Description:
Knee joint failure often results from advanced, end stage joint disease that generally involves complete destruction of cartilage (i.e., bone-on-bone changes). Several grading systems are available to grade articular cartilage disease. The Outerbridge classification is the most widely used system of judging articular injury to the knee. This system allows delineation of varying areas of chondral pathology based on the qualitative appearance of the cartilage surface and can assist in identifying injuries that are suitable for repair techniques. The characterization of cartilage in this system is as follows:

• Grade 0: normal
• Grade l: cartilage with softening and swelling
• Grade ll: a partial-thickness defect with fissures on the surface that do not reach subchondral bone or exceed 1.5 cm in diameter
• Grade lll: fissuring to the level of subchondral bone in an area with a diameter more than 1.5 cm
• Grade lV: subchondral bone exposed

A second system often used for grading cartilage disease is the Kellgren-Lawrence grading scale. This scale defines injury as follows:

• Grade 1: doubtful narrowing of joint space and possible osteophytic lipping
• Grade 2: definite osteophytes, definite narrowing of joint space
• Grade 3: moderate multiple osteophytes, definite narrowing of joint space, some sclerosis and possible deformity of bone contour
• Grade 4: large osteophytes, marked narrowing of joint space, severe sclerosis and definite deformity of bone contour

The two scales are comparable, with the end point of Grade IV/4 being what is usually described as bone-on-bone. As the grade of disease increases, there is a stronger association with symptoms such as pain, stiffness and swelling.

Unicompartmental Knee Replacement (UKR) 
Unicompartmental OA can occur in any of three existing compartments of the joint: medial, lateral or patellofemoral. In comparison to TKR, UKR is typically recommended for individuals with less severe disease, and who have better knee function. During a unicompartmental knee replacement only a single compartment is replaced. Only the bony area in the single damaged compartment needs to be resurfaced. The ends of the femur and tibia are capped with metal coverings, and a plastic insert is placed between the two metal components for smooth gliding. Evidence suggests that with appropriate patient selection, UKRs are a successful option for patients with OA of the knee. UKR may be performed through standard exposure or utilizing minimally invasive surgery with modified instruments.

Medial or Lateral Compartment: Unicompartmental knee replacement has been proposed as an alternative to TKR for patients with disease limited to the medial or lateral compartment, with the proposed advantages being less pain, quicker recovery and better long-term results. A unicompartmental knee replacement requires a smaller and less invasive incision that does not interrupt the anterior and posterior cruciate ligaments, which are the main muscles controlling the knee (American Academy of Orthopaedic Surgeons [AAOS], 2006).

UKA is considered to be as safe and effective as TKA and high tibial osteotomy, although it is associated with a risk for development or progression of disease in adjacent compartments. Published scientific data confirm medium- to long-term outcomes associated with unicompartmental replacement are comparable to those of primary TKR in select patient groups (Dabov and Perez, 2003; Meek et al., 2004; Koopman and Moreland, 2005). Clinical studies have shown that patients treated with unicondylar knee replacement have better functionality and greater range of motion than patients treated with total knee replacement (Sun and Jia, 2012; Rougraff, et al., 1991; Newman, et al., 1998). Authors have also reported on the survival rate of prostheses, most of which approach at least 10 years (Murray, et al., 1998; Berger, et al., 1999). Newman et al. (2009) reported the 15-year follow-up results of the study published in 1998, and noted a 15-year survivorship rate, based on revision or failure for any reason, was 89.8 percent for UKR compared to 78.7 percent for TKR. In addition, it is possible that in later years a patient could wear out the initial knee replacement, thus requiring a revision. Research has shown that a unicondylar knee implant can be revised more easily than a total knee replacement.

Patellofemoral Replacement: Isolated OA of the patellofemoral joint occurs infrequently. Surgical treatment for isolated patellofemoral arthritis has been proposed for individuals with disabling isolated arthritis or degeneration of the patellofemoral compartment, who have failed to respond to other conservative and/or surgical treatment options, and/or is unwilling to undergo other surgical alternatives such as patellectomy or TKR. Patellectomy has been associated with poor clinical outcomes, and TKR, particularly in younger, more active individuals, is often discouraged due to complexities of the procedure, need for future revision and residual pain (Leadbetter, et al., 2008). Results of other procedures for treating patellofemoral arthritis, such as chondroplasty, lateral release, soft tissue reconstruction, realignment osteotomy and resurfacing procedures, can lead to lengthy recovery and variable outcomes. A patellofemoral knee replacement replaces only the worn articular surface underneath the patella and its articulating trochlear surface. Potential advantages of patellofemoral replacement include a less invasive approach, less bone resection and tissue destruction, decreased operative time, and blood loss, shorter rehabilitation and more normal knee kinematics.

