Introduction

Aberrant movement of the lumbar spine is thought to be related to chronic low back pain. It is suggested that the aberrant movement is caused by less optimal neuromuscular control and that this in turn creates excessive tissue stress, which may be responsible for persisting or recurrent symptoms. Investigating whether these movement patterns exist may help in establishing rehabilitation goals for the individual in front of you. In this light, the use of valid tests is crucial. Therefore, the purpose of this study was to examine the inter-rater reliability of visual inspection of the presence/absence of aberrant movement patterns during the prone hip extension test.

Methods

A cross-sectional study investigating the inter-rater reliability was conducted, including 18 participants between 20 and 40 years of age without low back pain and 26 with low back pain in remission. Being in remission of chronic low back pain implied that these individuals were currently pain-free but had had low back symptoms for more than 3 months OR they had a history of recurring low back pain symptoms for at least 2 episodes interfering with the activity of daily living or requiring treatment.

The observations were carried out by two physiotherapists who received training prior to the start of the study. Patients were prone and were asked to extend the hip. Three repetitions of this movement were performed, while the physiotherapists observed whether aberrant movements like lumbar extension, lumbar lateral flexion, or pelvic rotation occurred.

Results

The results of this study indicate that agreement between both observers was rather high (more than 70%) and kappa values ranged from fair to moderate, although the lower limits of the confidence intervals reveal only slight to fair agreements. Aberrant movements observed in this trial were lumbar extension and pelvic rotation. Lumbar lateral flexion was not observed to occur. The findings indicate that there was a significant association between the presence of aberrant movements and chronic low back pain remission.

Questions and thoughts

The cross-sectional research design used in this study prevented the establishment of causal relationships. Therefore the association between the presence of aberrant movements in those with remiss chronic low back pain cannot be used to state that the aberrant movements are responsible for the recurring low back pain complaints. It only gives an interesting insight that should be further explored in detail before conclusions can be drawn.

Prior to the study commencement, observers were trained to rate the aberrant movements during the prone hip extension test by an expert. Findings were discussed and discrepancies were resolved together with the expert. This training is good as it is likely to improve the quality of the data collection of a rather subjective measurement. However, the clinical observation of the expert had apparently been validated with an electromagnetic tracking system, however, no reference was made to the validation study. Therefore, we remain a bit skeptical about this statement and these procedures.

Before data collection, the level of acceptable agreement between both raters was set at 80%. The results of this study revealed that only once, the 80% mark was reached. Thus, the conclusion of the study should at least be adapted that agreement was good but did not reach the acceptable threshold that was set beforehand. However in literature, often 75% is thought to be necessary for a measurement to be rated as acceptable and thus the authors have been strict. In our opinion, it is always better to be underestimating a value than overestimating and over-inflating conclusions.

An important question we ask ourselves when reading this paper is related to the population studied. The study recruited individuals between 20-40 years and the mean age of the population was 25 years. Knowing that the prevalence of (chronic) low back pain increases with age, it is very uncommon that this population reflects the low back pain population seen in clinical practice. Therefore, the generalizability of the findings should at least be questioned.

Talk nerdy to me

Sample size calculation revealed that at least 29 participants were required and the authors were able to recruit 44. However it was not clearly stated if the sample size calculation was performed beforehand, so this may be a potential limitation.

The raters were blinded to the group participants belonged to (having chronic low back pain or not) and rated the aberrant movements independently, which is required in an inter-rater reliability study. They observed the patient at the same time, which is good as this way it cannot be expected that a learning effect or altered movement strategies were present due to for example increasing pain over the course of the repetitions. But in another way, it may be risky to rate the participants at the same time as both observers could potentially influence each other non-verbally by for example their facial expressions.

Prevalence and bias-adjusted kappa were calculated as well, and this increased the kappa values to moderate and substantial inter-rater reliability. However, it is also important to present the prevalence, positive agreement, negative agreement, and relative frequency in each cell of the data contingency table, but this, unfortunately, was not done in the current study.

Take home messages

A good inter-rater reliability is important in the evaluation of a clinical test. The current study aimed to investigate the inter-rater reliability of observing aberrant movements when performing the prone hip extension test. The findings show that overall, agreement between both observers was good and reliable. Kappa, which accounts for agreement by chance, indicates that agreement is fair to moderate, which is to be expected with this rather subjective assessment (visual inspection)

Bearing this in mind, sure, good neuromuscular control is important, but it should be clear that this is not the only factor in the occurrence of or in the persistence of low back pain. Nevertheless, this study showed that the prone hip extension test is a reliable test to use between different examiners as it shows fair to moderate agreement. There was an association between the presence of aberrant movements during this test and remission of chronic low back pain. This does not mean that both are causally related, but the presence of these aberrant movements may be an interesting observation to examine in patients with recurring low back pain in a step toward therapy.

If you want to learn more about the kappa statistic, we refer you to our youtube channel where Kai explains the background of it in detail: https://www.youtube.com/watch?v=DfNo32nL_fo

Reference

Kong-Oun, S., Prasertkul, W., Fungkiatphaiboon, P., & Wattananon, P. (2022). The inter-rater reliability of clinical observation of prone hip extension and association between aberrant movement and chronic low back pain. Musculoskeletal Science and Practice, 57, 102476.