Kei Yoneta, Takeshi Miyaji, Akihiro Yonekura, Takashi Miyamoto, Kenichi Kidera, Hiroyuki Shindo, Scott A Banks, Kenji Hoshi and Kazuyoshi Gamada*
Department of Integrated Rehabilitation, Faculty of Health Sciences, Hiroshima International University, Higashihiroshima, Japan
Received date: April 22, 2015 Accepted date: August 24, 2015 Published date: August 27, 2015
Citation: Yoneta K, Miyaji T, Yonekura A, Miyamoto T, Kidera K, et al. (2015) Comparison of in vivo Kinematics in Primary Medial Osteoarthritic and ACL Deficient Knees during a Leg Press . Int J Phys Med Rehabil 3:300. doi:10.4172/2329-9096.1000300
Copyright: © 2015 Yoneta K, et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Visit for more related articles at International Journal of Physical Medicine & Rehabilitation
Background: Primary knee osteoarthritis (OA) is a progressive and disabling disorder affecting up to 13% of individuals aged 65 years and older. Anterior cruciate ligament deficiency (ACLD) is known to be a major precursor of early development of degenerative changes in the knee. There is a possibility of becoming a help of the disease process clarification of knee OA appearance of disease by investigating the relativity of knee OA and ACLD.
Methods: Fifteen OA, 9 ACLD, and 9 uninvolved knees were enrolled. In vivo knee kinematics was obtained using a 3D-to-2D registration technique utilizing CT-based bone models and lateral fluoroscopy during a leg press activity.
Results: The OA knees were in greater external rotation than the uninvolved and ACLD knees, while there were no differences between the uninvolved and ACLD knees. Reduced screw home motion was observed in OA knees. Knee kinematics in the earlier stages of knee OA appeared to change at mid flexion angles, while in the later stages at all flexion angles.
Conclusions: The OA knees showed grater abnormal kinematics as compared than the ACLD at small load of a leg press device. Level of Evidence: Prognostic Level III.
Knee osteoarthritis; Joint disorder; Kinematics
Knee osteoarthritis (OA) is a progressive and disabling joint disorder affecting up to 13% of individuals aged 65 years and older , but the etiological mechanism remains unknown. Primary knee OA is known to involve a complex and heterogeneous etiology, including both biochemical and biomechanical factors . The medial compartment is affected in the majority of knee OA and at least 25% of patients with knee OA demonstrate isolated medial compartment disease . Although biochemical factors contribute to the systemic factors influencing disease development and progression, such factors do not explain why knee OA commonly occurs in the medial compartment. Researchers have suggested that biomechanical factors contributing to the development of knee OA include body weight, knee alignment, muscle strength, knee kinematics, and strenuous activities [1,2]. Biomechanical factors including knee kinematics that produce abnormal stress on the medial compartment are not well understood.
Several studies have suggested that rotational kinematics is modified in knees with primary OA [4-7]. Scarvell et al.  reported that OA knees displayed a modified screw home motion with reduced tibial external rotation between 90° and 10° flexion compared with those in normal knees. Similarly, Saari et al.  studied OA knees using dynamic radiostereometry and reported decreased tibial internal rotation between 50o and 20o flexion during weightbearing active extension. Moro-oka et al.  and Hamai et al.  used a 3D-to-2D model registration technique and reported that femoral external rotation (i.e. tibial internal rotation) during knee flexion was reduced in knees with medial OA compared to that in normal knees. These studies utilizing accurate and reliable kinematic measurement techniques published after the year 2000 agreed that OA knees exhibit reduced tibial external rotation during knee extension and greater tibial external rotation.
