Literature review
15.3.2012
Do Bioabsorbable Fixation Devices Leave Holes
in Bone After their Degradation?
Author:
Harri Heino
Director, R&D, Bioretec Ltd.
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TABLE OF CONTENTS
1
2
3
4
Literature review .............................................................................................................3
Experience with Bioretec products ...............................................................................4
Conclusions ....................................................................................................................6
References .......................................................................................................................7
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Literature review
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1
Literature review
Juutilainen et al. has compared the bone mineral density changes during bone healing after
bimalleolar ankle fracture treated either with metallic or bioabsorbable implants in a
retrospective study. The patient selection criterion was bimalleolar ankle fracture only on one
side, leaving other side to serve as a control. Patients were asked to participate the study and
allow the bone mineral density (BMD) measurements. There were three groups of implants in
this study, namely metallic, PLLA and PGA devices. Totally 39 patients were included in the
study (17 in metallic, 14 in PGA and 8 in PLLA device group). PGA patient group was further
divided in two follow up time groups (mean 1, 3 and 3 years). Screw hole visibility at different
follow up times was reported. BMD measurements were also carried out for the screw holes
specifically, when screw holes were visible.
Generally fracture healing was asymptomatic in all groups. In 3 out of 9 patients the screw
holes were visible at 1,3 years follow up in PGA group, whereas 1 out 5 five patients of the
same group had visible screw holes at 3 years follow up. In the PLLA group 6 out of 8
patients had visible screw holes at mean 3.9 years follow up. There was, however, relatively
large variation of follow up times and the two patients, who had no visible screw channels left
had actually also the longest follow up times, namely 4.3 and 5.1 years. The bone mineral
densities in the screw channels were generally lower than in surrounding bone. A denser
sclerotic ring was noted around the screw holes. Authors noted this to be reported by several
other authors as well in different fracture fixation indications. Based on the BMD
measurements it seems, that BMD of the healing fracture area was better preserved or even
increased with bioabsorbable fixation comparing to metallic fixation.[1]
Landes et al. report also sclerotic rings and hypodense core of the screw holes in their 5 year
follow up study on maxillary and mandibular osteosynthesis using bioabsorbable screws and
plates. They claim 24 months reossification time for screw holes after fixation with PLGA
devices.[2]
Jukkala-Partio et al. report on their experimental work on femoral neck osteotomy fixation on
sheep using 6.3 and 4.5 mm PLLA screws. Three parallel screws are used in fixation of this
demanding osteotomy. According their findings at 5 year follow up screw holes were still
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Literature review
15.3.2012
radiologically visible and some implant material was found in histological analysis. At 7 years
and four months follow up screw channels were filled with bone and no implant material was
found in histological examination.[3][4]
2
Experience with Bioretec products
No specific study has been carried out to follow the implant channel filling with tissue and
remodeling to bone. Some isolated data, however, has become available about implant long
term degradation and implant channel filling with tissue. Two cases are presented below.
First case is a 54 year old female patient with bimalleolar fracture treated on the lateral side
with metallic fixation devices and two pieces of ActivaScrew™ 4.5 mm on the medial side.
The metal hardware was removed 13 months after the operation to resolve the problems with
pain, irritation and swelling. An MRI was carried out at 2 years and six weeks in order to find a
reason for the stiffness and pain. The figures below show the native x-ray at 11 weeks and
MRI at 2 years 6 weeks.
Figure 1 Left: Post operative native x-ray at 11 weeks. Right: Postoperative MRI at 2
years 6 weeks.
At 2 years 6 weeks the implant channels of the medial side are still partially visible in MRI.
The channels are most likely filled with soft tissue, but it cannot be clearly stated based on
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Literature review
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this MRI result only. On the lateral side the holes of the removed metal hardware are also
clearly visible as well as the metal particles as a residue of the removed fixation devices.
The second case is a 58 year old female patient with lateral malleolar fracture. The fracture
was initially treated conservatively, but was fixed surgically with two ActivaPin™ 2.0 mm
because to persisting pain. Clinical result of the treatment was good, but because of a
forefoot problem a MRI analysis was carried out 2 years 6 months postoperatively. The figure
below shows the MRI view of the implantation area.
Figure 2 MRI of lateral malleolus at 2 years 6 months.
2 years 6 months after implantation it was hard to find any traces of the implanted devices. A
few millimeter long trace of one of the implant channels could be found, thus the channels
have mostly been filled with bone.
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3
Conclusions
It seems that the implant holes are mostly filled slowly with new bone after implant
degradation. Sometimes the holes can, however, be visible in radiological imaging for a
relatively long time. There seems to be a positive correlation between the biodegradation time
and the time, which the drill holes are radiologically visible. The drill holes with more rapidly
degrading implants seem to ossify more rapidly than those with more slowly degrading
implants. Bone density increase around implant holes is also typically seen, when
bioabsorbable implants are used. This is a natural reaction of bone to adapt to the stress
pattern during weeks or months, when implant gradually loses its strength and stiffness. Bone
gets stronger around the implant hole to compensate the lost bone mass in the implant area,
as the stresses are gradually transferred from the implant to the bone during bone healing
and implant degradation. These phenomena are well in line with the fact that we have not
encountered a single case, where a refracture would have been caused by the holes left in
bone after biodegradation of bioabsorbable fixation implants. These kinds of refractures are,
however, occasionally seen after metal implant removal. In this case the bone is weakened by
the stress shielding effect of the metal implants, making the bone prone to refracture after the
supporting effect of metallic implants is suddenly removed.
The experiences with bone hole filling after in patient degradation are well aligned with the
reviewed publications. As Activa™-products degrade within approximately two years in
human body the holes can be expected to be fully filled with bone within approximately 3-4
years.
As a summary, holes in bones after fixation with bioabsorbable fixation devices can be
sometimes radiologically visible for relatively long time. To our knowledge these occasionally
slowly filling holes have never caused any clinical problem as the bone, surrounding the drill
hole, has normally compensated the missing bone material during implant degradation. The
hole fill rate seem to depend on the degradation rate of the bioabsorbable material.
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4
References
[1]
Juutilainen T, Hirvensalo E, Majola A, Partio E, Pätiälä H, Rokkanen P, Kinnunen
J;Bone Mineral Density in Fractures Treated with Absorbable or Metallic Implants;
Annales Chirurgiae et Gynaecologiae, 86: 1 (1997)
[2]
Landes C, Ballon A, Roth C; Maxillary and Mandibular Osteosyntheses with PLGA
and P(L/DL)LA Implants: A 5-year Inpatient Biocompatibility and Degradation
Experience; Plastic and Reconstructive Surgery, June (2006) p. 2347-2360
[3]
Jukkala-Partio K, Pohjonen T, Laitinen O, Partio E, Vasenius J, Toivonen T,
Kinnunen J, Törmälä P, Rokkanen P; Biodegradation and Strength Retention of
Poly-L-Lactide Screws In Vivo. An Experimental Long-Term Study in Sheep;
Annales Chirurgiae et Gynaecologiae, 90 (2001) p. 219-224
[4]
Jukkala-Partio K, Laitinen O, Vasenius J, Partio E, Toivonen T, Tervahartiala J,
Kinnunen J, Rokkanen P; Healing of Subcapital Femoral Osteotomies with SelfReinforced Poly-L-lactide Screws: An Experimental Long-Term Study in Sheep;
Arch Orthop Trauma Surg, 122 (2002) p. 360-364
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