This article appeared in a journal published by Elsevier. The attached copy is furnished to the author for internal non-commercial research and

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1 This article appeared in a journal published by Elsevier. The attached copy is furnished to the author for internal non-commercial research and education use, including for instruction at the authors institution and sharing with colleagues. Other uses, including reproduction and distribution, or selling or licensing copies, or posting to personal, institutional or third party websites are prohibited. In most cases authors are permitted to post their version of the article (e.g. in Word or Tex form) to their personal website or institutional repository. Authors requiring further information regarding Elsevier s archiving and manuscript policies are encouraged to visit:

2 Clinical Biomechanics 24 (2009) Contents lists available at ScienceDirect Clinical Biomechanics journal homepage: In vivo kinematics of anterior cruciate ligament deficient knees during pivot and squat activities Satoshi Yamaguchi a, *, Kazuyoshi Gamada b, Takahisa Sasho c, Hideyuki Kato d, Masaki Sonoda e, Scott A. Banks a a Department of Mechanical and Aerospace Engineering, University of Florida, 330 MAE-A P.O. Box , Gainesville, FL , USA b Department of Physical Therapy, Hiroshima International University, Hiroshima, Japan c Department of Orthopaedic Surgery, Graduate School of Medicine, Chiba University, Chiba, Japan d Department of Radiological Technology, Chiba University Hospital, Chiba, Japan e Orthopaedics and Sports Medicine, JFE Kawatetsu Hospital, Chiba, Japan a r t i c l e i n f o a b s t r a c t Article history: Received 29 February 2008 Accepted 5 August 2008 Keywords: Knee Kinematics Anterior cruciate ligament Pivot 3D 2D model registration Background: Knee kinematics during pivoting activities are not well studied, but might provide insight critical to understanding the pathology of the anterior cruciate ligament deficient knee. The purpose of this study was to compare in vivo kinematics during weight bearing pivot and squat activities in patients with unilateral anterior cruciate ligament deficient knees, and to contrast those kinematics with the uninjured contralateral knees. Methods: Eight unilateral anterior cruciate ligament deficient patients with a mean age of 41 (SD 7) years were enrolled. Anterior cruciate injury was confirmed by positive Lachman test and MRI. Lateral fluoroscopic images of pivot and squat activities were recorded for both anterior cruciate ligament deficient and contralateral knees. Three-dimensional tibiofemoral kinematics and centers of rotation for each knee were determined using 3D 2D model registration techniques. Findings: During pivoting, the tibia of the anterior cruciate ligament deficient knee was significantly more anterior than the contralateral knee during tibial neutral to internal rotation. The pivot activity showed lateral centers of rotation in both anterior cruciate ligament deficient and contralateral knees while squatting showed medial centers of rotation. Interpretation: This dynamic method might be useful to objectively characterize restoration of dynamic function in knees with various types of anterior cruciate ligament reconstructions. These results also indicate kinematics during squatting type activities cannot be extrapolated to predict knee kinematics during pivoting types of activities. Ó 2008 Elsevier Ltd. All rights reserved. 1. Introduction Ruptures of the anterior cruciate ligament (ACL) are common among athletes with approximately 80,000 injuries in the United States every year (Griffin et al., 2000). ACL injury often leads to kinematic changes in the knee, resulting in symptoms of instability (Scavenius et al., 1999), meniscal and chondral lesions (Tandogan et al., 2004), and osteoarthritic changes over time (Gillquist and Messner, 1999). Conservative treatment of these patients often is unsatisfactory (Hawkins et al., 1986), and reconstructive surgery typically is recommended for individuals hoping to return to competitive and recreational sports. In vivo studies of squatting and walking have shown increased tibial anterior translation, and altered tibial rotation in ACL deficient (ACLD) knees using a variety * Corresponding author. address: y-satoshi@mvb.biglobe.ne.jp (S. Yamaguchi). of methods, including MRI (Barrance et al., 2007; Logan et al., 2004), skin-mounted markers (Andriacchi and Dyrby, 2005), and electrogoniometers (Kvist and Gillquist, 2001). Cadaver studies have analyzed knee kinematics under rotatory loads in ACLD and reconstructed knees (Kanamori et al., 2002; Loh et al., 2003), and shown increased anterior tibial translations under internal rotatory loads in ACLD knees. A few studies have analyzed in vivo kinematics during pivoting (Georgoulis et al., 2007; Ristanis et al., 2003) using skin-mounted marker based video analysis, and reported increased range of axial tibial rotation. However, these in vivo studies did not report anteroposterior tibial translation during pivoting. Pivoting activities are of specific interest because they often cause subjective instability and giving way in ACLD patients. The pivot shift test, in which passive pivoting stress is applied to the knee, commonly is used as a passive non-weight-bearing method to predict the dynamic stability of ACLD and ACL reconstructed /$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi: /j.clinbiomech

