This article is more than 5 years old. Information may no longer be current.

Mobile-bearing Unicompartmental Knee Arthroplasty (UKA)

Add topic to email alerts

Receive an email when new articles are posted on

Please provide your email address to receive an email when new articles are posted on .

Subscribe

Added to email alerts

You've successfully added to your alerts. You will receive an email when new content is published.

Click Here to Manage Email Alerts

You've successfully added to your alerts. You will receive an email when new content is published.

Click Here to Manage Email Alerts

Back to Healio

We were unable to process your request. Please try again later. If you continue to have this issue please contact customerservice@slackinc.com.

Back to Healio

A 46-year-old obese male laborer (height, 1.83 m; weight, 102 kg; body mass index [BMI], 35.3) has continuous, moderate to severe pain in the posterior right knee. The patient underwent unsuccessful conservative medical and surgical treatment, including two open arthrotomies with medial meniscectomy and removal of loose bodies and arthroscopic debridement 2 years earlier. Examination revealed a varus knee >10°; range of motion, 5° to 110°; minimum laxity, 6° to 9°; and normal anterior-posterior stability.

Results of a poll of the audience attending the Challenging Cases in Total Joint Replacement: Paying Attention to the Details symposium held on February 14, 2007, in San Diego found that more than two-thirds of respondents would perform either total knee arthroplasty (TKA) (41%) or unicompartmental knee arthroplasty (28%) in this patient. A high tibial osteotomy (HTO) was indicated by 18% of respondents, and 14% recommended a combination of conservative pain relief with a recommendation that this younger man accept some discomfort.

Over the past decade, the advantages of UKA over TKA have become increasingly evident. For example, studies show that UKA provides better range of motion, a higher level of activity, and increased patient satisfaction compared with TKA.^1,2

Traditional patient selection criteria for UKA, determined nearly 2 decades ago,³ have become outdated (with the exception of an intact anterior cruciate ligament [ACL]) and have previously excluded many patients. For a number of reasons, the patient in this sample case history does not appear to be an appropriate candidate for UKA, as determined by the traditional patient selection criteria. The patient is physically active, has a flexion contracture of 5°, is younger than 60 years old, and weighs more than 82 kg. In fact, study results indicate that no more than 5% to 7% of all patients meet the 1989 patient selection criteria for UKA,^4-7 thus denying many suitable candidates access to this procedure.

Advantages of UKA over TKA

In the investigator’s experience, 35% or more of all knee patients present with an anterior medial arthritic pattern—that is, full-thickness cartilage loss in the medial joint space, anterior disease with preserved bone posteriorly on both the tibia and femur, and a fully correctible deformity with intact, full-thickness lateral cartilage. With this pattern of disease, the ACL remains intact so that a ligamentously healthy knee is reconstructed through UKA to achieve normal kinematics.

By contrast, TKA eliminates not only the unhealthy one-third of the knee, but the remaining two-thirds of the joint and previously normal ligamentous structures. The investigators’ early experience with Oxford mobile-bearing UKA in the United States has been the subject of two reports. This article reviews those earlier results.^8,9

Results of Oxford Mobile-bearing UKA

Approved in July 2004, the Oxford mobile-bearing UKA device was implanted in 318 patients over an 18-month period (July 2004–December 2006). These patients were followed for an average of 6 months (range, 1.5-27 months). Average hospital stay was 1.3 days (range, 0-3 days), and approximately 97% of patients were discharged directly home.

