Double-bundle ACL surgery demonstrates superior rotational kinematics to single-bundle technique during dynamic task.

BACKGROUND: While traditional surgical repair of the anterior cruciate ligament is able to restore anterior-posterior knee stability, laxity in the transverse plane remains. Double-bundle reconstruction has demonstrated greater rotational restraint than the single-bundle technique under passive loading conditions; however, no comparison has been made under physiological weight-bearing conditions. The purpose of this study was to determine differences in rotational knee kinematics during a dynamic task in patients who had received either a single- or double-bundle reconstruction. METHODS: Twenty-two patients exhibiting isolated anterior cruciate ligament rupture were randomly allocated either a single or double-bundle reconstruction. Three-dimensional knee kinematics were measured during a dynamic cutting activity prior to and following surgery. Functional range of rotation was compared between groups pre- and post-operatively and kinematics were assessed against uninjured control subjects. FINDINGS: No difference in overall range of rotation was found under physiological loading conditions. However, a significant interaction of the midpoint of the range of movement was observed; a greater external rotational shift in the single-bundle group followed reconstruction, while the kinematics of the double-bundle patient group shifted closer to those of the control group. INTERPRETATION: The double-bundle reconstruction demonstrated superior outcome in rotational kinematics to the single-bundle technique.

Modeling, validation and application of a mathematical tissue-equivalent breast phantom for linear slot-scanning digital mammography.

This paper presents a mathematical tissue-equivalent breast phantom for linear slot-scanning digital mammography. A recently developed prototype linear slot-scanning digital mammography system was used for model validation; image quality metrics such as image contrast and contrast-to-noise ratio were calculated. The results were in good agreement with values measured using a physical breast-equivalent phantom designed for mammography. The estimated pixel intensity of the mathematical phantom, the analogue-to-digital conversion gain and the detector additive noise showed good agreement with measured values with correlation of nearly 1. An application of the model, to examine the feasibility of using a monochromatic filter for dose reduction and improvement of image quality in slot-scanning digital mammography, is presented.

Gait before and 10 years after rhizotomy in children with cerebral palsy spasticity.

OBJECT: Selective dorsal rhizotomy is a neurosurgical procedure performed for the relief of spasticity in children with cerebral palsy, but its long-term functional efficacy is still unknown. The authors sought to address this issue by means of an objective, prospective study in which quantitative gait analysis was used. METHODS: Eleven children with spastic diplegia (mean age at initial surgery 7.8 years) were evaluated preoperatively in 1985 and then at 1, 3, and at least 10 years after surgery. For comparison, 12 age-matched healthy individuals were also studied. Retroreflective targets were placed over the hip, knee, and ankle joints, and each individual's gait was videotaped. The video data were subsequently entered into a computer for extraction and analysis of the gait parameters. An analysis of variance yielded a significant time effect (p < 0.05), and post hoc comparisons revealed differences before and after surgery and with respect to the healthy volunteers. The knee and hip ranges of motion (59 degrees and 44 degrees, respectively, for healthy volunteers) were significantly restricted in children with spastic diplegia prior to surgery (41 degrees and 41 degrees, respectively), but were within normal limits after 10 years (52 degrees and 45 degrees, respectively). The knee and hip midrange values (31 degrees and 3 degrees, respectively, for healthy volunteers), indicative of posture, were significantly elevated preoperatively (42 degrees and 15 degrees) and increased sharply at 1 year (56 degrees and 18 degrees), but by 10 years they had decreased to within normal limits (36 degrees and 9 degrees). Step length and velocity improved postoperatively but were not within the normal range after 10 years. Ten years after surgery these patients not only had increased ranges of motion, but also used that movement at approximately a normal midrange point. CONCLUSIONS: Selective dorsal rhizotomy is an effective method for alleviating spasticity. Furthermore, the authors provide evidence to show that lasting functional benefits, as measured by improved gait, can also be obtained.

Anterior cruciate ligament reconstruction and joint dynamics during stair climbing.

Athletes with anterior cruciate ligament (ACL) deficiencies exert decreased knee extension moments during level walking (quadriceps avoidance gait), and yet within a few months of ACL reconstruction they are often expected to return to competitive sport. To investigate this issue further, 10 normal subjects and seven ACL deficient patients were evaluated both pre- and post-operatively (mean follow-up of 6 months), and each performed multiple trials ascending a staircase which consisted of three steps. Bilateral joint angles, moments, powers, and work were measured and the data were ensemble averaged and statistically analyzed (repeated measures ANOVA with significance level set at 0.05). Anterior-posterior knee laxity decreased significantly (from 7.9 mm to 5.8 mm) while subjective knee function also improved following ACL reconstruction (knee score increased from 70.4 to 88.5). Pre-operatively, there were no statistically significant differences in biomechanical parameters between the patients' ACL-deficient and intact sides and the normal subjects. Post-operatively, however, statistically significant reductions were seen for the peak moment (91.9 vs 22.5 Nm), power (181 vs 84 W), and work performed (28.0 vs -5.6 J) at the injured knee, which was also the knee from which the patellar tendon graft had been harvested. These reductions were accommodated by significant increases in excursion, moment, and power at the contralateral ankle joint. The results indicate that while the ACL reconstruction were successful in restoring anterior-posterior knee stability, the decrease in knee power and work performed post-operatively by the injured (i.e., donor) knee suggests that donor site morbidity may need to be critically evaluated over a long-term period.