3 72 S. Yamaguchi et al. / Clinical Biomechanics 24 (2009) knees. Weight-bearing kinematics of ACLD and healthy knees during pivoting activities, although directly relevant to ACL injury and the function of ligament reconstructions, remain little explored. Knee kinematics have been shown to differ between weightbearing and non-weight-bearing activities (Dyrby and Andriacchi, 2004; Johal et al., 2005), and between several different weightbearing activities (Banks and Hodge, 2004; Komistek et al., 2003) in healthy knees and knees with arthroplasty. However, these comparisons only are for sagittal plane activities and no studies have contrasted knee kinematics during non-sagittal plane activities such as pivoting. 3D 2D model registration techniques have been used to measure in vivo 3D kinematics of total knee arthroplasty (Banks and Hodge, 2004) and ACLD knees (Dennis et al., 2005; Li et al., 2006). The purpose of this study was to quantitatively compare in vivo kinematics during pivot and squat activities in patients with unilateral ACLD knees, and to contrast kinematics with the contralateral knees. We hypothesized that (1) Kinematics during weight-bearing pivoting recreates rotatory instability in the ACLD knee so that the tibia translates more anteriorly in the ACLD knee than the contralateral healthy knee, and (2) Because different passive structures are loaded in extension and flexion, pivoting near extension will exhibit kinematics different from squatting in both ACLD and contralateral healthy knees. 2. Methods 2.1. Patients Eight unilateral ACLD patients (four males and four females) with a mean age of 41 (SD 7) years were enrolled in this study. ACL injury was confirmed by positive Lachman test with apparent side-to-side difference as well as MRI findings. Exclusion criteria included other knee ligament injuries, history of contralateral knee injuries, age less than 20 years, or obvious osteoarthritic changes (IKDC grade C or D) on radiographs. Three patients with partial posterior medial meniscectomy, which were less than one-third of the meniscus, were included. A mean interval from injury to the testing was 108 (SD 108) months, and a mean KT-1000 sideto-side difference at manual maximal force was 5 (SD 1) mm. A mean Tegner activity score was 4 (SD 2). Three patients had the injury in the dominant legs, and the other five patients in the nondominant legs. All patients provided written consent before participating in this IRB approved study. into polygonal surface models (Geomagic Studio, Geomagic, Research Triangle Park, NC, USA). Anatomic coordinate systems were embedded in each bone model. A cylinder was fitted to the medial and lateral posterior condyles, and the flat-faces of the cylinder were aligned with the medial and the lateral epicondyles. The central axis of the cylinder was defined as the mediolateral axis, and the midpoint of the axis was defined as the femoral origin. The proximal/distal femoral axis was defined as the line parallel to the long axis of the distal femoral shaft and passing through the origin. The anteroposterior axis was formed as the cross product of the medial/lateral and proximal/distal axes. The tibial medial/ lateral axis was defined as a line bisecting the anterior/posterior halves of the tibial plateau and parallel to a line tangent to the posterior tibial plateau. The origin was defined as the midpoint of this axis, and the anteroposterior axis was defined as the line perpendicular to the mediolateral axis and parallel to the tibial plateau, passing through the origin. The proximal/distal axis was the cross product of the medial/lateral and anteroposterior axes. In vivo three-dimensional position and orientation of the femur and the tibia were determined using shape matching techniques, including previously reported techniques (Banks and Hodge, 1996; Fregly et al., 2005; Moro-Oka et al., 2007a), manual matching, and automated matching using nonlinear least-squares (modified Levenberg Marquardt) techniques. The bone model was projected onto the distortion-corrected fluoroscopic image, and its three-dimensional pose was iteratively adjusted to match its silhouette with the silhouette of the fluoroscopic image (Fig. 1). The best-case accuracy of this matching method was 0.53 mm for in-plane translation, 1.6 mm for out-of-plane translation, and 0.54 for rotations in a previous study (Moro-Oka et al., 2007a) Data processing and statistical analysis Knee kinematics were determined from the three-dimensional position of each bone model using Cardan angles (Tupling and Pierrynowski, 1987). Anteroposterior translation was defined as the motion of the tibial origin relative to the femoral origin along the tibial anteroposterior axis, consistent with previous studies in sports medicine. Kinematics were analyzed in 10 flexion increments for squatting. The pivoting activity was normalized from 2.2. Data acquisition and model-image registration Lateral fluoroscopic images of squat and pivot activities for both ACLD and contralateral knees were recorded at 15 frames per s. For weight-bearing pivoting, patients pivoted on the full weight-bearing knee from maximal tibial external rotation to maximal internal rotation with the knee slightly flexed and the foot flat on the floor. Squatting was performed