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Unicondylar Interpositional Spacer as a Treatment of Unicompartmental Arthritis of the Knee

Policy Number: MP-125

Latest Review Date: June 2022

Category:  Surgery                                                     


Unicondylar interpositional spacer device is considered investigational for treatment of osteoarthritis of the knee.


The interpositional unicondylar spacer (e.g., UniSpacer™) device was developed as an alternative treatment for patients suffering from the early stages of osteoarthritis of the knee.  The interpositional unicondylar spacer UniSpacer™ is indicated for the treatment of isolated, moderate degeneration of the medial compartment (grade III-IV chondromalacia) with no more than minimal degeneration (grade I-II chondromalacia, no loss of joint space) in the lateral condyle or patellofemoral compartment.

This device was developed for patients with severe knee pain who have exhausted traditional treatment plans such as anti-inflammatory medications and arthroscopy, but are not yet ready for total knee replacement surgery.

The interpositional unicondylar spacer is a small, kidney-shaped insert made of cobalt alloy.  It is geometrically designed to self-center within the knee and move with the knee, not against it.  The femoral articulating surface is cup shaped (concave) to capture the femoral condyle.  The tibial surface is designed to replicate the anatomy of the tibial plateau with the meniscus removed.  It is not fixed in place, but remains centered under the weight-bearing portion of the femur through all angles of flexion.  The ligaments surrounding the knee are re-tensioned and act as cables that hold the femur against the device.  It comes in a wide range of sizes, depending on the weight and size of each patient.

The procedure is done under general or regional anesthesia.  Using arthroscopy, debridement and resection of the medial meniscus is done.  The device is inserted into the joint space, above the affected medial tibial plateau, and rests within the boundaries of the resected meniscus.  The procedure takes about one hour to complete, and the patient usually goes home within 24 hours.

The procedure is not suitable for patients with significant patellofemoral disease or significant lateral compartment disease, or those with subchondral bone loss.  The anterior and posterior cruciate ligament structures must be intact.

The UniSpacer™ is manufactured by Sulzer Orthopedics in Austin, Texas.  The device received U.S. FDA clearance for marketing in January 2001.  The FDA approved indication is for treatment of “moderate degeneration of the medial compartment of the knee (grade III-IV chondromalacia) with no more than minimal degeneration (grade I-II chondromalacia, no loss of joint space) in the lateral condyle and patellofemoral compartments”.  Additional unicondylar interpositional spacers have received FDA clearance.  They include the Oti Unicondular Interpositional Spacer Osteoimplant (2002) and the Knee Interpositional Mini-repair System (2003).  

Other interpositional unicondylar devices have received 510(k) approval: the Oti Unicondular Interpositional Spacer Osteoimplant (2002), the Knee Interpositional Mini-Repare System (2003), and the Repicci II® (2002).  The Knee Interpositional Mini-Repair System is a patient-specific design with specification taken from magnetic resonance scans. These devices are indicated for the uncemented treatment of medial and/or lateral tibial articulating surfaces of the osteoarthritic knee with grade ii-IV chondromalacia.  The Recippi II is a partial knee replacement designed to remove as little bone from the knee as possible.


Osteoarthritis (OA), previously called degenerative joint disease, is the most prevalent form of arthritis in the U.S.  The causes of OA of the knee are not always known, but biomechanical stresses affecting the articular cartilage and subchondral bone and biochemical changes in the articular cartilage and synovial membrane are important in its pathogenesis. The guidelines for medical management of OA of the knee, published by the American College of Rheumatology, include:  patient education, weight loss, PT and OT, acetaminophen, nonsteroidal antiinflammatory drugs, topical analgesics, and intraarticular steroid injections.

If patient response is inadequate, referral to an orthopedic surgeon may be indicated.  Surgical treatment options include arthroscopy with debridement, proximal tibial osteotomy, and total knee replacement.  The decision to proceed with total knee replacement is usually only considered in people over the age of 60.

The interpositional unicondylar spacer device was designed for patients who are in general good health, still fairly young, and have arthritis only in the medial compartment of their knee.  The majority of patients treated are under age 65 and, therefore, not yet ideal candidates for total knee replacement.  The device helps to relieve the arthritic pain and improve joint stability by restoring ligament tension and normal knee alignment, while preserving the patient’s natural bone. The interpositional unicondylar spacer (UniSpacer™) device is only used by specially trained surgeons.

Some of the potential risks associated with the use of the interpositional unicondylar spacer include the general risks associated with any surgical procedure, such as infection, cardiovascular, pulmonary, and urinary complications, and the risks associated with knee surgery, such as scarring from incision, pain, dislocation, need for revision, numbness, and weakness.

