Radial Head Replacement Using Evolve Proline Modular Radial Head System (Wright Medical)

The AP and lateral radiographs show a comminuted, displaced radial head fracture.
The main radial head fragment is displaced and dislocated posterior to the capitellum.

The patient is supine with the arm on an arm table. It is important to ensure that the body is positioned close to the edge of the table. This allows adequate intra-operative fluoroscopy images.
A gown pack can also be placed under the elbow to aid intra-operative visualisation.

A Kocher’s approach is used which utilises the intermuscular plane between anconeus (radial nerve) and extensor carpi ulnaris (posterior interosseous nerve, PIN).
The relevant landmarks include:
lateral epicondyle (A)
olecranon (B)
and radial head (localised on pronation/supination of forearm)
With the elbow flexed, the incision is sited 2-3cm proximal to the lateral epicondyle and extends distally to the posterior border of the ulna 10cm distal to the tip of the olecranon.
The distal extent of the incision is important to help define the anatomy and particularly the intermuscular plane.
The fascia is incised in line with the incision.
The forearm is maintained in pronation to move the PIN away from the surgical approach.

The incision is made through the skin and subcutaneous layer down to the fascial layer.
The subcutaneous fat is swept off the fascia to minimise the risk of injury to the lateral cutaneous nerve of forearm. This allows adequate exposure of the anatomy and identification of the muscle planes for the approach.
If greater exposure is required, the incision can be extended proximally along the lateral intermuscular septum.
The lateral cutaneous nerve of forearm is a branch of the musculocutaneous nerve. It runs a variable course but passes behind cephalic vein and divides into a volar and dorsal branch.
The volar branch descends along the radial border of the forearm to the wrist and supplies sensation to the lateral half of the volar forearm skin.
The dorsal branch descends along the dorsal surface of the radial forearm to the wrist. It supplies sensation to the lower two thirds of the dorsolateral forearm skin.

Before proceeding further one should orientate oneself with the deeper anatomy.
A – lateral epicondyle
B – anconeus
C – extensor carpi ulnaris

The fascia is incised between extensor carpi ulnaris (A) and anconeus (B).
Note that plane between the 2 muscle bellies is ill defined.
It is best identified by looking at the orientation of the muscle fibres and also by a dip in the convexity of the muscle fascia due the tethering of the deep fascia between the two compartments.
Distally, the proximal fibres of supinator are split. Note the forearm remains in pronation and approach is on the dorsal aspect of the radial neck to minimise risk of injury to the PIN.
The PIN is a continuation of the radial nerve after it divides from the superficial sensory branch in the arm. Proximally, the PIN is separated from the joint by the brachialis muscle. Distally, it passes under the arcade of Frohse at the proximal edge of supinator before continuing on the dorsal surface of the interosseous membrane.

Deep to the fascia, the capsule is incised and the haemarthrosis is evacuated. The capular incision is extended distally.
Care is taken to protect the humeral attachment of the lateral collateral ligament (LCL). This is ensured by staying anterior to the centre of rotation of the capitellum (A).
Note that the LCL can be ruptured from the mechanism of injury. It this is the case, it needs to be repaired.
The LCL originates from the lateral epicondyle of the humerus and attaches to the supinator crest of the ulna.
The annular ligament is identified distally and incised to expose the radial neck. It is separated from the capsular layer and tagged so that it can be repaired separately on closure.
The annular ligament is usually incised in line with the approach towards the dorsal aspect of the radial neck to minimise risk of injury to the PIN. Care is taken to ensure that the annular ligament is not incised by its ulnar attachment posteriorly as it may compromise repair if there is very little tissue to reattach at the end of the procedure.

The radial head can now be clearly identified and assessed
It is rotated and dislocated posteriorly in relation to the capitellum.

The posteriorly dislocated radial head fragment is defined.
The image shows that it is devoid of soft tissue attachment.
The fracture is assessed in relation to remaining fragments and whether it is repairable.
In this case, it was excised and preparation made to proceed to a radial head replacement.

Once the radial head is excised, an assessment of the coronoid can be made (seen at the tip of forceps).
The coronoid acts as an anterior butress to prevent posterior subluxation.
Regan and Morrey classified coronoid fractures into:
Type 1 – Coronoid tip fracture
Type 2 – Fracture involving up to 50% of height
Type 3 – Fractures greater than 50% of height
In general, minimally displaced fractures can be treated conservatively if the elbow is stable.
If the there is concern regarding stability, it may require fixation to enhance stability.
Note: If it is felt that the coronoid fragment may require fixation, a Kaplan approach may give a better exposure to the coronoid. This utilises the intermuscular plane between extensor carpi radialis brevis (ECRB) and extensor digitorum communis (EDC). These are supplied by the radial nerve. Care must be taken as the PIN is at greater risk.

