FUNCTION OF THE RADIAL HEAD

The head of the radius works together with the other bones, ligaments, and tendons in and around the elbow joint to the stabilize the articulation.

It serves to check instability in three planes:

In the coronal plane, it works with the medial collateral ligament to prevent valgus instability.

In the sagittal plane, it works mainly with the posterolateral ligamentous structures, but also with the coronoid process and the medial ligaments to prevent posterior dislocation.

In the axial plane, it works with the interosseous membrane to prevent the shaft of the radius riding up. Proximal translation of the radius would adversely affect the inferior radio-ulnar joint.

Thus, the radial head may be considered as a multifunctional conjoint stabilizer of the elbow.

 

FRACTURE MECHANISMS: ISOLATED AND ASSOCIATED FRACTURES

These fractures are always the result of indirect trauma, involving a combination of valgus, axial compression, and supination forces in varying proportions. The fracture may be an isolated lesion; frequently, though, the injury mechanism will be responsible for associated bony and ligamentous lesions, which may affect any of the stabilizers of the elbow together with the radial head. Such isolated or associated injuries may involve

The bony stabilizers, such as the coronoid process;

The medial collateral ligament, and even the joint capsule, in the more extensive injuries encountered in dislocations;

The interosseous membrane, in Essex-Lopresti injuries.

The severity of a fracture is a function of the extent of the associated injuries.

 

Given the many associated lesional patterns that may be encountered, there is a need for a classification system that takes account of the trauma only: since the variety of associated patterns is infinite, it is preferable to be guided by a system that indicates what can be done by way of repairing the articular platform of the radius. At our centre, the classification used is based upon the one devised by Mason (Fig. 1):

 

Figure 1

Stage I: Undisplaced segmental fractures. These may be treated with early exercises.

Stage II: Displaced segmental fractures of all kinds. These fractures may be managed with anatomical reduction and internal fixation, usually using screws.

Stage III: Comminuted fractures. In these fracture patterns, anatomical reconstruction and a sufficiently sound construct to allow an exercise regime are less likely to be achievable.

Stage IV: Fractures of the radial neck. These fractures are rare in adults. In some cases, stabilizing surgery (axial Métaizeau pinning; miniplates) may be beneficial.

 

WHEN SHOULD ONE CONSIDER A RADIAL-HEAD PROSTHESIS?

1. INTERNAL FIXATION OR PROSTHETIC REPLACEMENT?

Regardless of whether the fracture is an isolated injury or associated with other lesions, internal fixation is the preferred option, providing that stable anatomical reduction can be achieved, so as to enable an exercise regime to be instituted immediately (Fig. 2).

 

Figure 2

If internal fixation is not possible, or if a successful outcome is uncertain, it should not be considered. The patient is not helped by IF that does not restore the anatomical pattern or which requires protective immobilization.

2. RESECTION OR REPLACEMENT?

If the radial-head fracture is definitely isolated, resection should give satisfactory medium- and long-term results, as documented in the literature.

If, however, the radial-head fracture is associated with other destabilizing injuries, resection may be expected to lead to complications.

Among the early complications are the recurrence of a dislocation (Fig. 3 a and b), as well as early instability, or the failure of the overstressed fixation construct.

 

Figure 3	Figure 3b

The later complications include signs of mediolateral instability, recurrent valgus instability, and posteromedial OA (Fig. 4), anteroposterior instability with recurrence of subluxation or even dislocation, and proximal-distal instability, with disturbance of the inferior radio-ulnar joint (Fig. 5).

 

Figure 4	Figure 5

In an attempt to prevent the occurrence and progression of such complications, various implants have been devised, over the past 50 years, for the replacement of the radial head.

3. WHICH PROSTHESIS?

The patterns currently available - whether rigid or elastic - have produced less than optimal results. There have been instances of mechanical failure, poor acceptance by the host bone or joint, and even biological problems. In 1988, the concept of the floating radial-head prosthesis was devised.

The design is based upon the following principles:

Use of materials that are known to be well tolerated: polyethylene and cobalt chromium alloy (which has superseded the titanium alloy used in the first devices);

Fixation to cope with the axial, flexion, and torsion forces acting upon the implant. To this end, the device has a long tapering stem that is fixed in the radial shaft with acrylic cement inserted under pressure, as required by “modern cementing” technique;

Accurate anatomical restoration through the shape of the implant, which reproduces the neck/shaft angle of the radius, and thus allows physiological supination;

Allowance for different patient patterns (modular system, offering different sizes, stems, and heads);

Achievement of maximum congruency, both with respect to the condylar cartilage and the radial notch, through the use of a ball-and-socket joint inside the prosthesis, which allows the cup to position itself at any angle of flexion, extension, pronation, and supination.

The first floating radial-head prosthesis incorporating these design features was implanted in December, 1988 (Fig. 6).

