Fig. 8.1
Lateral entry of humeral nail leads to rotator cuff tear and greater tuberosity fracture with posterior migration
Fig. 8.2
The axis of the proximal humerus is aligned with the top of the humeral head fragment, passing through the “hinge point” [39]. Entry portal for a straight nail is 5 mm posterior to the bicipital groove and 5 mm medial the GT. ∆M medial offset, ∆P posterior offset
8.3.2 Iatrogenic GT Fractures
These fractures are also related to a lateral entry point with bent and large-diameter nails (Fig. 8.1). The same is true for fracture malreduction—varus malalignment is frequent.
8.3.3 Acromial Impingement Secondary to Protrusion of the Proximal End of the Nail
This occurrence is related to (1) lateral entry with a bent nail (once again!) and (2) improper seating of the nail (Fig. 8.3) when using poor insertion jigs (which do not allow clear visualization of the nail’s proximal end on the image intensifier). This complication can be avoided by proper seating of a straight nail below the subchondral bone and by using precise and radiolucent instrumentation.
Fig. 8.3
Acromial impingement can be secondary to protrusion of a straight nail and/or lateral entry portal with a curved nail
8.3.4 Surgical Neck Nonunions
They are related to the unsuitable design of some nails, which are too long and too large distally, leading to premature “locking” through interference inside the distal medullary canal with distraction at the fracture site (Fig. 8.4). This complication can be easily avoided by using a straight, short, and small-diameter—i.e., a low-profile—IM nail with a fluted and smooth tip.
Fig. 8.4
Surgical neck nonunion due to distal locking of a too long and too big nail. Arrow denotes distraction at fracture site, circle denotes early cortical contact
8.3.5 Failures of Proximal Fixation
Failures of proximal fixation (i.e., loss of tuberosity reduction and proximal screw loosening/back out ) represent the number-one complication encountered with IM nailing of proximal humerus fractures. Based on our experience, failure of tuberosity and proximal screw fixation is due to two main factors: (1) absence of (or poor) locking mechanism for proximal screws in some nails (e.g., Polarus), what can be called bone–based fixation, and (2) poor proximal screw orientation in all existing nails, what can be referred to as humeral head–based (lateromedial) orientation and fixation:
The ability of any screw to hold in osteopenic bone is limited [5, 6, 34, 37, 40], and secure fixation of the proximal screws should rely on a locking mechanism within the nail (via threaded holes). Such a nail-based fixation is superior to any bone-based fixation (Fig. 8.5). Reduction and fixation of both tuberosities provides additional support for the head—the so-called box theory [7–12].
Fig. 8.5
Loss of reduction and fixation and proximal screw loosening/back out related to the absence of locking mechanism for proximal screws (bone-based fixation)
Humeral head–based screw orientation and fixation is a flawed biomechanical concept. Unfortunately, in all proximal humeral nails and other methods of fixation alike available today, the proximal screws are oriented toward the humeral head. Again, this error arises from the fact that surgeons have tried to apply to the shoulder what they had learned about the hip, although the two are not the same (Fig. 8.6). While it is logical to orient the proximal screws into the femoral head for a femoral neck fracture, since the goal is to counteract vertical shearing forces, it is illogical to do the same in a 3- or 4-part proximal humerus fracture, in which the deforming forces are oriented mainly in the horizontal plane.
Fig. 8.6
While it is logical to orient screws in the femoral head to resist to vertical shearing forces (arrow) in proximal femur fractures, it is not logical to do so in proximal humerus where displacement of the bone fragments is horizontal, due to pulling forces on greater tuberosity and lesser tuberosity (arrows) by the rotator cuff muscles
In a recent CT scan-based study of 4-part proximal humerus fractures, we demonstrated that the main vertical fracture plane separating the tuberosities is located posterior to the bicipital groove, and that the principal displacement of such fractures occurs in the transverse (horizontal) plane [4, 11, 13, 41]. In unstable 3- and 4-part fractures, displacement occurs because of the pull of the rotator cuff muscles on their attached tuberosities in the transverse plane, widening the gap created by the fracture plane posterior to the bicipital groove. The GT is pulled posteromedially by the infraspinatus and teres minor muscles, while the lesser tuberosity (LT) is pulled anteromedially by the subscapularis muscle (Fig. 8.7).
