Hydroxyapatite

Background

Hydroxyapatite (HA) is a naturally occurring mineral, comprised of calcium and phosphorus and found in vertebrate bone and teeth. It mainly imparts rigidity to these structures. Besides being biocompatible (compatible with living systems), Hydroxyapatite is bioactive, in a sense that it demonstrates a surface chemical activity which leads to a solid bond with the bone.

Key factors [1]:

• Ability to integrate in bone structures and support bone ingrowth
• Formation of a strong connection between implant and tissue
• No formation of fibrous connective tissue
• Shorter healing process than for implants with metallic surfaces
• Protection against the release of metallic substrates

Medical use:

The chemical stability and excellent biocompatibility of HA made it an attractive material choice in orthopaedics and dentistry [2].

Over 20 years ago, scientists began proposing that living bone would react to HA as it does to itself because HA and bone are biocompatible to each other. According to one of the earliest HA pioneers, Rudolph GT Geesink, MD, PhD, we know that HA coatings are transformed by osteoclastic activity and actively take part in the bone remodeling process. This biocompatibility would encourage a seamless interface between HA and living bone tissue. HA itself is a brittle ceramic. However, plasma spraying it onto metallic substrates allows it to retain its positive biological properties while allowing the substrate to provide the mechanical strength necessary for load transfer to host tissue.

PureFix™

What is PureFix™?

PureFix™ HA is Stryker Orthopaedics’ own brand of Hydroxylapatite coating. It is manufactured using a proprietary and technologically advanced in-house process - providing the strictest control over the HA coating parameters (composition, purity, particle size & shape, and thickness). Suitable for application to on-growth surfaces, a nominal 50 µm coating of the HA is also applied to ABG™II Standard and ABGII Modular [3].

How is the PureFix™A coating applied to the stem?

Although a number of techniques may be used for the application of an HA coating, plasma spray techniques have become the most widely employed method among manufacturers. This process employs a plasma torch, electric arc and a high temperature carrier gas to deposit the HA compound onto the implant substrate. The use of this application process allows a pre-determined thickness of HA to be applied using a line-of-sight coverage over the surface. In addition to the in-house application process, you can further differentiate the PureFix™ HA coating as one of the first Hydroxylapatite coating to enter the US Market more than 12 years ago. Since its introduction, it has been the subject of many publications and is recognized for its clinical success; particularly in the Stryker Orthopaedics Omnifit™-HA Hip Multi-center clinical study [3].

BACK to common Materials and Technologies

[1] Wintermantel E., Medizintechnik mit biokompatiblen Werkstofffen und Verfahren; Suk-Woo Ha. 3., überarb. und erw. Aufl.,Berlin; Heidelberg; New York; Barcelona; Hongkong; London; Mailand; Paris; Tokio: Springer, 2002
[2] Epinette J.A., Manley M.T., Fifteen Years Of Clinical Experience with Hydroxyapatide Coatings in Joint Arthroplasty, Springer-Verlag France, 2004
[3] Data on file at Stryker®