Louis F. Draganich

Coactivation of the hamstrings and quadriceps during extension of the knee.

The electromyographic activities of six muscles of the thigh were recorded, using bipolar surface electrodes, during active extension of the knee by six healthy men. The signal amplitudes were normalized to those recorded during isometric maximum voluntary contractions. Extension of the knee from 90 to 0 degrees (full extension) was performed at the rate of 10 degrees per second with the leg unimpeded and with weights of 1.8, 3.6, 5.4, or 7.2 kilograms attached to the ankle. The hamstrings were found to coactivate with the quadriceps during the terminal phase of extension. Coactivation of all three hamstrings was found to occur at joint angles of as much as 9 degrees, with the maximum at full extension of the knee and the strength of the signals ranging to as much as 20 per cent. The signals of all of the flexors and extensors increased with increasing loads on the ankle and, with the exception of the rectus femoris at 9 degrees of flexion, they also increased as the knee extended. The results of this study support the hypothesis that the hamstrings function synergistically with the anterior cruciate ligament to prevent the anterior tibial displacement that is produced by active contraction of the quadriceps in the terminal degrees of extension of the knee. This information is important for the physical conditioning of healthy individuals in preparation for athletic endeavors. Furthermore, if coactivation of the hamstrings with the quadriceps is mediated by sensors other than, or in addition to, those of the anterior cruciate ligament, then strengthening of the hamstrings appears to be an important adjunct to rehabilitation programs after repair or reconstruction of that ligament.

Stepping over an obstacle increases the motions and moments of the joints of the trailing limb in young adults

Tripping over obstacles is the most frequently mentioned causes of falls. Thus, this study was performed to test the hypotheses that when crossing obstacles, toe-obstacle clearance and the three-dimensional motions and moments at the hip, knee, and ankle of the trailing limb (limb crossing the obstacle last) increase with obstacle height. Data were collected using an optoelectronic digitizing system and force platform. Fourteen healthy young adults were tested during unobstructed level walking and when stepping over obstacles of 51, 102, 153, or 204 mm heights. Toe-obstacle clearances of the trailing foot increased from 31 mm during unobstructed gait to an average of 146 mm when stepping over obstacles of any of these heights. Obstacle height was not found to affect toe-obstacle clearance. When the toe of the trailing limb was over the obstacle, the flexion angles of the hip and knee increased linerly with obstacle height. Compared to flexion of the hip or ankle, flexion of the knee appears to be of primary importance when crossing obstacles with the trailing limb. The maximum extension moment at the hip joint during late stance decreased linearly with obstacle height. At the knee joint, the maximum flexion moment during early stance and the maximum adduction moment during late stance increased linearly with obstacle height. At the ankle joint, the maximum dorsiflexion moment during late stance increased linearly with obstacle height. These greater demands on motions and moments may affect the abilities of those elderly having decreased muscle strengths to step over obstacles.

Motion of the whole body's center of mass when stepping over obstacles of different heights

Tripping over obstacles and imbalance during gait were reported as two of the most common causes of falls in the elderly. Imbalance of the whole body during obstacle crossing may cause inappropriate movement of the lower extremities and result in foot-obstacle contact. Thus, this study was performed to investigate the effect of obstacle height on the motion of the whole bodys center of mass (COM) and its interaction with the center of pressure (COP) of the stance foot while negotiating obstacles. Six healthy young adults were instructed to perform unobstructed level walking and to step over obstacles of heights corresponding to 2.5, 5, 10, and 15% of the subjects height, all at a comfortable self-selected speed while walking barefoot. A 13-link biomechanical model of the human body was used to compute the kinematics of the whole bodys COM. Stepping over the higher obstacles resulted in significantly greater ranges of motion of the COM in the anterior-posterior and vertical directions, a greater velocity of the COM in the vertical direction, and a greater anterior-posterior distance between the COM and COP. In contrast, the motion of the COM in the medial-lateral direction was less likely to be affected when negotiating obstacles of different heights.

The effect of femoral tunnel position and graft tensioning technique on posterior laxity of the posterior cruciate ligament-reconstructed knee.

