Intramedullary Locking Nail Fixation of Proximal Humerus Fractures: Rationale and Technique

Fig. 5.1

Insufficient stability of the fixation with pinning and example of early loss of reduction

Fixed-angle locked plates are very popular at the moment and have become a kind of “gold standard” for the treatment of PHFs [10]. However, there is some risk of complications, including hardware failure, screw penetration, and loss of reduction [11–15].

In case of two-part fractures, the risk of humeral head necrosis because of additional bone devascularization can occur (Fig. 5.2).

Fig. 5.2

Avascular necrosis of the humeral head after plating

In case of three-and four-part fractures, we feel that locking plates provide inadequate biomechanical fixation because the screws are head-oriented, instead of being tuberosity-oriented. This may lead to what we have called the “unhappy triad after locking plate” which combines (1) humeral head necrosis, (2) loss of reduction and posterior migration of the greater tuberosity (i.e., a massive, retracted posterosuperior rotator cuff tear) because of the inadequate orientation of the screws, and (3) glenoid erosion and destruction because of screw penetration (Fig. 5.3).

Fig. 5.3

“Unhappy” triad: humeral head necrosis, tuberosity migration, glenoid erosion

The catastrophic results after failures of three- and four-part fracture plating have been clearly underestimated. The fact is that a failure after a locking plate burns all the bridges. A revision with hemiarthroplasty is not possible because of glenoid erosion and GT migration. An anatomical TSA is not possible either, for the same reasons, and more specifically because of the posterosuperior cuff insufficiency. The surgeon has to discuss the indication of reverse shoulder arthroplasty (RSA) often in a young patient. Unfortunately, it will be a RSA with poor functional results because of stiffness and absence of external rotator muscles.

Complications and Technological Problems Related to Previous Conventional IM Nails

Some reports on IM nails for displaced proximal humerus fractures have reported a high complication rate of 40 % [16–24] and a high revision rate of up to 45 % [25–29]. Based on our own experience, most of the complications and problems observed with existing IM nails are related to inadequate design of the nail itself, the inadequate orientation of proximal screws, the absence of locking mechanism for proximal screws and the inadequate accompanying instrumentation.

Iatrogenic rotator cuff tears are seen when surgeons use a lateral entry portal to insert the IM nail, which is unavoidable with a proximally bent IM nail (Fig. 5.4).

Fig. 5.4

Bent nail and its lateral entry point, leading to cuff tendon injury

The obvious advantage of a straight and low-profile nail is that it can be inserted through the muscular (not the tendinous) part of the supraspinatus and the superior part of the humeral head (not the greater tuberosity and the tendon footprint).

Acromial impingement (secondary to protrusion of the proximal end of the nail) is related to poor instrumentation and use of bended nail (Fig. 5.5). It can be avoided by using a precise and radiolucent instrumentation and a straight nail. Both iatrogenic cuff tears and nail protrusion are sufficient to explain the 20–45 % of postoperative shoulder pain reported in the literature after intramedullary nailing of humeral fractures.

Fig. 5.5

Proximal hardware protrusion and associated sub-acromial impingement

Surgical-neck non-union is 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 and distraction at the fracture site (Fig. 5.6). This complication can be easily avoided by using a short, and small-diameter IM nail (low-profile) and by intraoperative compression of the fracture site.

Fig. 5.6

Distraction at the fracture site

Surgical-neck malunion in internal rotation is related to the absence of adapted instrumentation to control fracture and nail rotation. The most commonly committed error is to fix the fracture with the arm in internal rotation (the hand on the abdomen), which leads to an internal-rotation malunion of the diaphysis. Control of humeral retroversion and nail rotation is therefore of paramount importance.

Screw backout (and loss of tuberosity reduction) has a reported prevalence of 10–24 % with conventional intramedullary devices (Fig. 5.7). This complication is due to the absence of a locking mechanism for proximal screws: the screws are simply threaded into the interlocking holes in many IM nails. These conventional IM nails fail as they rely only on screw torque in the bone to provide stabilization (Head-based fixation). The locking technology applied to the proximal screw holes, almost eliminates the possibility of screw backout.

Fig. 5.7

Screw backout and loss of reduction

Screw protrusion (and glenoid erosion) is another potentially disastrous complication seen with conventional IM nails (and locking plates) (Fig. 5.8). Again, this complication is related to the fact that the screws are oriented toward the head (Head-based fixation) and consequently toward the glenoid surface. Screw placement into the tuberosities rather than in the humeral head avoids the risk of this complication (Tuberosity-based fixation).

