Cemented distal femoral endoprostheses for musculoskeletal tumor: improved survival of modular versus custom implants

Abstract

Background: Advocates of newer implant designs cite high rates of aseptic loosening and failure as reasons to abandon traditional cemented endoprosthetic reconstruction of the distal femur.

Questions/purposes: We asked whether newer, modular distal femoral components had improved survivorship compared with older, custom-casted designs.

Patients and methods: We retrospectively reviewed 254 patients who underwent distal femoral endoprosthetic reconstruction. We excluded two patients with cementless implants, 27 with expandable prostheses, and 39 who had a nontumor diagnosis. This left 186 patients: 101 with older custom implants and 85 with contemporary modular implants. The minimum followup was 1 month (mean, 96.0 months; range, 1-336 months). The tumor was classified as Stage IIA/IIB in 122 patients, Stage IA/IB or benign in 43, and Stage III or metastatic in 21.

Results: Kaplan-Meier analysis revealed overall 10-, 20-, and 25-year implant survival rates of 77%, 58%, and 50%, respectively, using revision of the stemmed components as an end point. The 85 modular components had a greater 15-year survivorship than the 101 custom-designed implants: 93.7% versus 51.7%, respectively. Thirty-five stemmed components (18.8%) were revised for aseptic loosening in 22 patients, implant fatigue fracture in 10, infection in two, and local recurrence in one.

Conclusions: Cemented modular rotating-hinge distal femoral endoprostheses demonstrated improved survivorship compared with custom-casted implants during this three-decade experience. Patients with low-grade disease and long-term survivors of high-grade localized disease should expect at least one or more revision procedures in their lifetime.

Level of evidence: Level IV, therapeutic study. See the Guidelines for Authors for a complete description of levels of evidence.

Fig. 1A–C

(A) A custom endoprosthesis featuring a body casted by the lost-wax method and used from 1980 to 1985 is shown. The stem, based on the Zickel nail design, was welded to the body. (B) An extramedullary porous coating was added to the prosthesis used from 1985 to 1990, which acts as a scaffolding for soft tissue ingrowth. This presumably protects the stem from debris wear and may reduce aseptic loosening. (C) A contemporary modular endoprosthesis used since 1990 features titanium segments and Co-Cr-Mo alloy Morse tapers that prevent cold welding.

Fig. 2

The Lacey, Kinematic, and Noiles rotating-hinge mechanisms used in this series are shown.

Fig. 3A–B

Kaplan-Meier survivorship analyses show (A) custom (n = 101) versus (B) modular (n = 85) implant survival. The dashed lines represent the 95% CI.

Fig. 4

The Kaplan-Meier survivorship analysis shows overall prosthesis survival (n = 186). The dashed lines represent the 95% CI.

Fig. 5

The Kaplan-Meier survivorship analysis shows survival among patients with low-grade or benign disease (Group 1; n = 43).

Fig. 6

The Kaplan-Meier survivorship analysis shows survival among patients with high-grade localized (Stage IIA/IIB) disease (Group 2; n = 122). The dashed lines represent the 95% CI.

Fig. 7

The Kaplan-Meier survivorship analysis shows patient and prosthesis survival among patients with Stage III primary sarcoma, metastatic disease to the distal femur, myeloma, or lymphoma (Group 3; n = 21). The dashed lines represent the 95% CI.

Fig. 8A–D

The common modes of mechanical failure seen in this series of cemented rotating-hinge distal femoral endoprostheses from 1980 to 2008 are shown. (A) A radiograph shows aseptic loosening of a custom-casted femoral stem 24 years after the index reconstruction. The absence of extramedullary porous coating on the proximal body is evident. In our series, there were 22 total instances of aseptic loosening: 19 custom and three modular. (B) Fatigue fractures of a custom-casted femoral stem (right) and femoral body (left) are illustrated. There was only one fatigue fracture of a modular component, which was a casted (not forged) Morse taper segment. In our series, there were 10 total fatigue fractures: nine custom and one modular. (C) An axial photograph shows a fractured hollow, custom-casted femoral body. (D) In our series, there were 22 failures of the rotating-hinge bushings, as illustrated in this photograph, 15 custom and seven modular.

Fig. 9A–B

(A) An AP radiograph of the femur shows aseptic loosening of the femoral stem 12 months after endoprosthetic reconstruction with a contemporary modular implant. We suspect this occurred owing to last-minute rotational adjustment of the stem as the cement was curing. (B) A lateral radiograph shows the femur 12 years after revision to a larger cemented stem and in this case with cross-stem pin fixation, which is our preferred method of reconstruction for the majority of failures attributable to aseptic loosening.

Fig. 10

A graph shows implant versus patient survival for the entire study cohort. Modular implants performed better than custom implants, with 15-year survival rates of 93.7% versus 51.7%, respectively. Patients with low-grade or benign disease and long-term survivors with high-grade localized disease should expect to undergo at least one revision procedure in their lifetime.