High Tibial Osteotomy
The IDEAL Candidate:
– young (age 65)
– severe tricompartmental disease
– severe ligamentous laxity on the concavity of the deformity (medial side)
– medial/lateral subluxation of 1 cm – this is BAD – HTO will not resolve this instability
– excessive deformity (>15o varus)
– inflammatory arthritis
– patients can expect to maintain a high level of activity
– patients should be warned to expect less than full pain relief
– patients should expect that disease progression will probably allow the pain relief to last 5-7 years. (ie. A temporizing procedure)
The single most important factor in outcome is the post-operative alignment of the knee. Exactly how much correction required is unclear, but it appears that you need an OVERcorrection to an anatomic valgus of 8-10o. Patients with 7-13 degrees of valgus do far better than those with less than 7!
The Normal Mechanical Axis
– from center of hip to center of ankle
– normally lies in 1.2o of varus (ie, it is not quite vertical) – but everything is a lot easier to think about if you call it 0o.
– normally goes through the central third of the knee
– generally speaking, it parallels the anatomic axis of the tibia
The Anatomic TibioFemoral Angle = 5-7o of valgus
– the distal femur is in about 8-9o of valgus
– the proximal tibia is in about 3o of varus (hence the approximate 5-7 of valgus for the anatomic tibiofemoral anlge)
The Anatomic Femoral Axis = 6o of valgus to the mechanical axis
So even though the anatomic tibio-femoral angle is 5-7, you want them overcorrected to 8-10!
A high pre-operative lateral thrust/adductor moment is bad – these patients have a higher loss of correction.