Fig. 5.8

Articular penetration of the screws and glenoid erosion

Nail toggling and fracture malreduction (Fig. 5.9). 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 physiologic displacement of proximal humerus fractures.

Fig. 5.9

Nail toggling, tuberosity migration, and varus displacement leading to malreduction

Based on the analysis of these pitfalls, the specifications of the ideal device can be defined (Table 5.1).

Table 5.1

Complications and problems related to existing IM nails, their causes, and possible technologic/design-related solutions

Complications	Cause	Technologic solution
1. Nail design
Rotator cuff tendon tears	Bent, large-diameter nail with lateralized entry point	Straight, small-diameter nail for medialized entry point
Iatrogenic greater-tuberosity fracture through entry point	Bent, large-diameter nail with lateralized entry point	Straight, small-diameter nail + awl + reamer to facilitate medialized entry point
Acromial Impingement secondary to nail protrusion	Proud/lateral (bent) nail + poor instrumentation	Straight, low-profile nail with accurate targeting device
Surgical neck non-union	Excessive nail length and size; obligatory distal locking	Shorter nail with fluted distal tip
2. Proximal screws
Loss of tuberosity reduction and fixation	Poor (humeral head-based) screw orientation (=latero-medial)	Optimal (tuberosity-based) screw orientation (=posteroanterior)
Loss of tuberosity reduction and fixation	Poor or absent locking mechanism for proximal screws (=bone-based fixation)	Secure locking into nail through threaded holes (=nail-based fixation)
Proximal-screw loosening and back-out	Unlocked proximal screws (=bone-based fixation)	Secure locked proximal screws (=nail-based fixation)
Proximal-screw penetration through articular cartilage	Poor screw orientation (latero-medial)	Locking screws with posteroanterior orientation
Axillary nerve damage	Low/oblique proximal-screw positioning	Optimal screw position (high enough, horizontal)
Long-head-of-biceps tendon and bicipital groove damage	Uncontrolled nail rotation = penetration of bicipital groove	Control of nail rotation through instrumentation
3. Distal screw instrumentation
Nail toggling, fracture displacement, malalignment	Aligned (non-divergent) distal screws	Divergent distal screws allowing nail centering and adding stability
Nail malrotation and surgical neck malunion	Uncontrolled nail and fracture rotation	Specifically designed instrumentation allowing accurate rotational control

Design of the Aequalis IM Locking Proximal Humerus Nail

The novel design of the Aequalis Proximal Humerus Nail combines unique features that allow a less invasive surgical intervention, maintenance of the vascularization of the fracture fragments, angular stability of proximal fixation, and optimal screw orientation for fixation of the tuberosities.

The design of the Aequalis Proximal Humerus Nail is based on five principles: fixation of the tuberosities, supporting the humeral head, angular-stable locked screws, centering within the medullary canal, and medial articular insertion point (Fig. 5.10).

Fig. 5.10

Design of the Aequalis Nail

This straight, cannulated titanium nail, 130 mm long, offers several unique design features that support these five principles. The straight design of the nail avoids insertion through the rotator cuff tendon and reduces the potential for a varus reduction, and cannulation allows for a minimally invasive percutaneous technique. The divergent tuberosity based fixation provides optimum independent fixation of the greater and lesser tuberosities (Fig. 5.11), which also serves to maintain positioning of the humeral head without requiring screws to enter the central humeral head (Fig. 5.12).

Fig. 5.11

Tuberosity based orientation of the proximal screws

Fig. 5.12

No screw directed towards the head

The proximal screws are “locked” in the nail via a polyethylene bushing, providing angular stability for tuberosity and humeral head fixation.

Two interlocking screws that are divergent accomplish distal fixation by 20°, which minimizes toggle of the nail and allows for distal centering in cases of a large humeral canal.

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, can help achieve accurate rotational alignment of the proximal (epiphyseal) bone fragment in reference to the diaphysis.

The nail’s design and optimal screw orientation must be chosen after extensive study of the three-dimensional morphology and geometry of the proximal humerus [30] and of the pathophysiology of displaced unstable two-, three-, and four-part fractures [31–34].

The nail is indicated for two-, three-, and four-part fractures according to Neer’s classification, non-unions, malunions, and impending pathological fractures. The design of the nail and its instrumentation allows effective insertion through an open or percutaneous approach.

