Matthew S. Shapiro

Direct measurement of resultant forces in the anterior cruciate ligament. An in vitro study performed with a new experimental technique.

A new technique was used to measure the resultant forces in the anterior cruciate ligament during a series of loading experiments on seventeen fresh-frozen cadaver specimens. The base of the ligaments tibial attachment was mechanically isolated with a coring cutter, and a specially designed load-transducer was fixed to the bone-plug that contained the ligaments tibial insertion so that the resultant forces were directly measured by the load-cell. Although the magnitudes of values for forces varied considerably between specimens for a given test condition, the patterns of loading with respect to direction of loading and the angle of flexion of the knee were remarkably consistent. Passive extension of the knee generated forces in the ligament only during the last 10 degrees of extension; at 5 degrees of hyperextension, the forces ranged from fifty to 240 newtons (mean, 118 newtons). When a 200-newton pull of the quadriceps tendon was applied to extend a knee slowly against tibial resistance, however, the force in the ligament increased at all angles of flexion of the knee. Internal tibial torque always generated greater forces in the ligament than did external tibial torque; higher forces were recorded as the knee was extended. The greatest forces (133 to 370 newtons) were generated when ten newton-meters of internal tibial torque was applied to a hyperextended knee. Fifteen newton-meters of applied varus moment generated forces of ninety-four to 177 newtons at full extension; fifteen newton-meters of applied valgus moment generated a mean force of fifty-six newtons, which remained unchanged with flexion of the knee. The force during straight anterior translation of the tibia was approximately equal to the anterior force applied to the tibia. The application of 925 newtons of tibiofemoral contact force reduced the mean force in the ligament that was generated by 200 newtons of anterior pull on the tibia by 36 per cent at full extension and 46 per cent at 20 degrees of flexion.

Allograft Reconstruction of the Anterior and Posterior Cruciate Ligaments After Traumatic Knee Dislocation

Seven patients (average age, 26.3 years) with traumatic knee dislocations were retrospectively evaluated more than 2 years (average, 51 months) after having fresh- frozen allograft anterior and posterior cruciate ligament reconstructions. All patients were treated consecutively at an average of 9.6 days after injury. Two patients had arterial injuries and three patients had or developed common peroneal nerve palsy. Five patients had 20 additional injuries. All patients were enlisted in an early, aggressive physical therapy regimen with early pro tected weightbearing. Four patients required a manipu lation under anesthesia for arthrofibrosis at an average of 16.8 weeks postoperatively (range, 6 to 33 weeks). At followup, only one patient had significant pain, three patients had rare or occasional giving way, and all seven were able to return to school or to the workplace. The functional grading was excellent in three patients, good in three patients, and fair in one patient. No patient had a significant flexion contracture; the average flexion arc was 118° (range, 105° to 135°). Knee dislocation is a very traumatic injury, often resulting in a painful, dys functional knee. Anterior and posterior cruciate liga ment reconstructions in young, active patients can minimize pain and optimize functional outcome. Arthrofibrosis is a common occurrence in these pa tients, and manipulation under anesthesia is frequently required.

Direct in vitro measurement of forces in the cruciate ligaments. Part I: The effect of multiplane loading in the intact knee.

