2013 ISAKOS ABSTRACTS e83

flexion, it was defined as a substantially translated-lateralshift (STLS) type. Finally, among patients with a lesstranslated patella when the average value of % POCDs(0�-50�) was larger than the average + 1SD of those in HV,it was defined as a less translated-lateral path (LTLP) type.When the value was smaller, it was defined as a lesstranslated-central path (LTCP) type.Results: Each average value of % MT and % POCDs(0�e50�) in patients with RPD and those �SD in HV were14.0 and 15.6 in STMS, 14.4 and 25.3 in STLS, 6.4 and 18.0in LTLP, 6.1 and 3.9 in LTCP and 5.5 � 2.8 and 6.4 � 10.9in HV, respectively. Each average value of % POCD at0� through 50� were 22, 18, 16, 14, 12 and 11 in STMS, 22,20, 24, 26, 30 and 31 in STLS, 18, 19, 18, 17, 18 and 18 inLTLP, 8, 4, 2, 2, 4 and 4 in LTCP and 10, 8, 6, 5, 5 and 5 inHV, respectively. Twenty-nine knees (53%) were classifiedas STMS type, 10 (18%) as STLS type, 9 (18%) as LTLPtype, 4 (7%) as LTCP type and 3 (5%) were unclassified.Discussion: Our approach based on patellar trackingcould classify 95% of the patients, suggesting usefulness ofthis classification system. While the patellae in patientswith RPD are generally believed to move into mediallywith knee flexion to be treated with a medial stabilizationprocedure including medial patella-femoral ligamentreconstruction (MPFLR), it was striking that only half ofthe patients showed this tracking type (STMS). It wasworthy of notice that about 20% of the patellae movedlaterally with knee flexion (STLS), which were regarded asthe tracking pattern of habitual dislocation. Those mayneed MPFLR as well as lateral release. The LTLP type mightbe regarded as a kind of mild type of RPD because thepatellae showed less change of mediolateral translation inspite of lateral tracking. While less than 10% of the subjectsshowed a very similar tracking pattern to that of thenormal knee (LTCP), those may be good candidates forconservative treatment in view of patellar tracking. Thus,we should not manage RPD as a single entity in the patellardisorder but take the different subtypes of RPD intoaccount at the time of treating them.Conclusion: Patients with RDP can be classified into thefour types based on the patellar tracking.

Paper #80: Tibial Rotational Osteotomy and DistalTuberosity Transfer for Obligatory CongenitalPatella Dislocation e Surgical Technique and SevenYear Follow-Up MICHAEL DREXLER, MD, CANADAPRESENTING AUTHOR

TIM DWYER, MBBS, CANADADE JUAN NG, FRACS(ORTH), AUSTRALIA

NIKOLAUS REISCHL, MD, CANADAMEIR MARMOR, MD, USAFAHAD GULAM ATTAR, FRCS (TR & ORTH), MRCSED, MBCHB,UNITED KINGDOM

JOHN CHARLES CAMERON, MD, FRCSC, CANADA $ HollandOrthopaedic & Arthritic Centre, Toronto, Ontario, Canada

SUMMARYCongenital dislocation of the patella is a rare condition

with two clinical syndromes: fixed and obligatory disloca-tion of the patella. A series of patients presenting with

obligatory congenital patella subluxation in combinationwith excessive external tibial torsion >45�, underwenttibial derotation osteotomy and tibial tuberosity transferachieving a satisfactory outcome in terms of pain relief.

ABSTRACT DATAIntroduction: Congenital dislocation of the patella isa rare condition with two clinical syndromes: fixed andobligatory dislocation of the patella. In addition to short-ened quadriceps muscles, hypoplastic patellae and hypo-plastic trochlear grooves, excessive external tibial torsion(EETT) is a common finding, and EETT >30� is known tocontribute to the progression of knee instability and oste-oarthritis. This study evaluates the long term outcomes ofpatients undergoing simultaneous tibial derotation osteot-omy and tibial tuberosity transfer for the treatment ofobligatory congenital dislocation of the patella.Methods: Between 1998 and 2011, a combined tibialderotation osteotomy and tibial tuberosity transfer wasperformed in twelve patients (fifteen knees) withcongenital patella subluxation in combination with EETT.Clinical and functional evaluation was carried out usingpreoperative and postoperative Knee Society Score (KSS),the Western Ontario and McMaster Universities Osteoar-thritis Index (WOMAC) questionnaire and the short form12 (SF-12), as well a visual analogue score (VAS) painscale.Results: The mean follow-up period was 84 months(range, 15 to 156). The mean patient age was 36 years(range, 19 to 70 years). Patients presented with a meanpre-operative external tibial torsion of 620 (range,55-70�), with an average rotational correction of 350(range, 30-45�) after surgery. Significant improvementwas found in the KSS part I (p < 0.0001) (from37.3�14.2 to 89�11 points) and KSS part II (p < 0.0001)(from 25.2�26 to 84.6�13.9 points). Quality of life, asmeasured using the SF-12 outcome, also improvedsignificantly (p < 0.0001), as did all WOMAC question-naire score subscales (p < 0.0001). The VAS preoperativestatus for pain improved from 8.8�1.9 to 2.4�1.5. Twopatients had a nonunion of the tibial osteotomy site; onepatient required bone grafting, whilst another patientrequired revision to TKA.Conclusions: A series of patients presenting withobligatory congenital patella subluxation in combinationwith excessive external tibial torsion >45�, underwenttibial derotation osteotomy and tibial tuberosity transferachieving a satisfactory outcome in terms of pain relief andimproved function. We recommend this procedure beperformed in patients with congenital patella dislocationwho have associated EETT >45�.

Paper #81: Isolated Medial Patellar Femoral Liga-ment Reconstruction for Recurrent Patella Disloca-tion: A Prospective Cohort Study MARIO RONGA, MD,PROF., ITALY PRESENTING AUTHOR

FRANCESCO OLIVA, MD, PHD, ITALYUMILE GIUSEPPE LONGO, MD, MSC, PHD, ITALYNICOLA MAFFULLI, MD, PHD, MS, FRCS(ORTH), UNITED KINGDOM $