Two-Part Surgical Neck Fracture with a Percutaneous Technique

Rationale

In two-part (surgical-neck) fractures, the epiphysis is correctly oriented and has a fixed position, because the internal-rotator and external-rotator muscles are still attached and balanced. In other words, the head is facing the glenoid and is stable. The diaphysis is medially displaced (due to the medial pull of the pectoralis major, latissimus dorsi, and teres major) and in internal rotation (because the forearm is usually held against the belly) (Fig. 5.13).

Fig. 5.13

Action of the muscles in case of surgical neck fracture: Adduction and internal rotation of the diaphysis

Two main complications are specifically encountered with two-part (surgical neck) fractures, and must be anticipated:

Rotational malunion which occurs when the nail is locked proximally and distally with the arm in internal rotation; this leads to decreased humeral retroversion and consequently, external rotation. This complication can be avoided by using the outrigger alignment guide as described above.

Surgical neck non-union that occurs in cases of persistent distraction at the fracture site. This complication can be avoided by using a “backslap technique”: consisting in retrograde hammering after first distal locking, which impacts the surgical neck fracture site, preventing non-union.

Percutaneous “Backslap” Technique

In two-part (surgical neck) fractures, the procedure can be performed percutaneously. The starting point is located either anterior or posterior to the acromio-clavicular joint, depending on the displacement of the epiphyseal fragment. The anterior portal is preferred in instances where the epiphyseal fragment is displaced in valgus whereas the posterior location or the “Neviaser” portal is preferred in instances where the epiphyseal fragment has varus angulation (Fig. 5.14).

Fig. 5.14

Starting points of the percutaneous approach (left shoulder)

These entry points avoid the insertion point of the rotator cuff by staying medial to the tendon insertion and passing though the muscle fibers of the supraspinatus. The goal is to enter the humeral head medially and to leave about 5-mm of cartilage lateral. The surgeon must never try to enter the greater tuberosity and should not be afraid to pass through the cartilage of the humeral head: the hole in the cartilage will be filled with fibrous tissue and there is no functional consequence.

After location of the starting point under fluoroscopy with a spinal needle, an incision is made which is large enough (about 8-mm) to allow passage of the humeral nail. A blunt Kelly forceps is used to spread the muscle fibers down to the humeral head (Fig. 5.15).

Fig. 5.15

Control of the location under fluoroscopy. Patient positioning should allow access of the C-arm to obtain adequate radiographs

A specific cannulated awl is then introduced into the incision and with a twisting motion and downward pressure advanced into the humeral head. The awl can then be used to manipulate the head fragment and allow for the passage of the guide-wire. It is crucial that the entry point for the nail is medial enough and enters the cartilage and not the greater tuberosity and the supraspinatus insertion. The guide wire is inserted through the awl and image intensification is used to confirm the awl and guide-wire position in the humeral head and the distal humerus (Fig. 5.16). The cannulated reamer is used to open the proximal portion of the bone and the nail is inserted with the attached targeting jig.

Fig. 5.16

Insertion of the guide wire through the awl

The Aequalis IM nail, which is cannulated, is introduced percutaneously, along the guide-wire first through the epiphysis and then through the diaphysis. The depth of the nail is confirmed under fluoroscopy utilizing a K-wire placed through the lateral side of the jig. The nail is inserted somewhat more deep (2 or 3 mm) to allow for backslapping and compression. The K-wire should be at the level of the top of the GT, slightly below the level of the head to ensure the proper depth (Fig. 5.17).

Fig. 5.17

Introduction of the nail and assessment of its depth

At this stage, the diaphysis is still independent of, and can be rotated around, the epiphyseal fragment. The patient’s arm must then be brought in neutral rotation to help with rotational alignment: this allows for the correct rotation of the diaphysis relative to the humeral head, which is again confirmed under fluoroscopy. A version rod “outrigger” is attached and aligned with the supinated forearm: this allows for the correct rotation of the nail inside the humerus, and consequently the correct orientation of the proximal and distal screws.

The first distal trocar for the static screw is then introduced and drilled with a calibrated drill. The correct screw placement is confirmed under fluoroscopy (Fig. 5.18). The second distal screw ensures that the nail is centered within the diaphysis. The distal screws are small (3.5-mm) in diameter and their length is usually 22 or 24-mm. Following screw placement distally, the slap hammer can be attached to the nail and by “backing the nail out” utilized to compress the fracture fragments. The slot in the guide should be flushed with the top of the humeral head: this allows for confirming that the nail is at the right height. Fluoroscopy is used to confirm compression at the fracture site and correct height positioning. The outrigger ensures correct rotation is maintained during compression (Fig. 5.19).