Ethical approval
Before we use the PSI and the new balancer device, we obtained approvals from the Changsha No. 3 hospital ethics committee and 3D printing technology medical application research institute of Changsha. A written informed consent was obtained from each patient in gap balancing group after the oral explanations on the detail of this study.
Study design
Data were obtained from the total knee arthroplasty finished in Changsha No. 3 hospital. 152 cases (150 knees) who underwent cemented primary TKA between August 2014 to June 2016. Most TKA finished during this period adopted two surgical techniques: the first one is traditional measured resection technique and the other one is gap balanced technique assisted by a new balancer device and PSI. We collected the clinical data of these patients for retrospective analysis. The study enrolled patients aged 22-85 years, inclusive with noninflammatory degenerative joint disease that was suitable candidates for cemented primary TKA. Exclusion criteria were as follows: Patients who had inflammatory arthritis, psychosocial disorders limiting rehabilitation, previous knee arthroplasty (including unicomartmental, biocompartmental or patellofemoral joint arthroplasty), prior patellectomy, prior high tibial osteotomy, or primary TKA in the affected knee and postoperative follow-up less than 3 years. Finally, 150 penitents (152 knees) were studied. Measured resection technique was adopted intraoperation in 70 patients (70 knees) and gap balanced technique assisted by a new balancer device and PSI was adopted intraoperation in 80 patients (82 knees). We collected the data of patient demographics (gender, age, BMI), Knee Society score (KSS), alignment and deformity details pre-operation and the flexion of knee, VAS pain scores and radiographic photoporation at 12 weeks and 36 weeks.
The flexion of knee, Knee Society score (KSS), VAS pain scores and radiographic assessments were assessed preoperatively and postoperatively at 6 weeks,12 weeks, 1 year, and then annually. The mechanical leg axis hip–knee angle (HKA) was measured on a lower extremity long-standing radiograph. Mechanical axis of the lower limb was measured using digital radiographs and special software (PACS, BOWEI Electronic Information, Hunan, China). All the measurements of radiograph were performed by an independent physician.(Table 1)
Table 1 Demographic data and preoperative status and alignment and deformity pre-operation
Variable
|
Total
|
GB group (n = 82)
|
MR group (n = 70)
|
p value
|
Age
|
67±11.3
|
70.2 (55 to 76)
|
71.1 (52 to 78)
|
0.42
|
Gender (female)
|
152(62.32%)
|
62(75.61%)
|
48(68.57%)
|
|
BMI
|
24.30±3.99
|
24.12±3.79
|
24.37±4.01
|
0.38
|
KSS knee score
|
37.13±21.81
|
39.03±21.92
|
35.72±19.16
|
0.31
|
Preoperative flexion
|
91.9±17.4
|
92.2°± 15.4°
|
90.3±17.2°
|
0.57
|
Alignment
|
|
|
|
|
Valgus:n(mean alignment)
|
41(-10.8±6.5)
|
17(-7.9±5.1)
|
24(-12.7±6.3)
|
0.34
|
Neutral:n
|
20
|
8
|
12
|
0.56
|
Varus:n(mean alignment)
|
91(6.0±2.1)
|
57(5.9±1.7)
|
34(6.2±2.3)
|
0.51
|
The new gap balancer device tool (gap balancer)
The gap balance tool was designed by the orthopedics research team of Changsha No. 3 hospital. The balancer device is consisting of three parts: a handle with holes to place the line device connect with a lower platform plate, an inverse “U” like balancer pole with scale on both lateral and medial part to measure the gap and a teetertotter condyle holder. This device is ultimately designed to permit surgeons to find a line paralleled with tibial plate under a proper tension in 90°flexion, the balancer device was sterilized by a plasma sterilizer in order to be used during the operation. Our group obtained invention patent of this balancer device (patent number:201820329898.0).
Preparation of PSI
The patients were examined by CT scan before operation and then imaged with 64-row volumetric CT (SOMATOM Sensation 40, Siemens, Malvern, PA) with 5 mm slice thickness. The images were stored in DICOM format and analyzed by the mimics 17.0 (Materialise, Belgium). The angle and plate of both tibia and femoral distal bone resection and the prosthetic components size were designed before surgery by 3D printing technology medical application research institute of Changsha and printing by Beijing Engineering Technology R&D Center. The objective was to achieve a neutral mechanical axis for the femur and tibia. Planning was reviewed and confirmed by the surgeon in each case. The resection plates of the tibia were designed at a 90°angle to the longitudinal tibial axis with 3°posterior slope. The flexion degree in the sagittal plane for the femoral component was depending on personal anatomical features. The templates were sterilized by a plasma sterilizer before surgery. Our group obtained invention patent of these PSI and the design method (patent number ZL201520623218.2 and ZL201510507788.X).
Surgery
All knees were operated through a standard midline incision and a medial parapatellar arthrotomy, using a cruciateretaining prosthesis(Smith & Nephew Legion,LINK and AKMEDICAL).
GB Group PSI were used to perform resection of the proximal tibia and femur distal. Anterior dislocated the tibia and to place the line device to make sure again that the osteotomy plane of the tibia is perpendicular to the anatomical axis of the tibia. It is critical to remove all osteophytes before releasing the soft tissue, including posterior femoral and tibial osteophytes. Then released the soft tissue to achieve a symmetrical extension gap. Distal femoral and proximal tibial cuts are measured by the balancer device (Figure 1) so that the cut surfaces are parallel. No soft tissue release after this step. Subsequently, the knee is brought into 90°flexion, balancer device is introduced and tensed to make sure the medial and lateral balance is equal,then mark a line on the bone parallel to the pole in the balancer device. Appropriate 4-in-1 resection block post parallel to the line mark before, and the block is utilized to perform anterior, posterior, and chamfer bone cuts. Measuring and recording the lateral and medial gap by the calibrations on the balancer device.
MR Group After adequate exposure of the knee, an extramedullary guide was used to perform resection of the proximal tibia and femur distal. Femur is drilled in order to introduce internal femoral alignment rod into the intramedullary canal, followed by distal cutting block with preset parameters. Posterior referencing cutting block is utilized to identify the potential component size. And then an appropriate 4-in-1 resection block is utilized to perform anterior, posterior, and chamfer bone cuts. Previously decided trial sizes and polyethylene are introduced and the knee is evaluated for tracking stability in the AP and Varus and valgus planes for balance.
The processing for tibial plateau, patella and patellar tracking of both GB and MR group is consistent with traditional surgeries.
Statistical analysis
Data were stored and analyzed with use of SPSS 24.0 software (SPSS INC., Chicago, IL, USA). Demographic data were presented as mean±standard deviation(SD).The categorical variables were compared with a chi-square or Fisher’s exact tests. Differences and correlations of p<0.05 were considered statistically significant.