The clinical outcome of the reduction of the patellar inferior pole fracture with wire cerclage through a generated bone hole, in combination with patellar concentrator: a retrospective comparative study

Patella is the largest sesamoid bone in the human body, the inferior pole of which connects to the patellar ligament. Patellar fractures account for 1% of total body fractures, whereas inferior pole fractures account for 9.3–22.4% of patellar fractures [1]. The inferior patellar pole fracture is typically comminuted, with low bone mass, thereby making it is difficult to fix [2, 3]. Generally, upon fracture, the knee extension device is destroyed, which results in limited knee joint movement. As a result, surgical intervention is required.

At present, two major surgical procedures are available for the correction of inferior pole fractures. The first method removes the comminuted inferior pole of the patella and reconstructs the insertion point of the patellar ligament via a suture anchor or drilling hole. But this method often leads to bone defect, high tension within the patellar ligament, dislocation of the patella femoral joint, and so on [4]. Therefore, most scholars prefer an alternative method of correction, which utilizes patellar concentrator, steel wire, Kirschner wire, basket plate, and other materials to reduce and fix the fracture of the inferior pole of the patella [1, 3, 5‐9]. There are multiple fixation methods, each with its unique advantages and disadvantages. However, there are certain common complications that need to be resolved. For example, internal fixation loosening, internal fixation cutting, difficult fixation of the comminuted bone mass, symptomatic implants, and so on [10, 11].

Although the anchor suture technique can be used to repair the inferior patellar fracture, it often requires auxiliary external fixation and early rehabilitation to be effective [3, 7, 8]. In addition, compared with Kirschner wire tension band technology, non-metallic fixation technology has the same clinical effect [12, 13], but a long-hinged knee brace was required for 3 weeks after operation [14]. Kirschner wire tension band is a common method of fixing patellar fractures. However, in comminuted fractures of the lower pole of the patella, this may lead to further displacement of the fracture, particularly, while inserting the Kirschner wires from the inferior pole. Compared to the Kirschner wire tension band, patellar concentrator has less symptomatic implants. Therefore, patellar concentrator can be effectively used to fix patellar inferior pole fracture, whilst permitting early rehabilitation, with a low incidence of post-operative complications [10]. In other works, scholars reported that separate vertical wiring can be used to fix the inferior patellar fracture. However, this may lead to wire cutting, particularly, in elderly patients with osteoporosis, which may lead to fixation failure [15]. Several scholars also used the percutaneous cerclage technique to reduce and fix the lower patellar pole fractures, with good outcomes, however, one case experienced wire slippage [16].

Based on the above findings, we employed the technique of wire cerclage through a generated bone hole to reset the inferior patellar pole fracture, and combine this technique with the patellar concentrator in the experimental group, whereas the control group only received patellar concentrator. The purpose of this study was to retrospectively analyze the surgery-related indexes and clinical outcomes of the two afore-mentioned fixation methods. Our hypothesis was that, compared to the patellar concentrator only technique, the wire cerclage through a generated bone hole, along with the patellar concentrator, will achieve a more satisfactory fracture reduction and produce a more enhanced clinical outcome.

The inferior patellar pole fracture is often comminuted, and the small bone mass is difficult to fix. Fortunately, the comminuted bone block connects to the patellar ligament, so it can be reduced via anchor suture technology [3, 7, 8]. However, the suture is elastic and requires additional protection via external fixation after operation. Additionally, there is a great risk in early exercise. Hence, to ensure early exercise after patellar fracture surgery, one must follow the principle of tension band fixation, which states that during exercise the muscle contraction converts tension to power of axial compression. The Kirschner wire tension band fixation technique achieves excellent outcomes in the treatment of patellar fractures, however, patients often complain of implant discomfort [17]. Therefore, some scholars use the screw tension band fixation method instead [15]. However, it is not easy to implant the Kirschner wire or screw into the patella in appropriate positions [18]. This, in turn, aggravates the displacement of the patellar inferior pole fracture. Fortunately, using the patellar concentrator abrogates the need to drill holes in the patella, which avoids the problem of fracture displacement caused by Kirschner wire or screw implantation. In addition, the design of the patellar concentrator conforms to the principle of the tension band, which places continuous pressure on the fracture end [19]. Hence, the patellar concentrator possesses advantages of both simple operation and early functional exercise, and is suitable for various types of patellar fractures [5, 10]. However, our results revealed that the patellar concentrator alone produces poor reduction of the inferior patellar pole fracture. Lateral comminuted fractures were earlier shown to be difficult to fix with patellar concentrator alone [20], so multiple C-arm fluoroscopies are needed to ensure proper reduction. In addition, repeated reduction may negatively affect blood supply to the fracture site and thereby prolong healing time.

