Purpose

Recently published meta-analyses reported that opening wedge high tibial osteotomy (OWHTO) significantly increases leg length and thus, closing wedge HTO should be preferred in patients with unilateral medial compartment knee osteoarthritis (OA) to prevent leg length discrepancy, in particular if large correction is necessary as the amount of correction and leg length increase after OWHTO are significantly correlated. Yet, theoretical considerations suggest that patients with unilateral medial compartment OA present with a shortened involved lower extremity due to the medial compartment height loss and subsequent varus deformity. This study aimed therefore to assess the pre- and postoperative leg length of the involved lower extremity in patients submitted to OWHTO and compare it to the unaffected contralateral side. It was hypothesized that patients present with decreased preoperative length of the involved leg when compared to the contralateral side and that OWHTO would subsequently restore native leg length.

Methods

Sixty-seven patients that underwent OWHTO for unilateral medial compartment knee osteoarthritis that received pre- and postoperative full leg length assessment were included in this retrospective study. Patients that presented with varus or valgus deformity (>3°) of the contralateral side were excluded. A musculoskeletal radiologist assessed imaging for the mechanical axis, full leg and tibial length of the involved and contralateral lower extremity. Statistical analysis determined the pre- and postoperative leg length discrepancy and the influence of the mechanical axis.

Results

The majority of patients (62.7%) presented with a decreased length of the involved leg with a mean preoperative mechanical axis of 5.0 ± 2.9°. Length discrepancy averaged -2.2 ± 5.8 mm indicating a shortened involved extremity (p=0.003). OWHTO significantly increased the mean lengths of the tibia and lower limb by 3.6 ± 2.9 mm and 4.4 ± 4.7 mm (p<0.001), leading to a postoperative tibial and full leg length discrepancy of 2.8 ± 4.3 mm and 2.2 ± 7.3 mm (p<0.001 and p=0.017, respectively). Preoperative leg length discrepancy was significantly correlated with the preoperative mechanical axis of the involved limb (r=0.292, p=0.016) and the amount of correction was significantly associated with leg lengthening after OWHTO (r=0.319, p=0.009). Patients with a varus deformity of = 6.5° (n=14) presented with a preoperative length discrepancy of -4.5 ± 1.6 mm (p<0.001) that was reduced to 1.8 ± 3.5 mm (p=0.08).

Conclusion

Patients submitted to OWHTO present with preoperative length discrepancy that is directly associated with the varus deformity of the involved extremity. As OWHTO significantly increases leg length, particularly patients with large varus deformity may benefit from native leg length restoration.