Bruce A. MacWilliams

Functional Elbow Range of Motion for Contemporary Tasks

BACKGROUNDnElbow range of motion for functional tasks has been previously studied. Motion arcs necessary to complete contemporary tasks such as using a keyboard or cellular telephone have not been studied and could have implications on what is considered to be a functional arc of motion for these tasks. The purpose of this study was to determine elbow range of motion, including flexion-extension, pronation-supination, and varus-valgus angulation, with use of three-dimensional optical tracking technology for several previously described positional and functional tasks along with various contemporary tasks.nnnMETHODSnTwenty-five patients performed six positional and eleven functional tasks (both historical and contemporary). Elbow flexion-extension, varus-valgus, and forearm rotation (pronation and supination) ranges of motion were measured.nnnRESULTSnPositional tasks required a minimum (mean and standard deviation) of 27° ± 7° of flexion and a maximum of 149° ± 5° of flexion. Forearm rotation ranged from 20.0° ± 18° of pronation to 104° ± 10° of supination. Varus and valgus angulations ranged between 2° ± 5° of varus to 9° ± 5° of valgus. For functional tasks, the maximum flexion arc was 130° ± 7°, with a minimum value recorded as 23° ± 6° and a maximum value recorded as 142° ± 3°. All of these were for the cellular telephone task. The maximum pronation-supination arc (103° ± 34°) was found with using a fork. Maximum pronation was found with typing on a keyboard (65° ± 8°). Maximum supination was found with opening a door (77° ± 13°). Maximum varus-valgus arc of motion was 11° ± 4°. Minimum valgus (0° ± 6°) was found with cutting with a knife, while maximum valgus (13° ± 6°) was found with opening a door.nnnCONCLUSIONSnFunctional elbow range of motion necessary for activities of daily living may be greater than previously reported. Contemporary tasks, such as using a computer mouse and keyboard, appear to require greater pronation than other tasks, and using a cellular telephone usually requires greater flexion than other tasks.

A computationally efficient optimisation-based method for parameter identification of kinematically determinate and over-determinate biomechanical systems

This paper introduces a general optimisation-based method for identification of biomechanically relevant parameters in kinematically determinate and over-determinate systems from a given motion. The method is designed to find a set of parameters that is constant over the time frame of interest as well as the time-varying system coordinates, and it is particularly relevant for biomechanical motion analysis where the system parameters can be difficult to accurately determine by direct measurements. Although the parameter identification problem results in a large-scale optimisation problem, we show that, due to a special structure in the linearised Karush–Kuhn–Tucker optimality conditions, the solution can be found very efficiently. The method is applied to a set of test problems relevant for gait analysis. These involve determining the local coordinates of markers placed on the model, segment lengths and joint axes of rotation from both gait and range of motion experiments.

Mechanical axis following staple epiphysiodesis for limb-length inequality.

BACKGROUNDnStaple epiphysiodesis is an option for the treatment of limb-length discrepancies, but it is not without complications. The purpose of this study was to review the outcomes of staple epiphysiodesis, including changes in the mechanical axis.nnnMETHODSnThe study included patients who underwent, between 1990 and 2005, staple epiphysiodesis of the femur or tibia, or both, to address limb-length discrepancy. We reviewed preoperative, postoperative, and final long standing anteroposterior radiographs of fifty-four patients to assess limb-length discrepancy, shifts in the mechanical axis, changes in the mechanical axis zone, and changes in the anatomic lateral distal femoral angle and the medial proximal tibial angle. Postoperative radiographs were also reviewed to assess the adequacy of staple placement.nnnRESULTSnThree staple epiphysiodesis groups were identified: fifteen patients who underwent a distal femoral staple epiphysiodesis, eighteen who underwent a proximal tibial procedure, and twenty-one who underwent combined distal femoral and proximal tibial procedures. Fifty percent (twenty-seven) of the fifty-four patients showed a shift in the mechanical axis of > or =1 cm as compared with the preoperative measurement. Eighty-nine percent of these large shifts were varus in nature. The proximal tibial and combined epiphysiodeses resulted in significantly larger shifts in the mechanical axis (p = 0.002 and p = 0.006, respectively) and zone changes (p = 0.009 and p = 0.006, respectively) than did the distal femoral procedures. Six patients ultimately underwent a high tibial osteotomy to correct a post-stapling varus deformity. The proximal-lateral aspect of the tibia was by far the most common location for inadequate staple placement.nnnCONCLUSIONSnMechanical axis deviation is common following staple epiphysiodesis for the treatment of limb-length discrepancy. Proximal tibial and combined distal femoral and proximal tibial staple epiphysiodeses, even if done well technically, lead to clinically relevant shifts in the mechanical axis of the lower extremity more than half of the time. Distal femoral staple epiphysiodesis may still be a safe option for the treatment of limb-length discrepancy, but we advise caution when utilizing proximal tibial staple epiphysiodesis to treat limb-length inequality.

