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


METHODS
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.


RESULTS
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.


CONCLUSIONS
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.
Department of Orthopedic Surgery, Stavanger University Hospital, P.O. Box 8100, Stavanger, 4068, Norway. knut@harboe.org.|Department of Clinical Medicine, University of Bergen, Bergen, Norway. knut@harboe.org.
Knut
K
Harboe
Department of Pathology, Stavanger University Hospital, Stavanger, Norway. christian.lycke.ellingsen@lyse.net.
Christian Lycke
CL
Ellingsen
Department of Clinical Medicine, University of Bergen, Bergen, Norway. einar@sudmann.no.
Einar
E
Sudmann
Department of Clinical Dentistry, Biomaterials, University of Bergen, Bergen, Norway. gjerdet@iko.uib.no.
Nils Roar
NR
Gjerdet
Department of Clinical Medicine, University of Bergen, Bergen, Norway. soreide@mac.com.|Department of Gastrointestinal Surgery, Stavanger University Hospital, Stavanger, Norway. soreide@mac.com.
Kjetil
K
Søreide
Department of Clinical Medicine, University of Bergen, Bergen, Norway. kari.indrekvam@helse-bergen.no.|Kysthospitalet in Hagevik, Clinic of Orthopedic Surgery, Haukeland University Hospital, Bergen, Norway. kari.indrekvam@helse-bergen.no.
Kari
K
Indrekvam
D000818:Animals; D019644:Arthroplasty, Replacement, Hip / Q000009:adverse effects / Q000295:instrumentation*; D001696:Biomechanical Phenomena; D005269:Femur / Q000503:physiopathology / Q000601:surgery*; D006041:Goats; D006621:Hip Joint / Q000503:physiopathology / Q000601:surgery*; D006622:Hip Prosthesis; D023421:Models, Animal; D011474:Prosthesis Design; D011475:Prosthesis Failure; D013314:Stress, Mechanical; D013997:Time Factors; D016474:Weight-Bearing