Background

Aetiology Unicompartmental OAKnee Medial Compartment 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

 

HTO Lateral Closing Wedge

 

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

 

HTO 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