Fig. 8.7
Tuberosity migration related to poor (humeral head) orientation of proximal screws, which are parallel to the main vertical fracture line, splitting both tuberosities. (a) GT greater tuberosity, LT lesser tuberosity. Arrows denotes horizontal pulling forces on tuberosities. (b) Displaced greater tuberosity
It follows that orienting the proximal screws from lateral to medial leads to their placement too closed and too parallel to the vertical fracture plane separating the tuberosities (Fig. 8.8). Such screws cannot counteract the pulling forces of the rotator cuff muscles. Moreover, this goes against one of the fundamental biomechanical principles espoused by the AO/ASIF [2–4, 42]: “any screw should be oriented as perpendicular to the fracture line as possible” (Fig. 8.9). Therefore, to comply with this principle as well as resist the deforming forces, the proximal screws of any nail (or plate) should be placed in a posteroanterior direction to fix the GT and an anteroposterior direction to fix the LT. In other words, optimal proximal screw orientation must be tuberosity based (i.e., sagittal) and not humeral head based (i.e., coronal).
Fig. 8.8
In 2- and 3-part fractures, the main vertical fracture line is located behind the bicipital groove; proximal screw orientation must be perpendicular to this line (i.e., tuberosity oriented) and not parallel to it (i.e., humeral head oriented)
Fig. 8.9
According to a basic biomechanical principle, screws should be oriented perpendicular to the fracture line. With the Aequalis IM nail, the proximal screws are tuberosity oriented (i.e., perpendicular to the main fracture line) and captured inside the nail (nail-based fixation) in order to resist to pulling forces of infraspinatus and teres minor muscles on greater tuberosity (GT) and subscapularis muscle on lesser tuberosity (LT)
8.3.6 Proximal Screw Penetration of the Articular Cartilage
This is another potentially disastrous complication seen with IM nails (and locked plates) [5, 6, 16, 43, 44], leading to chondrolysis and early degenerative changes due to glenoid erosion (Fig. 8.10). Again, screw placement into the tuberosities rather than in the humeral head avoids the risk of this complication altogether.
Fig. 8.10
Humeral head screw penetration leads to glenoid erosion in case of secondary bone impaction or necrosis; it can be seen with both proximal humeral plates and nails whose proximal screws are oriented toward humeral head
8.3.7 Injury to Anatomic Structures
Injury to anatomic structures (axillary nerve, long head of the biceps) with proximal screws is possible. Injury to the axillary nerve occurs when laterally placed proximal screws are too low. Prince et al. [7–12, 45], comparing several different interlocking nails, concluded that proximal and lateral screws should be aimed horizontally, not obliquely, and placed within 4–5 cm of the acromion. Injury to the long head of the biceps (LHB) and bicipital groove can occur when rotation of the nail is not accurately controlled.
8.3.8 Nail Toggling and Fracture Malreduction
Fracture comminution and poor bone quality are not uncommon in elderly patients. This can lead to loss of fracture reduction and fixation. Varus bending represents a frequent physiological displacement of proximal humerus fractures. Varus deformity can interfere with shoulder elevation and should therefore be corrected during surgery and counteracted with the inserted fixation device (Fig. 8.11).
Fig. 8.11
Nail toggling and fracture malreduction or malunion because of poor centering of the nail (in valgus or varus)
8.3.9 Nail Malrotation and Surgical Neck Malunions
They are related to the neglect of nail and fracture rotation. The most commonly committed error is fracture fixation with the arm in internal rotation, which leads to an internal rotation malunion.
8.4 Concept, Design, and Rationale of the Aequalis IM Nail
The Aequalis IM nail has been designed specifically to optimize tuberosity-fragment fixation and provide stable support for the humeral head, improving proximal humeral reconstruction and fixation in osteopenic bone (Fig. 8.12). The nail’s design and optimal screw orientation have been chosen after extensive study of the three-dimensional morphology and geometry of the proximal humerus [4, 11, 13, 39] and after revisiting the pathophysiology of displaced, unstable 2-, 3-, and 4-part fractures [1, 7, 39, 46].
Fig. 8.12
Aequalis IM nail’s concept: straight nail provides head support; proximal screw orientation provides tuberosity-based fixation; catching the nail with short screws is enough to provide secure bone-fragment fixation (nail-based fixation); and distal divergent screws provide nail centering and stabilization
8.5 Nail Design
As was shown in the previous section, the concept and design of all existing nails are poorly adapted to proximal humeral anatomy and not adapted at all to the common fracture patterns or poor bone quality that surgeons routinely encounter. Those nails are too long, too large, often bent, not centered, and with poorly oriented and poorly fixed proximal screws [9, 24–34, 37, 40].
In addition to being straight and cannulated, the Aequalis IM nail is of a low profile: its proximal diameter is 9 mm and distal diameter 8 mm, while its length is 130 mm (instead of 150 mm for most other nails). It is made of titanium alloy, the modulus of elasticity of which is close to that of bone. Since tuberosity orientation is different on each side, two nails exist: a green one for the right shoulder and a blue one for the left shoulder (Fig. 8.13).
