Sensory deficits in runners with an overuse injury

There has been a lot of  work done over the years (and I done a tiny bit of it) that have contributed to our understanding of sensory input to gait, postural issues and the effects of running shoes (or lack of them) and foot orthoses. Some have been dismissive of it and others have extrapolated way beyond what the research is actually saying to make it into almost a cult! I certainly jumped on the bandwagon for a while, but have backed off more as I learn and understand more about it and actually did a study on it that came to naught! Despite that, I still follow the issue with interest. This study appeared a few days ago and I been thinking about it and not sure what to make of it. I have not been able to read the full text, so what I say needs to be tempered in that context.

Differences in Joint Position Sense and Vibratory Threshold in Runners With and Without a History of Over-Use Injury.
Switlick T, Kernozek TW, Meardon S.
J Sport Rehabil. 2014 Jun 25
CONTEXT:
A relationship between altered postural control and injury has been reported in sports. Sensorimotor function serves a fundamental role in postural control and is not often studied in runners. Persons who sustain running injury may have altered sensorimotor function contributing to risk of injury or re-injury.
OBJECTIVES:
To determine if differences in knee and ankle proprioception or plantar sensation exist between injured and non-injured runners.
DESIGN:
Retrospective Case Control Study.
SETTING:
University Campus.
PARTICIPANTS:
20 runners with a history of lower extremity overuse injury and 20 non-injured runners were examined. Injured runners were subcategorized into 2 groups based on site of injury: foot/ankle and knee/hip.
MAIN OUTCOME MEASURES:
Active absolute joint repositioning error of the ankle at 20° inversion and 10° eversion and the knee at 15° and 40° knee flexion was assessed using an isokinetic dynamometer. Vibratory threshold at the calcaneus, arch, and great toe was determined for each subject using a hand-held electric sensory threshold instrument.
RESULTS:
Runners in the injured foot/ankle group had increased absolute error during ankle eversion repositioning (6.55 ± 3.58º) compared to those in the non-injured (4.04 ± 1.78º; ; p=0.01) and the hip/knee (3.63 ± 2.2; p=0.01) groups. Runners in the injured group, as a whole, had greater sensitivity in the arch of the plantar surface (2.94 ± 0.52 V) than non-injured runners (2.38 ± 0.53 V; p=0.02).
CONCLUSIONS:
Differences in ankle eversion proprioception between runners with a history of ankle and foot injuries and non-injured runners were observed. Runners with a history of injury also displayed an increased vibratory threshold in the arch region compared to non-injured runners. Poor ankle joint position sense and increased plantar sensitivity suggest altered sensorimotor function following injury. These factors may influence underlying postural control and contribute to altered loading responses commonly observed in injured runners.

I can’t say much about the methods and analysis as I have not read the full paper (if I get it I will comment back later).

I will comment on two findings:

  • they found that the group of runners in the injured group had a greater range of eversion before it was detected by the subject (at least that is how I interpret what the abstract says). This indicates that there is possibly a proprioceptive deficit in the injured group. However this was only 6.55 vs 4.04 degrees; ie about 1.5 degrees difference between the two groups. While that was  statistically significant, is 1.5 degrees clinically meaningful? I did calculate Cohen’s d for the effect size from there data and it was 0.88 which is pretty good.
  • the other finding was vibration perception being measured in 3 areas, but only one of them (the arch) being statistically significant different.The injured group were less  sensitive, needing 2.94 volts before they detected the vibration compared to the non-injured group that needed 2.38 volts. Again, this was statistically significantly different, but how clinically meaningful is the difference of 0.56 volts? Again, I calculated the effect size to be a very good 1.06.

This was a retrospective study and not prospective so the chicken and egg comes into it. Did the sensory issues (as small as what they are) exist prior to the injury and was this a risk factor via reduced sensory input creating postural and gait issues or did the sensory issues develop post injury due to some sort of central sensory issue as a result of the pain from the injury? I guess the fan boys from either end of the spectrum will interpret this in the context of their own biases to claims that this study shows one or the other depending on their biases!

As always, I go where the evidence takes me until convinced otherwise, and this study does tell me that there are probably some small sensory deficits in runners with an overuse injury. I say probably as I have not reviewed the full paper yet. The deficits are small, but the study design used does not tell us if the deficit existed prior to the injury or developed following the injury.

., Switlick, T., Kernozek, T., & Meardon, S. (2014). Differences in Joint Position Sense and Vibratory Threshold in Runners With and Without a History of Over-Use Injury Journal of Sport Rehabilitation DOI: 10.1123/jsr.2013-0089

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