from a position of bilateral stance to maximum squatting, with a widened stance to avoid overlapping of the contralateral knee on fluoroscopy. Patients were required to perform both activities in two seconds per one cycle, although the motion speed was not strictly controlled. Patients practiced the activities until comfortable, and then three cycles of each activity were recorded. Patients underwent CT scanning with a 0.5 mm slice pitch spanning approximately 75 mm above and below the knee joint line. Geometric bone models of the femur and the tibia were created from the images: the exterior cortical bone edges in the CT images were segmented using commercial software (SliceOmatic, Tomovision, Montreal, CA, USA) and these points were converted Fig. 1. Bone models were projected onto the distortion-corrected fluoroscopic image and their three-dimensional pose was iteratively adjusted to match with the fluoroscopic image.

4 S. Yamaguchi et al. / Clinical Biomechanics 24 (2009) averaging 2 mm from maximum tibial external rotation to neutral rotation, followed by 2 mm posterior tibial translation from neutral to maximum tibial internal rotation (Fig. 3a). The ACLD knees showed 5 mm greater tibial anterior translation from external to neutral rotation, and maintained a more anterior tibial position from neutral to internal rotation. There was a significant difference between tibial translation in ACLD and Contralateral knees (P < 0.001, two-way ANOVA), and pair-wise comparisons showed ACLD knees had significantly more tibial anterior translation after 56% of the pivot cycle. For example, the tibiae of ACLD knees were located at 10.4 (SD 2.3) mm and contralateral knees at 7.0 (SD 1.0) mm at 77% of the cycle. Tibial rotation during pivoting averaged 22 and 24 in ACLD and contralateral knees, and we could not detect a significant difference between groups (P = 0.20, twoway ANOVA, Fig. 3b). Knees with meniscectomy (N = 3) showed greater anterior tibial translation and more tibial external rotation than non-meniscectomy ACLD knees (N = 5) Squatting Fig. 2. A center of rotation was determined from all data frames for each motion trial. Each line represents the instantaneous alignment of the femur with respect to the tibia, and the white cross indicates the average center of rotation for the knee. This figure shows a medial center of rotation. 0% at maximum tibial external rotation to 100% at maximum tibial internal rotation. An average mediolateral center of rotation was determined for each trial from estimated tibiofemoral contact points. These medial and lateral contacts were computed as the geometric center of the region having less than 6 mm tibiofemoral separation (Moro-Oka et al., 2007b), and the line connecting these two points represented the instantaneous mediolateral axis of the femur. This line was projected onto the transverse plane of the tibial plateau for each frame of data. The center of rotation was determined for all data frames of each trial by solving the least-squares system of equations (Banks and Hodge, 2004), and expressed as a percentage of the tibial width, 50% (lateral) to +50% (medial) (Fig. 2). An average kinematic curve for each knee was created from three trials of data, and these average curves were combined to create group averages. Statistical analysis for kinematic data was performed using repeated measures analysis of variance and post-hoc pair-wise comparison (Tukey) to compare ACLD and contralateral knees. Similarly, an average center of rotation value in each knee was computed from three trials of data, and these average values were then combined to create group averages. Repeated measures analysis of variance was used to compare ACLD and contralateral knees and to compare pivoting and squatting. The level of significance was set at P<0.05. Additionally, the ACLD knee group was subdivided into two groups; patients with partial medial meniscectomy (N = 3) and patients without meniscectomy (N = 5), to address the effect of meniscectomy on knee kinematics in the ACLD knee. A kinematic curve and a center of rotation value were computed for each subgroup. Statistical analysis was not performed to compere these two groups due to the very small sample size. ACLD knees showed greater tibial anterior translation over the entire flexion arc during squatting (P < 0.001, two-way ANOVA, Fig. 4a), with significant pair-wise differences from 10 to 80 flexion. For example, the tibiae of ACLD knees were located at 8.9 (SD 3.1) mm and contralateral knees at 4.8 (SD 1.1) mm at 10 flexion. From extension to flexion, the tibia translated 3 4 mm 3. Results 3.1. Pivoting There was greater anterior tibial translation in ACL deficient knees during pivoting from neutral to maximum internal rotation. The contralateral healthy knees showed anterior tibial translation Fig. 3. Tibial anterior translation and internal rotation relative to the femur during pivoting from maximum tibial external rotation to maximum tibial internal rotation. MMtomy: patients with medial meniscectomy; non-mmtomy: patients without meniscectomy. The tibia of the ACLD knee was significantly anterior to the tibia of the contralateral knee (Fig. 3a, P < 0.001). Circles represent significant differences in post-hoc pair-wise comparisons (P < 0.05). There was no difference in tibial rotation between the ACLD and the contralateral knees (Fig. 3b, P = 0.20).

