Analysing the long-term results of using and those of survival terms for unicompartmental knee arthroplasty

Отдаленные результаты применения и сроки выживаемости одномыщелковых эндопротезов конструкции Oxford III (Biomet) мало изучены с момента, как этот эффективный метод был внедрен в практику. Проведено исследование и анализ отдаленных исходов 400 одномыщелковых эндопротезирований конструкцией Oxford III (Biomet) у 320 пациентов в возрасте от 48 до 82 лет (средний возраст 69 лет) на момент операции. Средняя продолжительность наблюдения составила 9,3 года (от 5 до 15). При анализе отдаленных результатов через пятнадцать лет после эндопротезирования показатели по шкале Knee Society score значительно увеличились с 56,2 (от 41 до 93) до операции до 88,6 (от 61 до 97, р=0,036) после операции; функциональные показатели увеличились с 59,2 (от 45 до 94) до 88,2 (от 55 до 98, р=0,023) соответственно. Средний показатель по шкале Oxford Knee score увеличился с 25,8 балла (от 12 до 39) до 40,1 балла (от 28 до 54). Ревизионное эндопротезирование было проведено у 21 больного (5,25 %). У пяти больных было проведено тотальное эндопротезирование коленного сустава. Малоинвазивное одномыщелковое эндопротезирование конструкцией Oxford III (Biomet) позволило достичь удовлетворительных отдаленных клинических результатов. Ключевые слова: коленный сустав, одномыщелковое эндопротезирование, клинические результаты.


INTRODUCTION
Within a few decades after introducing Oxford design unicompartmental implant several improved versions of these implants have been developed [1,2].
And, of course, the use of minimally invasive approach led to the possibility of achieving good postoperative results [3,4].
Despite many orthopedists have already widely used this method [5,6], long-term survival results of using Oxford III (Biomet) design unicompartmental implant are poorly studied since this effective method has been implemented in practice.
Re-analyzing the results in patients during a prolonged postoperative period and studying the survival of Oxford III (Biomet) design unicompartmental implants was the purpose of our research.

MATERIALS AND METHODS
The patients operated on within the period of 2000-2011 were included for the study.After screening the patients data we remained and prospectively analyzed 320 patients with 400 knees operated with the follow-up periods of 1, 5, 10 and 15 years.The average follow-up period was 9.3 years (5 to 15).The recent long-term postoperative outcomes (15 years) for 35 joints in 31 patients were analyzed by our authors.The mean age of patients at the time of surgery was 69 years (range: 48 to 82).The mean age of 31 patients in the study was 76 years (range: 63 to 88), 23 of them (74%) were women.Indications for surgery were osteoarthritis and destructive changes in the medial femoral condyle with uninjured integrity of the ligaments.
Operations were performed by the same surgeon by a minimally invasive technique (medial parapatellar arthrotomy) using Oxford III (Biomet, Warsaw, Indiana) design.Tibial and femoral components were fixed with cement (Stryker Orthopaedics, Mahwah, New Jersey).All the necessary medicine and physical therapy have been done.The patients discharged from the hospital on Day 4 after surgery with further control observation after two (2) weeks, three (3) months, six (6) months and one (1) year.The patients were followed subsequently at 5, 10 and 15 years.
All the patients studied were evaluated by the Knee Society score (KSS) system, functional Oxford knee score (OKS) scale, as well as range of motion (ROM) in the knee before and after surgery evaluated.Anterior-posterior (AP) and lateral X-ray views were obtained during every followup visit using Star-PACS PiView STAR 5.0.-6.0 software (Infinitt Healthcare Co., Seoul, Korea). Eshnazarov K., Hong-Chul L., Karimov M. Analysing the long-term results of using and those of survival terms for unicompartmental knee arthroplasty // Гений ортопедии.2016.№ 1. С. 60-65.

Патология суставов
For statistical analysis we used 12.0 software version (SPSS Inc., Chicago, Illinois).The differences between the mean preoperative and postoperative clinical parameters were analyzed by Student t-test.The cumulative survival rate was analyzed and calculated by 95% confidence intervals (CI).

RESULTS AND DISCUSSION
When analyzing the long-term results fifteen years after the knee unicompartmental arthroplasty the Knee Society score revealed a significant increase in the parameters from 56.2 (41 to 93) before surgery to 88.6 (61 to 97) after surgery; the functional scores increased from 59.2 (45 to 94) to 88.2 (55 to 98), respectively; the mean Oxford Knee score increased on the average from 25.8 points (12 to 39) before surgery to 40.1 points (28 to 54) after surgery.Preoperative ROM averaged 129° (from 120° to 135°), and postoperative one -135° (from 118° to 142°).Clinical values before surgery and 1, 5, 10, and 15 years after surgery summarized in Table 1.
Despite the existing methods of the knee unicompartmental arthroplasty the implementation of the Oxford III (Biomet) implant in 1998 was quickly and widely appreciated by many doctors [7,8].Some authors achieved almost the same clinical results [9,10,11], however, the follow-up periods in their studies were shorter comparing with our study.The cumulative survival rate of unicompartmental implants at the final follow-up was 93.8% (from 90.5 to 97.6); the results by stages are shown in Table 2.According to our data, the survival rate is nearly identical during the last ten years, and it decreases gradually during the full observation period.According to the data of other authors, their short-and mid-term results were lower than our results [12,13,14].
Complications of several types developed after the knee unicompartmental arthroplasty in the world practice, such as polyethylene wear and failure, aseptic loosening, polyethylene insert dislocation, contralateral osteoarthritis, infection, tibial fractures, limited range of motion, and unexplained pain [15,16,17].According to the literature, further progressing arthrosis of the left femoral condyle was the cause for the most revisions [18,19], but as for our practice, most reoperations (17 patients) were performed for polyethylene insert dislocation which amounted to 17 (4.25 %) of the total number of the joints operated.On the whole, revision arthroplasty was performed in nineteen ( 19) patients (4.75 %) of their total number, other researchers presented the data from 0 to 29 % of revisions [20,21,22].Five patients underwent total knee arthroplasty (Table 3).The development of osteoarthrosis of the lateral femoral condyle was the cause of total knee arthroplasty in four of them.Some authors reported the lower limb overcorrection to be an often cause of the required performing total interventions after unicompartmental arthroplasty [23,24,25].In 0.5-3.0 % of cases this has led to polyethylene insert dislocation postoperatively in the short-and mid-term follow-up.As for our studies, this amounted to 13 cases (3.25 %) in the long-term periods.The implant polyethylene insert dislocation backwards was observed in one case (Fig. 1).The wear of polyethylene insert without dislocation was revealed in two patients.Femoral component instability was observed only in one patient, and in another onepostoperative infection, which required performing total revision arthroplasty of the knee.Гений Ортопедии № 1, 2016 г.

Table 1
Clinical evaluation of the patients' condition before and after performing unicompartmental knee arthroplasty by OKS, KSS and FS score systems (CD) -Standard Deviation, PO -Postoperatively.

Table 2
Results of the cumulative survival rate (CSR) of the patient over the period

Table 3
Complications related to unicompartmental knee arthroplasty