The unicompartmental knee arthroplasty (UKA) could be a useful method for the treatment of medial compartment osteoarthritis (OA) of the knee in patients younger than 60 years of age. 

The unicompartmental knee arthroplasty (UKA) is often performed in older patients aged above 60 years. Results of some recent studies showed that the incidence of UKA is also increasing in relatively younger patients who less than 60-year-old. However, in young patients, UKA is a challenging procedure due to their high expectation of postoperative knee function and long-life expectancy.

Previous studies have suggested that UKA offers good outcomes concerning pain relief and improvement of knee and function scores and recovery of range of motion (ROM). However, there is still controversy over the long-term survivorship of the implant due to lack of evidence.

Therefore, the purpose of this study was to investigate the long-term survivorship and functional outcome of UKA in younger patients aged below 60.

Rationale behind the research:

A relatively small number of studies have been published on the long-term results of UKA in younger patients.

Therefore, this study investigated the long-term survivorship and functional outcome of UKA in patients aged below 60-year-old based on minimum 10-year follow-up clinical data.

Objective:

To evaluate the long-term clinical results and survivorship of unicompartmental knee arthroplasty (UKA) in patients younger than 60 years of age. 

Study outcomes:

• Clinical assessment:

Knee joint pain and ROM were assessed, and knee score and function score were calculated using the Knee Society Clinical rating system.

• Radiographic assessment:

The tibiofemoral angle was measured, and the presence of bony change, component loosening/wear, and dislocation of components were examined on the weight bearing radiographs of the knee.

Time period: 3 months, 6 months, and 12 months 

Study Outcomes

• Clinical Outcome:

The mean Knee Society knee score was significantly improved from 52.8 points to 85.4 points. The Knee Society knee function score was also significantly improved from 56.6 points to 84.7 points. The mean ROM was restored from 130.7° to 132.8°. The mean tibiofemoral angle was changed from 1.2° varus to 4.7° valgus. According to the Knee Society clinical rating system, 63 cases (69.2%) were classified as excellent, 24 cases (26.4%) as good, and 4 cases (4.4%) as fair by Insall’s criteria.

• Complications:

The most prevalent postoperative complication occurred was mobile bearing dislocation which was followed by implant loosening, polyethylene wear, mobile bearing impingement against the osteophyte, periprosthetic fracture, medial collateral ligament injury, and lateral compartment osteoarthritis. There was no case of infection. Reoperation other than revision knee arthroplasty was required in 5 cases (4.2%) at a mean of 1.2 years after surgery (range, 0 to 3.2 years). Revision knee arthroplasty was performed in 15 cases (12.5%) at a mean of 6.0 years after surgery (range, 0.3 to 11.8 years).

• Survivorship:

The 10-year cumulative survivorship was 92.8%, and the 13-year survivorship was 90.4% when conversion to total knee arthroplasty (excluding simple bearing change) was defined as a failure (Figure 1). When all revision surgeries including mobile bearing change were identified as the failure, the 10-year cumulative survivorship was 89.3% (95% CI, 83.7 to 95.2) and the 13-year survivorship was 85.8% (95% CI, 79.3 to 92.8) (Figure 2). 

Figure 1: Kaplan Meier survivorship analysis curve showing the survival rate of unicompartmental knee arthroplasty of 92.8% (95% confidence interval [CI], 88.1 to 97.7) at 10 years and 90.4% (95% CI, 84.9 to 96.3) at 13 years with conversion to total knee arthroplasty as the end point. +: censored

Figure 2: Kaplan-Meier survivorship analysis curve showing the survival rate of unicompartmental knee arthroplasty of 89.3% (95% confidence interval [CI], 83.7 to 95.2) at 10 years and 85.8% (95% CI, 79.3 to 92.8) at 13 years with failure for any reason as the end point. +: censored

The present study evaluated the long-term follow-up results of UKA in younger patients who underwent the procedure for degenerative osteoarthritis. The results of minimum 10-year follow-up showed excellent knee function and satisfactory implant survivorship in this patient population. The results confirmed the hypothesis that UKA would offer good long-term results in patients aged below 60-year-old patients. Treatment of degenerative osteoarthritis of the knee in young patients is challenging. In particular, UKA has been recommended for the patients aged above 60 years. However, a growing body of studies has demonstrated favorable outcomes of UKA, which has led to an increase in the incidence of UKA in relatively younger patients (age<60 years).

A study by Pennington et al. showed significant outcomes of UKA in patients aged below 60 years. At 11 years’ follow-up period the mean Hospital for Special Surgery knee score was 94 points, and the mean UCLA activity score was 6.5 point. Less than 60-year-old patients in the study obtained significant improvement after UKA with a mean Knee Society knee score of 87 points, a mean Knee Society function score of 84 points, a mean Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) score of 85 points and a mean ROM of 125°. A recent excellent or good results obtained in 53 (96.4%) of total 55 cases of UKA performed in patients below 60-year-old patients. Streit et al. (2017) reported that at a mean of 5 years after the surgery on patients less than 60 years showed high satisfaction and excellent clinical results. In the current study, we found significant improvement in our less than 60-year-old patients after Oxford phase 3 mobile bearing UKA. At a mean follow-up of 12.1 years, the postoperative Knee Society knee score and function score was 85.4 points, and 84.7 points, respectively, and the mean ROM was improved to 132.8°. Thus, excellent or good results were achieved in 95.6% of the total patients.

On the survivorship of fixed bearing UKA in patents aged below 60 year, Parratte et al reported that the 12-year survivorship of Miller-Galante metal-backed prosthesis (n=35) was 80.6% in ≤50-year-old patients. Another study conducted by Pennington et al showed the 11-year survivorship was 92% in ≤60-year-old patients after MillerGalante fixed bearing UKA. Recent studies on Oxford mobile bearing UKA have demonstrated excellent survival rates: 97% 5-year survivorship in ≤60 years (118 cases) and 95% 12-year survivorship in ≤59 years (55 cases). In the current study, revision knee arthroplasty was performed in 15 of 106 cases. When failure was defined as revision knee arthroplasty including mobile bearing change, the 10-year cumulative survivorship was 89.3%, and the 13-year cumulative survivorship was 85.8%.

Studies comparing two different age groups directly after UKA are rare. Thompson et al reported that the mean Knee Society knee score at 2 years after fixed bearing UKA was significantly higher in patients younger than 60 years old than patients 60 years and older (93.3 vs. 77.7), which they attributed to the improved modern implant design and surgical technique. The Oxford knee score and AKS scores were not significantly different between groups, whereas the AKS function score and Tegner activity score were higher in patients younger than 60 years. There was no significant difference in the 10-year survivorship between the younger patients (97.3%) and the older patients (95.1%). 

The UKA performed in patients aged below 60 years were good concerning the Knee Society knee score and function score and ROM, and the survivorship was satisfactory. Therefore, it will be suggested as a useful therapy for medial compartment osteoarthritis of the knee in patients below 60 years of age.