Notably, 47% of these procedures were performed in patients a BMI of >32, making them unsuitable candidates for UKA under traditional criteria. Twenty-six percent of patients in the study had a BMI of >35 or were considered morbidly obese.⁸

In a study of 294 fixed-bearing UKA procedures performed in 255 patients, 91.4% of the UKA implants reached 10-year survivorship. Obesity and need for revision correlated at 81 kg and a BMI of 32.6.¹⁰ The investigators previously researched the role of obesity in the early failure of a fixed-bearing UKA design with an all-polyethylene tibial bearing and found that in patients with a BMI of >32, the failure rate was more than 17% at <3 years, In the nonobese patients, failure from loosening, wear, pain, or progression of disease was 5%.¹¹ However, in 4 years of experience with the mobile-bearing UKA, the investigators found no difference in early failure between obese and nonobese patients.^8,9 A fixed-bearing, cementless procedure is more likely to fail earlier from catastrophic wear or metallosis. In contrast, a completely unconstrained and conforming mobile-bearing UKA device shows negligible wear. Results from studies have shown an average polyethylene penetration rate of only 0.02 mm/year with the mobile-bearing UKA.¹²

With respect to patient age, approximately half (47.5%) of the patients who underwent UKA with a mobile-bearing device in the present series were <60 years old at the time of surgery (as in the profile in Sample Case History). The only viable alternative to mobile-bearing UKA in these young patients may be HTO. Experience has shown that as many as 20% of patients who undergo HTO will require TKA within 10 years and 35% within 15 years.¹³ Unlike UKA, HTO creates a difficult extra-articular deformity and does not address or treat the intra-articular disease of arthritis. In contrast, in UKA, the prosthesis eliminates the existing arthritic condition, corrects the alignment of the limb, and restores normal kinematics.

Notably, 15-year follow-up data show no differences in joint survivorship between patients who underwent UKA at <60 years of age and those >60 years old at the time of surgery.¹² Thus, no increase in early complications or change in early outcomes is observed in either younger or older groups.

UKA Experience and the Kneecap

In the investigators’ experience in querying UKA candidates preoperatively, 67% of patients had isolated medial compartmental pain, with 21% reported global pain (not isolated to one area of the knee), and 6% reported anterior knee pain. In masked radiographic evaluations, 43% of UKA patients had significant patellofemoral joint arthritis, including 15% who had moderate-to-severe medial facet disease and 17% who had moderate-to-severe lateral disease (Altman grade >2 or more).⁸

Nonetheless, data from patients who underwent Oxford mobile-bearing UKA show no difference in long-term follow-up between patients with an abnormal patellofemoral joint at time of surgery and patients with a normal patellofemoral joint, as evidenced by the long-term study reported by Svard et al and Price et al (Figure).^14,15 Additionally, Price et al and the Swedish Knee Arthroplasty Register,¹⁶ (the world’s largest prospective study) have reported no revisions of this mobile-bearing UKA device due to patellofemoral disease, in contrast to the experience with fixed-bearing devices.

Similarly, no significant relationship has been observed radiographically between the Oxford Knee Score at 1 year and medial Altman grade. The same findings have been seen intraoperatively with the status of the patellofemoral cartilage, and no relationship was observed between extensive full-thickness joint loss in the trochlear groove and the 1-year Oxford Knee Score. Furthermore, in both respects there was a slight trend toward better outcome measures in patients with more severe patellofemoral disease shown on radiographic assessment or uncovered intraoperatively.¹⁷ This finding conforms to the investigators’ 2.5-year follow-up data showing no difference between patients with and without patellofemoral disease.⁸ Moreover, there was also no difference in pain at up to 2.5 years in patients who had reported isolated medial pain preoperatively and those who did not.⁸

In the investigators’ report of 318 UKAs, there were six (1.9%) UKA failures: three (0.9%) loose tibias thought to be related to technical errors, with undersized tibial component and excessive slope; one (0.3%) medial tibial plateau fracture, also a technical error; one (0.3%) case of sepsis; and one (0.3%) case of unexplained pain that was treated with revision TKA. At the most recent follow-up, however, no significant anterior knee pain or dislocations of the mobile bearing have been observed in the initial series. In a 15-year study of patients who underwent Oxford UKA, Svard¹⁴ reported a 95% rate of survivorship using the anteromedial osteoarthritis criteria of correctible anterior medial disease. In the 20-year report of that same series, Price et al reported 92% survivorship at 20 years.¹⁵

To date, the investigators have performed more than 800 mobile-bearing Oxford UKA procedures and continue to achieve ongoing early success with more than 98% survivorship. In the knee with normal functioning anterior cruciate and medial collateral ligaments, knee kinematics can be restored with UKA. This outcome cannot be achieved by any available TKA device. The early failure rate is low, and the recovery is rapid with this conservative partial knee replacement procedure.

