Clinical analysis of an anchor nail combined with a titanium cable in the treatment of lower patella fractures.

OBJECTIVE: This study was performed to evaluate the clinical effect of an anchor nail and titanium cable for lower patella fractures and identify an effective treatment.
METHODS: Thirty-five patients with lower patella fractures were treated using anchor nail and titanium cable technology. The anchor was fixed to the main part of the patella; the lower patella was then fixed. A bone tunnel was created, and the titanium cable was fixed. The fracture was allowed to heal without tension. Postoperative radiographs were obtained at regular follow-up evaluations. The Böstman function scores were used to assess postoperative complications.
RESULTS: All patients were followed for an average of 15 months. The fracture healing time ranged from 12 to 24 weeks. The postoperative Böstman function scores were as follows: average, 28.6 points; excellent and good scores in 28 and 7 patients, respectively (100% rate of excellent and good scores). At 6 and 12 months postoperatively, the maximum degree of active extension of the affected knee joint was comparable with that of the healthy contralateral joint.
CONCLUSION: The combination of an anchor nail and titanium cable for lower patella fractures is simple and clinically satisfactory, restores knee function well, and is a worthy orthopedic method.

Introduction

The lower one-fourth of the patella without a cartilage surface is referred to as the lower patella, and it is approximately 15 mm in length. The lower patella is associated with a special type of patella fracture (extra-articular fracture). The OTA type is 34A1, and this fracture accounts for 5% of all patella fractures.[1] An important part of the knee extension device involves transmission of the quadriceps muscle strength to the tibial tuberosity, which is essential for completing flexion and extension of the lower extremities. In the present study, patients with patella fractures were treated with anchor-and-protection titanium cable technology from January 2017 to July 2018. The purpose of this study was to evaluate a simple and effective method for clinical treatment of such fractures.

Materials and methods

General information

The inclusion criteria were X-ray or computed tomography examination establishing the diagnosis of lower patella non-pathologic fractures, fractures without knee joint dysfunction prior to injury, unilateral tibial fractures without other fractures, and willingness to cooperate with follow-up evaluations and recommendations.

The exclusion criteria were bilateral tibiofibular fractures, pathologic fractures, severe medical problems affecting knee function, combination with other fractures, and unwillingness or inability to cooperate with follow-up evaluations and recommendations.The surgical methods and research content of this study were approved by the hospital ethics committee, and all patients provided written informed consent.

Surgical method

After establishment of anesthesia, the patient was placed on the operating table in the supine position. An approximately 8-cm-long median incision was made to the patella nodule. The patellar ligament and upper part of the tibial tuberosity were exposed, and the fracture end and joint cavity were completely cleaned. Two to three anchors were fixed to the proximal part of the patella, and the anchors were then inserted through the distal fracture block. After completion of the reduction, the anchor line was knotted in the lower part of the patella. Four Krackow sutures were drilled, and one Herbert nail was drilled from the inside and outside of the tibial tuberosity. The Herbert nail tunnel was drilled in the proximal part of the patella with a 2.0-mm Kirschner wire parallel to the tibial tuberosity.

Postoperative treatment

Postoperative infection prophylaxis was administered for 1 day, and all patients’ legs were fixed with a knee brace. Knee flexion exercises were performed at 30° in the first week after surgery, at 60° in the second week, and at 90° in the third week with regular follow-up.

Evaluation indicators

The patients’ radiographs were reviewed with regard to the following aspects postoperatively and at the follow-up evaluations: anchor removal, disconnection of the lower end of the patella, fracture healing, breakage of the titanium cable, knee joint pain, and postoperative function of the patella. The fractures were assessed 6 months after surgery. The function scores of the affected limbs were evaluated as follows: excellent, 28 to 30 points; good, 20 to 27 points; and poor, <20 points. The maximum degree of active knee flexion and extension of the bilateral knee joints was recorded 6 and 12 months after surgery.

Statistical analysis

The data of the two groups were analyzed using SPSS 17.0 statistical software (SPSS Inc., Chicago, IL, USA). The results are expressed as mean ± standard deviation. The data of the two groups were compared using the t-test and chi-squared test. Differences were considered statistically significant at P < 0.05.

Results

This study included 35 patients with lower patella fractures (21 men, 14 women; age range, 19–68 years; average age, 42 years). The fractures were present on the left side in 17 patients and on the right side in 18. The causes of injury were falls in 24 patients and car accidents in 11. The time from injury to surgery ranged from 2 to 5 days.

