The may not be related to a recent trauma.4

The goal of modern orthopedic is to obtain the anatomical union of fracture and give a good functional return of the patient. To obtain this, it requires rigid internal fixation by using an appropriate implant. The success of internal fixation depends on multiple factors. Implant failure often lengthens the healing process, leads to re-fractures and increase the cost for the patients. It often requires additional complicated surgeries. This shows the importance of exploring causes of implant failure.1

Implant failure can result from faulty implants or external factors such as surgeons experience and adherence to AO principles, improper type of implant for particular fracture type and non-compliance of the patients with post-operative instructions, particularly weight bearing in lower limbs surgery.2, 3 Patients with implant failure usually present with pain and deformity of the operated limb. It may or may not be related to a recent trauma.4

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Revision surgery is always challenging to an orthopedic surgeon because the tissues are scared and removal of broken implants are always difficult. Also, there is a high chance of neurovascular injury and post-operative infection.5, 6 Few studies have demonstrated that quality of implant as the main cause of implant failure.7, 8 Other studies have shown that early weight bearing may be the cause of early implant failure.9

In our study, we have focused on mechanical and biological causes i.e., the pattern of fracture, proper used of the implant, adherence to AO trauma surgery principles and post-operative weight bearing. We are of the opinion that combination of two or more than two of these causes leads to early implant failure. Hence this study was designed.

The purpose of this study was to identify a possible cause of implant failure, which is being used in our setup for fixation of different fractures. The intent of this research was to determine the reasons for implant failures and prevent the failures.

 

Materials and Methods

The study was conducted at the Orthopaedic unit of Green Pastures Hospital, Pokhara and United Mission Hospital, Tansen and from Jan to Dec 2017.  Twelve patients were included in the study. The inclusion criteria were all patients of both genders, who presented to our unit with complaints of pain, deformity or inability to bear weight after fixation of the fracture of either limb. The patient with pathological fractures, radiological osteoporotic bones, recent significant trauma and infected implants were excluded.

Thorough histories were taken from the entire patient. Necessary investigations including physical examinations and radiographic studies were performed. During the preliminary examination, patients were asked for correct postoperative activities including, time of the beginning of a range of motion and weight bearing. The patients were also asked about the possible history of recent trauma and smoking history. The possibility of infection was also determined. The clinical, radiological and biochemical evaluation was done for evidence of infection.

Pre and postoperative x rays were studied for the pattern of fracture and proper use of implant and adherence to AO trauma surgery principles. For dynamic compression plate (DCP) upper limb (Humerus) surgery at least 6-8 cortices should be engaged above and below the fracture, in lower limbs, 8 cortices above and below should be engaged with appropriate screw size. In intramedullary nailing maximum possible reaming should be done so that most part of the nail is in contact with bone. Pollar screws are indicated while nailing for proximal and distal end fractures of long bone. At least 3 cannulated screws should be used for fixation of a femoral neck fracture. Recent x-rays were studied for the level of implant failure, screws failure, non-union or malunion and for planning retrieval of broken implants. In revision surgeries, appropriateness of implants, signs of corrosion, erosion or any welding of implants and any signs of infection were also assessed. In ten cases bone grafting was done.

 

Results

Out of the 12 patients with implant failure, 8 were male and 4 female with mean age of 33 (range 12 to 60 years). Distribution of these failed implants is shown in (Table 1).

 

Table 1: Distribution of implant failure (n=12)

 

Name of implants

No. of failures

Plate

8

Screw

1

Nail

2

K-wire

1

Total

12

 

All the failed implants were broadly classified into 4 groups. There were 8(66%) failed DCP implants. Failed intramedullary nails were 2(16%). Both cases were of proximal tibia fracture. In both cases, simply nailing was done without good reduction and without a pollar screw. In one case proximal interlocking screw was broken. The proximal broken part was actually a welded area, which failed under stress. In revision surgery, lag screws with neutralization plate (DCP) and bone graft were used. So instability was the causes of implant failure.

