CAM 70188

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

Category:Surgery   Last Reviewed:July 2019
Department(s):Medical Affairs   Next Review:April 2999
Original Date:April 2003    

Interpositional unicondylar spacers are metallic implants that 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). 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 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 devices approved by the U.S. Food and Drug Administration (FDA) 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 years and weights ranged from 53-168 kg). (1) At one-year follow-up, 63 patients (66 knees) still had the implant; the five failed implants (7 percent) were converted to total knee arthroplasty for inadequate pain relief. Ten patients (14 percent) had their implants revised to another size because of persistent pain (n=6) or dislocation (n=4), and 17 patients (24 percent) required manipulation under anesthesia to correct postoperative arthrofibrosis. The rate of revision at one year was 21 percent, with an additional 24 percent 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 two-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 (preoperative: 22, postoperattive: 26), with complaints of pain during normal walking for 32 knees and activities limited by pain in 15 patients (41 percent of implants). Persistent postoperative swelling was present in nine 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.


  1. Scott RD, Joyce MJ, Ewald FC et al. McKeever metallic hemiarthroplasty of the knee in unicompartmental degenerative arthritis. Long-term clinical follow-up and current indications. J Bone Joint Surg Am 1985; 67(2): 203-7.
  2. Emerson RH, Potter T. The use of the McKeever metallic hemiarthroplasty for unicompartmental arthritis. J Bone Joint Surg Am 1985; 67(2):208-12.
  3. ECRI. Metallic Interpositional Resurfacing Prosthesis for the Knee Joint [Forcast]
  4. Sisto DJ, Mitchell IL.  UniSpacer arthroplasty of the knee.  J Bone Joint Surg Am. 2005 Aug;87(8):1706-11.
  5. Springer BD, Scott RD, Sah AP, Carrington R. McKeever hemiarthroplasty of the knee in patients less than sixty years old.  J Bone Joint Surg Am. 2006 Feb;88(2):366-71.  
  6. Griffin T, Rowden N, Morgan D, et al. Unicompartmental knee arthroplasty for the treatment of unicompartmental osteoarthritis: A systematic study. ANZ J Surg. 2007;77(4):214-221.
  7. Khanna G, Levy BA. Oxford unicompartmental knee replacement: Literature review. Orthopedics. 2007;30(5 Suppl):11-14.
  8. Bailie AG, Lewis PL, Brumby SA, Roy S, Paterson RS, Cambell DG. The Unispacer knee implant: Early Clinical Results. J Bone Joint Surg Br. 2008 Apr;90-B(4):446-450.

Coding Section

Codes Number Description
CPT 27599 Unlisted procedure, femur or knee
ICD-9 Diagnosis  715.00-715.98 Osteoarthrosis (code range)
ICD-10-CM (effective 10/01/15)  M150  Primary generalized (osteo)arthritis 
  M159  Polyosteoarthritis, unspecified
  M151  Heberden's nodes (with arthropathy) 
  M152  Bouchard's nodes (with arthropathy) 
  M1991  Primary osteoarthritis, unspecified site 
  M19019  Primary osteoarthritis, unspecified shoulder 
  M19029  Primary osteoarthritis, unspecified elbow 
  M19039  Primary osteoarthritis, unspecified wrist 
  M19049  Primary osteoarthritis, unspecified hand 
  M1610  Unilateral primary osteoarthritis, unspecified hip 
  M1710  Unilateral primary osteoarthritis, unspecified knee 
  M19079  Primary osteoarthritis, unspecified ankle and foot 
  M1993  Secondary osteoarthritis, unspecified site 
  M19219  Secondary osteoarthritis, unspecified shoulder 
  M19229  Secondary osteoarthritis, unspecified elbow 
  M19239  Secondary osteoarthritis, unspecified wrist 
  M19249  Secondary osteoarthritis, unspecified hand 
  M167  Other unilateral secondary osteoarthritis of hip
  M175  Other unilateral secondary osteoarthritis of knee 
  M19279  Secondary osteoarthritis, unspecified ankle and foot 
  M1993  Secondary osteoarthritis, unspecified site 
  M1990  Unspecified osteoarthritis, unspecified site 
  M189  Osteoarthritis of first carpometacarpal joint, unspecified 
  M169  Osteoarthritis of hip, unspecified 
  M179  Osteoarthritis of knee, unspecified 
  M158  Other polyosteoarthritis 
  M153  Secondary multiple arthritis 
  M159  Polyosteoarthritis, unspecified 
  M169  Osteoarthritis of hip, unspecified 
  M179  Osteoarthritis of knee, unspecified 

Procedure and diagnosis codes on Medical Policy documents are included only as a general reference tool for each policy. They may not be all-inclusive.

This medical policy was developed through consideration of peer-reviewed medical literature generally recognized by the relevant medical community, U.S. FDA approval status, nationally accepted standards of medical practice and accepted standards of medical practice in this community, Blue Cross and Blue Shield Association technology assessment program (TEC) and other non-affiliated technology evaluation centers, reference to federal regulations, other plan medical policies and accredited national guidelines.

"Current Procedural Terminology© American Medical Association.  All Rights Reserved" 

History From 2014 Forward     


Annual review, no change to policy intent. 


Annual review. No change to policy intent. 


Annual review. No change to policy intent 


Annual review. No change to policy intent 


Added ICD-10 codes to policy. 


Annual review, no change to policy intent. Added coding and guidelines.


Annual Review. No changes made.

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