Biomechanical Criteria Research Articles

Arthroscopic Treatment of Massive Rotator Cuff Tears

Ten patients with painful, massive (greater than 5 cm), complete rotator cuff tears involving primarily the supraspinatus were treated with arthroscopic acromioplasty and rotator cuff debridement. All patients except one had normal active motion and strength preoperatively. All patients had roentgenographically normal acromiohumeral distance and an anterior-inferior acromial osteophyte. The goal was to obtain pain relief without loss of motion of strength. This was accomplished in all patients. This study shows that normal shoulder function is possible with a massive unrepaired tear of the rotator cuff. Normal function in the face of an unrepaired cuff tear can occur only if there is a balance of two important force couples, one in the coronal plane and the other in the transverse plane. This balance depends upon the functional integrity of the anterior cuff, the posterior cuff, and the deltoid. In patients whose cuff tears satisfy these anatomic and biomechanical criteria, the achievement of pain relief through arthroscopic debridement and decompression seems to be all that is necessary for normal pain-free function.

Biomechanical Analysis of Intrinsic Tendon Healing in Vitro and the Effects of Vitamins A and E

This in vitro study was designed to test the hypothesis that flexor tendons have an intrinsic capability to heal as judged by rigorously defined biomechanical criteria. Rabbit forepaw flexor tendons (n = 114) were transected and repaired in zone II and cultured in standard media or media supplemented with vitamin A or E. Tenorrhaphies were disrupted at 0, 2, 8, and 12 weeks after repair by fixed-speed tensiometry. The following parameters were calculated: true stress, true strain, and normalized energy absorption. Statistical analysis was by Student's t test. Peak stress (strength) increased equally in all groups over time (p less than 0.05), while normalized energy absorption (toughness) was markedly higher in the vitamin E-treated group after 2 weeks' incubation (p less than 0.05). These data represent the first biomechanical evidence of intrinsic tendon healing in vitro. Biomechanical methodology and vitamin effects are discussed in detail.

The Influence of Growth Hormone on the Reversibility of Articular Cartilage Degeneration in Rabbits

Growth hormone has chondrogenic affects on normal as well as on damaged articular cartilage. In this study, the influence of growth hormone is investigated on early degenerative changes in the articular cartilage in 72 New Zealand white rabbits. Cartilage lesions were created in femoral condyles using an immobilization model. Cartilage damage was assessed using biochemical, histologic, and biomechanical criteria. Growth hormone had no influence on prevention of immobilization abnormalities but had a significant affect on healing of established lesions.

Evaluation of Handle Positions Using Force/Endurance Relationship of an Isometric Holding Task

Almost all the published studies on container handle positions have used the psychophysical, physiological, and biomechanical criteria to evaluate the best handle locations on container. The primary intent of this investigation was to determine if force endurance relationship curves could be used as criterion for comparing the handle positions. Ten subjects participated in a factorial experiment involving four handle positions (2/2, 3/7, 8/8, and 6/8), and four levels of exertion (25%, 50%, 75%, and 100% of maximum lifting capacity). On any treatment condition, the subjects held the box till their endurance limit. The endurance time and the rate of perceived exertion (RPE) were the dependent measures. For the RPE, it was observed that the asymmetric position 6/8 was the best. Similarly the handle position 6/8 had the longest endurance as observed by a third order polynomial fit. The differences among the handle position were consistent across all levels and exertions tested. Further, it appears that the maximum lifting capacity is closer to the grip strength of the non-dominant hand.

Temporal biomechanics of posterior cervical spine injuries in vivo in a rabbit model.

There are numerous clinical and biomechanical criteria for determination of acute spinal instability. No data, however, exist on the biomechanical behavior of the injured, untreated spine during the healing period. Using a rabbit model, this study was designed to quantify changes in the mechanical properties of the injured spine over time. Sixteen rabbits were assigned to four injury groups: Injury 1 (C4-5 supra/intraspinous ligament transection), Injury 2 (C4 laminectomy), or Injury 3 (C4 laminectomy, plus bilateral facet capsular ligament transection). The fourth injury group was Sham (posterior exposure of C4-5, no spinal injury). Preinjury range of motion was determined by standardized flexion-extension radiographs on all animals. Postinjury flexion-extension radiographs were taken at 4, 8, and 12 weeks. At the end of 12 weeks, animals were killed. Mean range of motion at C4-5 for all injury groups decreased from preinjury values. The greatest decrease was for the most severe injury. At 8 weeks, the range of motion for this injury was less than half of the preinjury level and increased to 62% of the preinjury level at 12 weeks.

In vivo muscular force analysis during the isometric flexion on a monkey's elbow

An experimental method has been developed to analyse muscular forces and torques in vivo during isometric flexion of the elbow in small monkeys ( Macaca fascicularis). A mini-transducer was built with a view to measure forces in situ, without cutting tendons. The positions of tendon insertions were measured on anatomical parts, then integrated in a series of calculations aiming of deducing the lever arms of forces to be included in a torque equilibrium relationship. Muscle activity of the three main flexors was measured for five angles of isometric flexion between 70° and 110°, 0° corresponding to the full extended forearm. The analysed signals were selected using physiological and biomechanical criteria. Then, results corresponding to force participation, and torque participations, were worked out; they are presented and discussed in the present paper.

Determination of safe load.

The biomechanical criteria adopted by the National Institute for Occupational Safety and Health are shown to be based on considerations that are not consistent with current experimental data and theoretical principles. It is therefore suggested that these standards ought to be replaced, and a rationale for doing so is proposed.

What Criteria Exist for Determining How Much Load Can Be Lifted Safely?

A literature survey on recommendations for the maximum weight of the load and work loads is presented. Three different criteria are reviewed to determine the "safe" weight and permissible work loads that a person can lift. These are biomechanical, psychophysical, and metabolic/heart rate. A comparison of recommended load limits based on each of the three criteria is presented. Maximum weight of the load and work loads based on the three criteria are also compared. The comparison shows that (1) the recommendations based on a given criterion are not in agreement, (2) the maximum permissible weights of the load based on psychophysical studies are lower than those based on biomechanical criteria, and (3) the psychophysical fatigue criteria, as compared to physiological fatigue criteria, will result in greater work loads at higher frequencies of lifting. Load-pace tradeoff and effects of lifting technique and location of load on acceptable work loads are also discussed.