Coverage Policy Manual
Policy #: 2003031
Category: Surgery
Initiated: July 2003
Last Review: October 2018
  Unicondylar Interpositional Spacer as a Treatment of Unicompartmental Arthritis of the Knee

While osteoarthritis of the knee is typically a bilateral disease, some patients may have signs or symptoms confined to the medial or lateral compartment, often as a result of specific injury.  Initial treatment of uni- and bicompartmental disease is similar, i.e. analgesics, viscosupplementation and arthroscopic debridement.  If focal cartilage defects are present, other therapies such as autologous chondrocyte or osteochondral transplants may be considered.  (See policies:  Autologous Chondrocyte Transplantation-1997014 and Osteochondral Autograft Transfer (OATS)-1998142)  When patients fail to respond to these more conservative therapies, patients with bicompartmental disease typically consider total knee replacement.
However, patients with unicompartmental disease are often younger and may not be considered ideal candidates for total knee arthroplasty.  Additional options in this subset of patients include high tibial osteotomy for those with medial compartment disease and a varus deformity, and unicompartmental knee arthroplasty, consisting of both a tibial and femoral component.  This prosthesis leaves intact both cruciate ligaments, the patellofemoral joint and the opposite compartment, thus preserving nearly normal knee kinematics. Unicompartmental arthroplasties are typically performed in older patients with a low level of physical activity.
Finally, an interpositional arthroplasty may be considered in the young active patient as an alternative to an osteotomy or unicompartmental arthroplasty.  An interpositional arthroplasty refers to a prosthesis that is essentially placed on the tibial surface, with preservation of the ligaments, minimal resection of underlying bone, and minimal fixation.  In the past, McKeever, MacIntosh and Sbarbaro prosthesis have been used, however it appears that these devices are rarely used now.   Recently, a cobalt alloy device, referred to as a "unicondylar interpositional spacer" or "UniSpacer" has been FDA approved as an additional interpositional arthroplasty device.  The device, manufactured by Sulzer Orthopedics (Austin, TX), consists of a kidney shaped device designed to mimic the shape of the medial tibial condyle as it articulates with the femoral condyle.   After arthroscopic debridement and resection of the medial meniscus the device is inserted into the joint space above the affected medial tibial plateau, resting within the boundaries of the resected meniscus. The femur then articulates against the curved surface of the device.  The device is intended to be used without cement and is held in place by its geometry and the surrounding soft tissue structures.   By filling the joint space that was once occupied by the now missing cartilage, the device is designed to restore the correct tension to lax collateral ligaments.
The FDA approved indication for the UniSpacer device is for "moderate degeneration of the medial compartment of the knee (grade III-IV chondromalacia) with not more than minimal degeneration (grade I-II chondromalacia, no loss of joint space) in the lateral condyle and patellofemoral compartments."

The use of a unicondlylar interpositional spacer for the treatment of unicompartmental arthritis does not meet member benefit certificate primary coverage criteria that there be scientific evidence of effectiveness.
For members with contracts without primary coverage criteria, the use of a unicondylar interpositional spacer as treatment for unicompartmental arthritis is investigational. Investigational services are specific contract exclusions in most member benefit certificates of coverage.

A search of the literature failed to identify any articles in the published peer-reviewed literature regarding the use of a cobalt alloy interpositional arthroplasty device. Several case series of other interpositional devices were identified in literature published in the 1980s.  These case series are inadequate to permit scientific conclusions regarding the role of interpositional arthroplasty devices as alternatives of osteotomy, unicompartmental arthroplasty, and total knee arthroplasty.
2008 Update
A search of the MEDLINE database for the period of February 2007 through March 2008 identified one prospective study of 18 consecutive patients with isolated medial compartment osteoarthritis who provided informed consent for insertion of a Unispacer knee implant. Seventeen patients (94%) reported persistent symptoms between 3 and 6 months after surgery. (Bailie et al, 2008)  At an average 17 month follow-up (3 to 26 months range), 12 (67%) patients had required further interventions, and 8 (44%) were classified as implant failures. The authors described these results as “disappointing”. While current data indicate that the unicondylar interpositional spacer does not improve the net health outcome, this technology is in an early stage of research and development.
2013 Update
A search of the MEDLINE database through August 2013 did not reveal any new literature that would prompt a change in the coverage statement.
2014 Update
A literature search using the MEDLINE database through September 2014 did not reveal any new information that would prompt a change in the coverage statement.
2015 Update
A literature search conducted through September 2015 did not reveal any new information that would prompt a change in the coverage statement.
2016 Update
A literature search conducted through September 2016 did not reveal any new information that would prompt a change in the coverage statement.
2018 Update
A literature search was conducted through September 2018.  There was no new information identified that would prompt a change in the coverage statement.   

References: Bailie AG, Lewis PL, et al.(2008) The Unispacer knee implant: EARLY CLINICAL RESULTS. J Bone Joint Surg Br, 2008; 90-B:446-50.

Emerson RH, Potter T.(1985) The use of the McKeever metallic hemiarthroplasty for unicompartmental arthritis. J Bone Jt Surg Am 1985; 67:208-12.

Hallock RH, Fell BM.(2003) Unicompartmental tibial hemiarthroplasty: early results of the UniSpacer knee. Clin Orthop Relat Res, 2003; (416):154-63.

Scott RD, Joyce MU, Ewald FC, et al.(1985) McKeever metallic hemiarthroplasty of the knee in unicompartmental degenerative arthritis. Long-term clinical follow-up and current indications. J Bone Jt Surg Am 1985; 67:203-07.

Sisto DJ, Mitchell IL.(2005) UniSpacer arthroplasty of the knee. J Bone Joint Surg Am, 2005; 87:1706-11.

Group specific policy will supersede this policy when applicable. This policy does not apply to the Wal-Mart Associates Group Health Plan participants or to the Tyson Group Health Plan participants.
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