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Interventional procedure consultation document

Implantation of a shock or load absorber for mild to moderate symptomatic medial knee osteoarthritis

Osteoarthritis of the inner aspect of the knee can cause pain and inflammation, especially when the knee joint bears too much weight.

Implantation of a shock or load absorber involves attaching a device between the thigh bone and the shin bone, alongside the knee joint, to share some of the load on the knee when standing. The procedure can be reversed because no tissue or bone is removed.

The National Institute for Health and Care Excellence (NICE) is examining implantation of a shock or load absorber for mild to moderate symptomatic medial knee osteoarthritis and will publish guidance on its safety and efficacy to the NHS. NICE’s Interventional Procedures Advisory Committee has considered the available evidence and the views of specialist advisers, who are consultants with knowledge of the procedure. The Advisory Committee has made provisional recommendations about implantation of a shock or load absorber for mild to moderate symptomatic medial knee osteoarthritis.

This document summarises the procedure and sets out the provisional recommendations made by the Advisory Committee. It has been prepared for public consultation. The Advisory Committee particularly welcomes:

·      comments on the provisional recommendations

·      the identification of factual inaccuracies

·      additional relevant evidence, with bibliographic references where possible.

Note that this document is not NICE’s formal guidance on this procedure. The recommendations are provisional and may change after consultation.

The process that NICE will follow after the consultation period ends is as follows.

·      The Advisory Committee will meet again to consider the original evidence and its provisional recommendations in the light of the comments received during consultation.

·      The Advisory Committee will then prepare draft guidance which will be the basis for NICE’s guidance on the use of the procedure in the NHS.

For further details, see the Interventional Procedures Programme manual, which is available from the NICE website.

Through its guidance NICE is committed to promoting race and disability equality, equality between men and women, and to eliminating all forms of discrimination. One of the ways we do this is by trying to involve as wide a range of people and interest groups as possible in the development of our interventional procedures guidance. In particular, we aim to encourage people and organisations from groups who might not normally comment on our guidance to do so.

In order to help us promote equality through our guidance, we should be grateful if you would consider the following question:

Are there any issues that require special attention in light of NICE’s duties to have due regard to the need to eliminate unlawful discrimination, advance equality of opportunity, and foster good relations between people with a characteristic protected by the equalities legislation and others?

Please note that NICE reserves the right to summarise and edit comments received during consultations or not to publish them at all where in the reasonable opinion of NICE, the comments are voluminous, publication would be unlawful or publication would otherwise be inappropriate.

Closing date for comments: 28 August 2014

Target date for publication of guidance: November 2014





1                      Provisional recommendations

1.1                  Current evidence on the safety and efficacy of implantation of a shock or load absorber for mild to moderate symptomatic medial knee osteoarthritis is inadequate in quantity and quality. Therefore, this procedure should only be used in the context of research.

1.2                  Further research into implantation of a shock or load absorber for mild to moderate symptomatic medial knee osteoarthritis should involve comparative studies against existing forms of management. Studies should record patient selection, functional outcomes, quality of life and complications. They should also report the nature and timing of any further surgery on the knee and the effect of removing the device. A minimum follow-up period of 23 years is needed. NICE may review the procedure on publication of further evidence.

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2                      Indications and current treatments

2.1                  Osteoarthritis of the medial compartment of the knee is the result of progressive deterioration of the articular cartilage and menisci of the joint. This leads to exposure of the bone surface and chronic excessive joint loading during movement. Symptoms include joint pain, stiffness, local inflammation, limited movement and loss of knee function.

2.2                  Treatment depends on the severity of the osteoarthritis. Conservative treatments include analgesics and corticosteroid injections to relieve pain and inflammation, and physiotherapy and exercise to improve function and mobility. When symptoms are severe, surgery may be indicated. Options include high tibial osteotomy and unicompartmental or total knee arthroplasty.

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3                      The procedure

3.1                  The aim of this procedure is to lighten the load on the knee when the person is standing by inserting a load absorber, thereby reducing pain and potentially delaying the need for further surgery. This device is implanted subcutaneously outside the knee joint, along its medial aspect. It is secured to the femur and tibia. It is intended to keep surrounding structures including bone, muscle and ligaments intact, allowing subsequent surgery to be performed if necessary. The device can be removed at a later date.

