amount of osseous ingrowth, mineralization, and matu-ration of healing tissue and is bone-specific1-2. Betterunderstanding of the quality and quantity of newly-formed mineralized tissue and surrounding host bone iscrucial to our understanding of tendon graft to bonetunnel healing. We aimed to develop a method for theassessment of the quantity and quality of newly-formedmineralized tissue along bone tunnel after ACL recon-struction using micro-CT. Previous study reported thatthe application of calcium phosphate3 and mensenchy-mal stem cells (MSC)4 enhanced the osteointegration oftendon graft. We hypothesized that the combined treat-ment with both calcium phosphate and MSC has syner-gistic effect on tendon graft to bone tunnel healing. Wehence also reported our preliminary results of the mi-cro-CT analysis of changes of mineralized tissue alongthe bone tunnel after treatment with calcium phosphateand MSC.Methods: The ACL of rabbits were bilaterally recon-structed with semitendinous grafts. The tendon graft waseither untreated, hybridized with calcium phosphate,coated with MSC in fibrin glue or both. The changes inBMD/bone microarchitecture at the interface were mon-itored by �CT at week 0, 2 and 6. The specimen wasscanned perpendicular to the long bone axis covering theentry and exit of bone tunnel. To quantify the time- andregional-dependent changes of newly-formed mineral-ized tissue, a circular 2.7mm region of interest (ROI)inside the bone tunnel was chosen and 3-dimensionallyreconstructed using the built-in software after threshold-ing. BMD/bone microarchitectural parameters were cal-culated for ROI for the whole femoral and tibial tunnels.Results: For the femoral tunnel, calcium phosphate�MSCgroup has lower connectivity density, trabecular number,thickness and BMD as well as higher trabecular separa-tion compared to the MSC-only group. The differenceswere statistically significant for all these parameters(p�0.05) except trabecular thickness. There was no stat-ically significant difference in all these parameters be-tween the two groups at tibia though the calciumphosphate�MSC group showed higher connectivity den-sity, trabecular number, trabecular thickness and BMDand lower trabecular separation.Conclusion/Discussion: We have developed a methodfor the assessment of bone quality and quantity alongbone tunnel. Our preliminary result showed that thecombined treatment with calcium phosphate and MSChas negative effect on the amount and microarchitectureof mineralized tissue ingrowth at femur. Mineralizationof tendon graft might have harmful effect on healing.The effect might be bone-specific as these changes werenot observed at tibia. Further studies would be done to

confirm this observation as the sample size was small.Besides osseous ingrowth and mineralization, collagenfiber connection between bone and graft and graft re-modeling are also important to healing and hence theoverall mechanical strength of the complex. Histology isrequired to further confirm the effect of calcium phos-phate and MSC on ACL reconstruction.Acknowledgement: This study was supported by HongKong Research Grant Council Earmarked Grant 06-07(4497/06M).References:

1. Arnoczky SP, Torzilli PA, Warren RF, Alien AA.(1988) Biologic fixation of ligament protheses andaugmentation: an evaluation of bone ingrowth inthe dog. Am J Sports Med,16,106-12.

2. Grassman SRM, McDonald DB, Thornton GM,Shrive NG, Frank CB. (2002) Early healing pro-cesses of free tendon grafts within bone tunnels isbone-specific: a morphological study in a rabbitmodel. The Knee; 9, 21-26.

3. Mutsuzaki H, Sakane M, Nakajima H, Ito A, hattoriS, Miyanaga Y, Ochiai N, Tanaka J. (2004) Calci-um-phospahte-hybridized tendon directly promotesregeneration of tendon-bone insertion. J BiomedMater Res A, 70(2), 319-327.

4. Lim JK, Hui J, Li L, Thambyah A, Goh J, Lee EH.(2004) Enhancement of tendon graft osteointegra-tion using mesenchymal stem cells in a rabbitmodel for anterior cruciate ligament reconstruction.Arthroscopy, 20(9), 899-910.

Paper 127: Tunnel Widening Following AnteriorCruciate Ligament Reconstruction: A Study in SheepRUPERT MELLER, MD, GERMANY, PRESENTING AUTHOR

CHRISTOPH HURSCHLER, MD, GERMANY

FRANK WITTE, PHD, GERMANY

BEATRIX DREYMANN, RESIDENT, GERMANY

ALEXANDRA NEDDERMANN, MD, GERMANY

CHRISTIAN KRETTEK, PROF., GERMANY

EMAR WILLBOLD, PHD, GERMANY

ABSTRACTBackground: A common clinical concern following an-terior cruciate ligament reconstruction is expansion ofthe bone tunnels as seen radiographically. The etiologyand clinical relevance of this phenomenon remain un-clear.

It was our aim to investigate 1) the diagnostic powerof plain x-rays versus computed tomography, 2) to ana-lyze the relationship of tunnel enlargement and jointstability and 3) to look for histological changes associ-ated with tunnel widening.

