Severely comminuted femoral fractures (Proceedings)

Severe fractures of the femur can be divided into those fractures which must be reconstructed directly and those that can (and should) be reconstructed indirectly. The former include both intra-articular and periarticular fractures of the femoral head and femoral condyles, and diaphysis in the latter.

Comminuted diaphyseal femoral fractures

Despite their initial outward appearance, these fractures are very straight-forward to address. The basic principle is bridging fixation whereby there is sufficient bone stock available at either bone end to purchase the implants, thus providing the requisite stability across the fractures for bone healing. These fractures can be handled with any number of fixation devices: IM pin and external skeletal fixator (ESF), interlocking nail (IN), bridging plate (spanning, standard or locking plate), bridging plate/rod (standard or locking), orthogonal or opposite double plate (standard or locking).

IM pin /ESF

In this fixation, the IM pin bridges the fracture and is of sufficient size to neutralize the bending forces at the fracture (pin size approximately ≥ 2/3 of the medullary canal diameter). The IM pin acts to bring the fracture back out to length and simultaneously re-establish axial alignment. Because of the nature of the comminuted fracture, there is no provision for maintaining length (collapse of the fracture can occur along the pin), nor is there neutralization of rotation. In addition, because the IM pin does not fill the entire medullary cavity at the level of the fracture there is no neutralization of shear forces. The addition of an ESF satisfactorily address all of these forces; however, a minimum of a 4-pin ESF is necessary with 2 pins in each major bone fragment on either side of the comminution. The ESF can be applied as a Type-1a or 1b device. The advantage of the latter is additional strength to the fixation, but at the cost of placing additional fixation pins; furthermore, none of these pins are in the frontal plane, thus they penetrate more soft-tissue as compared to a Type 1a ESF applied parallel to the frontal plane. In the femur, another issue is the position of the connecting bar relative to the distance of the fixation pin insertion into the bone; this length is large due to the anatomic configuration of the abundant soft-tissues present (quadriceps and biceps femoris mm.). This increased length also will decrease the strength of the fixation. One method to overcome some of these strength issues is to use a "tie-in" configuration of the IM pin with the ESF, where the proximal extent of the IM pin is left long and incorporated into the ESF.

The largest disadvantage an ESF is the amount of soft-tissue penetration of the fixation pins through the musculature of the femur, and issues with the pin/soft-tissue interface. Large wounds are not uncommon around the fixation pin(s) despite attempting to place them in areas of minimal soft-tissue coverage over the bone. This is especially true in high motion areas, such as the lateral side of the stifle (distal femur) and proximally with an IM pin that exits to be incorporated into the ESF. The result is development of a large open granulating wound around these pins. More problematic, however, is the degree of patient discomfort from these pins. They also inhibit adequate physical therapy and function; therefore, they can retard or prevent full functional outcomes.

Interlocking nail

The IM pin (or nail) again bridges the fracture and is of sufficient size to neutralize the bending forces at the fracture (nail size 80% of the medullary canal diameter). The IM nail acts to bring the fracture back out to length and simultaneously re-establish axial alignment. In this case, screws or bolts are applied through the bone and nail in order to provide the requisite neutralization of both compressive and rotational forces. Because of the generally bigger nail diameter (compared to an IM pin) and the purchase of the nail at both bone ends, there is improved neutralization of shear forces. The screws or bolts, however, do not purchase the nail, but simply pass through it resulting in some rotational movement – termed "slack". The bolts have a smaller tolerance than the screws; therefore, there is less rotational motion of each fragment compared to screws. This is generally not a problem with highly comminuted fractures )low strain). A new IM nail is underdevelopment (BioMedtrix) that eliminates this issue.

The limitation with this technique is the limited number of nails available (length and width) to match the myriad of femoral bone dimensions of the various breeds of small animals. In addition, the fracture must be sufficiently diaphyseal so that the holes in the nails are not within the fracture line. For this reason, nails are designed for placing 1 or 2 bolts in either end, whereby only a single hole is present in the end to increase the working distance of the nail. The remaining problem is the occasional difficulty encountered in placing the bolt through the nail in the distal femur. Because of the long length of the aiming device, there is less overall rigidly in the alignment with nail in the bone. Intraoperative imaging eliminates this issue. Nail holes too close to the fracture site, or screws used in lieu of bolts have resulted in implant failure prior to healing.