 

Figure 6

4. THE ROLE OF RADIAL-HEAD REPLACEMENT

In the emergency surgery of fresh lesions, the implantation of a prosthesis is vital for joint stabilization and for the restoration of a sound lateral platform, which is of particular importance because it allows the surgeon to dispense with the notoriously difficult repair of the medial soft tissues. Sometimes, internal fixation will be required as well; this need arises particularly in cases where the radial-head fracture is associated with a segmental or a comminuted fracture of the proximal end of the ulna.

In older injuries, on the other hand, the implantation of a prosthesis will be only one of several measures to be taken: depending on the injury pattern, elbow release, distal translation of the radial shaft, coronoid reconstruction, etc. will be required in addition to radial-head replacement.

 

 

 

SURGICAL TECHNIQUE

1. PATIENT POSITIONING

The patient is positioned supine, with a pneumatic tourniquet on his or her arm. Instead of a conventional arm board, which prevents the surgeon from standing facing the joint undergoing surgery, a short board that stops at the apex of the olecranon should be used. This way, the surgeon need not change position: rotation of the patient’s shoulder will provide access to the elbow from a lateral or a medial approach, and even from behind, on the posterior border of the ulna.

2. INCISION (FIG. 7)

 

Figure 7

A conventional incision is used, preferably a lateral one between the extensor carpi radialis brevis and the extensor digitorum muscles, rather than the posterolateral one of Cadenat, in the extensor carpi ulnaris/anconeus interval. The incision exposes the annular ligament, which must be dissected free before being incised.

3. RADIAL NECK EXPOSURE (FIG. 8)

 

Figure 8

Two angled spike retractors are inserted. The one against the radial tuberosity most be handled with care, with the forearm pronated, so as to align the shaft in the surgical field and to carry the radial nerve out of the field medially.

4. DIVISION OF NECK, AND INSPECTION

The neck is divided with an oscillating saw (Fig. 8). Bone-cutting forceps should not be used, since they would splinter the hard bone. The resection level is at the tuberosity, 23 mm distal to the humeral condyle. The measurement is checked (Fig. 9) after resection. The congruency of the elbow joint is checked, by direct visual inspection of the humero-ulnar joint line in the upper part of the radial notch. A specially designed endcutting mill (Fig. 10) is used to trim and level the resected surface.

 

Figure 9	Figure 10

5. PREPARATION OF THE IMPLANT BED

Reamers of increasing diameter (Fig. 11a, b) are used to prepare the bed to the desired diameter of 6.5 mm or 8 mm.

 

Figure 11	Figure 11b

6. INSERTION OF TRIAL COMPONENT

The trial component allows the ROM to be checked, care being taken to ensure that the implant neck is orientated in the plane of the abducted thumb, with the forearm in pronation (Fig. 12). The cup (available in a 19 mm and a 22 mm diameter) must not protrude beyond the condyle. The trial gauge must show a clearance of 0.5-1 mm (Fig. 13 a and b).

 

Figure 12

 

Figure 13	Figure 13b

7. PACKING THE SHAFT WITH BONE CHIPS

At a distance of 10 mm from the tip of the implant stem, the canal is packed with bone chips, using a serrated conical impactor (Fig. 14).

 

Figure 14

8. FIXATION WITH LOW-VISCOSITY PRESSURIZED CEMENT

The canal is dried using a small-bore Manovac® drain, and cement is inserted under pressure, with an injector with a large-bore nozzle (Fig. 15). The implant is impacted until its collar is seated on the resected surface of the radius (Fig. 16).

 

Figure 15	Figure 16

9. SNAP-FITTING THE CUP (FIG. 17)

 

Figure 17

10. STABILITY TESTING

The elbow is taken through its range of flexion-extension (Fig 18a, b) and pronation-supination, both before and after the repair of the annular ligament. A check is made to confirm that the cup is stable under the condyle, and that congruency is maintained between the implant and the bone against which it articulates.

 

Figure 18	Figure 18b

11. WOUND CLOSURE

The annular ligament (if present) is repaired, and the muscle and tendon layer is closed.

12. REHABILITATION

Rehabilitation is started immediately after surgery; the actual programme will depend upon the stability assessment made at surgery. All patients are treated with ice and anti-inflammatories.

 

 

 

TECHNICAL DETAILS AND ASSOCIATED PROCEDURES TIPS AND TRICKS IN DIFFERENT INJURY PATTERNS

1. FRESH INJURIES

a. Radial-head fracture + medial collateral ligament damage

This is straightforward, except that care must be taken to ensure that all the radial-head fragments are recovered from the anterior compartment (Fig. 19a-c). Intraoperative stability testing may show joint opening in valgus, without any associated anteroposterior instability. We have never found it necessary to repair the lesion of the medial capsule: the restoration of a sound radiocapitellar articulation turns the medial capsular tear into an “isolated” lesion, which, as a rule, has a favourable prognosis. Remedial exercises may be performed throughout the ROM; between physiotherapy sessions, the elbow should be splinted with a plaster backslab or placed in a sling.

