The present study compared HTO to UKA for the treatment of compartmental knee osteoarthritis. This meta-analysis of 25 studies showed that UKA achieved fewer complications, better functional outcomes (excellent/good), and reduced knee range of motion compared to HTO. No significant differences were detected between HTO and UKA in terms of visual analogue scale, revision rate, and free walking speed.
Conventionally, UKA has been used for patients over 60 years, less than 82 kg, single compartment osteoarthritis, less than 15-degree angular deformity, and more than 90-degree range of motion 9,15. UKA is contraindicated in active patients with inflammatory arthritis and less than 60 years old. However, some studies showed that UKA provided promising outcomes in younger and obese patients 16,17. A retrospective series of 41 patients showed that UKA achieved a 92% survival rate at 11 years in patients ranged from 35 to 60 years old 18. Another study including 62 patients, with 11.2 years follow-up, reported that UKA was associated with favourable outcomes and a 94% survival rate at 12 years in patients aged 60 years or younger 19. Advances in the surgical procedures and implant designs, besides increased experience with the technique, have extended the surgical indications for UKA.
Both HTO and UKA share similar indications, such as patients aged 55 to 65 years, patients without obesity, patients with moderate activity, mild varus malalignment, joint stability, good range of motion, and moderate single compartmental osteoarthritis. The selection of suitable patients, accurate osteotomy types, and specific surgical techniques are important in the success of HTO 20. HTO is used for young patients less than 60 years, normal weight, active patients with radiographic single-compartment osteoarthritis, stable/unstable joint, range of motion with flexion more than 120 degrees, and localized pain to the tibiofemoral joint line 21. A comparative study by Trieb et al. showed a higher failure rate in the HTO group in ≥ 65 years patients versus younger patients 22. Furthermore, a prospective study including 132 patients demonstrated that a preoperative BMI of more than 27.5 kg/m2 was a risk factor for early failure of HTO 4. Another investigation utilized a Markov model to simulate theoretical groups of patients 40, 50, 60, and 70 years of age undertaking primary HTO or UKA. The results demonstrated higher revision risks at follow-up durations of 5 and 10 years in the HTO compared to the UKA group for patients ≥ 50 years 23. A large retrospective review in the USA showed that HTO was performed more commonly in patients aged 40 to 44 years and UKA was more common in patients aged 60 to 64 years 24. Selecting the correct patient is the key to success. In the present meta-analysis, the included patients’ ages ranged from 30 to 84 years, which might explain why the revision rate did not differ significantly between the HTO and UKA groups.
Several techniques of HTO have been developed including opening wedge, closing wedge, dome, and “en chevron” osteotomies. Opening wedge and closing wedge are the most frequently used techniques. No differences in most of the clinical outcomes were found except the operation time 25. Currently, HTO seems common again; however, there were more post-surgical complications in the HTO group compared to the UKA group in the current meta-analysis. These findings accord with previous meta-analyses 26,27. The postoperative complications included the rate of infection, venous thrombosis, cortical fracture, and peroneal nerve injury. A systematic review of 12 HTO studies showed that HTO had a complication rate up to 47% postoperatively 28. The significantly higher proportion of complications after HTO may be due to surgical techniques, long-standing cast immobilization, late limb load, and inadequate fixation following HTO operation.
Regarding the knee functional outcomes, the current meta-analysis showed that the rate of excellent/good outcomes was significantly higher in the UKA group versus the HTO group, while the range of motion was higher in the HTO group versus the UKA group. However, there were no significant differences between the compared groups regarding the visual pain scale. The differences in functional outcomes and range of motion results indicate that further factors might impact functional results. Osteotomy targets transferring the mechanical axis from the abnormal position to the normal area 29, which leads to improved pain and better gait, delaying the progression of osteoarthritis 20. Nevertheless, the degenerative compartment persists. Formerly, patients undergoing HTO were placed in a plaster cast from the groin to the ankle for six weeks, and the osteotomy took several months to heal postoperatively. Compared to UKA, a resurfacing technique, in which the degenerative compartment is replaced while the normal compartments are preserved. Some studies reported on the use of modern techniques such as TomoFix plate in the HTO group compared to UKA. Koh et al. enrolled patients with OWHTO performed using TomoFix plate vs UKA. The study reported that patient satisfaction was higher in the UKA group than the HTO group in active patients 30. Kim et al. used TomoFix plate in OWHTO vs UKA and reported that HTO and UKA had similar pain and functional outcomes at 12 and 24 months postoperative 31. These results accord with the findings of Takeuchi et al 32, Jeon et al. 33, Ryu et al. 34.
UKA is associated with less perioperative blood loss, quicker recovery, and no immobilisation. A report by Jeon et al. showed a better postoperative activity level following UKA compared to HTO at 6 months, whereas at 12 months and 2-year follow-up no significant differences were reported in the compared groups 33. A study by Borjesson et al. reported an increased free walking speed from 1.07 to 1.16 m/s in the UKA group compared to the HTO group which was associated with decreased free walking speed from 1.07 to 0.94 m/s three months postoperatively. However, comparable results were observed between the two groups at the follow-up durations of 1 and 5 years 35. Based on the previous reasons, UKA offers improved postoperative functional outcomes than HTO in short-term follow-up while no difference was found in long-term results.
Strengths and limitations
The current meta-analysis included some new studies up to 2021 30,31,36−39; thus, our results are more up to date. We determined search methods and performed a comprehensive search using many electronic databases and we followed the PRISMA checklist when reporting this manuscript. However, a limitation of our meta-analysis is the heterogeneity in some of the included outcomes. The heterogeneity might be due to the included different study designs, matching criteria, sample size, operative techniques, and measurement of outcomes. These variances may lead to significant between-study heterogeneity, which can impact the results in the current study. We used the random effects model to decrease the impact of heterogeneity; however, it does not eliminate it.