Open Wedge High Tibial Osteotomy: A Roentgenographic Comparison of a Horizontal and an Oblique Osteotomy on Patellar Height and Sagittal Tibial Slope (SS-62)

Abstract

Medial opening wedge (OW) high tibial osteotomy (HTO) preserves bone stock while having to only perform one cut, with the advantage of intra-operative adjustment to the desired correction. However, several studies showed that conventional supratubercle horizontal OW is associated with decreasing patellar height and increasing the sagittal tibial slope; both of which can also potentially affect future conversion to a TKR. We hypothesized that performing an oblique osteotomy at the level or distal to the patella tendon insertion could decrease the osteotomy's effects on lowering the patella and increasing the sagittal tibial slope. Hence, the purpose of this study is to evaluate the radiographic effects of a horizontal osteotomy made proximal to the patellar tendon insertion versus on oblique osteotomy made at the level or distal to the patellar tendon insertion on the shift in coronal weight bearing line, sagittal tibial slope and patellar height. A retrospective review of all open wedge HTO cases done by the senior author from January 1998 to August 2005 was performed. Patients were excluded if the indication for surgery was instability or if they had simultaneous ligament repair. Two consecutive cohorts are compared in this study. Initially, the surgeon performed 22 HTO with a horizontal cut proximal to the patellar tendon insertion and a subsequent 19 knees had an HTO with a more distal oblique cut made which would cross at the level or occasionally, distal to, the patella tendon insertion.. The HTO was then fixed open with the appropriate size first generation non-locking Puddu(r) plate (Arthrex, Naples, Fl, USA) (Figure 2). In both groups, the Puudu(r) plate was placed as posteriorly as possible to minimize the increase in sagittal tibial slope. Either autogenous tri-cortical iliac crest bone graft or femoral head allograft and bone substitute were inserted in the osteotomy in all but one patient which had an opening less then 7.5 mm. The patellar height as measured by Blackburne and Peel ratio was decreased in the horizontal group from 0.85 ± 0.16 to 0.67 ± 0.12 post-operatively signifying a lowering of the patella (Table 2). The oblique group trended toward a change in patellar height as the ratio only decreased by 0.05 from a pre-operative value of 0.89 ± 0.09 to 84 ± .13 (p=0.07). The sagittal tibial slope increased following a horizontal HTO from 7.7 ± 4.6o to 10.7 ± 3.8o; this change was statistically significant (p<0.001) In the oblique group however, the slope was not significantly increased: 6.5 ± 4.0o pre-operatively to 7.0 ± 4.1o post-operatively (p=0.90). The more distal oblique osteotomy did not statistically affect the patellar height or the sagittal tibial slope while still allowing a similar coronal correction to the proximal horizontal group. Additionally, the more distal oblique osteotomy has the advantage of a technically easier exposure being distal to the periarticular capsule and allowing easier access to the posterior aspect of tibia for neurovascular protection. Caution should be exercised not to osteotomize too distally into lateral cortical bone to avoid instability and early loss of correction.