Unicompartmental knee arthroplasties: Tips and tricks
The number of unicompartmental knee arthroplasties (UKAs) being performed is increasing. This is due in part to the prevalence of osteoarthritis and expanded indications for the procedure. UKA poses technical demands that requires experience and surgical frequency for best outcomes. Surgeons should keep proper patient selection, biomechanics, and alignment front of mind when undertaking an UKA.
Unicompartmental knee arthroplasty (UKA) is less forgiving in terms of surgical error and surgeons need sufficient training and experience for good results—this is only achieved with a significant annual volume of procedures.
Robert Hube, Professor of Orthopedic Surgery Charité—University Medicine, Berlin, Germany, and Past President of the German Knee Society, acknowledges the challenges but also asserts that it is possible to achieve excellent UKA outcomes. “The surgical priorities for UKAs are achieving the correct alignment based on preoperative planning, correctly positioning the components, and securing sufficient fixation of the implants.”
OCM—Orthopedic Surgery Center Munich
Patient selection is key
As discussed in Part 1 and Part 2 of this article series, proper patient selection is critical for UKA success. Over time, indications and contraindications for the procedure have evolved from patient characteristics such as body mass index (BMI) and age, among others  to the consideration of more pathoanatomical indications.
To see if published contraindications to UKA actually generated poorer outcomes, Hamilton et al looked at 1000 mobile-bearing UKAs (818 patients), comparing the outcomes at 10- and 15-years follow-up of 322 traditionally indicated knees and 678 contraindicated knees. They concluded that for their study group, there was “evidence that patients with the previously reported contraindications do as well as, or even better than, those without contraindications” .
In 2015, six surgeons with combined experience of 8,000 UKAs (representing between 10% to 50% of their primary knee practices) published a consensus statement in the Journal of Surgical Orthopedic Advances on the indications and contraindications for medial UKA (see Table 1).
All the same, consensus is no substitute for a surgeon’s experience and does not take into account the need for patients to be involved in the decision-making to a certain degree. When choosing between options, for example UKA or total knee arthroplasty (TKA), lifestyle, activity levels, scarring, and other factors may be weighted differently by a patient than by their surgeon .
Does anterior cruciate ligament stability make a difference?
On the matter of the stability of the anterior cruciate ligament (ACL), Robert Hube says, “A successful UKA requires a stable knee. If the muscles have compensated for the compromised ACL, and the knee is about functionally stable, in my opinion the patient is still a candidate for a UKA.”
A cadaveric study of 15 knees looked how fixed-bearing UKA in ACL-intact, partial ACL, and ACL-deficient knees would affect the posterior tibial slope’s restoration of knee stability and flexion. The researchers determined that a slope of just 1° in ACL-deficient knees almost doubled the degree of translation compared to ACL-intact knees, leading them to conclude that UKA in ACL-deficient knees was “challenging” .
Of course, UKA is not limited to the medial compartment; lateral UKA accounts for roughly 10% of cases . In this situation, Robert Hube says that there is insufficient data to indicate whether medial or lateral UKA is a better candidate if there is also a compromised ACL. “If the knee is functionally stable, I would go for both, medial and lateral UKA. The problem is that most of the knees with a deficient ACL are not stable. In these cases, we would go for a TKA. However, this is in contrast to data for high tibia osteotomies. Here, we can achieve good results even with insufficient ACL.”
Even if the “right” patients are selected for UKA, another important factor that has been shown to impact outcomes: surgeon experience.
Read the full article with your AO login
- Surgeon experience makes a difference
- Preoperative planning to limit intraoperative decisions
- Mobile or fixed bearing?
- Biomechanical basics
- Proper sizing and positioning are important
- Undercorrect is correct
- A word on osteophytes
- Tibial slope considerations
- In summary
More AO resources
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This series of articles was created with the support of the following specialists (in alphabetical order):
University Hospital of Marseille
OCM—Orthopedic Surgery Center Munich
Waldkliniken Eisenberg—German Center of Orthopedics
This issue was created by Word+Vision Media Productions, Switzerland
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