Effect of hamstrings muscle action on stability of the ACL-deficient knee in isokinetic extension exercise
Introduction
The primary function of the anterior cruciate ligament (ACL) is to limit anterior translation of the tibia relative to the femur. Injury to the ACL often results in loss of thigh muscle strength, so much so that open-chain (i.e., knee-extension) and closed-chain (i.e., weight bearing) exercises are routinely prescribed to maintain quadriceps muscle strength [1], [2], [3], [4]. Even though weight-bearing exercises are emphasized in most ACL rehabilitation protocols, isokinetic knee-extension exercise is still commonly used in the eight weeks to six months post-injury and post-operative periods [1], [2], [3], [4]. Unfortunately, knee-extension exercise causes relatively large forces to be transmitted to the ACL in the intact knee, and yields much larger-than-normal anterior tibial translation (ATT) when the ACL is absent [5], [6], [7]. Some studies have found that the risk of injury to passive structures such as the menisci, which provide secondary restraint to ATT, is greatly increased [8], [9], [10]. ACL insufficiency may also lead to degenerative changes inside the knee consistent with osteoarthritis [11], [12]. As a result, rehabilitative methods have been sought which limit ATT in the ACL-deficient knee during isokinetic knee-extension to levels present in the intact joint [1], [13], [14].
A large number of in vivo [15], [16], [17], [18], [19], [20], in vitro [5], [21], and modeling studies [6], [22], [23], [24] have shown that hamstrings co-contraction can reduce ATT in the ACL-deficient knee. Hamstrings activation may reduce ATT since these muscles insert on the back of the tibia, and they may therefore apply a posterior pull to the leg. Imran and O’Connor [23] used a two-dimensional model to study the effectiveness of hamstrings co-contraction force on ATT during isometric extension. Their calculations showed an inverse relationship between ATT and hamstrings force, with hamstrings co-contraction being least effective in reducing ATT near extension. These findings are well supported by experimental measurements reported by Hirokawa et al. [21]. Relatively little is known, however, about the amount of hamstrings activation needed to keep ATT within normal limits during functional activity. Liu and Maitland [24] estimated the amount of hamstrings activation needed to stabilize the ACL-deficient knee during level walking; however, their analysis was quasi-static and their findings apply only to a single instant of the gait cycle. To our knowledge, no study has reported on the effect of hamstrings muscle action on stability of the ACL-deficient knee during dynamic rehabilitation exercises like isokinetic extension.
It is also not clear whether hamstrings co-contraction is more effective in reducing ATT than is low-resistance extension exercise (i.e., knee-extension at high speeds). Wilk and Andrews [25] measured ATT in ACL-deficient patients for speeds ranging from 60 to 300 deg/s. They reported a linear drop in ATT as knee-extension speed increased, but no comparison of the effect of hamstrings co-contraction was made.
The main objective of the present study was to investigate the effect of hamstrings muscle action on stability of the ACL-deficient knee during isokinetic exercise at various speeds. The analysis was based on a sagittal-plane model used previously to study load sharing between the muscles, ligaments, and bones during isometric knee-extension [6], [26], [27], [28], isokinetic exercise [7], and squatting [22]. The limit of knee-joint stability was defined as the peak ATT calculated for maximum isometric contractions of the quadriceps in the normal knee in the absence of hamstrings co-contraction. Four specific questions were addressed:
- (1)
What is the relationship between ATT and speed for isolated contractions of the quadriceps during isokinetic exercise?
- (2)
What is the relationship between ATT and hamstrings muscle activation during isokinetic knee-extension?
- (3)
Which factor has a greater effect on ATT in the ACL-deficient knee, knee-extension speed or hamstrings co-contraction force?
- (4)
In the range of extension speeds currently prescribed for rehabilitation, what level of hamstrings activation is needed to stabilize an ACL-deficient knee?
