High Tibial Osteotomy

Justification for high tibial osteotomy (HTO)

• Running and jumping produces surface loads exceeding the limits of polyethylene
  • Running à force 3 times (3X) body weight.
  • Deep flexion à Patello-femoral joint 8X body weight.
• In this setting of unicompartmental knee replacement (UKR) there will be early failure.
• Thus if patient wishes to continue with sport or manual work, HTO is the justifiable choice.
  • Gives good function with return to full activity.
  • Downfall is predictable deterioration in results over time – it is a “time buying” procedure.

Biomechanics

• Normal load bearing is 60% medial, 40% lateral.
• Rationale has been to shift mechanical axis into the lateral (preserved) compartment.
  • Recent studies suggest that to unload the medial compartment valgus of ~ 25° would be required
  • Thus relieving effect of Valgus HTO must be something else
    • ¯ Venous pressure
    • ¯ Stress on subchondral bone
    • Inflammatory effect encouraging new blood supply to subchondral bone

Options

Lateral closing wedge will:

• Shorten the leg
• Produce Patella alta (theoretically) – BUT in practice it is associated with patella Baja.
• • Theoretically - it shortens the distance between the tibial plateau and the tibial tuberosity.
  • In practice – Baja results from patella tendon scarring and contracture
  • This data came form series where post-operation immobilisation in plaster was used
  • Recent studies show the baja can be eliminated by rigid internal fixation and aggressive post-op mobilisation
• Increase the Q angle.
• Create lateral collateral ligament (LCL) laxity.

Medial opening wedge will:

1. Lengthen the leg.
2. Produce Patella baja.
3. Displace the tibial tubercle laterally.
4. Tense the MCL

Barrel vault (dome) osteotomy will:

1. Not change limb length
2. Be more stable
3. Possible scar the extensor mechanism

• Osteotomy is made above the tibial tubercle
  • Osteotomies below the tubercle have a 4 times ­ non-union rate
• Healing is more reliable with lateral closing wedge than medial opening wedge

Opening Vs closing wedge osteotomy

Indications:

1. Unicompartmental arthritis with axial malalignment
   1. Osteoarthritis (OA)
   2. Avascular necrosis (AVN)
2. Posterolateral (PL) instability

• • Soft-tissue procedure alone will fail in the setting of varus malalignment
  • May have a role as the sole treatment of PL instability

3. In chondral resurfacing

• • These experimental procedures will also fail in varus malalignment
  • Difficult to distinguish results of HTO alone Vs HTO + chondral treatment

Contraindications:

1. Disease in other compartments

• • Mild patellofemoral arthritis is OK

2. Inflammatory arthritis
3. Coronal malalignment  > 20°
4. Stiff knee
   1. FFD > 15°
   2. Flexion < 90°
5. Unstable knee – Varus thrust

• • Small thrust no problem
  • Large thrust correlates with poor results – if performed take care to over-correct

6. > 3mm of medial bone loss
7. Subluxation > 1cm

• • > 1cm is an absolute contraindication
  • Some authors consider any subluxation a contraindication

8. Obesity

• • > 1.32 X ideal body weight correlates with poor results

9. Cosmetic tolerance

• • Some women will not accept the “knock-knee” appearance that will result

Coventry’s criteria

1. Active patient < 65
2. Pain localised to involved compartment (correlating with X-ray findings)
3. Radiographically normal lateral compartment
4. Varus deformity < 15°
5. Mobile knee
   1. < 15° FFD
   2. > 90° flexion
6. Stable knee – Intact medial collateral ligament (MCL)
7. Internal derangement corrected by osteotomy

Pre-op assessment

1. Clinical
   1. ROM
   2. Stability
   3. Angular deformity
   4. Ipsilateral hip function
2. Radiographic
   1. Normal weight bearing knee series

• • • Looking for disease in other compartments
    • Full length, 3 joint, weight bearing series
    • Normal values:
      • Mechanical axis - 0°
      • Tibiofemoral angle - 6°

3. Arthroscopic – NO

• • Of no prognostic value

4. Trial offset short-leg walking cast

Technique

Aim

1. Mechanical axis – 2-5° Valgus

1. Normal being 0° (or 1° varus)

2. Anatomical alignment – 8-10° Valgus

• • Normal being 6° valgus

3. Mechanical axis passing through 62% of tibial plateau (through the lateral plateau)

• • This point corresponds to an alignment of 10° anatomical valgus

Calculating how much to remove

1. Mathematically from pre-op films

• • Wedge height = Tibial width X tan a
    • Where a = desired correction

2. “Bauers rule of thumb” – 1mm of wedge = 1° of correction

• • This will result in an under-correction
    • 1mm=1° only if tibia is 56mm wide
    • Average adult tibial width is 75.2mm at tibial flare

3. Direct measurement off Xray

•  
  • Anatomical method

• • • Draw anatomical axis of tibia and femur and calculate current tibio-femoral axis
    • Calculate wedge needed to achieve an tibio-femoral angle of 9° valgus
    • Measure the size of the wedge
  • Mechanical method

• • • Draw mechanical axis of tibia and femur, and measure the existing mechanical axis
    • Redraw the tibial mechanical axis in order to create a mechanical axis of 3° valgus
    • Measure the size of the resulting wedge

