Present day knowledge dictates that athletes wanting to return to sport, younger individuals, and patients who experience knee instability despite rehabilitation are likely candidates for ACL reconstruction surgery (Dhillon, 2014). Arthroscopically assisted ACLR using either the patella or hamstring tendon is the standard surgical treatment for patients (Gianotti, Marshall, Hume & Bunt, 2009). Magnussen, Carey and Spindler (2010) found in their systematic review that there is no significant difference in knee stability and strength between those two grafts.
There is general consensus that physiotherapy plays an important role in the rehabilitation of ACL reconstruction patients to premorbid level of function post-operatively. The rehabilitation progresses essential components of a knee’s function, such as range of motion, stability, neuromuscular control and arguably the most significant: quadriceps’ strength (Cooper & Hughes, 2017). Grindem, Snyder-Mackler, Moksnes, Engebretsen and Risberg (2016) found a 33 per cent re‑injury rate in patients that had less than 90 per cent strength of their non ACLR leg. The challenge during the early stages of rehabilitation is that the graft is undergoing increasing necrosis and hypocellularity, markedly at the centre of the graft, resulting in reduced graft mechanical strength (Janssen & Scheffler, 2013). Despite this, it is vital that this graft and tissue are mechanically loaded, however the level of load is paramount. If the graft is under‑loaded it can lead to significant loss of tensile strength (Ménétrey, Duthon, Laumonier & Fritschy, 2008), whereas conversely, a significant overload of mechanical stress can similarly reduce graft tensile strength (Ekdahl, Wang, Ronga & Fu, 2008).
It is recognised that overloading the graft contributes to graft laxity (Cuomo, Reddi Boddu Siva Rama, Bull & Amis, 2007). ACL graft laxity risks compromising normal knee biomechanics through increased tibial anterior translation and internal rotation, resulting in increased contact stress (Simon et al., 2015). Therefore, ACL graft laxity can significantly contribute to secondary meniscal degeneration, subchondral sclerosis (Kiapour & Murray, 2014) and graft re-rupture (Hewett, 2017). For this reason the open kinetic chain [OKC] versus closed kinetic chain [CKC] approach is heavily debated. It is speculated that OKC exercises (where the distal segment of the limb is free to move) result in increased anterior tibial translation and hence overload the new graft (Escamilla, Macleod, Wilk, Paulos & Andrews, 2012). The use of CKC exercises conversely, (where the distal segment of the limb is fixated) is encouraged in the ACLR rehabilitation process and can be dated back to recommendations made by Henning, Lynch and Glick (1985). It is hypothesised that CKC reduces tibial anterior displacement secondary to co‑contraction of the hamstrings in combination with joint compression forces (Escamilla et al., 2012). CKC exercise is not always practical however. Sigward, Chan, Lin, Almansouri and Pratt (2018) found that an ACLR patient will compensate away from their reconstructed knee through weight distribution for at least 5 months post-operatively during loaded or unloaded squats. This weight distribution coupled with the body’s ability to compensate for weak quadriceps by engaging gluteus maximus and calf muscles to achieve knee extension (Thompson, Chaudhari, Schmitt, Best & Siston, 2013) means that quadriceps’ strength adaptations can be difficult to achieve in CKC. Furthermore Escamilla et al. (2012) showed that a 12-repetition maximum knee extension from 0-90 degrees has comparable, if not less, peak shear forces on the ACL than walking across level ground.
So, to OKC or to not OKC?
There is a moderate level of evidence to suggest that OKC exercises do not contribute to increased ACL laxity or reduced self-reported function during rehabilitation of ACLR when compared to CKC exercises. There is a significant need for a greater volume of high-quality research to help pilot new guidelines for practitioners of the multidisciplinary team. Until there is strong evidence, practitioners are advised to use clinical judgment and post operative orders as well as take a cautious approach when prescribing OKC exercises during the first 12 weeks of ACLR recovery. Should OKC exercises be prescribed, current evidence suggests they not be used as a replacement to CKC exercises but rather a supplement, and only when the exercise could not be substituted for a CKC exercise.
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