The dynamisation of locking plate osteosynthesis by means of dynamic locking screws (DLS)—An experimental study in sheep

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The dynamisation of locking plate osteosynthesis by means of dynamic lockingscrews (DLS)—An experimental study in sheep

Michael Plecko a,g,1, Nico Lagerpusch b,1, Daniel Andermatt c, Robert Frigg c, Rudolf Koch c, Michele Sidler b,Peter Kronen b,d, Karina Klein b, Katja Nuss b, Alexander Burki e, Stephen J. Ferguson e, Ulrich Stoeckle f,Jorg A. Auer b, Brigitte von Rechenberg b,d,*a Trauma Hospital Graz, Austriab Musculoskeletal Research Unit (MSRU), Equine Hospital, Vetsuisse Faculty, University of Zurich, Switzerlandc Synthes GmbH, Solothurn, Switzerlandd Competence Center for Applied Biotechnology and Molecular Medicine, (CABMM), Equine Hospital, Vetsuisse Faculty, University of Zurich, Switzerlande Institute for Surgical Technology and Biomechanics, University of Berne, Berne, Switzerlandf Berufsgenossenschaftliche Unfallklinik Tubingen, Tubingen, Germanyg Trauma Division, University Hospital Zurich, University of Zurich, Switzerland

Introduction

The introduction of the biologic fracture healing principleresulted in a shift of paradigms in recent trauma surgery.1 Whileprimary stability and exact reduction of fragments was achieved

with a wide and open approach to the fracture site, the key elementof the biologic osteosynthesis is the protection of soft tissues at thefracture site and minimal invasive surgery with only smallincisions to anchor the implant to the bone.2 Indirect reductionof the fragments and the use of locking plates with a slight distanceto the bone surface should protect and maintain the periosteumwith its local vascularisation and promote fracture healing.3

Although intramedullary nailing is very popular for treatment, thefixation of metaphyseal and shaft fractures of the tibia with lockingplates instead of intramedullary nails resulted in reducedcomplication rates and shorter duration of surgery includingdecreased costs for the hospital (�27%).4 However, disturbedfracture healing is still reported in 10–20% of cases that were fixedwith locking Plates.5,6 Asymmetric callus formation such thatcallus was mainly seen at the trans-cortex but clearly less or nocallus is found at the cis-cortex underneath the plate was one of themajor complications.7 This was considered to be the result of thehighly locking technology especially at the cis-cortex.

Injury, Int. J. Care Injured 44 (2013) 1346–1357

A R T I C L E I N F O

Article history:

Accepted 23 October 2012

Keywords:

Dynamic locking screws

Fracture healing

Locking plate

A B S T R A C T

In this in vivo study a new generation of locking screws was tested. The design of the dynamic locking

screw (DLS) enables the dynamisation of the cortex underneath the plate (cis-cortex) and, therefore,

allows almost parallel interfragmentary closure of the fracture gap. A 458 angle osteotomy was

performed unilaterally on the tibia of 37 sheep. Groups of 12 sheep were formed and in each group a

different osteotomy gap (0, 1 and 3 mm) was fixed using a locking compression plate (LCP) in

combination with the DLS. The healing process was monitored radiographically every 3 weeks for 6,

respectively 12 weeks. After this time the sheep were sacrificed, the bones harvested and the implants

removed. The isolated bones were evaluated in the micro-computed tomography unit, tested

biomechanically and evaluated histologically.

The best results of interfragmentary movement (IFM) were shown in the 0 mm configuration. The

bones of this group demonstrated histomorphometrically the most distinct callus formation on the cis-

cortex and the highest torsional stiffness relative to the untreated limb at 12 weeks after surgery.

This animal study showed that IFM stimulated the synthesis of new bone matrix, especially

underneath the plate and thus, could solve a current limitation in normal human bone healing. The DLS

will be a valuable addition to the locking screw technology and improve fracture healing.

� 2012 Elsevier Ltd. All rights reserved.

* Corresponding author at: Musculoskeletal Research Unit, Equine Department,

University of Zurich, Winterthurerstr. 260, CH-8057 Zurich, Switzerland.

Tel.: +41 44 635 8410; fax: +41 44 635 8917.

E-mail addresses: [email protected] (M. Plecko),

[email protected] (N. Lagerpusch), [email protected]

(D. Andermatt), [email protected] (R. Frigg), [email protected]

(R. Koch), [email protected] (M. Sidler), [email protected]

(P. Kronen), [email protected]

(K. Klein), [email protected] (K. Nuss), [email protected]

(A. Burki), [email protected] (S.J. Ferguson),

[email protected] (U. Stoeckle), [email protected] (J.A. Auer),

[email protected] (B. von Rechenberg).1 Both authors have contributed equally to the study.

Contents lists available at SciVerse ScienceDirect

Injury

jo ur n al ho m epag e: ww w.els evier . c om / lo cat e/ in ju r y

0020–1383/$ – see front matter � 2012 Elsevier Ltd. All rights reserved.

http://dx.doi.org/10.1016/j.injury.2012.10.022


The stiffness of fixed angled plate osteosynthesis is mainlydependent on the distance from bone to implant. For internalfixator systems such as the locking plate technology with only asmall distance to the bone, this means high primary stability,8,9

with low interfragmentary movement (IFM).10,11 The latter ismandatory as a stimulus for new bone formation.12–14 Inter-fragmentary strain is described as a quotient of intrafragmentarydislocation due to micromotion (dL) and fracture gap (L): e = dL/L.15

This means, the smaller the fracture gap, the higher theinterfragmentary strain and the higher the strain the moredifficulties are encountered to produce healthy granulation tissue.e-Values between 2 and 10% provide a status of relative stabilitywith enough micromotion to stimulate new bone formation.8,16

Values exceeding 10% lead to bone resorption instead.17 Addition-ally, the direction of IFM is also important.18 Axial compressionbetween 0.2 and 1.0 mm and perpendicular to the fracture lineincrease mineralized callus formation,19 while shear forces aremore critical.20,21

The elasticity of a fixation using locking implants can beimproved if the surgeon leaves the screw holes close to the fracturesite empty. For instance, if two screw holes on either side of thefracture site are left empty, the elasticity is increased by 50%. The lossof mechanical stability needs to be compensated by choosing alonger Plate.22,23 However, this elastic osteosynthesis according toSturmer24 results in most cases in a dynamisation of the trans- butnot the cis-cortex, hence, asymmetric callus formation will occur.

The idea of dynamisation was pursued by Bottlang et al.,25 whodeveloped a locking screw with only transcortical threads(Zimmer1 MotionLocTM Screw). The concept is similar to a lagscrew exhibiting a thread-less screw shaft in the cis-cortex. Thisgap between the edges of the original drill hole and the core of thescrew facilitates an almost parallel interfragmentary movement atthe fracture site. Because of the special configuration of the fixationdevice (arrangement of the screws, size and form of plate) theimplant stability is even increased against bending and torsionalforces. Gardner et al.,26 achieved a similar situation by simplyoverdrilling the drill hole in the cis-cortex. However, this settingresulted in a significant reduction of axial stiffness of the implant.Nevertheless, in an experimental setting of cyclic loading insynthetic bone, no implant failures were encountered using thisconfiguration. Doebele et al.,27 addressed the problem with a moresophisticated solution, the ‘‘dynamic locking screw’’ (DLS). Therethe lockingpin-sleeve design of the DLS allows minimal movement(0.2 mm) within the screw, without compromising the screw–bone interface or the plate–screw interface. Biomechanical tests insynthetic bone using the DLS showed that this dynamisationresulted in a 16% loss of axial stiffness while bending stiffness andoverall implant stability was maintained at the same level. Thisreduction of axial stiffness facilitates an increase of 50% in IFM atthe cis-cortex and thus, an almost equal parallel overall compres-sion at the fracture gap.

