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01.12.2015 | Research article | Ausgabe 1/2015 Open Access

BMC Musculoskeletal Disorders 1/2015

Can bone apposition predict the retention force of a femoral stem? An experimental weight-bearing hip-implant model in goats

BMC Musculoskeletal Disorders > Ausgabe 1/2015
Knut Harboe, Christian Lycke Ellingsen, Einar Sudmann, Nils Roar Gjerdet, Kjetil Søreide, Kari Indrekvam
Wichtige Hinweise

Competing interests

Each author certifies that he or she has no commercial associations (e.g., consultancies, stock ownership, equity interest, patent/licensing arrangements, etc.) that might pose a conflict of interest in connection with the submitted article.

Authors’ contributions

KH and ES designed the study and performed the animal studies. KH and CLE performed the histological preparations and scoring. KH drafted the manuscript. NRG, KS and KI contributed the interpretation of results. All authors contributed to the manuscript revisions and approved the final version of the manuscript for submission.



The increasing incidence of prosthesis revision surgery in the Western world has led to an increased focus on the capacity for stem removal. We previously reported on a femoral stem implanted in goats with an approximate 15% reduction in retention force by drilling longitudinally orientated grooves on the side of the stem. In this current study, we aimed to histologically evaluate the bony apposition towards this stem and correlate this apposition with the pullout force.


We analyzed the femora of 22 goats after stem removal. All stems remained in place for 6 months, and the goats were allowed regular loading of the hip during this time. For histological evaluation, all femora were immersed in EDTA and decalcified until sufficiently soft for standard technique preparation. We evaluated bone apposition, the presence of foreign particle debris and other factors. The apposition was evaluated with a scoring system based on semi-quantitative bone apposition in four quadrants. Kappa statistics were calculated for the score. We correlated the retention force with the amount of bone apposition.


The stem drilling was the only significant factor influencing the retention force (p = 0.020). The bone apposition Kappa score comparing poor and good apposition scores was fair (κ = 0.4, 95% CI 0.00–0.88). Signs of foreign body reaction were noted in 5 of 22 goats.


Based on the current findings in an experimental goat model, it appears that the effect of drilling tissue/bone out of the longitudinal grooves has a more significant impact on the retention force required to remove the stem than the amount of bone apposition outside the stem grooves. This observation may be further explored in the research of stem designs that are potentially easier to remove.
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