Magnetic resonance-guided focused ultrasound surgery treatment of non-spinal intra-articular osteoblastoma: feasibility, safety, and outcomes in a single-center retrospective analysis

Figures & data

Figure 1. Intra-articular osteoblastoma of the elbow (distal humerus). Transverse T2-weighted MRI obtained during treatment: the # indicates the transducer that generates the ultrasound; the dashed arrow is the US pathway between the transducer and the lesion (dashed line) that is free from structures that could interfere with the progression of the US beam.

Table 1. Baseline characteristic of patient population.

Sex
Men (%)	2 (33.33%)
Women (%)	4 (66.67%)
Age (year ± SD)	21.2 ± 8.3
BMI (Kg/m^2 ± SD)	21.38 ± 3.98
Mean diameter (mm ± SD)^a	12.7 ± 4.71
Mean area (mm^2 ± SD)	107.17 ± 62.87
Mean volume (mm^3 ± SD)	1043.02 ± 820.49

Data are expressed in numerical value and, in brackets, in %; continuous variables are expressed as mean ± standard deviation (SD).

^a Longitudinal diameter.

Figure 2. Intra-articular osteoblatoma of the femoral neck. (a) Transverse T1-weighted fat-suppressed MRI with intra-articular administration of Gd-contrast: the lesion is indicated by the dashed line. (b) Transverse T2-weighted fat-suppressed MRI. Note the edema around the lesion (@) and the intra-articular reactive fluid (arrow) less evident that in the previous case as showed in Figure 1 and in this figure. (c) Transverse T2-weighted MRI obtained during treatment: the # indicates the transducer that generates the ultrasound; the dashed arrow is the US pathway between the transducer and the lesion (dashed line). (d) Transverse T2-weighted fat-suppressed MRI during the follow up: complete disappearance of the bone edema and of the reactive intra-articular fluid.

Table 2. Timing of the treatment.

Time localizer-to-first sonication (min ± SD)	62.6 ± 46.05
Time first sonication-to-last one (min ± SD)	53 ± 34.09
Total procedure time (min ± SD)	115.4 ± 31.35
Effective ablation time (min ± SD)	5.75 ± 3.02

Continuous variables are expressed as mean ± standard deviation (SD).

Figure 3. Intra-articular osteoblastoma of the elbow (distal humerus), the same lesion of Figure 1. (a) and (b) Transverse T2-weighted fat-suppressed MRI and (c) and (d) axial CT: the lesion is indicated by a dashed line in (a) and by an arrow in (c). In (b) and (d), note the disappearance of the lesion (bone healing), of the bone edema, and of the reactive intra-articular fluid.

Table 3. ANOVA analysis between lesions size and treatment variable.

Dependent	Sum of the square type III	Degree of freedom	Mean square	F-value	p-Value
Diameter
No_sonication^a	1.588	1	1.588	0.115	0.792
Energy_max^b	15,846.014	1	15,846.014	0.01	0.937
Temperature^c	43.209	1	43.209	0.246	0.707
Time (each s.)^d	6.33	1	6.33	45.299	0.094
Area
No_sonication^a	9.487	1	9.487	0.686	0.56
Energy_max^b	656.12	1	656.12	0	0.987
Temperature^c	4.877	1	4.877	0.028	0.895
Time (each s.)^d	20.257	1	20.257	144.957	0.053
Volume
No_sonication^a	1.062	1	1.062	0.077	0.828
Energy_max^b	4787.985	1	4787.985	0.003	0.966
Temperature^c	57.613	1	57.613	0.328	0.669
Time (each s.)^d	18.766	1	18.766	134.287	0.055

^a Number of sonication performed during the treatment.

^b Max energy reached during the treatment.

^c Max temperature reached during the treatment.

^d Time of each sonication: evaluated by the operator as good in ensuring an effective ablation.

Figure 4. Sagittal reformatting of CT of the cases of the previous figures before (a) and (c) and 1 year after treatment (b) and (d). Note the complete disappearance and ossification of both the lesions with the restitutio ad integrum of the bone segments.