Guided Growth for Genu Valgum in Mucopolysaccharidoses: Beware the Rebound

Background: Genu valgum is common in mucopolysaccharidoses (MPS) patients. Improved life expectancy has led to a focus on quality of life, including the management of genu valgum to preserve mobility and reduce pain. This study assesses outcomes of guided growth for coronal plane knee deformities, including correction rates, complications, and rebound deformity. Methods: A retrospective review of patient notes was undertaken. Presugery and postsurgery standardized long leg alignment films radiographs were assessed for mechanical axis deviation (MAD), genu valgum angle, mechanical lateral distal femoral angle (mLFDA) and mechanical medial proximal tibial angle (MPTA). All patients underwent tension band plating. Statistical analysis was undertaken using Prism software (GraphPad Software Inc., San Diego, CA). Results: Since 2010, of 103 patients referred, 69 knees in 35 patients required surgery for genu valgum deformity. Mean radiographic follow-up was 5.5 years (24 to 110 mo). Fifty limbs (82%) corrected to a normal zone 0/1 MAD from a mean preoperative genu valgum of 19.5 degrees (range: 11.1 to 34.1 degrees). Plate removal occurred at a mean of 34 months with a mean 2.1 degrees valgus achieved (P<0.0001). Forty-four of corrected knees exhibited rebound genu valgum of 15.2 degrees (range: 12.1 to 25.4 degrees) at a mean of 17.2 months (range: 6 to 33 mo) following plate removal. In 8 knees, correction was ongoing. Early age at initial surgery was a significant predictor of recurrence (P<0.002). During treatment, 11 knees (18%) failed to correct fully. Type 4 MPS (P<0.016) and a higher preoperative genu valgum (P<0.005) were statistically significant risk factors for failure. There were no infections. In 3 limbs, screw loosening was observed. Conclusions: Our study presents the largest cohort of MPS patients undergoing guided growth for genu valgum with high rates of success and low complications. Surgery should be undertaken before 20 degrees of genu valgum is evident, especially in type 4 MPS. Recurrence is common and surgery may need to be repeated. Overcorrection of the mechanical axis into varus with close follow-up may limit the number of episodes of guided growth. Level of Evidence: Level IV.