Bridging plate

The area of comminution simply is bridged with a plate. A standard plate (e.g., DCP) is prone to failure at the level of the screw-holes due to the stress-riser located at this level. With the development of the LC-DCP design, this problem was minimized due to the uniform plate stiffness obtained, which eliminates the stress-riser over an empty screw hole. However, overall plate rigidity remains unsatisfactory. Alternatively, a spanning plate with a solid mid-section of plate (no holes) can be used to bridge the area of comminution. With the advent of locking plates, this fixed angle construct has been used to span an area of comminution with improved security at the screw-bone interface. However, there remains the limitation to overall plate strength, which is unchanged compared to a standard plate (e.g., no difference in bending strength and stiffness between an LC-DCP and LCP).

Bridging plate/rod

The addition of an IM pin to a bridging plate increases the strength of the overall fixation provided, and the plate type no longer is a limiting factor. Any stress-risers due to open screw holes are eliminated by the addition of the IM pin in conjunction with the plate. It has been demonstrated that pin size directly affects the overall strength of this fixation. However, using a large diameter IM pin interferes with subsequent screw fixation of the plate to the bone; therefore, a compromise to the IM pin size is made. Despite this compromise, it has been shown that the addition of the IM pin provides significantly greater construct stability than a plate alone. An IM pin that occupies 40% the diameter of the marrow cavity reduces the stress on the plate by ≥ 50%; more importantly, this extends the fatigue life of the plate at least 10-fold. Importantly, it also was demonstrated that an IM pin of too small a diameter was not effective. An IM pin that occupied only 25% of the IM canal, for example, only reduced the stress in the plate by a factor of 10%; therefore, appropriate pin size is critical.

Recently, with the advent of fixed angler constructs (locking plates) there has been some decreased use of this technique, re: addition of the IM pin. This is due to two issues: one is the misconception that the overall strength of locking fixation is improved over standard plates (see comment above), and the greater difficulty of placing fixed angled screws into the bone with an IM pin already in place. Locking screws are larger in diameter than standard screws, and also do not allow angulation to miss the IM pin. There is no large advantage to using a locking construct unless there is limited bone purchase to a short fragment end in which a limited number of screws can be applied.

This method of plate/rod fixation is the most commonly used and successful method of bridging comminuted diaphyseal femoral fractures.

Multiple plate fixation

This is not a popular method of fixation for the reasons of increased complexity, additional expense and cost to the biology. In the past it was thought that this form of fixation resulted in osteoporosis of the bone due to stress protection, and therefore was not used – this despite the excellent stability provided. The idea of mechanical stress protection has, however, been shown not to be the issue, but that of interference with the bone's vascular supply as a result of compressing a standard plate to the bone surface. With the advent of locking plate fixation, this problem is circumvented to a degree depending upon the configuration of the plate design employed. All locking plates tout a preservation of the blood supply under the plate; however, depending upon the plate configuration and the method of application, the blood supply may be compromised to a lesser or greater degree. In some instances, locking plate fixation is no different from standard plate fixation in preserving the vascularity.

Periarticular femoral fracture

All of the previously described methods of fixation can be employed in periarticular fractures; however, the limitation involves the ability to adequately obtain sufficient implant purchase in the short distal metaphyseal bone fragment. The ESF devices continue to be limited by the soft-tissue interference, their relative lack of stability compared to plate fixation, and the soft-tissue consequences of less than ideal patient comfort and function due to the penetration of the soft-tissues. The interlocking nail is limited by the length of the remaining metaphyseal bone fragment so as to anchor a bolt through the nail in an intact short bone fragment. The bridging plate has all of the previous limitations described, but in addition, a limited purchase of screws in a shortened bone fragment. The addition of an IM pin as a plate/rod construct can overcome this deficiency, but is limited by the pin purchase also obtained in a short metaphyseal bone segment. This deficit can be overcome by placing >1 pin into the bone, generally by cross-pining the short fragment by inserting pins from the joint surface (distal femoral condylar pins started laterally just cranial to the origin of the long digital extensor tendon and the mirror position medially). Such pins are of smaller diameter and will not interfere with subsequent screw placement. A limitation, however, is if <3 screws can be placed due to a short bone fragment.

