Design of the guide device
The device was designed by solidworks2012 software (USA). The design process turned to professional engineers, which could meet the functional requirements of the design and fit for industrial production. Two U-shaped arms of the device constitute the main structure through the cross bar c. Sleeves a and b are both divided into inner and outer doubled layer sleeves, while the outer sleeve is fixed on the main structure of the device and the inner sleeve can slide onto the outer sleeve. The centerline of Two U-shaped arms is controlled by the main structure of the device. The plane of the bottom of the tray e is parallel to the plane of the centerline of sleeves a and b, and both bar c and rod d have rulers. The tray e touches the front surface of the patella, and the distance between the plane of K-wires and the front surface of the patella is adjusted by sliding rod d. The distance between sleeves a and b is adjusted by the cross bar c.
Clinical study
This study protocol was approved by our hospital Ethics Committee. This retrospective study reviewed patients with patellar fractures who underwent MTBW surgical treatment from June 2014 to August 2018. The inclusion criteria are shown as follows: (1) transverse fractures with or without a single additional fragment; (2) 18 to 65 years without previous knee surgery; (3) the articular displacement is greater than 2 mm or fragment separation is greater than 3 mm on radiography; (4) C1 and C2 type with consideration to AO classification; (5) MTBW with or without a navigation device; (6) follow-up at least a 12-month. The exclusion criteria: (1) associated with a fracture of the distal femur or tibial plateau; (2) previous knee diseases such as osteoarthritis. According to these criteria, 112 patients were included in the study. The patients were divided into C-MTBW and P-MTBW according to the surgical technique with or without the precise navigation device. There were 58 patients treated with the C-MTBW method and 54 patients treated with P-MTBW by the precise navigation device. We needed to record and analyze the operation time and the number of fluoroscopy, postoperative internal fixation imaging, function and complications.
All patients underwent the standard MTBW technique. Approach and reduction techniques depend on the standard technique according to the AO principle, while the difference was that the P-MTBW group uses a self-designed precise navigation device to guide the K-wires. Adjusting the device parameters according to the width and thickness of patella measured before surgery. The distance of K-wires was set at one third of the widest diameter of the patella, and the level of the K-wires was set according to the thickness of the outer third of the patella. After setting the parameters of device, K-wire was implanted through the sleeve.
Postoperative management and evaluation
For all patients, an elastic bandage was used for 48 hours after surgery for reducing swelling. Isometric quadriceps exercise and straight leg raises were started when pain had subsided. The knee joint was protected by the knee adjustable brace that allows 60° of motion after surgery,90°of motion after two week and no restriction after four weeks. Postoperative follow-ups were arranged for one and two weeks, 1, 2, 3, 6 and 12 months, and the amount duration was longer than one year. Common complications included incision infection, failure of internal fixation, fracture displacement and K-wire irritation. After one year of surgery, the knee function was evaluated according to the Iowa knee score criteria.
Postoperative imaging usually was used to evaluate the reduction of the fracture, which ignored the assessment of the internal fixation position. We believe it is necessary to establish a standard evaluation strategy for K-wires of MTBW technique. All patients should have standard x-rays of the knee on two planes after surgery. An AP viewing and a lateral view are evaluated according to the angle between the K-wires. The angle is measured by two senior doctors respectively. If the error is within 2°, the average value is taken. If the error exceeds 2°, we seek help from the third doctor. If the angle at both views is less than 5°, it is defined as excellent; If the angle at one view is between 5° and 15 °, it is defined as good; If the angle at both views is between 5° and 15 °, it is defined as fair; If the angle at any view is more than 15 °, it's bad.
Data were presented as mean±SD for continuous variables and the number of categorical variables. To compare two groups, there was a two-sample t test used for continuous variables, Pearson Chi-square tested for categorical variables and Wilcoxon rank sum tested for ordinal categorical variables. The differences were presented as mean (95%CI) for continuous variables and odds ratio (95% CI) for categorical variables. The significance level was set at 0.05 for all the tests, and data was entered and analyzed with SPSS21.0 statistical software (SPSS Inc, Chicago, IL, USA).