Fig. 8.13
The Aequalis IM nail is short, low profile, and cannulated; there are two nails to allow tuberosity-based fixation: a green one for the right shoulder and a blue one for the left shoulder; the proximal (yellow) screws are tuberosity oriented and self-tapped; the distal (violet) screws are 20° divergent for self-centering
As explained earlier, a straight nail design is preferable to a bent one for at least three reasons: (1) it avoids passage through the rotator cuff tendons and GT; (2) it allows alignment of the epiphyseal fragment with the diaphysis; and (3) it gives structural support to the humeral head fragment (acting as a strut/peg), since the IM axis is actually in line with the top of the humeral head—the so-called hinge point [7, 39]. A cannulated nail allows percutaneous technique, while a short nail avoids unexpected distal locking of the device, thus preventing fracture distraction and surgical neck nonunion.
8.6 Proximal Locking Screws
In contrast to all previous devices, the proximal locking screws of the Aequalis nail are oriented to fix not the humeral head fragment but the two tuberosities. Reduction and fixation of both tuberosities indirectly provides additional head support—the so-called box theory [7, 41].
Four cannulated, yellow, 5 mm, proximal locking screws exist: two posterior locking screws for the GT, one anterior locking screw for the LT, and one (optional) lateral locked screw for the lower part of the humeral head (at the surgical neck level (Fig. 8.13). The screws are self-tapping (to easily engage the bone), with flat heads (to provide stronger fixation) and low profile (to avoid impingement with surrounding tissues). The design of the screw-hole pattern allows optimal screw positioning and prevents damage to anatomic structures, such as the axillary nerve, bicipital groove, or long head of the biceps tendon. The lowest proximal screw is at a safe distance from the axillary nerve: in 20 cadaver tests, the shortest distance from this screw to the nerve was 6 mm [46].
Rigidity of fixation of the proximal screws is not provided by purchase inside the osteopenic bone, but by locking within the nail itself, thanks to a polyethylene bushing located inside the nail’s proximal part. From a practical standpoint, this eliminates the need to look for purchase in the opposing cancellous bone with long screws; short screws stabilized by the nail itself provide sufficiently strong tuberosity fixation. In other words, with the Aequalis nail, catching the nail with short screws is enough to provide secure bone-fragment fixation.
Another important advantage of the proximal locking screw configuration of the Aequalis nail is that if the humeral head fragment necroses secondarily, the screws cannot erode the glenoid, as they are shorter and oriented in the sagittal plane. Moreover, anatomic reduction and healing of the tuberosities, together with the absence of screws directed into the humeral head, will facilitate secondary humeral arthroplasty if it should become necessary.
8.7 Distal Divergent Screws
Nail toggling movements are an issue with existing humeral nails. This could be even more of an issue with our shorter nail. However, diverging distal screws can eliminate such toggling and, in addition, allow automatic centering of the nail within the medullary canal. The nail has two violet, 4.5 mm, divergent distal screws (Fig. 8.13).
Distal locking of the nail protects the fracture against derotation or collapse and prevents migration of the implant itself. The Aequalis IM nail has the capacity to lock statically (if one uses the more distal, round hole) or dynamically (if one uses only the more proximal, oblong hole).
8.8 Radiolucent and Accurate Instrumentation
A radiolucent targeting guide facilitates accurate insertion and positioning of the nail and screws, with easy fluoroscopic visualization. A version rod, aligned with the forearm, helps achieve accurate rotational alignment of the proximal (epiphyseal) bone fragment in reference to the diaphysis (Fig. 8.14).
Fig. 8.14
Entry portal for the nail must be anterior to the acromion, allowing to pass through the supraspinatus muscle fibers (and not the tendon) and through the cartilage. For simple two-part fractures, percutaneous approach with fluoroscopic control is possible
8.9 Surgical Technique: Pearls and Pitfalls
The patient is placed in the beach-chair position with the elbow flexed at 90°. An image intensifier is used for obtaining anteroposterior (AP) and axillary intraoperative views.
Each type of proximal humerus fracture (2-, 3-, or 4-part) has its own pathophysiology and complications; the surgical technique must therefore vary accordingly. Three-dimensional CT scan images reveal the exact fracture geometry and allow accurate preoperative planning.
Three surgical approaches are possible depending on the fracture type and the surgeon’s preference:
The percutaneous approach, in which the deltoid muscle and supraspinatus are bluntly split through a superior, 1 cm incision
The superior transdeltoid approach, in which the anterior head of the deltoid is detached from the anterior acromion with the tip of the acromion to expose the rotator cuffRelated posts:
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