Anterior cruciate ligament deficiency (ACLD) is known to be a major precursor of the early development of degenerative changes in the knee  and kinematic changes after ACL injury may play a role in accelerating the degeneration process. Ajuied et al.  performed a meta-analysis and showed that ACL injury predisposes knees to osteoarthritis. Yamaguchi et al.  reported that rotational kinematics of ACLD and contralateral healthy knees differed only at 10° hyperextension during squatting activity, although the tibia in ACLD knees showed anterior translation from 10° hyperextension to 80° flexion. In their review, Chaudhari et al.  concluded that cartilage degeneration after ACL injury could be caused by a kinematic gait change that shifts the ambulatory load applied to the cartilage. Haughom et al.  showed that ACL rupture leads to increased rotational laxity of the knee. On the other hand, bone bruise at the posterior edge of the lateral tibial plateau  may be associated with soft tissue injury leading to soft tissue adhesion, which may cause the external rotation contracture that we often see clinically. Andriacchi et al.  noted that cartilage homeostasis would not be maintained by abnormal kinematics after ACL rupture and cartilage degeneration would be initiated. Accordingly, abnormal kinematics in ACLD knees may explain the accelerated degeneration process leading to secondary knee OA. A comparison of kinematics among ACLD, primary osteoarthritic, and normal knees may provide new information on common abnormalities in knee motion. However, to our knowledge, no study to date has compared kinematics between ACLD knees and primary OA knees.
The primary purpose of this study was to determine if there are any kinematic differences among primary medial OA, ACL deficient and uninvolved knees. We hypothesized that knee kinematics would differ among the three groups: specifically, reduced tibial internal rotation motion and reduced posterior translation of the lateral femoral condyle during knee flexion as well as greater tibial external rotation throughout the flexion range would demonstrate a progression from uninvolved to ACLD to medial OA knees. The secondary purpose was to determine if knee kinematics change with disease progression in primary medial knee OA.
The study protocol was approved by the local ethics committee and written informed consent was obtained from all subjects prior to enrollment. Nine ACL deficient knees of 9 male patients with a mean age of 27.0 (95%CI: 21.232.8) years, 9 contralateral knees in the same patient group, and 16 OA knees of 10 patients (3 males and 7 females) with a mean age of 68.7 (95%CI: 64.373.1) years were examined in this study. The uninvolved knees were the asymptomatic knees contralateral to the ACLD knees. ACLD was confirmed by MRI and arthroscopy by a single orthopaedic surgeon (T.M.). All of the OA patients were over 40 years old and all OA knees were diagnosed with primary OA based on the American College of Rheumatology criteria. Radiographic severity of OA was classified using the Kellgren-Lawrence System and showed an average of grade II (95%CI:1.62.4) (5 knees with grade I, 6 with grade II, 5 with grade III). Patients with ACLD knees were between 20 and 40 years and were scheduled for ACL reconstruction. The other inclusion criterion for all groups was the ability to perform leg press activity. Exclusion criteria included knee ligament injuries other than ACL injury, history of contralateral knee injuries, and age younger than 20 years. The interval between ACL injury and testing ranged from 1-38 months. None of the uninvolved or ACLD knees showed any radiographic signs of OA.
Overview of 3D-to-2D registration technique
Knee kinematics was analyzed using a 3D-to-2D registration technique utilizing CT-based bone models and lateral fluoroscopic images [15-17] (Figure 1). Knee kinematics was determined by 3-dimensional positions of each bone model using Cardan angles . 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 rotation .
Figure 1: 3D-to-2D Registration Technique. Calibrated fluoroscopic images and 3D bone models of the femur and tibia were utilized to obtain in vivo, 6° of freedom positions and orientation of bone models using the joint track program. The bone modelas were projected onto the fluoroscopic images, and there three dimensional pose were iteratively adjusted to match there silhouette with the silhouette of the bones on the fluoroscopic images.
Activity and fluoroscopic imaging
Leg press activity was chosen for kinematic analyses. During fluoroscopic imaging, subjects were seated in a leg press device (Figure 2) (Minato Medical Science Co., Ltd) with a fixed footplate and sliding seat. The slope of the sliding rail was 5o. To measure weightbearing knee kinematics without inducing pain and/or fear, we utilized leg press activity. The advantages of utilizing the leg press activity include: 1) adjustability of loads to achieve knee flexion greater than 90°; 2) activity similar to squatting; and 3) stabilization of the pelvis to eliminate compensatory motion secondary to pain and/or weakness. Considering these advantages, we thought that the leg press activity would be the best method to identify quasi-weightbearing knee kinematics. During leg press activity, subjects were asked to straighten the knee without rotating the hip or foot. Subjects performed the leg press activity 5 times with a target knee flexion angle of 90° and extension angle of 0°. With the toes pointing upward and the feet parallel, the patients performed 5 repetitions of each activity in one session. Since this is a cross sectional study, only one session was performed. The pelvis was pressed against the backrest and not mobile during the leg press activity. Therefore, the ankles, knees and hips are thought to be the only joints that influenced the knee kinematics. Before radiographic exposure, the patients practiced leg press activities until the motion became smooth and they felt comfortable performing the exercise. The weight load on the leg press device was adjusted so that each patient could perform the required leg press activity without feeling pain or demonstrating pain-related abnormal kinematics. The weight load for uninvolved/ACLD and OA knees averaged 10kg and 5kg, respectively. The load was selected based on each subject’s ability to perform the experimental task without compensatory motion due to pain and/or fear.