5 74 S. Yamaguchi et al. / Clinical Biomechanics 24 (2009) ). Average centers of rotation during pivoting were located in the lateral tibia in both ACLD and contralateral knees. Average centers of rotation during squatting were located in the medial tibia in both ACLD and contralateral knees. 4. Discussion Fig. 4. Tibial anterior translation and internal rotation relative to the femur during squatting. MMtomy: patients with medial meniscectomy; non-mmtomy: patients without meniscectomy. The tibia of the ACLD knee was significantly anterior to the tibia of the contralateral knee (Fig. 4a, P<0.001). The tibia of the ACLD knee was significantly internally rotated to the tibia of the contralateral knee (Fig. 4b, P < 0.001). Circles represent significant differences in post-hoc pair-wise comparisons (P < 0.05). anteriorly in both ACLD and contralateral knees. Tibial internal rotation with flexion averaged 23 and 22 in ACLD and contralateral knees (Fig. 4b). ACLD knees showed more tibial internal rotation over the flexion arc (P < 0.001, two-way ANOVA), but we could not detect significant pair-wise differences from 0 to 110 flexion. Knees with meniscectomy (N = 3) showed greater anterior tibial translation and more tibial external rotation than non-meniscectomy ACLD knees (N = 5), similar to the pivoting results Comparison between pivoting and squatting There was a significant difference in mean center of rotation between pivoting and squatting (P < 0.001, two-way ANOVA, Table Table 1 Average (SD) centers of rotation for pivoting and squatting in ACLD and contralateral knees Pivoting a (%) Squatting a (%) ACLD knee b (N = 8) 5(7) 19(8) Non-MMtomy (N = 5) 4(9) 17(6) MMtomy (N = 3) 6(5) 22(10) Contralateral knee b (N = 8) 5(4) 23(10) MMtomy: patients with medial meniscectomy; non-mmtomy: patients without meniscectomy. a Significant difference between pivoting and squatting, P < b P=0.45. Weight-bearing kinematics of ACLD knees is a topic of enduring interest since it remains challenging to use common clinical assessments, such as laxity and pivot shift tests, precisely to predict dynamic knee function or disability. Two goals of this study were: (1) To examine ACLD knee kinematics during pivoting and squatting as the weight-bearing dynamic analogs to clinically performed laxity and pivot shift tests and (2) To contrast knee kinematics in pivoting and squatting to determine if either activity fully elucidates ACLD or healthy knee kinematics. We observed anterior tibial subluxation in the ACLD knees for both pivoting and squatting activities, and observed different patterns of motion between the pivoting and squatting activities. This study has a number of limitations. First, the number of the patients was relatively small and the patients had a wide range of times post-acl injury. However, there was no correlation between side-to-side differences in anterior tibial translation and time from injury in this study (P = 0.85 and R = 0.08 for pivoting, and P = 0.21 and R = 0.49 for squatting, Pearson s correlation coefficient). Second, we used the uninjured contralateral knees as the control group, which some suggest do not represent normal function (Reider et al., 2003). This point remains controversial, as other studies have failed to demonstrate a kinematic difference between contralateral knees of ACL deficient patients and knees in normal subjects (Shefelbine et al., 2006). Third, 3D 2D image registration methods using single-plane fluoroscopy provide poor measurement accuracy for out-of-plane (i.e. mediolateral) translations (Moro-Oka et al., 2007a). ACL deficiency has been shown to affect tibial mediolateral translation in studies utilizing bi-plane imaging techniques (Li et al., 2006). Although bi-plane techniques provide smaller measurement errors, single-plane methods provide a less restricted field of view and permit patients to perform dynamic activities more naturally. Fourth, there might be gender difference in knee kinematics of ACL deficient patients. We standardized the testing activities in order to avoid knee in positions which have been seen in female ACL deficient subjects. We did not observe any significant gender differences in this study. The pivot shift test is a widely accepted method to assess instability of ACLD and reconstructed knees and correlates to patient s subjective functionction (Kocher et al., 2004). However, the pivot shift is a qualitative evaluation depending greatly on the examiner s subjective impression (Bach et al., 1988). We observed anterior tibial subluxation in ACLD knees