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MP 7.01.88 Unicondylar Interpositional Spacer as a Treatment of Unicompartmental Arthritis of the Knee

Medical Policy
Original Policy Date
Last Review Status/Date
Reviewed with literature search/9:2009
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Our medical policies are designed for informational purposes only and are not an authorization, or an explanation of benefits, or a contract.  Receipt of benefits is subject to satisfaction of all terms and conditions of the coverage.  Medical technology is constantly changing, and we reserve the right to review and update our policies periodically.


Interpositional unicondylar spacers are metallic implants which are inserted into the joint space between the affected tibial plateau and femoral condyle. Instead of being fixed, the spacers are held in place by the geometry of the curved implant, ligament tension, and surrounding soft tissue structures. Metallic interpositional unicondylar spacers have been developed as possible alternatives to osteotomy or unicompartmental arthroplasty for treatment of unicompartmental knee arthritis.

While osteoarthritis of the knee typically involves both medial and lateral components, some patients may have signs or symptoms confined to only one compartment, often as a result of specific injury. Initial treatment of uni- and bicompartmental disease is similar, i.e., analgesics, viscosupplementation, and arthroscopic debridement (see policy No. 2.01.31 ). When patients fail to respond to these more conservative therapies, surgical interventions may be indicated.

Older patients with arthritis typically consider total knee replacement, but may be considered for unicondylar knee arthroplasty. The metal-to-plastic unicondylar prosthesis has both tibial and femoral components but leaves intact both cruciate ligaments, the patellofemoral joint, and the opposite compartment, thus preserving nearly normal knee kinematics. Unicompartmental arthroplasties are typically performed in patients with isolated medial arthritis who are older than 60 years, have a low level of physical activity, and weigh less than 180 lbs.

Younger patients are usually not considered ideal candidates for total knee arthroplasty since they would be expected to need at least one additional total knee replacement in their lifetimes. The preferred option for young patients with unicompartmental disease is high tibial osteotomy. Those with medial compartment disease may also be candidates for unicompartmental arthroplasty or for fixed metallic hemiarthroplasty. MacIntosh and McKeever hemiarthroplasty devices were used primarily between 1950 and 1970, but their use has decreased with the refinement of total knee arthroplasty procedures. These devices require bone cuts that might complicate future arthroplasty procedures.

Metallic interpositional unicondylar spacers have been developed as possible alternatives to osteotomy or unicompartmental arthroplasty. These devices do not require any bone resection or mechanical fixation for proper function. Following debridement and resection of the meniscus, the device is fit to the joint space above the affected tibial plateau and held in place by its geometry, ligament tension and the surrounding soft tissue structures. The uncemented implant adapts to the kinematics of the knee, with a smooth metallic curved surface against which the femur articulates. Preservation of bone is important for the use of interpositional spacers as a bridge procedure in active young adults or for overweight patients who would not be candidates for unicompartmental arthroplasty.

In 2001, a cobalt alloy device, referred to as a 'unicondylar interpositional spacer' or 'UniSpacer' received clearance for marketing through a U.S. Food and Drug Administration (FDA) 510(k) process as an interpositional arthroplasty device, listing the MacIntosh and McKeever prostheses as predicate devices. The FDA clearance 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 Orthoglide Medical Knee Implant, which received 510(k) approval in 2006, is also indicated for “uncemented use in the treatment of moderate degeneration of the medial compartment of the knee,” but for grade II-IV chondromalacia.

Two other interpositional devices have received 510(k) approval, the Oti Unicondular Interpositional Spacer Osteoimplant (2002) and the Knee Interpositional Mini-Repair System (2003), listing the UniSpacer as a predicate device. The Knee Interpositional Mini-Repair System is a patient-specific design, with specifications 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.


Unicondylar interpositional spacer is considered investigational as a treatment of unicompartmental arthritis of the knee.

Policy Guidelines

There is no specific CPT code for this procedure. The CPT code 27599 (unlisted procedure, femur or knee) would be the most appropriate code for the insertion of this device.

Benefit Application

BlueCard/National Account Issues

State or federal mandates (e.g., FEP) may dictate that all FDA-approved devices may not be considered investigational, and thus these devices may be assessed only on the basis of their medical necessity.


Two retrospective reports were identified on the use of the UniSpacer. The largest group of patients reported was 71 UniSpacer implants in 67 patients (ages ranged from 38-83 and weights ranged from 53-168 kg). (1) At 1-year follow-up, 63 patients (66 knees) still had the implant; the 5 failed implants (7%) were converted to total knee arthroplasty for inadequate pain relief. Ten patients (14%) had their implants revised to another size because of persistent pain (n =6) or dislocation (n =4), and 17 patients (24%) required manipulation under anesthesia to correct postoperative arthrofibrosis. The rate of revision at 1 year was 21%, with an additional 24% requiring manipulation due to arthrofibrosis.

Another group reported their experience with 37 UniSpacer implants in 34 patients (ages ranging from 42–75 years) with baseline Knee Society functional and objective rating scales of 69 and 62 points, respectively. (2) At 2-year follow-up, functional and objective ratings had improved by about 10 points; there were no excellent, 10 good, 15 fair, and 12 poor results. Six of the 12 poor results were due to dislocation, and the 12 were revised to total knee arthroplasty. There was no significant change in average pain scores (pre: 22, post: 26), with complaints of pain during normal walking for 32 knees and activities limited by pain in 15 patients (41% of implants). Persistent postoperative swelling was present in 9 patients. No publications were identified on the use of other FDA-approved uncemented spacers.

Based on the lack of controlled trials, combined with the high proportion of failures and adverse events in the identified retrospective reports, the use of interpositional unicondylar spacers is considered to be investigational.

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. (3) 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. The unicondylar interpositional spacer is considered investigational; the policy statement remains unchanged.

2009 Update
A literature search of the MEDLINE database was performed for the period of April 2008 through July 2009. No new clinical reports were identified.


  1. Hallock RH, Fell BM. Unicompartmental tibial hemiarthroplasty: early results of the UniSpacer knee. Clin Orthop Relat Res 2003; (416):154-63.
  2. Sisto DJ, Mitchell IL. UniSpacer arthroplasty of the knee. J Bone Joint Surg Am 2005; 87(8):1706-11.
  3. Bailie AG, Lewis PL, Brumby SA, et al. The Unispacer knee implant: EARLY CLINICAL RESULTS. J Bone Joint Surg Br 2008; 90-B(4):446-450.





CPT 27599 Unlisted procedure, femur or knee 
ICD-9 Diagnosis  715.00 – 715.98  Osteoarthrosis (code range) 


Interpositional Spacer, Knee
Oti Unicondular Interpositional Spacer Osteoimplant
Knee Interpositional Mini-Repair System
Orthoglide Medical Knee Implant

Policy History

Date Action Reason
04/29/03 Add to Surgery section New policy
11/9/04 Replace policy Policy updated with literature search; no change in policy statement
08/17/05 Replace policy Policy updated with literature search; no change in policy statement
02/15/07 Replace policy Policy rewritten; additional FDA-approved devices added. References updated; reference numbers 1 and 2 added and old references removed; no change in policy statement
05/08/08 Replace policy  Policy updated with literature search; reference 3 added; no change in policy statement 
09/10/09 Replace policy Policy updated with literature search through July 2009; policy statement unchanged

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