The aim of this study was to demonstrate that the DLS in factresulted in a more symmetrical callus formation and improvedbone healing also at the cis-cortex. In addition, the influence ofdifferent gaps (0, 1 or 3 mm) between the fragments was to betested. The study was based on the hypothesis that the fixationwith DLS results in a less rigid situation at the osteotomy sitemainly at the cis-cortex and thus, bone healing would be promotedthrough micromotion and increased strain within the fracture gap.It was expected that the direct apposition (0 mm gap) and a 3 mmgap would show better bone healing compared to the 1 mm gap.

Materials and methods

Dynamic locking screw: All implants were provided through theindustrial partner (Synthes, GmbH, Solothurn, Schweiz). A total of

37 locking plates (3.5 mm 12 hole broad LCP/159 mm, stainlesssteel, VP4045.12) and 333 DLS (3.5 mm Dynamic Locking Screw,self-tapping, Star Drive, cobalt-chrome, 09.213.0.XX) wereimplanted into the animals. The DLS consists of 2 parts: the innerpin-core with the locking screw head and the outer sleeve with thethreads (Fig. 1). The pin is connected to the sleeve and free near thescrew head. This design allows micromotion of 0.2 mm in eachdirection between the pin-head and the sleeve, while the pin–head–plate and the sleeve–bone interface remains stable.

Animal groups: A total of 37 Swiss Alpine sheep were used forthis study. Animals were adult females, in average 3 years (3 � 1y)old and 61.5 kg (�9.1 kg) of body weight. Tibias were operatedalternating between right and left hind limb. Animals weredistributed in three groups and sacrificed at 6 and 12 weeks aftersurgery. In group 1 (G1) the two fragments was completely apposedat the osteotomy site (0 mm), while in group 2 (G2) a 1 mm gap and ingroup 3 (G3) a 3 mm gap was created (Fig. 2).

All animal experiments were authorized through the localfederal veterinary authorities and conducted according to theSwiss laws of animal welfare and protection (authorisationnumber 02/2007).

Surgery: Before surgery all animals were checked for healthstatus and only healthy animals were used for this study.Anaesthesia was induced with xylazine (0.1 mg/kg BW, StreuliPharma AG, Uznach, Switzerland), buprenorphine (0.01 mg/kg BW,Temgesic1, Essex Chemie AG, Luzern, Switzerland), ketamine (3–5 mg/kg BW, Vetoquinol AG Bern, Switzerland), diazepam (0.1 mg/kg BW, Roche Pharma AG, Reinach, Switzerland) and propofol (0.2–0.4 mg/kg BW, Fresenius Kabi AG, Stans, Switzerland) andmaintained with intravenous propofol constant rate infusion (1–6 mg/kg BW/h) plus isoflurane inhalation anaesthesia throughoutthe procedure (1–1.5 vol%, Abott AG, Baar, Switzerland). Prophy-lactic peri- and postoperative antibiosis was applied usingbenzylpenicilline (30,000 IU/kg BW, Streuli Pharam AG, Ulznach,Switzerland) and gentamicine (4 mg/kg BW, Veterinaria AG,Zurich,Switzerland). Tetanus serum (3000 IU, Veterinaria AG, Zurich,Switzerland) was applied preoperatively. Carprofen (4 mg/kg BW,Pfizer AG, Zurich, Switzerland) and buprenorphine (0.01 mg/kgBW, Temgesic1, Essex Chemie AG, Luzern, Switzerland) wasadministered pre- and postoperatively as analgetic medication.

The sheep were placed in lateral recumbency with the limb tobe operated on the table and the upper limb removed from thesurgery area. After routine preparation of the surgical field a medialapproach to the tibia diaphysis was selected using electrocauteryto control bleeding. The osteosynthesis plate was contoured to thebone surface after precise realignment of the fragments such thatthe distal end was positioned approximately 1.5 cm proximal tothe tarsocrural joint. The drill holes in the proximal part of theosteotomy site are referred to P1-P6 with P1 being the mostproximal, while those of the distal part of the plate were referred toas D1–D5, again D1 being the most proximal. A LCP drill sleeve wasfixed to the stacked locking hole at the proximal end of the plate(P1). A centering sleeve was introduced and a 1.6 mm Kirschnerpin inserted into the proximal tibia shaft. Subsequently the drill

Fig. 1. The DLS – Dynamic Locking Screw is pictured schematically. The outer sleeve

with the threads is cut open to visualize the internal core and the small gap between

inner core and outer sleeve. Note that the gap is largest close to the head and is not

present at the tip of the screw.

M. Plecko et al. / Injury, Int. J. Care Injured 44 (2013) 1346–1357 1347


holes D2 and D3 were drilled in the distal fragment and measured.To the measured length 2 mm were added to include the distancebetween locking plate and bone surface after final fixation. Screwswere inserted using the power drill equipped with a torquelimiting attachment. The periosteum was incised at the osteotomysite and together protected with the soft tissue including thecranial tibial artery with 2 Hohman retractors. Thereafter, the LCPwas removed and exchanged for a customized LCP, where acutting-guide was mounted (Fig. 3 cutting guide) providing astandardized angle (458) and proximo-lateral direction of theosteotomy. The cutting-guide contained two slits that allowed forparallel cuts and removal of a 3 mm bone slice.

The LCP was then reapplied, the screws inserted loosely into D2and D3 before four 2 mm pins were placed between the bonesurface and the plate to maintain an equal distance. The screwswere tightened and the osteotomy side reduced using reductionclamps. Care was taken to keep the osteotomy line parallel and tomaintain correct axial alignment. With the LCP in place drill holeP2 and P4 were placed in the proximal fragment and the constructfixed by introducing DLS. Thereafter the drill holes P1, P3, P5 andD5 were drilled, measured and prepared using self-tappingstandard locking head screws before introducing the DLS.Thereafter the locking screws of P2, P4, D2 and D3 were alsoremoved exchanged for DLS. The decision for tapping the screwholes first with locking screws instead of using the DLS (also selftapping screws) was based on the brittle bone structure in sheep toavoid the risk of fissures during inserting the slightly more blunttips of the DLS. This step could be avoided in a more elastic bonelike in humans. After inserting all screws the space holder and

position pins were removed and all screws were retightened usingthe T-handle coupled to the torque limiting attachment.

For group G2 and G3 the procedure was slightly changed suchthat after completion of the osteotomy a 1 mm (G2) or 3 mm (G3)space holder was introduced into the osteotomy line to guaranteethe designed osteotomy gaps while repositioning the fracture andfixing the plate.

The wound was closed routinely in three layers usingresorbable suture material and skin staples.

Postoperative care: A full limb cast extending from the claws toabove the stifle joint was applied to support the limb during thefirst weeks of bone healing. Analgesia (caprofen) and antibiosis(benzylpenicillin and gentamicin) were continued for 3 dayspostoperatively. The casts were changed every 3 weeks and after 9weeks the claws were left open at the sole. Animals were kept insmall stalls in groups of two sheep for 6 weeks and thereafter inlarger pens for the rest of the study in groups of 6 animals.