Bicompartmental Knee Replacement/Bi-unicompartmental Knee Replacement
Bicompartmental knee replacement has been proposed for some patients with disease limited to the medial and patellofemoral compartments. With the bicompartmental knee replacement, only the diseased medial and patellofemoral compartments are replaced while sparing the lateral compartment and cruciate ligaments. In theory, retention of the cruciate ligament(s) maintains more normal knee function and mobility. It has been suggested this approach is associated with less pain and reduced tissue trauma, resulting in a more rapid recovery (Rolston, et al., 2007). Bi-unicompartmental replacement has also been reported in the published literature. This approach has been used for treating bicompartmental (i.e., medial and lateral) arthritis (Confalonieri and Manzotti, 2006). 

Policy:
Unicompartmental knee replacement (i.e., partial replacement, single compartment) is MEDICALLY NECESSARY as an alternative to total knee replacement for advanced knee joint disease due to conditions such as osteoarthritis, osteonecrosis and traumatic arthritis, when ALL of the following conditions are met:

• Radiological evidence of articular cartilage loss and severe joint destruction with findings of bone-on-bone changes (e.g., Outerbridge Grade IV, Kellgren-Lawrence Grade 4) limited to a single compartment
• Knee examinations demonstrate good alignment and ligamentous stability
• Persistent knee pain despite an appropriate course of nonsurgical management (e.g., NSAIDs, analgesics, light exercise, assistive device, bracing, viscoelastic supplementation)

Bicompartmental and bi-unicompartmental knee arthroplasty is investigational and/or unproven and therefore considered NOT MEDICALLY NECESSARY for osteoarthritis of the knee and all other indications because their effectiveness has not been established.

Rationale:
Unicompartmental knee arthroplasty is a popular treatment for unicompartmental knee arthritis. Roche and associates (2009) stated that a recently developed computer-assisted surgery/robotic system has the potential to improve alignment in and results of UKA. Pearle et al. (2009) stated that indications for UKA include mechanical axis of less than 10 degrees varus and less than five degrees valgus, intact ACL and absence of femoro-tibial subluxation. Appropriately selected patients can expect UKA to last at least 10 years. Failures in UKA are not common and involve technical errors that are thought to be corrected with use of newly developed robotic technology such as the MAKO robotic arm system (MAKOplasty). The surgeon using this technology may be able to arrive at a set target, enhance surgical precision and avoid outliers. However, whether improved precision will result in improved long-term clinical outcome remains a subject of research.

Sinha (2009) reported that the early outcomes of UKA performed with a robotically assisted navigation system have been favorable. The surgical technique enhances accuracy of bone preparation and component positioning. Technical errors of the system have been minimal. The surgeon's learning curve is not adversely affected. Early patient outcomes are excellent and complications minimal. The authors noted that further follow-up studies will help to determine whether these early outcomes are sustained over time.

Lonner (2009) noted that modular bicompartmental arthroplasty is an emerging knee-resurfacing approach that provides a conservative alternative to TKA. Isolated bicompartmental arthritis involving the medial or lateral and patello-femoral compartments, but with no significant deformity or bone deficiency, preserved motion and intact cruciate ligaments, can be effectively managed with this treatment method. For the many young and active patients with isolated bicompartmental arthritis, given the potential durability of the procedure and the prosthesis, it is appropriate to use an approach that is more conservative than TKA. Robotic arm assistance for modular bicompartmental arthroplasty optimizes component position and alignment, which may improve system performance and long-term durability. In addition, a percentage of patients who undergo isolated unicompartmental or patello-femoral arthroplasty may later develop progressive arthritis in an unresurfaced compartment. Their cases may be effectively managed with a staged modular approach to resurfacing the degenerating compartment, but additional study is needed.

