The effects of femoral stem and neck length on cement strains in a canine total hip replacement model.
OBJECTIVE
To determine the effects of femoral prosthesis stem length and head size on cement strains in a canine hip replacement system.


METHODS
An in vitro experimental model.


METHODS
(1) Three standard and 3 1-cm shortened femoral implants with +3 femoral heads. (2) Two standard implants with +0, +3, and +6 femoral heads.


METHODS
Femoral stems were embedded in polymethylmethacrylate cement. A uniaxial proximodistal-oriented strain gauge was applied to the cement on the medial and lateral aspects of the construct 1.5 cm, 6.0 cm and 7.0 cm distal to the collar. Each construct with a +3 femoral head was mounted in a materials testing system. An axial compressive load (0-200 N) was applied to the femoral head and cement strains were recorded. Additionally, 2 standard length constructs were also tested with +0 and +6 femoral heads. The effects of stem length and neck length on cement strains were assessed with analysis of variance.


RESULTS
Strains increased at all locations with increasing loads for all constructs. Shorter implants had higher strains by 152% and 171%, lateral (P =.003) and medial (P =.0025) to the stem tip. No significant strain differences were noted, at any strain gauge location, between different neck lengths (P values ranged from.20 to.67).


CONCLUSIONS
Although a shorter implant stem has a potential to improve implant fit, it led to significantly higher cement strains that may increase the risk for aseptic loosening. Changes in femoral neck length did not significantly affect cement strains under the conditions tested.


CONCLUSIONS
Shortening of the femoral stem currently cannot be recommended in canine total hip replacement. The existing use of variable neck lengths likely does not increase the risk of failure of the femoral stem.
Dassler
Christopher L
CL
J.D. Wheat Veterinary Orthopedic Research Laboratory and the Department of Surgical and Radiological Sciences, School of Veterinary Medicine, University of California, Davis, CA 95616, USA.
Schulz
Kurt S
KS
Kass
Philip
P
Stover
Susan M
SM
D000818:Animals; D001696:Biomechanical Phenomena; D001843:Bone Cements; D004285:Dogs; D006619:Hip Dysplasia, Canine / Q000601:surgery*; D006622:Hip Prosthesis / Q000662:veterinary*; D008953:Models, Anatomic; D019904:Polymethyl Methacrylate; D011474:Prosthesis Design / Q000662:veterinary; D013314:Stress, Mechanical
D001843:Bone Cements; D019904:Polymethyl Methacrylate