Minimally Invasive Osteosynthesis Techniques of the Femur

Key points

Clinical anatomy of the femur

The proximal end of the femur is composed of the nearly hemispherical femoral head, which caps the dorsocaudal and medial aspects of the femoral neck. The neck is about as long as the diameter of the femoral head, and is slightly compressed from cranial to caudal.¹ Femoral neck anteversion describes the cranial (anterior) projection of the femoral head and neck relative to the anatomic axis of the femur. The anteversion angle in normal dogs has been reported to be 12° to 40°, with a mean value

Methods of reduction

In multifragmentary metaphyseal and diaphyseal fractures, it is only essential to achieve functional reduction, which consists of restoration of length, mechanical and/or anatomic axis, and torsional alignment of the major bone segments that are attached to the joint surfaces. Precise anatomic reduction of each bone fragment is not necessary, and doing so may jeopardize the blood supply to these fragments and/or the main bone segments. Stabilization of the 2 major bone segments with relative

Techniques of indirect reduction for diaphyseal fractures of the femur

Indirect reduction of diaphyseal fractures is a demanding technique, because the fracture fragments are neither directly visualized nor manipulated. A clear understanding of normal anatomy is necessary for surgeons to accurately restore limb length, axis, and rotation. Various methods must be used to assess the accuracy of reduction. Preoperative, intraoperative, and/or postoperative comparison with the intact opposite limb is useful to establish the normal anatomic shape of the limb and

Interlocking nail

The interlocking nail is ideally suited to minimally invasive, percutaneous osteosynthesis, because it can be placed through small stab incisions. In addition, the large diameter fills a considerable amount of the medullary cavity; thus, the placement of the nail from the medullary cavity of one major segment into the other achieves good reduction. A nail can be placed normograde from proximal to distal, or normograde from distal to proximal. The latter requires an approach to the stifle joint,

External skeletal fixation

External skeletal fixation is well suited to provide distraction and temporary stabilization during implant (typically bone plate) placement. Because of the overlying muscle mass of the femur and the associated morbidity with long-term application of fixation pins, external skeletal fixation is not typically the first choice of definitive fixation for most femoral fractures. In select cases, particularly metaphyseal or diaphyseal fractures in feline or small canine patients, an alignment pin

Elastic plate osteosynthesis

Several factors must be considered when stabilizing femoral shaft fractures in growing animals. The growth plates must be preserved for normal growth to occur; ideally, the periosteum should not be damaged during the surgical approach or application of fixation, and the cortices are thin, therefore the purchase of bone screws is poor. In a review of 8 cases of femoral diaphyseal fracture in young, growing dogs treated by intramedullary pin fixation, 7 of 8 puppies had radiographic evidence of

Assessment of axis and torsion with local landmarks

Intraoperative image intensification is the ideal method to assess limb alignment and adequacy of reduction. However, this modality is not available to every veterinary surgeon. Therefore, surgeons must be well versed in several intraoperative methods to assess alignment of the limb using local landmarks and anatomic features.

Hip rotation test

The hip rotation test is a clinical method that compares the hip range of motion with the unaffected normal side, or normal range-of-motion values. The technique is easy to perform, and does not require fluoroscopy. However, the estimation of range of motion may be incorrect, and depends on the position of the pelvis on the surgical table. Ideally, the range of motion of the unaffected normal hip is assessed preoperatively in both internal and external rotation. To perform this test, the hip is

Lesser trochanter shape sign

The lesser trochanter shape sign is an intraoperative radiological or palpation assessment in which the shape of the lesser trochanter is compared with that of the contralateral femur. Obtain a true craniocaudal view of the contralateral femur using a horizontal beam, angled beam, or elevated torso view¹⁵; alternatively, an image can be taken and stored in the image intensifier. Before fixing the distal main fracture segment to the proximal main segment, the patella is oriented cranially, and

Greater trochanter position sign

The position of the greater trochanter can be used in a fashion similar to that of the shape of the lesser trochanter to assess rotational alignment of the 2 main bone segments. With the distal femur positioned such that the patella faces cranially, the greater trochanter is typically in a true lateral position, which can be confirmed by preoperative palpation of the unaffected contralateral limb, and/or by assessment of the mediolateral radiograph of the unaffected contralateral limb.