Fluorescence markers: For documentation of calcium depositionintravital fluorochromes were injected at 3 (calceingreen: 5 mg/kgBW), 6 (xylenolorange: 90 mg/kg BW), 9 (oxytetracyclin: 25 mg/kgBW) and 12 weeks (calceinblue: 30 mg/kg BW), always 48 h beforethe actual full date.

Sacrifice: Animals were sacrificed at the faculty ownedslaughterhouse at either 6 or 12 weeks. The operated and intactcontralateral tibia were immediately harvested, cleansed fromsurrounding soft tissues and callus formation was documented.

Radiographs: Before recovery craniocaudal and lateromedialradiographs were taken of each sheep to assure proper fixation.Control radiographs were also taken every 3 weeks at the time ofcast changes. At the time of sacrifice the tibiae were radiographedagain (2 views/bone) in the Faxitron (55 kV, 5 s, Cabinet x-rayfaxitron series, model 43855 A, HP, Oregon, USA) after cleansing ofall other tissues. Thereafter, bones were enwrapped in moistgauzes (0.9% NaCl), sealed in plastic bags, kept cool at 4 8C beforebeing subjected to mechanical testing.

Evaluation

Biomechanical testing: Before torsion tests were conducted allimplants were removed and the proximal tibia plateau wasresected using an oscillating saw. Two screws each were insertedinto the proximal and distal part of the bone to increase holdingpower within the polymethylmetacrylate (PMMA) block requiredfor inserting the bone into the servo-hydraulic test machine (MTS,858 Mini Bionix1, USA). The distance between the proximal anddistal PMMA blocks was standardized to 16 cm leaving the

Fig. 2. The different groups and their configurations are shown schematically: G1 = 0 mm gap; G2 = 1 mm gap; G3 = 3 mm gap. All three groups show a 2 mm gap between

plate and bone surface.

Fig. 3. The cutting guide template is illustrated. Two saw blades are inserted into the

slits and demonstrate the 3 mm section that was cut out in group G3.

M. Plecko et al. / Injury, Int. J. Care Injured 44 (2013) 1346–13571348


osteotomy site in the most central part of the test setup. Duringtesting bones were kept moist with 0.9% NaCl. Non-destructivetorsion tests were conducted, where operated and intact contra-lateral limbs were subjected to rotation at a constant angularvelocity up to a peak torque of 10 Nm. Results were reported as thetorsional stiffness (N mm/8), normalized to the value for thecontralateral limb.

Histology: After biomechanical testing the bones were cut at thelevel between P4/P5 and D1/D2 and immersed in 40% ethanol forfixation. Preparation of non-decalcified bone section was con-ducted as reported before.28 Briefly, dehydration was performed ina series of ethanol (40, 50, 70, 80, 90, 96, 100%) at 4 8C beforedefatting in xylene under vacuum. Infiltration in fluid PMMA wascontinued for 7 days before cold polymerisation was allowed for 3weeks in airtight plastic containers at 4 8C. Polymerisation wascompleted in a water bath and in the incubator at 37.5 8C. Groundsections were cut (EXAKT1 Band System 300/301, Exakt Appara-tebau GmbH & Co. KG, Norderstedt, Germany), fixed on Acropalslides (Perspex GS Acrylglas Opal 1013, Wachendorf AG, Basel,Switzerland) and polished (30–40 mm) before surface stainingwith toluidine blue. Native sections (50 mm) were prepared onglass slides for fluorescence microscopy.

Qualitative evaluation of histology sections was performed aswell as quantitative measurements. Sections were visualized witha light macroscope (Leica M4201, Leica-microsystems, Heerbrugg,Schweiz) and digitalized in TIF format for further measurements.

Microradiography: Before ground sections were glued on slidesmicroradiographs were taken of these sections (Faxitron: 55 kV,12 s).

Histomorphometry: Digitalized pictures were prepared to astandard of 3 cm bone length with the osteotomy site in thecentre. Thereafter, old and new bone matrix as well as granulationtissue was marked with different colours using a specializedsoftware program (Adobe Photoshop 3.0), such that percentage ofeach fraction could be calculated with a specialized histomor-phometry program (Leica Qwin1). In addition, measurementswere performed for total callus and percentages of periostealcallus at the trans- and cis-cortex each, as well as for endostealcallus in relation to the total bone area. While interfragmentarycallus was included in total callus, it was excluded for thecalculation of periosteal and endosteal callus alone. Furthermore,4 cm sections were calculated where the osteotomy site was againpositioned in the centre. Within the bone marrow percentage ofendosteal callus as well as granulation tissue was calculated.Screw holes were excluded from calculations and considered asbackground.

Digitalisation of fluorescence sections: Native sections weredigitalized in TIF format using a fluorescence microscope (LeicaDM 6000B1, Leica CTR 60001) with the according software (LAS AF60001). By means of the ‘‘stitching function’’ the entire osteotomyand callus area could be visualized and measured in one digitalizedpicture. The 4 colours were visualized separately with specialfilters (L5 for calcein green, N3 for xylenol orange, D foroxytetracyclin and A4 for calcein blue) and also combined in anoverlay picture. The pictures were evaluated macroscopically.

Micro-computer tomography (mCT): Bone sections were sub-jected to mCT evaluations while in 70% ethanol (b-cube AG, Zurich,Switzerland). Standard settings were used for all sections (70kVp,200 ms, isotropic nominal resolution of 50 mm). Each measure-ment was performed twice and three analysis volumes werecalculated, namely the periosteal external callus, the endostealinternal callus as well as callus underneath the implant (LCP). Alsohere, the total callus volume was calculated, whereof the variousfractions were set in relation and given in percentage.

Radiographs: All radiographs were evaluated through two boardcertified radiologists blinded to the study. A combination of

quantitative and semi-quantitative scores was given. On cranio-caudal radiographs the width of the gap was measured betweenthe cis-cortex (A) and trans-cortex (B) such, that the distancebetween the fracture fragments was taken without considering theforming callus tissue in between. Thereafter, the amount of callusdensity was graded in relation to the cortex with 0 = no density,1 = mild density, 2 = moderate density and 3 = normal density(equal to cortex). Density of endosteal and periosteal callus wasgraded the same way. The volume of the periostal and endostealcallus were scored from 0 to 4 in relation to the osteotomy site.Missing callus was scored = 0, callus < osteotomy site = 1, cal-lus > osteotomy site = 2 and callus completely bridging theosteotomy site = 3. When the osteotomy line was completelybridged and the amount of callus was already reduced due toremodelling a score = 4 was given.

Microradiography: Evaluation of microradiographs was per-formed also for callus formation. A line was drawn in the middle ofthe osteotomy site followed by two parallel lines proximally anddistally at a 20 mm distance (4 cm total width). By means of a rulerthe following values in mm were measured: maximum height ofperiosteal callus thickness at the cis- and trans-cortex (limitationat 2 mm at the cis-cortex due to implant) and diameter of corticalbone distally and proximally at the height of the parallel lines(20 mm). The original cortex served as limit. The same principlewas applied to measure the cortical diameter of the cis- as well asthe trans-cortex. Thereafter, the width of the gap was measuredbetween the fragments at the cis- and trans-cortex. In contrast tothe measurements of the radiographs, here the actual cortical gapwas measured by taking the callus formation into account. If thegap was bridged with calcified tissue at least on one spot a value of0 mm was recorded. If no bridging was present, the rest gap wasmeasured at its widest point.

