Short- or long-stem prosthesis for intramedullary bypass of proximal humeral fractures with severe metaphyseal bone loss: evaluation of primary stability in a biomechanical model

Background Proximal humeral fractures with substantial metaphyseal comminution are challenging to treat. In the elderly with osteoporotic bone, arthroplasty sometimes remains the only valuable option; however, the minimally required length of stem fixation is not known. The aim of this study was to...

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Bibliographic Details
Published in:Journal of shoulder and elbow surgery 2013-12, Vol.22 (12), p.1682-1688
Main Authors: Spross, Christian, MD, Ebneter, Lukas, MSc, Benninger, Emanuel, MD, Erschbamer, Matthias, MD, PhD, Erhardt, Johannes, MD, Jost, Bernhard, MD
Format: Article
Language:English
Subjects:
Aged
arthroplasty
Arthroplasty, Replacement - methods
Biomechanical Phenomena
comminution
Female
fracture
Fractures, Comminuted - diagnostic imaging
Fractures, Comminuted - physiopathology
Fractures, Comminuted - surgery
Humans
Humerus - diagnostic imaging
Humerus - physiopathology
Humerus - surgery
Intramedullary bypass
Joint Prosthesis
Models, Biological
Orthopedics
Osteoporosis - diagnostic imaging
Osteoporosis - physiopathology
Osteoporosis - surgery
proximal humerus
Radiography
Shoulder Fractures - diagnostic imaging
Shoulder Fractures - physiopathology
Shoulder Fractures - surgery
Shoulder Joint - diagnostic imaging
Shoulder Joint - physiopathology
Shoulder Joint - surgery
Torque
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Summary:Background Proximal humeral fractures with substantial metaphyseal comminution are challenging to treat. In the elderly with osteoporotic bone, arthroplasty sometimes remains the only valuable option; however, the minimally required length of stem fixation is not known. The aim of this study was to investigate the primary stability of cemented short- and long-stem prostheses with different intramedullary fracture bypass lengths. Materials and methods Osteoporotic composite bone models of the humerus (Synbone, Malans, Switzerland) with 3 different fracture levels (group A, 6 cm distal to surgical neck; group B, 7 cm distal to surgical neck; and group C, 8 cm distal to surgical neck) were prepared with a cemented standard short (S)– or long (L)–stem prosthesis and were tested for torque to failure. As a reference, we used models with intact bone (group R-O) and a short-stem prosthesis implanted at the surgical neck (group R-P). The radiographic bypass index (BI) was calculated before testing (fracture level to stem tip [in millimeters]/outer cortical diameter at fracture level [in millimeters]). Results The resulting BIs of each group were as follows: 1.7 in group A-S, 3.4 in group A-L, 1.4 in group B-S, 3.2 in group B-L, 1.0 in group C-S, and 2.9 in group C-L. Compared with group R-O, the torques to failure of groups B-S and C-S were significantly lower, whereas only group C-S was significantly weaker than group R-P ( P < .01). Comparing short- and long-stem bypasses of different fracture heights, we found that only group C-L showed a significantly higher resistance to torque ( P < .01). Conclusions A short-stem bypass with a BI of 1.7 was sufficient for primary stability tested by torque to failure in this biomechanical setting. For smaller BIs, a long-stem prosthesis should be considered.
ISSN:1058-2746
1532-6500
DOI:10.1016/j.jse.2013.02.012