Hydroxyapatite-coated collars reduce radiolucent line progression in cemented distal femoral bone tumor implants

Abstract

Background: Aseptic loosening of massive bone tumor implants is a major cause of prosthesis failure. Evidence suggests that an osteointegrated hydroxyapatite (HA)-coated collar would reduce the incidence of aseptic loosening around the cemented intramedullary stem in distal femoral bone tumor prostheses. Because these implants often are used in young patients with a tumor, such treatment might extend the longevity of tumor implants. Questions/purposes We asked whether (1) HA-coated collars were more likely to osteointegrate; (2) HA collars were associated with fewer progressive radiolucent lines around the stem-cement interface; and (3) HA-coated collars were associated with less bone loss at the bone-shoulder implant junction?

Methods: Twenty-two patients were pair-matched to one of two groups--either (1) implants with a HA-coated ingrowth collar (HA Collar Group); or (2) implants without an ingrowth collar (Noncollar Group). Age, sex, and length of followup were similar in both groups. HA-coated collars were developed and used at our institution from 1992 to address the high failure rate attributable to aseptic loosening in patients with massive bone tumor implants. Before this, smooth titanium shafts were used routinely adjacent to bone at the transection site. The minimum followup was 2 years (mean, 7 years; range, 2-12 years). Radiographs obtained throughout the followup period were analyzed and osteointegration at the shaft of the implant quantified. Radiolucent line progression around the cemented stem was semi-quantitatively assessed and cortical bone loss at the bone-shoulder implant junction was measured during the followup period.

Results: Comparison of the most recent radiographs showed nine of 11 patients had osteointegrated HA collars, whereas only one patient in the Noncollar Group had osteointegration (p > 0.001). The radiolucent line score quantified around the cemented stem was lower in the HA Collar Group when compared with the Noncollar Group (p = 0.001). Results showed an increase in cortical bone loss at the bone-shoulder implant junction in the Noncollar Group when compared with the HA Collar Group (p < 0.001).

Conclusions: Osteointegration at the implant collar resulted in fewer radiolucent lines adjacent to the intramedullary cemented stem and decreased cortical bone loss immediately adjacent to the transection site. These results suggest that the HA collar may help reduce the risk of aseptic loosening in patients with this type of implant, but longer followup and a larger prospective comparison series are necessary to prove this more definitively.

Figures

Fig. 1A–B

(A) An AP radiograph of a noncollared implant obtained 3 years after surgery shows a clear radiolucent margin separating the newly formed extracortical bone growth with the implant surface (white arrows). This collar was considered not ingrown. The red arrows indicate the radiolucent lines that are present at the cement-bone interface in the stem fixation. (B) An AP radiograph of the pair-matched HA-coated collared implant obtained 1 year after surgery shows bone integration in the grooves with direct contact with the implant surface (white arrows). This collar was considered ingrown.

Fig. 2

An AP radiograph shows the dividing lines that created six zones along the medial and lateral intramedullary stem length, respectively. A maximal score of 12 would indicate the presence of a radiolucent line in all 12 of the divided zones. Twelve zones also were assessed on mediolateral radiographs.

Fig. 3

A mediolateral radiograph of an implant in the Noncollar Group at 1 year postsurgery shows cortical loss adjacent to the implant shoulder.

Fig. 4A–B

(A) An AP microradiograph from a patient in the Noncollar Group at 4-year followup shows radiolucent lines separating the implant surface and bony pedicle. (B) An AP microradiograph from a pair-matched patient in the HA Collar Group at 1-year followup shows osteointegration of the collar.

Fig. 5

The thicknesses (mm) of the radiolucent lines measured between the extracortical bone pedicle and implant shaft in the HA Collar and Noncollar Groups during the study period are shown.

Fig. 6

The radiolucent line scores measured along the cemented stem in the HA Collar and Noncollar Groups during the study period are shown.

Fig. 7

The amounts of cortical bone loss measured adjacent to the implant shoulder in the HA Collar and Noncollar Groups during the study period are shown.