In a pilot study, Lonner et al. (2010) compared the post-operative radiographical alignment of the tibial component with the pre-operatively planned position in 31 knees in 31 consecutive patients undergoing UKA using robotic arm-assisted bone preparation and in 27 consecutive patients who underwent unilateral UKA using conventional manual instrumentation to determine the error of bone preparation and variance with each technique. Radiographically, the root mean square error of the posterior tibial slope was 3.1 degrees when using manual techniques, compared with 1.9 degrees when using robotic arm assistance for bone preparation. In addition, the variance using manual instruments was 2.6 times greater than the robotically guided procedures. In the coronal plane, the average error was 2.7 degrees +/- 2.1 degrees more varus of the tibial component relative to the mechanical axis of the tibia using manual instruments, compared with 0.2 degrees +/- 1.8 degrees with robotic technology, and the varus/valgus root mean square error was 3.4 degrees manually, compared with 1.8 degrees robotically. The authors concluded that further study will be necessary to determine whether a reduction in alignment errors of these magnitudes will ultimately influence implant function or survival.

Paratte and associates (2010) stated that recent literature suggests patients achieve substantial short-term functional improvement after combined bicompartmental implants, but longer-term durability has not been documented. These investigators examined if (i) bicompartmental arthroplasty (either combined medial unicompartmental UKA and femoro-patellar arthroplasty (PFA) or medial UKA/PFA, or combined medial and lateral UKA or bicompartmental UKA) reliably improved Knee Society pain and function scores; (ii) bicompartmental arthroplasty was durable (survivorship, radiographical loosening or symptomatic disease progression); (iii) durable alignment can be achieved; and (iv) the arthritis would progress in the unresurfaced compartment. These researchers retrospectively reviewed 84 patients (100 knees) with bicompartmental UKA and 71 patients (77 knees) with medial UKA/PFA. Clinical and radiographical evaluations were performed at a minimum follow-up of five years (mean of 12 years; range of five to 23 years). Bicompartmental arthroplasty reliably alleviated pain and improved function. Prosthesis survivorship at 17 years was 78 percent in the bicompartmental UKA group and 54 percent in the medial UKA/PFA group. The high revision rate, compared with TKA, may be related to several factors such as implant design, patient selection, crude or absent instrumentation or component mal-alignment, which can all contribute to the relatively high failure rate in this series.

Literature Review: 
The reported short- and mid-term results for patellofemoral arthroplasty vary across studies but in general are good and support improvement in pain, function and mobility. Although limited, there is some recent data supporting long-term safety and efficacy (van Jonbergen, et al., 2010). Some patient populations overlap among studies, and most are in the form of retrospective and prospective case series (Meding et al., 2007; Ackroyd et al., 2007; Sisto and Sarin, 2006; Ackroyd and Chir, 2005; Leadbetter et al., 2005). Randomized controlled trials are limited. Average follow-up periods range from 3.75 years to 17 years (Argenson et al., 2005; Merchant, 2004; Kooijman et al., 2003; Smith et al., 2002; Tauro et al., 2001; de Winter et al., 2001). Various scales have been used to assess clinical outcomes, and include the ADL scale, Knee Society scores, follow-up radiographs, modified Hungerford and Kenna knee score, the Bristol Knee score and subjective questionnaires, making comparisons across studies difficult. However, good and excellent results ranged from 45 percent to 93 percent across studies. Improved survivorship has been reported with more recent implant designs (Odumenya et al., 2010; van Jonbergen et al., 2010).

Revision rates also vary across studies. Revision is often performed as result of progression of OA, malposition, loosening, stiffness, maltracking and/or wear and tear of the patellar component (Anderson et al., 2005; Koojman et al., 2003; Smith et al., 2002; de Winter et al., 2001). In a published review of the literature Delanois et al. (2008) reported that survival rates for patellofemoral arthroplasty ranged as follows: 95 percent to 100 percent at a mean follow-up of five years, 85 percent to 90 percent at seven to eight years, was 75 percent at 10 years and 58 percent at 16 years. Authors suggest clinical results are dependent on prosthetic design, patient selection and technical proficiency.

In 2009, van Jonbergen and colleagues evaluated whether or not patellofemoral arthroplasty compromised the results of total knee arthroplasty. The authors compared 13 subjects who underwent patellofemoral arthroplasty and required TKR with a control group of 13 subjects who underwent primary TKR. The results of the study demonstrated patellofemoral arthroplasty did not have a negative effect on the outcome of later TKR (Jonbergen et al., 2009). Lonner et al. (2006) also evaluated patients who received TKR after patellofemoral arthroplasty (n = 12) to determine if results are compromised by prior arthroplasty. The mean interval to revision TKR for this study group was four years (range of one to 9.7). The results of this study suggested that TKR was not compromised when revision was performed for a failed patellofemoral replacement. Furthermore, the authors of this study noted the primary implants were able to be utilized again unless the patellar component was worn, loose or malpositioned.

