Hip Outcome Survey (HOS)
There are over 41 hip outcome reporting measures in use today and many of them are tailored towards an older age group which by definition is a less mobile and less active demographic. Because of this, many of these reporting measures fall victim to the ceiling effect – a statistical term for the phenomenon that occurs when the highest score on a rating tool is unable to properly assess a patient’s level of ability. For instance, younger patients tend to be significantly more active than elderly patients. As such, rating tools with a median age of 60 may fail to account for the activities carried out by people in their 20s or 30s.
In 2006, the Hip Outcome Survey (HOS) was developed to help address this issue. As younger patients have different goals, expectations and quality of life benchmarks post-treatment, it was felt that a reporting measure with these concerns in mind would be more representative than many of the pre-existing surveys.
The HOS is a self-administered questionnaire with a scoring system composed of 2 sub-scales. The Activities of Daily Living (ADL) sub-scale made of 19 items and a Sports sub-scale composed of 9 items. The ADL sub-scale focuses on a wide range of functions from small activities such as putting on socks, standing and sitting, to more demanding activities like squatting, twisting and pivoting on the affected leg.
The second category, the Sports sub-scale looks at the ability of an individual to perform specific errands such as running one mile or swinging items like a golf club. This scale asks respondents about activities they carry out using their normal technique and includes movements like starting, stopping quickly, lateral and cutting motions.
Both subscales are marked separately and 17 items from the Activities of daily living scale are scored from 0 to 4, with 0 being ‘unable to do’ and 4, ‘no difficulty’. ‘Not applicable’ responses are also possible options. The total score is then multiplied by 4 to get the highest potential score which can be no greater than 68. The sports sub-scale is marked in a similar fashion with the highest potential score being 36. An overall higher score from both of these sub-scales represents a greater level of function.
Unlike many patient-reported outcome measures, the HOS scoring system focuses on a younger, more active patient population –which is evidenced by the questions seen in the survey and helps to remove the ceiling effect that is present in other PROMs.
As mentioned, the primary strength of the HOS survey is its applicability to those individuals with a very high level of physical functioning, such as athletes. Currently, only three other PROMs exist with this key feature in mind –The Harris Hip Score (MMHS), the Nonarthritic Hip Score (NHS), and the MAHORN (Multicenter Arthroscopy of the Hip Outcomes Research Network).
Additionally, other traditional hip scoring systems make it difficult to determine whether activities are limited by hip pain or if the pain felt is related to other pre-existing causes such as knee or back pain. To solve this problem, the HOS measure allows respondents to address this by specifically answering ‘Not applicable’ if any pain felt is related to another cause. The ‘Not applicable’ responses are removed from the overall score and have no effect on the final outcome.
Another strength of HOS instrument is its robustness as a reporting tool. This was demonstrated by a study carried out in 2011 that found that the HOS has the greatest amount of clinimetric evidence (rigor of rating scales and indexes for the description of clinical phenomena) as compared to other similar alternatives (4).
The effectiveness of the HOS survey is based on the total number of questions that a respondent is able to answer and it has been suggested that for a valid outcome a minimum of 14 of the ADL questions must be answered. However, because the nature of the survey assumes a relatively moderate level of activity to begin with, some physicians may find that this measure is not always appropriate for their older, more sedentary patients thereby making it ineffective for some people in this demographic.
Additionally, very little literature exists with regards to the correlation between HOS and other hip reporting tools.
Overall, the Hip Outcome Score which was designed to assess higher-level activities (i.e. those required in athletics) appears to be a reliable reporting tool for healthcare providers with a younger patient demographic.
- Tijssen, M., van Cingel, R., van Melick, N., & de Visser, E. (2011). Patient-Reported Outcome questionnaires for hip arthroscopy: a systematic review of the psychometric evidence. BMC musculoskeletal disorders, 12(1),
- Safran, M. R., & Hariri, S. (2010). Hip arthroscopy assessment tools and outcomes. Operative techniques in orthopaedics, 20(4), 264-277.
- A Physical Therapy Program Versus Surgery for Femoroacetabular Impingement: Randomized Clinical Trial
- Lodhia P., P Slobogean G., K Noonan V., K Gilbart M. (2011). Patient-reported outcome instruments for femoroacetabular impingement and hip labral pathology: a systematic review of the clinimetric evidence.