Statistical analysis: All values were subjected to statisticalanalysis using a specialized software program (SPSS1 Base for MacOS X, Version 18.0, Chicago, Illinois). A factorial analysis of variance(ANOVA) was used to calculate statistically significant overalldifferences between groups for data obtained of biomechanicaltesting, histomorphometry, mCT and microradiography. An analy-sis of repeated measures was conducted to document differencesbetween groups for radiographical scores. Mean values andstandard deviations were calculated. Posthoc tests according toBonferroni were used to assess individual differences betweengroups. p-Values <0.05 were considered as statistically significant.

Results

Surgeries could be performed in all 37 sheep withoutcomplications. Also recovery and the postoperative period wentwell for all except one sheep with a wound dehiscence and onesheep with screw loosening and implant failure. While the wounddehiscence was only superficial and healed well after appropriatetreatment, the sheep with implant failure at 3 weeks had to beeuthanized. Therefore, only 36 sheep were used for finalevaluation.

Biomechanical testing was possible in 34 sheep. In one sheep ofG1 a non-union was present which made testing meaningless. Inone sheep of G3 a mal-union was detected rendering a very lowvalue of 19% of the contralateral sound tibia’s stiffness. Althoughthere was bone bridging present one sheep of G2 revealed onebroken screw in P2, of which the core was left within the bone alsoduring testing. Results of tests are summarized in Fig. 4. Briefly, at 6weeks the highest stiffness values were recorded in animals of G2with the 1 mm gap, followed by G1 (0 mm) and last G3 (3 mm).This changed at 12 weeks, where animals of G1 revealed thehighest values, followed by G3 and then G2, which demonstratedthe lowest stiffness. Values were always higher at 12 weeks,



although statistically significant values were only found for G3–6w(p = 0.012).

Histomorphometrical measurements corresponded to dataobtained at mechanical testing (Table 1), at least at 6 weeks.There, the highest volume of new bone matrix was found for G2. At12 weeks the highest bone volume was detected in G3. The amountof new bone matrix was decreased in G2 at 12 weeks compared to 6weeks. In contrast increased values were noted in G1 (p = 0.078)and G3 (p = 0.001). If new matrix was measured significantdifferences were present between G2 and G3 at 12 weeks(p = 0.005).

Percentage of old bone matrix was similar in G1 and G2, butslightly less in G3 at 6 weeks. At 12 weeks either equal or slightlyreduced values were noticed in all groups. Granulation tissueoccupied 47–57% of the total area at 6 weeks, with the lowestvalues in G2 at 6 weeks. At 12 weeks this changed. At that timepoint values in both, G1 and G3 were lower than G2. However,differences were significant only for G3 (p = 0.030).

Significant negative correlations were noticed between granu-lation tissue and new bone matrix (at 6 weeks r = 0.745,p < 0.0001; at 12 weeks r = 0.719, p = 0.001).

The different fractions of callus in relation to total bone volumeare described in Table 2. Comparable to the other data, the totalpercentage of callus volume was highest in G2 at 6 weeks followedby G1 and G3 at a lower level. At 12 weeks G1 and G3demonstrated increasing values, whereas G2 had significantlylower values (p = 0.013). Periosteal callus at the cis-cortex revealedat 6 weeks volumes between 1.0 and 1.7% which increasedsignificantly at 12 weeks for G1 (p = 0.001) and G3 (p = 0.002),while in G2 only a tendency for an increased periosteal callusformation was noticed. When callus at the cis-cortex wascompared at 12 weeks, G1 had significantly more callus presentcompared to G2 (p = 0.005). The highest values of periosteal callusat the trans-cortex at 6 weeks were found for G3, followed by G2and last G1. Differences within groups were highest for G2 and lessfor G1 respectively G3. The largest volume of endosteal callus at 6weeks was found in G2, while at 12 weeks an increased callusvolume was noticed for G1 and G3 and a significant decrease for G2(p = 0.004). A strong correlation was found between total andendosteal callus volume (6 weeks postop: r = 0.840, p < 0.0001; 12weeks: r = 0.820, p < 0.0001). The endosteal callus in relation tothe bone marrow cavity was highest in G2, but significantly lowerat 12 weeks (p = 0.022) when G2 showed the lowest values(Fig. 5a). For G1 endosteal callus remained almost the same overtime whereas the volume had an increasing tendency for G3.

Fluorescence sections: Evaluation at 6 weeks demonstrated forG1 a dominance of calcein green and xylenol orange incorporationat the trans-cortex and only minor depositions at the cis-cortex.Intrafragmentary deposition of xylenol organge was also predom-inant. At 12 weeks a clearly more prominent and wider callus wasfound at the cis-cortex still consisting mainly of calcein green andxylenol orange. Oxytetracylcin and calcein blue depositions weremainly found inter- and intracortically as well as seam ofremodelling in all callus fractions.

In G2 activity of calcein green and xylenol orange was relativelyminor. Instead oxytetracyclin and calcein blue markers wereprominent at 6 respectively at 12 weeks. Calcein green activity wasalso diminished at the cis-cortex in G3. Bridging of the gapoccurred already in the xylenol orange phase, but mostly only inthe oxytetracyclin and/or calcein blue phase.

Micro-computer tomography (mCT): Bones were evaluated onlyfor the 12 weeks group (Fig. 6). Total callus values were highest forG3, followed by G1 and last G2. The same was true for endostealcallus, where a significantly lower callus volume was foundbetween G3 and G1 (p = 0.008). Periosteal callus fractions werealso highest for G3 > G1 > G2. If periosteal callus was divided incallus volume underneath the plate (cis-cortex) G3 showed thehighest volume followed by G2 and last G1. However, if periostealcallus at the trans-cortex was studied G2 had more callus followedby G3 and then G1. A strong correlation was found between totaland periosteal callus values (r = 0.900, p < 0.0001).

biomechnical data

0

20

40

60

80

100

120

G1-6 w G1-12 w G2-6 w G2-12 w G3-6 w G3-12 wweeks

tors

iona

l stif

fnes

s, re

l. to

inta

ct

oppo

sing

sid

e %

Fig. 4. The graph presents the biomechanical data, where the torsional stiffness

relative to the intact opposing side is given in percentage. In all groups the stiffness

is higher at 12 weeks compared to 6 weeks. Differences between time points are

lowest in G2 (1 mm gap), although this group has a slight tendency for lower values

compared to G1 (0 mm gap) and G2 (3 mm gap).

Table 1Histomorphometric measurements: mean values and standard deviations relative

to total bone area are given in percentages of total area measured.

Groups Period New bone

matrix

Old bone

matrix

Granulation

tissue

G1 6 weeks 15 � 4 34 � 5 51 � 6

12 weeks 24 � 5 32 � 5 44 � 8

G2 6 weeks 21 � 9 32 � 4 47 � 6

12 weeks 17 � 3 32 � 4 51 � 3

G3 6 weeks 15 � 3 28 � 5 57 � 6

12 weeks 29 � 5 26 � 2 45 � 6

Table 2Histomorphometric mearsurements: mean values and standard deviations of different fractions of callus in relation to total bone volume are given in percentages in total area

measured.

