Unicondylar interpositional spacers, have been proposed as a treatment for early-stage osteoarthritis of the knee. The spacers are kidney-shaped metal inserts which are designed to function as a self-centering bearing in the knee. The spacer fits between the natural bone structures of the knee and is not affixed with cement or screws. This document addresses unicondylar interpositional spacers.

Note: Please see the following related document for additional information:

• SURG.00105 Bicompartmental Knee Arthroplasty

Investigational and Not Medically Necessary:

Use of unicondylar interpositional spacers is considered investigational and not medically necessary for all indications.

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.  One case series conducted by Hallock and colleague (2003),  reported one and two year data on 71 UniSpacer Knee System implants in 67 patients as a treatment of isolated medial compartment osteoarthritis of the knee. The mean age and weight of these patients was 54 years and 94 kg (207 lb), respectively. All knees were evaluated using the Lysholm scoring scale, the Knee Society clinical rating system, radiographic limb alignment, and range of motion (ROM). The mean Lysholm score improved 88%in the 1 year group and 140% in the two year group.  The mean Knee Society knee score improved 169% and 193%, respectively. The mean Knee Society function score improved 31% and 65%, respectively. Five implants (7%) were revised to total knee arthroplasty (TKA) and 10 implants (14%) were revised to another UniSpacer Knee System implant. The reasearachers concluded that the early results suggest that an intra-articular metallic spacer is a viable treatment option for OA in younger patients.

Sisto (2005) reported on the experience of a single surgeon with the UniSpacer as a treatment for isolated medial compartment arthritis of the knee. From April 2002 through November 2002, thirty-seven UniSpacer arthroplasties were performed in 34 patients (18 women [19 knees,] and 16 men [18 knees]) who had a mean age of fifty-five years. . The Ahlbäck radiographic evaluation scale was used to grade the severity of arthritis. Twelve patients had had a previous arthroscopic meniscectomy. The mean preoperative Knee Society function score was 60 points (range, 40 to 80 points), and the mean preoperative Knee Society objective score was 62 points (range, 40 to 76 points). After a mean duration of follow-up of 26 months (ranging from 24 to29 months), the mean postoperative total function score was 69 points (range, 40 to 82 points), and the mean Knee Society objective score was 72 points (range, 45 to 88 points). There were 10 good, 15 fair, 12 poor results and no excellent results.  Six of the twelve poor results were in knees that had dislocation of the UniSpacer which then resulted in the patients undergoing a total knee arthroplasty. The researchers concluded that the UniSpacer arthroplasty should not be used as a treatment of degenerative arthritis of the medial compartment of the knee.

Bailie and colleagues (2008) conducted a prospective study to determine the early clinical outcomes of 18 consecutive patients with osteoarthritis of the knee that were treated with the Unispacer knee implant between June 2003 and August 2004. . Between 3 and 6 months after surgery, seventeen patients (94%) reported persistent symptoms. At an average 17 month follow-up (3 to 26 months range), 12 (67%) patients had required further interventions, and 8 (44%) required revision within two years. The authors concluded that the use of the Unispacer in isolated medial compartment osteoarthritis is associated with a high rate of revision surgery and provides unpredictable pain relief.

In light of the lack of well-designed studies supporting the efficacy of the device, conclusions regarding the net benefit of unicondylar interpositional spacers cannot be drawn.  Further studies on patient outcomes, particularly in comparison with standard treatments, are essential to determine efficacy.

Description of Disease
Osteoarthritis (OA) is a degenerative condition of the joints and is the most common form of arthritis. OA commonly affects hands and weight-bearing joints such as the knees, hips, feet, and spine. The condition is characterized by a progressive breakdown of the cartilage lining the articular ends of bones required for proper cushioning and smooth function of joints. The breakdown of this cartilage leads to bones rubbing against each other causing pain, loss of movement, and destruction of the joint. OA affects an estimated 20.7 million Americans, mostly after age 45, with women more commonly affected than men. The severity of OA varies widely. Most people with OA report some limitation in movement or daily activities due to pain or diminished range of motion.

There is no cure for OA. Treatment focus is on reducing pain and improving joint movement through exercises to keep joints flexible and improve muscle strength, medications and heat/cold therapy to control pain, joint protection to prevent strain or stress on painful joints, weight control, and surgery.

Description of Technology
Many different types of surgical procedures have been developed to treat OA of the knees including knee debridement, high tibial osteotomy, and partial (unicompartmental) and total knee arthroplasty (replacement). Although often beneficial, such procedures can also be associated with long recovery periods, compromise of the joint to future interventions, and treatment failure after a short period of improvement. In addition, most procedures do not address mechanical alignment issues.

