Patients who suffer from pain after hip replacement surgery with a metal hip implant could be suffering from a complication known as a pseudotumor, according to a study by Dutch researchers.

The study was published in the June 2012 British edition of the Journal of Bone and Joint Surgery. The researchers examined the records of 119 patients who underwent metal-on-metal total hip replacement from 2005 to 2007.

Of those patients, 108 underwent imaging studies as a follow-up exam an average of 3.6 years after surgery. In those patients, 42 were diagnosed with a hip pseudotumor, a rate of 39 percent.

This higher rate of occurrence of hip pseudotumor in those patients was far higher than had been previously reported, the researchers noted. Some sources had reported rates as low as one to four percent. The researchers said the higher rate is a cause for great concern.

Furthermore, 13 of the patients had such severe hip replacement surgery complications that they had to undergo revision surgery to replace their metal-on-metal hip implant with a different implant that used polyethylene components.

The researchers also noted a higher instance of pseudotumors among patients who showed elevated levels of metal ions in their blood, or metallosis, brought on by their implant. Patients with these higher levels of metal ions were four times as likely to develop a hip pseudotumor than those with lower ion levels.

A pseudotumor is a growth of tissue around a joint, other than cancer, scar tissue, or bursa. Symptoms of pseudotumors can include pain, swelling, clicking and subluxation (a partial dislocation of the joint).

The study’s authors commented that symptoms like swelling, clicking, and pain after hip replacement that are severe enough to require revision surgery could be a sign that there may be a large pseudotumor present with extensive destruction of tissue in the area.

Metal-on-Metal Hip Implant Lawsuits

Pseudotumors are one of several possible hip replacement surgery complications that have led to a huge amount of litigation over metal-on-metal hip implants. Thousands of plaintiffs in these hip implant lawsuits allege that their hip implant surgery complications resulted from defective design of their implants.

Some plaintiffs report suffering from more than just pain, reporting hip implant surgery complications including inflammation, swelling, or loss of mobility. Some report loosening of the artificial joints. Certain cases have been severe enough to require revision surgery to replace the implant.

The elevated levels of metal ions that the researchers noted in their study are also at issue in some of these hip implant lawsuits. Plaintiffs say that some metal-on-metal hip implants shed metal debris into the surrounding tissue, causing pain after hip replacement, death of the surrounding tissue, or failure of the implant.

This wave of litigation has already resulted in millions of dollars in settlements and jury awards. In December 2015 a jury awarded $11 million dollars to a former ski instructor who suffered soft tissue damage caused by metal that had shed from her hip implant. Manufacturer DePuy has reportedly agreed to pay $2.5 billion to settle claims over its ASR hip implants.

However, even after these and other positive results for plaintiffs, thousands of hip implant lawsuits still remain pending.