Implants
In this study, the implants were weight-bearing, cemented-type, single-component articular implants fabricated from either PEEK or CoCrMo alloy and designed for implantation in the femoral head of goats. The implants had a highly polished curved articulate surface with a 6.1 mm diameter and extended to a cylindrical stem with four grooves. The articulating surfaces of both the PEEK implant and CoCrMo implant were polished to less than 0.3 μm. (Fig. 1)
Animals
Twelve adult goats, aged 2.5 ± 0.31 years and weighing 60.4 ± 6.7 kg, were used for surgery. The animals were divided according to the choice of implants used, as follows: PEEK group (n=6) and CoCrMo group (n=6). The un-operated right hip joints of goats served as a control. The study was undertaken after receiving approval from the Animal Ethical Committee of the Renji Hospital, Shanghai Jiaotong University, School of Medicine (Shanghai, China).
Surgical Procedure
All animals assigned to the experimental groups underwent unilateral implantation of the device in the femoral head. Surgery was performed on the right hind limb under general anesthesia. Under sterile conditions, the limb was disinfected with iodine after shaving the wool and then draped. After the joint was dislocated, the femoral head was exposed, and a tapered defect representative of a grade IV osteochondral lesion was produced using a punch (a diameter of 6mm). The defect was matched with the implant, with a diameter of 6.1mm and a depth of 10mm, which were also homogenous to all the samples. The implant was then fixed into the surgically created osteochondral defect site with bone cement fixation, using custom insertion instruments to ensure device alignment and surface continuity of the implant and articular surface (Fig. 1).
General macroscopic articular evaluation
Two observers (Wangketao and Liuyuxin) inspected and evaluated the hip joint of goats according to the scoring system guidelines as described by O’Driscoll et al15; 16. The scoring system evaluates the joint through range of motion, intra-articular fibrosis, and cartilage appearance. (Table 1).
Histology of cartilage in the femoral head and observation of bone-implant interface
Cartilage tissue samples were obtained from predefined locations(the cartilage of the peri-implant in the femoral head and opposite to the implant in the acetabulum) and fixed in 10% buffered formalin for 48 h, embedded in paraffin, and then cut into 7-μm sections. The sections were stained with hematoxylin and eosin and Safranin-O for cartilage evaluation. Two independent and blinded reviewers examined the sections using light microscopy and evaluated the articular cartilage using the Mankin score17. We analyzed the histology of the peri-implant cartilage in the femoral head and the cartilage opposite to the implant in the acetabulum using the Mankin score for sections stained with HE and Safranin O.
The histology-assigned femoral head containing the implants were embedded in PMMA and sectioned along the anteroposterior axis (100 μm thick) in a longitudinal direction through the middle of the implant using an Exakt diamond blade saw. The center section of the implant was mounted on a plastic microscope slide using cyanoacrylate and polished to a final thickness of 50 μm. The sections were etched using 0.1% formic acid and subsequently stained with Van Gieson for bone-implant interface evaluation.
Micro‐CT examination
The femoral head of goats’ left hip joint of the hind limb and components were examined using a micro‐CT system (SCANCO medical AG, Barsersdorf, Zurich, Switzerland) with 43‐μm axial slices. CT data were examined in the transverse and sagittal planes. Three‐dimensional images were reconstructed using Geomagic Studio 10.0 software program (Research Triangle Park, Chapel Hill, NC, USA). The cancellous bone was analyzed from the peri-implant zone (removal of bone cement and prosthesis), which was selected as the region of interest (ROI). We analyzed cancellous Bone Density(BD), Bone Volume/Tissue Volume (BV/CV), trabecular number (Tb.N), and trabecular thickness (Tb.Th) around the implant to assess peri-implant bone quality for evaluation of the stress shielding effect.
Statistical analysis
Statistical analysis was performed with one-way analysis of variance using PASW for Windows software (ver. 18.0; SPSS Inc., Chicago, IL, USA). All data were expressed as means ± standard deviation (SD), and overall significance was set at p < 0.05.