Distal femoral metaphysis/epiphysis (supracondylar fracture)

In cases where a very short bone fragment (supracondylar fracture) is present, multiple plates – or specially designed plates, are useful to obtain greater screw purchase. There are, however, a limited number of specialty plates available in veterinary surgery. In this area, multiple plate fixation can aid in the fixation. With standard plates at this level, two plates applied (one medial and one lateral) may be difficult to place screws such that there is no interference with the opposite plate (re: penetration of the trans cortex with bicortical screws). It is here where the locking plates provide their utility – either as a single of double plate due to the ability to secure fixation into a short segment of bone with a minimum of 2 screws and the ability to use monocortical screw fixation.

Proximal metaphysis/epiphysis (subtrochanteric fracture)

Despite the short length of fracture fragments at this level, this is not a particularly difficult problem to gain adequate bone purchase for either standard or locking screws. The plate can be contoured over the greater trochanter in order to obtain greater coverage and thus a greater number of screws to purchase the bone. Contouring the plate in this area can be simplified by also contouring the bone (with a high speed bur) whereby any acute bony contours are eliminated to facilitate plate contouring. It must be recognized, however, that the addition of screws in the trochanter is of limited benefit as they purchase only the trochanter. A significant advantage to obtain excellent bone purchase at this level, though, is the dense bone at the calcar (area of the lesser trochanter), which is the bony reinforcement at the level of attachment of the femoral neck. Two screws are sufficient to gain excellent stable fixation at this level: one screw is directed into the femoral neck proximally (it is important to recognize the anatomy whereby this screw must be started sufficiently distal to purchase the neck throughout its length), and the second screw, placed just proximal to the femoral neck screw, is directed transversely (or even distally) – bypassing the neck screw – to the calcar. Certainly, a 2nd orthogonal plate at this level (usually applied cranially can significantly add to the strength of the fixation.

Femoral neck fracture

Multiple small pins (K-wires) or screws must be placed within the femoral neck. Once again, it is imperative to be familiar with the anatomic position of the neck in relationship to the femoral shaft – such that these implants traverse the neck. Anatomic reduction of this fracture is imperative due to the large forces generated at this level. Any degree of motion with a less than perfect reduction will lead to micromotion and a nonunion – and ultimate implant failure. In cases where there are bone defects present due to the high degree of comminution – especially at the base of the femoral neck – a cranially applied orthogonal plate can adequately buttress the defect; once again, the locking plates have an advantage when limited number of screws can be applied.

Intra-articular femoral fracture

The basic orthopedic premise of precise anatomic reconstruction of the joint surface must be followed. The surgical approach must be atraumatic and the exposure must be extensive so that all components of the injury can be visualized and become fully accessible to manipulation and fixation (this point is stressed, re: a "more than adequate" exposure). For the head of the femur this includes taking down the vastus lateralis so as to visualize the neck and head simultaneously. Distally, a simple surgical approach is to perform an osteotomy of the tibial tuberosity so as to reflect the quadriceps m. proximally, thus obtaining an unobstructed view of the entire distal femur.

The surgical reconstruction begins with anatomical reconstruction of the articular surface, with elevation of any depressed portions from any impacted fragments. All these fragments initially are held in position with Kirschner wires (K-wires: small diameter pins of 0.8-mm – 1.5-mm). Any remaining defects subsequently are grafted with bi-cortical or tri-cortical grafts vs. compacted autogenous cancellous grafts. Finally, secure fixation of the articular components is obtained with IFC. The metaphyseal and diaphyseal components of the fracture also must be carefully reduced; the metaphysis is buttressed to prevent axial overload, and the diaphysis must be securely fixed to the articular component. The latter is an often overlooked aspect of the fixation. As noted previously, the locking plates may have an advantage in helping to rigidly secure these short fragments to the diaphysis, especially if multiple plates are used. Such rigid fixation thereby allows initiation of early postoperative motion.

Postoperative physical therapy

It is absolutely imperative that postoperative physical therapy (PT) be employed in order to regain limb function. Many of these fractures have considerable damage to the soft tissues – the high energy fracture creation is also energy absorbed by the soft-tissues – and the result is significant damage to the regenerative ability of the extraosseous blood supply – the most important aspect of early fracture healing. Intraoperative placement of closed suction drains help to carry excessive buildup of fluid (blood, lymphatic) away from the area. Cold application and intermittent compression also will aid in the removal of fluid and decrease the postoperative swelling, as well as early motion. All of these factors are intended to obtain an ambulatory, functional status at the earliest opportunity – and can only be obtained with sufficiently stable and secure fixation.

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