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Migration and cyclic motion of a new short-stemmed hip prosthesis : a biomechanical in vitro study
Publikationstyp
Journal Article
Publikationsdatum
2006-10
Sprache
English
Enthalten in
Volume
21
Issue
8
Start Page
834
End Page
840
Citation
Clinical Biomechanics 21 (8): 834–840 (2006)
Publisher
Elsevier
Background
Uncemented, short-stemmed hip prostheses have been developed to reduce the risk of stress shielding and to preserve femural bone stock. The long-term success of these implants is yet uncertain. Prerequisite for osseointegration is sufficient primary stability. In this study the cyclic motion and migration patterns of a new short-stemmed hip implant were compared with those for two clinically successful shaft prostheses.
Methods
The prostheses were implanted in paired fresh human femura and loaded dynamically (gait cycle) with increasing load (max 2100 N) up to 15,000 cycles. Relative displacements between prosthesis and bone were recorded using a 3D-video analysis system.
Findings
The short stem displayed a biphasic migration pattern with stabilisation at maximum load. Initial migration was predominantly into varus and was greater than that for the shaft prostheses. Failure occurred in cases of poor bone quality and malpositioning. Cyclic motion of the short prosthesis was less than that for the shaft prostheses. Surface finish showed no effect. System stiffness for the new stem was lower than for the shaft prostheses.
Interpretation
The new stem tended to migrate initially more than the shaft prostheses, but stabilised when cortical contact was achieved or the cancellous bone was compacted sufficiently. Bone quality and correct positioning were important factors for the short stem. The lower cyclic motion of the new stem should be favourable for bony ingrowth. The lower system bending stiffness with the new implant indicated a more physiological loading of the bone and should thereby reduce the effects of stress shielding.
Uncemented, short-stemmed hip prostheses have been developed to reduce the risk of stress shielding and to preserve femural bone stock. The long-term success of these implants is yet uncertain. Prerequisite for osseointegration is sufficient primary stability. In this study the cyclic motion and migration patterns of a new short-stemmed hip implant were compared with those for two clinically successful shaft prostheses.
Methods
The prostheses were implanted in paired fresh human femura and loaded dynamically (gait cycle) with increasing load (max 2100 N) up to 15,000 cycles. Relative displacements between prosthesis and bone were recorded using a 3D-video analysis system.
Findings
The short stem displayed a biphasic migration pattern with stabilisation at maximum load. Initial migration was predominantly into varus and was greater than that for the shaft prostheses. Failure occurred in cases of poor bone quality and malpositioning. Cyclic motion of the short prosthesis was less than that for the shaft prostheses. Surface finish showed no effect. System stiffness for the new stem was lower than for the shaft prostheses.
Interpretation
The new stem tended to migrate initially more than the shaft prostheses, but stabilised when cortical contact was achieved or the cancellous bone was compacted sufficiently. Bone quality and correct positioning were important factors for the short stem. The lower cyclic motion of the new stem should be favourable for bony ingrowth. The lower system bending stiffness with the new implant indicated a more physiological loading of the bone and should thereby reduce the effects of stress shielding.
Schlagworte
Primary stability
Short-stemmed implant
Total hip replacement
DDC Class
610: Medicine, Health
620: Engineering