Magnesium and its alloys as orthopedic biomaterials: a review.

Human tissue is structured mainly of self-assembled polymers (proteins) and ceramics (bone minerals), with metals present as trace elements with molecular scale functions. However, metals and their alloys have played a predominant role as structural biomaterials in reconstructive surgery, especially orthopedics, with more recent uses in non-osseous tissues, such as blood vessels. With the successful routine use of a large variety of metal implants clinically, issues associated with long-term maintenance of implant integrity have also emerged. This review focuses on metallic implant biomaterials, identifying and discussing critical issues in their clinical applications, including the systemic toxicity of released metal ions due to corrosion, fatigue failure of structural components due to repeated loading, and wearing of joint replacements due to movement. This is followed by detailed reviews on specific metallic biomaterials made from stainless steels, alloys of cobalt, titanium and magnesium, as well as shape memory alloys of nickel–titanium, silver, tantalum and zirconium. For each, the properties that affect biocompatibility and mechanical integrity (especially corrosion fatigue) are discussed in detail. Finally, the most critical challenges for metallic implant biomaterials are summarized, with emphasis on the most promising approaches and strategies.

Metallic implant biomaterials

Biodegradable metals are breaking the current paradigm in biomaterial science to develop only corrosion resistant metals. In particular, metals which consist of trace elements existing in the human body are promising candidates for temporary implant materials. These implants would be temporarily needed to provide mechanical support during the healing process of the injured or pathological tissue. Magnesium and its alloys have been investigated recently by many authors as a suitable biodegradable biomaterial. In this investigative review we would like to summarize the latest achievements and comment on the selection and use, test methods and the approaches to develop and produce magnesium alloys that are intended to perform clinically with an appropriate host response.

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Degradable biomaterials based on magnesium corrosion

Bioactive glass in tissue engineering

The development of binary Mg–Ca alloys for use as biodegradable materials within bone

In vivo corrosion of four magnesium alloys and the associated bone response.

Between May 1984 and December 1986, 23 patients with a history of medial meniscectomy and anterior knee instability were entered into a long-term prospective study of the results of medial meniscal transplantation combined with reconstruction of the anterior cruciate ligament. In 17 cases a lyophilized meniscal allograft was used and in 6 cases a deep-frozen meniscal allograft was used. The patients’ clinical outcomes were evaluated 3 and 14 years postoperatively by clinical assessment, Lysholm score, radiographs, magnetic resonance imaging, arthrography, and, in some cases, arthroscopy. Two anterior cruciate ligament reconstruction control groups were used for comparison, one group having previously undergone meniscectomy and one with intact menisci. The follow-up rate was 100% after 14 years. The Lysholm score was 84 ± 12 points at 3 years postoperatively and 75 ± 23 points at 14 years. Patients with deep-frozen meniscal transplants generally had better results than patients with lyophilized meniscal tr...

Long-Term Results of Meniscal Allograft Transplantation

The clinical outcome of patients treated either by high tibial osteotomy or unicompartmental arthroplasty for medial unicompartmental osteoarthritis of the knee was compared in a prospective randomised study. In total, 32 patients received a high tibial osteotomy (HTO) and 28 patients a unicompartmental arthroplasty (UKA). More intra- and postoperative complications were observed after HTO. Patients were assessed at an average of 2.5 (1.6–5), 4.5 (3.6–7), and 7.5 years (6.6–10) after the operation. Using the Knee Society Score, 71% (15) of patients after osteotomy and 65% (13) after replacement had a knee score of excellent or good 7–10 years postoperatively. The Kaplan–Meier survival analysis 7–10 years postoperatively showed a survivorship of 77% for UKA and 60% for HTO. Although the unicompartmental prosthesis used in this series has not shown promising results, we conclude that with the advanced design of unicompartmental prosthesis today, UKA offers better long-term success.

High tibial osteotomy versus unicompartmental joint replacement in unicompartmental knee joint osteoarthritis: 7-10-year follow-up prospective randomised study.

A new technique for ACL reconstruction is presented. The middle third of the patellar tendon is anchored to the inner surface of the lateral femoral condyle under direct visual control. The transplant is fixed tibially beneath a bone block removed from the ventral tibial head. Thirty-three patients were evaluated preopera tively and 27 months (range, 24 to 30 months) post operatively. The mean preoperative function score (Lysholm scoring scale) was 72 ± 14 points; the mean postoperative score was 84 ± 13 points. The Lachman test was positive for all patients preoperatively, but the test results in the postoperative follow-up examination were negative—1+ in 31 knees and 2+ in 2 knees. All 33 knees elicited a definite "hard" end point. The post operative KT-1000 measurement for anterior tibial dis placement showed no significant difference between the operated versus the unoperated knee. Before their knee injury all patients had been engaged in sports. At the follow-up examination, 13 patients had made a fu...

Carl Joachim Wirth

Papers

In vivo corrosion of four magnesium alloys and the associated bone response.

Long-Term Results of Meniscal Allograft Transplantation

High tibial osteotomy versus unicompartmental joint replacement in unicompartmental knee joint osteoarthritis: 7-10-year follow-up prospective randomised study.

Reconstruction of the anterior cruciate ligament. A new positioning and fixation technique.

A dynamic shoulder model: reliability testing and muscle force study.