3.2                  The procedure is performed with the patient under general anaesthesia and supine. Fluoroscopy is used to confirm alignment of the knee joint. Two incisions, over the medial aspect of the femoral and tibial condyles respectively, are made. A femoral base plate is inserted through the proximal incision, and attached to the medial femoral cortex using surgical screws; similarly a tibial base plate is attached to the medial tibial cortex. A tunnel is created between the 2 incisions beneath the skin using blunt dissection and the load absorber is implanted in this tunnel. The load absorber is attached to the 2 base plates. Its function is checked and the wounds are closed.

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4                      Efficacy

This section describes efficacy outcomes from the published literature that the Committee considered as part of the evidence about this procedure. For more detailed information on the evidence, see the interventional procedure overview.

4.1                  A case series of 99 patients reported that statistically significant mean improvements of 56%, 50% and 38% were observed for the Western Ontario and McMaster Universities Osteoarthritis Index questionnaire (WOMAC) pain, function and stiffness scales respectively (all p<0.001) during a mean follow-up period of 17 months. All WOMAC domain scores significantly improved during a mean follow-up period of 17 months, independent of age, gender, BMI or disease severity (K-L grade) (p<0.01). WOMAC clinical success rates (defined as ≥20% improvement from baseline) were 78% for pain, 78% for function and 69% for stiffness.

4.2                  The case series of 99 patients reported that knee pain severity improved significantly after the procedure, from 59±19 at baseline to 23±22  (assessed on a 0-100 visual analogue scale) at 1 year, representing a 60% reduction in pain (p<0.001). The authors reported that the percentage of patients achieving the ‘minimal clinically important difference’ for pain severity increased throughout the follow-up period, from 60% at 6 weeks to 76% at 1 year.

4.3                  The case series of 99 patients reported that the mean range of motion of the knee decreased from 119°±13° at baseline to 105°±19° at 6 weeks after the operation. It gradually increased to baseline levels at 1 year follow-up.

4.4                  The case series of 99 patients with symptomatic medial knee osteoarthritis refractory to conservative treatment and treated with a load absorber reported that all devices were successfully implanted and activated.

4.5                  The specialist advisers listed key efficacy outcomes as reduction in knee pain, improved function and activity, patient-reported outcomes (for example, Oxford knee score; WOMAC scores, Knee Society Score, UCLA activity score; EQ-5D; Patient satisfaction scales) and delayed need for knee replacement.

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5                      Safety

This section describes safety outcomes from the published literature that the Committee considered as part of the evidence about this procedure. For more detailed information on the evidence, see the interventional procedure overview.

5.1                  Infection of the tibial wound attributed to prolonged physical activity was reported 6 weeks after the procedure in a case report of 1 patient. The patient was initially treated with antibiotics but the infection did not resolve. The patient subsequently had a 2-stage revision procedure involving removal of the load absorber with antibiotics for 6 weeks followed by insertion of a new absorber 3 months after the infection was resolved.

5.2                  Device fracture 7 months after implantation was reported in a case report of 1 patient. A 2-stage revision procedure was performed and the device was completely removed without any further complications.

5.3                  Persistent pain led to removal of the device in 4% (4/99) of patients between 2 and 10 months after implantation, in the case series of 99 patients.

5.4                  Surgery was done for failure to improve symptoms in 6% (6/99) of patients in the case series of 99 patients: 4 patients had total knee arthroplasty and 2 had high tibial osteotomy.

5.5                  Recurring pain within 6 months of implantation was reported in 2 patients in the case series of 99 patients. Further details were not reported.

5.6                  The specialist advisers reported anecdotal events as soft tissue irritation, impingement, dislocation, or uncoupling of the device needing removal. Theoretical adverse events listed include thrombotic events (deep vein thrombosis leading to pulmonary embolism); stiffness of the knee; and bone loss adjacent to anchoring sites, compromising future salvage surgery including joint replacement.

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Bruce Campbell
Chairman, Interventional Procedures Advisory Committee
July 2014

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 It is the responsibility of consultees to accurately cite academic work in order that they can be validated.