The use of custom-designed patellofemoral prosthetic devices versus off-the-shelf designs has been done with the goal of improving clinical outcomes. However, published data evaluating these methods are lacking. Patellofemoral arthroplasty has been associated with progression of OA in surrounding compartments and revision to TKR. However, it is unclear which patients are specifically at risk for development of tibiofemoral OA. Patient selection criteria have not been clearly defined, although potential candidates include individuals with severe isolated patellofemoral OA who have failed other treatments, are not candidates for or have failed other surgical options, have residual pain and/or are unwilling to undergo TKR. Although there is no general consensus, patellofemoral arthroplasty may be considered a salvage procedure prior to a TKR.

Literature Review: 
Morrison et al. (2011) reported the results of a prospective trial comparing early functional outcomes of subjects with OA of the medial and patellofemoral compartments who underwent either TKR or bicompartmental knee replacement (n = 33, 21 respectively). Outcomes were assessed at three months, one year and two years postoperatively and included SF-12 and WOMAC scores, ROM and radiographs to determine loosening. At three months, the authors reported the bicompartmental group had significantly better pain scores (P = 0.20) and better physical function (P = .015). However, these results did not continue beyond three months. There were no differences in scores at one or two years. The bicompartmental group also had more complications (P = .045) and a near significant trend of increased revision arthroplasty rate at two years follow-up (P = .054). The authors acknowledged that the benefits of sparing the lateral compartment and anterior cruciate ligaments in this cohort of subjects were not established.

In 2010, Heyse et al. reported the results of a retrospective case series involving nine subjects who underwent medial and patellofemoral bicompartmental arthroplasty. The average follow-up was 11.8 ± 5.4 years and included radiologic evaluations and clinical scores (KSS and WOMAC). The authors noted there were no surgical revisions, the KSS and WOMAC scores were improved and all patients were satisfied or very satisfied with the outcomes (Heyse et al., 2010). Limitations of this study include small sample population and results that cannot be generalized to larger populations.

Parratte et al. (2010) reported the results of a retrospective case series evaluating bicompartmental arthroplasty (n = 155; 84 had bi-unicompartmental and 71 had medial UKA and patellofemoral). The minimum follow-up was five years, average 11.7, and ranged from 5 – 23 years using Knee Society, function scores and radiographs. Bicompartmental arthroplasty relieved pain and improved Knee Society and function scores. Results were mixed in regard to durability. A 17-year survival to revision, radiograph loosening or disease progression was 78 percent in the group of subjects who underwent bi-unicompartmental replacement and 54 percent in the group who underwent medial unicompartmental/patellofemoral replacement. The authors reported 17 revisions in the bi-UKA group and 28 in the med-UKA/PFA group.

In 2008, Confalonieri et al. reported the results of a comparison of 22 patients who underwent bi-unicompartmental knee replacement with a similar group who underwent computer assisted TKR. The authors noted that at 48 months follow-up there were no statistical differences in surgical time, Knee Society scores, Functional and Italian Orthopaedic UKR Users Group score between groups. There was a statistically significant difference in WOMAC Function and Stiffness score in favor of the Bi-Uni group. TKR implants were statistically better aligned and positioned. As noted by the authors, these results suggest that Bi-UKR is a viable option. However, the study is flawed by its retrospective design, lack of randomization, use of different implants and different alignment systems (Confalonieri et al., 2008).

In order to estimate the utility of the Journey Deuce^™ Knee System (Smith and Nephew Inc., Memphis, Tenn.), a bicompartmental prosthetic device, Rolston and colleagues (2007) reported the results of a series of 95 patients who were implanted with the bicompartmental device since 2003. Follow-up for this group of patients extended 33 months. The authors reported the following: 82 of 95 patients were discharged two days after surgery, the average range of motion for the group was 0° to 117°; most patients were able to walk without an assistive device two weeks post-surgery; and there was less blood loss compared to that for TKR patients. In addition, there was no lateral joint line tenderness, and the patients did not have patellofemoral pain. In 2011, Palumbo et al. reported the results of 36 subjects who received the Journey-Deuce prosthesis. Outcomes were measured using the WOMAC scores, range of motion, Knee Society functional survey and pre- and post-operative pain scores. A total of 31 percent of the subjects were unsatisfied with the surgery, and 53 percent would not repeat the procedure. The overall survival rate was 86 percent; 14 percent required conversion to TKR at a mean 19 months for persistent pain. Short-term survival of the prosthesis was unacceptably low, and the authors noted they no longer implant the device at their institution.

