Aetiology Unicompartmental OA
Trauma
Meniscectomy
Osteonecrosis
Varus or valgus malalignment
Goals of Osteotomy
Relief of pain
Improve function
No loss of ROM
No or slight restriction of activity
Allow heavy functional demands
Indications
1. Medial compartment OA + varus malalignment
- pain localised to involved compartment
- typically male < 60 with high level of activity
- flexion > 90o
- FFD < 15
- varus < 15o
- no lateral subluxation (<10 mm)
- medial bone loss < 3 mm
- ACL intact
2. Osteochondritis Dissecans of MFC
3. SPONK MFC
4. Posterolateral instability with varus knee
- a PLC reconstruction in setting of varus knee with fail
5. Chondral grafting MFC
Contra-Indications
Patient Factors
- lateral compartment OA
- PFJ compartment OA
- inflammatory arthritis
- peripheral vascular disease
- obesity > 1.32 x ideal body weight
Technical Factors
- lateral subluxation of tibia >1cm
- lateral thrust
- FFD > 10-15o
- Flexion < 90o
- Varus > 15°
- Valgus knee (HTO in this setting will create oblique joint line)
Concept
HTO works well in a select group of patients
- no activity modification required compared with TKR
- results tend to deteriorate with time
- modern fixation techniques have superior results
Rationale
Assumes primary cause of unicompartmental OA is mechanical
Mechanical
Provides realignment of limb
- reduces abnormal loading stresses on damaged cartilage and bone
Redistributes forces to unaffected lateral compartment
Biological / Regenerative
Some evidence fibrocartilaginous proliferation in unloaded compartment
Options
Lateral Closing Wedge HTO
Medial Opening Wedge HTO
Lateral Closing Wedge Osteotomy
Advantage
- large area cancellous bone under compression
- inherent stability
- good union rates
- early weight bearing
- quadriceps provide compression
Disadvantage
- patella baja (improved by early ROM with good fixation)
- more difficult to obtain desired correction / 2 osteotomies required
- must completely excise exact size wedge of bone (difficult to do)
- must disrupt proximal tibia-fibula joint (risk injury CPN)
- shortens leg
- creates LCL laxity
- decreases proximal tibial bone stock
Medial Opening Wedge
Advantage
- easier to obtain desired correction (only single osteotomy required)
- less surgical dissection
- no proximity to CPN
- no need to mobilise proximal fibula
- tighten MCL
- maintain bone stock especially with large corrections
Disadvantage
- relatively unstable
- risk loss of fixation
- delayed / non union
- NWB
- require bone graft
- lengthens leg
- displaces patella / increases PFJ forces
Decision Making
Small Correction 10 - 12o
- either technique fine
- closing wedge more difficult but union rates hight
Large correction i.e. 20o
- opening wedge probably indicated
- otherwise sacrificing too much bone / risk patella baja / subsequent TKR very difficult
Results
Outcomes
Coventry et al JBJS Am 1993
- 87 knees with varus OA
- age 63 (41-79)
- 2/3 male, 1/3 female
- 87% survival at 5 years, 66% at 10 years
- poor outcome with relative weight > 1.32 ideal
- best outcome with valgus angle > 8o
- 94% survival at 5 and 10 years
Naudie et al CORR 1999
- minimum 10 year follow up 106 HTO
- 70% survival at 5 years, 50% survival at 10 years, 40% 15 and 30% 20 years
- age > 50, lateral tibial thrust, preoperative knee flexion < 120 and insufficient correction associated early failure
- patients younger than 50 with flexion > 120o had 95% 5 year and 80% 10 year survival
OW v CW HTO
Brouwer et al JBJS Am 2007
- RCT of OW v CW aiming for 40 overcorrection
- achieved 3.4o average in CW and 1.3o in OW
- concluded OW had more accurate correction, but no clinical difference
Smith et al Knee 2010
- meta-analysis
- no difference in infection / DVT / non union / CPN palsy or revision to TKR
- opening wedge had increased posterior slope and increased angle correction
- opening wedge also had higher incidence patella baja