Is The Single Leg Squat Assessment Valid?

Picture from Wilczynski et al, 2020

A visual assessment we use when seeing a patient in our clinic especially when they have knee or hip pain is the single leg squat (SLS). We stand the patient in front of a full length mirror and ask them do do a SLS on the non painful knee/ hip first before comparing with the painful side.

Picture from Vasiljevic et al, 2020

We look at the patient's movement quality when they execute the SLS. We observe how effective they are throughout the entire movement, their balance and fluidity to keep the knee stable instead of letting the knee flop inwards (or inward knee displacement). 

Being able to assess movement quality during the SLS can provide valuable insight into the risk of lower limb injuries. They are usually associated with the severity of symptoms and also helps with prognosis of lower limb injuries.

Assessing the patient visually like this is widely used in many health care, rehabilitation and injury prevention programs. This is also a much more cost effective alternative compared to complex biomechanical analyses. It's also much faster.

Ressman and colleagues (2019) have found that the SLS is both reliable and feasible for use in individuals with lower limb conditions.  However, a recent systematic review (Gomes et al, 2023) 'questioned' the validity (or soundness) of the SLS and whether it was useful in clinical settings (like health care clinics).

Gomes et al (2023) found 10 studies evaluating 3 different methods of visual assessment of the SLS (Crossley scale, Whatman score and medial knee displacement). They found very low to moderate certainty evidence that the 3 methods were totally accurate and sound. Hence, it may not be effective relying solely on visual assessment methods for clinical outcomes. 

They wrote that their findings DO NOT nullify the significance of assessing movement quality of patients but that it was essential for future robust research to develop scales that are sound. Only then that they can assist practitioners in their clinical decision making.

We will still use the SLS when assessing patients in our clinic. I defintely understand where the researchers are coming from. The need to justify whether our assessments and treatment work, otherwise governments, insurance companies and of course self paying patients will not want to come to us anymore.

A more experienced clinician would be able to discern movement quality over a less experienced one. Some of the included studies did not control for speed and depth of the squat. These confounding factors will affect movement quality. Some of the review's key findings were based only on one study, so findings should be interpreted with caution.

References

Gomes DA, Da Costa GV, Martins EC et al (2023). Are Visual Assessments Of The Single-leg Squat Valid To Be used In Clinical Practice? A Systematic Riview Of Measurement Properties Based On The COSMIN Guideline. PT in Sport. 63: 118-125. DOI: 10.1016/j.ptsp.2023.07.009.

Ressman J, Grooten WJA and Barr EA (2021). Visual Assessment Of Movement Quality In The Single Leg Squat Test: A Review And Meta-Analysis Of Inter-Rater and Intrarater Reliability. BMJ Open Sp Ex Med. 5:e00541. DOI: 1136/bmjsem-2019-00541.