Is a Resorbable Citrate-based Bioceramic Device Associated With Osseous Integration? An Early Retrospective MRI...

Bioresorbable fixation devices may be advantageous because they eliminate the question of whether they ought to be removed, have biomimetic qualities, and minimize artifacts seen on MRI. Most bioresorbable devices utilized during orthopaedic surgery consist of thermoplastic polymers derived from lactic and glycolic acids. These devices are linked to implant-related osteolysis, inflammation, and bone tunnel enlargement, and their integration with surrounding bone is inconsistent. Citregen®, a resorbable composite of a citrate-based thermoset polymer and hydroxyapatite, recently has been approved for use in the United States; yet to date, there are no published studies documenting device-related MRI findings.

(1) Was there observable bone tunnel enlargement on MRI at a minimum of 2 years after implantation of a resorbable citrate-based bioceramic device? (2) Were there other observable adverse findings (such as bone marrow edema or device breakage) on MRI at a minimum of 2 years after implantation of a resorbable citrate-based bioceramic device? (3) Did citrate-based bioceramic devices demonstrate integration with surrounding bone on MRI at a minimum of 2 years after implantation? (4) What was the frequency of early clinical complications after soft tissue fixation with citrate-based bioceramic interference devices?

All 15 patients who underwent tendon transfer or ligament reconstruction in the foot and ankle during a 21-month time period were treated with citrate-based bioceramic interference devices. This group of patients had a median (range) age of 55 years (21 to 75), and 10 were male. Most presented with degenerative or work-related conditions; two had athletic injuries. Two patients were lost to follow-up, and MRI scans performed on 13 patients (25 devices) more than 2 years after surgery were reviewed separately in retrospective, blinded fashion by two investigators. For each device, surrounding bone was assessed for bone tunnel enlargement, which was quantified in millimeters by measuring the width of any gap between the inner surface of the bone tunnel and the outer diameter of the device threads. An intraclass correlation coefficient of 1.0 was achieved, indicating absolute agreement between raters with regard to width of gap measured to the nearest millimeter. The proportion of bone marrow edema abutting the total cross-sectional circumference of each device was quantified using a five-point interval scale (0%, 0% to 25%, 26% to 50%, 51% to 75%, and 76% to 100%). Percentage intervals assessed on the five-point scale demonstrated high interrater reliability (prevalence-adjusted, bias-adjusted kappa [PABAK] = 0.92). Qualitative assessment for other adverse findings, such as cysts, sinus tracts, peridevice fluid, and device breakage, was also performed. The proportion of osseous integration along the long axis of each device was also quantified using a five-point interval scale (0%, 0% to 25%, 26% to 50%, 51% to 75%, and 76% to 100%). Percentage intervals assessed on the five-point scale demonstrated high interrater reliability (PABAK = 0.92). Retrospective chart analysis was used to document the number of complications at the most recent follow-up.

There was no measurable bone tunnel enlargement around any of the devices. Two devices showed bone marrow edema limited to 25% or less of device circumference. Osseous integration occurred around all devices, with 21 of 25 implants showing near-complete (76% to 100%) integration along their long axes. Clinically, there were no device-related complications at median follow-up of 36 months in the 13 patients who were accounted for at a minimum of 2 years (range 2 to 4 years).

In our study of a citrate-based thermoset polymer with hydroxyapatite, common problems associated with other resorbable devices were not seen. Although these findings are promising, our series was very small and had multiple limitations. Therefore, this study should not serve as a basis to recommend widespread use of this material without publication of larger and more rigorous studies that independently replicate our findings.

Level IV, therapeutic study.