At present, the reported wire cerclage fixation is commonly used as an auxiliary fixation procedure for other types of fracture fixation [21]. In a prior report, an author successfully used percutaneous steel wire cerclage fixation technique to reduce and fix an inferior patellar pole fracture [16]. Moreover, another scholar employed modified cerclage wiring to correct comminuted patellar fracture, with satisfactory results [20]. Given these evidences, it was likely that the steel wire cerclage method can be used for reducing and fixing patellar fractures. Since the traditional wire cerclage method involves the steel wire passing under the quadriceps tendon and encompassing the patella, the wire can easily slip and cause fixation failure [16]. To avoid steel wire sliding and unstable fixation, we generated a bone hole for the wire to provide a fixed fulcrum. In addition, we employed the suture method to guide the patellar wire cerclage, which made it easy to operate and saved operation time. Compared to the control group, the experimental group had comparable operation time and intra-operative blood loss, and conducted relatively less C-arm fluoroscopies to confirm proper fixation. Additionally, unlike single wire cerclage, the multiple vertical wire cerclage provided ample strength to protect the knee joint from early exercises [15]. Furthermore, separate vertical wiring combined with the Krackow suture [6] or combined with rim-plate [22] was reported to provide secure fixation and favorable clinical outcomes. However, in the process of penetrating vertical wires, the risk of fracture displacement cannot be avoided. Moreover, although plates are often used for reduction and fixation of comminuted fractures, plates placed at the starting point of the patellar ligament can cause significant discomfort [9]. Particularly, in elderly patients with osteoporosis, fixation failure may be caused by wire cutting problems [15]. Therefore, after wire cerclage reduction, we used patellar concentrator fixation to protect the knee joint from early exercise damage. This not only prevented fracture displacement caused by perforating Kirschner wire or screw at the patella fracture, but also significantly reduced stress cutting caused by the direct contact of the patellar concentrator with patella. Good reduction and firm fixation are the premise of early rehabilitation exercise [1, 23]. Based on our analysis, the initial range of motion of our experimental group was markedly enhanced, compared to the control group.

Based on earlier reports, the normal range of InsallSalvati ratio is 0.8–1.2, and less than 0.8 represents patella baja [24]. The degree of patellar fracture reduction may affect the longest diagonal of the patella, and, therefore, the InsallSalvati ratio. In a previous report, suture bridge anchorage decreased the InsallSalvati ratio, with no patella-femoral pain and limited range of motion [3]. In our study, the InsallSalvati ratio was within normal range after operation in both the control and experimental groups. However, the InsallSalvati ratio was slightly higher and closer to the normal value in the experimental group. The Bostman score is commonly used to evaluate the clinical efficacy of patellar fracture fixations. In a study that treated patellar inferior pole fracture with a mini-plate usage and tension band, the average Bostman score was 28.1 at the 1 year follow up post operation [1]. Additionally, in a study comparing a Novel Tension Band and Patellotibial Tubercle Cerclage, the average Bostman scores were 28.5 and 25.8, respectively [23]. In our study, the average Bostman score of the experimental group was 27.44 and 28.75 at the 6-and 12-month follow ups, respectively.

We encountered certain limitations in our study, namely, limited case numbers and short follow-up duration. Hence, more cases from multiple trauma centers and results from long-term follow up are needed to verify our conclusions. In the future, we plan to use this reduction technique for other types of patellar fractures.

Patellar inferior pole fracture can be easily reset with a simple wire cerclage through a generated bone hole. However, special caution is necessary to avoid stripping excess soft tissue around the fracture to prevent comminuted bone block displacement and augment difficulty of reduction. Compared to the patellar concentrator alone, the procedure of steel wire cerclage combined with patellar concentrator achieves a more satisfactory reduction of the patellar inferior pole fracture, with reliable fixation, early functional exercise, and fast fracture healing.