Currently, there are few studies published in the medical literature that allow for adequate evaluation of the use of unicondylar interpositional spacers in the clinical setting. Bailie et al. (2008) identified 1 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. At an average 17-month follow-up (range, 3 to 26 months), 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. The unicondylar interpositional spacer is considered investigational; the policy statement remains unchanged.

In their review article Borus and Thornhill (2008) state, “Recent increased interest in less invasive surgical techniques has led to a concurrent resurgence in unicompartmental knee arthroplasty. The procedure has evolved significantly over the past three decades. Proponents of unicompartmental knee arthroplasty cite as advantages lower perioperative morbidity and earlier recovery. Both clinical outcome and kinematic studies have indicated that successful unicompartmental knee arthroplasty functions closer to a normal knee. Recent reports have demonstrated success in expanding the classic indications of unicompartmental knee arthroplasty to younger and heavier patients. Both fixed- and mobile-bearing implants can yield excellent clinical outcomes at >10 years, but with different modes of long-term failure. Proper execution of surgical technique remains critical to optimizing outcome. Long-term studies are needed to appropriately define the role of less invasive unicompartmental surgical approaches as well as the role of computer navigation.”

Sisto and Mitchell (2005) reported on the experience of a single surgeon who performed 37 Unispacer arthroplasties for treatment of medial compartment arthritis in 34 patients. After a mean duration follow-up of 26 months, there were no excellent, 10 good, 15 fair, and 12 poor results. Six of the poor results occurred because of Unispacer dislocation. The investigators do not recommend Unispacer arthroplasty for treatment of arthritis of the knee.

A 2006 study evaluated 24 patients (26 knees) with unicompartmental knee osteoarthritis who were managed with McKeever tibial hemiarthroplasty. A total of 13 knees were successfully revised at an average of 8 years after the original procedure. Ten knees retained devices with an average follow-up of 16.8 years. The investigators concluded that the McKeever device is a reasonable surgical option for patients who are not candidates for osteotomy or total knee replacement.

Hallock and Fell (2003) reported 1- and 2-year data on 71 Unispacer knee devices. The mean Knee Society knee score improved 169% in the 1-year group and 193% in the 2-year group. A total of 5 implants were revised to total knee arthroplasty and 10 implants were revised to another Unispacer knee device.

Practice Guidelines and Position Statements

American Academy of Orthopaedic Surgeons (AAOS)

In an updated 2013 guideline, the AAOS recommended against using a free-floating interpositional device for patients with symptomatic unicompartmental osteoarthritis of the knee. The guideline notes that the supporting evidence is lacking and requires the work group to make a recommendation based on expert opinion by considering the known potential harm and benefits associated with the treatment.


Osteoarthritis (OA), UniSpacer™, unicondylar interpositional spacer, Oti Unicondular Interpositional Spacer Osteoimplant, Knee Interpositional Mini-Repare System, Repicci II®  (2002), OrthoGlide


The FDA currently lists five unicondylar spacer devices as having received 510(k) clearance for marketing in the United States.

  • Knee Interpositional Mini-Repair System (KIMRS)- K033242
  • OrthoGlide Lateral Knee Implant- K073233
  • OrthoGlide Medical Knee Implant- K053094
  • Oti Unicondular Interpositional Spacer- K022779  
  • Unicondylar Interpositional Spacer- K003269


Coverage is subject to member’s specific benefits.  Group specific policy will supersede this policy when applicable.

ITS: Home Policy provisions apply

FEP contracts: FEP does not consider investigational if FDA approved and will be reviewed for medical necessity. Special benefit consideration may apply.  Refer to member’s benefit plan.


CPT codes:


