Short-term results of the Oxford phase 3 unicompartmental knee arthroplasty for medial arthritis

Objectives: We evaluated short-term results of the Oxford phase 3 unicompartmental knee arthroplasty (UKA) in patients with medial compartment arthritis. Methods: The study included 38 patients (28 females, 10 males; mean age 67 years; range 56 to 75 years) who underwent UKA for isolated medial knee osteoarthritis. At the time of surgery, 28 patients were in the age group of 56-64 years, and 10 patients were in the age group of 65-75 years. All the patients had Ahlback grade 2 primary medial compartment arthritis that had been unresponsive to conservative treatment. None of the patients had symptoms of patellofemoral arthrosis. Patients underwent UKA with the Oxford phase 3 cemented meniscal-bearing unicondylar prosthesis using minimally invasive surgery. The results were assessed preoperatively and at final controls according to the Knee Society clinical and functional rating system. Postoperative radiographic evaluations were made according to the Oxford criteria. The mean follow-up period was 24 months (range 18 to 32 months). Results: The mean preoperative active knee flexion increased from 121.8 (range 110 to 130) to 130.9 (range 120 to 140) postoperatively (p<0.05). There was no limitation in knee extension both pre- and postoperatively. The mean preoperative and postoperative knee scores were 64.6 (range 47 to 80) and 97.5 (range 89 to 100), and the mean functional scores were 59.6 (range 45 to 80) and 92.1 (range 70 to 100), respectively (p<0.05). All the patients had an excellent knee score, while functional scores were excellent in 27 patients (71.1%) and good in 11 patients (28.9%). Postoperative radiographic measurements showed that the position of the femoral components was within acceptable ranges in all the patients with a mean of 3 valgus (range 5 valgus to 8 varus) and 0.5 extension (range 3 extension to 2 flexion). The positioning of the femoral components in relation to the mechanical axis was central in 30 patients and 2-mm lateral (range 2 mm medial to 4 mm lateral) in eight patients. The position of the tibial components was also within acceptable ranges in all the patients with a mean of 1.5 varus (range 2 varus to 2 valgus) and a mean posterior inclination of 6.2 (range 5 to 7). All the tibial components showed full congruency with the medial, lateral, anterior, and posterior planes, except for one which had a 4-mm undersizing in the anterior plane. The polyethylene insert was central and parallel to the tibial component in all the patients. No osteophytes or cement debris that might lead to impingement were observed. All the components remained in position until the final controls. Complications such as insert dislocation, infection, pulmonary embolism, deep venous thrombosis, or neurovascular injury were not observed. None of the patients required revision surgery. Conclusion: Our findings show that, with proper patient selection and strict adherence to the surgical technique, short-term results of the Oxford phase 3 unicompartmental knee prosthesis are excellent or good in the treatment of medial compartment osteoarthritis.