Cerebral palsy and rhizotomy. A 3-year follow-up evaluation with gait analysis.

A recent increase in the popularity of selective rhizotomy for reduction of spasticity in cerebral palsy has led to a demand for more objective studies of outcome and long-term follow-up results. The authors present the results of gait analysis on 14 children with spastic cerebral palsy, who underwent selective posterior rhizotomy in 1985. Sagittal plane gait patterns were studied before surgery and at 1 and 3 years after surgery using a digital camera system. The parameters measured included the range of motion at the knee and thigh, stride length, speed of walking, and cadence. The range of motion at the knee was significantly increased at 1 year after surgery and further improved to a nearly normal range at 3 years after surgery. In contrast, postoperative measurements of thigh range exceeded normal values at 1 year, but decreased toward normal range at 3 years. While improvements in range of motion continued between Years 1 and 3, the children developed a more extended thigh and knee position, which indicated a more upright walking posture. Stride length and speed of walking also improved, while cadence remained essentially unchanged. This 3-year follow-up study, the first to examine rhizotomy using an objective approach, has provided some encouraging results regarding early functional outcome.

The effect of rhizotomy on movement in patients with cerebral palsy.

Selective posterior lumbar rhizotomy has recently become an alternative method for relieving spasticity in patients with spastic cerebral palsy. This procedure involves the selective sectioning of the lumbosacral posterior nerve rootlets. Because the whole nerve root is not cut, tactile and proprioceptive sensation remain intact. The present study measured the changes that occurred in 29 patients with spastic cerebral palsy 2 days before surgery and from 4 to 14 months after surgery. Each patient was used as his or her own control. In addition to the clinical evaluation of function, gait was analyzed on appropriate patients with a simple digital camera and microcomputer. The results indicated positive gains after rhizotomy. These gains were, however, dependent on the patients' abilities before surgery. The most significant improvement occurred in thigh and knee ranges of movement. This somewhat controversial new method of treating spasticity shows promise in improving the quality of life of patients with spastic cerebral palsy and in facilitating their treatment.

Gait analysis of cerebral palsy children before and after rhizotomy.

Over the past decade, selective posterior rhizotomy has been used successfully to reduce spasticity in patients with cerebral palsy. Although clinical evaluation of these patients revealed functional improvement following surgery, more objective analysis of the outcome of this surgery was sought. Kinematic gait analysis of 14 patients with spastic cerebral palsy was performed before and after selective posterior rhizotomy. Measurements of stride length, thigh range of motion, knee range of motion, average speed of walking, and cadence were made. Statistically significant increases in stride length, thigh range and knee range were found. Average speed was increased and cadence was virtually unchanged. These results corroborate clinical findings of improvement in gait of spastic patients with cerebral palsy following selective posterior rhizotomy.

Computer simulation of human motion in sports biomechanics.

This chapter has covered some important aspects of the computer simulation of human motion in sports biomechanics. First the definition and the advantages and limitations of computer simulation were discussed; second, research on various sporting activities were reviewed. These activities included basic movements, aquatic sports, track and field athletics, winter sports, gymnastics, and striking sports. This list was not exhaustive and certain material has, of necessity, been omitted. However, it was felt that a sufficiently broad and interesting range of activities was chosen to illustrate both the advantages and the pitfalls of simulation. It is almost a decade since Miller [53] wrote a review chapter similar to this one. One might be tempted to say that things have changed radically since then--that computer simulation is now a widely accepted and readily applied research tool in sports biomechanics. This is simply not true, however. Biomechanics researchers still tend to emphasize the descriptive type of study, often unfortunately, when a little theoretical explanation would have been more helpful [29]. What will the next decade bring? Of one thing we can be certain: The power of computers, particularly the readily accessible and portable microcomputer, will expand beyond all recognition. The memory and storage capacities will increase dramatically on the hardware side, and on the software side the trend will be toward "user-friendliness." It is likely that a number of software simulation packages designed specifically for studying human motion [31, 96] will be extensively tested and could gain wide acceptance in the biomechanics research community. Nevertheless, a familiarity with Newtonian and Lagrangian mechanics, optimization theory, and computers in general, as well as practical biomechanical insight, will still be a prerequisite for successful simulation models of human motion. Above all, the biomechanics researcher will still have to bear in mind that his or her model is merely a simplified representation of the real-world system and, as such, has certain limitations. In conclusion, it is evident that the path we have followed has been an interesting and varied one. The way ahead looks equally interesting and diverse, and we can certainly look forward with confidence to the exciting challenges and benefits that computer simulation of human motion will bring.