An in vitro model of impaction during hip arthroplasty

• Published in: Journal of biomechanics Vol. 82; pp. 220 - 227
• Main Authors: Doyle, Ruben, Boughton, Oliver, Plant, Daniel, Desoutter, George, Cobb, Justin P., Jeffers, Jonathan R.T.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Ltd 03-01-2019; Elsevier Limited
• Subjects: Acetabulum; Acetabulum - cytology; Acetabulum - surgery; Aged, 80 and over; Arthroplasty (hip); Arthroplasty, Replacement, Hip; Biomedical materials; Bone (long); Bone implants; Boundary conditions; Cadavers; Compliance; Computer simulation; Female; Femur; Femur - cytology; Femur - surgery; Fractures; Hip; Hip arthroplasty; Hip Prosthesis; Humans; Impact loads; Impaction; In-vitro testing; Joint surgery; Laboratories; Laboratory tests; Male; Mechanical Phenomena; Soft tissues; Surgery; Surgical implants; Transplants & implants; Velocity; United Kingdom > UK; United States > US; Boundary conditions; In-vitro testing; Compliance; Hip arthroplasty; Impaction
• ISSN: 0021-9290; 1873-2380
• DOI: 10.1016/j.jbiomech.2018.10.030

Impaction is required to properly seat press-fit implants and ensure initial implant stability and long term bone ingrowth, however excessive impaction or press-fit presents a high fracture risk in the acetabulum and femur. Current in-vitro impaction testing methods do not replicate the compliance of the soft tissues surrounding the hip, a factor that may be important in fracture and force prediction. This study presents the measurement of compliance of the soft tissues supporting the hip during impaction in operative conditions, and replicates these in vitro. Hip replacements were carried out on 4 full body cadavers while impact force traces and acetabular/femoral displacement were measured. Compliance was then simulated computationally using a Voigt model. These data were subsequently used to inform the design of a representative in-vitro drop rig. Effective masses of 19.7 kg and 12.7 kg, spring stiffnesses of 8.0 kN/m and 4.1 kN/m and dashpot coefficients of 595 N s/m and 322 N s/m were calculated for the acetabular and femoral soft tissues respectively. A good agreement between cadaveric and in-vitro peak displacement and rise time during impact is found. Such an in-vitro setup is of use during laboratory testing, simulation or even surgical training.