Specially designed load-transducers that measured the resultant forces exerted by the posterior and anterior cruciate ligaments on their respective femoral and tibial insertions were applied to eighteen fresh-frozen cadaveric knees for a series of controlled loading experiments. The mean force in the posterior cruciate ligament at 5 degrees of forced hyperextension of the knee was 23 per cent of the mean force in the anterior cruciate ligament. When the knee was hyperflexed by application of 10.0 newton-meters of bending moment to the tibia, the mean force in the posterior cruciate ligament was 55 per cent of that in the anterior cruciate ligament. Quadriceps tendon pull increased the force in the posterior cruciate ligament in twelve of the fourteen specimens to which it had been applied, at 80 and 90 degrees of flexion only. The force generated in the posterior cruciate ligament by applied internal tibial torque was greatest when the knee was in 90 degrees of flexion; the force in the anterior cruciate ligament was greatest when the knee was fully extended. External tibial torque generated force in the posterior cruciate ligament in only eight specimens, and only at 80 and 90 degrees of flexion. The levels of force that were generated in the posterior cruciate ligament by applied varus and valgus bending moment were greatest at 90 degrees of flexion of the knee; the levels of force in the anterior cruciate ligament were greatest with the knee in full extension. With the knee flexed 90 degrees and the tibia in neutral rotation, fifty newtons of applied posterior tibial force increased the mean force in the posterior cruciate ligament by 58.4 newtons; at full extension, no increase in the force in the ligament was recorded, indicating that tensed capsular structures were absorbing the applied load. When the tibia was internally or externally rotated by applied tibial torque, the increases in the force in the ligament from applied posterior tibial force were sharply diminished.

A Biomechanical Study of Replacement of the Posterior Cruciate Ligament with a Graft. Part I: Isometry, Pre-Tension of the Graft, and Anterior-Posterior Laxity*

Twelve fresh-frozen knee specimens from cadavera were subjected to anterior-posterior laxity testing with 200 newtons of force applied to the tibia; testing was performed before and after a femoral load-cell was connected to a mechanically isolated cylindrical cap of subchondral femoral bone containing the femoral origin of the posterior cruciate ligament. The posterior cruciate ligament then was removed, the proximal end of a thin trial isometer wire was attached to one of four points designated on the femur, and displacement of the distal end of the wire relative to the tibia was measured over a 120-degree range of motion. The potted end of a ten-millimeter-wide bone-patellar ligament-bone graft was centered over the femoral origin of the ligament and attached to the femoral load-cell. Isometry measurements were repeated with the wire attached to the bone block of the free end of the graft in the tibial tunnel. Force was recorded at the load-cell (representing force in the intra-articular portion of the graft) as pre-tension was applied, with use of a calibrated spring-scale, to the tibial end of the graft. A laxity-matched pre-tension of the graft was determined such that the anterior-posterior laxity of the reconstructed knee at 90 degrees of flexion was within one millimeter of the laxity that was measured after installation of the load-cell. Anterior-posterior testing was repeated after insertion of the graft at the laxity-matched pre-tension. The least amount of change in the relative displacement of the trial wire over the 120-degree range of flexion occurred when the wire was attached to the proximal point on the femur (a point on the proximal margin of the femoral origin of the posterior cruciate ligament, midway between the anterior and posterior borders of the ligament). The greatest change in the relative displacement was associated with the anterior point (a point on the anterior margin of the femoral origin of the ligament, midway between the proximal and distal borders). The mean relative displacements of the trial wire when it was attached to a point at the center of the femoral origin of the ligament were not significantly different from the corresponding mean displacements of the distal end of the graft when the proximal end of the graft was centered at this point. At 90 degrees of flexion, the force recorded by the load-cell averaged 64 to 74 per cent of the force applied to the tibial end of the graft. The laxity-matched pre-tension of the graft at 90 degrees of flexion (as recorded by the load-cell) ranged from six to 100 newtons (mean and standard deviation, 43.0 ± 33.4 newtons). With the numbers available, the mean laxities after insertion of the graft were not significantly different, at any angle of flexion, from the corresponding mean values after installation of the load-cell. CLINICAL RELEVANCE: Isometer readings from a trial wire attached to a point on the femur provided an accurate indication of the change in the length of a graft subsequently centered at that point. Anteriorly placed femoral tunnels should be avoided, as the isometer readings indicated increased tension, with flexion of the knee, in a graft placed in this region. The force in the intra-articular portion of the graft was always less than the force applied to the bone block in the tibial tunnel. Therefore, the femoral end of the graft should be tensioned to avoid frictional losses from the severe bend in the graft as it passes over the posterior tibial plateau. With correct pre-tensioning of a graft, normal anterior-posterior laxity at 0 to 90 degrees of flexion can be restored. However, because of the considerable range in the laxity-matched pre-tensions, we recommend that the pre-tension be greater than forty-three newtons for all patients to ensure that normal laxity is restored.