All patients were followed up for an average of 15 months (range, 9–18 months). The fracture healing time ranged from 12 to 24 weeks, and no patients developed anchor withdrawal, fracture disconnection, titanium cable fracture, knee extension weakness, grade V quadriceps muscle strength, or knee pain. The postoperative Böstman function scores of the tibial fractures 6 months after surgery were as follows: the average score was 28.6 points, and 28 and 7 patients had excellent and good scores, respectively (100% rate of excellent and good scores). The knee joints were stable postoperatively. At 6 and 12 months postoperatively, the maximum degree of active extension of the affected knee joint was −1.8° ± 2.1° to −2.0° ± 1.6° and was comparable with that of the healthy contralateral joint (−1.4° ± 1.2° to −1.2° ± 1.0°). There was no statistically significant difference between the two groups (Table 1). The maximum degree of active knee flexion (128° ± 4.2° to 129° ± 5.3°) was higher than that in the healthy contralateral joint (132° ± 3.8° to 130° ± 3.4°) at 6 and 12 months postoperatively. There was no statistically significant difference between the two joints (Table 2). Specifically, we paid much more attention to a male patient aged 39 years old. We performed the comminuted fracture of the right lower tibia. The preoperative X-ray film indicated the right knee fracture (Figure 1a). The CT scan and 3D reconstruction image demonstrated the present treatment on the right knee fracture (Figure 1b and 1c). After intra-operative anchor and titanium cable fixation (Figure 1d), X-ray was performed to measure the effects of fracture treatment (Figure 1e). Three and six months later, the results of X-ray showed the amazing therapeutic effects (Figure 1f to 1i). In summary, these results told us that the treatment principles fitted well with the health condition of this patient.

Table 1.

Maximum degree of active knee extension of both knees 6 and 12 months postoperatively.

Group (number of cases)	6 months	12 months	t value	P value
Healthy limb (n = 35)	−1.4° ± 1.2°	−1.2° ± 1.0°	1.862	>0.05
Injured limb (n = 35)	−1.8° ± 2.1°	−2.0° ± 1.6°	2.128	>0.05
t value	2.374	2.048
P value	>0.05	>0.05

Table 2.

Maximum degree of active knee flexion of both knees 6 and 12 months postoperatively.

Group (number of cases)	6 months	12 months	t value	P value
Healthy limb (n = 35)	132° ± 3.8°	130° ± 3.4°	3.741	>0.05
Injured limb (n = 35)	128° ± 4.2°	129° ± 5.3°	3.446	>0.05
t value	2.984	3.219
P value	>0.05	>0.05

Patient, male, 39 years old, comminuted fracture of the right lower tibia. a pre-operative X-ray film. bc. pre-operative right knee CT scan and three-dimensional reconstruction image. d. intra-operative anchor, titanium cable fixation. e. x-ray of the patient after the operation. fg. X-ray 3 and 6 months after the operation.

Discussion

Fracture characteristics and treatment principles

The lower one-fourth surface of the patella contains no cartilage and is approximately 15 mm in length. Fractures of this portion of the patella are extra-articular fractures.[2] The lower patella has important anatomic significance in that it contains cancellous bone, anterior cortical bone and an infraorbital vascular ring, and the patellar ligament attachment point constitutes the knee extension device. Lower pole fractures may occur during knee joint flexion or strong quadriceps traction. Obvious swelling develops after fracture because of the presence of the infraorbital vascular network. The patellofemoral ligament breaks, and the knee extension device is destroyed. Traumatic arthritis of the patellofemoral joint can also occur.[3] The principles of treatment of lower patella fractures are preservation of the length of the patella, restoration of the knee extension device and biomechanics, assurance of effective and reliable internal fixation to avoid loss of reset, performance of early knee joint function exercises, avoidance of joint stiffness, and prevention of traumatic arthritis.[4]

Fracture treatment methods

Two treatment methods are available for lower patella fractures: retaining the length of the tibia and shortening the length of the tibia. The advantage of the former treatment method is that bone–bone healing occurs, which restores the integrity of the knee extension device and biomechanics.[5-7] The disadvantage of the latter treatment method is that the patellar ligament moves up and the patellofemoral joint surface is “faulty.” Long-term biomechanical changes can cause traumatic arthritis. In addition, healing occurs by bone scarring, and the bone strength is poor.[8]

Tension band fixation is a classic treatment

The Kirschner wire tension band transforms the surface tension of the tibia into compressive stress, pressurizes the fracture end, and promotes fracture healing. It is a classic tension band fixation technique but is generally used for lower jaw fractures. Because the lower pole is small and comminuted, the tension band cannot be firmly fixed. The bone readily slips off after exercising, making the fixation invalid. Some scholars have recommended changing the fixation method to a cannulated nail tension band to achieve better therapeutic results. Zhang et al.[9] described the treatment outcomes of 139 cases of lower patella fractures with four methods. The results showed that the cannulated nail tension band had the best fixation effect and most effectively restored knee function. Sun et al.[10] used a new modified technique to treat 21 cases of lower patella fractures with a hollow nail combined with a gasket and achieved a good therapeutic effect. However, Hoshino et al.[11] analyzed the postoperative complications of 448 patients with lower patella fractures treated with Kirschner wires and cannulated screws. The results showed that the fracture reduction rate was 3.5% and 7.5%, respectively, most of which involved comminuted fractures. Caution should be exercised for comminuted lower patella fractures.

