Abstract
Aims and Objectives:
What is the effect of polycarbonate-urethane (PU) interpositional knee spacers on load distribution in 3D printed knee models and can this be a potential treatment for knee osteoarthrosis (KOA)?
KOA accounts for 83% of the total OA burden associated with tremendous physical and mental limitations in patients’ lives, but also with an enormous impact on health care systems worldwide [1]. An interpositional mimicked knee spacer could serve as an additional treatment in patients with medial KOA and postpone more invasive treatment options. To date, existing spacers failing to reveal satisfactory results, primarily due to dislocation and methodological issues [2, 3]. This study aimed to examine whether and to what extent a set of differently shaped PU-spacers can reduce stress in the medial knee compartment.
Materials and Methods:
A knee simulator was utilized to investigate the knee joint loading via pneumatic actuators with and without the insertion of four different spacer types into the medial compartment of six 3D printed knee models (material: PLA). The knee models corresponded to six cadaveric right limbs, which were segmented from CT-scans to create CAD models using a reverse engineering approach (Figure 1).
Figure 1: Depiction of the performed work sections. The loading conditions were performed by applying simulated muscle forces (quadriceps: 700 N, hamstrings: 250) induced by pneumatic actuators. Joint contact stress and stress distribution were determined using Tekscan Pressure Mapping Sensors 4000 (50 Hz, Tekscan Inc., South Boston, USA). Thirty cycles of flexion-extension motion were recorded between 180-90° with each spacer-type in the each printed knee model.
Results:
All spacer types showed reduced mean stress values by 71-75% compared to the no-spacer test condition (Figure 2a, b). This result was associated with a redistribution of the acting force to a larger area (+145-295%) induced by the corresponding spacer-type.
Figure 2: a) Time series representing the mean stress curve progressions for all test conditions b) Exemplary peak stress distribution map for no-spacer and spacer M1f125 condition. The mentioned relationship exhibits the major functional principal of the mimicked knee spacer, namely to reduce knee joint loads, hence providing pain relief in the osteoarthritic knee.
Conclusion:
The results of the current study demonstrate that a knee spacer could theoretically complement the common treatment options for KOA, avoiding loss of bone, preserving the natural bone stock, reducing pain, and extending the time to one of the other treatment methods without compromising the patient’s future knee replacement. However, several major aspects must be considered in future studies including, e.g. spacer geometry, testing in cadaveric knees, higher acting forces and limb kinematics.
References
[1] Vos T et al. (2012). Lancet, 380: 2163-2196.
[2] Bailie AG et al. (2008). J Bone Joint Surg Br, 90: 446-450.
[3] Shemesh M et al. (2014). J Mech Behav Bi