Variation in the patellar tendon moment arm identified with an improved measurement framework

Abstract

The mechanical advantage of the knee extensor mechanism depends heavily on the patellar tendon moment arm (PTMA). Understanding which factors contribute to its variation may help improve functional outcomes following arthroplasty. This study optimized PTMA measurement, allowing us to quantify the contribution of different variables. The PTMA was calculated about the instantaneous helical axis of tibiofemoral rotation from optical tracked kinematics. A fabricated knee model facilitated calculation optimization, comparing four data smoothing techniques (raw, Butterworth filtering, generalized cross-validated cubic spline-interpolation and combined filtering/interpolation). The PTMA was then measured for 24 fresh-frozen cadaveric knees, under physiologically based loading and extension rates. Combined filtering/interpolation enabled sub-mm PTMA calculation accuracy throughout the range of motion (root-mean-squared error 0.2 mm, max error 0.4 mm), whereas large errors were measured for raw, filtered-only and interpolated-only techniques at terminal flexion/extension. Before scaling, the mean PTMA was 46 mm; PTMA magnitude was consistently larger in males (mean differences: 5 to 10 mm, p < .05) and was strongly related to knee size: larger knees have a larger PTMA. However, while scaling eliminated sex differences in PTMA magnitude, the peak PTMA occurred closer to terminal extension in females (female 15°, male 29°, p = .01). Knee size accounted for two-thirds of the variation in PTMA magnitude, but not the flexion angle where peak PTMA occurred. This substantial variation in angle of peak PTMA has implications for the design of musculoskeletal models and morphotypespecific arthroplasty. The developed calculation framework is applicable both in vivo and vitro for accurate PTMA measurement.

The compartmental approach to revision of partial knee arthroplasty results in nearer-normal gait and improved patient reported outcomes compared to total knee arthroplasty

“…However, while the overall scores were significantly different, the mean differences in OKS failed to exceed the “minimal important difference” threshold of five points [ 5 ] though the median score reached it. Although not validated for analysis by individual question, it is noteworthy that the largest differences were seen in the use of transport, kneeling and giving way, activities which rely heavily on the isokinetic quadriceps strength and extensor efficiency of the knee, where differences between CPKA and TKA are known to exist [ 13 , 24 , 11 ]. This ties in well with the gait data, since the most significant differences are seen in early stance, during weight acceptance and mid-stance, were the quadriceps are at their most active [ 30 ].…”

Patellofemoral Joint Loading Progression Across 35 Weightbearing Rehabilitation Exercises and Activities of Daily Living

“…This scheme of equations also includes 2 knee tendons of clinical importance—the patellar and quadriceps tendons. Thus, we additionally present the equations derived from up-to-date data 12,37 to estimate patellar tendon moment arm and force (Equations 5 and 6), as a unified point of reference for future biomechanics research on the anterior knee structural complex.…”

Patellar Tendon Load Progression during Rehabilitation Exercises: Implications for the Treatment of Patellar Tendon Injuries

“…For determining patellar tendon force, first, a knee angle-dependent cubic polynomial function for patellar tendon moment arms (equation 1) was derived from a recent imaging study database, which reported data from 0°(neutral) to 120°o f knee flexion (39). This polynomial was extrapolated for patellar tendon moment arms during hyperextension up to 10°a nd set moments arms in extreme knee flexion to equal of 120°when it approached a plateau (39,40). Next, the patellar tendon force was estimated by dividing the knee moment by the patellar tendon moment arm at the specific knee angle during each time instance of motion (equation 2).…”