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Created: Jan 26, 2018
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Week 3 Report: Ankle Joint Functionality
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Introduction: Breaking an ankle can lead to problems with mobility throughout one's lifetime. Many patients with broken ankles undergo surgery, which sometimes includes the placement of hardware to aid functionality. The current standard is to later remove this hardware after the patient heals. However, according to Wagoner, Creech, Nolan, and Meyr, there are many complications associated with the hardware extraction surgery, including pain, intra-articular fixation, and carcinogenesis (Wagoner, Creech, Nolan, & Meyr 2015). This study looks if there are differences in ankle functionality between patients who undergo hardware extraction and those that retain their hardware. 

Methods: We followed an orthopedist who performed surgery on 19 patients with broken ankles. 9 of these patients had their hardware removed after healing, while 10 of them retained their hardware. We then obtained the percentage of functionality from all 19 patients, yielding interval ratio data. A QQ test was used to determine if normality conditions were satisfied. Because the sample size of 19 was small (>30) and normality conditions were not satisfied, a Mann Whitney test was used to compare group medians. 


Result 1: Ankle Joint Functionality QQ Plot   [Info]
Right click to copy

The QQ plot above depicts the data values for the percentage of functionality of the group with hardware removed and the group with hardware retained. As the data values did not fall on the 45 degree line, normality conditions were not satisfied. Thus, a Mann Whitney Test was used to determine if the median percentage of functionality for the group with hardware removed was greater than the median percentage of functionality for the group with hardware retained. The p-value of 0.9727 rejected our research hypothesis, indicating that those with hardware removed do not experience greater functionality compared to those with hardware retained. 

Result 2: Mann-Whitney Ankle Joint Functionality   [Info]
Hypothesis test results:
m1 = median of Hardware Removed
m2 = median of Hardware Retained
m1-m2 : m1 - m2
H0 : m1-m2 = 0
HA : m1-m2 > 0
Differencen1n2Diff. Est.Test Stat.P-valueMethod
m1 - m22910-17670.9727Norm. Approx.

With 95% confidence, we can determine that the median difference in functionality between the hardware removed group and the hardware retained group is between -30 and 1. 

Result 3: Confidence interval ankle joint   [Info]
95% confidence interval results:
m1 = median of Hardware Removed
m2 = median of Hardware Retained
m1-m2 : m1 - m2
Differencen1n2Diff. Est.L. LimitU. LimitMethod
m1 - m2910-17-301Exact (95.652645)

Conclusion: There are differences in functionality between the hardware removed group and the hardware retained group, and there does not appear to be greater functionality for the hardware removed group. Because of the small sample size and lack of normality, a Mann Whitney test was the best choice to depict the findings. The small sample size would make these results difficult to generalize for the entire population. It is unfortunate that confounding factors were not accounted for, as other comorbidities and factors can affect ankle functionality. For example, obesity, history of multiple prior injuries, etc. can all negatively impact ankle functionality. Future studies should include larger, stratified samples in order to be able to generalize results for the population and account for confounding factors. 


Wagoner, M.R., Creech, C.L., Nolan, C.K., & Meyr, A.J. (2015). Pictorial Review and Basic Principles of Foot and Ankle Hardware Extraction. Foot & Ankle Specialist, 8(4), 305-313. doi:10.1177/1938640015585964 



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By nku.dr.nolan
Jan 28, 2018

Hi Rosemary - overall this looks good, but I think I see one mistake in the hypothesis test that probably messed up the results. Why would we only care about "greater than", using a one-sided test? Seems like we would want to just compare, to figure which treatment method is better.

In your conclusion, the thing to go after is that CI - specifically the "30" part of it. If we saw a difference of 30 degrees, that would surely be important. So this is telling us that (confounding potential aside) we don't have a large enough sample to know if one is better.

Hope this helps!
By carrie.ayers
Jan 28, 2018

Hi Rosemary,

All of your graphs look great and liked how you chose to incorporate the results of the QQ plot instead of just stating the information. As Tonya and Kyleigh stated, addressing confounding factors would certainly need to be taken into account and the need for a larger sample size is very important. I also feel that gender should be a confounding variable that needs to be taken into account due to bone strength.
By tonya.mcgowan01
Jan 27, 2018

Hi Rosemary,
Your plots look very nice. I agree with Kyleigh, in that possible confounding factors in your conclusion should be taken into account. Prior ankle injury could certainly affect the outcome of future injuries and recovery.
By kyleigh.odom711
Jan 27, 2018

I like that you addressed the possible confounding factors in your conclusion. There are a lot of issues that could affect ankle mobility with/without hardware, it is hard to generalize this population in one sample.

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