An, Kai‐Nan

The measurement of intradiscal stress has been primarily limited to nucleus pulposus pressure. Intradiscal stress profilometry is a technique that measures stress in both the nucleus pulposus (hydrostatic) and annulus fibrosus (compression). Evidence from animal studies suggests that distraction may affect disc physiology and promote repair. A study was performed to determine the reliability of intradiscal stress profilometry measurements in the anterior, posterior, and nucleus regions of cadaveric lumbar discs. Four fresh-frozen human lumbar motion segments were prepared and tested. Five profiles were obtained during two conditions of compression and three conditions of distraction. Discs were then graded for degenerative change. Reliability was judged by within-specimen coefficients of variation. The coefficients of variation were smaller (more reliable) for compression conditions than for distraction conditions. Within-specimen coefficients during compression ranged from 1.58% to 37.2% in the nucleus, 3.9% to 67.4% in the anterior annulus, and 2.3% to 25.5% in the posterior annulus. The reliability of intradiscal stress profilometry is acceptable for repeated measures studies evaluating within-specimen changes, but the sample size will vary depending on the test conditions used and the disc region of interest.

Ankle disk training has been used as an exercise in sports medicine clinics to help protect against ankle sprains. This study investigated the effects of ankle disk training on the contraction pattern of the anterior tibialis, posterior tibialis, peroneus longus, and flexor digitorum longus muscles in a simulated ankle sprain. Twenty adults were recruited and divided into a control group and an experimental group. A platform with a trapdoor was used to simulate a lateral ankle sprain. Electromyographic data were recorded from each sub ject in pretraining and posttraining tests. The experi mental group underwent ankle disk training for 8 weeks between the pretraining and posttraining tests. In the pretraining test, the four muscles started to contract simultaneously; in the posttraining test, the contrac tions of the anterior and posterior tibialis muscles were delayed. This delay favors the correction of excessive ankle inversion. This study examined the effects of one form of proprioceptive training on muscle reaction times, and its results may explain why such training can help protect against ankle sprains.

We defined foot and ankle motion with respect to the neutral position. Thirteen normal fresh-frozen speci mens of the human foot were used. The foot was placed in the extreme positions of pronation, supina tion, dorsiflexion, and plantar flexion, and positions of multiple bones were monitored simultaneously with a magnetic tracking device to determine rotation of the talocrural, subtalar, metatarsal-navicular, and talo navicular joints under the various conditions. In prona tion, the most rotation occurred at the metatarsal-na vicular level, followed by the navicular-talar, talar-tibial, and calcaneal-talar levels. In supination, most rotation occurred at the navicular-talar level, followed by the calcaneal-talar, talar-tibial, and metatarsal-navicular levels. In dorsiflexion, most rotation occurred at the talar-tibial level, followed by the navicular-talar, calca neal-talar, and metatarsal-navicular levels. In plantar flexion, most rotation occurred at the talar-tibial level, but there was considerable motion at the navicular- talar, metatarsal-navicular, and calcaneal-talar levels. Understanding the specific joint motions that occur with various positions of the foot and ankle is important because measurements of joint mobility may assist in establishing diagnoses, monitoring clinical conditions, determining indications for operative treatment, as sessing results of treatment, and following the progress of rehabilitation.

The purpose of this study was to analyze intersegmen tal forces at the tibiofemoral joint and muscle activity during three commonly prescribed closed kinetic chain exercises: the power squat, the front squat, and the lunge. Subjects with anterior cruciate ligament-intact knees performed repetitions of each of the three exer cises using a 223-N (50-pound) barbell. The results showed that the mean tibiofemoral shear force was posterior (tibial force on femur) throughout the cycle of all three exercises. The magnitude of the posterior shear forces increased with knee flexion during the descent phase of each exercise. Joint compression forces remained constant throughout the descent and ascent phases of the power squat and the front squat. A net offset in extension for the moment about the knee was present for all three exercises. Increased quadri ceps muscle activity and decreased hamstring muscle activity are required to perform the lunge as compared with the power squat and the front squat. A posterior tibiofemoral shear force throughout the entire cycle of all three exercises in these subjects with anterior cru ciate ligament-intact knees indicates that the potential loading on the injured or reconstructed anterior cruci ate ligament is not significant. The magnitude of the posterior tibiofemoral shear force is not likely to be detrimental to the injured or reconstructed posterior cruciate ligament. These conclusions assume that the resultant anteroposterior shear force corresponds to the anterior and posterior cruciate ligament forces.