Unlisted procedure, arthroscopy


Unlisted procedure, femur or knee



  1. American Academy of Orthopaedic Surgeons (AAOS).Treatment Of Osteoarthritis of the Knee (Non-Arthroplasty). May 18, 2013.
  2. Bailie AG, Lewis PL, Brumby SA, et al.  The Unispacer knee implant:  Early clinical results.  Br J Bone Joint Surg, April 2008; 90(4): 446-450.
  3. Blue Cross Blue Shield Association.  Unicondylar interpositional spacer as a treatment of unicompartmental arthritis of the knee.  Medical Policy Reference Manual, May 2008.
  4. Borus T, Thornhill T.  Unicompartmental knee arthroplasty. J Am Acad Orthop Surg. 2008 Jan;16(1):9-18.
  5. Courtine M, Labattut L, Martz P, et al. The unicompartmental knee implant UniSpacer™: Ten-year outcomes after treatment for medial tibio-femoral osteoarthritis. Orthop Traumatol Surg Res. 2021 May;107(3):102873.
  6. Hallock RH. The unispacer knee system:  Have we been there before.  Orthopedics 2003;  26(9): 953-954.
  7. Hochberg Marc C, et al. Guidelines for the medical management of osteoarthritis.  Arthritis and Rheumatism; 38(11): 1541-1546.
  8. Scott RD UniSpacer:  Insufficient data to support its widespread use.  Clin Orthop 2003; 416: 164-166.
  9. Sisto DJ and Mitchell IL.  UniSpacer arthroplasty of the knee.  J Bone Joint Surg Am 2005; 87(8): 1706-1711.
  10. Springer BD, Scott RD, Sah AP, et al. McKeever hemiarthroplasty of the knee in patients less than sixty years old. J Bone Joint Surg Am. 2006 Feb;88(2):366-371.
  11. U.S. Food and Drug Administration (FDA). 510(k) Summary: Knee Interpositional Mini-Repair System (KIMRS) K033242.
  12. U.S. Food and Drug Administration (FDA). 510(k) Summary: OrthoGlide Lateral Knee Implant K073233. January 8, 2008.  
  13. U.S. Food and Drug Administration (FDA). 510(k) Summary: OrthoGlide Medical Knee Implant K053094. February 6, 2006.  
  14. U.S. Food and Drug Administration (FDA). 510(k) Summary: Oti Unicondular Interpositional Spacer K022779.  
  15. U.S. Food and Drug Administration (FDA). 510(k) Summary: Unicondylar Interpositional Spacer K003269.
  16. Zimmer formerly Centerpulse Orthopedics, Inc.,


Medical Policy Group, June 2003 (3)

Medical Policy Administration Committee, July 2003

Available for comment July 28-September 10, 2003

Medical Policy Group, June 2004

Medical Policy Group, June 2005 (1)

Medical Policy Group, June 2006 (1)

Medical Policy Group, June 2007 (1)

Medical Policy Group, February 2009 (1)

Medical Policy Group, November 2009 (2)

Medical Policy Administration Committee, November 2009

Medical Policy Group November 2010 (1)  Verbiage updated to reflect generic device in policy, no policy statement change.

Medical Policy Group, March 2012: Effective March 12, 2012 Policy no longer scheduled for regular literature reviews and updates.

Medical Policy Group, July 2019 (7): Reviewed by consensus. Updated Key Points and References. There is no new published peer-reviewed literature available that would alter the coverage statement in this policy.

Medical Policy Group, June 2021 (7): Reviewed by consensus. Updated Key Points, Approved by Governing Bodies and References.  Added Key Word: "OrthoGlide". There is no new published peer-reviewed literature available that would alter the coverage statement in this policy.

Medical Policy Group, July 2022 (7): Reviewed by consensus. Updated Key Points and References. There is no new published peer-reviewed literature available that would alter the coverage statement in this policy.


This medical policy is not an authorization, certification, explanation of benefits, or a contract. Eligibility and benefits are determined on a case-by-case basis according to the terms of the member’s plan in effect as of the date services are rendered. All medical policies are based on (i) research of current medical literature and (ii) review of common medical practices in the treatment and diagnosis of disease as of the date hereof. Physicians and other providers are solely responsible for all aspects of medical care and treatment, including the type, quality, and levels of care and treatment.

This policy is intended to be used for adjudication of claims (including pre-admission certification, pre-determinations, and pre-procedure review) in Blue Cross and Blue Shield’s administration of plan contracts.

The plan does not approve or deny procedures, services, testing, or equipment for our members. Our decisions concern coverage only. The decision of whether or not to have a certain test, treatment or procedure is one made between the physician and his/her patient. The plan administers benefits based on the member’s contract and corporate medical policies. Physicians should always exercise their best medical judgment in providing the care they feel is most appropriate for their patients. Needed care should not be delayed or refused because of a coverage determination.

As a general rule, benefits are payable under health plans only in cases of medical necessity and only if services or supplies are not investigational, provided the customer group contracts have such coverage.

The following Association Technology Evaluation Criteria must be met for a service/supply to be considered for coverage:

  1.  The technology must have final approval from the appropriate government regulatory bodies;
  2.  The scientific evidence must permit conclusions concerning the effect of the technology on health outcomes;
  3.  The technology must improve the net health outcome;
  4.  The technology must be as beneficial as any established alternatives;
  5.  The improvement must be attainable outside the investigational setting.

Medical Necessity means that health care services (e.g., procedures, treatments, supplies, devices, equipment, facilities or drugs) that a physician, exercising prudent clinical judgment, would provide to a patient for the purpose of preventing, evaluating, diagnosing or treating an illness, injury or disease or its symptoms, and that are:

  1.  In accordance with generally accepted standards of medical practice; and
  2.  Clinically appropriate in terms of type, frequency, extent, site and duration and considered effective for the patient’s illness, injury or disease; and
  3.  Not primarily for the convenience of the patient, physician or other health care provider; and
  4. Not more costly than an alternative service or sequence of services at least as likely to produce equivalent therapeutic or diagnostic results as to the diagnosis or treatment of that patient’s illness, injury or disease.