All knees underwent CT scanning with a 0.5 mm slice pitch spanning approximately 150 mm above and below the knee joint line. Geometric bone models of the femur and tibia were created from the CT images. Exterior cortical bone edges were segmented using 3D-Doctor software (Able Software Corp., Lexington, MA) and were converted into polygonal surface models using Geomagic Studio software (Geomagic, Research Triangle Park, NC, USA). Local coordinate systems were embedded in each bone using the custom VHKneeFitter (University of Colorado, Aurora, Co) program that allows all the procedures detailed below to be performed in a virtual space with high reproducibility.
The cylindrical axis (CA) was utilized as a reference line of the femoral coordinate system  (Figure 3A). The femoral origin was defined as the midpoint between the medial and lateral ends of the CA, which were defined as points on the CA crossing the bony surface medially and laterally, respectively. A plane through the origin perpendicular to the CA was defined as the sagittal plane on which the vertical axis (VA) would be located. The distal one-third of the femoral shaft was projected onto the sagittal plane and the central line of the projected femoral shaft was drawn. A line through the origin parallel to this central line in the sagittal plane was defined as the VA. The anteroposterior axis (APA) was obtained by a cross product of the CA and VA.
Figure 3: Local coordinate system of femur and tibia. A) The femoral coordinate system was embedded using cylindrical axis of the posterior femoral condyles. B) Tibial coordinate system was embedded using virtual rectangle matched in the tibial cross section at the top of the fibular head level. Then, the rectangle was translated superiorly so that it fit the bottoms of both tibial plateau.
The tibial coordinate system (Figure 3B) was defined around a virtual rectangle fitted onto the contour of the tibial plateau. To avoid highly variable morphology and high prevalence of spur formation at the posterior contour of the osteoarthritic tibial plateau, the rectangle was fitted at the level of the top of the fibular head parallel to the tibial plateau plane. The four lines of the rectangle were fitted onto the co-tangent of the posterior contours of the medial and lateral tibial condyles, the medial and lateral tangents of the medial and lateral tibial condyles, respectively, and the anterior tangent of the medial tibial condyle. Then, the rectangle was translated superiorly so that it fit the bottoms of both tibial plateaus. The center of the rectangle was defined as the tibial origin, through which the medial/lateral and anteroposterior axes were defined as two axes of the tibial coordinate system. The vertical axis of the tibia was, by definition, a cross product of these two axes proximally.
Model registration and data processing
In vivo three-dimensional positions and orientations of the femur and the tibia were determined using a 3D-to-2D registration technique [15-17]. With the custom JointTrack program (sourceforge.net/projects/jointtrack), 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 bones on the fluoroscopic images. Manual matching was first performed, then an automated matching procedure was performed using the nonlinear least-squares (modified Levenberg-Marquardt) technique. Once the registration procedures were complete for a sequence of the activity, 6 degrees-of-freedom joint kinematics was computed using a commercial software 3D-JointManager (GLAB Inc., Higashi-Hiroshima, Japan). Because the local coordinates were defined around the intra-articular morphology of the tibia and femur, the joint kinematics may differ from clinical measurement, primarily due to the tibial posterior slope. Kinematics was analyzed in 5° increments of knee flexion after B-spline curve approximation was performed. Comparisons were performed using values between 10 and 65° flexion, where observations from all knees were available. We defined the magnitude of the screw-home motion as the difference of external rotation positions between 65° and 10° flexion. The locations of condylar contact were estimated as the lowest point on each femoral condyle relative to the transverse plane of the tibial plate.
