Knee joint loading indices before and 3 months after arthroscopic partial medial meniscectomy

Purpose: Increased knee adduction moment (KAM) is considered an important marker of medial compartment loading in knee osteoarthritis (OA) research. Patients undergoing arthroscopic partial medial meniscectomy (APMM) are at increased risk of developing medial compartment knee OA. APMM may contribute to altered knee joint loading patterns. The aim of this pilot study was to determine the short-term changes in knee joint loading indices after medial APMM. Methods: We investigated indices of knee joint loading using 3D gait analysis in 16 patients (13 men, 46.0 (SD 6.9 yrs), 178.7 (7.0) cm, 81.1 (10.7) kg, 25.4 (3.5) kg/m2) undergoing APMM for a medial meniscus tear. All patients had no radiographic knee OA (i.e. K/L grade 0 or 1) in the leg undergoing APMM and in their uninjured control leg at the baseline assessment prior to surgery. Exclusion criteria were: back problems, previous knee surgery, other co-morbidities affecting lower extremity function, low activity level (i.e. only indoor walking). Patients were assessed prior to and 3 months post APMM. Walking gait data were collected (100 Hz) using a 6-camera Vicon MX system (Vicon, Oxford, UK) with the Plug-in-Gait marker set. Ground reaction forces were recorded in synchrony with the cameras (1000 Hz) using two force plates (AMTI, OR6-7-1000, Watertown, MA, USA). The following indices of knee joint loading were calculated using inverse dynamics and reported relative to body size (Nm/BW*HT%): peak KAM, KAM impulse (i.e. the positive area under the KAM-time curve) and peak knee flexion moment. All motion data were collected barefoot during gait at patients' self-selected walking speed. Variables were calculated for each trial, then averaged over five trials. At the follow-up patients were instructed to walk with the same speed, allowing a margin of ± 5%. Paired t-tests were used to test for differences in the change of knee joint loading indices between operated and control legs from before APMM to the 3 month follow-up and to evaluate potential differences between the operated and control legs at the baseline. Results: From pre surgery to 3 month post APMM, there was a significantly larger increase in KAM impulse in the operated leg compared with the control leg (p = 0.03). A tendency towards a larger increase in peak KAM was also observed in the operated compared with the control leg (p = 0.10) (Table 1). Loading indices were generally higher in the control knee compared to the leg undergoing APMM prior to surgery, even though this only approached statistical significance for peak knee flexion moment (peak KAM, p = 0.29; KAM impulse, p = 0.14; peak flexion moment, p = 0.06). Conclusions: Our preliminary data indicate that knee joint loading indices increase within the first 3 months post medial APMM compared to the non-operated contralateral knee. Whether this is influenced by changes in pain status or is a result of APMM per se warrants further investigation.Table 1Knee joint loading indices before and 3 month after surgery in the operated and contralaterOperated legControl legPREPOSTCHANGEPREPOSTCHANGEDifference in change, P-valuePeak KAM (Nm/BW*HT%)3.05 (0.65)3.36 (0.70)0.32 (0.11)3.28 (0.89)3.29 (0.90)0.01 (0.13)0.10KAM impulse (Nms/BW*HT%)1.15 (0.26)1.32 (0.31)0.17 (0.06)1.24 (0.29)1.26 (0.39)0.02 (0.04)0.03PFlex. moment (Nm/BW*HT%)2.56 (1.25)2.69 (1.16)0.12 (0.25)3.33 (1.05)3.28 (1.35)-0.05 (0.26)0.60Values are mean (SD).KAM = external Knee Adduction Moment.PFlex moment = external Peak Flexion Moment. Open table in a new tab Values are mean (SD). KAM = external Knee Adduction Moment. PFlex moment = external Peak Flexion Moment.