The unicondylar interpositional spacer (e.g., UniSpacer®, Centerpulse Orthopedics, Inc.) has been proposed as an alternative to the more invasive surgical interventions mentioned above.  This device is used in patients with joint degeneration/destruction limited to one compartment (normally the inside or medial compartment) of the knee joint.  The unicondylar interpositional spacer consists of a metallic hemispherical spacer that can be surgically implanted in the joint space between the affected bone ends. The device is self-aligning and requires no cement or screws to keep it in place.  

Proposed Benefits
The implantation of unicondylar interpositional spacers has been proposed as a less invasive surgical procedure for selected cases of osteoarthritis of the knee. One suggested advantage is that the bone ends rub on the polished metal surface of the device sparing further bone wear from bone to bone contact. In addition, it has been suggested that the less invasive surgical procedure may decrease further joint destruction common in many other knee operations.

Possible Risks
Implanting a unicondylar interpositional spacer carries the risks of any significant surgical procedure including infection and bleeding into the site.  In addition, the surgical treatment may eventually fail necessitating conversion to a full unicompartmental or total knee arthroplasty.

In a review of the Unispacer®, RD Scott concluded the eventual role of the Unispacer is uncertain and the procedure is technically demanding, making its widespread success unlikely. (Scott, 2003) A recent study reported the experience of a single surgeon with UniSpacer® arthroplasty for the treatment of isolated medial compartment arthritis of the knee, wherein thirty-seven UniSpacer® arthroplasties were performed in thirty-four patients for the treatment of arthritis primarily involving the medial compartment of the knee. After follow-up of approximately twenty-six months, there were no excellent, ten good, fifteen fair, and twelve poor results.  Six of the twelve poor results were in knees that had dislocation of the UniSpacer®. All twelve knees were revised to a total knee arthroplasty. Although this is a single small study, more research needs to be performed on this device. (Sisto, 2005.)

The Arthritis Foundation on their website states: "There have been many developments in recent years that continue to improve hip and knee arthroplasty. Only future study will determine the ideal implants and techniques for both the knee and hip. When done well in properly selected patients, these surgeries can provide many years of decreased pain and increased function", supporting the fact more study is needed.

Unicompartmental: related to either the inside (medial) or outside (lateral) half of the knee joint

Unicondylar interpositional spacer: a specialized hemispheric metallic device that can be surgically implanted into the joint space of the knee; this device has been used as a treatment for arthritis that affects only part of the knee (unicompartmental arthritis)

The following codes for treatments and procedures applicable to this document are included below for informational purposes.  Inclusion or exclusion of a procedure, diagnosis or device code(s) does not constitute or imply member coverage or provider reimbursement policy.  Please refer to the member's contract benefits in effect at the time of service to determine coverage or non-coverage of these services as it applies to an individual member.

When Services are Investigational and Not Medically Necessary:
When the code describes a procedure indicated in the Position Statement section as investigational and not medically necessary. 

Peer Reviewed Publications:

1. Bailie AG, Lewis PL, Brumby SA, et al. The Unispacer knee implant: Early clinical results. J Bone Joint Surg Br. 2008;90(4):446-450.
2. Emerson RH, Potter T. The use of the McKeever metallic hemiarthroplasty for unicompartmental arthritis.  J Bone Joint Surg Am 1985;67:208-212.
3. Hallock RH, Fell BM.  Unicompartmental tibial hemiarthroplasty: early results of the Unispacer® knee.  Clinical Orthopedics and Related Research. 2003; 416:154-163.
4. Scott RD.  The UniSpacer®: insufficient data to support its widespread use.  Clinical Orthopedics and Related Research.  2003; 416:164-166.
5. Sisto DJ.  Unispacer arthroplasty of the knee.  J Bone Joint Surg Am. 2005;87(8):1706-1711.

1. Arthritis Foundation. Osteoarthritis: Available at: http://www.arthritis.org/conditions/DiseaseCenter/oa.asp. Accessed on April 25, 2009.
2. National Institute of Arthritis and Musculoskeletal and Skin Diseases.  Handout on Health: Osteoarthritis: Available at: http://www.niams.nih.gov/hi/topics/arthritis/oahandout.htm. Accessed on April 25, 2009. 

Knee Interpositional Mini-Repair System
OrthoGlide(^TM)
Preservation™ Unicondylar Knee Prosthesis
Unicompartmental Knee Arthroplasty
Unicompartmental Osteoarthritis
Unicondular Interpositional Spacer
Unicondylar Interpositional Spacer
UniSpacer^® Knee System

The use of specific product names is illustrative only.  It is not intended to be a recommendation of one product over another, and is not intended to represent a complete listing of all products available.