Femur Fractures

section epub:type=”chapter” role=”doc-chapter”>

Femur Fractures

Ian Gordon Holsworth

15.1 Introduction

Fracture of the femur in companion animals is common, often involves high force impact and is complicated by the extensive muscular envelope that surrounds the bone. The combination of traumatic hemorrhage at the fracture site and along the muscular planes, swelling and edema of the associated soft tissues, contraction of the muscular surround, fracture site displacement, and a propensity for the hip and stifle joint to lose their rotational alignment makes successful fracture repair challenging. The restoration of linear and rotational alignment of the femur along with the need to have a stable repair construct has lent the femoral fracture to bone plate repair. The evolution of plate design and capabilities has seen the locking plate (LP) become a staple of femoral fracture repair over the past 15 years. The ability to affix the bone screws securely to the bone plate and the fracture segments has, in the author’s opinion, improved the strength and durability of the fracture repair construct and decreased implant and therefore construct failure. The relative strength of the LP in comparison to the more traditional dynamic compression plate (DCP) with or without the addition of an intramedullary (IM) rod has also been investigated experimentally to determine the relative biomechanical qualities of the different construct types. A more recent trend in the orthopedic surgical field is away from the classic open reduction and internal fixation (ORIF) toward biological osteosynthesis and the development of minimally invasive plate osteosynthesis (MIPO) with a limited surgical approach and reduced iatrogenic trauma. This approach hopes to preserve bone vascularity, improve fracture consolidation, decrease infection rate and avoid the need for bone grafting and transforms the plate construct into an internal extramedullary splint. The MIPO treatment goal is the anatomic reconstruction of the articular area, if involved, and axis, rotation and length reestablishment for the metaphyseal‐diaphyseal area. The placement of a plate that bridges the fracture site and is only affixed to the femur proximally and distally with a limited number of bone screws is the underlying technical guideline. The establishment of sufficient fracture site stability with a degree of relative instability with MIPO is in contrast to the more traditional anatomic reduction and rigid fixation by bone plates with the goal of the technique being absolute fracture stability. The challenge of the MIPO technique is the decreased operative visualization of the fracture segments, the adjustment of the surgeon to less open visual cues to anatomic restoration and the need in many cases for intraoperative fluoroscopic examination. The term minimally invasive percutaneous plate osteosynthesis (MIPPO) is used to describe the use of small, multiple surgical skin incisions and the development of skin “windows” to access the bone surface. The plates are placed blindly up the bone shaft under the muscular layer to lie adjacent but not compressing the periosteum. In cases of concurrent articular fracture, the use of a transarticular approach and retrograde plate osteosynthesis (TARPO) is utilized to expose the articular surface by arthrotomy, reduce the articular fracture anatomically and implant the epiphysis area sufficiently to provide rigid stability to the articular fracture repair. The adjacent metaphyseal‐diaphyseal zone is then stabilized under MIPO guidelines.

Internal fixators can be expected to maintain but not obtain fracture reduction, so care must be taken to ensure adequate fracture reduction before insertion of the locked screws. The challenge to the trauma surgeon of reestablishing the length, axis and rotation of displaced femoral fractures during minimally invasive techniques is an ongoing area of both intraoperative imaging and surgical technique refinement.

15.2 Anatomy

In the normal dolichocephalic and mesocephalic dog, the femoral shaft in the diaphyseal region has a slight caudal curve in the sagittal plane and a slight medial curve in the frontal/coronal plane at the distal diaphyseal‐metaphyseal junction. The measurement of the anatomic and mechanical angles of the femur and pelvic limb has been performed and documented by several authors for several different dog breeds [14].

The relative location of the femoral head in comparison to the frontal plan of the femoral condyles is very important in terms of restoration of the femoral alignment of the femur during fracture repair. The measurement of this angle has been investigated with multiple imaging modalities and there is large variation between individuals [510].

The tendency of the femoral head and neck’s sagittal axis to rotate into a significantly increased anteverted location in relationship to the distal femur postfracture must be recognized and addressed during the realignment phase of femoral fracture repair. Failure to do so can lead to permanent femoral deformity and the resultant stability and biomechanics of the hip joint may be compromised. If adversely affected to a significant degree there is a propensity for hip luxation and development of hip joint osteoarthritis.

The use of computer tomography and three dimensional modeling has further allowed assessment and quantification of the other morphometric parameters of the canine femur which has improved both our understanding of the bone geometry present and subsequently our efforts to restore the patients femoral alignment to prefracture conformation [11].

15.3 Biomechanics

Under load, the medial cortical wall of the femoral diaphysis is the compression aspect of the bone, the lateral aspect the tension aspect. The proximal femur has a complex biomechanical loading pattern due to the offset femoral head. The femoral neck is under a complex interplay of both compressive and tension forces during normal daily activity. Neutralization of these forces to allow progressive bone healing is the surgical goal. Fracture configuration, including the degree of comminution, will affect the choice of surgical implant and its placement location. Accepting the limitations and challenges of the individual fracture and devising an appropriate response is the surgical challenge. Placement of the bone plate on the lateral, tension aspect, is commonly performed although medial aspect plating, while far less common, can also be used if the fracture configuration favors it, LPs are used or there is significant lateral thigh skin abrasions or open trauma to the thigh.

15.4 Materials

The advent of LPs in their myriad of forms from a range of manufacturers gives individual surgeons options to choose. Experimental comparison between standard limited‐contact dynamic compression plates (LC‐DCP) and LP plates mechanically has not shown the LP to be superior biomechanically in most aspects of testing, but the LP also did not underperform in a consistently significant way [1217]. Personal experience with many LP types has been very positive personally and they have become first choice and invaluable in the author’s clinical practice. Individual surgeons are faced with choosing an implant type based on availability and personal preference. There are inherent differences in mechanical strength between different LP types, which are to be expected and accepted by the surgeon [18, 19].

The lack of plate compression to the bone appears to affect construct stiffness adversely in some biomechanical models with a suggestion that ideally the LP be placed at 2 mm or less from the bone surface [20]. To adhere to this guideline in the femur, contouring of the plate may be necessary in both the proximal and distal aspects of the bone shaft. The degree of LP contouring possible by the surgeon intra‐operatively varies between designs. Overcontouring without protection of the threaded plate holes can lead to distortion of the plate hole threads with a resultant inability to correctly lock the threaded screwheads into the plate. The presence of combination compression or locking holes in some LP designs with half of the hole a dynamic compression design for use with standard screws and the other half conical and threaded allows the surgeon to chose the appropriate screw for the current repair.

The addition of an IM rod to the femoral bone and plate construct to increase construct stability and fatigue life is an approach that has been used widely with traditional and now locking plating systems to good effect [21]. Biomechanical comparison in a femoral fracture model of a LC‐DCP‐IM rod to a LP alone showed the LC‐DCP‐IM construct had higher stiffness and resistance to failure, lower inter‐fragmentary motion and lower plate strain and stress. A pin of any size increases resistance to axial loads, but a pin size of 30% or more of intra‐medullary diameter is required to increase bending stiffness. Plate length changes do affect stiffness, but the presence of an IM pin has more overall construct strength significance [22, 23]. When comparison of a combined LP intramedullary pin (LP‐IM) construct is made to the LC‐DCP‐IM construct experimentally in canine femurs, there was no significant difference biomechanically [24].

Only gold members can continue reading. Log In or Register to continue

Jun 13, 2021 | Posted by in SUGERY, ORTHOPEDICS & ANESTHESIA | Comments Off on Femur Fractures
Premium Wordpress Themes by UFO Themes