The use of rapid prototyped implants to simulate knee joint abnormalities for in vitro testing: A validation study with replica implants of the native trochlea

Abstract

To investigate the biomechanical effect of skeletal knee joint abnormalities, the authors propose to implant pathologically shaped rapid prototyped implants in cadaver knee specimens. This new method was validated by replacing the native trochlea by a replica implant on four cadaver knees with the aid of cadaver-specific guiding instruments. The accuracy of the guiding instruments was assessed by measuring the rotational errors of the cutting planes (on average 3.01° in extension and 1.18° in external/internal rotation). During a squat and open chain simulation, the patella showed small differences in its articulation with the native trochlea and the replica trochlea, which could partially be explained by the rotational errors of the implants. This study concludes that this method is valid to investigate the effect of knee joint abnormalities with a replica implant as a control condition to account for the influence of material properties and rotational errors of the implant.

The Effect of Trochlear Dysplasia on Patellofemoral Biomechanics

“…This study applied a novel validated method to replace the original cadaveric trochlea with different types of custom-made rapid prototyped (RPT) implants for experimental testing. 27 This method facilitates the investigation of isolated TD in all its variations.…”

“…To evaluate the effect of the trochlear shape on patellofemoral biomechanics, a validated method to simulate bony deformities in cadaveric specimens was applied. 27 For each cadaveric knee, 5 types of custom trochlear implants were created on a 3-dimensional printer (multimaterial 3D Connex350 printer; Objet Ltd). The trochlear cartilage layer was simulated by using a rubberlike material with a hardness comparable with cartilage (Shore A 80-90, tested according to ASTM standard D-2240); the rest of the implant was printed by a hard rubberlike material closer to bone (Shore A 90-100, tested according to ASTM standard D-2240).…”

“…Monitoring of the position was facilitated by the transparent material and perforations in the guiding instrument. 27 The instrument was then fixed with pins at the anterior and lateral side. After fixation, an oscillating saw blade was guided through the lateral slot in the instrument to remove the femoral trochlea.…”

Rapid prototyping of replica knee implants for in vitro testing

“…In accordance with the surface roughness tests the ABS implants, which underwent post-treatment with acetone vapor, performed best during the kinematic experiments. PJM implants showed the worst results, which has been used in previous studies of van Haver et al [4] and Schröder et al [5]. Schröder et al stated that friction with PJM implants decreases under high loads down to original implant level during an active movement and can therefore be neglected.…”

“…Problematic is the expensive and time consuming manufacturing process of these new implants, when multiple designs have to be evaluated [3]. Since there are different requirements for in vitro tests than for in vivo implantation, especially in terms of durability and biocompatibility, rapid prototyping technologies might have the potential to offer an easy and fast access to various implant designs [4] and [5] investigated the use of rapid prototyping for in vitro knee experiments and concluded that replica prostheses manufactured by PolyJetModelling can reproduce the original implant kinematics, although higher friction levels under low axial loads have been determined. Despite their promising results, these studies only regarded the femoral component and one material and manufacturing technology.…”