Two Different Methods to Measure the Stability of Acetabular Implants: A Comparison Using Artificial Acetabular Models

Abstract

The total number of total hip arthroplasties is increasing every year, and approximately 10% of these surgeries are revisions. New implant design and surgical techniques are evolving quickly and demand accurate preclinical evaluation. The initial stability of cementless implants is one of the main concerns of these preclinical evaluations. A broad range of initial stability test methods is currently used, which can be categorized into two main groups: Load-to-failure tests and relative micromotion measurements. Measuring relative micromotion between implant and bone is recognized as the golden standard for implant stability testing as this micromotion is directly linked to the long-term fixation of cementless implants. However, specific custom-made set-ups are required to measure this micromotion, with the result that numerous studies opt to perform more straightforward load-to-failure tests. A custom-made micromotion test set-up for artificial acetabular bone models was developed and used to compare load-to-failure (implant push-out test) with micromotion and to assess the influence of bone material properties and press-fit on the implant stability. The results showed a high degree of correlation between micromotion and load-to-failure stability metrics, which indicates that load-to-failure stability tests can be an appropriate estimator of the primary stability of acetabular implants. Nevertheless, micromotions still apply as the golden standard and are preferred when high accuracy is necessary. Higher bone density resulted in an increase in implant stability. An increase of press-fit from 0.7 mm to 1.2 mm did not significantly increase implant stability.

Kinematic performance of a novel temporomandibular joint replacement prosthesis under bite-force conditions in dogs and cats

“…14,46 Micromotion under load of the temporal and mandibular components was small (≤ 60 µm during bite simulations) and was comparable with the micromotion of acetabular or glenoid components used in human total joint replacement. 47,48 By bending the mandibular plate during surgery, the TMJR procedure also enabled the adjustment of occlusion to correct malocclusion. The ability to alter occlusion is beneficial considering that problems such as mandibular malunion and ankylosis alter occlusion.…”

Acetabular Wall Weakening in Total Hip Arthroplasty: A Pilot Study

“…Huber and Noble used multiple configurations to examine the fixation traits of a six-finned acetabular cup in both primary and revision THA and then compared it to two commonly used cups without fins [ 38 ]. The use of 20-pounds-per-cubic-foot (pcf) density bone surrogates for acetabular cup stability has also been previously successfully done by [ 11 , 31 , 40 ], where all chose this density due to the high success rates in previous studies. Goossens et al designed a study using bone surrogates to investigate the relationship between relative bone-implant micromotions and the more commonly used load-to-failure implant stability metrics.…”

“…Goossens et al designed a study using bone surrogates to investigate the relationship between relative bone-implant micromotions and the more commonly used load-to-failure implant stability metrics. This study was conducted to provide better insight during the preclinical testing of new acetabular cup designs, new surgical procedures, and to provide a useful tool for surgical training [ 40 ]. Hickernell et al also used bone surrogates to compare initial shell stability under different reaming techniques with HS (hemispherical) and NHS (nonhemispherical) acetabular components [ 11 ].…”

Comparison of Test Setups for the Experimental Evaluation of the Primary Fixation Stability of Acetabular Cups

“…With both test methods, the acetabular cup tilt could only be measured via the displacement transducer of the test machine crosshead and not with external transducers (e.g., linear variable differential transducers). Therefore, it was not possible to determine with sufficient accuracy the tilting of the acetabular cups corresponding to the critical micromotions (150 µm); thus, a direct link between micromotions and fixation stability, as shown in the literature [ 15 , 24 ], was not possible. A further limitation was that at the time of the investigation, the exact position of the CoR of the acetabular cup in relation to the external cup geometry and in relation to the CoR of the femoral head was not available due to missing construction data (CAD) of the acetabular cup.…”

“…In order to ensure the best possible bone ingrowth of cementless acetabular cups, the primary stability of press-fit cups has been experimentally investigated and characterized in recent decades. Therefore, various experimental models were developed to determine the fixation stability [ 2 , 17 , 18 , 19 , 20 , 21 ] and micromotion [ 15 , 22 , 23 , 24 ] as well as implant migration as a measure for the primary stability and to determine the deformation behavior of acetabular cups [ 25 , 26 , 27 ]. Determination of the primary fixation stability of press-fit acetabular cups has been performed predominantly using the lever-out method [ 1 , 2 , 28 , 29 , 30 ].…”