Mathematical modeling and forward-dynamics computer simulation were used to address these questions. A forward-dynamics simulation approach is necessary to study the relationship between hamstrings muscle activation and ATT because the level of hamstrings activation (and ultimately hamstrings co-contraction force) could be controlled more directly in the model. Also, high muscle forces generated during isokinetic extension exercise makes the use of in vitro measurement methods impractical for determining the dependence of ATT on quadriceps and hamstrings force.
Section snippets
Methods
The model presented in Shelburne and Pandy [27] has been expanded to permit simulation of an isokinetic knee-extension activity conducted in a sitting position with the hip flexed to 60°. The only structures not fixed to the ground were those distal to the femur. The lower leg was modeled as a rigid body consisting of a shank and a foot; the ankle was held fixed in the neutral (standing) position throughout the activity. Because all motion was confined to the sagittal plane, the lower leg’s
Results
ATT was inversely related to extension speed in both the intact and ACL-deficient knee (Fig. 3(A) and (B)). The effect of speed on ATT was uniform whether or not the ACL was present (Fig. 4). For example, the difference in ATT between the intact and ACL-deficient knee for isometric extension and for extension at 360 deg/s was around 6.5 mm (compare 0 and 360 deg/s in Fig. 4). Furthermore, no matter how fast the knee was extended, peak ATT occurred at 10° of flexion for the ACL-deficient knee,
Discussion
Perhaps the most significant limitation of the analysis is that the model itself is comparatively simple. The model knee accounts only for relative movements of the bones in the sagittal plane. Furthermore, the model bones are assumed to be rigid, so that there is only point contact between the femur and tibia and between the femur and patella. Other simplifications incorporated in the model include modeling the tibial plateau and patellar facet as flat surfaces; neglecting the influence of the
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2024, Musculoskeletal Science and PracticeKnee flexion angle and muscle activations control the stability of an anterior cruciate ligament deficient joint in gait
2021, Journal of BiomechanicsCitation Excerpt :Stability of an ACLD joint is influenced and maintained by an interplay between these two crucial parameters; smaller activity indices needed at smaller KFA whereas larger ones can be tolerated but require greater KFA. In the first half of stance, this can be achieved by an increase in KFA (Alkjaer et al., 2003; Beard et al., 1996; Chen et al., 2012; Frank et al., 2016; Fuentes et al., 2011; Shabani et al., 2015), a decrease in the knee flexion moment (Berchuck et al., 1990; Gardinier et al., 2012; Hurd and Snyder-Mackler, 2007; Ren et al., 2018), and/or an increase in hamstrings coactivity (Liu and Maitland, 2000; Shao et al., 2011; Sharifi et al., 2017; Sharifi et al., 2018; Shelburne et al., 2005; Yanagawa et al., 2002). In the second half of stance, on the other hand, the stability improves with increases in KFA (Boerboom et al., 2001; Gao and Zheng, 2010; Gardinier et al., 2012; Hurd and Snyder-Mackler, 2007; Ren et al., 2018; Roberts et al., 1999; Zeng et al., 2019) and/or in hamstrings forces while deteriorates with increases in gastrocnemii (Capin et al., 2017; Courtney and Rine, 2006; Houck et al., 2007; Huang et al., 2019; Papadonikolakis et al., 2003; Robbins et al., 2019).
Knee flexion with quadriceps cocontraction: A new therapeutic exercise for the early stage of ACL rehabilitation
2016, Journal of BiomechanicsCitation Excerpt :A possible way to prevent anterior tibial pull during OKC knee-extension exercises is related to hamstring cocontraction. In fact, hamstring cocontraction is inherent to natural knee extension and serves important physiological functions, such as stabilizing the tibiofemoral (TF) joint and reducing the mechanical loading of the ACL (Renström et al., 1986; Solomonow et al., 1987; Baratta et al., 1988; Draganich and Vahey, 1990; Aagaard et al., 2000; Yanagawa et al., 2002). Hamstring force actually yields compressive (stabilizing) TF force and posterior (ACL-unloading) tibial pull within the entire range of knee motion (Herzog and Read, 1993).