**2. Pathomechanics of distal femoral fractures**

The most frequent mechanical complication of distal femoral fractures (DFF) is nonunion, reported in up to 19% of patients [3, 4]. Along with nonunion, varus collapse and hardware failure come together. This continues to occur despite advances in fracture fixation implants for this injury, reflecting the need for better understanding of different factors that influence the outcome. Modern implants include those advocated by the AO Foundation decades ago, such as the 95 degree blade-plate and the Dynamic Condylar Screw (DCS) [5–8]. Such devices are seldom used nowadays for acute fracture treatment. Being made of stainless steel, they provided strong fixation and resistance to fatigue, improving dramatically the quality of fixation and ultimately the results. However, their inherent stiffness was still a cause for atrophic nonunions (**Figure 1**). Advances in the knowledge of concepts such as stress and strain highlighted the importance of the mechanical environment in the process of bone healing [9–11]. Application of these concepts by the surgeon is the basis for the construction of biomechanically sound osteosynthesis, in which highly rigid constructs are being replaced by others allowing controlled micromotion, and subsequent stimulus for callus formation.

In more recent years, both anatomical, locked plates (LP), and retrograde interlocking intramedullary nails (RIMN) became the standard for operative management [4, 12]. Both types of fixation show similar rates of bone healing and functional outcome, despite dissimilarities. In some studies, intramedullary devices perform better than plates in terms of axial stiffness, whilst in others side plates were superior [13, 14]. Nonetheless, both methods are also associated with a high

#### **Figure 1.**

*Extraarticular distal femoral fracture, treated with a short Dynamic Condylar Screw (DCS). At follow up, nounion and failure in varus occurred. Metaphyseal comminution and a short side plate and working length are considerations to be taken into account to explain the result.*

### *Management of Distal Femoral Fractures DOI: http://dx.doi.org/10.5772/intechopen.110692*

incidence of mechanical failures [4, 15–18]. Although having improved mechanical capabilities compared to previous implants, improper use, or unawareness of the importance of the balance between rigidity, stability and bone healing promotion, can lead to failure (**Figure 2**) [19].

Numerous in vitro reports have been published in recent years, showing improved mechanical capabilities with fixation techniques that combine lateral locking plates and medially placed additional plates, as well as the combination of lateral locking plates and locked intramedullary retrograde nails ("augmented RIMN") [20–25]. These studies report a significant increase in resistance to axial, rotational and bending forces, along with increased stiffness of such constructs, which has led to their application for clinical use, in pursuit of minimizing complications derived from implant failure. Several mechanical stress studies, as well as clinical studies, focus on fractures with bone defects and/or comminution, including fractures in osteoporotic patients, because they have high risk for failure. Ricci et al. published an analysis of the factors that may influence failure of fixation in distal femoral fractures, treated with laterally placed locked plates [26]. Various types of fractures were included: 64%

#### **Figure 2.**

*(a) A3 closed fracture in a 50 year-old patient, treated with anatomical locking plate. AP x-ray at follow up shows atrophic nonunion. Selection of the length of the plate, together with the distribution of screws, may have played a role in the outcome. (b) Same fracture pattern in a 44 year-old patient, with more extended working length and less screw density. Uneventful consolidation has occurred after 6 months.*

of 335 fractures were simple metaphyseal (A1 and A2), or simple articular (C1 or C2). They found that there were factors out of reach from the surgeon, such as severity of the injury (high energy, open fractures), young age (with more severe injuries), comorbidities such as diabetes, and smoking. Plate length, on the other hand, was also a contributing factor: shorter plates were associated with failures more frequently than long plates. The surgeon must therefore balance what is inherent to the fracture and the patient, with the available implants, elaborating a strategy that will ultimately lead to a construct design capable of minimizing the risk of failure.

In our opinion, DFF differ in the pathomechanical analysis that can be made whether they are simple extraarticular, comminuted extraarticular, or intraarticular, as well as if present in young or older (osteopenic) patients. Older patients with poor

#### **Figure 3.**

*Distal extraarticular fracture in a 75 year old patient with concomitant severe ipsilateral hip arthritis and rigidity. Despite absence of comminution, fixation was done with RIMN, augmented with a locking plate. This was decided in consideration of the age of the patient, and the incresed torsional stresses that the construct will withstand throughout the healing process, due to hip stifness.*

#### *Management of Distal Femoral Fractures DOI: http://dx.doi.org/10.5772/intechopen.110692*

bone quality present inherent difficulties in obtaining stable internal fixation. There is data underlying the difficulties to accomplish "limited" weight-bearing in patients of advanced age, so it should be assumed that patients of a certain age will submit the construct to high forces from the early postoperative period [27, 28]. These considerations have decisive influence on the selection of the operative method.

Of note is the fact that advances in implant stability and rigidity may also present concerns about delayed healing. There is the need to balance the overall strength/ stiffness of the construct and the appropriate micromotion that promotes callus formation. With patients of advanced age, however, the benefits of construct stability and endurance may outweigh the achievement of fracture healing, at least initially [28–31]. Postoperative compliance with controlled or "limited" weight bearing is very difficult to achieve in geriatric patients, as mentioned above. Therefore, implant stability and strength is of primary importance (**Figure 3**). These considerations do not apply, nonetheless, in the young patient with similar fractures. In this setting, promotion of bone healing is paramount for long term success and functional restoration. Therefore, careful and judicious application of any fixation method or technique should balance the maintenance of proper reduction while favoring bone healing, the latter by the means of providing a mechanical environment with adequate strain.

As aforementioned, a sound mechanical construct should take into consideration the quality of bone, the general status and age of the patient, and also the type of fracture. We consider it appropriate to analyze distal femoral fractures broadly distinguishing between those with and without articular involvement. Articular involvement has requirements for adequate fixation that differ from extraarticular fractures, whether comminuted or not. Anatomic articular reduction and rigid fixation is a principle that remains unchanged since first advocated by the AO [32]. This requires the use of individual screws for fragment fixation and articular restoration, which is most often followed by implantation of plates and/or intramedullary nails to unite the articular segment to the diaphysis. Within these two main categories, management decisions can be

#### **Figure 4.**

*Flowchart as a proposal for the management of distal femoral fractures. DFR: distal femoral replacement.*

made when we include other components in the analysis (those inherent to the fracture and the patient) pertinent to the treatment plan. This could work as an algorithm for proper selection of surgical approach, implants and design of the construct (**Figure 4**).
