June 2016

Out on a limb: Subjectivity & sensitivity

1Limb-JordanaBy Jordana Bieze Foster, Editor

Listening to what patients have to say is an important part of healthcare. But, 
as research continues to demonstrate, it’s no substitute for objective measurements.

It’s well documented that patients are not necessarily reliable when it comes to self-reporting information such as height, weight, shoe size, dietary practices, and physical activity levels. So it shouldn’t be surprising that preoperative scores on an assessment tool focused largely on self-reported pain and function isn’t ideal for predicting clinical outcomes after total hip arthroplasty (THA).

A recent study from the University of Illinois at Chicago (UIC) found that preoperative measures predicted clinical response after THA much more accurately when objectively measured preoperative gait mechanics were considered along with the largely subjective Harris Hip Score (HHS) (see “Gait and THA outcomes: Hip mechanics have predictive value,” page 15).

Preoperative HHS alone predicted clinical response with a sensitivity of 57%, which is actually pretty impressive for a subjective test. But, when preoperative peak hip external 
rotation moment was added to the predictive model, the sensitivity improved to 71.4%.

Self-reported information is convenient and inexpensive to obtain, but on its own may be too unreliable to drive clinical decisions.

Including gait mechanics in the predictive equation doesn’t just make it more accurate—it also makes it more useful. Even knowing that higher preoperative HHS values are associated with nonresponse after THA, implementing an intervention to reduce those HHS values preoperatively makes little clinical sense, and is likely unethical as well. But, knowing that low preoperative hip external rotation moments are associated with nonresponse after THA—and that those moments remain low postoperatively in nonresponders, which the UIC group also found—suggests such patients could benefit from physical therapy interventions to improve hip function postoperatively, and likely also improve clinical response by doing so.

Clinical nonresponse after THA affects a considerable number 
of patients. In the 124-patient UIC study, the clinical nonresponse rate was 11%, which is consistent with reports in the literature 
that range from 5% to 15%. Given that more than 300,000 procedures are done annually just in the US, up to 45,000 patients will not have a positive response.

And there’s reason to believe the actual number of THA nonresponders might be even higher. In a study published in the February issue of the American Journal of Physical Medicine & Rehabilitation, researchers from the University of Colorado in Aurora reported that patients tend to overestimate their level 
of function following total hip replacement, compared with performance-based tests; this may be because the degree of pain relief they experience makes them feel able to function at a higher level than they actually can.

It would be nice if more THA nonresponders could be identified using the HHS alone. It certainly would be more convenient and less expensive than conducting detailed gait analysis on every THA patient. But it also would be much less accurate, which would mean thousands of patients not receiving the rehabilitation they need to address specific underlying mechanical issues.

What patients have to say is important. But what objective data have to say is too important to ignore.

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