Distal Tibial Rotation Osteotomies Normalize Frontal Plane Knee Moments

BACKGROUNDnTorsional deformities of the lower extremity are common in children and are often corrected with rotational osteotomy. The effects of torsional abnormalities, and the effects of corrective osteotomy, are not well understood. A study of children with isolated idiopathic tibial torsional pathology undergoing a single corrective procedure may assist in understanding the biomechanics of torsional deformities and the effect of surgical correction.nnnMETHODSnPreoperative and postoperative gait analyses were performed for eight subjects (eleven sides) with idiopathic excessive inward tibial torsion and ten subjects (fourteen sides) with excessive outward tibial torsion. Sagittal ankle and frontal knee moments were assessed and compared with those for age-matched controls.nnnRESULTSnPreoperatively, subjects exhibited abnormal frontal knee moments at push-off. Subjects with inward tibial torsion demonstrated excessive internal valgus moments, and subjects with outward tibial torsion demonstrated reduced internal valgus or relative internal varus moments compared with the control subjects. Ankle power was significantly reduced in the inward torsion group but not in the outward torsion group. Surgical correction of the torsional deformities normalized frontal plane knee moments in both inward and outward torsion groups and restored ankle power in the inward torsion group.nnnCONCLUSIONSnIn the present study, excessive tibial torsion adversely affected frontal knee moments and was associated with other kinematic and kinetic abnormalities. Corrective osteotomies improved all variables studied here and restored many to the values found in the control group.

Assessment of three-dimensional lumbar spine vertebral motion during gait with use of indwelling bone pins.

BACKGROUNDnThis study quantifies the three-dimensional motion of lumbar vertebrae during gait via direct in vivo measurement with the use of indwelling bone pins with retroreflective markers and motion capture. Two previous studies in which bone pins were used were limited to instrumentation of two vertebrae, and neither evaluated motions during gait. While several imaging-based studies of spinal motion have been reported, the restrictions in measurement volume that are inherent to imaging modalities are not conducive to gait applications.nnnMETHODSnEight healthy volunteers with a mean age of 25.1 years were screened to rule out pathology. Then, after local anesthesia was administered, two 1.6-mm Kirschner wires were inserted into the L1, L2, L3, L4, L5, and S1 spinous processes. The wires were clamped together, and reflective marker triads were attached to the end of each wire couple. Subjects underwent spinal computed tomography to anatomically register each vertebra to the attached triad. Subjects then walked several times in a calibrated measurement field at a self-selected speed while motion data were collected.nnnRESULTSnLess than 4° of lumbar intersegmental motion was found in all planes. Motions were highly consistent between subjects, resulting in small group standard deviations. The largest motions were in the coronal plane, and the middle lumbar segments exhibited greater motions than the segments cephalad and caudad to them. Intersegmental lumbar flexion and axial rotation motions were both extremely small at all levels.nnnCONCLUSIONSnThe lumbar spine chiefly acts to contribute abduction during stance and adduction during swing to balance the relative motions between the trunk and pelvis. The lumbar spine acts in concert with the thoracic spine. While the lumbar spine chiefly contributes coronal plane motion, the thoracic spine contributes the majority of the transverse plane motion. Both contribute flexion motion in an offset phase pattern.nnnCLINICAL RELEVANCEnThis is a valid model for measuring the three-dimensional motion of the spine. Normative data were obtained to better understand the effects of spine disorders on vertebral motion over the gait cycle.

A cadaver knee simulator to evaluate the biomechanics of rectus femoris transfer

A cadaver knee simulator has been developed to model surgical transfer of the rectus femoris. The simulator allows knee specimens six degrees of freedom and is capable of modeling both the swing and stance phases of human gait. Experiments were conducted using a mechanical hinge analog of the knee to verify that time, flexion angle, and knee extension force measurements recorded when using the simulator were not influenced by its design or operation. A ballistic double pendulum model was used to model the swing phase of gait, and the contributions of hip and ankle torques and hamstrings cocontraction were included when modeling the stance phase of gait. When modeling swing, range of motion and time to peak knee flexion in swing for the hinge knee were similar to those of in vivo test subjects. Measurements of hinge knee extension force when modeling stance under various biomechanical conditions matched those predicted using an analytical model. Future studies using cadaver knee specimens will apply techniques described in this paper to further our understanding of changes in knee biomechanics caused by rectus femoris transfer surgery.