Knee Stability Presentation O-264 S267

IN-VIVO EVALUATION OF KNEE DYNAMIC STABILITY IN ANATOMICAL DOUBLE-BUNDLE ACL RECONSTRUCTION

Nicola Lopomo (1,2), Simone Bignozzi (1), Stefano Zaffagnini (1), Sandra Martelli (1), Andrea Visani (1), Maurilio Marcacci (1)

1. Laboratorio di Biomeccanica, Istituti Ortopedici Rizzoli, Bologna, Italy;

2. Dipartimento di Bioingegneria, Politecnico di Milano, Milano, Italy

Introduction The pivot-shift clinical test is commonly used for the qualitative evaluation of knee dynamic stability [Hoshino, 2007]. With the aim of controlling the static antero-posterior laxity as also tibial subluxation, many surgeons have started performing anatomical double-bundle (DB) ACL reconstructions [Zelle, 2007], since it seems to have superior outcomes with respect to the Lachman’s test and pivot-shift phenomenon, but a quantitative assessment about the global laxity is still not provided. The aim of this study was thus to quantify intra-operatively the improvements in knee dynamic stability, compared to standard evaluations, due to an anatomical DB ACL reconstruction, paying attention to pivot-shift test. Methods Fifteen patients (32.8±7.6 y) that consecutively underwent anatomical DB ACL reconstruction, were included in this preliminary study. To evaluate the joint stability we used a navigation system focused in kinematic acquisitions [Zaffagnini, 2006]. The operating surgeon performed manually both static clinical tests at maximum force (valgus/varus (VV) rotation at 0° and 30° of flexion, internal/external (IE) rotation at 30° and 90°, antero/posterior (AP) displacement at 30° and 90°) and dynamic pivot-shift test. Anatomical DB ACL reconstruction was, then, performed [Yagi, 2002] and the same kinematic tests were re-acquired. The surgeon was blinded on test results. Statistical analysis was performed comparing data derived from each stress test (fig. 1) using paired Student’s t-test (p=0.05) For what concerns pivot-shift test the decomposition of AP translation, IE and VV rotations with respect to flexion/extension angle.

Figure 1. Static Test Results.

For each decomposition we evaluated the areas included by the curves (the ‘hysteresis’ of the unstable joint) and the difference in the coupled peaks before and after the surgery at a specific flexion angle. A typical result is shown in fig. 2. Results As shown in fig. 1. all static laxities were significantly reduced (p<0.01). Interesting results have been obtained with the analysis of pivot-shift test: coupled peaks in AP translation, at 25.0±1.8º of flexion, are reduced from -11.3±4.7mm to -3.1±3.1mm (p<0.01) after reconstruction as also in IE rotation are reduced from 10.8±4.7º to 2.6±4.9º (p<0.01) after surgery. The analysis of the area highlighted a huge recovery of the dynamic stability of the joint, from 211.5mm*deg to 57.3mm*deg (p<0.01) (Fig. 2).

Figure 2. Example of pivot-shift decomposition. Discussion Over the good outcome for what concerns static laxities, the navigated protocol showed that all ACL-deficient knees had a positive pivot-shift test before the surgery with huge value in the tibial subluxation, while anatomical DB seems to eliminate both static anterior/posterior instability (Lachman test) and to control pivot-shift reducing tibial translation and controlling tibial rotation. References Hoshino et al, Am J Sports Med, 35:1098-104, 2007. Yagi et al, Am J Sports Med, 230:660-6, 2002. Zaffagnini et al, Knee Surg Sports Traumatol Arthrosc, 14:811-6, 2006. Zelle et al, J Am Acad Orthop Surg, 15:87-96, 2007.

16th ESB Congress, Oral Presentations, Wednesday 9 July 2008 Journal of Biomechanics 41(S1)