Humerus, proximal—introduction
Introduction
Incidence
Fractures of the proximal humerus are the third most common fractures seen in clinical practice. Most often these fractures are seen in elderly women and are the result of a simple fall from a standing height. Less frequently in both men and women fractures of the proximal humerus occur following high-velocity injuries seen as a result of sports or motor vehicle accidents.
Current methods of treatment
The first clinical reports using minimally invasive plate osteosynthesis (MIPO) in the proximal humerus focused on the stabilization of humeral shaft fractures extending into the proximal humeral epiphysis, using long helical plates. The implant started laterally below the tip of the greater tuberosity and ended on the anterior surface of the humeral shaft. In recent years clinical reports of the use of MIPO in the proximal humerus have described an extended anterolateral approach and the advantage of this more direct approach to stabilize these fractures. More recently a MIPO approach for the treatment of proximal humeral fractures through an anterolateral deltoid-split incision has been promoted since it does not disturb the anterior humeral circumflex artery, which runs in the bicipital groove. There is a lower risk of damaging the axillary nerve with this approach as compared to the extended anterolateral approach. There is insufficient evidence that this approach is more advantageous than the standard deltopectoral approach, but recent developments to minimize damage to soft-tissue using special aiming and insertion devices have made this MIPO technique a valuable alternative to the standard deltopectoral approach.
Indication and contraindications for MIPO
Displaced surgical neck fractures (11-A3), including those with metaphyseal extensions, three-part fractures (11-B1 and 11-B2), especially those with large posterior tuberosity fragments, and four-part valgus impacted fractures (11-C1 and 11-C2) where the soft-tissue attachments to the tuberosities remain intact, are indications for MIPO. Both direct fracture manipulations through the fracture gaps and indirect fracture reduction using ligamentotaxis are possible using this approach. MIPO allows good preservation of the blood supply without disturbing much of the subacromial space. Dislocation fractures and grossly displaced proximal humeral fractures are difficult to properly reduce through this approach unless this can be achieved by ligamentotaxis or by the use of an extended lateral approach which has an inherent risk of compromising the axillary nerve.
Surgical anatomy
The MIPO approach to the proximal humerus starts at the anterolateral edge of the acromion ( Fig 12.1-1a ). The deltoid fascia and the anterior fibrous raphe are visible between the anterior and the middle heads of the deltoid muscle. The axillary nerve will be encountered when the raphe is split in line with the muscle fibers 3.5 cm below the intact greater tuberosity or 6 cm below the inferior edge of the acromion. The nerve crosses the operative field transversely. The anterior motor branch of the axillary nerve, which exits the quadrilateral space posteriorly, is easily palpated with the finger and may be exposed when needed when it is incarcerated in a fracture gap. In general it is not necessary to expose the nerve, but if fracture reduction needs a wider approach it is recommended to leave adjacent muscular tissue around the nerve to prevent disruption of the latter during preparation or reduction maneuvers. The anterior and posterior branches of the axillary nerve are elevated from the bone with the fibrous raphe, so are not endangered by this approach. The axillary nerve can be elevated more than 10 mm before it becomes taut, leaving enough space for the palpating fingertip or the passage of a tunneling instrument or plate. It is most important to keep instruments and plate in contact with the bone to avoid trapping the axillary nerve between the bone and the plate.
The nonvascularized “bare spot” lies directly under the fibrous raphe. Plate positioning in this area therefore does not disturb vascularity of the anterior circumflex artery if the plate is positioned > 5 mm lateral to the bicipital groove. The same holds true for the posterior circumflex artery ( Fig 12.1-1b ). This approach avoids exposure of the anterior circumflex humeral artery, which is at risk when using the standard deltopectoral approach.
The deltoid muscle inserts into the deltoid tuberosity. This is a U-shaped structure with a central vertical ridge. The insertion of the muscle onto the bone is about 10 cm long and covers a significant part of the posterolateral and lateral aspects of the humeral shaft at this point. The proximal part of the insertion needs to be detached when using a proximal humeral plate, whereas the more distal part of the insertion causes resistance to the passage of longer plates when stabilizing proximal humeral fractures extending into the metaphyseal area. For this reason a helical plate configuration has been proposed. Proximally use of this plate avoids detaching the deltoid insertion and distally the plate is at a safe distance from the radial nerve. The radial nerve winds around the dorsal aspect of the proximal humerus to appear laterally in the middle of the humeral shaft, running between the brachialis and the brachioradialis muscles on the lateral aspect of the distal third of the humerus. Therefore, when applying long plates for fractures of the proximal humerus extending distally down the humeral shaft the anatomical position of the nerve must be carefully understood and plates positioned so as to preserve the nerve. In the distal third of the humeral shaft an anterolateral approach is recommended. The fascia overlying the biceps muscle is divided and the biceps muscle is retracted medially. The musculocutaneous nerve which runs down the arm between the brachialis and biceps brachii is identified and preserved. When using a helical plate configuration, the brachialis muscle is then split and the plate is fixed on the anterior surface of the distal humerus ( Fig 12.1-2 ). If a straight, eg, metaphyseal plate is applied to the lateral aspect of the humerus the radial nerve should be visualized due to its proximity to the plate. In this area do not use Hohmann retractors as their use could endanger the radial nerve.
Preoperative assessment
The preoperative assessment includes a thorough, full clinical and x-ray examination.
Clinically it is important to assess the neurovascular status of the upper limb with special attention given to the integrity of the brachial plexus and the axillary nerve, especially after a shoulder dislocation. The vascular status of the arm needs assessment when there is a history of a high-velocity trauma. In these cases other associated injuries to the shoulder girdle should also be excluded.
X-ray assessment includes AP, axillary, and transscapular views. In three- and four-part fractures a CT scan with 3-D reconstruction helps to better define the extent of the injury and the displacement. This is especially true when considering a MIPO approach that allows limited visualization of the fracture site. Fracture classification also seems to be more reliable when using 3-D CT reconstructions.
A preoperative plan—including a plan B if problems occur with the original plan—should be designed either on paper or using planning software. The preoperative plan should outline the fractured fragments, the implant, the steps of the reduction technique, the temporary fixation of the fracture for image intensifier control, including the steps and the positions of the screws for definitive fixation. The preoperative plan should also consider patient and image intensifier positioning.
Operative procedure
The following sections describe in detail the MIPO technique for three- to four-part fractures of the proximal humerus utilizing an anterolateral deltoid-split approach. A 5-hole PHILOS plate 3.5 and standard instruments are used.
Patient and image intensifier positioning
The patient is placed in a beach-chair position with the injured arm slightly internally rotated. The image intensifier is positioned at the head of the patient, with the image intensifier above the shoulder. The x-ray source is placed posteriorly to the humerus with the x-ray beam nearly horizontal. Because the beam is perpendicular to the hanging humerus, it is ideally directed parallel to the glenoid cavity (true AP view). For the lateral view, the humerus is either internally or externally rotated leaving the image intensifier position unchanged throughout the entire procedure ( Fig 12.1-3 ).
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