Medial Unicompartmental Arthroplasty of the Knee

Jason M. Jennings, MD, DPT; Lindsay T. Kleeman-Forsthuber, MD; Michael P. Bolognesi, MD

Disclosures

J Am Acad Orthop Surg. 2019;27(5):166-176. 

In This Article

Emerging Indications

High Body Mass Index and Weight

Traditional weight restrictions for UKA are based on the notion that heavier patients place excess load on implants that increases the risk of aseptic loosening. Recent studies suggest that this dogma may not be true. Hamilton et al[9] compared patients with weight over 180 lbs with those under 180 lbs and found no difference in functional scores between groups and implant survival at 15 years. In a meta-analysis of 6 national registries and 31 clinical studies, no increased risk for poor outcomes or revision was noted in patients with a BMI over 30.[10]

Patient age

Younger patients tend to be more active at baseline and have higher expectations for their function after surgery, potentially predisposing them to higher implant wear and loosening. In a meta-analysis of registries and clinical studies, age lower than 60 years was associated with a higher likelihood of revision; however, younger patients had much better functional outcome scores.[10] Hamilton et al[9] found conflicting results with no notable difference in the 15-year survival, including time or indication for revision, for patients younger than 60 years compared with that for patients older than 60 years. The role of bias should be considered when evaluating patient age, because revision may be pursued earlier in young patients who fail to achieve their expected activity level. Ultimately, an earlier time to revision may be acceptable for younger patients as long as functional scores are consistently high.

Presence of Patellofemoral Joint Osteoarthritis

Some have proposed that PFJ arthritis is indicative of knee malalignment and that correction of this deformity with UKA will offload the PFJ from further articular damage and pain. van der List et al[10] identified five cohort studies assessing outcomes of UKA with PFJ arthritis and found no difference in functional outcomes or risk for revision compared with those without evidence of PFJ arthritis. Similarly, Hamilton et al[9] found similar functional scores in those with and without exposed bone of the PFJ when a mobile-bearing (MB) implant was used, and no difference in revision at 10-year follow-up. The acceptance of UKA for patients with PFJ disease may not be applicable for both fixed-bearing (FB) and MB implants. Berger et al[11] found progression of PFJ arthritis as the primary mode of failure at 15-year follow-up in their series of patients with an FB implant; however, further evidence on this subject is limited at this time.

Anterior Cruciate Ligament Insufficiency

Absence of a functioning anterior cruciate ligament (ACL) has historically been considered a contraindication to UKA, given high rates of failure observed in ACL-deficient patients.[12] This dogma has recently been challenged with several studies showing acceptable outcomes in ACL-deficient patients. Boissonneault et al[13] compared outcomes of ACL-deficient patients with those of ACL-intact patients and found better functional scores in the ACL-deficient group at 5-year follow-up with only one revision for lateral compartment arthritis progression. A recent meta-analysis failed to find a higher incidence of revision in ACL-deficient patients.[10] Some have argued that better outcomes can be achieved for medial UKA when simultaneous ACL reconstruction is performed.[14] Mancuso et al[14] compared outcomes of UKA between ACL-deficient patients and those with simultaneous ACL reconstruction and found higher implant survival in the ACL-reconstructed group (97%) compared with that in the ACL-deficient group (88%). Patients with an MB implant demonstrated higher revision rates than those with FB implants, with the most common reason for revision being tibial component loosening.[14] Longer follow-up studies are needed to determine whether ACL reconstruction improves long-term survival, but collectively these studies demonstrate promising early outcomes and survivorship for UKA in ACL-deficient patients.

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