Nickel-titanium-polyfluorene, adjustable jawbone, basket mesh, and wire and cable internal fixation

Several surgical methods are suitable for treatment of lower patella fractures (i.e., nickel-titanium-polyfluorene, adjustable jawbone, basket mesh, and wire and cable internal fixation), but they are limited to single or transverse fractures of the patella. Maintenance of reduction and firm fixation is difficult for comminuted fractures of the lower pole.

Anchor technology

Lower patella fractures are often accompanied by patellofemoral ligament rupture. Treatment using the anchor technique not only reconstructs the patellar ligament but also restores the fracture end.[12] A wire anchor is currently used to replace the tendon mechanics in rotator cuff injury and joint ligament reconstruction.[13] This technique is characterized by minimal trauma and excellent outcomes.[14] Zhang and Tang[15] reported 11 cases of lower patella fractures that were treated with anchor nails. The results were excellent in nine cases and good in two cases. These results were satisfactory, and there was no need for secondary removal. However, the fixation strength of the simple anchor was weaker. Gypsum assists fixation, often secondary to stiffness of the knee joint.

In the present study, the combined anchor and titanium cable technique for the treatment of lower patella fractures not only restored the biomechanics of the patellar ligament but also transmitted the force through the titanium cable, and the fracture end was healed without tension, achieving a better therapeutic effect. The anchor did not withdraw, the fracture did not break again, no titanium cable was broken, knee extension was not weak, and the quadriceps muscle strength was grade V. No patients developed knee pain, and the knee flexion and extension activity was not different from that of the healthy contralateral joint. The reasons for these findings are as follows. First, an anchor nail is a special titanium alloy suture material that has strong resistance to pull-out and allows for easy reconstruction of ligaments or the tendon fulcrum. Anchor nails have strong histocompatibility and no need for secondary surgery after the first operation. The load-carrying capacity of the line is relatively large, and the stretchability is strong (2.5 times that of ordinary suture).[15-17] Second, the titanium cable has strong flexibility and large tensile strength. The trans-patellar ligament is fixed on the tibial tuberosity and the tibia; this can cause the knee joint stress to be short-circuited, greatly reducing the stress on the lower part of the patella. Third, the titanium cable should be locked and fixed when the knee is bent at 90°. At this time, the knee extension force is transmitted to the tibial tuberosity through the tibia and the titanium cable so that the lower patella achieves bone–bone healing in a tension-free environment; this also provides early protection of the knee joint. At the same time, the quadriceps and patella tendon ligaments reached the highest point of the patella. In the present study, the postoperative knee joint was in a relaxed state regardless of the flexion and extension of the ligament, which protected the lower patella from pulling and causing a re-avulsion fracture. Fourth, the surgeon must protect the patellar fat pad during surgery because the underarm ring is located here, thus reducing blood damage. Fifth, the normal distance between the lower patella and the tibial tuberosity should be restored to ensure biomechanical stability, and the ligament needs to be sutured with Krackow knots. Finally, the tibial tuberosity bone tunnel is replaced with Herbert nails to avoid a fracture caused by the titanium cable, thus cutting the tibial tuberosity.

In summary, the anchor and titanium cable technique for the treatment of lower patella fractures can achieve good fracture reduction and strong fixation, reconstruct the patella ligament, restore the quadriceps muscle, and restore the integrity of knee extension. The stress of the lower part of the patella is borne by the titanium cable, which can create a static environment for fracture healing and avoid cracking of the fracture end and the device, ensuring biomechanical stability. There is no need for postoperative plaster fixation, which is more conducive to early functional exercise of the knee joint. Complications such as knee joint stiffness and adhesion are reduced, and the curative effect is good. However, this study was limited by several factors. The sample size was relatively small, the follow-up time was short, the long-term effects and possible complications were not fully evaluated, whether the titanium cable was irritating to the patella ligament was unclear, and no control group was established. The relationship between this technology and other methods of fixation cannot be clarified, and the lack of biomechanical evaluation requires further exploration.