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We hypothesized, that 1) tunnel widening is mostaccurately diagnosed by computed tomography, 2) tun-nel widening results in increased anteroposterior transla-tion and that 3) there are certain histological changesassociated with this phenomenon.Methods: 30 skeletally immature sheep with an age offour months underwent an ACL reconstruction with asoft tissue graft. Graft fixation was achieved using theEndobutton and Suture Washer devices. The animalswere sequentially sacrificed 3, 6, 12 and 24 weeks fol-lowing surgery. After sacrifice, each ACL reconstructedknee was radiographically examined by plain x-rays andcomputed tomography. Anteroposterior translation wasexamined using an UFS roboter. The bone surroundingthe tunnel was histologically analyzed. Statistical analy-sis included 1-way ANOVA, student-t and Pearson cor-relation coefficient tests.Results: A tunnel enlargement of 20% or more waspresent in 9 animals on the femoral site. Measurementson plain x-rays systematically underestimated the trueamount of tunnel widening as determined by the CTscan. Animals with tunnel widening did not demonstratean increased anteroposterior translation. However, wid-ening of the femoral tunnel was significantly associatedwith a higher stiffness of the graft (p�0.05) and a hy-pertrophy of the graft throughout the remodeling process.The histological analysis of the bone tunnels demon-strated an increase of bone volume in animals withtunnel enlargement. However, no statistically significantcorrelation could be found between the number of oste-oclasts and the presence of tunnel widening.Conclusion: In this large animal model of ACL recon-struction, animals with significant tunnel widening didnot suffer anteroposterior instability. In contrast, in thoseanimals the tunnel widening was associated with a sig-nificantly higher stiffness of the graft. The surroundingbone systematically responded by an increase of bonevolume.Clinical Relevance: Corresponding to the current opin-ion in humans, tunnel widening is not associated withknee instability in this animal study. Increased graftstiffness may play a role in the etiology of tunnel wid-ening. Our data support the biomechanical concept ofthis phenomenon. A grading scheme is proposed. Furtherresearch is needed.

Paper 128: Comparison of Engineered BMP Peptide-Coated and Non-Coated Bioresorbable InterferenceScrews on Tendon-Bone Healing in an Ovine ModelYAN LU, MD, USA, PRESENTING AUTHOR

MARK MARKEL, DVM, PHD, USAWILLIAM L. MURPHY, PHD, USA

BRETT NEMKE, BS, USAJAE-SAM LEE, PHD, USABEN K. GRAF, USA

ABSTRACTTendon grafts plus bioresorbable interference screws

transplanted into bone tunnels have been widely used foranterior cruciate ligament (ACL) reconstruction. How-ever, interference screw fixation has the potential tonegatively influence tendon bone healing. The purpose ofthis study was to determine whether a bioresorbableinterference screw coated with an engineered peptidederivative of bone morphogenetic protein-2 (eBMP2)improved tendon-bone healing compared to the screwwithout sub-BMP coating. We hypothesized that theeBMP2-coated bioresorbable interference screw wouldresult in better biomechanical and histologic outcomesfor tendon bone healing.

Fourteen mature female sheep were utilized in thestudy. In each of the 14 sheep, each stifle was random-ized to either receive a eBMP2-coated interference screwor non-coated interference screw (n�14/treatment). Thesheep were euthanized at 6 weeks after surgery. Eightsheep were subjected to biomechanical testing for peakload at failure and stiffness, and 6 sheep were used forhistologic analysis according to a semiquantitative scor-ing scale. The Student’s paired t-test and the Kruskal-Wallis test were used for statistical analysis for mechan-ical testing data and the histologic subjective scoresbetween the two treatment groups, respectively.

Peak load at failure for the eBMP2-coated interferencescrew group (mean�SD: 449.3�84.7 N) was not signif-icantly different from the non-coated group (421.0�61.8 N) (p�0.22). Stiffness for the eBMP2-coated inter-ference screw group (157.3�39.6 N/mm) had a trend tobe greater than that for the non-coated group(140.6�20.3 N/mm) (p�0.12). Histologic analysis dem-onstrated that the tendons in the eBMP2-coated interfer-ence screw group had better new bone formation andmore mesenchymal cell proliferation (pre-osteoblasts) atthe tendon bone interface than the non-coated group(p�0.02).

The results of this study demonstrated that the eBMP2-coated bioreorbable screw significantly improved tendonbone healing in this ovine model.

This eBMP2 coating material may be useful as acomponent of other bone healing approaches.

Paper 129: Injectable Hydrogel to Enhance TendonGraft-Bone Tunnel Healing in Anterior Cruciate Lig-ament Reconstruction CHIH-HWA CHEN, MD, TAIWAN,PRESENTING AUTHOR

e410 ABSTRACTS