A clinical prediction rule for identifying patients with patellofemoral pain who are likely to benefit from foot orthoses: a preliminary determination. (2010)

Abstract
OBJECTIVE:
To develop a clinical prediction rule to identify patients with patellofemoral pain (PFP) who are more likely to benefit from foot orthoses.

DESIGN:
Posthoc analysis of one treatment arm of a randomised clinical trial.

SETTING:
Single-centre trial in a community setting in Brisbane, Australia.

PARTICIPANTS:
42 participants (mean age 27.9 years) with a clinical diagnosis of PFP (median duration 36 months).

INTERVENTIONS:
Foot orthoses fitted by a physiotherapist.

MAIN OUTCOME MEASURES:
Five-point global improvement scale at 12-week follow-up, dichotomised with marked improvement equalling success.

RESULTS:
Potential predictor variables identified by univariate analyses were age, height, pain severity, anterior knee pain scale score, functional index questionnaire score, foot morphometry (arch height ratio, mid-foot width difference from non-weight bearing to weight bearing) and overall orthoses comfort. Parsimonious fitting of these variables to a model that explained success with orthoses identified the following: age (>25 years), height (<165 cm), worst pain visual analogue scale (<53.25 mm) and a difference in mid-foot width from non-weight bearing to weight bearing (>10.96 mm). The pretest success rate of 40% increased to 86% if the patient exhibited three of these variables (positive likelihood ratio 8.8; 95% CI 1.2 to 66.9).

CONCLUSION:
Post-hoc analysis identified age, height, pain severity and mid-foot morphometry as possible predictors of successful treatment of PFP with foot orthoses, thereby providing practitioners with information for prescribing foot orthoses in PFP and stimulating further research.

My comments:

This study was a follow up on an earlier study by the same authors that I also blogged. That study found foot orthotics with arch supports only had a modest beneficial effect in treating patellofemoral pain, with success (defined as those patients experiencing a marked improvement) in only 40% with the use of orthotics in those with patellofemoral pain.

What they did in this study was go back and look at the 40% who had success and see what factors they had in common, so that physical therapists can better predict who is likely to benefit from orthotic use.  They found four variables that increased the odds orthotics would help.

1. being over 25 years old
2. being shorter than 165 cm (shorter than 5’5”)
3. worst pain less than 53.3 mm on a VAS (pain at worst less than 5.33 out of 10)
4. midfoot width difference greater than 10.96 mm (a more mobile foot that flattens more when you put weight on it)

What they found was if the patient had 3 out of 4 of those variables, the chance of success more than doubled from 40% up to 86%.  2 out of 4 and you still had a 61% of success.

So the take home is that if you are over 25, not too tall (less than 5’5”), your pain isn’t too bad (less than ~5/10 at worst), and your foot flattens more than usual (probably you will need someone to measure that), there is a pretty good chance that orthotics with arch supports will help lessen patellofemoral pain.  With newer research showing patellofemoral pain is multifactorial, principally involving hip and thigh muscle weakness, orthotics should probably be considered only part of the solution in some people and study helps us decide who those people are.