The victim was working with a colleague for W A Bowler Ltd on the installation of a beam and block floor at Hillside Care Home in the Uplands area of Swansea in March 2010.
The man was at one end of a 174kg beam, and his co-worker was at the other end.
They were using lifting straps to manually hoist the beam into position when the colleague accidentally let go of one end of the beam, causing it to fall downwards and hit the concrete beneath.
The see-saw effect created caused the end of the five-metre long beam he was holding to hit him in the groin and throw him upwards. He suffered a hairline fracture to his pelvis and paralysis to the nerve endings in his left leg.
Swansea Crown Court heard that W A Bowler Ltd had been contracted by another firm to carry out the work.
The court was told that the defendant did not provide suitable equipment for the job to be done safely, which resulted in its employees undertaking potentially dangerous manual handling works.
W A Bowler Limited of Highmead House, Llanelli, Carmarthenshire, pleaded guilty to breaching safety regulations and was fined £3, 000 with costs of £4, 847.35.
Speaking after the hearing, HSE inspector Hayley Healey said: “Injuries as a result of manual handling are widespread and in this case it was entirely foreseeable that serious injury could occur. The degree of risk here was particularly high in terms of the weight involved.
“The employer failed to provide equipment which would allow the job to be done safely and, as a result, a worker suffered significant injuries in what was a completely preventable incident.”