S22 Oral Presentations expressed genes. In late OA, proinflammatory genes prevailed. In response to exercise in early OA the major molecules upregulated were IL-6, Lif, chemokines Cxcl1 and Ccl2, transcription factors of MAPK family, and growth factors. In late OA, effects of exercise were not obvious and the gene expression profiles were similar to untreated OA joints. Support NIH AR048781 and HD040939. 025 GAMMA-LOOP DYSFUNCTION CONTRIBUTES TO QUADRICEPS INHIBITION IN PATIENTS WITH KNEE JOINT OSTEOARTHRITIS D. Rice, P.J. McNair, G. Lewis Auckland Univ. of Technology, Auckland, New Zealand Purpose: A consequence of osteoarthritis (OA) at the knee joint is an inability to fully activate the quadriceps muscles, leading to marked weakness that impairs function and quality of life. Normal function of the gamma loop is essential to achieve full voluntary muscle activation as it provides tonic excitatory input to the quadriceps alpha motoneuron pool. There is evidence that traumatic ligament damage alters sensory output from the knee joint and impairs transmission of signals in the gamma loop. In individuals with knee OA, degeneration of joint structures (e.g. joint capsule) may simultaneously damage the sensory endings located within these tissues, reducing afferent output and impairing the gamma-loop. However, this has not yet been investigated. Thus, the purpose was to determine whether quadriceps gamma-loop dysfunction is present in individuals with OA of the knee joint. Methods: Thirteen subjects with radiographically confirmed knee OA and ten age and gender matched controls with no history of knee joint pathology participated in this study. All subjects were seated in a custom designed chair with the knee joint fixed in 90° of flexion. The lower leg was strapped to a metal attachment in series with a strain gauge at the level of the ankle joint. Maxi- mum effort isometric contractions of the quadriceps and hamstring muscles were then performed and force together with EMG was collected from the vastus lateralis (VL), vastus medialis (VM), medial hamstrings (MH) and lateral hamstrings (LH). Following the first set of maximum isometric contractions, 20 minutes of 50Hz vibration was applied to the infrapatellar tendon using an electromechanical tapper. After tendon vibration, maximum effort isometric contractions of the quadriceps and hamstrings were repeated, with force and EMG collected in an identical manner to baseline testing. Quadriceps and hamstrings peak force were converted into torque measurements and normalised as a per- centage of body mass for each subject. The root mean square (RMS) of the EMG signals was calculated and used in subsequent analyses. If a gamma loop dysfunction is not present, the effect of vibration is to decrease strength and EMG levels, usually by 8-10%. If present, then strength and EMG levels will not change following vibration. Thus one sample t-tests were undertaken to analyse whether percent changes in torque and EMG differed from zero after vibration in each group. The alpha level was set at 0.05. Results: Following tendon vibration, quadriceps peak torque de- creased significantly in the control group (p < 0.05) but did not change in OA subjects (p >0.05). Hamstrings peak torque was un- changed in both groups (p >0.05). Similarly, after tendon vibration the RMS values of VM and VL decreased (p<0.01) in the control group, but was unchanged in the OA group (p >0.05). RMS values of MH and LH remained unchanged in both groups (p > 0.05). Conclusions: The results suggest that quadriceps gamma-loop dysfunction was present in patients with OA of the knee joint. Prolonged tendon vibration induces a temporary gamma loop dys- function by blocking transmission in Ia afferent nerve fibres. The subsequent loss of excitatory input from primary muscle spindles reduces alpha motor neuron excitability, preventing full activation of the muscle. Thus, a decrease in quadriceps peak torque and RMS values is expected after vibration. In contrast, a lack of change in quadriceps activation seen in OA subjects suggests that Ia afferent transmission was already impaired, thus torque and EMG levels were unaffected by vibration. In conclusion, gamma loop dysfunction contributes to quadriceps activation deficits in patients with OA, partially explaining the marked weakness and atrophy that is often observed in this muscle group. 026 PAIN, FUNCTION AND MUSCLE STRENGTH IN MENISCECTOMIZED PATIENTS AT HIGH RISK OF OA COMPARED TO AGE- AND GENDER MATCHED CONTROLS J.B. Thorlund, P. Aagaard, E.M. Roos Inst. of Sports Sci. and Clinical Biomechanics, Univ. of Southern Denmark, Odense M, Denmark Purpose: Reduced quadriceps muscle strength has been pro- posed as one of the candidates for self-reported pain and func- tional limitations and as a predictor of future OA in meniscec- tomized patients. Traditionally, measures of maximal isometric or concentric muscle strength have been the parameters of choice to describe deficits in muscle capacity in this patient group. How- ever, during functional tasks like gait and stair walking eccentric muscle strength might be more important to control the descent of center of mass, absorbing impacts and thus decrease knee joint loading. The aim of this study was twofold: 1) to compare different aspects of quadriceps muscle strength (i.e. concentric and ec- centric peak torque) in middle-aged patients who had undergone meniscectomy for a symptomatic degenerative tear with age and gender matched controls; 2) to study the role of muscle strength on self-reported pain and function in meniscectomized patients. Methods: Patients: 31consecutive patients (21 men, 46±6 yrs, 175±7 cm, BMI 26±4, 21±6 month post-surgery) operated for a symptomatic non-traumatic medial meniscal posterior horn tear. Exclusion criteria: miss-classified by the surgical code system, previous cruciate ligament injury, severe cartilage changes defined as deep clefts or visible bone at meniscectomy or self-reported co-morbidity factors limiting participation in the study. 31 controls (19 men, 46±6 yrs, 175±10 cm, BMI 26±4) identified through the Danish social security number system. Exclusion criteria; previous cruciate ligament injury or other knee surgery or self-reported co-morbidity factors limiting participation in the study. Strength tests: Concentric and eccentric peak torques were mea- sured at 30 deg s -1 for the quadriceps muscle in an isokinetic dynamometer (KinCom) in the operated and non-operated leg for the patients and in both legs for the controls. Self-reported outcomes: The Knee Injury and Osteoarthritis Score (KOOS) was used to assess knee-related pain, symptoms, function in daily life, sports and recreation function and quality of life. Separate subscale scores from 0 to 100, worst to best, were calculated. Statistics: Strength and KOOS scores in patients and controls were compared by one way ANOVA and Mann-Whitney tests, respectively. To determine the relationship between concentric and eccentric muscle strength and the KOOS subscales Sport and Recreation Function and Pain, which are thought to be dependent on muscle strength, Spearman correlations were used. Results: Strength: Concentric and eccentric quadriceps strength did not differ between the operated and non-operated leg, and no differences were observed between patients and controls (Table 1). KOOS: Large differences were observed between patients and controls; Pain 83±16 vs. 97±5 (p<0.001), symptoms 82±16 vs. 94±9 (p<0.001), ADL 89±14 vs. 99±3 (p<0.001), Sport/Rec 69±24 vs. 95±8 (p<0.001), QOL 69±23 vs. 91±11 (p<0.001).