To our knowledge, this is the first study to compare implant survival between cemented and cementless OUKA in Asian patients. The most important finding of this study is that we observed no significant difference in 5-year implant survival between the two fixation methods. This result is similar to the findings of studies reported from the West. Akan, et al. (13) performed a retrospective study that found no significant difference in the revision rate between cemented and cementless OUKA (7.1% vs. 4.9%. p=0.155) at a mean follow-up time of 42 and 30 months, respectively. The multicenter retrospective study of Kerens, et al. revealed no significant difference in the implant survival rates between cemented (84% at 54 months) and cementless OUKA (90% at 34 months). Pandit, et al. (14) conducted a randomized controlled trial of 33 cemented and 30 cemented OUKA. At the 5-year follow-up, no revision cases were reported in their study. Stempin, et al. collected data from a prospective cohort study with an average follow-up time of 7 years and found no significant difference in the revision rate between cemented (3.4%) and cementless OUKA (2.0%). In South Africa, Campi, et al. (9) performed a survival analysis in a prospective cohort of 522 cemented and 598 cementless OUKA. Their results showed no significant difference in 5-year implant survival between cemented and cementless OUKA (95.1% vs. 95.8%, p=0.97).
However, contradictory results were reported from larger or longer-term studies. Knifsund, et al. (15) collected data from the Finnish Arthroplasty Register, and they found the 5-year survival of cemented OUKA to be significantly shorter than that of cementless OUKA (88.9% vs. 92.3%, p<0.05). A large propensity-matched NJR-based study also showed the risk of revision in cementless OUKA to be 24% less than that of cemented OUKA within 10 years (5). Additionally, a recent meta-analysis of 901 patients revealed cementless OUKA to be associated with a lower revision rate after follow-up for at least two years (odds ratio: 1.83, 95% confidence interval: 0.90-3.73).
Considering the different types of OUKA failure in our study, the most common reason for reoperation in cemented OUKA was bearing dislocation. In cementless OUKA, the most common reasons were osteoarthritis progression and infection. Our study's reoperation rate for bearing dislocation was higher than the rates from Western registry-based data (5, 15). A meta-analysis by Ro, et al. (16) found the mean reoperation rate per 100 observed component years for bearing dislocation after OUKA to be higher in Asians (0.53, 95% CI: 0.41-0.64) than in Westerners (0.14; 95% CI: 0.12-0.17). There are factors that may explain this problem. Hyperflexion knee or floor activities are commonly performed in Asian populations, and these activities resulted in anterior tibial subluxation and strained anterior cruciate ligament that increased the risk of bearing dislocation (17). Another possible explanation is that repetitive hyperflexion activity might cause impingement between the polyethene bearing and the remaining osteophytes or meniscus (12, 17). Furthermore, a relatively smaller tibia in Asians compared to Westerners result in tibial component size mismatch that could lead to mediolateral overhang of the tibial component. This overhang creates more space for bearing motion and might cause an imbalance in soft tissue tension. This hypothesis may also increase the chance of bearing dislocation.
The results of our study also demonstrated OUKA to be a safe procedure for treating medial compartmental knee osteoarthritis in Asians relative to complications, morbidity, and mortality. We had only one patient with 90-day morbidity in our series, with no complications and no mortality. This is similar to the results from a study in 2,316 OUKA from the National Surgical Quality Improvement Program that reported an overall complication and 90-day morbidity rate of 3.2% with no mortality (18).
Limitations
This study also has some mentionable limitations. First, our study had a comparatively small number of cases enrolled in the cementless group because the cementless prosthesis was introduced in Thailand in 2014. It is possible that the small number of cementless cases could have limited the statistical power of our study to identify independent predictors of OUKA implant survival. Gupta, et al. (3) found that cemented OUKA had superior implant survival in women aged <65 years, and in men aged 55 to 74. They suggested age and gender to be important factors to consider when determining the OUKA fixation technique. Second, our study reported only short- to mid-term implant survival, and study of longer-term outcomes is needed. Third, all procedures were performed by medium- to high-volume surgeons. As such, different outcomes might be observed in low-volume surgeons. From the NJR database, the 10-year survival rate for cemented and cementless OUKA was 86.8% and 81.8% in low-volume surgeons (<10 cases/year); 94.3% and 92.5% for medium-volume surgeons (10 to <30 cases/years); and, 97.5% and 94.2% for high-volume surgeons (≥30 cases/year), all respectively (19). Fourth and last, because of this study's retrospective design, we were not able to evaluate functional or patient-reported outcomes. Implant survivorship was the only outcome that could be confidently assessed. However, many of these outcomes have already been studied in previous trials.