We report the effects of femoral tunnel position and graft tensioning technique on posterior laxity of the posterior cruciate ligament-reconstructed knee. An isometric femoral tunnel site was located using a specially de signed alignment jig. Additional femoral tunnel positions were located 5 mm proximal and distal to the isometric femoral tunnel. With the graft in the proximal femoral tunnel, graft tension decreased as the knee flexed; with the graft in the distal femoral tunnel, graft tension in creased as the knee flexed. When the graft was placed in the isometric femoral tunnel, a nearly isometric graft tension was maintained between 0° and 90° of knee flexion. One technique tested was tensioning the graft at 90° of knee flexion while applying an anterior drawer force of 156 N to the tibia. This technique restored sta tistically normal posterior stability to the posterior cru ciate ligament-deficient knee between 0° and 90° for the distal femoral tunnel position, between 0° and 75° for the isometric tunnel position, and between 0° and 45° for the proximal tunnel position. When the graft was tensioned with the knee in full extension and without the application of an anterior drawer force, posterior trans lation of the reconstructed knee was significantly dif ferent from that of the intact knee between 15° and 90° for all femoral tunnel positions.

Placing the trailing foot closer to an obstacle reduces flexion of the hip, knee, and ankle to increase the risk of tripping

This study was performed to test the hypothesis that reducing the horizontal distance between the trailing foot (foot crossing the obstacle last) and obstacle, during stance just prior to stepping over the obstacle, would reduce flexion of the hip, knee, and ankle joints of the trailing limb when the toe is over the obstacle to reduce the vertical toe-obstacle clearance and increase the risk of tripping. Fourteen healthy young adults stepped over an obstacle of 51, 102, 153, and 204 mm height in a self-selected manner (i.e., toe-obstacle distance was not controlled) and for toe-obstacle distance targets of 10, 20, 30, and 40% of their step lengths measured during unobstructed gait. The reductions in toe-obstacle distance resulted in linear decreases in flexion of the hip, knee, and ankle when the toe was over the obstacle. Toe-obstacle clearance of the trailing limb decreased significantly as toe-obstacle distance decreased. The reductions in toe-obstacle distance led to contact of the trailing (but not the leading) foot with the obstacle, the closer the obstacle the greater the number of contacts. The reductions also resulted in linear decreases in swing time of the trailing limb from toe-off to when the toe was over the obstacle. The height of the hip was not affected by toe-obstacle distance. Angular velocity of knee flexion was found to increase linearly as toe-obstacle distance decreased and appears to be of primary importance in avoiding obstacle contact.

An in vitro study of an intraarticular and extraarticular reconstruction in the anterior cruciate ligament deficient knee

The biomechanical effectiveness of an extraarticular ACL reconstruction, an intraarticular ACL reconstruc tion, and the combination of these on both anterior stability and internal rotational stability of the ACL de ficient knee was investigated in six cadaver knees. The extraarticular reconstruction consisted of the Müller anterolateral femorotibial ligament iliotibial band teno desis, and the intraarticular reconstruction used the middle third of the patellar tendon in the manner of Clancy. The extraarticular reconstruction was found to over- constrain internal tibial rotation of the ACL excised knee between 30° and 90° ( P < 0.05). While the isolated extraarticular reconstruction did not return normal an terior stability to the ACL deficient knee (P < 0.05), it did significantly reduce the anterior laxity of the ACL deficient knee between 30° and 90° of knee flexion (P < 0.05). For the combined reconstruction, the intraarticular procedure was performed and then only enough ten sion was applied to the extraarticular reconstruction to take up slack in the tenodesis without shifting the rotatory position of the tibia from that produced by the intraarticular procedure alone. Neither the intraarticular reconstruction nor the combined procedure resulted in any significant shifts from normal (P < 0.05) in the rotatory position of the unloaded tibia; during loading neither resulted in rotational displacements significantly different from normal; and both of these procedures reduced the increased anterior laxity of the ACL defi cient knee to a level not statistically different from normal. Because the extraarticular reconstruction shared the load when performed with the intraarticular reconstruc tion as part of a combined procedure, we concluded that it would be useful as an adjunctive procedure in appropriate clinical situations.

Effects of knee pain relief in osteoarthritis on gait and stair-stepping.

Osteoarthritic knee pain affects patient mobility. Relief of knee pain in osteoarthritis has been reported to increase loading of the knee during gait, but it is unknown whether such pain relief enhances knee loading during more demanding activities such as stair-stepping. The gait of 19 patients and stair-stepping of 14 patients with painful medial compartment osteoarthritis of the knee was assessed before and after pain-relieving intraarticular injection of the knee and compared with those of 21 healthy control subjects. There were significant increases in gait velocity, cadence, maximum external knee adduction moment (indicating increased loading in the medial compartment of the knee), and maximum external hip adduction and ankle abduction moments immediately after the injection. With the exception of velocity and ankle abduction moment, these variables were returned to levels that were not statistically different from those of the control subjects. However, no significant differences were found during stair-stepping in the external adduction-abduction moments about the knee, hip, or ankle after injection. Furthermore, the postinjection magnitudes of these variables during stair-stepping were significantly less than those of the controls. Therefore, although the relief of knee pain is sufficient to enhance gait function in osteoarthritis of the knee, it is insufficient to enhance stair-stepping function.

