Plastic deformation of forearm.

AA Bhaskar, SS Shah 
 Department of Orthopaedics, KEM Hospital, Parel, Mumbai.

Correspondence Address:
A A Bhaskar
Department of Orthopaedics, KEM Hospital, Parel, Mumbai.

Full Text

::   Case report

A 22-year-old man, textile worker was admitted with polytrauma at King Edward Memorial Hospital, Bombay. He had sustained an unusual injury while working in the textile factory. His entire body was caught between rotating cylinders that are used to wind cloth. The entire episode was over quickly. The patient came to the emergency ward in a state of shock. Roentgen examination revealed bilateral fracture shaft femur in the middle third regiontransverse, fracture of right humerus in the distal onethird with, an unusual posterior bow and a plastic deformation of both radiusulna on the right side. [Figure:1] & [Figure:2] The proximal and distal radiusulna joint were normal and fracture of ulna styloid was seen. [Figure:3]

After the patient was haemodynamically stabilised, he was operated for fracture shaft femur and humerus. There was no attempt made to correct the forearm curvature. Patient was asymptomatic for the forearm deformity except terminal restriction of pro-nation. There was no sign of periosteal callus formation in the deformed bones. No functional disability is attributed to the bowing except the obvious cosmetic deformity.

::   Discussion

Plastic deformation refers to bending of the bone without any evidence of discontinuity in the cortex. Bone is in a state of dynamic biomechanical flux at different age groups. While bone has been considered a brittle material when loaded in tension, it has become evident that bone initially exhibits ductile behaviour.

Elongation of bone tissue under tensile or elongating loads may continue between 2 percent and 7 percent of the overall length of the bone depending on the age and area of bone. After this continued elongation results in permanent plastic deformation which is essentially an irreversible process. Microscopically, plastic deformation is characterised by small fractures along the concave border of the tubular bone. If a plastically deformed bone is subsequently clinically loaded, the total deformation will increase until a point when the last load applied will result in failure (i.e. fracture)[1].

Plastic deformation always occurs in children due to a large plateau of plastic response present compared to that of an adult[2]. It has been rarely reported in adults. The oldest individual in Rydholms[3] series was sixteen years. Some remodelling of the deformity can occur in patients less than 10 years of age. However, no periosteal callus may be seen for several months.

Correction of significant bowing must be attempted in the acute phase under general anaesthesia. A great deal of force and manipulation will be required to slowly straighten the curvature. Immobilisation in a long arm cast is necessary for 6 weeks to achieve healing and avoid recurrence of deformity[1].

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