Kinematically Aligned Total Knee Arthroplasty with Patient-Specific Instrument

Kinematically aligned total knee arthroplasty (TKA) is a new alignment technique. Kinematic alignment corrects arthritic deformity to the patient's constitutional alignment in order to position the femoral and tibial components, as well as to restore the knee's natural tibial-femoral articular surface, alignment, and natural laxity. Kinematic knee motion moves around a single flexion-extension axis of the distal femur, passing through the center of cylindrically shaped posterior femoral condyles. Since it can be difficult to locate cylindrical axis with conventional instrument, patient-specific instrument (PSI) is used to align the kinematic axes. PSI was recently introduced as a new technology with the goal of improving the accuracy of operative technique, avoiding practical issues related to the complexity of navigation and robotic system, such as the costs and higher number of personnel required. There are several limitations to implement the kinematically aligned TKA with the implant for mechanical alignment. Therefore, it is important to design an implant with the optimal shape for restoring natural knee kinematics that might improve patient-reported satisfaction and function.

The Accuracy of Alignment Determined by Patient-Specific Instrumentation System in Total Knee Arthroplasty

PURPOSE: The aim of this study is to assess the accuracy of alignment determined by patient-specific instrumentation system in total knee arthroplasty (TKA). MATERIALS AND METHODS: Twenty-seven TKAs using patient-specific instrument were reviewed. The intraoperative pin location determined by the patient-specific guide was recorded using imageless navigation software. Data recorded included tibial coronal alignment and posterior slope, femoral coronal alignment and sagittal alignment, and transepicondylar axis. A discrepancy within ±3° in each plane was considered an acceptable result. RESULTS: On the tibia, an acceptable alignment was obtained in 24 (88.1%) in the coronal plane and 21 (77.8%) in the sagittal plane. On the femur, a satisfactory alignment was obtained in 25 (92.6%) in the coronal plane and 24 (88.1%) in the sagittal plane. Based on the transepicondylar axis, a satisfactory alignment was obtained in 23 (85.1%). CONCLUSIONS: Satisfactory alignment was obtained in more than 85% of each plane of the femur and in the coronal plane of the tibia and relative to the transepicondylar axis. Sufficeint experience and precise preoperative planning are required to improve the accuracy of sagittal alignment of the tibia.

3D Computed Tomography Assist in Making the Protocol for Primary TKA Using PSI / 中山大学学报(医学科学版)

[Objective]To investigate the feasibility of making the protocol with computed tomography data for total knee arthroplasty using patient-specific femoral and tibial cutting blocks.[Methods]54 consecutive patients diagnosed with osteoarthritis were divided randomly into two groups. Every patients accepted 3-dimentional computed tomography scan for bilateral legs before operation,the protocol were made for every patients before operation.When making the pre-operative protocol,we accepted the prothesis surpass the osteotomy edge finitely,tibia prothesis rotational orientation according to the outline of the tibial osteotomy. The thickness of the posterior condyle of femur resected was as the same with the prothesis posterior condyle as possible. The patients in trial group undergone total knee arthroplasty(TKA) using patient-specific instruments(PSI)according to the preoperative protocol,while the patients in the control group undergone TKA using custom instruments(CI).The operation time,the times that the scale of the prosthesis were altered intraoperation,the mean thickness of the posterior condyle of femur resected in the operation,AKS score 3 months and 1 year after the operation were recorded and compared between the two groups. Plain film radiography after the operation were analyzed.[Results]No significant differences were found between two groups with respect to the operation time. 8 patients altered to a lesser prosthesis in the CI group during the operation,all in bibia contrast to no one need alteration in the PSI group.The thickness of the osteotomy on the posterior condyle of femur in the PSI group is bigger than that of CI group as a result.The AKS score of the patients in the PSI group is higher than that of CI group 3 months after the opera-tion,whereas no significant difference was found 1 year after the operation.[Conclusion]The reconstructed image by thin layer CT can be used for preoperation protocol for TKA,which might be helpful in deciding the size of femour prosthesis;the implants can surpass the edge of the osteotomy finitely in TKA,which is not necessarily cause any complain.We can orient the tibia prosthesis rotation according to the outline of the osteotomy of the patients'tibia.

Patient-Specific Instruments Based on Knee Joint Computed Tomography and Full-Length Lower Extremity Radiography in Total Knee Replacement / 中华医学杂志(英文版)

<p><b>Background</b>Restoring good alignment after total knee replacement (TKR) is still a challenge globally, and the clinical efficiency of patient-specific instruments (PSIs) remains controversial. In this study, we aimed to explore the value and significance of three-dimensional printing PSIs based on knee joint computed tomography (CT) and full-length lower extremity radiography in TKR.</p><p><b>Methods</b>Between June 2013 and October 2014, 31 TKRs were performed using PSIs based on knee joint CT and full-length lower extremity radiography in 31 patients (5 males and 26 females; mean age: 67.6 ± 7.9 years; body mass index [BMI]: 27.4 ± 3.5 kg/m). Thirty-one matched patients (4 males and 27 females; mean age: 67.4 ± 7.2 years; mean BMI: 28.1 ± 4.6 kg/m) who underwent TKR using conventional instruments in the same period served as the control group. The mean follow-up period was 38 months (31-47 months). Knee Society Score (KSS), surgical time, and postoperative drainage volume were recorded. Coronal alignment was measured on full-length radiography.</p><p><b>Results</b>Twenty-three (74.2%) and 20 (64.5%) patients showed good postoperative alignment in the PSI and control groups, respectively, without significant difference between the two groups (χ= 0.68, P = 0.409). The mean surgical time was 81.48 ± 16.40 min and 72.90 ± 18.10 min for the PSI and control groups, respectively, without significant difference between the two groups (t = 0.41, P = 0.055). The postoperative drainage volume was 250.9 ± 148.8 ml in the PSI group, which was significantly less than that in the control group (602.1 ± 230.6 ml, t = 6.83, P < 0.001). No significant difference in the KSS at the final follow-up was found between the PSI and control groups (91.06 ± 3.26 vs. 90.19 ± 3.84, t = 0.95, P = 0.870).</p><p><b>Conclusions</b>The use of PSIs based on knee joint CT and standing full-length lower extremity radiography in TKR resulted in acceptable alignment compared with the use of conventional instruments, although the marginal advantage was not statistically different. Surgical time and clinical results were also similar between the two groups. However, the PSI group had less postoperative drainage.</p>