during in vivo weight bearing pivoting from neutral to maximum tibial internal rotation. Kanamori et al. (2002) showed in vitro increased tibial anterior translation with neutral to internal tibial torques, consistent with our in vivo results. Our results suggest pivoting with fluoroscopic observation may provide an objective and precise measure of knee motions useful for study of knee pathomechanics or the efficacy of knee reconstruction procedures. We could not detect a clinically significant difference in tibial rotation between ACLD and healthy contralateral knees with the numbers available. This is consistent with results of Kanamori et al. (2002), who reported increasing internal tibial torque did not significantly affect tibial rotation between ACL intact and ACL deficient knees. On the contrary, Ristanis et al. (2003) investigated rotational knee stability during a landing-and-pivoting activity using skin-mounted marker based video analysis, and reported ACLD knees had significantly larger ranges of rotation. It is likely

6 S. Yamaguchi et al. / Clinical Biomechanics 24 (2009) activity differences account for the contrary findings our pivoting activity intentionally forced weight-bearing tibial rotation from one extreme to the other, while kinematics during the landing-pivot activity likely remained within each individual s normal functional limits of tibial rotation. If ACL integrity does not affect total weight-bearing tibial rotation, but does affect the normal functional rotation range, the results of the two studies do not conflict. Knee centers of rotation were lateral for pivoting and medial for squatting in both ACLD and contralateral knees. The center of rotation provides a simple metric to describe the general pattern of knee motion over an entire activity (Banks and Hodge, 2004). This metric permits intuitive comparisons between activities. Komistek et al. (2003) compared kinematics in healthy knees during deep knee bends and rising from a chair, and showed a medial center of rotation for both activities. Johal et al. (2005) similarly showed a medial center of rotation pattern during several sagittal plane activities. In contrast, Koo and Andriacchi (2008) recently have shown the center of rotation in healthy knees is predominantly lateral during gait. Banks and Hodge (2004) showed activity dependence in knee kinematics by demonstrating significantly different centers and magnitudes of rotation between gait and stair activities in patients with total knee arthroplasty. The present study clearly demonstrated the difference between a sagittal plane squatting activity and non-sagittal plane pivoting activity in both ACLD and contralateral knees. This indicates kinematics during squatting type activities cannot be extrapolated to predict kinematics during pivoting type activities, and suggests analysis of squatting type activities may not be enough to elucidate entirely the pathomechanics of ACLD knees. We combined meniscectomized patients and non-meniscectomized patients in our ACLD group to investigate clinically typical ACLD knees, which often have meniscal injury or meniscectomy. Importantly, the main kinematic findings for the entire ACLD group were also found comparing the meniscectomized ACLD knees with contralateral knees. The ACLD group was divided into two subgroups to explore the contribution of the medial meniscus to stability of ACLD knees. Greater tibial anterior translation and external rotation was observed in the meniscectomized knees during pivoting and squatting activities. Although the number of patients was quite small, these results are consistent with cadaver studies demonstrating the important stabilizing role of the medial meniscus against anterior tibial loads in the ACLD knee (Allen et al., 2000). 5. Conclusions Tibial anterior subluxation was observed in the ACLD knee during weight-bearing pivoting. This dynamic evaluation might be useful to objectively characterize restoration of dynamic function in knees with various types of ACL reconstructions. We observed lateral centers of rotation during pivoting and medial centers of rotation during squatting, suggesting kinematics during squatting activities cannot be extrapolated to predict kinematics during pivoting activities. Conflict of Interest Statement No funds or benefits were received in support of this study. Acknowledgements The authors thank Tsuguo Morikawa, Kan Tsuchiya, Hideshige Moriya, and Masahiko Suzuki for data collection. We also thank Nicholas J. 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