Murray E. Maitland

The effect of hamstring muscle compensation for anterior laxity in the ACL-deficient knee during gait

The hamstring muscles have been recognized as an important element in compensating for the loss of stability in the ACL-deficient knee, but it is still not clear whether the hamstring muscle force can completely compensate for the loss of ACL, and the consequences of increased hamstring muscle force. A two-dimensional anatomical knee model in the sagittal plane was developed to examine the effect of various levels of hamstring muscle activation on restraining anterior tibial translation in the ACL-deficient knee during level walking. The model included the tibiofemoral and patellofemoral joints, four major ligaments, the medial capsule, and five muscle units surrounding the knee. Simulations were conducted to determine anterior tibial translation and internal joint loading at a single selected position when the knee was under a peak external flexion moment during early stance phase of gait. Incremental hamstring muscle forces were applied to the modeled normal and the ACL-deficient knees. Results of simulations showed that the ACL injury increased the anterior tibial translation by 11.8mm, while 56% of the maximal hamstring muscle force could reduce the anterior translation of the tibia to a normal level during the stance phase of gait. The consequences of increased hamstring muscle force included increased quadriceps muscle force and joint contact force.

Test-retest Reliability of Isokinetic Hip Adductor and Flexor Muscle Strength

OBJECTIVE To determine the test-retest reliability of eccentric hip flexor and adductor peak torque and endurance using a Cybex Norm isokinetic dynamometer and to evaluate muscle soreness after exercise as a result of the testing procedure. DESIGN Prospective test-retest reliability study. PARTICIPANTS A total of 19 male volunteers (21-43 years old). INTERVENTION Tests included hip flexor and adductor peak torque strength measured at 60 degrees/s (concentric and eccentric) and endurance measurements (total work done over 20 continuous concentric/eccentric contractions at 150 degrees/s). Subjects were tested on three occasions at 1-week intervals. MAIN OUTCOME MEASURES Repeated measures analysis of variance was performed for all dependent variables including the subjects dominant and nondominant side among the three test sessions. Intraclass correlation coefficients (ICCs) were calculated to compare the data between sessions. In addition, simple linear regression analysis was completed to determine the relationship between session measurements for all measures with ICC > 0.75. RESULTS The main findings of this study are that eccentric peak hip adductor torque was reliably measured on a Cybex Norm isokinetic dynamometer using a continuous eccentric/ concentric cycle protocol at a speed of 60 degrees/s (ICC > 0.84). Peak concentric adductor torque and peak eccentric and concentric hip flexor torque were less reliable using the same protocol (ICC < 0.67). Endurance measurements, using total work done over 20 repetitions, were not reliable for hip flexor and adductor muscle groups using a continuous eccentric/concentric cycle protocol at a speed of 150 degrees/s (ICC < 0.55). Posttest muscle soreness was found to be of significant concern with such a protocol. CONCLUSION The results from this test-retest reliability study confirm the reliability of eccentric peak hip adductor torque measurements for use clinically and in future research. In addition, the need to assess posttest muscle soreness after isokinetic muscle testing is confirmed.

A correlation between the distribution of biological apatite and amino acid sequence of type I collagen.

SummaryWe have determined the localization of apatite within type I collagen fibrils of calcifying turkey leg tendons by both bright field and selectedarea dark field (SADF) electron microscopy and have compared this to computer-modeled, chick type I collagen amino acid sequence data. Apatite crystals occur in both the gap and overlap zones at early stages of mineralization in an asymmetric pattern that corresponds to the polarity, N-to C-orientation, of the collagen molecule. Based on comparisons with computer-generated models of known amino acid sequence of collagen, it was determined for early stages of mineral deposition that apatite is restricted by areas of high hydrophobicity. The gap zone is less hydrophobic than the overlap zone on average but each of these zones had areas of high hydrophobicity that correlated with sites of low localization of mineral. Possible interactions between hydrophobic regions and the process of mineral deposition are discussed.

A Client-Computer Interface for Questionnaire Data

Our purpose was to assess efficiency and patient acceptance of a simple, inexpensive method of direct client-computer interface. A computerized version of the Sickness Impact Profile (SIP) was developed with the standard keyboard replaced by a numeric keypad. Forty-eight volunteer clients of an occupational rehabilitation center completed both the paper format and the computer format in randomized order, then were asked to compare the two methods in four areas. The majority of subjects rated the computer as easier to use and as the preferred method. Most subjects rated the computer and paper formats as equivalent in comfort and understanding. A summary score established that significantly more individuals preferred the computer format over the paper format (p = .02). Efficiency was determined by the mean time to score the test and produce a report (computer 39s, paper 309s). The correlation coefficients for the physical, psychosocial, and overall scores were very acceptable being greater than 0.90. These data indicate that a simple client-computer interface for the SIP is preferred by clients and is more efficient compared to the paper and pencil format.

Does Cybex testing increase knee laxity after anterior cruciate ligament reconstructions

Long-term stability of the knee after anterior cruciate ligament reconstruction is imperative. Testing protocols that use isokinetic systems are commonly performed despite controversies as to their safety. The purpose of this study was to test whether one episode of isokinetic testing would cause an increase in anterior tibial translation. Twenty-four subjects who had anterior cruciate ligament recontructions 153 to 300 days earlier volunteered for the study. Initially, subjects walked on a treadmill at 5 km/hr for 10 minutes to test the effect of exercise on displacement measurements. One week later, subjects performed a maximal knee flexion-exten sion test on the Cybex dynamometer at 60, 150, and 240 deg/sec. Anterior tibial displacement at 133.5 N was obtained from force-displacement curves pro duced by KT-2000 arthrometer testing at nine intervals: before exercise on the treadmill, at four intervals after treadmill exercise, and at four intervals after Cybex testing. Repeated measures analysis of variance did not show a significant exercise effect, interaction be tween type of exercise and time interval, or change after Cybex testing for the reconstructed knee displace ment, the contralateral knee displacement, or side-to- side difference. The average difference before and after Cybex testing was 0.1 mm for the reconstructed knee. In conclusion, a single Cybex test, performed at least 6 months after surgery, did not affect anterior tibial displacement in this study sample.