Groups Period Total callus Periosteal callus cis-cortex Periosteal callus trans-cortex Endosteal callus

G1 6 weeks 14.1 � 3.9 1.7 � 0.7 7.6 � 2.9 4.8 � 5.2

12 weeks 18.6 � 5.7 6.1 � 1.3 6.2 � 3.5 6.2 � 4.0

G2 6 weeks 20.7 � 8.7 1.3 � 0.6 9.4 � 4.7 9.9 � 4.6

12 weeks 9.4 � 4.2 2.3 � 1.3 6.1 � 4.6 1.1 � 0.7

G3 6 weeks 13.2 � 2.1 1.0 � 0.6 9.5 � 2.6 2.7 � 1.8

12 weeks 22.6 � 4.6 5.2 � 3.4 8.3 � 4.8 9.1 � 3.9



Evaluation of radiographs: Results of all groups and time pointsare depicted in Tables 3a, 3b and 3c and Fig. 5b. Brieflysummarizing results, significant differences were found for gapwidth between G3 and G1/G2 for both time points, alsoimmediately after surgery (p < 0.05). Increasing callus volumesover time were found in all groups with basically higher values atthe trans-cortex at earlier time points and increasing values at thecis-cortex at later time points. Also here, higher volumes werefound for G3 compared to G1/G2, although individual fractionsvaried between time points and cis- and trans-cortex at the twotime points and various groups.

Evaluation of microradiographs: The periosteal callus thicknessat the trans-cortex was between 6.0 and 6.5 mm at 6 weeks anddecreased significantly at 12 weeks for G1 (p = 0.003) and G2(p = 0.023) (Table 4). The thickness had also decreased for G3, butwithout statistical significance. The relationship was inverse forthe cis-cortex, where the thickness of periosteal callus had an

increasing tendency over time. While at 6 weeks G1 had the widestcallus followed by G2 and then G3, the thickest callus formationwas found in G3 at 12 weeks (p = 0.052) before G1 and then G2. Theouter diameter of bone was very similar (18.3–20.2 mm) for allgroups and varied only slightly (1.4 mm) between the two timepoints. Instead, values of the proximal fragment for the internaldiameter of the bone marrow cavity varied considerably with arange between 7.6 and 11.0 mm in the 6 and 12 weeks groups. Inthe distal fragment an outer diameter of 18.7–20.3 mm and aninternal diameter with a range of 9.8–12.0 mm was detected. Thediameter of the cis-cortices in the proximal and distal fragmentwas very similar (4.1–5.0 mm) while a wider range was found forthe trans-cortices (3.9–5.1 mm). The width of the osteotomy gap atthe cis-cortex was smaller in all 12 week groups compared to the 6weeks groups and was significant for G2 (p = 0.019) and G3(p < 0.0001). This was also true for the trans-cortex. However,differences were smaller and not significant.

Fig. 5. An overview of microradiographs, histology ground and fluorescence sections (a) and radiographs (b) is assembled. One sample per group illustrates bone healing over

time (PMMA embedded specimens, ground or native sections; ground sections are surface stained with toluidine blue).



Discussion

In this study the effective dynamisation of locking plateosteosynthesis by means of dynamic locking screws (DLS) wasdemonstrated. The use of these new implants induced strong callusformation at the cis-cortex resulting in high mechanical stiffness at12 weeks postoperatively and indicating complete bridging of theoblique osteotomy. Of all groups, the group with 0 mm gap showedthe fastest bone healing compared to groups with 1 mm and 3 mmgaps.

The animal model and equipment used allowed good standar-disation. Overall complications rates were very low (1/37)confirming the appropriate application of the osteotomy modeland choice of implant size. The sheep served well as experimentalanimal to study new bone formation due to their similar bonemetabolism to humans as well as its size of bone. Thebiomechanical situation of the oblique osteotomy allows conclu-sions that are relevant for human surgery. Since osteotomies were

proven to heal equal to spontaneous fractures the overall settingdid not differ too much from a clinical setting. Differences toclinical situations in humans are the use of casts postoperatively toavoid fractures as a result of torsional and shear forces as well asthe use of stainless steel plates with an overall higher rigiditycompared to titanium alloys. These were adaptations to sheepbehaviour, since sheep use their limbs immediately after surgeryand at full weight bearing capacity. Instead human patients usecrutches and adapt weight bearing according to recommendationsof their orthopaedic surgeon. Nevertheless, both measures taken toreduce spontaneous fractures in sheep did not influence resultssignificantly and thus, may be negligible. Furthermore, althoughDLS are self-tapping screws, we choose to tap the threads withconventional locking screws. The reason for this is the brittlenature of sheep bone and the more rounded tip of the DLScompared to the conventional locking head screw. In early tests ofthe newly designed DLS a slightly lower cutting capacity wasexperienced in cadaveric sheep bone. Therefore, cutting was

Fig. 5. (Continued ).



performed with the conventional locking screws, where theadvantage of a more pointed tip reduced the risk of fissureformation. As the human bone is more elastic compared to sheepbone, this should not pose a problem and DLS can be used as self-tapping screws in clinical settings.

Animal numbers with 6 animals per group were relatively low,but in accordance with statistical standards. Costs and reasons ofanimal welfare were prohibitive to use more animals per group,which would have possibly resulted in more significant differences

between groups. However, especially groups 2 and 3 showedrelatively high standard deviations, which may be explained withthe gap and subsequent relatively higher micromotion betweenfragments, especially at the cis-cortex. Power calculations made itquestionable whether a double increase of animal numbers wouldhave altered the results. Nevertheless, results were sufficientlyclear to show either significant differences or strong tendencies ofbone healing especially at the cis-cortex and also at the trans-cortex.

Fig. 6. mCT pictures show callus formation in samples of group 1, 2 and 3. For each group three representative samples were chosen from a cortex and bone marrow view.

Table 3aEvaluation of radiographs: mean values and standard deviations of gap size and callus size as well as density at cis- and trans-cortex are given for G1 at different time points.

Gap widths are recorded in mm, whereas densities are given in scores.

Time Parameter Timepoint (weeks)