Statistical analyses for kinematic data were performed using repeated measures analysis of variance (groups × flexion angle) with the repeat factor being the flexion angle, and post-hoc pair-wise comparison (Tukey-Kramer test) to compare the 3 knee groups. In the uninvolved and OA knees, kinematic differences associated with OA severity were examined using repeated measures analysis of variance and post-hoc pair-wise comparison (Dunnet T3) in order to compare the uninvolved knees to the 3 OA knees graded I to III. The magnitude of the screw-home motion was compared using one-way analysis of variance and post-hoc comparison (Bonferroni) to compare the 3 knee groups. The level of significance was set at p<0.05. Statistical analyses were performed using SPSS ver 13 (SPSS Inc., Chicago, US)and G*Power ver. 3 (University of Kiel, Kiel, Germany).
The average maximum extension and flexion angles for all subjects were 7° ± 6° (range, -6° to 20°) and 83 ± 9° (range, 69° to 99°), respectively. Significant differences among the 3 knee groups with regard to the demographic data are summarized in Table 1.
|All||grade I||grade II||grade III|
|Age (yo)||Average 95%CI||27 21.2?32.8||27 21.2?32.8||68.7 64.3?73.1||59.8 54.2?65.4||74.2 69.8?78.5||71 60.9?81.1||OA vs Uninvolved (p<0.001),ACLD (p<0.001)grade 0 vs grade?,?,?(p<0.001)|
|Height (cm)||Average 95%CI||1.73 1.67?1.79||1.73 1.67?1.79||1.54 1.49?1.59||1.57 1.45?1.70||1.51 1.41?1.61||1.55 1.43?1.68||OA vs Uninvolved (p<0.001),ACLD(p<0.001) Uninvolved vs grade ?(p=0.006)|
|Weight (kg)||Average 95%CI||77.7 59.0?96.4||77.7 59.0?96.4||62.8 57.5?68.0||65.1 51.0?79.3||59.1 51.3?67.8||64.8 53.6?76.1|
|BMI (kg/m2?||Average 95%CI||25.9 20.6?31.2||25.9 20.6?31.2||26.3 25.3?27.2||26.2 23.8?28.6||25.9 23.5?28.3||26.8 25.5?28.1|
|Max flexion (°)||Average 95%CI||85.3 79.3?91.3||85.6 78.3?92.8||79.3 75.3?83.2||76.4 72.3?80.5||82 72.1?92.0||78.9 69.1?88.6|
|Max extension(°)||Average 95%CI||6.9 11.1?2.6||7.3 13.4?1.2||7 9.8?4.1||10.7 16.1?5.4||5.6 11.4?-0.3||4.9 10.8?-1.1|
|SHM(°)||Average 95%CI||11.9 8.5?15.4||8.1 4.6?11.6||6.8 5.5?8.7||6.5 3.7?9.3||8.3 5.1?11.6||7.5 1.0?14.1||Uninvolved vs OA (P=0.016) Uninvolved vs grade ?(P=0.048)|
|One-way ANOVA tested for differences between the three groups with Bonferonni post hoc procedures. (a=0.05)
ACLD: Anterior Cruciate Ligament Deficiency
OA: primary medial osteoarthritis
uninvolved: asymptomatic knee contralateral to the ACLD knee
Table 1: Demographics of the OA, ACLD and uninvolved.
During leg press activity, OA knees showed less tibial internal rotation than that of the uninvolved knees at 40° through 65° flexion, and less than that of the ACLD knees at 20° through 65° flexion (Figure 4A). There were no significant differences in rotation positions between uninvolved and ACLD knees at 10° through 65° flexion (Figure 4A). At 10° through 65° flexion, the lateral femoral condylar contact points on the tibia of the OA knees were more anterior than those of the uninvolved and ACLD knees (Figure 4B). The medial femoral condylar contact points on the tibia of the OA knees were significantly more anterior than those of the uninvolved and ACLD knees at low flexion angles (Figure 4C). The magnitude of the screw home motion (i.e. amount of tibial external rotation) from 65° to 10° flexion was 11.9° (95%CI: 8.5, 15.4) in uninvolved knees. We found significantly reduced screw home motion in OA knees (average 6.8°, 95%CI: 5.5, 8.7) than uninvolved knees (p=0.016) (Table 1).