Knee laxity in symptomatic osteoarthritis

Twenty-two patients with primary osteoarthritis (OA) of the knee were studied to determine the effects of OA on laxity of the knee joint. Laxity was measured with a Genucom Knee Analysis System. Ten knees had mild OA (> 50% preservation of joint space). Fifteen knees had moderate OA (some preservation of joint space, but < 50%). Eighteen knees had severe OA (no joint space). A group of 18 knees from 9 healthy (asymptomatic) subjects of ages similar to those of the OA patients were used as controls. Compared to control knees, severe OA knees had less total anteroposterior (AP) translation (12.2 versus 6.6 mm, p < 0.025) and less total tibial rotation (79 versus 59 degrees, p < 0.01). Compared to early OA knees, knees with severe OA had 57% less average total AP translation (15.2 versus 6.6 mm, p < 0.01), 31% less total varus/valgus rotation (15 degrees versus 10.4 degrees, p < 0.016), and 26% less total internal/external tibial rotation (80.1 degrees versus 59 degrees, p < 0.007). These data indicate that osteoarthritic knees tend to have less laxity than normal knees, probably because of a combination of contracture of the ligaments and pressure of osteophytes against ligaments and other capsular structures.

Osteoarthritis of the knees increases the propensity to trip on an obstacle

Tripping on an object is the most frequent cause of falls. We examined the effects of painful osteoarthritis of the knee on obstacle avoidance success rates in older adults. Obstacle avoidance success rates, pain, body mass index, visual acuity, contrast sensitivity, depth perception, and single-leg stance duration were evaluated in 17 patients with painful osteoarthritis of the knees (age range, 59.6 ± 8.1 years) and 14 age-matched healthy control subjects (age range, 61.1 ± 10.0 years). The patients with osteoarthritis of the knees had a 37% lower obstacle avoidance success rate, a 54% lower single-leg stance duration, and a 24% greater body mass index than the control subjects. Age, visual acuity, contrast sensitivity, and depth perception were not different between the two groups. Obstacle avoidance success rates and single-leg stance durations decreased linearly as pain increased in the patients with osteoarthritis of the knees. Obstacle avoidance success rates also decreased linearly as single-leg stance duration decreased in the patients with osteoarthritis of the knees. Osteoarthritis of the knees reduced obstacle avoidance success rates, supporting epidemiologic studies that have found osteoarthritis to be a risk factor for falls. This study showed that pain associated with osteoarthritis of the knees increased the propensity to trip on an obstacle (the greater the pain the greater the propensity to trip and fall) and underscores the importance of treating pain associated with osteoarthritis.

The Effects of Removal and Reconstruction of the Anterior Cruciate Ligament on the Contact Characteristics of the Patellofemoral Joint

Seven cadaveric knees were used to investigate the effects of removal and reconstruction of the anterior cruciate ligament with a bone-patellar tendon-bone graft on contact characteristics of the patellofemoral joint during physiologic levels of quadriceps muscle loads at 30°, 60°, and 90° of knee flexion. Loads were applied to the quadriceps tendon to equilibrate externally applied flexion moments equivalent to one-third of values for maximum isometric extension moments. Patellofemoral contact areas and pressures were measured using pressure-sensitive film. Excision of the anterior cruciate ligament resulted in significant decreases in the total patellofemoral contact area by as much as 94 mm2 (68%), the medial facet contact area by as much as 55 mm2 (93%), the combined average contact pressure by 0.7 MPa (21%), the medial facet average contact pressure by 2.3 MPa (70%), the combined peak contact pressure by 3.0 MPa (38%), and the medial facet peak contact pressure by 5.4 MPa (76%), all at 30° of knee flexion. Excision of the anterior cruciate ligament also resulted in significant decreases in total, medial facet, and lateral facet patellofemoral contact areas at 60° and 90° of knee flexion. Intraarticular reconstruction returned these to levels not significantly different from those of the intact knee.