Outcome of Transverse Patella Fractures Fixed With Cannulated Screws and Stainless Steel Tension Band Wiring

Background: Tension band supplemented by K-wires has long been the denitive technique for patellar fractures xation. However, it is not without drawbacks. The stainless streel cable-cannulated screw tension band technique, may shorten healing time, decrease the complications and provide early range of knee motion. Herein, the current study evaluates the clinical and radiological outcome of this surgical modality. Methods: This prospective study was conducted on 21 patients (13 males and 8 females) with transverse fracture patella from June 2017 to April 2021. The surgical xation consisted of two 4.0-mm parallel partially threaded cannulated cancellous screws with a gure-of-eight stainless steel tension band wiring. Follow-up was at least 10 months. Assessment criteria included the Lysholm score for knee function, ROM, VAS for pain, fracture reduction, fracture healing time, and complication rates. After 3 postoperative weeks, slab was removed and immediate rehabilitation were commenced. Results: The average Lysholm scores were 82.9 ± 4.4 SD, 87.8 ± 5.3 SD, and 92.7 ± 3.6 SD after 3, 6, and 10 months, respectively. VAS scores for pain were 2.6 ± 3.0 SD, 1.4 ± 2.6 SD, and 0.5 ± 2.3 SD at 3, 6 and 10-month, respectively. The patients had gained total ROM after 3, 6 and 10 months. The mean fracture healing time was 2.1 months (range, 1.5 - 3.1 months). Two patients experienced skin irritation by wire tails. Conclusion: The stainless steel cannulated screws and tension band construct provides a good alternative in treatment of transverse patellar fractures. It could yield stable xation, low complication rate while providing early mobilization and accelerated rehabilitation.


Introduction
Patellar Fractures are severe injuries that comprise about 1% of all skeletal fractures and are common within the age group of 20-50 years [1]. Transverse fractures, are the commonest type and usually happen through indirect trauma [2].
Selecting the ideal modality for managing patellar fractures represents a serious task [3,4]. Fractures with displacement more than 2 mm or articular step off can be treated either closed or open with complementary xation. It has been globally accepted that fractures with less than 8 mm displacement are the only ones that are suitable to the closed reduction and xation techniques [5][6][7].
Tension band supplemented by longitudinal K-wires has long been the de nitive technique for xation of patella. However, it is not without drawbacks, such as bad reduction, loosening, and skin irritation [1,3]. So the stainless streel cable-cannulated screw tension band technique could be alternative xation method. Depending on the fact that the addition of the screws to the tension band technique provides compression throughout the ROM and by resisting the tensile loading force during terminal extension. This technique shortens the fracture healing time, decreases the complications and provides early range of knee motion [8,9], low rates of anterior knee irritation and implant failure [10].
Previously conducted biomechanical studies have revealed that the cancellous screws alone or in combination with tension band wiring provides stable xation as long as the fracture is well reduced with less than a 1-mm gap between the fracture fragments [7]. As such, Benjamin et al. have recommended screw xation for transverse patellar fractures in patients with adequate bone stock [11]. Similarly, studies by Dargel et al. and Carpenter et al. have demonstrated that, screw xation is more stable and rigid than the modi ed tension band wiring technique [12,13].
Herein, the current study evaluates the clinical and radiological outcome of the cannulated screws and tension band construct in xation of transverse patellar fractures. Furthermore, it assesses the described technique while providing early mobilization and accelerated rehabilitation.

Material And Methods
This prospective study was conducted on 25 patients with transverse fracture patella from June 2017 to April 2021. The last case was operated upon on May 2020. The surgical xation consisted of two 4.0-mm parallel partially threaded cannulated screws with a gure-of-eight tension band made using a 1.25-mm stainless steel wire. Four patients were lost to follow-up. So, we had reviewed 21 patients, with AO/OTA 34-C1 fractures in 15 patients and 34-C2 fractures in six. The study included 13 males and 8 females, aged 20 to 69 years (mean, 44 years). Follow-up was at least 10 months (range, 10-19-months).
Mechanism of injury included fall accidents (18 patients) and car accidents (3 patients). Operations were considered when the articular displacement was greater than 2 mm or fragment separation was greater than 3 mm on radiographs. The injury-operation interval was 1 to 8 days (mean, 2 days).
The inclusion criteria were (1) AO/OTA 34-C1 fractures, ie, patellar fractures primarily with a transverse fracture line; and (2) AO/OTA 34-C2 fractures, ie, transverse fractures with a single additional fragment created by a longitudinal fracture line. Assessment criteria included the Lysholm score for knee function, ROM, pain score using VAS, fracture reduction, fracture healing time, and complication rates.