There was 1(8.3%) failed cannulated screws (for the neck of femur fracture fixation). There was one case of K-wire breakage. It was used for clavicle fracture in a young patient.

In all cases, the union was achieved in 4 months (range 3 to 6 months) and they were able to perform activities of daily living. Average follow up was 6.7 months (range, 6 weeks to 11 months.) No signs of corrosion or erosion were found during revision surgery.

 

Discussion

Orthopedic implants are being used for last hundred years.10 Mechanical failure of implants falls into 3 categories, plastic, brittle and fatigue failure. In plastic failure, the implant fails to maintain its original shape resulting in a clinical failure. The defect in design or metallurgy causes brittle failure. Fatigue failure occurs as a result of repetitive loading on an implant. There is always a race between fatigue of the implant and fracture healing. Therefore, this should be realized by the operative surgeon while inserting an implant. Interference in periosteal blood supply leads to plate failure. The reason for brittle and plastic failure includes minor loads in small plates and secondary major trauma in large plates.11, 12

Fatigue failure is the most common cause of plate failure. Poor surgical technique and improper application of plate are other causes of plate failure. If fracture fails to unite then fatigue failure of the plate is evitable.13 An intramedullary nail provides relative stability for long bone fracture as well as a good biological environment for bone healing. It also allows early mobilization of the limb and functional recovery. However, nail fails due to fatigue of the implant due to cyclical loading.14 Unstable fracture configuration, the distal location of the fracture and small diameter of the nail or instability can lead to early fatigue failure.15 Delayed union or non-union of the fracture and rotational instability at the fracture site in unlocked nail due to rotation of fracture fragments are the other causes of failure.16

Different studies have been done on implant failure and on the chemical composition of the implants. Different techniques were used to determine the cause of implant failure and implant quality in each study.4, 9, 17-20 To assess the chemical composition of the failed implant is not feasible in our current set up.

In a study by Sharma4, the most common reason for failure was a traumatic event before complete healing of the fracture. In that study, plate failures were more common than nail failures in lower limb long bone fractures. There was one (2.4%) implant failure associated with deep infection that led to revision surgery and removal of the implant. Barbosa9 in the study of three cases of implant failure concluded that surgical and design errors were the cause of implant failure. In the study by Azevedo18 in Brazil showed that the most of the implants did not meet ISO standards. Such type of laboratory test is not possible in our setup. Vallier21 et al. reported medial comminution as the main cause of implant failure with use of the locking compression plate (LCP) condylar plate fixation of the distal femoral fracture.

The surgical technique and fracture pattern are the important factors in determining the success of the implant. We found that combination of causes like implant selection, fracture pattern, quality of fixation and post-operative care (protective weight bearing) as the cause of implant failure in our study. Inappropriate surgery and inadequate screw cortices above and below fracture were the main cause of plate failure. Most of the plate failed at or near fracture site. Inappropriate choice of implant, violation of principles in surgery and early weight bearing was the causes of nail failure. The reason for K-wire failure was inappropriate implant choice for the fracture pattern, which was used for a clavicle fracture. There were two chronic smokers. This may be the cause of non-union leading to implant failure.

As a rule, one should not violate the well-defined surgical principles while treating any surgical patient. The treatment is completed only when the patent is rehabilitated to the normal life. And clear instruction must be given to the patient regarding postoperative weight bearing. One of the limitations of this study was a small number of samples and there was no statistical significance. In spite of the limitations as a retrospective one, it has highlighted the improper selection of implants and violation of principles as risk factors for implant failure.

 

Summary

Our study shows that plate failure is more common than other implants failure. The most important causes of implant failure are a selection of the implant, type of fracture, surgical techniques, and post-operative care. Apart from these, another important aspect is not following the techniques of the application according to recommended principles of fracture fixation. In all cases, fracture union was achieved with proper implant selection and proper procedure considering fracture pattern and bone involved.