Is there a difference in sagittal alignment of Blount's disease between radiographic and clinical evaluation?

BACKGROUND

A procurvatum deformity of the proximal tibia often is seen in patients with Blount's disease. If left untreated, it can lead to progressive angulation in the sagittal plane and altered contact stresses across the knee.

QUESTIONS/PURPOSES: We asked the following questions: (1) Is the mean angle of procurvatum measured from full-length lateral radiographs of the tibia greater than that of procurvatum measured from clinical photographs of the affected lower extremity? (2) Is there a linear relationship between radiographically measured procurvatum and radiographically measured procurvatum?

METHODS

We treated 72 patients surgically for Blount's disease between 1997 and 2012; of those, 29 patients were excluded from this analysis because they did not have adequate photographs or radiographs, leaving 43 patients (60% of the patients treated surgically; 47 limbs total), mean age of 13 years (range, 6-25 years), who underwent surgical realignment for Blount's disease were retrospectively evaluated at a median of 97 months after surgery (range, 24-170 months). Genu procurvatum was measured from full-length lateral radiographs of the tibia and clinical photographs of the affected lower extremity. We then assessed the relationship between radiographically measured procurvatum and clinically measured procurvatum using linear regression analysis.

RESULTS

The mean preoperative radiographically measured procurvatum (12.3°; range -3.1° to 55.2°) was larger than the clinically measured procurvatum (6.0°; range, -1° to 45°; p = 0.024). The mean postoperative radiographically measured procurvatum (4.2°; range -4.8° to 30.3°) was larger than the clinically measured procurvatum (2.1°; range, -2° to 20°; p = 0.041). Preoperatively and postoperatively, radiographically measured procurvatum and clinically measured procurvatum were well correlated (linear regression p < 0.001). After surgical realignment, the mean improvement in radiographically measured procurvatum (8.2°) was larger than that measured for clinically measured procurvatum (3.8°) (p = 0.018).

CONCLUSIONS

In patients with Blount's disease, visual inspection of the extremity can underestimate the procurvatum deformity of the proximal tibia relative to the measurable deformity on radiographs. Furthermore, surgical correction of proximal tibial procurvatum does not lead to clinical hyperextension of the knee.

LEVEL OF EVIDENCE: Level IV, diagnostic study. See Guidelines for Authors for a complete description of levels of evidence.