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This article presents a series of case studies on the rare complication of meniscal bearing fractures after unicompartmental knee arthroplasty (UKA). The authors describe the symptoms, radiographic findings, and surgical interventions of six patients who experienced this complication. They suggest that a 3 mm bearing thickness may be a risk factor for fracture, but the role of BMI is inconclusive. The authors emphasize the importance of considering meniscal bearing fracture as a potential diagnosis in patients with sudden symptoms after UKA and recommend a systematic diagnostic approach to avoid overlooking this complication. [Extracted from the article]

Dislocation of meniscal bearing insert is a rare but wellrecognised complication in meniscal bearing unicompartmental knee arthroplasty (UKA). On the other hand, fracture of meniscal bearing insert of phase III Oxford UKA has only been reported once in the current literature. The authors report a case of fracture and posterior dislocation of one of the fragments of the meniscal bearing insert in a mobile bearing medial UKA. The fracture was only diagnosed during the revision surgery. The posteriorly dislodged fragment was subsequently retrieved through the same skin incision and a new polyethylene insert of the same size was implanted.

In 2012-2014 total 67 unicompartmental arthroplasty surgeries with use of Oxford knee meniscal bearing were performed. The surgeries were performed by a single surgeon. Minimally invasive approach was used. All patients were evaluated clinically, radiographically and with Oxford Knee score scale, Knee Society score scale and functional scale. Obtained data was processed with nonparametric Mann-Whitney-Wilcoxon test. Results were processed using the statistical analysis application package SPSS, version 10.07. Analysis of of mid-term results showed that the average for Oxford Knee score increased from 16.4 (95% CI 9-23) to 41.3 (95% CI 29-47). Average for Knee Society score scale increased from 42.7 (95% CI 31-55) to 88.6 (95% CI 73-100). No occurrence of early postoperative complications have been reported. Statistically significant improvements of knee function in patients after unicompartmental arthroplasty have been observed. Unicompartmental arthroplasty currently can be considered as an advanced treatment option for medial knee joint pathology. Meniscal bearing cemented prostheses such as Oxford III are preferable.

Introduction: Correct rotational alignment of the tibial component is crucial for total knee arthroplasty (TKA). Several studies have indicated that the best rotational orientation of the tibial component is close to the medial border of the tibial tubercle. However, it remains obscure whether it is always right. Thus, the objective of current study was to quantify tibial rotational alignment in 120 primary rotating platform TKAs using the medial border of tibial tubercle as a landmark between July 2008 and June 2010. Methods: The femoral component was positioned parallel to the transepicondlylar axis, and a rotating platform trial insert was used to determine tibial insert rotational alignment relative to the most medial aspect of the tibial tubercle with the knee in full extension. Rotational alignment of the components was detected based on radiograph and CT scan. This investigation is based on the premise that all neutral points would lie within 10° of the mean. Results: The mean divergence external to the medial border of the tubercle was 2.3°±3.5°. However, six of the knees (5%) had neutral points ≥10° from the mean, including two valgus knees measured 10° of internal rotation and four varus knees measured 10° of external rotation. Conclusion: Using the medial border of tibial tubercle as a landmark does not always result in a good femorotibial rotational alignment. Surgeons using fixed bearings component should be aware of this effect to avoid suboptimal outcomes resulting from tibiofemoral rotational malalignment in full extension. Level of evidence: Diagnostic study, Level II-3. [ABSTRACT FROM AUTHOR]

Abstract: Background: The Oxford Medial Partial Knee Replacement (PKR) has been in clinical use for more than 20years. The current surgical technique requires a number of judgements to be made, and even in the most experienced hands surgery can be challenging. We present an alternative surgical technique, which we believe addresses the unpredictability of the current method. The technique is based on precise femoral positioning prior to tibial resection. Method: A prospective series of 125 Oxford Medial PKRs was performed using this new technique and a radiographical analysis was performed. We used meniscal thickness, meniscal position and femoral position as measures of reproducibility of the procedure. Results: Variability in meniscal thickness has been minimised with a 3mm meniscal bearing used in 21 knees (15%), 4mm (the target thickness) in 73 knees (59%) and 5mm in 30 knees (24%). The mean meniscal position relative to the tibial tray upright was 2mm (SD 1mm). Femoral component position relative to the tibial tray, which defines the excursion of the meniscus was also assessed. Mean coronal plane alignment was 2° of valgus (SD 2.8). Mean flexion/extension was 3.8° (SD 3.1). The mean rotation was 10° internal (SD 5°). Conclusion: We believe this new technique makes this procedure more reproducible, and should be considered as a viable alternative to the current recommended technique. It may be a better technique for those surgeons who are relatively inexperienced with this prosthesis. [Copyright &y& Elsevier]