In cases

Cortical step sign

The correct rotation of simple transverse or oblique fractures may be assessed by the thickness of the cortices of the proximal and distal segments. This assessment is accurate when considerable torsional deformity is present in human patients,¹⁶ but is not likely as accurate in dogs and cats because the femoral cortices are thin.

Diameter difference sign

Assessment of the similarity in periosteal (clinical) or endosteal (radiological) diameter of the proximal and distal main bone segments is useful to diagnose rotational alignment and malalignment in reducible simple transverse or oblique fractures. This test is only relevant in areas in which the cross section of the bone is oval rather than round; this is known as the diameter difference sign. This sign is positive in the presence of rotational malalignment, and the diameters of the 2 bone

Femoral head and neck version sign

In a normal femur, approximately one-half of the femoral head projects cranial to the greater trochanter, which can be confirmed preoperatively by assessment of the mediolateral view of the unaffected contralateral femur. With the distal femur positioned such that the patella faces cranially, palpation of the femoral head and neck through the proximal portal can be used to clinically evaluate the version of the femoral head and neck. In addition, intraoperative fluoroscopy, if available, can be

Radiographs of intact opposite limb

A mediolateral view and a true craniocaudal view of the contralateral femur using a horizontal beam, angled beam, or elevated torso view¹⁵ are invaluable for preoperative planning and intraoperative reference (Fig. 13). The mediolateral view is more useful for assessing limb length than the craniocaudal view, because it is more likely that the femur is parallel to the radiographic cassette or detector in this view, mitigating the likelihood of foreshortening caused by malposition. In addition,

Prevention of femoral torsion

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  Keep in mind that this complication is a common pitfall, and aim to prevent it.¹⁶

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  Be familiar with the various methods to detect this complication intraoperatively so it may be addressed before application of final fixation.

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  If possible, use a radiolucent operating table and intraoperative fluoroscopy to assess alignment rather than a traction table. Although a traction table can be used to maintain length of the limb, the torsional alignment cannot be assessed clinically while traction is

Coronal plane: varus-valgus malalignment

Coronal plane malalignment occurs more commonly in metaphyseal fractures than diaphyseal fractures because the metaphyseal cortex is not as straight as that in the diaphysis. Therefore, the bone plate must be accurately precontoured and positioned on the bone in the same location as during the precontouring process. An intraoperative technique to assess coronal plane alignment of the pelvic limb is the cable technique.¹⁶ In this technique, image intensification and a sterile marking pen are

Sagittal plane: procurvatum-recurvatum malalignment

In proximal femoral fractures with the lesser trochanter attached to the proximal segment, the proximal segment has a tendency to be positioned in flexion, abduction, and external rotation because of the strong pull of the gluteals and external rotators. Counteracting these forces is necessary for accurate anatomic reduction of this segment. This reduction can be achieved with bone holding forceps and manual reduction, an external skeletal fixator or fracture distractor, or a so-called joystick

Limb length discrepancy

The femur is more commonly affected by limb length discrepancy than the tibia or radius/ulna because of the difficulty in evaluation of overall length caused by the overlying muscle mass. The most common form of limb length discrepancy is shortening, whereas lengthening rarely occurs. Clinical or radiological comparison with the unaffected contralateral limb is an accurate and reproducible method to determine limb length. The overall length of the femur from the greater trochanter to the

Summary

Indirect reduction techniques (Fig. 14 case study, right femur) and carefully planned and executed direct reduction techniques (see Fig. 14 case study, left femur) result in maximal preservation of the biology of the fracture site and bone fragments. These techniques, coupled with the use of small soft tissue windows for the insertion of instruments and implants, result in minimal additional trauma to the soft tissues and fracture fragments. Without direct visualization, MIO techniques are more