3 6 9 12

G1 6 w Gap width cis [mm] 1.2 � 0.3 0.8 � 0.3 0.7 � 0.3 0.7 � 0.3

Gap width trans [mm] 0.8 � 0.3 0.6 � 0.2 – –

Callus density – gap cis (0–3) 0.8 � 0.8 0.5 � 0.8 – –

Callus density – gap trans (0–3) 1.5 � 0.8 0.8 � 1.0 – –

Callus size cis (0–4) periosteal 0.0 1.4 � 1.3 – –

Callus density cis (0–3) periosteal 0.0 0.8 � 0.8 – –

Callus size cis (0–4) endosteal 0.2 � 0.4 2.2 � 0.4 – –

Callus density cis (0–3) endosteal 0.2 � 0.4 2.0 � 0.0 – –

Callus size trans (0–4) periosteal 1.7 � 0.5 2.7 � 0.4 – –

Callus density trans (0–3) periosteal 1.2 � 0.3 2.1 � 0.2 – –

Callus size trans (0–4) endosteal 0.8 � 0.8 2.5 � 0.8 – –

Callus density trans (0–3) endosteal 0.6 � 0.5 2.0 � 0.5 – –


Gap width trans [mm] 0.8 � 0.4 0.8 � 0.3 1.2 � 0.3 1.0 � 0.5

Callus density – gap cis (0–3) 0.0 1.3 � 0.5 1.6 � 0.5 1.3 � 0.5

Callus density – gap trans (0–3) 1.3 � 1.0 1.9 � 0.2 1.9 � 0.6 1.6 � 0.5

Callus size cis (0–4) periosteal 0.0 1.2 � 1.6 2.3 � 1.5 2.0 � 1.7

Callus density cis (0–3) periosteal 0.0 0.6 � 0.9 1.5 � 1.1 1.0 � 1.0

Callus size cis (0–4) endosteal 1.5 � 1.2 2.3 � 0.8 2.7 � 1.0 2.8 � 0.9

Callus density cis (0–3) endosteal 0.7 � 0.5 2.2 � 0.5 2.0 � 0.4 1.7 � 0.3

Callus size trans (0–4) periosteal 2.3 � 0.5 2.8 � 0.4 3.4 � 0.7 3.6 � 0.7

Callus density trans (0–3) periosteal 1.7 � 0.4 2.5 � 0.4 2.4 � 0.4 2.4 � 0.5

Callus size trans (0–4) endosteal 2.6 � 0.5 2.8 � 0.4 3.2 � 0.4 3.5 � 0.5

Callus density trans (0–3) endosteal 1.3 � 0.3 2.2 � 0.3 2.6 � 0.5 2.2 � 0.5



Controls with standard locking plates and static locked screwswere not performed in this study, since another complete studywas already performed in the same laboratory using the sameosteotomy model, where standards locking screws and identicalplates were used in different configuration (M. Plecko et al., Injury,resubmitted after revision2). Comparing data of both studies

revealed a strong tendency for better callus formation at the cis-cortex. Both studies used the same setup, e.g. identical evaluationand the same scientists.

The time points of 6 and 12 weeks were chosen out ofexperience with other studies conducted with sheep at our ownlaboratory.29,30 There, it was shown that at 4 weeks not much newcallus and interfragmentary bone formation was detected,whereas at 8 weeks callus formation was already prominent.Since callus formation at the cis-cortex at an early stage was thefocus of the study, an intermediate time point was chosen. In the

Table 3cEvaluation of radiographs: mean values and standard deviations of gap size and callus size as well as density at cis- and trans-cortex are given for G3 at different time points.



3 6 9 12

G3 6 w Gap width cis [mm] 2.9 � 0.5 2.9 � 0.5 – –


Callus density – gap cis 0.2 � 0.4 1.6 � 0.5 – –

Callus density – gap trans 0.2 � 0.4 1.1 � 0.7 – –

Callus size cis (0–4) periosteal 0.9 � 0.9 1.1 � 0.9 – –

Callus density cis (0–3) periosteal 0.7 � 0.7 0.8 � 0.7 – –

Callus size cis (0–4) endosteal 0.0 1.9 � 0.5 – –

Callus density cis (0–3) endosteal 0.0 1.2 � 0.4 – –







Callus density – gap cis 0.2 � 0.4 1.3 � 0.4 2.1 � 0.4 2.4 � 0.4

Callus density – gap trans 0.2 � 0.4 1.0 � 0.6 1.5 � 0.8 1.6 � 0.5

Callus size cis (0–4) periosteal 0.0 1.3 � 1.5 1.6 � 0.9 2.0 � 1.2

Callus density cis (0–3) periosteal 0.0 0.6 � 0.8 1.5 � 0.9 1.4 � 0.9

Callus size cis (0–4) endosteal 0.0 1.0 � 0.0 1.5 � 0.5 1.8 � 0.4

Callus density cis (0–3) endosteal 0.0 1.0 � 0.0 1.8 � 0.4 1.8 � 0.7





Table 3bEvaluation of radiographs: mean values and standard deviations of gap size and callus size as well as density at cis- and trans-cortex are given for G2 at different time points.



3 6 9 12

G2 6 w Gap width cis [mm] 1.0 � 0.3 0.9 � 0.2 – –


Callus density – gap cis (0–3) 0.5 � 0.8 0.0 – –

Callus density – gap trans (0–3) 0.7 � 0.9 0.0 – –

Callus size cis (0–4) periosteal 1.0 � 1.0 1.0 � 0.8 – –

Callus density cis (0–3) periosteal 0.8 � 0.8 1.8 � 0.8 – –

Callus size cis (0–4) endosteal 0.2 � 0.4 2.2 � 0.7 – –

Callus density cis (0–3) endosteal 0.2 � 0.4 1.6 � 0.4 – –







Callus density – gap cis 0.3 � 0.5 0.6 � 0.7 1.3 � 0.4 1.7 � 0.4

Callus density – gap trans 0.7 � 0.8 0.9 � 0.9 2.2 � 0.3 1.9 � 0.2

Callus size cis (0–4) periosteal 0.2 � 0.4 1.2 � 1.1 1.4 � 0.9 1.3 � 1.2

Callus density cis (0–3) periosteal 0.2 � 0.4 1.0 � 1.0 1.4 � 0.9 1.2 � 1.0

Callus size cis (0–4) endosteal 0.2 � 0.4 0.8 � 0.8 0.8 � 0.8 0.6 � 0.8

Callus density cis (0–3) endosteal 0.2 � 0.4 0.7 � 0.5 0.6 � 0.5 0.4 � 0.5





2 M. Plecko et al.: The influence of different osteosynthesis configurations with

locking compression plates (LCP) on stability and fracture healing after an oblique

458 angle osteotomy.



study of Bottlang et al.,31 mechanical tests and histology wereperformed at 9 weeks, when differences in callus formation werehighest. Our radiographic scoring revealed similar data, althoughwe used an oblique fracture model in our study. In contrary to ourstudy a transverse osteotomy model was used for the Bottlangstudy. This leads to a different biomechanical situation at theosteotomy site, especially regarding shear forces.

Biomechanical tests were performed at 6 and 12 weeks. Non-destructive tests were applied to preserve the samples forsubsequent histological processing. This allowed the determina-tion only of stiffness, but not of failure torque. However, in earlierstudies strong correlations between stiffness and failure torquevalues were established, such that the present results can beaccepted as predictive also of failure response. Stiffness increasedover healing time in all three groups, although only G3demonstrated significant differences within the group. Differencesbetween groups were not statistically significant, althoughtendencies were observed such that at 6 weeks G2 showed thebest results and at 12 weeks G1 followed closely by G3 and last byG2. Bottlang et al. showed significant differences in torque failurevalues at 9 weeks, but also not in stiffness.31 Due to the differentosteotomy pattern (oblique vs. transverse) as well as size and typeof implant used, results cannot be directly compared. However, asimilar tendency is present.

The mechanical values corresponded well with results obtainedfrom histomorphometry, although total callus volume has to beseen in perspective to the original gap. This explains the highestcallus volume in G3, where the 3 mm gap allowed the greatestfreedom for new tissue formation especially within the gap.32 Incontrast G2 showed the highest total callus volume at 6 weekssimilar to other observations, where the maximum of callusformation was reached at the same time and thereafter remodel-ling was predominant.33 The significant decrease of total callusvolume in G2 at 12 weeks and increase between week 6 and 9 forradiolographic scores supports this view that remodelling alreadytook place.

