Summary of main findings
The incidence of trochanteric pain in primary care is 1.8 patients per 1000 per year. In this study, after 1 year 76% of the responders still suffered from trochanteric pain, and after 5 years approximately 63% did. Due to possible selection bias, these figures would probably be lower in reality, but not lower than 36% and 29%, respectively.
Predictors associated with improvement within 1 year were duration of symptoms at the first visit to the GP and the absence of osteoarthritis in the lower limbs. Again, the duration of symptoms before the first visit to the GP, as well as having had a corticosteroid injection, were predictive for improvement within 5 years.
The strengths and limitations of this study
This study is vulnerable to different biases. The first is selection bias. This may be a result of the high number of non-responders (46%), and it is probable that patients with sustained symptoms were more likely to return the questionnaire. We were able to correct for this kind of bias in the calculation of the prognosis of trochanteric pain (best/worst-case scenario). Likewise, it could be that patients without symptoms at the time of the investigation did not return the questionnaire. Therefore, we expect that the real percentage with sustained symptoms is lower than observed, and will approximate those from the best-case scenario.
For the calculation of the incidence of trochanteric pain, however, the data are likely to be influenced by this selection bias. That is why we chose not extrapolate the 12% of patients who were inaccurately selected with pain located elsewhere to the non-responders group, but instead to calculate the incidence directly from the patients with trochanteric pain as reported by the GP.
The impact of trochanteric pain seems to be substantial; about 30–40% of the patients were impaired in their daily activities. However, these data are also prone to selection bias, because it is probable that the patients with sustained symptoms were more likely to return the questionnaire. Moreover, these data are also prone to a second type of bias introduced; the so-called recall bias (historical information reported by the participants is known to be inaccurate).
The third type of bias in this study is the bias by indication. An important finding of this study is that patients who received a corticosteroid injection in the region of the greater trochanter showed a better prognosis of their hip problems after 5 years. There might have been bias by indication; perhaps only patients with a lot of pain received an injection. Due to the retrospective character of this study, we were not able to correct for this potential confounder. However, assuming that the more severe cases have a worse prognosis, but also receive an injection earlier, this study gives an indication that corticosteroid injections are more effective than other treatments in trochanteric pain.
To look for other potential biases by indication, we analysed whether there were variables that might influence the GP to chose to give an injection. The only two variables found were pain elicited when the patient lay on the affected side, and the development of lower back pain at the time of follow-up. However, these variables do not significantly influence the model.
Finally, our results suggest that patients with OA had a higher risk of persistent symptoms after 1 year, compared to patients without OA. This finding may be biased because the greater trochanter is one of the sites to which hip or knee OA can refer to.14
As we only had information from the questionnaire, we did not have objective information about the condition of the patients. The data on OA were collected at the end of the follow-up period, and not when the symptoms of trochanteric pain began, therefore confusion between cause and consequence is possible. Nonetheless, we think that data on OA would not have changed much and would be fairly stable over a period of 1 year. Hence, we used these data in the model for the 1-year follow-up, but not for the 5-year follow-up.
Comparison with existing literature
Prognosis
This is the first study on the long-term prognosis of trochanteric pain. There are only a few case series available of patients receiving one type of intervention, but the longest follow-up time reported was 2 years. In that study a recovery rate of about 90% was reported.5 A different study reported on a follow-up after surgery of a maximum period of 60 months.15 These highly selected patients in secondary care are not comparable with our population in primary care.
Therapy
In our study population, 37% of patient received corticosteroid injection(s), and about 66% reported an improvement. This is comparable with the outcome of a case series in which about 61% of the patients had improved 6 months after local injection of corticosteroid and lidocaine.16
The improvement found in our study, however, differs from earlier case series in which all patients reported improvement after local corticosteroid injection(s).5,17 This discrepancy may be due to pre-selection of the patients (outpatient clinic) or the previously mentioned selection bias.
