Offloading braces ‘lighten the load’ for degenerative knee compartments

Study results show that 70% to 80% of unicompartmental knee arthritis patients had condylar separation with offloading braces.

In two Colorado studies on unicompartmental knee arthritis patients, researchers found that 70% to 80% of patients experienced condylar separation in degenerative knee compartments when wearing offloading knee braces. They also found 100% association between condylar separation and pain relief.

However, “not all braces are equally effective,” said Douglas Dennis, MD, who presented the study results at the Current Concepts in Joint Replacement Spring 2005. “[The braces’] effectiveness are dependent on patient compliance, brace fit and design, and leg girth, obviously providing less benefit in the obese patient,” Dennis said.

Fluoroscopic surveillance

The first study involved 45 medial compartment osteoarthritic patients tested under weight bearing, in vivo conditions using video fluoroscopy. All had medial bone-on-bone narrowing. Researchers aimed to find out if offloading knee braces separate the femur from the tibial condyle and if condylar separation relieves pain.

They analyzed the 40 test patients and five control patients (under fluoroscopic surveillance) in the frontal plane with and without the brace applied, but loosely applied the brace to the five control patients. Under fluoroscopic surveillance, the patients performed level gait on a treadmill, while researchers analyzed them at heel strike and mid stance. They also analyzed the patients’ subjective pain relief.

From the fluoroscopic video, researchers were able to digitize the midpoints of the medial and lateral femoral and tibial condyles. “Condylar separation was determined by measuring the distance between these digitized points both with and without a brace and a separation angle was also determined,” Dennis said.

Study 1: Results

At heel strike, 78% of patients had condylar separation after brace application with an average of 1.7 mm. Similarly, at mid stance, 70% had condylar separation after the brace with an average of 1.9 mm. “If we look at the control group, in which the brace was loosely applied, there was no condylar separation observed and no angular change observed either at heel strike or at mid stance,” Dennis said.

Results also showed that 85% of the patients reported pain relief with the brace. The 15% of patients without pain relief did not exhibit any condylar separation and all were obese, which was qualified as 20% over the ideal body weight.

At heel strike, 31 patients experienced condylar separation, reported pain relief and found the brace worthwhile, Dennis said. Of the remaining nine patients who did not have condylar separation at heel strike, six reported no pain relief. The fact that three patients did report pain relief indicated that “those three patients either had separation less than our error measurement of 0.3 millimeters or possibly the brace may have some placebo effect,” Dennis said.

Study 2

In the second study, researchers analyzed five medial arthritis patients again using fluoroscopy. However, this time they also analyzed five different offloading braces and added a sixth, an ACL brace, for a control.

The researchers also obtained thin-cut CT scans in all patients and created three-dimensional models of the femur, tibia and fibula. “[This] allowed us to do a three-dimensional analysis giving us our error value of 0.3 mm in determining condylar separation,” Dennis said.

Results demonstrated that the braces provided condylar separation, but in different amounts. Two of the five braces yielded better results.

Offloading braces mechanically resist the abduction and adduction moments that occur at early heel strike and midstance to reduce loads on the degenerative compartment and relieve knee pain, according to Dennis. The adduction moment is estimated at 36 to 50 N and increases in patients with co-existing varus deformity, creating a 70% to 75% medial compressive load at mid stance of normal gait.

For more information:
Dennis D. Off-Loading Braces: Lighten the Load. #24. Presented at Current Concepts in Joint Replacement Spring 2005. May 22-25, 2005. Las Vegas.