Introduction
Grading system | Features | |
---|---|---|
Anderson [1] | ||
A Normal | Normal post-operative appearances including seromas and small hematomas | |
B Infection | Fluid-filled cavity with high-signal T2 wall; inflammatory changes in soft tissues; ± bone marrow edema | |
C1 Mild MoM | Periprosthetic soft-tissue mass with no hyperintense T2-weighted fluid signal or fluid-filled peri-prosthetic cavity; either less than a maximum of 5 cm in diameter | |
C2 Moderate MoM | Periprosthetic soft-tissue mass/fluid-filled cavity greater than 5 cm in diameter or C1 lesion with either of the following: muscle atrophy or edema in any muscle other than short external rotators, or bone marrow edema: hyperintense on STIR | |
C3 Severe MoM | Any of the following: fluid-filled cavity extending through deep fascia, a tendon avulsion, intermediate T1weighted soft-tissue cortical or marrow signal, fracture | |
Hauptfleisch [2] | ||
Type 1 | Thin-walled cystic mass (cyst wall <3 mm) | |
Type 2 | Thick-walled cystic mass (cyst wall >3 mm, but less than the diameter of the cystic component) | |
Type 3 | A predominantly solid mass | |
Matthies [3] | ||
1 | Thin-walled | Fluid-like: hypointense on T1, hyperintense on T2 shape flat, with walls mainly in apposition |
2a | Thick-walled | Fluid-like: hypointense on T1, hyperintense on T2 shape not flat |
Or irregular | >50% of the walls not in apposition | |
2b | Thick-walled | Atypical fluid: hyperintense on T1, variable on T2 any shape |
Or irregular | ||
3 | Solid throughout | Mixed signal, any shape |
Other findings scored by the radiologists | ||
The dimensions of the pseudotumor | ||
Gluteus minimus muscle atrophy | ||
Gluteus medius muscle atrophy | ||
Presence of a fluid-filled bursa | ||
Soft-tissue erosion (extension of the pseudotumor into the surrounding muscles) | ||
Bone marrow edema | ||
Tendon tears |
Patients and methods
Screening protocol
Statistical analyses
Results
Demographics | Total (n = 240) | High risk group (n = 34) | Low risk group (n = 5) | Control group (n = 201) |
---|---|---|---|---|
Age in years, mean (SD) | 63.2 (7.4) | 62.9 (5.6) | 61.5 (3.0) | 63.3 (7.8) |
Follow-up in months, mean (SD) | 29.6 (10.0) | 31.4 (9.7) | 29.8 (8.1) | 29.3 (10.1) |
BMI, kg/m2, mean (SD) | 27.4 (4.3) | 28.5 (4.2) | 25.7 (6.1) | 27.1 (4.2) |
Gender, n (%) | ||||
Male | 79 (33) | 0 (0) | 5 (100) | 74 (36.8) |
Female | 161 (67) | 34 (100) | 0 (0) | 127 (73.2) |
Side, n (%) | ||||
Left | 99 (41) | 12 (35.3) | 4 (80) | 83 (41.3) |
Right | 141 (59) | 22 (64.7) | 1 (20) | 118 (58.7) |
Bilateral THAa | 75 | 16 | 0 | 59 |
Bilateral M2a-38b | 23 (46) | 5 (10) | 0 | 18 (36) |
Unilateral M2a-38 | 119 | 8 | 5 | 106 |
Indication, n (%) | ||||
Osteoarthritis | 218 (90.8) | 32 (94.1) | 4 (80) | 182 (90.5) |
Secondary osteoarthritis | 9 (3.8) | 1 (2.9) | 0 (0) | 8 (4.0) |
Collum fracture | 9 (3.8) | 1 (2.9) | 1 (20) | 7 (3.5) |
Osteonecrosis of the head | 4 (1.7) | 0 (0) | 0 (0) | 4 (2.0) |
Cobalt serum level, mean (SD) | 9.5 (15.0) | 19.8 (34.6) | 1.6 (0.9) | 8.0 (7.1) |
Classification of the pseudotumors
Findings on MRI | Observer 1 | Observer 2 |
---|---|---|
Pseudotumor | ||
Yes | 107 | 96 |
No | 133 | 144 |
Anderson | ||
C1 | 46 | 16 |
C2 | 58 | 65 |
C3 | 3 | 15 |
Hauptfleisch | ||
1 | 62 | 63 |
2 | 32 | 24 |
3 | 13 | 9 |
Matthies | ||
1 | 32 | 1 |
2a | 62 | 85 |
2b | 1 | 1 |
3 | 12 | 9 |
Dimensions of the pseudotumor | ||
Height in mm, mean (SD) | 26.4 (39.5) | 31.1 (45.0) |
Width in mm, mean (SD) | 17.1 (25.8) | 22.2 (31.9) |
Wall thickness in mm, mean (SD) | 0.5 (0.75) | 0.5 (0.69) |
Other findings | ||
Gluteus minimus muscle atrophy | 90 | 39 |
Gluteus medius muscle atrophy | 72 | 16 |
Presence of a fluid-filled bursa | 62 | 58 |
Soft-tissue erosion | 37 | 28 |
Bone marrow edema | 12 | 4 |
Tendon tears | 8 | 2 |
ICC | Kappa | p value |
---|---|---|
Presence of a pseudotumor | 0.56 | <0.001 |
Classification | ||
Anderson | 0.43 | <0.001 |
Hauptfleisch | 0.44 | <0.001 |
Matthies | 0.49 | <0.001 |
Other findings | ||
Gluteus minimus muscle atrophy | 0.26 | <0.001 |
Gluteus medius muscle atrophy | 0.33 | <0.001 |
Presence of a fluid-filled bursa | 0.6 | <0.001 |
Soft-tissue erosion | 0.59 | <0.001 |
Bone marrow edema | 0.29 | <0.001 |
Tendon tears | 0.19 | <0.001 |
Foci of susceptibility | 0.45 | <0.001 |
Matthies classification | No pseudotumor (n = 134) | Type 1 (n = 10) | Type 2a (n = 79) | Type 2b, (n = 3) | Type 3 (n = 14) |
---|---|---|---|---|---|
Mean serum cobalt (SD) | 7.8 (7.3) | 4.0 (5.1) | 13.1 (23.7) | 8.4 (6.1) | 10.2 (15.0) |
Male/female | 84/50 | 6/4 | 18/61 | 1/2 | 4/10 |
Pain | 64 | 7 | 38 | 2 | 7 |
Pseudotumor | Yes (%) | No (%) | Total (%) |
---|---|---|---|
Symptomatic | 54 (45.8) | 64 (54.2) | 118 (100) |
Asymptomatic | 52 (42.6) | 70 (57.4) | 122 (100) |