In 2006, Confalonieri and Manzotti reported the results of a retrospective analysis of bi-unicompartmental knee replacement performed on 24 knees with bicompartmental arthritis (medial and lateral). Clinical outcomes were evaluated at a minimum follow-up of 36 months and included Knee Society scores and a dedicated UKR score. The authors noted there were no revisions, and all clinical scores were improved and were similar to TKR.

Callahan et al. (1995) reported the results of a meta-analysis evaluating unicompartmental and bicompartmental knee replacement. The authors reviewed 46 studies evaluating UKR involving 2,391 patients and a mean follow-up of 4.6 years. For the bicompartmental evaluation, the total number of enrolled patients was 844, mean follow-up was 3.6 years and there were a total of 18 studies. The authors reported that outcomes for the bicompartmental knee replacement appeared worse compared to the UKR, although they noted that patients who underwent the bicompartmental approach had poorer baseline knee function. Consequently, no reliable conclusions regarding efficacy could be made.

Supporting evidence in the published scientific literature is limited and does not allow strong conclusions regarding improved patient outcomes with either a bi-unicompartmental or bicompartmental approach. There is no consensus among authors for optimal patient selection criteria and the advantages of performing bicompartmental or bi-unicompartmental knee replacement in comparison to standard treatment options such as TKR have not been clearly established in the scientific literature.

Definitions:
Three compartments of the knee:

• Patellofemoral: Area behind the kneecap riding over the end of the femur "trochlea/sulcus" groove
• Medial: The area of joint contact between the femur and tibia on the "inside" or medial aspect of the knee
• Lateral: The area of joint contact between the femur and tibia on the "outside" or lateral aspect of the knee

Total Knee Arthroplasty (also know as TKA, or Total Knee Replacement): Performed when all three compartments of the knee are affected by advanced joint disease. TKA involves removal of a thin layer of subchondral bone and overlying articular cartilage, with anatomic resurfacing of all three compartments and insertion of the implant and bearing surface.

Unicompartmental Knee Arthroplasty (also know as UKA or Partial Knee Arthroplasty): May be performed in patients with advanced joint disease limited to a single compartment (i.e., medial, lateral or patellofemoral)

• UKA of the medial or lateral compartment requires a smaller incision that does not interrupt the anterior and posterior cruciate ligaments, which are the main structures stabilizing the knee.
• UKA of the patellofemoral compartment treats degenerative disease underneath the patella and involves implantation of a prosthesis to resurface the articulation surfaces of the patella and femur.

Bicompartmental Knee Arthroplasty: Replacement of the medial and patellofemoral compartments, with sparing of the cruciate ligaments.

Bi-unicompartmental Knee Arthroplasty: UKA performed in the contralateral compartment of a knee previously treated with a UKA.

Unicondylar Interpositional Spacers (e.g., UniSpacer^TM): Metallic implants 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.

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49. Fuchs S, Rolauffs B, Plaumann T, et al. Clinical and functional results after the rehabilitation period in minimally-invasive unicondylar knee arthroplasty patients. Knee Surg Sports Traumatol Arthrosc. 2005;13(3):179-186.
50. Yang KY, Wang MC, Yeo SJ, Lo NN. Minimally invasive unicondylar versus total condylar knee arthroplasty -- early results of a matched-pair comparison. Singapore Med J. 2003;44(11):559-562.
51. Pennington DW, Swienckowski JJ, Lutes WB, Drake GN. Lateral unicompartmental knee arthroplasty: Survivorship and technical considerations at an average follow-up of 12.4 years. J Arthroplasty. 2006;21(1):13-17.
52. Walton NP, Jahromi I, Lewis PL, et al. Patient-perceived outcomes and return to sport and work: TKA versus mini-incision unicompartmental knee arthroplasty. J Knee Surg. 2006;19(2):112-116.
53. Pandit H, Beard DJ, Jenkins C, et al. Combined anterior cruciate reconstruction and Oxford unicompartmental knee arthroplasty. J Bone Joint Surg Br. 2006;88(7):887-892.
54. 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.
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Coding Section

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 Blue Shield Association technology assessment program (TEC) and other nonaffiliated technology evaluation centers, reference to federal regulations other plan medical policies, and accredited national guidelines.

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