This study compared and quantified electromyographic muscle activation of the rotator cuff with the isometric torque generated by performing shoulder rotation in various positions. Twenty healthy volunteers were tested in 29 shoulder positions. Using a Cybex II dy namometer synchronously with electromyography, surface electrodes were placed over the pectoralis major muscle and three parts of the deltoid muscle. Intramuscular wire electrodes were inserted into the four rotator cuff muscles. We found that the greatest external rotation isometric force is generated in the frontal and scapular planes in the neutral or full internal rotation positions. The sagittal, dependent, and the scapular plane with 45° of elevation in rotational posi tions of either full or half external rotation generated the greatest torques for internal rotation isometric force. The rotator cuff muscles generated greatest electro myographic activity in neutral to midrotational posi tions. The scapular plane with 90° of shoulder eleva tion in neutral rotation best isolated the subscapularis muscle. The infraspinatus-teres minor muscles were isolated in the sagittal plane with 90° of shoulder ele vation in a half externally rotated position. We were unable to isolate the supraspinatus muscle in any of these tested positions. These positions are recom mended for manual muscle testing and for strengthen ing these muscles.

The contribution of axial arm rotation to translation of the humeral head with the arm in the hanging position was examined using nine fresh-frozen cadaveric shoulders. Three standard clinical tests were simulated: anterior and posterior translation and sulcus tests. In both the anterior translation and sulcus tests, anterior and infe rior displacements were significantly restricted in inter nal rotation but not in neutral and external rotation. In the posterior translation test, no significant differences in displacement could be observed in internal, neutral, or external rotation. Since anterior and inferior translations of the humeral head were significantly affected by the rotation of the arm, we recommend that the anterior translation and sulcus tests be performed in various rotations.

This study analyzed forces in the tibiofemoral and pa tellofemoral joints during isokinetic exercise using an analytical biomechanical model. The results show that isokinetic exercise can produce large loads on these joints, especially during extension exercises. The tibio femoral compressive force (4.0 body weight) is approx imately equal to that obtained during walking but it occurs at 55° of knee flexion. Anterior shear forces (resisting force to anterior drawer) exist during exten sion exercise at less than 40° of knee flexion, with a maximum of 0.3 body weight. Posterior shear forces (resisting force to posterior drawer) exist during exten sion exercise at knee joint angles greater than 40° and during the flexion portion of isokinetic exercise. The maximum posterior shear force is 1.7 body weight. The patellofemoral joint can encounter loads as high as 5.1 body weight which are 10 times higher than during straight leg raises. These results suggest that isokinetic exercise should be used cautiously in patients with knee lesions.

The stabilizing capacity of the ligaments and articular surface in the ankle was determined under defined physiologic loading conditions. The concept of primary and secondary constraints was adapted to the ankle. With physiologic loading, the articular surface ac counted for 30% and 100% of stability in rotation and version, respectively. That the articular surface was the sole source of inversion and eversion stability under the prescribed physiologic loading conditions has not been previously reported. The demonstration that the articular surface resists inversion displacement in the loaded ankle supports the conclusion of previous studies that rotation, rather than inversion, may account for a type of clinically sympto matic ankle instability. Further, ankle instability may occur during loading and unloading but not once the ankle is fully loaded. The results of our study confirm the importance of the anterior talofibular and calcaneo fibular ligaments and suggest an important role for the deltoid ligament.