Once the fragments are cleared, a conservative perpendicular cut is made on the residual radial neck.
Care is taken when retracting the soft tissues radially to protect the Posterior Interosseous Nerve (PIN)

Once all the fragments are excised and retrieved, it is useful reconstruct the radial head to:
1. appropriately size up the prosthesis
2. ensure that all the fragments have been retrieved from the joint

The prosthesis is sized using the template .
It is sized off the inner diameter of the radial head’s articulating surface rather than the outer diameter the head that articulates with the proximal radioulnar joint.
For elliptically shaped head, the minimum diameter is selected. If in between sizes, it is preferable to downsize.
If a previous radial head excision has been performed, a radiograph of the contralateral normal radial head is used as a guide for sizing.

The radial neck canal is opened using the starter awl.
It is sequentially reamed by hand using the stem broaches by hand down to the depth indicator on the broaches.
Adequate reaming is achieved once there is cortical bone contact in the intramedullary canal.

If required, the last stem broach can be left in situ and a neck planer can be applied over the broach and rotated clockwise to ensure that the neck cut is perpendicular to the axis of the of the radial neck
This allows the prosthesis to sit square on the neck.
Excessive planing is avoided to ensure that an appropriate length prosthesis can be implanted.
Note, when retracting, it is important to avoid levering over the course of PIN to prevent iatrogenic injury.

When selecting the appropriate trial components, the prosthesis should fit easily into the canal.
It is designed to sit slightly loose but not sloppy in the canal to allow the implant to toggle and conform with the capitellum during range of motion. The trial selected is usually a size down from the last reamer used.
The prosthesis is modular and is made up of a head and stem component.
Both components are available in a standard size with a +2mm and +4mm option.
This allow a possible build-up of +8mm in total and allows flexibility in matching the patient’s anatomy.
Ideally, the head component is matched to the patient’s native radial head to ensure a congruent articulation with the proximal radioulnar joint.
The stem component is to allow restoration of the radial length which ensures a congruent and stable radiocapitellar articulation.
Note that in the image, there is an increase in radiocapitellar space present due to the release of the annular ligament during the approach. It is useful to have tagging sutures to the incised annular ligament to aid reduction and stability of the radiocapitellar joint when assessing prosthesis size and length.

The elbow is screened under fluoroscopy to ensure that the radial head replacement is appropriate in size for radiocapitellar articulation and proximal radioulnar articulation and height.
This is best shown on AP with the elbow in extension with the forearm in supination.
Radial height is assessed by restoring the articulation in line or even just proximal to the level of the coronoid (to account for the cartilage layer).
When assessing radial height, it is important to avoid overstuffing the radiocapitellar articulation. This is assessed by radial opening of the ulnohumeral articulation.
If critical, there does appear to be some opening of the ulnohumeral articulation on the trial images.

In most injuries, the proximal radius is mobile enough that the implant can be assembled on the back table and inserted as a monoblock implant.
The head and stem components are selected. This image shows the selected head placed on the sizing and assembly dish.

The selected stem is placed onto the head component.

The stem impactor is placed over the stem and impacted using a mallet.

The proximal radius can be retracted laterally to allow a straight run down the axis of the radial neck.
The implant is inserted manually.
There is usually enough clearance for the prosthesis to pass the capitellum on insertion.

Once the implant is seated, it is assessed for congruency on range of movement and stability.
The annular ligament (anterior leaflet held in forceps) has already been separated from the capsular layer.
If there are concerns regarding stability or tracking, the tagging sutures to the annular ligament leaflets can be temporarily tied or secured with an artery clip to restore the integrity of the annular ligament.
This stabilises the radial head and allows more normal tracking of the radiocapitellar joint.

The prosthesis is also screened under image intensifier.
It is important to note that the prosthesis is fully seated and that the joint line has been restored to or just proximal to the level of the coronoid.

Once satisfied, closure can be commenced.
It is worth noting at this stage that if the LCL is ruptured, it will need to be repaired (see described technique).
It is usually ruptured from the humeral attachment at the lateral epicondyle (origin) and the free end can usually be seen on the undersurface of the muscle fascia.
It can also be palpated as a thickening of the muscle fascia and is usually more robust. The LCL acts as a sling for the radial head and if the injury is missed, can lead to posterolateral instability.
The LCL complex is composed of:
lateral ulnar collateral ligament – attaches to supinator crest on ulna
radial collateral ligament – blends with annular ligament deep to common extensor tendon
annular ligament – from posterior to anterior margin of radial notch on the ulna and encircles the radial head
accessory lateral collateral ligament – inferior border of annular ligament to supinator crest

The annular ligament is repaired using 1-0 vicryl interrupted sutures.
Care it taken not to overtighten the repair to minimise any restriction in pronation and supination.

The fascial layer is repaired using 1-0 vicryl in a continuous running stitch.

The fat layer is repaired using 2-0 vicryl to minimise the dead space.
The skin layer is closed using a 3-0 monocryl subcuticular stitch.

Dressings are completed using steristrips/opsite/wool/crepe.