Rupture of Lisfranc's Ligament in Athletes*

Ligamentous injuries to the tarsometatarsal joints are uncommon and usually result from violent trauma to the forefoot. A more subtle tarsometatarsal injury consisting of an isolated diastasis of the first and second tarso metatarsal rays has recently been described. This injury is thought to be caused by a rupture of Lisfrancs liga ment. Nine injuries that occurred during athletics are described. History and physical findings are crucial for arousing the clinicians suspicion for this injury, but con firmation can best be obtained by comparison weight bearing radiographs; the space between the first and second metatarsal bases may be widened 2 to 5 mm. Nonoperative treatment consisting of casting and the use of crutches for 4 to 6 weeks was successful in re turning patients back to athletics; however, the time to return to competition averaged 4 months.

Quality of life assessment in elite collegiate athletes

The objectives of this study were to establish baseline Medical Outcomes Study Short Form Health Survey (SF-36) data for Division I collegiate athletes and to determine the effects of injury severity and training time. All participating athletes (N = 562) at a major university were evaluated with the SF-36. Regression analysis was performed to identify predictive factors. When the men without injury were compared with a previously established norm group, there was a significant increase in the role emotional score. In the women without injury there were significant increases in mental component summary, physical function, role emotional, mental health, and vitality scores when compared with the norm group. Serious injury was a predictor of lower scores in all domains, whereas minimal injury was predictive of lower physical component summary, role physical, bodily pain, social function, and general health scores. Increased training time was predictive of higher mental component summary, role physical, vitality, and general health scores. Elite collegiate athletes scored differently from previously established age-matched norms, and injury was a strong predictor of lower scores.

Diagnosis of Glenoid Labral Tears: A Comparison Between Magnetic Resonance Imaging and Clinical Examinations

We studied 54 patients with shoulder pain secondary to anterior instability or glenoid labral tears refractory to 6 months of conservative management with no evi dence of rotator cuff lesions. All patients had sufficient preoperative clinical data, magnetic resonance imag ing, and shoulder arthroscopy results for analysis. The ability to predict the presence of a glenoid labral tear by physical examination was compared with that of mag netic resonance imaging (conventional and arthro gram) and confirmed with arthroscopy. There were 37 men and 17 women (average age, 34 years) in the study group. Of this group, 64% were throwing athletes and 61% recalled specific traumatic events. Clinical assessment included history with specific attention to pain with overhead activities, clicking, and instances of shoulder instability. Physical examination included the apprehension, relocation, load and shift, inferior sulcus sign, and crank tests. Shoulder arthroscopy confirmed labral tears in 41 patients (76%). Magnetic resonance imaging produced a sensitivity of 59% and a specificity of 85%. Physical examination yielded a sensitivity of 90% and a specificity of 85%. Physical examination is more accurate in predicting glenoid labral tears than magnetic resonance imaging. In this era of cost con tainment, completing the diagnostic workup in the clinic without expensive ancillary studies allows the patients care to proceed in the most timely and economic fashion.

Changes in acromial morphology with age.

It has not been determined whether acromial morphology is an innate anatomic characteristic or whether it represents a degenerative process with type I acromions changing to type III acromions over time. The purpose of this study was to determine the incidence of the three types of acromial morphology with respect to age. The acromial morphology of 272 patients (176 patients with no signs of mechanical impingement or rotator cuff disease and 96 patients with mechanical impingement) was determined by supraspinatus outlet radiographs. In the entire group of 272 patients there was a significant increase in the incidence of type III acromions and a decrease in the incidence of type I acromions in patients older than 50 years of age (p = 0.046). In 176 patients with no symptoms there was a very significant increase in the number of type III acromions in those patients older than 50 years of age (p = 0.004) with a corresponding decrease in the incidence of type I acromions. The incidence of the three acromial types also varied between patients with and without symptoms of mechanical impingement. The incidence of the three acromial types varies with respect to the age of the patient and whether he or she has symptoms of mechanical impingement. This raises the possibility that type I acromions may progress to type II acromions and then further change into type III acromions over time.

