage lesions, and osseous alterations only can be identified several months after lesion, radiographic abnormalities unfortunately are late findings, when deformity or growth deficit are already established⁽³⁾.

Computed tomography allows a better evaluation of the interface between metaphysis and epiphysis, clearly demonstrating bone bridges localization and dimensions, to assist in the pre-surgical planning (Figure 4). Even so, it demonstrates only late findings, since it is dependent of fibrovascularized bridges ossification.

Scintigraphic studies frequently present inconclusive results, because of the lively osteogenic reaction associated with areas of osseous regeneration adjacent to areas of the bone bridge.

Evaluation by means of magnetic resonance imaging allows a direct identification of growth plate lesions characterized by low signal intensity in the physis that usually demonstrates homogeneous high signal intensity on T1- and T2-weighted images^(3,4). Precocious lesions with formation of fibrocartilaginous bridges may be demonstrated as transphyseal foci of contrast agent impregnation⁽³⁾. Late lesions are better demonstrated at spin echo, fast spin echo, coronal or sagittal, T1-weighted sequences, characterized by foci with fat signals similar to those of the adjacent bone marrow, serving as a bridge between metaphysis and epiphysis (Figure 3). The evaluation with 3D reformation also may be employed for pre-surgical planning^(1,5). Due these advantages associated with the fact of not requiring ionizing radiation, magnetic resonance imaging is considered the method of choice for evaluating bone bridges, especially in the early phase of development. Disadvantages are: high cost and the frequent necessity of sedation for the procedure^(1).

The surgical treatment is indicated in cases where bridges involve less than 50% of the epiphysis surface every time there is a possibility of growth for more than two years⁽¹⁾. In these cases, the bone bridge resection can be done with interposition of several materials like fat, surgical wax, muscular tissue or metacrylate. Angular deformities may require corrective osteotomies⁽⁵⁾. Multiple or centrally located bone bridges may not be approached due to the likelihood of injury to surrounding healthy tissues. In these cases, the evaluation by means of computed tomography or magnetic resonance imaging play an essential role in the pre-surgical planning^(1,5).

REFERENCES

1. Craig JG, Cramer KE, Cody DD, Hearshen DO, Ceulemans RY, van Holsbeeck MT, Eyler WR. Premature partial closure and other deformities of the growth plate: MR imaging and three-dimensional modeling. Radiology 1999;210:835–843.

2. Ogden JA. The evaluation and treatment of partial physeal arrest. J Bone Joint Surg [Am] 1987;69:1297–1302.

3. Jaramillo D, Shapiro F, Hoffer FA, et al. Posttraumatic growth-plate abnormalities: MR imaging of bony-bridge formation in rabbits. Radiology 1990;175:767–773.

4. Jaramillo D, Hoffer FA. Cartilaginous epiphysis and growth plate: normal and abnormal MR imaging findings. AJR 1992;158:1105-1110.

5. Saihan F. Three-dimensional MR imaging in the assessment of physeal growth arrest. Eur Radiol 2004;14:1600–1608.

Study developed at Instituto de Radiologia (InRad) and Instituto de Ortopedia e Traumatologia (IOT), Hospital das Clínicas da Faculdade de Medicina da Universidade de São Paulo (HC-FMUSP).

Publication Dates

• Publication in this collection
  26 Sept 2006
• Date of issue
  Aug 2006