الفهرس 
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Abstract
The radial head plays an important role in elbow flexion and extension as well as in forearm rotation.
It is one of three bones sharing in the cubital articulation and is held by the annular ligament forming the superior radio-ulnar joint, which shares the elbow a common synovial cavity.
It is a disc shaped structure whose upper surface is hollowed out to form a shallow cup for articulation with capitellum of the humerus.
The elbow joint is a classic simple hinge joint which moves only in flexion and extension that takes place in an oblique axis.
On other hand, the superior radio-ulnar joint is responsible for rotation of the forearm. The axis of this rotation passes between the center of the head of the radius and the base of the styloid process of the ulna.
The aim of this study is showing the results of using monoblock radial head prosthesis in treating Mason type III and type IV radial head fractures , especially if the medial collateral ligament is disrupted , including replacement of comminuted unfixable fractured head of radius and repair of the lateral collateral ligament and lateral ulnar collateral ligament .
We followed, from April 2011 to April 2013, twenty patients with Mason type III and type IV radial head fractures for whom we did replacement of comminuted unfixable fractured head of radius and repair of the lateral collateral ligament and lateral ulnar collateral ligament with short elbow immobilization in a plaster splint followed by physiotherapy.
During our follow up, May score on four parameters (pain , motion , stability and function ) was calculated, and clinical and radiological complications were assessed .
Our results were sixteen patients (80 %) excellent, two good, one fair and one poor. The average cumulative Mayo score was 93.5 %.
No patients developed re-dislocation post-surgically. Radiological results showed no case had secondary post-traumatic osteo-arthrosis or prosthesis breakage or loosening.
Operative management as described in our study can achieve elbow stability, functional range of motion and minimal complications.
CONCLUSION
Silicone radial head arthroplasty is no longer widely used because of problems with residual elbow instability, late arthritis, implant fracture, and fragmentation
The medium term results of our study with metallic radial head implants are encouraging; however, the long-term outcome with respect to loosening, capitellar wear, and arthritis has not been reported.
In radial head fracrures type (III) with rupture of the medial and lateral collateral ligament complex, we use radial head prosthesis with repair of lateral collateral complex , the patients after our procedure had mild residual strength and motion deficits.
In our study one patient required removal of the implant in other hospital.There was reliable restoration of stability and prevention of proximal radial migration.There were no prosthetic failures or signs of loosening.
Our advise after this thesis in cases of radial head fractures type (III) and (IV) which unfixable and associated with rupture of medial and lateral collateral ligaments , only we need insertion of radial head prosthesis and repair of lateral collateral complex.