Study zeroes in on predictive factors
By Jordana Bieze Foster
Researchers from Belgium are making progress toward identifying specific subsets of patients with patellofemoral pain who will benefit from brace treatment.
The use of orthotic devices to treat patients with PFP has long been a frustrating area for researchers, with multiple studies showing minimal or no effect across study groups despite marked improvements observed in some individual patients (see “Patellofemoral pain takes turn in spotlight.”)
This was underscored recently in the findings of a systematic literature review conducted by Dutch researchers focused on the additional effect of knee braces in patients with PFP when used in combination with exercise therapy. Investigators from Utrecht University concluded that moderate-level evidence points to no additional effect of knee braces on pain, and that evidence is conflicting with regard to the additional effect of bracing on function. That review was e-published in March by the British Journal of Sports Medicine.
But many researchers in the patellofemoral community are starting to follow what is becoming a growing trend across lower extremity medicine: Rather than looking for a single intervention to be effective for an entire heterogeneous group, they are focusing on specific characteristics that will identify those patients who are most likely to benefit from that intervention.
In the Belgian study, investigators from the University of Ghent found that military recruits who wore a patellofemoral brace were significantly less likely to develop PFP during basic training than a control group, and that five intrinsic risk factors predicted which recruits developed symptoms.
The findings were accepted for presentation in April at the IOC World Conference on Prevention of Injury and Illness in Sport. Although the authors were unable to attend the conference, the abstract was published along with the other conference abstracts in the April issue of BJSM.
The study population included 169 male military cadets who completed six weeks of strenuous basic training. Patellofemoral pain and other overuse injuries are particularly common during basic training, since many participants are unaccustomed to the levels of intense exercise required.
Forty three subjects were randomized to wear patellofemoral braces throughout training. The incidence of PFP in that group was 16.3%, which was significantly lower than the 33.7% incidence seen in the control group. Those figures were consistent with those seen in an earlier basic training study by the same group, published in the September 2004 issue of Knee Surgery, Sports Traumatology, & Arthroscopy, in which the incidence of PFP was 18.5% in braced recruits and 37% in controls.
The earlier study, however, did not look at which specific variables were predictive of PFP symptoms. In the current study, a delayed onset of the vasti (vastus medialis oblique and vastus lateralis), poor joint position sense, low knee extensor peak torque, and a low score on a military physical fitness test were predictive of developing PFP. In an earlier study published in the July-August 2000 issue of the American Journal of Sports Medicine, the same group found that patellofemoral pain in unbraced physical education students over a two-year period was predicted by a shortened quadriceps muscle, altered VMO muscle response time, decreased explosive strength, and a hypermobile patella.
In the current study, the researchers also found that expecting to sustain an injury was predictive of developing PFP. However, the questionnaire used to assess those expectations was not a validated measure, so the implications of that finding are unclear.
The findings regarding the five intrinsic predictive variables suggest that routine bracing of the subset of subjects with those characteristics could significantly reduce the incidence of PFP. But because PFP did develop in some braced subjects, further analysis of those predictive risk factors is still needed.