Print Unicompartmental Knee Replacement Surgery

Unicompartmental Knee Replacement Surgery






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.



Unicompartmental knee replacement in patients who are considered suitable candidates for surgical treatment of osteoarthritis, when damage to the joint is completely or almost completely confined to the medial or the lateral compartment of the knee is medically necessary.

Unicompartmental knee replacement in patients with osteoarthritis that involves more than one compartment of the knee, or for patients with any of the following contraindications in the affected knee is considered investigational:

  • Flexion deformity > 15°
  • A varus or valgus deformity > 15°
  • Inflammatory synovitis, crystalline deposits, or large, impinging osteophytes
  • Eburnated bone on the patella or trochlea; or ruptured anterior cruciate ligament.

Unicompartmental knee replacement in patients with rheumatoid arthritis is considered investigational.






The coverage guidelines outlined in the Medical Policy Manual should not be used in lieu of the Member's specific benefit plan language.

Medically Necessary is defined as those services, treatments, procedures, equipment, drugs, devices, items or supplies furnished by a covered Provider that are required to identify or treat a Member's illness, injury or Nervous/Mental Conditions, and which Company determines are covered under this Benefit Plan based on the criteria as follows in A through D:

A.  consistent with the symptoms or diagnosis and treatment of the Member's condition, illness, or injury; and

B.  appropriate with regard to standards of good medical practice; and

C.  not solely for the convenience of the Member, his or her Provider; and

D.  the most appropriate supply or level of care which can safely be provided to Member. When applied to the care of an Inpatient, it further means that services for the Member's medical symptoms or conditions require that the services cannot be safely provided to the Member as an Outpatient.

For the definition of Medically Necessary, “standards of good medical practice” means standards that are based on credible scientific evidence published in peer-reviewed medical literature generally recognized by the relevant medical community, and physician specialty society recommendations, and the views of medical practitioners practicing in relevant clinical areas and any other relevant factors. BCBSMS makes no payment for services, treatments, procedures, equipment, drugs, devices, items or supplies which are not documented to be Medically Necessary. The fact that a Physician or other Provider has prescribed, ordered, recommended, or approved a service or supply does not in itself, make it Medically Necessary.

Investigative is defined as the use of any treatment procedure, facility, equipment, drug, device, or supply not yet recognized as a generally accepted standard of good medical practice for the treatment of the condition being treated and; therefore, is not considered medically necessary. For the definition of Investigative, “generally accepted standards of medical practice” means standards that are based on credible scientific evidence published in peer-reviewed medical literature generally recognized by the relevant medical community, and physician specialty society recommendations, and the views of medical practitioners practicing in relevant clinical areas and any other relevant factors. In order for equipment, devices, drugs or supplies [i.e, technologies], to be considered not investigative, the technology must have final approval from the appropriate governmental bodies, and scientific evidence must permit conclusions concerning the effect of the technology on health outcomes, and the technology must improve the net health outcome, and the technology must be as beneficial as any established alternative and the improvement must be attainable outside the testing/investigational setting.



3/2003: Approved by Medical Policy Advisory Committee (MPAC)

3/10/2004: Code Reference section updated, CPT code 27447 deleted, ICD-9 procedure codes 81.54, 81.55 deleted, ICD-9 diagnosis codes 717.0-717.9, 718.86, 733.40-733.49, 733.92, 733.99, 836.0-836.69 deleted

11/13/2006: Policy reviewed, no changes

03/08/2013: Policy reviewed; no changes.

08/27/2015: Code Reference section updated for ICD-10. Removed ICD-9 procedure code 81.47 from the Covered Codes table and added ICD-9 procedure code 81.54. Deleted the Investigational Codes table.

06/01/2016: Policy number added. Policy Guidelines updated to add medically necessary and investigative definitions.



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This may not be a comprehensive list of procedure codes applicable to this policy. 

The code(s) listed below are ONLY medically necessary if the procedure is performed according to the "Policy" section of this document.

Covered Codes

Code Number




Arthroplasty, knee, condyle and plateau; medial OR lateral compartment



ICD-9 Procedure

ICD-10 Procedure


Total knee replacement (partial knee replacement, unicompartmental, bicompartmental, tricompartmental)


Replacement of Knee, Femoral Surface, Right Knee


Replacement of Knee, Femoral Surface, Left Knee


Replacement of Knee, Tibial Surface, Right Knee


Replacement of knee tibial surface, left knee

ICD-9 Diagnosis

ICD-10 Diagnosis


Primary localized osteoarthrosis, lower leg

M17.0 - M17.12

Primary Osteoarthritis of knee (code range)


Secondary localized osteoarthrosis, lower leg

M17.2 - M17.32

Osteoarthritis of knee, post-traumatic (code range)


Localized osteoarthrosis not specified whether primary or secondary, lower leg

M17.4 - M17.5

Other secondary osteoarthritis of knee (code range)


Osteoarthrosis, unspecified whether generalized or localized, lower leg


Osteoarthritis of knee, unspecified