Surgical technique
The operations were performed via an anterior longitudinal incision. Then routine dissection and reduction of the fracture were carried out. With a large towel clamp or Spanish clamp under intraoperative uoroscopy, we drilled two K-wires (2.0-mm diameter) in parallel from the lower to superior pole of the patella, with a 2-cm space and a 5-to 10-mm articular surface. The K-wires penetrated the superior cortex. The position of the K-wire was determined using intraoperative uoroscopy. One K-wire was rst replaced by guide pin. We drilled along the guide wire with a cannulated bit and, after measuring its depth, screwed a 4.0-mm stainless steel cannulated compression screw along the guide wire. The screw head remained proud of the patella cortex, and the proximal end of the screw should be close to, or embedded within the patella. We then screwed in the second cannulated screw and alternately tightened the screws. We removed the guide wire and threaded a 1.3-mm-diameter stainless steel cable through each of the cannulated screws. We then tightened the cable anterior to the patella to form the tension band, xed the cable with cable clamps, and cut off the excessive cable ( Fig. 1).

Postoperative protocol
Patients were put in a high above knee slab for 3 weeks with quadriceps femoris exercises soon after the operation, but without weight bearing. After 3 weeks slab was removed, and passive joint exion and extension exercises were commenced. Then, active joint exion and extension exercises were started 3 days later. Five weeks after the operation, patients were permitted to perform partial-weight bearing walking, and conventional radiographs were obtained, including lateral and AP patellar radiographs.
Seven weeks postoperative, patients were permitted to perform full ambulation. Patients were reexamined at 1, 2, 3, 6, and 10 months after the operation to observe the fracture healing.

Statistical analysis
Results were analyzed by SPSS® statistical software (SPSS Inc, Chicago, IL, USA). Logistic regression was used to determine whether age, gender, fracture type and injury mechanisms had an in uence on the postoperative general results, clinical improvement, implant evaluation and radiographic outcome. The impact of age, gender, fracture type, interval between injury and surgery, and health status on Lysholm scores and complications had been studied. The differences were considered to be statistically signi cant when p values were less than 0.05.

Follow-up
The mean follow-up was 13 months (range, 10-17 months). The patients were followed up as follows; at immediate postoperative hospital stay, weekly during rst postoperative month, every two weeks till the end of 3rd month, then every month till the last follow-up.

General results
The mean period between injury and operation was 16 hours (range, 5-72 hours). The mean operation time was 70 min (range, 45 to 100 min), the mean uoroscopy time was 0.5 min (range, 0.25 to 1 min), and the mean hospital stay was 2 days (range, 1 to 3 days). Tourniquet was applied during surgery, and no patient required blood transfusion postoperatively. No intraoperative complications had occurred.
The wounds had healed nicely in all patients at a mean time of 4 ± 2 SD weeks (range, 2-6 weeks). Moreover, there was improvement of symptoms and signs gradually during the regular follow-up. The knee pain, and oedema subsided gradually.

Radiological results
The mean fracture healing time was 2.1 months (range, 1.5 -3.1 months) with adequate fracture reduction. All fractures had healed well, and the mean postoperative fracture spacing of the articular surface was 0.3 mm (range, 0-2 mm).

Implants evaluation
Fixation with proper rigidity was accomplished and con rmed with image intensi er. The two partially threaded cannulated screws with the tension band used for xation were rigid enough throughout the bone union process in all patient, with no failure had occurred.

Complications
Complications rate was 2/21 (9.5 %). Two patients experienced skin irritation from wire tails, one of them required implant removal at 9 months postoperatively. There was no quadriceps atrophy, incomplete terminal extension of the knee, loss of xation, or patient dissatisfaction with overall knee function at nal follow-up.

