Background
Patient reported outcome measures (PROM) have become an integral part of clinician-patient practice. The Knee Injury and Osteoarthritis Outcome Score (KOOS) is a 42-item generic questionnaire used to evaluate a variety of knee pathologies that can result in post-traumatic osteoarthritis but is more broadly used. The Norwich Patellar Instability Score (NPI) is a 19-item disease-specific outcome measure that was designed for patellofemoral instability patients. These two PROMs have 16 questions that evaluate the same functions. The KOOS asks if there is difficulty with physical function over the last week while the Norwich asks if how often the patella feels like it will “pop-out”.
Purpose
The purpose of this study was to determine if patients that answered both KOOS and NPI questionnaires at the same timepoint answered comparable questions equivalently thus potentially eliminating the need to have patients complete both PROMs.
Methods
The KOOS and NPI responses were reviewed by two independent reviewers, and 16 comparable questions between the two questionnaires identified. For comparison purposes the scores of the KOOS (higher score indicates less problems) were inverted to match the directionality of the Norwich (higher score indicates more problems). The comparison was None, Mild, Moderate, Severe, Extreme (KOOS) to Never, Rarely, Sometimes, Often, Always (Norwich).
180 patients treated for patellofemoral instability with isolated medial patellofemoral ligament (MPFL) reconstruction who completed both surveys as part of an international mulit-center study were identified.The centers that contributed study subjects to the overall project were: University of Minnesota, The Ohio State University, OrthoSport Victoria, University of Tampere, Kobe University Orthopedic Surgery. Tria, Pontificia Universidad Católica de Chile These patients responded to the KOOS followed by the NPI prior to surgical treatment for their patella instability. Responses to the selected comparable questions were then analyzed using Chi-square.
Results
No statistically significant different differences were found between the responses to the following questions: Putting on socks (KOOS) – Crossing legs while sitting (Norwich), taking off socks (KOOS) – crossing legs while sitting (Norwich), Running (KOOS) – Running in a straight line on uneven surfaces (Norwich), and twisting/pivoting on injured knee (KOOS) – twisting/changing directions during sport (Norwich). The remaining 12 comparable questions evaluating descending stairs, ascending stairs, walking on a flat surface, getting in and out of a car, going shopping, squatting, jumping, twisting vs running sideways or looking over your shoulder, kneeling, were found to yield statistically different response distributions (p<0.05).
Conclusion
Only 4 of the 16 questions deemed to be comparable between the two questionnaires were found to have similar responses for a given patient despite both questionnaires being completed at the same encounter. The reasons for the differences are unclear but likely in part reflect the specific wording of the two questionnaires. The KOOS asks questions in terms of the degree of difficulty due to the knee whereas the NPI asks questions in terms of whether the patella will “pop out”. Respondent fatigue due to the length of time required to complete both questionnaires in the same sitting may also have played a role. Clinician conversation with the patient may elucidate the reasons for and meaning of these differences in responses.
The following centers contributed study subjects to the overall project: University of Minnesota, The Ohio State University, OrthoSport Victoria, University of Tampere, Kobe University Orthopedic Surgery. Tria, Pontificia Universidad Católica de Chile