References

1. Fisher N, Agarwal M, Reuben SF, et al. Sporting activity following Oxford medial unicompartmental knee arthroplasty. Knee. 2006; 13(4):296-300.
2. 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.
3. Kozinn SC, Scott R. Unicondylar knee arthroplasty. J Bone Joint Surg Am. 1989; 71(1):145-150.
4. Stern SH, Becker MW, Insall JN. Unicondylar knee arthroplasty. An evaluation of selection criteria. Clin Orthop Relat Res. 1993 Jan; (286):143-148.
5. Sculco TP. Orthopaedic crossfire—can we justify unicondylar arthroplasty as a temporizing procedure? in opposition. J Arthroplasty. 2002; 17(4 suppl 1):56-58.
6. Naudie D, Guerin J, Parker DA, Bourne RB, Rorabeck CH. Medial unicompartmental knee arthroplasty with the Miller-Galante prosthesis. J Bone Joint Surg Am. 2004; 86-A(9):1931-1935.
7. Ritter MA, Faris PM, Thong AE, Davis KE, Meding JB, Berend ME. Intra-operative findings in varus osteoarthritis of the knee. An analysis of preoperative alignment in potential candidates for unicompartmental arthroplasty. J Bone Joint Surg Br. 2004; 86(1):43-47.
8. Berend KR, Lombardi AV JR, Adams JB. Obesity, young-age, patellofemoral disease, and anterior knee pain: identifying the unicondylar arthroplasty patient in the United States. Orthopedics. 2007; 30(5 suppl):19-23.
9. Berend KR, Lombardi AV Jr. Liberal indications for minimally invasive oxford unicondylar arthroplasty provide rapid functional recovery and pain relief. Surg Technol Int. 2007; 16;193-197.
10. Heck DA, Marmor L, Gibson A, Rougraff BT. Unicompartmental knee arthroplasty. A multicenter investigation with long-term follow-up evaluation. Clin Orthop Relat Res. 1993; (286):154-159.
11. Berend KR, Lombardi AV Jr, Mallory TH, et al. Early failure of minimally invasive unicompartmental knee arthroplasty is associated with obesity. Clin Orthop Relat Res. 2005; 440:60-66.
12. Price AJ, Dodd CA, Svard UG, Murray DW. Oxford medial unicompartmental knee arthroplasty in patients younger and older than 60 years of age. J Bone Joint Surg Br. 2005; 87(11):1488-1492.
13. Michaela G, Florian P, Michael L, Christian B. Long-term outcome after high tibial osteotomy. Arch Orthop Trauma Surg. 2008; 128(1):111-115.
14. Svard UC, Price AJ. Oxford medial unicompartmental knee arthroplasty. A survival analysis of an independent series. J Bone Joint Surg Br. 2001; 83(2):191-194.
15. Price AJ, Waite JC, Svard UC. Long-term clinical results of the Oxford medial unicompartmental knee arthroplasty. Clin Orthop Relat Res. 2005; (435):171-180.
16. Svenska knäprotesregistret (Swedish knee registry), www.ort.lu.se/knee/pdf/skar2004engl.pdf. Accessed Sept. 7, 2007.
17. Murray DW, Dodd CA. FDA Advanced Instructional Course. San Diego, CA; 2008.

Authors

Drs Berend and Lombardi are from Joint Implant Surgeons, Inc, the Mount Carmel New Albany Surgical Hospital, and Ohio State University, Columbus, Ohio.

Drs Berend and Lombardi are consultants for Biomet, Inc. Dr Lombardi receives royalties from Biomet, Inc.