Introduction

For preoperative planning of Total Hip Arthroplasty (THA) it is paramount to choose the correct implant size to avoid subsidence with too small a component or fracture with too large a component. This planning can be done either in 2D or 3D. 2D templating from X-rays frontal images remains the gold standard technique in THA preoperative planning despite the lower accuracy with uncemented components. 3D planning techniques require a CT-Scan examination overexposing patients to radiation. Biplanar EOS^® radiographs are an alternative to obtain bone 3D reconstructions with a very low dose of radiation. The objective of this study was to evaluate the accuracy and reproducibility a novel 3D technique for THA preoperative planning based on biplanar low-dose radiographs.

Purpose of the study: It is relatively rare to observe villonodular synovitis in children. The predominant localization is in the large joints. Histology is required for definitive diagnosis but specific sequences of magnetic resonance imaging (MRI) has greatly improved diagnostic performance.

Material ad methods: we report four cases of hemopigmented villonodular synovitis observed in four girls aged 11–16 years (mean age 12 years) at diagnosis. Localizations were the knee joint in two, the metacarpophalangeal joint of the third finger in one and an intracarpal joint with scaphoid defects in the fourth. Plain x-rays centered on the joint involved and MRI spin echo T1 and T2 with fat saturation were obtained for all four children. Echo gradient with long TE sequences were also performed for the last two children because of the anomalies observed in the first two.

Results: The MRI findings enabled the diagnosis of hemopigmented villonocular synovitis in all four patients and was confirmed histologically (two biopsy specimens followed by dissection and two first-intention dissection specimens).

Discussion: The large joint localizations are often reported but the two cases involving the wrist and fingers are less common. The condition is usually revealed by repeated joint effusion which if punctured generally reveals a hematic discharge. Pain is classical and a mass is often palpated. Standard x-rays show intraosseous defects and MRI, using the three sequences together, generally provides the diagnosis. On the spin echo T1 sequence the synovial mass gives an intermediate signal compared with the low intensity signal of the joint fluid since the cholesterol deposits enhance the signal. In spin echo T2 sequence with fat saturation, the lesion produces a heterogeneous signal which is still intermediary because of the hemosiderin and cholesterol deposits which decrease the inflammatory aspect of the synovitis. These signs are highly suggestive and should be followed by an echo gradient long TE sequence. This is not a routine sequence but provides objective evidence of hyposignals within the synovial mass. This type of signal is specific for the presence of iron and thus hemosiderin.

Conclusion: MRI is the exploration of choice for the diagnosis of hemopigmented villonodular synovitis. It enables postoperative monitoring in search of recurrence.