This preliminary study of four elbow specimens inves tigates the relationship of articular geometry and liga mentous structures in providing stability to the elbow joint. A technique is presented that describes the con straining features of varus-valgus and distraction in extension and at 90° of elbow flexion. Valgus stability is equally divided among the medial collateral ligament, anterior capsule, and bony articulation in full extension; whereas, at 90° of flexion the contribution of the ante rior capsule is assumed by the medial collateral ligament which provides approximately 55% of the stabilizing contribution to valgus stress. Varus stress is noted to be resisted primarily by the anterior capsule (32%) and the joint articulation (55%) with only a small (14%) contribution from the radial collateral ligament. At 90° of flexion, little change is noted in the contribution to the radial collateral ligament (9%), but the anterior capsule offers only 13%, with the remaining stability (75%) arising from the joint articulation. In extension, the soft tissue resistance to distraction is provided minimally by either the radial (5%) or the medial (5%) collateral ligaments, and thus primarily originates from the anterior capsule (85%). At 90° of flexion, however, the capsule offers virtually no resistance to distraction (8%). The radial collateral ligament contributes 10% of the stability, while the medial collateral ligament ac counts for 78% of the resistance to distraction in this position. Too few specimens have been studied to form any conclusions for direct clinical applications at this time. However, the technique provides a reliable tool with additional studies for different positions and loading conditions underway. These efforts should disclose useful information that might be applied to the manage ment of chronic elbow instability, radial head or olecra non fracture, the design and implantation of elbow prostheses, or provide a rationale for other reconstruc tive procedures.

Purpose The purposes of this study were to investigate the differences between open and arthroscopic closure of the rotator interval (RI) on glenohumeral translation and range of motion. We also sought to determine if the addition of either an open or arthroscopic RI closure increases stability of the shoulder. Methods Fourteen fresh‐frozen (10 paired) cadaveric shoulder specimens were mounted in a custom testing apparatus, and glenohumeral translation and rotation were obtained by using an optoelectric tracking system (Optotrak Certus; Northern Digital, Ontario, Canada). Specimens were randomly allocated to either open (n = 7) or arthroscopic (n = 7) plication of the RI. The following were measured first with an intact and vented specimen and subsequently after an RI closure using either open or arthroscopic techniques: (1) range of motion in neutral and 90° abduction; (2) anterior and posterior translation at neutral rotation; (3) anterior translation at 90° abduction with external rotation; and (4) posterior translation at 90° flexion with internal rotation. Results Posterior stability was not improved from the intact state by either open (1.0‐mm change) or arthroscopic (0.1‐mm change) repair. The sulcus stability was improved in the open group (5.7 mm to 2.9 mm, P = .028), but not arthroscopically (5.1 to 4.1 mm, P = .499). Neutral anterior stability was improved after open repair (7.2 to 2.6 mm, P = .018), but not arthroscopically (2.3 to 2.4 mm, P = 0.5). However, anterior stability in external rotation (ER) at 90° abduction was improved in the arthroscopic repair group (5.5 to 3.1 mm, P = .006). The mean loss of ER in neutral was greater in the open group (40.8°) versus the arthroscopic group (24.4°, P = .0038). The arthroscopic group showed an 11.7° loss of ER in 90° abduction ( P = .018) versus the open group loss of 4.8°. There were no significant differences in loss of IR in either neutral or 90° abduction. Conclusions Posterior stability was not improved by either open or arthroscopic rotator interval repair, and sulcus stability only improved with the open technique. Anterior stability in neutral was improved after open repair and in the arthroscopic repair group with the arm abducted. There was a large loss of external rotation with both techniques. Clinical Relevance This study suggests that arthroscopic RI closure adds little to the overall posterior and inferior stability of the shoulder joint, although anterior stability may be improved. There is a potentially large loss of external rotation after either repair method.