Background

Aim

 

UKA is intended to be load sharing

- correct to neutral or slight varus

 

HTO is a load-shifting / load-sparing procedure

- over correct into valgus

 

UKA v TKR

 

Advantages UKA

 

1.  Rapid rehabilation

 

2.  Increased ROM

 

3.  More normal knee kinematics

- more normal gait

- preserves ACL, PCL, PFJ & lateral compartment

 

4.  Low complication rate 

- decreased infection, bleeding

 

Results

 

Laurencin  Clin Ortho 1991

- TKR one side, UKA other

- patients preferred UKA

 

Newman JBJS Br 1998

- randomised trial TKR v UKA

- UKA less perioperative morbidity, faster ROM, better knee scores

 

Disadvantages UKA

 

1.  Technically difficult

 

2.  Progressive OA of un-resurfaced compartments

 

3.  Inferior survivorship to TKR 

- higher revision rates in young

- revision rates in Australian Joint Registry approach TKR only in > 75 year old patient

 

4.  More difficult future TKR with poorer results

- revision rate of TKR post Uni is close to 10% 5 year in AJR

 

UKA v HTO

 

Advantages UKA

 

Fewer complications

- higher earlier success rate

- more rapid rehabilitation

 

Stukenborg et al Knee 2001

- randomised prospective

- 7 - 10 year survival

- 77% UKA

- 60% HTO

- higher complication rate in HTO

 

Indications 

 

Kozinn and Scott JBJS Am 1989

- minimal deformity

- only medial compartment OA

- asymptomatic mild PFJ OA

 

Unicompartmental OA +

- intact ACL 

- FFD < 5°  

- flexion > 90° (probably more, 110-130^o)

- maximum varus 15^o which is correctable to neutral

- older age group (> 60 years) 

- lower weight < 82 kg

- lower activity level

 

Only 6% of patients fulfil these criteria

 

Contraindications

 

Instability

- ACL deficiency

- tibial / joint subluxation

- lateral thrust

 

If ACL gone allows varus in all positions  

- subsequent global joint erosions

 

Significant OA changes in other compartment

- some surgeons ignore PF if non symptomatic

- only early changes in lateral compartment

- examine at time of surgery

 

Inflammatory arthritis

 

Assessment

 

One finger test

- patient points to affected compartment only

 

X-rays

 

AP / Lateral / Skyline

 

Patient 1

 

 

Patient 2

 

 

Surgical Principles

 

1.  Correct to neutral or slight varus

 

2.  Femoral component 

- should be centred on condyle 

- parallel to tibial component

- must not overstuff

- must not impinge on patella

 

3.  Tibial component 

- minimal resection

- must be perpendicular to long axis tibia

- must not be in varus

- should cap but not overhang medial cortex to prevent irritation of pes anserinus

 

4.  Balance flexion extension gaps

- don't overstuff with poly

- 2mm laxity in flexion and extension

 

Prosthesis

 

Oxford

 

 

Design

- spherical, constant radius femur, fully congruent

- mobile bearing (risk bearing dislocation)

- flat tibia

 

Variations on Oxford design

- fixed bearing

- all poly tibia

- uncemented tibia + screws

 

 

Complications

 

1.  Bearing dislocation

 

2.  Poly wear

 

 

3.  Pes anserine bursitis

 

4.  Patella impingement

- femoral component not flush in sagittal plane

- don't oversize femoral component

 

5.  Aseptic loosening

 

Cause

- no difference fixed v mobile bearing

- undercorrection of deformity

- malalignement of components

 

 

6.  Tibial Subsidence

- too much bone taken from tibia (into soft bone)

- overimpaction of tibial component

 

 

7.  Progressive OA

- overcorrection of deformity overloads lateral component

- degeneration of PFJ

 

 

8.  Infection

- 0.8% UKA

- 2% TKA

 

Results

 

UKA

 

Price and Svard AAOS 2000

- Oxford Knee

- 95% 10 year survival

 

Swedish knee registry

 

90% survival at 5 years

- failure rate varies 0 - 30% in different centres

 

Australian Joint Registry

 

12.1% revision rate at 7 years

- 3 times the revision rate of TKR

 

Risk of revision decreases with age

- < 55 20% 7 year revision

- > 75 6% 7 year revision

- but worse than TKA for all ages and gender

 

Prosthesis

- Oxford 11.5% 7 year revision

- LCS 20.4% 7 year revision

 

Revision of UKA to TKA

- 12.9% 5 year revision of that TKA

- 3.5 x primary TKA

 

Summary

- joint registry has poor results

- specialised centres have good results

- need to carefully select patients

- be an experienced unicompartmental surgeon

- perform good surgery

 

Lateral Unicompartmental Knee

 

Gunther et al 1996 with 53 Oxford knees

- 75% seven-year cumulative survival rates

- main problem was with dislocation of bearing

 

Findings

- suggest poorer results with lateral replacements

- suggests fixed bearing may be more suitable in lateral compartment

 

Conversion to TKR

 

 

Problem is bone loss

- up to 75% need grafting / augments

- need to take minimal bone at primary surgery

- watch closely for signs osteolysis

 

Results

- worse if need augments / stems