Figure 4: Comparisons of knee kinematics and contact points between the OA, ACLD and uninvolved knees. There were significant differences in all parameters by repeated measure ANOVA (p<0.05). Tukey-Kramer test was used for post-hot pairwise comparisons (p<0.05). *Significant differences between OA and uninvolved knees †Significant differences between OA and ACLD knees Error bars represent ± 1 standard deviation. ACLD: Anterior Cruciate Ligament Deficiency; OA: primary medial osteoarthritis; uninvolved: asymptomatic knee contralateral to the ACLD knee.
In a comparison between the 3 grades of OA knees and the uninvolved knees, tibial internal rotation at 40° through 65° flexion was significantly reduced in knees with grade II OA compared with that in the uninvolved knees (Figure 5A). Lateral femoral condylar contact points were significantly more anterior in grade II and III knees compared with those in uninvolved knees at all flexion angles, while grade I knees showed significant differences from the uninvolved knees only at 50° and greater flexion. Grade II knees showed significant differences from grade I knees at 45° through 55° flexion (Figure 5B). At low flexion angles, the medial femoral condylar contact points in grade II and III knees were significantly more anterior than those in uninvolved knees (Figure 5C).
Figure 5: Comparisons of knee kinematics and contact points between the OA knees with grade I-III and uninvolved knees. There were significant differences in all parameters by repeated measure ANOVA (p<0.05). Dunnet T3 was used for post-hot pairwise comparisons (p<0.05). *Significant difference between the uninvolved and grade I OA knees.†Significant difference between the uninvolved and grade II OA knees. ‡Significant difference between the uninvolved and grade III OA knees. ¶Significant difference between grade I and grade II knees Error bars represent ± 1 standard deviation. OA: primary medial osteoarthritis; uninvolved: asymptomatic knee contralateral to the ACLD knee
The aims of this study were to determine if there are any kinematic differences among medial primary OA, ACLD, and uninvolved knees and if knee kinematics of primary OA is modified with disease progression. The OA knees showed less tibial internal rotation and less screw-home motion compared with those in ACLD and uninvolved knees. Lateral femoral condylar contact points in the grade I knees were significantly more anterior only at flexion angles of 50° and greater, while those in grade II and III knees were significantly more anterior at all flexion angles compared with the same points in uninvolved knees. Unexpectedly, there were no detectable differences in rotational kinematics between the ACLD and uninvolved knees.
Our results demonstrating reduced internal rotation in OA knees during flexion are consistent with previous studies using modern technology. Saari et al.  reported that OA knees showed reduced internal tibial rotation between 50° and 20° flexion, in which rotation angles were determined relative to the full knee extension position. A series of studies by Moro-oka et al.  and Hamai et al.  also demonstrated reduced tibial internal rotation positions as well as reduced screw home motion during squatting in OA knees compared to those in uninvolved knees. In those studies, rotation was determined by contact locations rather than using a joint co-ordinate system. In the present study, the rotation angles are presented as absolute values based on a femoral and tibial anatomical coordinate system. Although the rotation angles presented in this study do not directly predict the condylar interactions especially in degenerative knees, our kinematic data using an embedded coordinate system facilitate a valid comparison of findings at different stages of knee OA and in non-degenerative, healthy knees in younger subjects. None of the previous studies presented statistical comparisons, and therefore the present study may be the first study using modern kinematic analyses to analyze statistical differences in kinematics between OA and uninvolved knees.
Unexpectedly, there were no detectable differences in rotational kinematics between the ACLD and uninvolved knees. Some studies have shown significant abnormalities in three-dimensional joint kinematics during walking in ACLD knees. Andriacchi et al.  reported reduced anterior translation and tibial external rotation before heel strike in ACLD knees. In addition, Georgoulis et al.  reported greater internal tibial rotation during theinitial swing phase in ACL-D knees compared to that in healthy knees. Gao et al.  showed greater varus and internal tibial rotation in ACL-deficient knees compared to those in ACL-intact knees. These studies examined the knee kinematics during walking, while the current study used leg press activity. The weight load of leg press activity may not stress the joint sufficiently to detect significant differences in knee kinematics between uninvolved and ACLD knees. However, even these limited weight loads detected significantly more abnormal kinematics in knee OA compared to those in uninvolved and ACLD knees. Therefore, knee OA may induce greater kinematic abnormality.