Abstract: Despite the fundamental value of wear simulation studies to assess wear resistance of total joint replacements, neither specialised simulators nor established external conditions are available for the human ankle joint. The aim of the present study was to verify the suitability of a knee wear simulator to assess wear rates in ankle prostheses, and to report preliminary this rate for a novel three-component total ankle replacement design. Four intact ‘small’ size specimens of the Box ankle were analysed in a four-station knee wear simulator. Special component-to-actuator holders were manufactured and starting spatial alignment of the three-components was sought. Consistent load and motion cycles representing conditions at the ankle joint replaced exactly with the prosthesis design under analysis were taken from a corresponding mechanical model of the stance phase of walking. The weight loss for the three specimens, after two million cycles, was 32.68, 14.78, and 62.28mg which correspond to a linear penetration of 0.018, 0.008, and 0.034mm per million-cycle, respectively for the specimens #1, #2, and #3. The knee wear simulator was able to reproduce load-motion patterns typical of a replaced ankle. Motion of the meniscal bearing in between the tibial and talar components was smooth, this component remaining in place and in complete congruence with the metal components throughout the test. [Copyright &y& Elsevier]

The poor results of total ankle replacement have been attributed to the inability of designers to restore adequately the critical mutual function of the ligaments and the articular surfaces. The purpose of this study was to design sagittal shapes of the articular surfaces for a new ankle prosthesis to be compatible with the geometry of the retained ligamentous structures. Several ligament-compatible pairs of articular surfaces were tested using a computerised version of a four-bar linkage model. The kinematics of the ankle when replaced by non-conforming two-component and by fully conforming three-component designs with either flat, concave or convex tibial surfaces were assessed by the model. A ligament-compatible convex-tibia fully-congruent three-component prosthesis showed the best features. The three-component prosthesis allows complete congruence over the entire range of flexion. A convex shape for the tibial arc was preferred because of the better degree of entrapment of the meniscal bearing. A 5 cm convex-tibia arc radius gave 2 mm entrapment together with 9.8 mm of tibial bone cut. Ligament elongation imposed by full congruence of the articular surfaces was less than 0.03% of the original length. The original patterns of joint kinematics and ligament tensioning are closely restored in the joint replaced by the proposed prosthesis. [ABSTRACT FROM AUTHOR]

SummaryWe investigated the tibio-talar mobility clinico-radiographically in 11 ankle joint prostheses before surgery and after 6 and 12 months. The radiologist and the orthopaedic surgeon were not involved in the radiographic procedures. The total preoperative radiographic range of motion was median 16° (range 13–50). At 6 months after operation it had increased to median 22° (range 15–36) and at 12 months to median 27° (range 19–38). The difference at 6 and 12 months was significant compared to the preoperative value (P = 0.05). The gain in motion took place in dorsiflexion that at 6 months had increased by 7° and at 12 months by 10°. There was no significant change in plantarflexion. The clinical measurements showed the same trend. However, the motion was significantly larger (45°, range 40–55). There was no correlation between clinical and radiographic measurements. True tibio-talar motion for ankle arthroplasty is determined best by radiography. [ABSTRACT FROM AUTHOR]

Meniscal bearing fracture is a rare complication of phase III Oxford unicompartmental knee replacement (UKR). We report a case of a meniscal bearing fracture that occurred 7 years after phase III Oxford medial UKR. The meniscal bearing showed uneven delamination of the polyethylene in the thinnest articular surface and an impingement lesion. This lesion initiated a fatigue crack that propagated to cause failure of the meniscal bearing. This is the first report of a meniscal bearing fracture without a posterior marker wire. [ABSTRACT FROM AUTHOR]