Interestingly differences in callus formation and stiffness inmechanical testing were not equally distributed between groupsover time. At 6 weeks the highest values for callus formationwere found in G2, which corresponded to higher stiffness values.It is easily explained why G3 had the lowest values for stiffness at6 weeks, since granulation tissue and new bone deposition had tobridge and fill a 3 mm gap. However, there was no gap to bridgein G1, where direct apposition was reached. The ‘‘strain-theory’’within the fracture gap15 may offer an explanation for thisoccurrence. With a 0 mm gap between fracture ends and withoutcompression the strain may be too low to stimulate new boneformation and bone resorption has to come first before newbone formation is initiated again. Indeed, the osteolysis in form

of ‘‘tear-drops’’34 is clearly visible in G1 at 6 weeks. However,since endosteal callus was most prominent in this group, thehighest stiffness values were obtained. According to the straintheory a 1 mm gap results in less strain for cells within thefracture gap20 and thus, improved primary bone stability may bereached. Nevertheless, at 12 weeks however, stiffness valueswere better in G1 and G3 compared to G2. This may be explainedwith the findings of Claes et al.,32 where small gaps resulted inbetter revascularisation and bone healing. The fact that G2showed lower stiffness may be explained such, that interfrag-mentary strain may be still elevated at this time tearing the finecapillaries apart35 and/or the high hydrostatic pressure may haveresulted in collapse of this area and impaired bone healing.36 Alsoat 12 weeks the fragments were not completely bridged withnew bone tissue.

Apart from callus volume its distribution has also to beconsidered. The goal of this study was to show that dynamisationallowed a more equally distributed callus formation especially atthe cis-cortex.7 This goal could be reached in all three groups. Infact at 12 weeks the volume of the cis-cortical callus (36.44%) waseven more pronounced in G1 compared to the trans-cortex(32.09%). The more even distribution of callus formation could alsonicely be demonstrated on microradiographs and mCTs. A limitingfactor in callus formation at the cis-cortex consisted of the plateitself, although a 2 mm gap between bone surface and implant waspresent. A greater gap may have improved callus formation, but atthe same time probably would have weakened the rigidity of themechanical construct.37

Rigidity was shown to moderate fracture healing in animalexperiments, where micromotion influenced callus formation.Clinically, this leads to dynamisation of fractures with delayedhealing such that selected screws were removed to encouragecallus formation at the fracture site. In the early days of fracturestudies, ‘‘stress protection’’ was thought to be secondary toreduced mechanical load on the bone. Later, biological factors suchas local impairment of vascularisation underneath the plate anddamage to the periosteum were held responsible for decreasedfracture healing at the cis-cortex. Changing the profile of theosteosynthesis plates at the side facing the bone lead to thedevelopment of the limited contact dynamic compression plates(LC-DCP) already improving the biological environment. Thelocking plate mechanism allowed further to lift the platecompletely from the bone surface providing better access tovessels, cell proliferation and new callus formation. However,delayed healing at the cis-cortex was still observed favouring themechanical aspect of ‘‘the stress protection’’ phenomenon again.Most likely a combination of both, the biomechanical andbiological aspects were involved. The results obtained in thecurrent study where dynamisation of the osteotomy gap was

Table 4Evaluation of microradiographs: mean value and standard deviations of thickness of periosteal callus, diameter of the tibia and width of the gap. All values are presented in

mm.

Parameters Groups

G1 G1 G2 G2 G3 G3

6 w 12 w 6 w 12 w 6 w 12 w

Periosteal callus thickness [mm] Cis 1.1 � 0.6 1.5 � 0.5 1.0 � 0.0 1.2 � 0.4 0.6 � 0.8 1.7 � 0.8

Trans 6.5 � 2.7 1.6 � 1.4 6.3 � 2.6 2.3 � 1.6 6.0 � 0.6 3.7 � 2.3

Outer diameter [mm] Proximal 19.8 � 1.0 19.0 � 1.8 20.2 � 0.8 19.0 � 1.3 18.3 � 0.8 19.7 � 2.3

Distal 20.1 � 0.8 19.1 � 1.0 20.3 � 0.8 19.3 � 1.4 18.7 � 1.2 19.4 � 1.4

Inner diameter [mm] Proximal 9.7 � 1.5 7.6 � 3.3 10.5 � 1.0 9.3 � 0.8 10.0 � 1.4 11.0 � 1.6

Distal 10.7 � 1.6 10.2 � 1.7 12.0 � 1.1 10.2 � 1.6 9.8 � 1.8 10.9 � 2.1

Gap [mm] Cis 0.4 � 0.3 0.0 � 0.0 0.9 � 0.2 0.0 � 0.0 2.4 � 1.0 0.0 � 0.0

Trans 0.1 � 0.1 0.0 � 0.0 0.6 � 0.3 0.0 � 0.0 2.0 � 1.4 0.7 � 1.6



achieved with DLS supports the theory that biological andmechanical issues were combined in delayed fracture healing ofthe cis-cortex.

A ‘‘jam’’ at the minute gap between the pin and sleeves or evenwear particles were not observed when DLS screws were removedand inspected. It can well be, that the inner screw peg is in contactwith the inner wall of the screw sleeve during loading. But this canonly be in one direction. For example, in a gap model axial load onthe extremity will cause that the pegs will hit the inner sleeve wallat the side away from the fracture. In the meantime, loads in allother directions will create micromotion at the fracture gap tostimulate healing. Instead of jamming rather cyclic loading willkeep the micromotion afloat. Sliding of the inner core along its longaxis within the outer sleeve was also not possible, since the innerscrew peg and the outer threaded sleeve are welded together at thefar end of the peg’s threaded head. The weld is done radial at thebottom of the sleeve thread.

The question for the ideal fracture gap in biological fracturehealing32 when bone fragments are only brought into appositionbut not under compression could be answered in this study foroblique fractures. Maximal apposition with bone contact offragments still seems to be the best option and stimulation forbone healing and resulted in the highest torsion stiffness valuessupporting earlier claims.38 DLS screws allow micromovement of0.2 mm in each direction. Therefore, the proximal and distalfragments are able to narrow the fracture end down for 0.4 mm. Itseems that this range of movement is optimal to enhance callusformation at the cis-cortex. In oblique fractures the dynamisationof the trans-cortex (although lower), however, may bring too muchaxial load on the tips of the bone fragments, since 4/6 were brokenout in G1 with the 0 mm gap. This may be less critical if aftersurgery immediate full weight bearing is delayed as is routine inhuman patients.

Conclusion

In summary it may be concluded from this study that a goodreduction of bone fragments at the time of fracture fixation is stillthe best option and will result in superior callus stiffness at earlytime points, at least in oblique fractures. Dynamisation of thefracture gap using DLS will lead to a more even callus distributionwhich ultimately will also lead to better stiffness at early timepoints and increased bone deposition between fracture fragmentsat 12 weeks postoperatively.

Conflict of interest statement

The manuscript is an extract of the thesis of Dr. Nico Lagerpusch(Vetsuisse Faculty, University of Zurich).

The study was financed by Synthes, GmbH, Solothurn,Switzerland.

Acknowledgements

The authors thank our histology technicians Kathi Kampf,Katalin Zlinszky and Sabina Wunderlin for their outstandinghistology specimens and med.vet. Henning Richter for graphicdesign of the figures. Also contribution of the industrial partner(Synthes GmbH), who funded the entire study, is highly acknowl-edged.

References

1. Wagner M. Advantages and disadvantages of locked plating. Orthopade2010;39:149–59.

2. Sommer C, Bereiter H. Actual relevance of minimal invasive surgery in fracturetreatment. Therapeutische Umschau 2005;62:145–51.

3. Hertel R, Eijer H, Meisser A, Hauke C, Perren SM. Biomechanical and biologicalconsiderations relating to the clinical use of the Point Contact-Fixator—evalua-tion of the device handling test in the treatment of diaphyseal fractures of theradius and/or ulna. Injury 2001;32(Suppl. 2):B10–4.

