Effects of Rotation and Osteotomy Angulation on Patellar Tendon Insertion Position during Circular Tibial Tuberosity Osteotomy Gian Luca Rovesti 1 , DVM, Diplomate ECVS, Nikola Katic 2 , DVM, Boris Dalpozzo 1 , DVM, Francesco Dondi 3 , DVM, PhD, and Gilles Dupr ´ e 2 , DVM, Diplomate ECVS 1 Clinica veterinaria M. E. Miller, Cavriago, Italy, 2 Clinic for Small Animal Surgery, Ophthalmology, Dentistry and Rehabilitation, Department for Small Animal and Horses, Veterinary Medicine University of Vienna, Vienna, Austria and 3 Department of Veterinary Medical Sciences, University of Bologna, Bologna, Italy Corresponding Author Gian Luca Rovesti, DVM, Diplomate ECVS, Via della Costituzione 10-42025, Cavriago (RE), Italy E-mail: grovesti@clinicamiller.it Received March 2012 Accepted September 2012 DOI:10.1111/j.1532-950X.2012.01079.x Objective: To evaluate the influence of rotation of the tibial tuberosity (TT) in the sagittal plane and angulation of osteotomy in the frontal plane (FPA) on the displacement of patellar tendon (PT) insertion. Study Design: Ex vivo biomechanical study. Sample Population: Canine tibiae (n = 36). Methods: Nine groups of 4 tibiae each had a circular osteotomy of the TT at an FPA from –20 ◦ to +20 ◦ with increments of 5 ◦ for each group. The osteotomized TT was rotated by angles of rotation (AORs) of 10 ◦ , 20 ◦ , or 30 ◦ in the sagittal plane. The craniocaudal (CCD), distoproximal (DPD), and mediolateral (MLD) displacements of a marker located at the PT insertion on the TT were evaluated radiographically. Differences between groups were analyzed by Mann–Whitney U test and Friedman 2-way ANOVA. Results: There was a significant correlation between the AOR and CCD. A positive FPA resulted in a high CCD and lateral shift of the TT at every AOR. Performing an osteotomy at an FPA of 0 ◦ produced the maximum amount of DPD. Conclusions: FPA and AOR during circular osteotomy of the TT influence the final displacement of the PT insertion in all 3 planes. Rupture of the cranial cruciate ligament (CrCL) is one of the most common causes of pelvic limb lameness in dogs. 1, 2 Many causal mechanisms exist to explain CrCL rupture, 3–6 and many surgical techniques for subsequent stifle stabiliza- tion have been proposed. 7–12 Since Slocum’s investigations into the forces acting around the stifle joint 4 and the intro- duction of the tibial plateau leveling osteotomy (TPLO) in 1993, 13 increasing interest has emerged in the use of tibial osteotomies to treat CrCL insufficiency in dogs. 14–18 Tibial tuberosity advancement (TTA) was developed using a biomechanical approach that identified the quadriceps muscle as the main force acting on the stifle joint, leading to an overall force vector parallel to the patellar tendon (PT). The aim of the TTA technique is to modify the angle between the PT and tibial plateau (TP) by advancing the tibial tuberosity (TT), thus obtaining a PT-TP angle of 90 ◦ with the stifle at 135 ◦ of flexion. 19 This is achieved by an osteotomy of the tibial crest and insertion of a titanium cage in the osteotomy site. 14 Healing time for the gap be- tween the advanced TT and the tibial metaphysis in course of TTA was reported to be >14 weeks in 41% of cases 20 and Study was performed at the Veterinary Medicine University of Vienna and at the Clinica Miller in Cavriago and Statistical Evaluation at the University of Bologna. >12 weeks in 16% of cases. 15 Although it was shown there is no need for a cancellous bone graft over the gap, 20 this view was subsequently questioned. 21 Unfortunately, none of the current osteotomy techniques limits progression of degenerative joint disease (DJD), and to date, no technique has emerged as superior. 19 Reported complications for all techniques usually reflect the surgeon’s ability level and the technical difficulties inherent to the procedure. 19 A new technique with the same rationale as TTA, called circular tibial tuberosity osteotomy (cTTA) was recently described. 22 It is performed by a circular osteotomy of the TT followed by a craniad rotation. The main theoretical ad- vantage of the technique is that it allows a continuous degree of correction, with no need for standard cage sizes. Rather, the osteotomy results in continuous contact between the TT and the tibial metaphysis, without creating a gap at the osteotomy site. This makes interfragmentary compression possible and therefore obviates the need for cancellous bone grafting. No further details were provided 22 ; however, the angle between the frontal plane of the tibia and the plane of the osteotomy may profoundly affect the direction in which the bone will move during rotation. 19, 23 Our purpose was to evaluate the influence of the an- gulation of osteotomy in the frontal plane (FPA) of the TT Veterinary Surgery 42 (2013) 51–59 C  Copyright 2012 by The American College of Veterinary Surgeons 51