Options for fibula

1. Excision of fibula head – Leo

• • Safe zone is the proximal 40mm, and then again > 15cm distal to head

2. Removal of infero-medial portion of fibula head
3. Disruption of proximal tib-fib joint

Surgical technique

Closing wedge

1. Setup – Knee at 90° against lateral support
2. Mark incision-Curvilinear incision (apex posterior), joining 3 points

•  
  • Distal aspect of tibial tubercle
  •  Passing over fibula head
  • Proximally passing just posterior to mid-lateral joint line
  • Leaves the Styloid process with the lateral collateral ligament (LCL) still attached (biceps is partially detached – it inserts for a long distance down the neck)
  • Proximal half corresponds to course of common peroneal nerve (CPN)

3. Dissect down to fascia and find CPN

• • Dissect it out to the fibula neck

4. Detach origin of anterior and lateral compartments, lifting them subperiosteally from the anterolateral tibia and fibula neck
5. Excise the fibula head

• • Excises a segment of ~ 2cm long using osteotome

6. Expose the proximal tibia
   1. Anteriorly incise under the retinacular fibres of the patellar tendon to pass a Homan under the patella tendon, across the anterior tibia
   2. Posteriorly incise the joint capsule at the tibial flare

•  
  • The capsule will fall posteriorly and a second homan can be passed all the way across the back of the tibia – you can see right across

7. Place 21g needle into the joint space
8. Use a broad osteotome to mark a line parallel to the joint line

• • This is the plane of the osteotomy – it is parallel to the joint
  • Place the posterior homan parallel to this – this homan will be your guide for the saw

9. Create osteotomy using oscillating saw
10. Insert Jig and make 2^nd cut

• • Where the second cut meets the first is used to tension the MCL

1. i.     Normal MCL – Cuts meet at medial cortex
2. ii.     Lax MCL – Cuts meet lateral to medial cortex (thus when wedge is closed the insertion of the MCL is taken distally to retension the MCL

11. Remove wedge of bone and fix with 1-2 staples
12. Close

• • In layers
  • No drain
  • WBAT
  • Valgus ROM brace for 6/52

Opening wedge

1. Vertical skin incision centred between medial border of tibial tubercle and anterior border of MCL
2. Identify and detach the pes anserinus
3. Transversely cut the anterior 1/2 of the superficial MCL

1. This does not affect stability because the deep MCL remains intact (along with the posterior 1/2 of the superficial MCL)

4. Pass a Homan deep to remaining MCL, and another deep to patella tendon
5. Under II control drill a Steinman pin obliquely from medial to lateral

• • Start 4cm distal to joint line, and finish 1cm distal to lateral joint line

6. Perform osteotomy – under and parallel to guide-wire

• • Complete with an osteotome
  • End 5mm form lateral cortex

7. Insert wedge opener to desired depth
8. Attach plate and spacer

• • Position anterior-posterior to adjust tibial slope as desired

9. Check with II and alignment rod
10. Fix plate
11. Insert bone graft from iliac crest
12. Close

Results

1. 5 year success – 80-90%
2. 10 year success – 40-60%

Relative risk factors for survival (5 and 10 year rates)

Only 2 factors are significant:

1. Weight
   1. < 1.17 ideal à 96% and 91%
   2. 1.17-1.32 à 95 and 81%
   3. > 1.32 à 78% and 56%
2. Angular correction achieved
   1. < 5° valgus à 63% and 63%
   2. 6-7° valgus à 87% and 87%
   3. > 8° valgus à 94% and 94%

Complications

1. General
   1. DVT
   2. Infection
2. Specific

• Early
  •  CPN palsy – 10%
  •  Vascular injury
  • Under or over-correction
  • Intra-articular fracture- Risk decreased by carrying osteotomy cut to within 10mm of cortex, and by leaving proximal fragment at least 15mm thick, and by gradual opening or closure of the osteotomy
  •  Compartment syndrom
• Late
  • Early loss of correction
  • Non-union
  • Failure

Conversion to TKR

Problems

1. Incision and skin flaps
2. Patella eversion and height

• Patella baja is more common
• Care must be taken to evert patella – may need quadriceps snip, turndown etc

3. Hardware removal

• Options
  •   2 stage removal
  •  Leave in if not a problem
  • Remove at time of TKR
  • Following lateral closing wedge HTO may need lateral tibial augment
  • Closing wedge HTO’s tend to result in loss of posterior slop (due to incomplete posterior closure of the osteotomy)

4. Proximal tibial deformity
   1. Tibial bone stock
   2. Altered slope
   3. Offset – if using stems may need off-set stems
   4. Jigging – IM jigging may be less accurate – use extramedullary jigging
5. Ligament balancing – Consider using PCL substituting design
6. Patella tracking – ­ Q-angle à higher rate of lateral release
7. Peroneal nerve scarring

Results

Variable

Some studies have shown no difference with primary TKR

3 series of bilateral TKR, one having had previous HTO – no difference

Others report results similar to that of revision TKR

HTO Vs Uni

Uni has a higher survivorship and less complications, however it is not the best option for young active person.

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