Review of The Research
It is clear that there is abnormal limb symmetry following procedures such as anterior cruciate ligament reconstruction (ACLR) (Noyes et al., 1991). In uninjured populations, using LSI’s for measures such as knee extension and flexion range of motion, endfeel and effusion have previously demonstrated excellent reliability (Lawrance et al., 2016). However, the same study suggests that when LSI’s are used for hip adduction strength, scores can show larger variation.
In patients who have had an ACLR, there is reduced maximum voluntary activation bilaterally in the quadriceps (Urbach et al., 1999; 2001). This is further supported by Palmieri-Smith et al., (2008), who suggests that this may also be due to arthrogenic (reflex) muscle inhibition. Depending on the measure being assessed and the stage of rehabilitation, LSI ‘pass’ scores can typically vary from 80-95%.
Another study found that even 7-months post ACLR, both male and female participants who scored mean LSI’s of 95.4% across 3 different hop tests, their raw scores (e.g. jump distance) were still much lower when compared to healthy participants (Gokeler et al., 2017). This data further supports that there is true bilateral muscle weakness present following ACLR, which is highly neural.
These implications lead us on to another study, where participants who were pre-operative ACLR completed a quadriceps strength test and hop test to gather LSI scores, with the same testing administered 6-months post-op (Wellsandt et al., 2017). At 6-months post-op:
- 40 participants achieved 90% LSI scores.
- However, only 20 participants achieved 90% of their pre-operative scores across all measures.
- Oppositely, 24 of the 40 participants who achieved 90% LSI 6-months post-op, did not achieve 90% of their pre-operative scores.
This means that even though participants scored 90% LSI 6-months post-op, over half still wasn’t at 90% of the level they were at before their operation. So, even though for some clinicians, this criteria may be a pass to progress rehabilitation, patients may not actually be at an acceptable level. This further supports the notion that there is bilateral quadriceps weakness following ACRL.
It also appears that LSI scores are significantly higher in a Single Hop for Distance and Triple Hop for Distance versus peak knee extension isokinetic torque and a bilateral power leg test (Nagai et al., 2020). This again is likely due to the decline in function of the unaffected limb (Patterson et al., 2020).