UKA: Who Gets One, Who Doesn’t
Which patients are appropriate candidates for a unicondylar knee arthroplasty – and why? Dr. Mark Pagnano shares his thoughts.
At the ICJR’s annual Winter Hip & Knee course in Vail, Colorado, Mark W. Pagnano, MD, from Mayo Clinic, Rochester, Minnesota, reviewed the current state of unicondylar knee arthroplasty (UKA) in the US, the indications and contraindications, and his choice of implant design and surgical technique.
UKA represents the best operation for a select group of patients with knee osteoarthritis, Dr. Pagnano said. This is a reliable procedure that can be very durable, as long as it is performed well. In his practice, patients have a faster recovery after UKA than after total knee arthroplasty (TKA), they achieve better range of motion, and they are happier.
But patient selection is critical. Dr. Pagnano noted that the ideal UKA candidate is the patient with:
- Antero-medial osteoarthritis
- Intact ACL
- Correctable varus deformity
- Intact lateral compartment
- Intact patellofemoral joint
- Good range of motion
In his practice, Dr. Pagnano sees UKA as an option for patients with isolated medial compartment disease and symptoms confined to the medial joint line. This is so important that during the preoperative visit, he wants the patient to specifically point to the medial joint line as the source of pain without prompting from him.
Because Dr. Pagnano uses a fixed-bearing UKA design, he is less concerned with whether the anterior cruciate ligament (ACL) is intact, as long as the patient is complaining of pain and not instability. He will accept patients with minor notch osteophytes, as well as mild patellofemoral changes on X-ray, as long as the patient has no patellofemoral symptoms.
Today about 35% of his knee arthroplasty patients satisfy these indications and receive a UKA.
Equally important are the contraindications to a UKA:
- Vague general knee pain, no matter what the X-ray looks like
- Grade 3 or 4 degenerative joint disease in the lateral or patellofemoral compartments on X-ray
- Unstable ACL-deficient knee
- Patient request a TKA instead of a UKA
Dr. Pagnano prefers an extramedullary alignment system for UKA, and he uses a fixed-bearing design because of the excellent long term results:
- At 10-year follow-up, fixed-bearing designs have proven to be durable
- With a fixed-bearing design, there is no risk of bearing dislocation
- Fixed-bearing design allows for a thinner titanium tray, which allows for a thinner tibial bone cut
- Metal-backed tibia designs are preferred in fixed-bearing devices, as they have shown to be more durable than the all-poly tibia designs
- Cemented fixation is preferred
The surgical approach utilized is a 1.5- to 3.5-inch incision with a mini-midvastus arthrotomy; no dislocation of the patella is needed.
Dr. Pagnano prefers the extramedullary alignment system because it allows him to adjust for limb correction before any bone cuts are made, with the alignment confirmed under C-arm fluoroscopy. It links the femoral and tibial bone cuts in extension, which accomplishes perfect alignment in extension. Extramedullary systems also minimize blood loss during the procedure, as no intramedullary device is placed.
Alignment under fluoroscopy ensures alignment at the ankle, the knee, and the hip. The distal femoral bone cut is made with the knee in extension, and the tibial bone cut is made with the knee in flexion.
With the knee in flexion, the femoral component rotation is set so the femoral and tibial components are perfectly parallel at 90° of flexion. This ensures the appropriate alignment of the femoral component.
The femoral component is sized to avoid anterior overhang. Dr. Pagnano sizes the femoral component to ensure that the leading anterior edge of the metal is recessed under the level of the articular cartilage.
Trial reduction with fluoroscopy ensures overall alignment and placement.
The tibial component is cemented first to allow room to remove posterior cement. The femoral component is then cemented and the final poly insert is placed. The cement is allowed to harden with the leg in extension.
A drain is used in all patients, and a local anesthetic injection around the knee is used for pain management. Weight-bearing is allowed as tolerated after surgery.
Half of Dr. Pagnano’s UKA cases are done as outpatient procedures. The other half are done with a 1-night hospital stay.
Durability of UKA
Meta-analyses of data from multiple national joint registries show a cumulative failure rate of 1.26% per year for TKA and 1.53% per year for UKA. But Dr. Pagnano believes that the small decrease in durability of the UKA is compensated by the increase in function and easier recovery as compared to TKA.
Patient age has an effect on durability of both UKA and TKA, and a higher failure rate is expected for patients under age 55 years, Dr. Pagnano said. However, in patients over age 65 years, it is not unreasonable to expect the arthroplasty to last the rest of the patient’s life.
In addition, data from high-volume surgical centers indicate that the functional outcomes of UKA will exceed those of TKA in most patients, he said.
Registry data comparing mobile- and fixed-bearing UKA show a slightly higher initial failure rate in mobile UKA, particularly in the first 3 years after surgery, and then a steady-state low failure rate through 10 years, Dr. Pagnano noted. Fixed-bearing UKA data show steady-state failure rates from the beginning.
Dr. Pagnano concluded that there is a role for UKA, and for a subgroup of patients, a UKA is indeed the best operation. Dr. Pagnano also believes that by taking steps to make the UKA procedure reproducible, reliable, and efficient, patient outcomes can be improved.
Dr. Pagnano’s presentation is available here.