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Unicompartmental knee resurfacing: when less is more

Mr Fares Haddad and Mr Nic Wardle review the pros and cons of partial knee resurfacing

Mr Fares Haddad and Mr Nic Wardle review the pros and cons of partial knee resurfacing

Case historyA 52-year-old car mechanic presented with a three-year history of gradually worsening pain on the inside of his right knee. The pain had cut his walking distance to half a mile and was keeping him awake at night.

He had been self-medicating with paracetamol, but this was no longer controlling the pain. He couldn't recall any specific episode of trauma to the knee, but was a keen amateur footballer in his youth. He was otherwise fit and well, with no other joint pain.

Diagnosis and managementUnicompartmental knee arthritis is char-acterised by degeneration of articular cartilage in the medial or lateral aspect of the tibiofemoral joint. There may be an association with trauma. Angular mal-alignment may contribute to development and progression of the disease, by over-loading the medial or lateral compart-ments. In active patients, such as this man, the disease tends to be progressive.

The process can include articular cartilage damage, including damage to both chondrocytes and extracellular matrix, meniscal damage, ligamentous damage and joint incongruity.Evaluation of this man should begin with a careful history to rule out more widespread disease and the possibility of an inflammatory cause.

The examination should include: assessment of alignment; palpation for joint line tenderness; evaluation of meniscal damage (eg, McMurray's test); assessment of ligamentous instability (Lachman's test, anterior and posterior drawer, pivot shift, valgus and varus stressing). The ipsilateral hip and ankle should also be examined.X-rays should include weightbearing AP views, lateral and patello-femoral skyline views to assess all three compartments for degenerative changes.

This man's gait was favouring his left leg, avoiding weight-bearing on his painful right knee. Examination of the weight-bearing right knee showed a 6° varus deformity which was fully correctible when supine.

Further examination revealed a mild effusion and marked tenderness along the medial joint line. No lateral or patello-femoral tenderness was found. A 5° fixed flexion deformity was detected, with a range of motion from 0° to 135°. Anterior and posterior cruciates were clinically intact. Plain X-rays revealed loss of medial joint space.

Treatment optionsNon-operative options include:

  • simple analgesics
  • oral and topical NSAIDs
  • dietary supplements (glucosamine)
  • aspiration of the effusion (for acute exacerbations)
  • intra-articular injection of steroid
  • weight loss, exercise and physiotherapy
  • correction of ankle, hindfoot or midfoot deformity with footwear and orthotics

Operative options include:

  • arthroscopy
  • osteotomy
  • unicompartmental replacement
  • unicompartmental knee athroplasty

Summing up

Medial unicompartmental arthroplasty is a highly-effective procedure in unicompartmental arthritis, with excellent 10-year survivorship. It should be considered in any patient meeting the criteria, regardless of age.

Knee arthroplasty

Unicompartmental knee arthroplasty (UKA) or resurfacing has evolved considerably over the past three decades. Initially it was restricted to patients fulfilling strict criteria but recent advances in surgical technique and implant design have opened UKA up to a younger population, who might have previously been treated by high tibial osteotomy or early total knee replacement (TKR).

Current indications for medial UKA are:

  • medial unicompartmental OA
  • functionally intact anterior cruciate ligament
  • fixed flexion deformity of no greater than 15°
  • correctable varus deformity
  • full thickness cartilage in the lateral compartment

Advantages over TKR include:

  • less extensive approach and dissection
  • no disturbance to the extensor apparatus
  • shorter recovery time ­ some centres offer UKA as a day-case
  • simpler revision to TKR if required
  • better range of motion
  • gives a better 'feel' and function
  • pain relief as good if not better
  • blood loss lower, transfusion rarely necessary
  • fewer postoperative complications

Minimally invasive medial UKA is now carried out through an incision from the medial pole of the patella to the tibial tuberosity.

A corresponding capsular incision is made. The patella is gently retracted laterally to allow access to the medial compartment. Both the femur and the tibia are then prepared for implantation. Following the cementing of the appropriately sized prostheses, closure is effected in layers.

Long-term outcomes

Follow up data of UKA has shown excellent survivorship of up to 98 per cent at 10 years for patients aged 35 to 90 (Murray et al 1998), failure defined as the need for revision arthroplasty. Initial concerns over polyethylene wear have been addressed through the improvement in implant design. The Oxford implant has reduced polyethylene wear to no more than 0.03 mm/year.

The presence of erosions on the medial side of the patello-femoral joint is not necessarily a contraindication, as it is unloaded at surgery through the correction of varus deformity. The Oxford Group reports no revisions for patello-femoral pain.Lateral UKA has not been as successful. Ashraf et al (2002) published figures showing 84 per cent 10-year survivorship, and 74 per cent at 15 years. Future improvement in implant design will no doubt help.

Fares Haddad is a consultant orthopaedic surgeon ­ he is clinical director at University College London HospitalsCompeting interests None declaredNic Wardle is a specialist registrar in trauma and orthopaedics at The Royal London Hospital ­ his special interest is joint arthroplasty and re-constructionand he has undertaken a thesis on bearing surfaces in lower limb arthroplastyCompeting interests None declared

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