Ankle sprain prophylaxis: an analysis of the stabilizing effects of braces and tape

Five cadaveric ankles were used to determine the ef fects of prophylactic bracing and tape on resisting an inversion moment applied to the ankle. The ankles were tested in neutral flexion and 30° of plantar flexion and with both low- and high-top shoes. Eight different strap-on braces were studied. High-top sneakers sig nificantly increased the passive resistance to inversion afforded by all braces and tape. Many of the braces functioned to resist inversion at a level that was com parable with or exceeded the capability of freshly ap plied tape. This finding was independent of the type of footwear. Braces that were not as effective as freshly applied tape nevertheless retained the advantage over tape in that they could be easily readjusted and their effectiveness restored, whereas the quality of the sup port provided with tape deteriorated with usage.

A Biomechanical Study of Replacement of the Posterior Cruciate Ligament with a Graft. Part II: Forces in the Graft Compared with Forces in the Intact Ligament*

A femoral load-cell was installed in twelve fresh-frozen knee specimens from cadavera, to measure the resultant force at the femoral origin of the posterior cruciate ligament during a series of tibial-loading tests. The posterior cruciate ligament was removed, and a ten-millimeter-wide bone-patellar ligament-bone graft was inserted. The knee was flexed to 90 degrees, the graft was pre-tensioned to restore the anterior-posterior laxity to that recorded after installation of the load-cell, and the loading tests were repeated. With the tibia locked in neutral rotation and a 200-newton posterior force applied to the tibia, the mean force generated in the intact posterior cruciate ligament ranged from 220 newtons at 90 degrees of flexion to thirty-six newtons at full extension. When the tibia was locked in external rotation during the posterior drawer test, the force was reduced when the knee was flexed 10 to 70 degrees; when the tibia was locked in internal rotation, the mean force was reduced at only 30 and 45 degrees of flexion. The mean forces in the graft were not significantly different, with the numbers available, from the corresponding values for the intact ligament during application of a straight posterior tibial force (neutral tibial rotation), during application of a fifteen-newton-meter flexion or extension moment (hyperflexion or hyperextension), during application of a ten-newton-meter varus or valgus moment, or during application of a ten-newton-meter internal or external tibial torque. With the numbers available, there were no significant differences between the mean tibial rotations associated with the intact posterior cruciate ligament and those associated with the graft at any angle of flexion, without or with applied tibial torque. CLINICAL RELEVANCE: The amount of force generated in the posterior cruciate ligament during the posterior drawer test depends on the angle of flexion at which the test is performed. When the angle of flexion is near 90 degrees, all of the posterior force applied to the tibia is transmitted to the ligament and the force in the ligament is not affected by the position of tibial rotation. When the test is performed at an angle of flexion near 30 degrees and in neutral tibial rotation, other structures (such as the collateral ligaments and the posterior part of the capsule) help to resist the posterior force applied to the tibia. The position of tibial rotation is important when the test is performed with the knee at an angle of flexion near 30 degrees, as secondary structures pre-tensioned by tibial torque act to reduce the amount of force carried by the posterior cruciate ligament even more. With a few minor exceptions, we found that the forces in a graft used to replace the posterior cruciate ligament were approximately the same as those in the intact ligament. Therefore, there appears to be little justification for restricting low-level rehabilitation activities once the fixation of the graft has healed. However, forces in the graft could be quite high during hyperextension and hypertension, as they are in the intact ligament. Thus, bracing in the early postoperative period may be advisable to prevent these motions.