Your surgeon has given you the most up-to-date information available today based on the most recent histories. For example, in a recent study from Thomas Jefferson University Hospital in Philadelphia, Pennsylvania one-third of one percent (0.32%) of their 9570 total hip patients developed a peroneal nerve palsy.
The peroneal nerve is a branch of the much larger sciatic nerve). It was pinched, pressed, cut, deprived of oxygen, or exposed to high heat. The result was muscle weakness, loss of normal motor function (movement), and altered sensation.
The large sciatic nerve splits just above the knee to form the tibial nerve and the common peroneal nerve. These two nerves travel to the lower leg and foot, supplying sensation and muscle control. The tibial nerve continues down the back of the leg while the common peroneal nerve travels around the outside of the knee and down the front of the leg to the foot. Either one of these nerves can be damaged by injuries around the knee.
In the end, only slightly more than half (57 per cent) of the patients with a peroneal nerve palsy recovered fully after their total hip replacement. These results are the same as reported by others. In general, it seems to take about a year for patients to regain as much of the lost sensory and/or motor function as possible. In some cases, this time period was extended to 18 months (one and a half years).
By taking a look at all the patient characteristics of the 31 patients and comparing them to the rest of the (much larger) group, the authors were able to see one prognostic factor (i.e., able to predict when peroneal nerve palsy is more likely to happen). Being significantly overweight (obese) influences recovery in a negative way. In other words, a larger body-mass index (BMI) is a red flag for potential nerve problems associated with total hip replacement.
Time to recovery ranged from one month up to 50 months (four years, two months). Time in the operating room and amount of blood loss did not seem to be significant factors in recovery time. Body size/weight was the main determining factor in whether or not there was full recovery (not whether it was complete or incomplete at the time of the injury).
This study was unable to identify a single body mass index (BMI) threshold (the number at which a nerve palsy is likely to develop). There was a trend observed: the higher the BMI, the greater the chance for incomplete recovery. The lower the BMI, the more likely the patient was to experience full sensory and motor recovery.