Background: The purpose of this study was to evaluate the results of surgery for Blount disease using a patient-derived outcome assessment. Our hypothesis was that an outcome score that quantitates the patient's level of satisfaction should correlate with specific ranges of correction for those radiologic variables traditionally used to evaluate Blount disease. The surgeon's aim should be to realign abnormal preoperative geometry to achieve those ranges that have a significant correlation with good outcome.
Methods: Medical records from 2 hospitals (Barbados and Trinidad) were reviewed and patients who had surgery for Blount's from 1997 to 2005 were identified and recalled. Responders completed a Blount's Outcome Questionnaire, were examined clinically, and standing radiographs were taken. The questionnaire was designed by modifying the AAOS Pediatrics-Parent/Child Outcome Instrument. Linear regression was used to assess the predictive effect of selected radiographic measures on a visual analog pain score and satisfaction score calculated from the questionnaire. The model was adjusted for confounders: country, age at the time of study, sex, body mass index, and years postsurgery. Variables in the adjusted model achieving significance at P<0.05 were included in a multiple regression analysis.
Results: Fifty knees in 41 patients were included. The median satisfaction score was 93%. The metaphyseal-diaphyseal angle (MDA) and anatomical femoral-tibial angle (aFTA), both had a quadratic effect on the pain score (P<0.001). The predicted pain score was minimized at the MDA range of 0 to -10 degrees and at the aFTA range of 0 to +5 degrees. A significant effect on the satisfaction score was noted for MDA (P=0.02) and aFTA (P<0.001) with scores maximized at the MDA range of +5 to -5 degrees and at positive aFTA (valgus angulation). For women the satisfaction scores were lower and the pain scores higher. Overweight patients had higher pain scores.
Conclusions: Results of this evaluation of the association between patient outcome scores (for pain and satisfaction) and postoperative clinical and radiologic variables support the recommendation that surgical correction should aim at producing an MDA score between -5 and +5 degrees and a valgus alignment with an aFTA score of 0 to 5 degrees.
Level of evidence: Therapeutic study, investigating the results of treatment. Level III.