Transverse fractures of the patella are the most common type of patellar fracture . In a cadaveric biomechanical study, Carpenter et al.  analyzed the stability of transverse patellar fractures fixed with three different techniques: modified tension bands, two parallel interfragmentary lag screws, and two cannulated lag screws with a tension band wire through the cannulations. The authors reported significantly better stability after fixation with cannulated screws and a tension band wire. Therefore, this technique was regarded as the “gold standard” for treating non-comminuted transverse patellar fractures. However, Hoshino et al. found that 30 out of 133 (22.6%) patients who received surgical treatment of transverse patellar fractures with metallic tension bands through double cannulated lag screws had to undergo secondary surgery to remove the device due to device irritation or wound infection . In China, Buddhism is the most popular religion . For Buddhists, the daily religious ritual of kneeling makes device irritation intolerable and results in a strong desire for device removal. The results of a systematic review conducted by Camarda et al. in 2016 indicated that fixation of patellar fractures with non-metallic devices is associated with a lower secondary surgery rate (1.6%) for device removal. Gosal et al.  fixed 16 patellar fractures with non-absorbable polyester sutures in accordance with the modified Pyrford technique and reported one fixation failure (6.3%). Similarly, Egol et al.  fixed patellar fractures in a Krackow-type fashion with non-absorbable sutures and reported an initial failure rate of 7.6%. Therefore, increasing the strength of the low-profile construct of sutures seems essential for treating patellar fractures and achieving satisfactory clinical outcomes as well as lower rates of complications and secondary surgeries.
In the current study, transverse patellar fractures were surgically treated with two cannulated screws plus the modified Pyrford technique with polyester sutures. No cases of post-operative failure of fixation or secondary displacement of fractures were observed. In the biomechanical study conducted by Carpenter et al. , the load to failure of transverse patellar fractures after fixation with screws only was lower than that after screws with a tension band; though, the difference was not significant (p = 0.06). Due to the better stability of transverse patellar fractures compared with comminuted patellar fractures, Gwinner et al.  reported that screw fixation without a tension band can be considered for such fracture types, although the strength of this technique is lower than the strength of cannulated screws with metallic tension band wire. Given the high stiffness and minimal tissue reaction to polyester sutures, Qi et al. fixed patellar fractures with polyester suture tension bands through two cannulated screws and reported a mean Lysholm score of 95.7[19–21]. In their study, Qi et al.  found no failure of fixation, secondary displacement, infection, or device migration or breakage. Similarly, Busel et al.  conducted a retrospective case series analysis in 2019 and found that the secondary surgery rate for device removal after fixation with non-absorbable sutures through cannulated lag screws was 8%; all device removals were due to hardware irritations. However, Kumar et al.  reported that the tension band technique with non-absorbable polyester sutures through cannulated lag screws was difficult, and even impossible to perform for small-diameter screw cannulation. The thickness of the needle required to hold the suture and the thickness of the folded suture when passing the cannulated screws were usually too large for screw cannulation. As an alternative to polyester suture tension bands through cannulated screws, a variety of fixation techniques using non-absorbable polyester sutures have been introduced for treating patellar fractures; these techniques provide sufficient stability for early rehabilitation after surgery[11, 24–27]. Until now, there was no consensus as to the best fixation technique with non-absorbable sutures for the treatment of patellar fractures. Camarda et al.  fixed patellar fractures with FiberWire following the Pyrford technique and reported a high rate of ‘excellent’ Bostman scores (76.4%) and an absence of failure of fixation. However, 11.8% of patients experienced secondary displacement of fractures . Furthermore, this study defined secondary displacement as a fracture gap less than 4 mm, which might be larger than the indication for surgery (gap > 3 mm) in the current study. In the biomechanical study conducted by Burvant et al. , the displacement rate of fractures fixed with screws plus the Pyrford techniques was dramatically smaller than the displacement rate of fractures fixed with the Pyrford technique only. Therefore, the superiority of the combined technique in this study over the modified Pyrford technique may be due to the more stable fixation.
In terms of the Bostman scores and gradings, our findings are consistent with those after fixation with cannulated screws and metallic tension bands as reported by Tan et al.  and with those after fixation with the modified Pyrford technique as reported by Camarda et al . The ROM in the current study was comparable, though somewhat smaller, than the ROM reported in previous studies that used tension band fixation with suture materials[11, 21, 30]. This is perhaps due to the concern of less stable fixation without metallic wires and the subsequent individual rehabilitation. In the current study, the post-operative infection rate was 3.8%, which is consistent with the post-operative infection rate of 3.6% after metallic tension band wire fixation for patellar fractures reported by Hoshino et al. However, the infection in the current study was resolved by oral antibiotics and no further surgery was required. In the clinical study conducted by Hoshino et al. , 43.8% of the infections required intravenous antibiotics administration or further surgical interference.
The relatively small sample size is the main limitation of this study. Thus, there is a need for treatment of more cases with the combined technique in order to improve the reliability of the research. Because of the absence of inclusion criteria in this case series study, the fixation technique decision for each patient was made by the surgeons, resulting in selection bias. Further, the nature of a case series study means that this study lacked a control group and may not be as reliable as a case-control study. This study may have also been affected by recall biases. Therefore, the conclusions of this study should be confirmed by a prospective randomized controlled study in the future.