Quadriceps Inhibition After Naturally Occurring Patellar Tendon Damage and Pain.
CONTEXT
After knee-joint injury, pain, effusion, and mechanoreceptor damage alter afferent signaling, which can result in quadriceps inhibition and subsequent weakness. The individual contributions of each factor to inhibition remain unclear due to confounding knee-joint injuries and indirect experimental models.


OBJECTIVE
To characterize the influence of naturally occurring knee damage and pain on quadriceps neuromuscular function in individuals with patellar tendinopathy.


DESIGN
Cross-sectional study.


SETTING
Research laboratory.


PATIENTS OR OTHER PARTICIPANTS
Twenty participants who self-reported patellar tendinopathy (PT) and 10 healthy control individuals underwent ultrasonic tendon assessment. Injured participants were dichotomized by an orthopaedic surgeon into groups with (1) pain and structural tendon abnormality and (2) regional pain alone.


MAIN OUTCOME MEASURE(S)
Quadriceps inhibition was assessed with the Hoffman reflex and the central activation ratio via the superimposed-burst technique. Normally distributed measures were analyzed using a 1-way analysis of variance and post hoc independent t tests. Kruskal-Wallis tests with post hoc Mann-Whitney U tests were used to analyze nonnormally distributed data. An a priori α level of P ≤ .05 was set.


RESULTS
Control participants presented with more spinal-reflex excitability (0.37 ± 0.23) than the PT (0.10 ± 0.06; P = .03) and regional-pain (0.18 ± 0.05; P = .02) groups. Knee-extension strength was greater in the control (3.37 ± 0.59 Nm/kg) than in the PT (2.41 ± 0.67 Nm/kg; P = .01) group but not the regional-pain group (3.05 ± 0.66 Nm/kg; P = .24). Control individuals presented with more quadriceps activation (97.93% ± 3.12) than the PT (84.44% ± 16.98; P < .01) and regional-pain (91.17% ± 10.56; P = .01) groups. No differences were present for any measures between the PT and regional-pain groups (P values > .05).


CONCLUSIONS
Deficits in spinal-reflex excitability, quadriceps activation, and strength were present in both the PT and regional-pain groups. A combination of pain and structural damage appeared to have the greatest negative effect on quadriceps function, as only the PT group presented with neuromuscular outcomes that failed to meet clinical thresholds.
['Davi|Steven M|SM|', 'Lepley|Adam S|AS|', 'Denegar|Craig R|CR|', 'DiStefano|Lindsay J|LJ|', 'Edgar|Corey M|CM|', 'Lepley|Lindsey K|LK|']
D000328:Adult D003430:Cross-Sectional Studies D005260:Female D006801:Humans D007718:Knee Injuries D008297:Male D008465:Mechanoreceptors D018908:Muscle Weakness D059352:Musculoskeletal Pain D009460:Neurologic Examination D017063:Outcome Assessment, Health Care D017847:Patellar Ligament D052097:Quadriceps Muscle D052256:Tendinopathy D014463:Ultrasonography
tendinopathy diagnostic imaging knee pain muscle inhibition