4. Huang P, Tang P, Yao Q. Comparison of LCP and locked intramedullary nailingfixation in treatment of tibial diaphysis fractures. Zhongguo Xiu Fu Chong JianWai Ke Za Zhi 2007;21:1167–70.

5. Haas NP. Callus modulation – fiction or reality? Chirurg 2000;71:987–8.6. Henderson CE, Bottlang M, Marsh JL, Fitzpatrick DC, Madey SM. Does locked

plating of periprosthetic supracondylar femur fractures promote bone healingby callus formation? Two cases with opposite outcomes. Iowa OrthopaedicJournal 2008;28:73–6.

7. Lujan TJ, Henderson CE, Madey SM, Fitzpatrick DC, Marsh JL, Bottlang M. Lockedplating of distal femur fractures leads to inconsistent and asymmetric callusformation. Journal of Orthopaedic Trauma 2010;24:156–62.

8. Egol KA, Kubiak EN, Fulkerson E, Kummer FJ, Koval KJ. Biomechanics of lockedplates and screws. Journal of Orthopaedic Trauma 2004;18:488–93.

9. Strauss EJ, Schwarzkopf R, Kummer F, Egol KA. The current status of lockedplating: the good, the bad, and the ugly. Journal of Orthopaedic Trauma2008;22:479–86.

10. Kubiak EN, Fulkerson E, Strauss E, Egol KA. The evolution of locked plates.Journal of Bone and Joint Surgery 2006;88(Suppl. 4):189–200.

11. Uhthoff HK, Poitras P, Backman DS. Internal plate fixation of fractures: shorthistory and recent developments. Journal of Orthopaedic Science 2006;11:118–26.

12. Claes LE, Heigele CA. Magnitudes of local stress and strain along bony surfacespredict the course and type of fracture healing. Journal of Biomechanics1999;32:255–66.

13. Claes LE, Heigele CA, Neidlinger-Wilke C, Kaspar D, Seidl W, Margevicius KJ,et al. Effects of mechanical factors on the fracture healing process. ClinicalOrthopaedics and Related Research 1998:S132–47.

14. Kaspar D, Seidl W, Neidlinger-Wilke C, Claes L. In vitro effects of dynamic strainon the proliferative and metabolic activity of human osteoblasts. Journal ofMusculoskeletal and Neuronal Interactions 2000;1:161–4.

15. Perren SM, Cordey J. Tissue differences in fracture healing (author’s transl).Unfallheilkunde 1977;80:161–4.

16. Perren SM. Physical and biological aspects of fracture healing with specialreference to internal fixation. Clinical Orthopaedics and Related Research1979:175–96.

17. Perren SM. Evolution of the internal fixation of long bone fractures. Thescientific basis of biological internal fixation: choosing a new balance betweenstability and biology. Journal of Bone and Joint Surgery British Volume2002;84:1093–110.

18. Kenwright J, Richardson JB, Cunningham JL, White SH, Goodship AE, AdamsMA, et al. Axial movement and tibial fractures. A controlled randomisedtrial of treatment. Journal of Bone and Joint Surgery British Volume1991;73:654–9.

19. Klein P, Schell H, Streitparth F, Heller M, Kassi JP, Kandziora F, et al. The initialphase of fracture healing is specifically sensitive to mechanical conditions.Journal of Orthopaedic Research 2003;21:662–9.

20. Claes L. Biologie und Biomechanik der Osteosynthese und Frakturheilung.Orthopadie und Unfallchirurgie up2date 2006;01(04):329–46.

21. Augat P, Burger J, Schorlemmer S, Henke T, Peraus M, Claes L. Shear movementat the fracture site delays healing in a diaphyseal fracture model. Journal ofOrthopaedic Research 2003;21:1011–7.

22. Stoffel K, Dieter U, Stachowiak G, Gachter A, Kuster MS. Biomechanical testingof the LCP – how can stability in locked internal fixators be controlled? Injury2003;34(Suppl. 2):B11–9.

23. Gautier E, Sommer C. Guidelines for the clinical application of the LCP. Injury2003;34(Suppl. 2):B63–76.

24. Sturmer KM. Elastic plate osteosynthesis, biomechanics, indications and tech-nique in comparison with rigid osteosynthesis. Unfallchirurg 1996;99:816–29.

25. Bottlang M, Doornink J, Fitzpatrick DC, Madey SM. Far cortical locking canreduce stiffness of locked plating constructs while retaining construct strength.Journal of Bone and Joint Surgery 2009;91:1985–94.

26. Gardner MJ, Nork SE, Huber P, Krieg JC. Stiffness modulation of locking plateconstructs using near cortical slotted holes: a preliminary study. Journal ofOrthopaedic Trauma 2009;23:281–7.

27. Dobele S, Horn C, Eichhorn S, Buchholtz A, Lenich A, Burgkart R, et al. Thedynamic locking screw (DLS) can increase interfragmentary motion on the nearcortex of locked plating constructs by reducing the axial stiffness. Langenbeck’sArchives of Surgery 2010;395:421–8.

28. von Rechenberg B, Leutenegger C, Zlinsky K, McIlwraith CW, Akens MK, Auer JA.Upregulation of mRNA of interleukin-1 and -6 in subchondral cystic lesions offour horses. Equine Veterinary Journal 2001;33:143–9.

29. Pongratz MC. Evaluation von zwei verschiedenen Osteotomiemethoden ineiner experimentellen Studie an Schafen. Vetsuisse Faculty Zurich UniversityZurich 2008:1–54.

30. Waibel A. Osteotomie: Der Einfluß des Sageblattes auf die Knochenheilung. Zurich:Vetsuisse University Zurich; 2005. p. 5–78.

31. Bottlang M, Lesser M, Koerber J, Doornink J, von Rechenberg B, Augat P, et al. Farcortical locking can improve healing of fractures stabilized with locking plates.Journal of Bone and Joint Surgery 2010;92:1652–60.

32. Claes L, Augat P, Suger G, Wilke HJ. Influence of size and stability of theosteotomy gap on the success of fracture healing. Journal of OrthopaedicResearch 1997;15:577–84.



33. Sturmer K. Histologie und Biomechanik der Frakturheilung unter den Bedin-gungen des Fixateur externe. Hefte Unfallheilkunde 1988;200:233–42.

34. Olerud S, Danckwardt-Lilliestrom G. Fracture healing in compression osteo-synthesis in the dog. Journal of Bone and Joint Surgery British Volume1968;50:844–51.

35. Noordeen MH, Lavy CB, Shergill NS, Tuite JD, Jackson AM. Cyclical micromove-ment and fracture healing. Journal of Bone and Joint Surgery British Volume1995;77:645–8.

36. Claes L, Eckert-Hubner K, Augat P. The fracture gap size influences the localvascularization and tissue differentiation in callus healing. Langenbeck’sArchives of Surgery 2003;388:316–22.

37. Ahmad M, Nanda R, Bajwa AS, Candal-Couto J, Green S, Hui AC. Biomechanicaltesting of the locking compression plate: when does the distance between boneand implant significantly reduce construct stability? Injury 2007;38:358–64.

38. Egger EL, Gottsauner-Wolf F, Palmer J, Aro HT, Chao EY. Effects of axialdynamization on bone healing. Journal of Trauma 1993;34:185–92.


Documents

The dynamisation of locking plate osteosynthesis by means of dynamic locking screws (DLS)—An experimental study in sheep