Huberti and Hayes measured patellofemoral contact area and pressure through knee flexion, and how they changed when the Q‑angle was raised or lowered by 10°.
Pressure‑sensitive film study of 12 fresh‑frozen cadaver knees from donors aged 56 to 75, tested from 20° to 120° of flexion.
Key Findings
From 20° to 90° at the physiological Q‑angle, pressure was nearly uniform over the contact area (within 0.25 MPa) in every knee, with about equal pressure on both facets.
Mean pressure rose from 2.0 MPa at 20° to 4.4 MPa at 90°, most steeply between 30° and 60°. Pressures were highest at 60° and 90°, not at 120°.
Contact moved from the distal third of the patellar cartilage at 20° to its proximal margin at 120°, covering about one‑fifth of the surface at 20° and one‑third at 90°.
At 120°, quadriceps tendon contact with the femoral groove carried about one‑third of the force on the patella (547 vs 1609 N) at under half its pressure.
Raising the Q‑angle 10° increased peak pressure 45% at 20° (p < 0.05), with no significant change at other angles. Lowering it 10° increased peak pressure significantly at every angle, by 23% to 53%.
Each Q‑angle change produced one of two patterns, unrelated to Wiberg patellar shape. Lowering it shifted load medially in 5 knees and onto both facets with crest unloading in 7, with higher peak pressure elsewhere.
Board pearl
The authors estimated that patellofemoral force can reach several times body weight: about 6.5 times at 90° under full quadriceps moments. These were aged knees with acute, not adapted, Q‑angle changes.
Authors' conclusion
Both increases and decreases in Q-angle lead to more non-uniform pressure distributions, with higher peak stresses and unloading of other areas. With both variations in Q-angle, two different contact patterns are observed, and these are not predictable on morphological grounds. This seems to contraindicate the use of reconstructive procedures directed toward further reductions in the Q-angle in chondromalacic patients with a normal Q-angle . Overcorrection of an increased Q-angle should also be avoided.
Huberti and Hayes measured patellofemoral contact area and pressure through knee flexion, and how they changed when the Q‑angle was raised or lowered by 10°.
Pressure‑sensitive film study of 12 fresh‑frozen cadaver knees from donors aged 56 to 75, tested from 20° to 120° of flexion.
Key Findings
From 20° to 90° at the physiological Q‑angle, pressure was nearly uniform over the contact area (within 0.25 MPa) in every knee, with about equal pressure on both facets.
Mean pressure rose from 2.0 MPa at 20° to 4.4 MPa at 90°, most steeply between 30° and 60°. Pressures were highest at 60° and 90°, not at 120°.
Contact moved from the distal third of the patellar cartilage at 20° to its proximal margin at 120°, covering about one‑fifth of the surface at 20° and one‑third at 90°.
At 120°, quadriceps tendon contact with the femoral groove carried about one‑third of the force on the patella (547 vs 1609 N) at under half its pressure.
Raising the Q‑angle 10° increased peak pressure 45% at 20° (p < 0.05), with no significant change at other angles. Lowering it 10° increased peak pressure significantly at every angle, by 23% to 53%.
Each Q‑angle change produced one of two patterns, unrelated to Wiberg patellar shape. Lowering it shifted load medially in 5 knees and onto both facets with crest unloading in 7, with higher peak pressure elsewhere.
Board pearl
The authors estimated that patellofemoral force can reach several times body weight: about 6.5 times at 90° under full quadriceps moments. These were aged knees with acute, not adapted, Q‑angle changes.
Authors' conclusion
Both increases and decreases in Q-angle lead to more non-uniform pressure distributions, with higher peak stresses and unloading of other areas. With both variations in Q-angle, two different contact patterns are observed, and these are not predictable on morphological grounds. This seems to contraindicate the use of reconstructive procedures directed toward further reductions in the Q-angle in chondromalacic patients with a normal Q-angle . Overcorrection of an increased Q-angle should also be avoided.