First Biomimetic Fixation for Resurfacing Arthroplasty: Investigation in Swine of a Prototype Partial Knee Endoprosthesis

Abstract

Resurfacing hip and knee endoprostheses are generally embedded in shallow, prepared areas in the bone and secured with cement. Massive cement penetration into periarticular bone, although it provides sufficient primary fixation, leads to the progressive weakening of peri-implant bone and results in failures. The aim of this paper was to investigate in an animal model the first biomimetic fixation of components of resurfacing arthroplasty endoprostheses by means of the innovative multispiked connecting scaffold (MSC-Scaffold). The partial resurfacing knee arthroplasty (RKA) endoprosthesis working prototype with the MSC-Scaffold was designed for biomimetic fixation investigations using reverse engineering methods and manufactured by selective laser melting. After Ca-P surface modification of bone contacting surfaces of the MSC-Scaffold, the working prototypes were implanted in 10 swines. Radiological, histopathological, and micro-CT examinations were performed on retrieved bone-implant specimens. Clinical examination confirmed very good stability (4 in 5-point Likert scale) of the operated knee joints. Radiological examinations showed good implant fixation (radiolucency less than 2 mm) without any signs of migration. Spaces between the MSC-Scaffold spikes were penetrated by bone tissue. The histological sections showed newly formed trabecular bone tissue between the spikes, and the trabeculae of periscaffold bone were seen in contact with the spikes. The micro-CT results showed the highest percentage of bone tissue ingrowths into the MSC-Scaffold at a distance of 2.5÷3.0 mm from the spikes bases. The first biomimetic fixation for resurfacing arthroplasty was successfully verified in 10 swines investigations using RKA endoprosthesis working prototypes. The performed research shows that the MSC-Scaffold allows for cementless and biomimetic fixation of resurfacing endoprosthesis components in periarticular cancellous bone.

Figure 1

Diagram of articular hyaline cartilage and subchondral bone with interdigitations interlocking with trabeculae of cancellous bone vs. the first biomimetic fixation of components of resurfacing arthroplasty endoprostheses by means of the multispiked connecting scaffold (MSC-Scaffold).

Figure 2

The main steps of 3D bone reconstruction: (a) swine femoral bone prepared for 3D scanning with reference markers attached; (b) 3D reconstruction of femoral bone; (c) fragment representing the lateral femoral condyle of the femur isolated from the 3D model of the femur.

Figure 3

The main stages of CAD-modeling of working prototype of partial RKA endoprosthesis: (a) 3D triangular representation of the articular surface of lateral condyle of the femur as imported to the CAD software; (b) view after adding thickness in the normal direction inwards; (c) a screenshot showing the manner of determining of the initial spike of the MSC-Scaffold; (d) a screenshot showing a preview of the multiplying of spikes using the “curve driven pattern” tool.

Figure 4

CAD model vs. SLM-manufactured prototype: (a) CAD model of the partial RKA endoprosthesis working prototype with the biomimetic MSC-Scaffold; (b) SLM-manufactured partial RKA endoprosthesis working prototype with the biomimetic MSC-Scaffold.

Figure 5

SEM image of the MSC-Scaffold's spikes subjected to electrochemical modification; the arrows show the plate-like shaped hydroxyapatite-like crystals at the lateral surface of the MSC-Scaffold's spikes.

Figure 6

The exemplary partial RKA endoprosthesis working prototype with the MSC-Scaffold implanted into the lateral femoral condyle in swine.

Figure 7

The main stages of micro-CT reconstruction of explanted knee joint: (a) exemplary 2D slice of the micro-CT reconstructed knee joint specimen with the RKA endoprosthesis working prototype with the MSC-Scaffold; (b) 3D view of the bone-implant specimen (RKA endoprosthesis working prototype) with (c) an exemplary fragment of the bone-implant specimen extracted for subsequent qualitative analysis.

Figure 8

The exemplary radiogram of operated swine knee joint at 4 weeks after implantation.

Figure 9

The retrieved specimen vs. its X-ray radiogram: (a) the exemplary specimen of operated swine knee joint with the implanted working prototype of partial knee resurfacing endoprosthesis harvested at 8 weeks after implantation; (b) the exemplary 2D digital X-ray radiogram of the resected at 8 weeks after implantation swine knee joint showing spaces between the spikes of the MSC-Scaffold of the implanted RA endoprosthesis working prototype penetrated with bone tissue and the two trabecular bone screws used for the reattachment of the femoral part of the lateral collateral ligament of the swine knee joint.

Figure 10

The exemplary 8th week after surgery histological sections (H+E staining) showing the interspike pore space of the MSC-Scaffold penetrated by matured trabecular bone tissue: bone trabeculae of periscaffold bone are considered as in equal age; bone-implant sections in (a) the longitudinal and (b) crosswise directions to the axis of the spikes.

Figure 11

Series of six exemplary micro-CT scan slices of the explanted bone-implant specimen established at six reference levels at the distances of (a) 3.5 mm, (b) 3.0 mm, (c) 2.5 mm, (d) 2.0 mm, (e) 1.5 mm, and (f) 1.0 mm from the spike bases of the MSC-Scaffold.

Figure 12

The percentage share of analyzed radiological phases: trabecular bone, spike material, and soft tissue of the explanted bone-implant specimen as a function of the distance from the spike bases.