Osteochondral microdamage from valgus bending of the human knee
Introduction
The knee is one of the most frequently injured joints in the human body, accounting for 19–23% of all injuries (Hootman et al., 2002). That percentage is even higher in the athletic population with the most common injury classification being internal knee trauma (Majewski et al., 2006). Epidemiological studies have shown there are over 80,000 anterior cruciate ligament (ACL) tears in the USA each year, with a total cost of more than $1 billion (Griffin et al., 2000). The medial collateral ligament (MCL) is frequently injured as well, both individually and in combination with the ACL (Majewski et al., 2006, Viskontas et al., 2008).
An additional complication of an acute knee injury is a significantly increased risk of developing post-traumatic osteoarthritis (OA) (Felson, 2004). Between 50% and 70% of patients with a complete ACL rupture and associated injuries have radiological changes consistent with chronic joint disease after 12–20 years (von Porat et al., 2004). Post-traumatic OA development in patients with ligament tears may be caused by acute damage to the articular cartilage and subchondral bone due to excessive compressive forces generated in the joint at the moment of injury (Fang et al., 2001; Frobell et al., 2008). In over 80% of ACL cases and 50% of MCL cases, there is a characteristic osteochondral lesion in the tibial plateau and/or the femoral condyle (Atkinson et al., 2008). Geographic bone bruises, in particular, are also a sign of cartilage softening, fissuring or overt chondral fracture in regions overlying bone bruises (Vellet et al., 1991, Johnson et al., 1998). Osteochondral microdamage that is a “footprint” of the pattern of the joint contact at the moment of ACL injury (Sanders et al., 2000, Viskontas et al., 2008) has been confirmed during isolated TF compression experiments in cadaver knees (Meyer et al., 2008a). Meyer et al. (2008a) also validate that these “footprints” are specific to the mechanism of ACL injury by comparing the TF contact pressures produced by TF compression, internal tibial torsion and more recently, hyperextension loading mechanisms (Meyer et al., 2008b).
Valgus bending of the knee is one of the most commonly referenced loading mechanisms for ACL rupture in athletes. This type of motion is described in over 60% of non-skiing ACL injuries (Boden et al., 2000). In basketball, approximately 37% of non-contact ACL injuries were termed “valgus collapse” (Krosshaug et al., 2007). Valgus bending of the knee is affected by many types of external forces, and associated with other motions of the joint. Specifically, there is a strong coupling between valgus bending and axial tibial rotation (Inoue et al., 1987, Matsumoto et al., 2001). In experiments that allow motion in five out of the six possible degrees of freedom (all except knee flexion/extension), ACL sectioning significantly increases valgus laxity, while MCL sectioning does not (Inoue et al., 1987). The estimated force in the ACL is highest at 30° of knee flexion for a 10 N m valgus bending moment (Fukuda et al., 2003). Other biomechanical studies, however, have shown significantly more restraint from the MCL than the ACL during valgus bending (Seering et al., 1980, Shapiro et al., 1991). Although valgus bending is frequently identified in video analysis of ACL injuries in sports, it is not clear if this motion induces the injury or occurs as a result of the ACL being torn (Olsen et al., 2004).
Few studies have documented the forces or relative joint displacements at failure levels under controlled loading of the knee joint. The objective of the current study was to apply failure level valgus bending moments to the knee and document the soft tissue injuries and osteochondral microdamage that occur during this event. The study was designed to measure the contact pressure occurring in the knee joint during failure level valgus bending moments. Additionally, in the current study valgus bending and TF compression were combined to better simulate an off balance jump landing. It was hypothesized that valgus bending would result in ligament failure and that during gross ligamentous injury to the knee valgus loads would generate high contact pressures in the lateral plateau causing acute osteochondral microdamages. These damaged regions may have the potential for development of post-traumatic OA, even after surgical reconstruction of the ligamentous injury.
Section snippets
Methods
Valgus bending experiments were conducted on paired TF joints from four male cadavers with an average age of 40 (15) years, where () indicates the standard deviation of the mean throughout the manuscript. The joints were procured through University sources (see “Acknowledgements”), stored at −20 °C and thawed to room temperature for 24 h prior to testing. The joints were sectioned approximately 15 cm proximal and distal to the center of the knee. The skin and muscle tissues were removed leaving
Results
All failures, except for one specimen, involved the MCL. There were also three cases of partial rupture or avulsion of the ACL (Table 1). The average failure valgus bending moment was similar between the isolated valgus bending and the combined valgus bending and TF compression experiments, yielding an average of 107 (64) N m (Table 1).
In the lateral compartment of the knee, both types of experiments generated high contact pressures with a maximum magnitude of 30 (8) MPa (Fig. 2). In the isolated
Discussion
The valgus bending mechanism of ACL rupture is associated with bone bruises in the lateral aspect of the tibial plateau and lateral femoral condyle (Hayes et al., 2000, Sanders et al., 2000). All of the combined valgus bending and TF compression specimens had cartilage fissures and subchondral bone microcracks, and three of the isolated valgus bending specimens had cartilage fissures with two of those also having subchondral bone microcracks. These osteochondral microdamages were located in the
Conclusions
In summary, the study used a cadaver model to validate the valgus loading “footprint” of osteochondral injury that has been previously documented in clinical cases of knee ligament rupture. Severe levels of TF contact pressure were documented on the lateral facet and these regions were associated with cartilage fissures and subchondral bone microcracks. The results of this study suggest that damage to the articular cartilage overlying MRI detected bone bruises in patients with ligament tears is
Acknowledgements
This study was supported by a grant from the Centers for Disease Control and Prevention, National Center for Injury Prevention and Control (CE000623). Its contents are the sole responsibility of the authors and do not necessarily represent the official views of the Centers for Disease Control and Prevention. The authors wish to gratefully acknowledge the Biomedical Imaging Research Center, Michigan State University and Dr. Robert Wiseman for scheduling time to use the microCT scanner. We also
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