Anterior cruciate ligament (ACL) deficiency increases the risk of early knee osteoarthritis (OA). Radiographic OA changes developed in 50 to 70% of ACL deficient (ACLD) knees within ten to twenty years after ACL injury (Gillquist and Messner, 1999, Roos et al., 1995). All of the ACLD knees demonstrated some evidence of OA changes such as joint space narrowing within 12 years following their ACL injury (Segawa et al., 2001). Since rotational and anterior instability after ACL injury are considered to contribute to early development of knee OA, studies of ACLD knee kinematics would be important to reveal the disease process and gather information which would support mechanisms to potentially slow OA progression.
In vivo knee kinematics during weight-bearing activities in the ACLD knee have been reported in recent years. Studies agreed that the tibia translates anteriorly to a greater degree in the ACLD knee than in the intact knee (Van de Velde et al., 2009, DeFrate, 2006, Yamaguchi et al., 2009). Medial and lateral contact points of the tibiofemoral joint in the ACLD knee were located more posteriorly than in the intact knee (Li, 2006, Logan et al., 2004). However, sample sizes in these studies were insufficient (under ten knees) to draw firm conclusions and a further study with sufficient sample size is needed. The aim of this study was to determine if there were any differences in the kinematics of the ACLD knee and the contralateral intact knee during a weight-bearing activity.
Knee kinematics are activity dependent, and several types of weight-bearing activities have been examined in previous studies (Van de Velde et al., 2009, DeFrate, 2006, Yamaguchi et al., 2009). The front lunge is commonly chosen in kinematic studies using lateral fluoroscopy to avoid overlapping of the contralateral knee (Van de Velde et al., 2009, DeFrate, 2006). However, a narrow base of support in this activity may not be suitable for an early rehabilitation phase of the ACLD knee. In contrast, a wide-based squat activity, with the feet oriented at 90[degrees] to each other and positioned 1.5 times shoulder-width apart, is considered to be a more stable rehabilitation exercise with wider base-of-support than that of the lunge activity for the ACLD knee and this does allow for lateral fluoroscopy. In addition, it is easy, stable and reproducible due to bearing the weight evenly on both feet and a lower center of mass with a greater base area. In a previous study, the wide-based squat activity involves increased anterior translation at -10~80[degrees] flexion angles and internal rotation of the tibia at low knee flexion angles (Yamaguchi et al., 2009). On the other hand, some studies reported that the tensile force in the ACL during squat was minimal or absent even at lower flexion angles, needless to say the tensile force was also minimal or absent at deep knee flexion angles (Escamilla, 2012, Escamilla et al., 2009, Beynnon et al., 2002, Toutoungi, 2000). Though these results may not allow direct comparisons, it is still unclear at which knee flexion angles tibial anterior translation during squat activity places the knee at risk.
We hypothesized that abnormal knee kinematics during wide-based squat are present at lower flexion angles in the ACLD knee as compared with the contralateral intact knee. A 2D/3D registration technique with lateral fluoroscopy was utilized to analyze dynamic knee kinematics in this cross-sectional study with sufficient sample size to test this hypothesis.
This study is a laboratory-based, cross-sectional study. The study protocol was approved by a local institutional review board. Subjects were recruited from patients visiting our hospital. Selection criteria included (1) males aged over 20 years old, (2) unilateral, isolated ACLD confirmed by MRI, (3) signs of knee instability by manual physical examinations, (4) symptoms of knee instability during daily activities, (5) no evidence of past knee injuries except for the ACL injury, (6) over 100 degrees range of motion (ROM) arc in bilateral knees during squat, (7) no previous injury or OA changes in the contralateral knee, and (8) written informed consent. Females were not enrolled in this study to avoid radiation exposures for potentially pregnant women. Thirty-three patients aged 29.2 [+ or -] 7.9 years (range 20-51 years) with unilateral ACLD and contralateral intact knees were enrolled in this study. The mean term between the ACL injury and the testing was 47.4 weeks (range 3.3 - 450 weeks, median ten weeks). Full passive knee range of motion arc and resolution of knee swelling were achieved for all subjects before testing began. All of the ACLD knees underwent ACL reconstruction following data acquisition due to persistent severe knee instability. All had a positive Lachman test, 31 knees had positive pivot-shift tests, and none had radiographic OA changes. All subjects were examined with anterior-drawer test using a KT-2000 arthrometer (MEDmetric Corp, San Diego, California) under anesthesia during the ACL reconstruction surgery. Anterior laxity ranged from 13.1 [+ or -] 2.3 mm in the ACLD knees to 7.3 [+ or -] 2.1 mm in the contralateral non-involved knees. There was a significant difference (p
Overview of analysis
Knee kinematics were analyzed using the 2D/3D registration technique utilizing CT scan and lateral fluoroscopy proposed by Banks et al. (Banks and Hodge, 1996, Hoff et al., 1998). Three-dimensional positions of femoral and tibial bone models in virtual space were obtained and knee kinematics were determined in Cardan angles (Andriacchi and Dyrby, 2005). Fregly et al. reported the accuracy of this technique was 0.42 mm for in-plane translation, 5.6 mm for out-of-plane translation, 1.3[degrees] for rotations with the 3D bone model and single-plane fluoroscopy (Fregly et al., 2005). Komistek et al. reported values of 0.45 mm for in-plane translation and 0.66[degrees] for rotations (Komistek et al., 2003). The best-case accuracy was reported to be 0.53 mm for in-plane translation, 1.6 mm for out-of-plane translation and 0.54[degrees] for rotations (Moro-oka et al., 2007). These data indicate that the accuracy of this technique is sufficient to investigate knee kinematics for in-plane translation and rotations.
Activity and fluoroscopic imaging
The wide-based squat (Figure 1) was chosen for knee kinematic analyses. First, the subjects stood on the pre-set foot prints, so that everyone maintained the same stance width. It allowed their feet to be oriented at 90[degrees] to each other and positioned 1.5 times shoulder-width apart. Then, the subjects performed the squat with their hips at 45[degrees] external rotation, during which the knee over the...