Increased Posterior Tibial Slope is Associated with ACL Graft and Contralateral ACL Injury after ACL...

2013 ISAKOS ABSTRACTS e85

(1) In the first part of the study the MPFL has beenloaded to failure after preconditioning with 10 cyclesbetween 5 and 20 N. During load to failure tests thefollowing parameters have been evaluated: Stiffness, Yieldload and Maximum load to failure.(2) In the second part of the study MPFL reconstruction

with the middle third of the quadriceps tendon has beenperformed. A 10-mm wide, 3-mm thick and 9-cm longstrip of quadriceps tendon was prepared. The tendon stripwas left attached at the patella and diverged 90� under-neath the prepatellar tissue. At the medial boarder of thepatella the tendon strip was fixed with two No2 non-resorbable sutures. The free part of the tendon strip hasbeen fixed in the clamp and the patella has been positionedin the fixation device identically to the intact MPFL testing.The constructs have been preconditioned with 10 cyclesbetween 5 and 20 N. Following preconditioning theconstructs were cyclically loaded 1000 times between 5 and50 N. During cyclic testing the maximum elongation hasbeen measured. After cyclic testing the constructs havebeen loaded to failure. The following parameters have beeninvestigated during the load to failure tests: Maximumelongation after 1000 cycles, Stiffness, Yield load andMaximum load to failure.For statistical analysis we used a Wilcoxon Rank test. The

significance was set at p<0.05.Results: (1) During the load to failure tests of the orig-inal MPFL the following results have been measured:Stiffness: 29.38 N/mm (+9.75), Yield load: 167.83 N(+80.01) and Maximum load to failure: 190.66 N (+ 82.8).(2) Maximum elongation after 1000 cycles was 2.09

mm (+0.75). In the load to failure testing of the quadri-ceps tendon reconstruction group we obtained thefollowing results: Stiffness: 33.6 N/mm (+.6.78), Yieldload: 147.08 N (+65.09) and Maximum load to failure:204.96 N (+77.79).There were no significant differences in all the tested

parameters between the intact MPFL and the recon-structed group using quadriceps tendon (Stiffness:p¼0.15, Yield load: p¼0.24 and Maximum load to failurep¼0.69).Discussion: The results of the present study support ourinitial hypothesis that the MPFL reconstruction techniqueusing a strip of quadriceps tendon demonstrated compa-rable biomechanical results to the intact MPFL.To our knowledge the present study is also the first to

investigate the stiffness of the original MPFL.In a biomechanical study by Lenschow et al. the stiffness

of various MPFL reconstruction techniques usinghamstrings was found to be between 87 and 97 N/mm.This is nearly three times the amount of the intact MPFL.This unnatural increased stiffness could possibly result ina higher patellofemoral pressure during knee flexion.Therefore MPFL reconstruction using a strip of quadri-

ceps tendon seems to be a promising alternative to widelyused hamstring reconstruction techniques. Complicationsof hamstring reconstruction techniques like patellar frac-ture or irritations at the patellar fixation site as well as therisk for loss of motion and patellofemural OA (caused byincreased patellofemoral pressure) may potentially beminimized or prevented.

Clinical Relevance: The tested quadriceps reconstruc-tion technique of the MPFL shows sufficient primarystability with comparable biomechanical parameters to theintact MPFL. Therefore this technique seems to be aninteresting alternative to the common reconstructiontechniques using hamstring grafts with potential to mini-mize complications.

ACKNOWLEDGMENTThe study was supported by a grant from the OSM

Research Foundation.

Paper #83: Increased Posterior Tibial Slope is Asso-ciated with ACL Graft and Contralateral ACL Injuryafter ACL Reconstruction JUSTIN WEBB, MBBS, FRACS,AUSTRALIA PRESENTING AUTHOR

ETIENNE LECLERC, MD, AUSTRALIA

LUCY J. SALMON, PHD, AUSTRALIA

LEO A. PINCZEWSKI, FRACS, AUSTRALIA

JUSTIN P. ROE, FRACS, AUSTRALIA $ North Sydney Orthopaedic& Sports Medicine Centre, Sydney, NSW, Australia

SUMMARYAn increased PTS is associated with an increased inci-

dence of long term further ACL injury after ACL recon-struction to both the reconstructed and the contralateralknee.

ABSTRACT DATAIntroduction: ACL injury is multifactorial, but previousstudies have shown that an increased PTS can be a riskfactor for primary ACL injury. The Purpose of this study isto determine if an increased PTS also predisposes toa second injury after ACL reconstruction, either an ACLgraft rupture or a contralateral ACL rupture.Methods: Two hundred consecutive subjects with iso-lated ACL rupture who underwent primary ACL recon-struction with hamstring tendon autograft betweenOctober 1993 and March 1996 were enrolled in the study.Both the 15-year outcome was known and radiographicPTS was measureable in 181 subjects. This included 131intact graft/contralateral ACL, 31 ACL graft ruptures, 15contralateral ACL ruptures and 4 who sustained both ACLgraft and contralateral ACL injury. The PTS was measuredon a digitized lateral radiograph of the knee using theProximal Anatomical Axis (PAA).Results: An increased incidence of further ACL injurywas found in subjects with a PTS greater than 12� whencompared to subjects with a PTS less than 12� (56% vs25%; p¼0.007). The average PTS was 9.2�. The averagePTS for any re-injury was 9.7� compared to 8.8� for nofurther injury. The average PTS for both ACL graft andcontralateral ACL rupture was 12.6�.Conclusion: An increased PTS is associated with anincreased incidence of long term further ACL injury afterACL reconstruction to both the reconstructed and thecontralateral knee. PTS should be considered when coun-selling patients returning to sports after ACL reconstruc-tion.