Use of a Biodegradable Magnesium
Implant for Osseous Fixation in Four Cases
W.T. McCartney a,bMVB, Dipl ECVS, DSAS (Orth), PhD, RCVS (S)E. Galvina,*B Eng, PhD
C. Cumminsb
C. Lallya
B.J. Mac Donalda B.Eng. M.Sc. Ph.D. C.Eng. MIEI
School of Mechanical & Manufacturing Engineering, Dublin City University,Dublin 9, Ireland.
b
NOAH, Baldoyle, Dublin 13, Ireland.
cVasorum Ltd., 2012 Orchard Avenue, Citywest Campus, Dublin 24, Ireland
aKEY WORDS: Fracture fixation,Magnesium, Implants
ABSTRACTDue to excessive hydrogen gas production,
early use of magnesium alloys as boneimplants was abandoned despite goodbiocompatibility. Recently, studies revealed
that magnesium alloys in vivo activatedbone cells,2 with good biocompatibility
and no harm to local tissues. In this study,
there was no problem with Hydrogen gas
production. The implants were very welltolerated, with no clinical signs of anyproblems. This may very well be the firstresearch to monitor the degradation ofmagnesium beyond 6 months. The final
radiographic images are intriguing. The
implant within the bone has corroded, buteven at 18 months, some of the magnesium
alloy appears to still remain. Essentially,
this study has apparently demonstrated
that by specially treating the magnesium
implant surface, the rate of corrosion isslowed significantly, and gas production is
not recorded, thus eliminating the original
reasons why magnesium implants wereabandoned.
Intern J Appl Res Vet Med • Vol. 13, No. 3, 2015.

INTRODUCTION
Early use of Magnesium alloys as bone implants was abandoned because of excessivehydrogen gas production despite good biocompatibility1. More recent studies discovered that Magnesium alloys in vivo activatedbone cells2. Furthermore there was good
biocompatibility, with no harm demonstrated
to local tissues from implanted Magnesium
alloys3. The advantage of Magnesium (40GPA) was that it has a similar modulus ofelasticity to cancellous bone (10-30GPA)
but the disadvantage was that it corroded
too quickly loosing mechanical strength andproducing Hydrogen gas at a rate of 1.08L
per gram of Magnesium.
A study was undertaken to firstly analyse
the mechanical strength of a Magnesium pin
and also its behaviour following corrosion.
The Magnesium alloy used in this study
was chosen because it has already passed
through clinical trials in human medicine4-8.
Then four clinical cases were selected for
fracture fixation using the biodegradable
pins.
METHODS AND MATERIALSThe pins were specially treated after produc-171

Table 1 Signalement of cases
Key
DSH- Domestic short hair
G Retriever- Golden retriever
CCLR- Cranial Cruciate Ligament rupture
CaseAgeSexBreedWeightHydrogen gas
production

Injury/problem

11yearF (n)DSH

3.5Kg24 yrs

F(n)

32yr

M(N)

G Retriever

35Kg

0CCLR

Terrier

15 Kg

048 yrF(N)Rottweiler

48 kg

0tion by extrusion using chemically etching to produce a more corrosion resistive
surface. Laboratory tested had confirmedthat the pins lost mechanical strength over
30 days immersion in saline. Comparison
between a 1.2mm diameter pin made ofstainless steel and magnesium alloy revealed
not dissimilar properties except in torsion
were the magnesium alloy was significantlyweaker. Because of this finding a method ofinsertion had to be worked out that allowed
insertion into a bone without damaging thepin itself.
Following different trial insertion methods the method of choice was found to beto predrill a hole the exact same size as theMagnesium pin and then insert the pin at
extremely low revolutions with no pressure
applied. Using this method a Magnesium pin
could be inserted into a bone sample. Oncethe technique of insertion had been optimised the implants were then used in actual
clinical cases.
Four clinical cases where selected:
fractured distal femurs in one dog (nonunioncase) and one cat and 2 cranial cruciate
deficient stifle repairs where the pins wereused to fixate the tibial tuberosity. Each case

172

0Distalfemur
fracture

OutcomeExcellent
Excellent

Fractured excellent
distalfemur
nonunion
CCLR

Excellent

was monitored weekly for any Hydrogen gas
production.
RESULTSThe case details are summarised in Table 1.
From the laboratory tests it was known thatthe mechanical properties of the material
were reduced significantly with increasing
immersion time. All cases healed uneventfully with no detection of hydrogen gas
production. The magnesium pins were stillvisible although to a much less degree 18
months postoperatively on radiographs (Fig1, 2, 3, 4, 5).
DISCUSSION
Corrosion and loss of material properties
were clearly detected in the laboratory tests,
which could be seen as a harsher than the
biological environment. The Magnesium
pins used in this study proved to be excellent bone implants apart from the very slow
torsion resistance which made insertion delicate. In fact insertion of the pins was technically challenging to ensure avoidance of pinfailure, and any other method apart fromvery slow drilling was possible for insertion.
There was no problem with Hydrogengas production and this may reflect the smallVol. 13, No.3, 2015 • Intern J Appl Res Vet Med.

Fig 1. Eight weeks postop TTA (Case 2)

Fig 2. Post op femur fracture (Case 1)

Fig 3. Eighteen months post op (Case 1)

Fig 4. Three weeks postop (Case 3)

Fig 5. Eighteen months post op (Case 3)

Intern J Appl Res Vet Med • Vol. 13, No. 3, 2015.

173

size of the implants or surface treatment ofthe implant. The implants were very welltolerated with no clinical signs of any problems. The pins would have been expected
to be 35% corroded by 6 months based on
previous studies. No studies have been madebeyond 6 months. Magnesium corrodes ina chloride environment usually by pitting
corrosion and the production of Magnesium
Hydroxide and Hydrogen gas. Magnesium
has a very similar density to bone which
may lead to difficult image interpretation.
Also in other studies a concentration ofCalcium and Phosphorus was noted in thedegradation layer around the Magnesium
implant. The local vascularity has a profound effect on the rate of degradation andin highly vascular areas the Magnesium will
degrade quicker.
As this is to the author’s best knowledge
the first research to monitor the degradationof Magnesium beyond 6 months the final
radiographic images are intriguing. The implant within the bone has corroded but evenat 18 months some of the Magnesium alloy
appears to still remain. This may in factreflect reduced vascularity as the healing
process comes to an end. Furthermore someof the outline of the implant may represent a
concentration of calcium but this cannot be
verified without sampling. Essentially thisstudy has apparently demonstrated that by
specially treating the Magnesium implantsurface the rate of corrosion is slowed significantly and gas production is not recorded, thus eliminating the original reasons why

174

magnesium implants were abandoned. The
study has limitations in relation to fracture
selection and case numbers, but the results
are encouraging and warrant further investigation.
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Vol. 13, No.3, 2015 • Intern J Appl Res Vet Med.