Discussion
Furthermost patellar fractures are usually managed operatively. The tension band technique accompanied by longitudinal K-wires has always been the core way for xation of such injuries [1,3,4,8].
Numerous investigations have shown that the cancellous screws supplemented with tension band wiring yields constant xation so long as the fracture is properly reduced [7,15].
Cannulated screw tension band technique was applied for patellar fractures in some studies, in order to provide proper reduction, direct fracture compression and earlier ROM [1]. No loss of xation had occurred among their patients [1]. Similarly, no hardware loosening, nor loss of xation had been reported in the current study. The probability of cable-cannulated screw loosening is trivial owing to the dense cancellous bone of the patella and the fact that the distal end of the cannulated screw is threaded. In addition, the cable tightly attaches to the patellar surface to limit the separation of fracture fragments as a tension band technique [1].
In the present series, patients were put in a postoperative high above knee slab for 3 weeks, with quadriceps contraction exercises commenced soon after operation without weight bearing. After 3 weeks, slab was removed and immediate passive ROM were encouraged to decrease muscular atrophy and intra-articular adhesions. Besides, it may improve articular cartilage nourishment and fracture healing process.
Tian et al. permitted active joint exion and extension exercises 7 days after the operation. One month later, their patients were permitted to perform partial-weightbearing. Patients were permitted to perform full ambulation after 8 weeks [1].
Bhati et al. encouraged patients to perform isometric knee extension and straight leg elevation exercises. Partial weight-bearing was permitted up to suture removal. Knee exion was allowed to less than 45 degrees in the rst week and gradually increased to 90 degrees in the 2nd week. The patients were provided with an exercise chart [16].
Posner et al. patients were put in a 24-hour hinged knee brace which was locked at full extension. Immediate weight-bearing as tolerated with the brace was allowed. At 2-week postoperative visit, formal physical therapy including progressive and controlled active knee exion movements were commenced. At 8-week postoperative visit, full ROM and active knee exion was allowed [17].
Lin et al. didn't apply any external immobilizers to any of their patients. Patients performed quadriceps contraction exercises soon after the operation. Unrestricted passive ROM was started early postoperatively, depending on the patient's pain tolerance. Active ROM was encouraged by 3 weeks postoperatively, and full weight-bearing was started by 8 weeks in their study [7].
Skin irritation is the main complication of the K-wire tension band. In some studies, symptoms attributable to wire irritation necessitated removal in approximately 15% of the cases [18,19]. In our study two patients (9.5 %) experienced skin irritation generated by wire tails, and one of them required implant removal at 9 months postoperatively. With the cable-cannulated screw tension band technique, the tail of the cannulated screw tightly attaches at the superior or inferior pole of the patella, and the screw threads are not exposed to the patellar surface. Furthermore, the diameter of the cable is only 1.3 mm, and it closely attaches to the patellar surface after being tightened reducing the risk of skin irritation and postoperative activity discomfort [2].
An article reported that painful hardware was the most common complication which occurred in 30.1 % of patients, and tension band loosening and migration was the second major complication, seen in 11.5 % of patients [7]. Although symptomatic implant irritation is not a serious complication, but it delays rehabilitation and potentially leads to stiffness that may require a second intervention with additional hospitalization and cost [7].
According to Baydar et al. [20], cannulated screws are more resistant to distraction forces than the tension band techniques to manage patellar fractures. Additionally, the exibility of K-wires can neutralize a part of the force that should act on the fractured bone leading to reduced compressive forces on fracture site, unlike cannulated screws tension band xation [21,22].
A disadvantage of the screws tension band xation method includes its technical di culty [21]. For example, it has been noted that it can be di cult to place K-wires appropriately with a minimally invasive technique, and it may have a substantial learning curve [7].
Unfortunately, the current study had some limitations. First, the small number of patients. Second, the short duration of follow-up. Third, the lack of comparison to the traditional technique of tension band technique. A fourth limitation is the stainless steel material used in the study. Although it is cheaper, but it is weaker in comparison to titanium screws tension band system and interferes with MRI.

Conclusion
The stainless steel cannulated screws and tension band construct provides a good alternative in treatment of transverse patellar fractures. It could yield stable xation, proper reduction and fracture healing, low complication rate while providing early mobilization and accelerated rehabilitation. A randomized, controlled trial with a larger number and longer follow-up is recommended.