Comparisons of kinematics between the 3 OA grades were performed anticipating that progression of the disease would be associated with changes in pathokinematics. All OA grades similarly demonstrated a tendency toward reduced internal rotation positions at all flexion angles. In addition, OA knees demonstrated greater anteroposterior translation of the contact points, while the uninvolved knees demonstrated medial pivot condylar kinematics, supporting the previous study by Scarvell et al. . In grade I knees, a posterior shift of the lateral contact points was detected only at 50° and greater flexion, suggesting reduced internal rotation positions at the mid flexion angles can be a potential biomechanical marker of early disease development. As the disease progressed to grades II and III, the lateral contact points shifted anteriorly in comparison with those in uninvolved knee at all flexion angles, suggesting that disease progression from grade I to II is associated with reduced tibial internal rotation positions at low flexion angles as well as the mid flexion angles. Anterior translation of the contact points indicated anterior positioning of the femur relative to the tibia, suggesting that flexion contracture of the knee limits extension as well as tibial anterior translation during knee extension. The loss of internal rotation in OA knees may be due to more severe contracture on the lateral side during knee extension. However, in the current study we were unable to clarify the reason for this abnormal motion.
The 3D-to-2D registration technique using lateral fluoroscopy or radiography is a well-established measurement method of dynamic weightbearing knee kinematics in vivo with standard errors within 2.2 mm for translation and 1.8 degrees for rotation . Since the use of leg press activity should reduce variability of load, body position, and hip and trunk motion, consistency of knee kinematics should be improved, providing greater sensitivity to detect small kinematic changes. Moreover, knee kinematics was computed based on a bony coordinate system that was assigned using a software program specially coded for assigning femoral and tibial coordinates with high reproducibility. Using the CA for the femur and the posterior co-tangent of both tibial condyles at the top of the fibular head for the tibia as reference lines for knee rotation, errors caused by potential spur formation or morphological changes due to degenerative changes should have been significantly diminished. Accordingly, the data are thought to be reliable with good internal validity.
There are several considerations needed for external validity of this study. First, leg press activity is not functional and the kinematics during leg press activity may not be applicable to patients’ regular weightbearing activities such as squatting or stair ascending/descending. Second, the uninvolved knee contralateral to the ACLD knee was used as the normal control group; therefore, the results of this study may not be consistent with a comparison of kinematics between OA knees and “true” normal knees.
This study has several limitations. First, degenerated menisci and articular cartilage were ignored in analyzing joint contact points. We considered meniscal damage concomitant findings of joint degeneration in most OA knees. In order to provide clinically meaningful information, such knees should not be excluded. Second, the 3D-to-2D image registration method using single-plane fluoroscopy provides limited measurement accuracy for out-of-plane motion ; therefore, we did not report these data. This may limit our ability to discuss involvement of lateral translation of the tibia, which is often seen on plain X-ray of OA knees. Third, patients with ACLD were significantly younger than those with knee OA. We were interested in the kinematics of fresh ACLD knees without secondary degeneration in order to determine which component of the 6 degrees-of-freedom knee kinematics is associated with the kinematics of primary knee OA. An age-matched control group would have included knees with early OA. We consider that asymptomatic knees without cartilage degeneration, instability, stiffness or subsequent abnormal kinematics are rare among subjects over 60 years old and there is no way to determine if a person is free from all potential causes of abnormal kinematics. We simply consider the knee contralateral to the ACLD knee healthier than asymptomatic knees in people over the age of 60. Accordingly, our patient selection was appropriate to answer the research questions. Finally, the small sample size in this study may have caused beta errors.
OA knees showed reduced tibial internal rotation positions and reduced screw home motion as compared with the ACLD and uninvolved knees under a limited load on a leg press device. In OA knees, knee kinematics may change at the mid flexion angles in the early stage of OA, and at all flexion angles in the later stages. Future studies should include sufficient sample size to compare kinematic differences between OA grades and utilize more functional activities such as squatting or stair ascending/descending.
This study was supported by Minato Medical Science Co. Ltd. and was partially funded by the Japan Rehabilitation Association and Arthrex, Inc.
Make the best use of Scientific Research and information from our 700 + peer reviewed, Open Access Journals