 

Figure 19	Figure 19b	Figure 19c

b. Radial-head fracture + dislocation

Often, there will be an associated fracture of the tip of the coronoid process Morrey Type I or, more rarely, Type II (Fig. 20). At surgery, the annular ligament will, as a rule, be found to be intact; however, there will be posterolateral avulsion of the capsule, tendons, and ligaments. These lesions will cause rotational instability and recurrent dislocation as a result of the radial head slipping posteriorly under the condyle. The surgical repair of these tears at the end of the procedure will restabilize the elbow; however, exercise physiotherapy will need to be performed very cautiously: extension should be in pronation only, while supination exercises should be performed with the elbow at 90°.

 

Figure 20

c. Radial-head fracture + comminuted fracture of the proximal end of the ulna (diepiphyseal fracture)

Such lesions are best approached by two incisions (one on the posterior border of the ulna, and the other anterolaterally over the radial head), rather than through a single incision. Once the radial head has been resected, reduction and fixation, especially of the coronoid process, may be checked through the lateral incision. In comminuted ulnar fractures that are difficult to stabilize, the radial-head prosthesis will afford sound protection of the construct (Fig. 21a, b).

 

Figure 21	Figure 21b

2. COMPLICATIONS OF RADIAL-HEAD FRACTURES

a. Radial-head fracture + stiffness

Stiffness is a frequent complication. Malunion or deformation of the radial head will require resection (if the head has not been removed before). Release must be performed to restore the full ROM; however, this will often reveal valgus or even anteroposterior instability, which will make it impossible for the elbow to be exercised in extension. The implantation of a radial-head prosthesis will relieve this instability, and allow the early institution of an exercise regime.

b. Radial-head fracture + lesions of the interosseous membrane

Essex-Lopresti lesions are difficult to diagnose, and may have been missed after the traumatic event. Such cases may have been managed by the resection of the fractured radial head. This ill-advised procedure results in disruption of the inferior radio-ulnar joint, which will, before long, lead to painful stiffness limiting forearm rotation. The radius will have to be released at the elbow and at the wrist. The return of the radial shaft to its normal position (which may not be fully possible) is then maintained by the implantation of the radial-head prosthesis.

c. Radial-head fracture + major post-traumatic instability

In valgus instability and in instability with recurrent dislocation in extension (Fig. 22), attempts should be made to restore the radial head by prosthetic replacement, and to restore the other bony structures (coronoid process) as well as the ligaments. Particular attention should be given to the posterolateral ligamentous structures and the medial collateral ligament.

 

Figure 22

d. Radial-head prosthesis and cartilage damage

Damage to the cartilage of the humero-ulnar joint as a result of chronic valgus instability can be managed by the palliative implantation of a floating-head prosthesis.

Damage to the condylar cartilage is seen in cases of radial-head malunion, or where a Silastic prosthesis has been used as a temporary or a long-term implant.

Since these lesions may progress, primary or secondary lateral elbow compartment replacement by condylar resurfacing plus radial-head replacement may be considered.

3. TECHNICAL ERRORS IN THE IMPLANTATION OF A FLOATING RADIAL-HEAD PROSTHESIS

The implant may be inserted in malrotation; the chief error consists in leaving the implant sitting too high (Fig. 23), which may lead to permanent subluxation and to the early onset of elbow pain and stiffness. These cases will need to be revised immediately or very early on, to remove the primary implant, reshape the bone bed with a drill, and insert a radial-head replacement in the correct position.

 

Figure 23

 

 

 

CONCLUSION

Since 1988, we have implanted more than 60 floating radial-head prostheses, which have been followed up in a prospective study. The arthroplasties were divided evenly between fresh cases and surgery for complications of radial fractures. All the arthroplasties were carried out following the principles outlined above. In the selection of patients, no account was taken of patient age.

The complication rate was very low: two implants had to be removed early on, one because of infection, and the other because of poor implant tolerance in a patient that had undergone several elbow operations previously.

Some additional procedures (removal of calcifications, additional stabilization) were required, usually in cases of radial fracture complications rather than in the acutely operated patients.

The short-term follow-up has shown the floating-head prosthesis to function well mechanically.

The medium- and long-term follow-up (4 - 9.5 years) of the initial cohort operated on between 1988 and 1994 has confirmed this good mechanical function, and, additionally, demonstrated the soundness of the concept in terms of freedom from adverse events.

Over the period of follow-up, the clinical results have not significantly deteriorated, and the radiological appearance of the implant-cement-bone interfaces, the host bone structure, and the joint spaces have remained essentially unaltered. Stress radiographs are routinely performed as part of the follow-up; these radiographs have confirmed that the ball-and-socket joint inside the implant continues to function properly.

While the implantation of a radial-head replacement may, thus, be beneficial, radial-head preserving surgery, with reduction and internal fixation of radial-head fractures, should still be performed wherever this is technically feasible.