The incidence of periprosthetic fractures of the ankle is increasing. However, little is known about the outcome of treatment and their management remains controversial. The aim of this study was to assess the impact of periprosthetic fractures on the functional and radiological outcome of patients with a total ankle arthroplasty (TAA).

A total of 505 TAAs (488 patients) who underwent TAA were retrospectively evaluated for periprosthetic ankle fracture: these were then classified according to a recent classification which is orientated towards treatment. The outcome was evaluated clinically using the American Orthopedic Foot and Ankle Society (AOFAS) score and a visual analogue scale for pain, and radiologically.

A total of 21 patients with a periprosthetic fracture of the ankle were identified. There were 13 women and eight men. The mean age of the patients was 63 years (48 to 74). Thus, the incidence of fracture was 4.17%.

There were 11 intra-operative and ten post-operative fractures, of which eight were stress fractures and two were traumatic. The prosthesis was stable in all patients. Five stress fractures were treated conservatively and the remaining three were treated operatively.

A total of 17 patients (81%) were examined clinically and radiologically at a mean follow-up of 53.5 months (12 to 112). The mean AOFAS score at follow-up was 79.5 (21 to 100). The mean AOFAS score in those with an intra-operative fracture was 87.6 (80 to 100) and for those with a stress fracture, which were mainly because of varus malpositioning, was 67.3 (21 to 93). Periprosthetic fractures of the ankle do not necessarily adversely affect the clinical outcome, provided that a treatment algorithm is implemented with the help of a new classification system.

Cite this article: Bone Joint J 2015;97-B:950–6.

Introduction: We developed a signal inducing bone cement for surgical interventions under MR guidance. This cement is based on conventional polymethylmeth-acrylate (PMMA), which is mixed with 0.9% saline solution and a contrast agent (CA), or with a hydroxyapatite based bone-filler (Ostim^®, aap Biomaterials, Germany). This signal inducing cement should allow bone filling procedures, like vertebro- and kyphoplasty, under MR guidance in an open Highfield MR Scanner. As we added the signal inducing substances (saline solution, CA, bone substitute) to the PMMA, we changed the biomechanical properties of the cement.

The purpose of this study was to evaluate the biomechanical properties of the signal inducing bone cement for vertebroplasty in a spine model.

Materials/Methods: We placed cadaveric vertebral bodies (n=18, of 4 lumbar spines) between the crosshead and baseplate of a universal testing machine (Zwick^®, Germany) and compressed to failure. Then, we injected cements into the broken vertebral bodies through a transpedicular approach on both sides, under image intensifier control. The so treated vertebral bodies were then tested again in the testing machine. We injected three cements: a conventional PMMA cement (BonOs^®, aap Biomaterials, Germany, 12g PMMA, 5 ml MMA), an NaCl-cement compound (3 ml 0.9% saline solution, 12g PMMA, 5 ml MMA) and a bone substitute-cement compound (3 ml Ostim^®, 12g PMMA, 5 ml MMA). As the CA amount is negligible (< 9μl), it was neglected for these tests. Each cement type was injected in 6 vertebral bodies.

We defined the initial strength (N) of the vertebral bodies as the load at failure, and the strength after treatment as the maximum load, which occurred within the first 6 mm of compression.

Results: The initial strength of the vertebral bodies (n=18) was 4179 N (SD 497 N). The strength after treatment was 7433 N (SD 503 N) for the conventional cements (n=6), 5900 N (SD 376) for the NaCl-cements (n=6), and 7000 N (SD 413 N) for the Ostim^®-cements (n=6).

Discussion: Although the PMMA cement is weakened by dilution with the signal inducing substances (saline solution, CA, bone substitute), the MRI-cements restored the initial strength of the vertebral bodies. The results suggest that these MRI-cements meet the biomechanical requirements for vertebroplasty, and can be used for MRI guided vertebroplasty.