[Biomechanical parameters and clinical outcomes of the Oxford Phase III unicompartmental knee replacement]. / Biomechanické parametry a klinické výsledky unikompartmentální náhrady Oxford Phase III.

PURPOSE OF THE STUDY: The kinematics of an intact knee joint and that of a knee replacement have been studied in many research centres. In the 1987 radiographic study, Bradley, Goodfellow and O'Connor reported the movement of a polyethylene insert in patients with unicompartmental Oxford knee replacement. Views with the knee at full extension and 90° of flexion were obtained and the movement of the meniscal bearings over this range of flexion was measured. The bearings were found to move backwards on the tibia through an average distance of 4.4 mm in all 16 patients. This measurement was in agreement with the then valid concept of knee biomechanics and a roll-back phenomenon. However, our observations had not always agreed with the results of these authors, but gave an impetus for a detailed evaluation of our own patient group. The aim of the study was to evaluate the dynamic relationship between the components of a unicompartmental Oxford knee replacement and elucidate it with the use of recent information from the field of biomechanics. A relationship of the obtained kinematic values to clinical outcomes was also investigated. Answers to the following hypotheses were sought: Would our results be in agreement with the British authors' findings? Would clinical outcomes depend on the kinematic properties of knee replacements? MATERIAL AND METHODS: The group comprised 33 patients, 23 women and 10 men. They all had replacement of the medial compartment of the knee. The construction of the unicompartmental Oxford Phase III knee replacement enabled us to locate the centre of rotation of the medial femoral condyle in relation to the tibial component at flexion and extension of the knee, using radiography. The patients were examined in a supine position with the knee at full extension, and subsequently views of the knee were obtained at 80°-90° flexion in accordance with the method used by the British authors. The clinical findings of knee joints were assessed using the American Knee Society (AKS) scoring system (Insall et al.). Pain was rated on the Visual Analogue Scale (VAS). The results were statistically evaluated with the t-test and Chi-square test. RESULTS: On moving the knee from extension to flexion, movement of the polyethylene insert ventrally by an average of 3.4 mm in relation to the tibia was recorded, i.e., "paradoxical" ventral translocation. In the patients with insert movement less than or equal to 3 mm, the average AKS score was 89 points, in those with movement over 3 mm it was 87 points. The average functional scores were 87 and 83 points in the patients with movement less than 3 mm and more than 3 mm, respectively. The average VAS score was 1.55 in the former and 1.18 in the latter. DISCUSSION: The unicompartmental Oxford Phase III knee replacement substitutes a flexion femoral facet and eliminates the role of an extension femoral facet. This is the reason why, at knee extension between -5° and +20°, the centre of rotation of the medial femoral condyle is in the centre of the flexion facet and not in that of the extension facet. When the stabilising functions of the extension tibial facet in the ventral direction and of the dorsal part of the insert in the dorsal direction are missing, the position of the contact surface centre becomes much dependent also on the strength and direction of external forces acting in the knee joint vicinity. CONCLUSIONS: The kinematic parameters of the unicompartmental Oxford Phase III knee replacement investigated in our group differed from the findings of the British authors. However, neither the magnitude nor the direction of movement had any effect on the clinical outcome of knee arthroplasty.

[Long-term results of unicompartmental knee joint replacement]. / Dlouhodobé výsledky unikompartmentální náhrady kolenního kloubu.

PURPOSE OF THE STUDY: To evaluate the long-term results of unicompartmental knee joint alloplasty (UKA) in a group of 21 patients. On the basis of their own results and literature data, the authors discuss effective strategies for treatment of unicompartmental osteoarthritis of the knee joint. MATERIAL: A group of 21 patients, who were implanted a total of 22 unicompartmental knee replacements, type St. Georg, Waldemar Link, between 1986 and 1992, were followed-up till 2002. Since two patients living permanently abroad were excluded, the group at the final evaluation consisted of 19 patients with a total of 20 knee replacements. METHODS: In 2002, all patients were clinically and radiologically examined. They were interviewed about their subjective evaluation of the knee joint after alloplasty, and clinical and functional findings were assessed. The evaluation of long-term results was based on The Knee Society Clinical Rating System. RESULTS: The average Knee Score value was 84 points and average Function Score value was 78 points. Out of the 20 knee replacements evaluated, only one failure of UKA was recorded at 9 years after the primary implantation. DISCUSSION: The authors discuss the current state of treatment in unicompartmental knee arthritis and present several different views based on literature sources. Opinions on indications for specific surgical methods are still controversial. The authors draw attention to comparisons of long-term results between patients with UKA and patients who underwent high tibial valgus osteotomy or total knee replacement. They discuss the advantages and disadvantages of UKA in comparison with the other therapies. They also pay some attention to repeat surgery in failed UKA. CONCLUSIONS: UKA implantation is a surgical method of managing unicompartmental arthritis of the knee joint. The results presented by the authors and corroborated by many literature data provide evidence that UKA is of great importance in the treatment of unicompartmental knee arthritis. If a consistent selection of patients is maintained, a precise operation technique is used and a reliable implant is chosen, excellent immediate as well as long-term outcomes will be achieved.