A retrospective cohort study on prevalence of postoperative complications in comminuted patellar fractures: comparisons among stabilized with Cannulated-Screw, Kirschner-Wire, or Ring-Pin Tension Bands

For comminuted patella fractures fixation ,RPTB fixation is superior to CSTB fixation and MKTB in lowering the failure rate and it hardware removal respectively.

Complex three-dimensional forces, including bending, tensile, and compressive forces, are exerted on the patella as the fracture heals. This set of forces can lead to implant failure or loosening with continued patella-femoral motion [19]. As a result, significant rates of fixation failures in the face of early rehabilitation protocols are widely observed [16, 20‐22]. For transverse and stellate fractures, previous studies demonstrated that fracture fixations using CSTB or MKTB have comparable failure rates [12, 13]. Laboratory biomechanical studies even show that the CSTB method has advantages over the MKTB method in fixation of transverse patellar fractures [5, 23, 24]. Notably, in clinical studies, comminuted fractures are more frequently encountered than transverse and stellate fractures. AO Type 34-3C was the most common patella fracture type,representing 2% of all fractures [25]. Most biomechanical studies have used the transverse osteotomy model instead of models that more realistically mimic comminuted fractures, limiting their clinical relevance. In our hospital, the selection of MKTB, CSTB, or RPTB fixation method is based on the treating surgeon’s preference because there is no consensus on and reliable evidence for the optimal treatment of C3 patellar fractures. To the best of our knowledge, our results reported here represent the first evidence from a large clinical study for the superiority of the RPTB over CSTB and MKTB method for fixation of comminuted patellar fractures.

Hoshino et al. observed a trend toward fewer fixation failures with the use of MKTB compared to CSTB for nearly half of the fractures classified as C3 fractures [16]. They concluded that the trend toward more fixation failures in the CSTB group might have met statistical significance if more patients were available for study. In the present study, we focused on evaluating the three different tension-band techniques in treatment of comminuted patellar fractures. Our results partially confirm the trend reported by Hoshino et al. [16]. In the present study, failure rate significantly increased with CSTB fixation of comminuted fractures compared with use of MKTB and RPTB methods.

With CSTB fixation, primary pressure is achieved by the two cannulated lag screws, [26] which are supplemented with a titanium cable; this bolsters the fixation through the cannulated screws. Unlike cannulated screws, ring pin and K-wires do not exert compression forces on the fragments directly. Instead, the compression effects on the patella are mainly generated by tightening the wires or cables [27]. In addition, the flexibility of K-wires and ring pins is another important difference compared with cannulated screws. Again, further biomechanical studies on comminuted fracture models are urgently needed in order to clearly elucidate the mechanism underlying our observations. Finally, some authors have found that the appropriate insertion of cannulated screws is technically difficult, because screws that are too short provide inadequate fixation, while screws that are too long may abrade the cable, causing to its to break prematurely [28]. Regardless of the mechanism, however, our results suggest that orthopedic surgeons should choose RPTB fixation over CSTB fixation for comminuted patellar fractures, since we observed that CSTB fixation contributed to a 2.08-times greater risk of fixation failure compared with RPTB.

Symptomatic implant irritation is the most commonly observed complication following fixation of a patellar fracture. Although symptomatic implant irritation is not a serious complication, it does require a second surgery, which increases the overall cost and brings additional burden to the healthcare system and patient. Most inserted K-wires used in TBCs tend to protrude and loosen, especially after migration. This leads to more soft-tissue irritation than that caused by cannulated screws and ring pins. Ring pins are designed to prevent postoperative migration by locking the pin with a cable through the ring. In the present study, symptomatic implants in RPTB fixations occurred at a similar rate postoperatively as that in CSTB fixations (using low-profile cannulated screws). Given that postoperative complications, like skin breakdown and infections, were indistinguishable among the groups, taken together, we conclude that RPTB fixation is superior to CSTB fixation in lowering the failure rate and it also has advantages over MKTB in hardware removal.

We recognize several strengths and limitations of our study. It’s a large cohort and which involves more than 300 samples, while limitations still exist. First, a number of different orthopedic surgeons treated the patients in the study, probably differing some in skill level. Patients also underwent slightly different rehabilitation programs as a result of different treating physicians. This could have affected study outcomes, particularly fixation failure rate. Second, the allocation of patients to MKTB, CSTB, or RPTB fixation groups was not random, given the observational nature of this study. Different surgeons had different preferences for the three techniques. Although we adjusted each outcome for possible confounding variables through use of multivariate regression, there may still have been other related factors we did not consider. Third, because it is a retrospective study, the lack of clinical information such as ROM(Range of motion)and extensor function is a limitation. Finally, there’s no generally accepted definition of symptomatic hardware. The implant removal could be suggested when the patient feel comfortable and is unable to bear it. But the final decision may vary slightly according to the endurance of different patients. Taken together, the finding of the advantages of RPTB fixation should be further confirmed in randomized trials.